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HomeMy WebLinkAboutMS 2024-0006; CARLSBAD BOULEVARD HOMES; REPORT OF PRELIMINARY GEOTECHNICAL INVESTIGATION; 2025-06-18 REPORT OF PRELIMINARY GEOTECHNICAL INVESTIGATION Proposed Carlsbad Boulevard Homes 5211 Carlsbad Boulevard Carlsbad, California JOB NO. 24-14681 17 June 2024 Revised 18 June 2025 Prepared for: Mr. John Norum and Mr. Kirk Moeller 17 June 2024 Revised 18 June 2025 Mr. John Norum Job No. 24-14681 Mr. Kirk Moeller KMJ Real Estate 2888 Loker Avenue East, Suite 220 Carlsbad, CA 92010 Subject: Report of Preliminary Geotechnical Investigation Proposed Carlsbad Boulevard Homes 5211 Carlsbad Boulevard Carlsbad, California Dear Mr. Norum and Mr. Moeller: In accordance with your request and per work agreement of January 15, 2024, Geotechnical Exploration, Inc. has performed a preliminary geotechnical investigation for your project in Carlsbad, California. The field work was performed on May 8, 2024. If the conclusions and recommendations presented in this report are incorporated into the design and construction of the proposed two 3-story single-family residences, it is our opinion that the site is suitable for the proposed project. This opportunity to be of service is sincerely appreciated. Should you have any questions concerning the following report, please do not hesitate to contact us. Reference to our Job No. 24-14681 will expedite a response to your inquiries. Respectfully submitted, GEOTECHNICAL EXPLORATION, INC. _______________________________ ______________________________ Jaime A. Cerros, P.E. Leslie D. Reed, President Senior Geotechnical Engineer C.E.G. 999/P.G. 3391 R.C.E. 34422/G.E. 2007 4~~-Geotechnical Exploration, Inc. SOIL AND FOUNDATION ENGINEERING • GROUNDWATER • ENGINEERING GEOLOGY • . erros, . . ·---=---r---'---'---=--1 ~---=------ 7420 TRADE STREET• SAN DIEGO, CA. 92121 • (858) 549-7222 • FAX: (858) 549-1604 • EMAIL: geotech@gei-sd.com TABLE OF CONTENTS I. PROJECT SUMMARY ........................................................................................ 1 II. SCOPE OF WORK ........................................................................................... 2 III. SITE DESCRIPTION ........................................................................................ 3 IV. FIELD INVESTIGATION, OBSERVATIONS & SAMPLING ......................................... 3 V. LABORATORY TESTING & SOIL INFORMATION .................................................... 4 VI. REGIONAL GEOLOGIC DESCRIPTION ................................................................ 8 VII. SITE-SPECIFIC SOIL & GEOLOGIC DESCRIPTION ................................................ 9 VIII. GEOLOGIC HAZARDS .................................................................................... 10 A.Local and Regional Faults ..................................................................... 10 B.Other Geologic Hazards ........................................................................ 12 C.Geologic Hazards Summary .................................................................. 14 IX. GROUNDWATER ........................................................................................... 14 X. CONCLUSIONS & RECOMMENDATIONS ............................................................ 16 A.Preparation of Soils for Site Development ............................................... 17 B.Seismic Design Criteria ......................................................................... 24 C.Foundation Recommendations ............................................................... 25 D.Retaining Wall Design .......................................................................... 28 E.Concrete Slab Performance and Concrete Slab On-Grade Criteria ............... 30 F.Site Drainage Considerations ................................................................. 32 G.General Recommendations .................................................................... 33 XI. GRADING NOTES ......................................................................................... 35 XII. LIMITATIONS .............................................................................................. 35 REFERENCES FIGURES I. Vicinity Map II. Plot Plan and Site-Specific Geology IIIa-e. Exploratory Excavation Logs IVa-b. Laboratory Test Results V.Geologic Map Excerpts and LegendsVI. Foundation Requirements Near Slopes VII.Retaining Wall Drainage Schematic APPENDICES A.Unified Soil Classification System B. Regional Geologic Description C. USGS Design Maps Summary Report D. Soil Moisture Information REPORT OF PRELIMINARY GEOTECHNICAL INVESTIGATION Proposed Carlsbad Boulevard Homes 5211 Carlsbad Boulevard Carlsbad, California JOB NO. 24-14681 The following report presents the findings and recommendations of Geotechnical Exploration, Inc. for the subject project. I. PROJECT SUMMARY It is our understanding, based on our discussions, that two new 3-story single-family residences (attached at the ground level garages) are proposed to be constructed in the central portion of the undeveloped lot. A conceptual grading plan prepared by PLSA Engineering, dated May 1, 2023, was made available for our review. The proposed development is to be constructed of standard-type building materials utilizing conventional continuous footings and slab on-grade. Encountered fill soil thicknesses ranged from approximately 1 to 1.5 feet in the area of the proposed development. The fills were previously placed and are considered undocumented. In addition, the upper 1 to 1.5 feet of the underlying formational materials have variable density and are not considered suitable in their existing condition. We recommend that the encountered existing fill and upper 1 to 1.5 feet of the underlain formational materials be removed and properly recompacted prior to all new fill placement and the construction of the new residences. Any new foundation excavation bottom soils should be evaluated and approved by our firm before forms and/or steel reinforcement placement. Foundation loads are expected to be typical for this type of relatively light construction. We have reviewed some preliminary plans that have been provided to us during the preparation of this report. However, when final plans are completed Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 2 they should be made available for our review. Additional or modified recommenda- tions may be provided at that time as warranted. In addition, the importance of thorough observation and soil testing during construction should be recognized by the client and the contractor(s) as required to provide appropriate documentation for any necessary as-built reports. Recom- mendations for observation and testing are provided in this report under Conclusions and Recommendations No. 9. Based on our current understanding of the proposed construction, it is our explicit opinion that the proposed site development would not destabilize neighboring properties or induce the settlement of adjacent structures or right-of-way improvements if designed and constructed in accordance with our recommendations. It is also our explicit opinion, based on our field investigation, review of pertinent geologic literature and analysis of geological maps, that neither an active nor a potentially active fault or landslide underlies the subject site. II. SCOPE OF WORK The scope of work performed for this investigation included a site reconnaissance, a geotechnical subsurface exploration program under the direction of our geologist with placement, logging and sampling of five exploratory handpit excavations (HP-1 to HP-5), review of available published information pertaining to the site geology, laboratory testing, geotechnical engineering analysis of the field and laboratory data, and the preparation of this report. The data obtained and the analyses performed were for the purpose of providing geotechnical design and construction criteria for the project earthwork, building foundations and slab on-grade floors. Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 3 III. SITE DESCRIPTION The subject property is known as Assessor’s Parcel No. 210-062-09-00, Lot 33 of Terramar Unit No. 1, Map No. 2696, in the City of Carlsbad and County of San Diego, State of California. Refer to the Vicinity Map, Figure No. I, for subject site location. The rectangular-shaped, approximately 6,000-square-foot lot is currently undeveloped. The property has grade elevations gently descending from east to west. The property is bordered on the north and south by similar residential properties at the approximate same elevation; on the east by Carlsbad Boulevard slightly higher in elevation; and on the west by similar residential property slightly lower in elevation. Vegetation on the site primarily consists of grasses, weeds, ice plant and some mature trees. Refer to the Plot Plan and Site-Specific Geologic Map, Figure No. II, for the location of the two proposed residences. Elevations across of the site range from approximately 51 feet above Mean Sea Level (MSL) at the southeastern corner of the property to approximately 44 feet above MSL at the northwestern corner of the property. Approximate elevations for the site were obtained from a preliminary site plan prepared by Kirk Moeller Architects, Inc. dated March 3, 2024. IV. FIELD INVESTIGATION, OBSERVATIONS & SAMPLING The field investigation consisted of a surface reconnaissance and a subsurface exploration program utilizing hand tools to investigate and sample the subsurface soils on May 8, 2024. Five handpits (HP-1 to HP-5) were excavated on the subject property to depths ranging from 3 to 4 feet in order to obtain representative soil samples and to define the soil profile on the site. The soils encountered in the handpits were continuously logged in the field by our representative and described Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 4 in accordance with the Unified Soil Classification System (refer to Appendix A). The approximate location of the handpits and other information are shown on the Plot Plan and Site-Specific Geologic Map, Figure No. II. Representative soil samples were obtained from the exploratory excavations at selected depths appropriate to the investigation. Relatively undisturbed chunk and drive samples and disturbed bulk samples were collected from the exploratory handpits to aid in soil classification and for appropriate laboratory testing. The samples were returned to our laboratory for evaluation and testing. Exploratory logs have been prepared on the basis of our observations and laboratory test results, and are attached as Figure Nos. IIIa-e and IVa-b. The exploratory excavation logs and related information depict subsurface conditions only at the specific locations shown on the plot plan and on the particular date designated on the logs. Subsurface conditions at other locations may differ from conditions occurring at the locations. Also, the passage of time may result in changes in subsurface conditions due to environmental changes. V. LABORATORY TESTING & SOIL INFORMATION Laboratory tests were performed on the retrieved soil samples in order to evaluate their physical and mechanical properties and their ability to support the proposed residential structures and improvements. Test results are presented on the Excavation Logs, Figure Nos. IIIa-e, and the Laboratory Test Results, Figure No. IVa- b. The following tests were conducted on the sampled soils: Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 5 1. Moisture Content (ASTM D2216-19) 2. Standard Test Method for Density of Soil In-place by the Drive- Cylinder Method (ASTM D2937-17e2) 3. Laboratory Compaction Characteristics (ASTM D1557-12r21) 4 Determination of Percentage of Particles Smaller than #200 Sieve (ASTM D1140-17) 5. Standard Test Method for Expansion Index of Soils (ASTM 4829- 21) 6. Resistivity and pH Analysis (CA Test 643 7. Water Soluble Sulfate (Department of Transportation California Test 417) 8. Water Soluble Chloride (Department of Transportation California Test 422) Moisture content and density measurements were performed by ASTM methods D2216-19, in conjunction with ASTM D1557-12r21 help to establish the in-situ moisture and relative density of the chosen retrieved samples. The test results are presented on the exploratory excavation logs at the appropriate sample depths and laboratory test results. Laboratory compaction values (ASTM D1557-12r21) establish the optimum moisture content and the laboratory maximum dry density of the tested soils. The relationship between the moisture and density of remolded soil samples helps to establish the relative compaction of the formational materials and soil compaction conditions to be anticipated during any future grading operation. The test results are presented on the exploratory excavation logs at the appropriate sample depths. The particle size smaller than a No. 200 sieve analysis (ASTM D1140-17) aids in classifying the tested soils in accordance with the Unified Soil Classification System and provides qualitative information related to engineering characteristics such as expansion potential, permeability, and shear strength. The test results are presented on the exploratory excavation logs at the appropriate sample depths. Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 6 The expansion potential of soils is determined, when necessary, utilizing the Standard Test Method for Expansion Index of Soils (ASTM D4829-19). In accordance with the Standard (Table 5.3), potentially expansive soils are classified as follows: EXPANSION INDEX POTENTIAL EXPANSION 0 to 20 Very low 21 to 50 Low 51 to 90 Medium 91 to 130 High Above 130 Very high Based on our laboratory testing, visual classification, the particle size smaller than No. 200 sieve analysis and our experience with similar soils, it is our opinion that the relatively limited thickness of existing on-site silty sand fill soils encountered in the area of the proposed residences have a very low expansion potential. The silty sand formational materials encountered below the fill soils at the location of HP-1 also have a very low expansion potential, with an expansion test resulting in an expansion index of 0. To assess soil corrosivity of the on-site soils, resistivity, pH, chloride and soluble sulfate tests were performed by an outside consultant (Clarkson Laboratory and Supply, Inc.) on samples of the formational materials (HP-3) most likely be in contact with concrete and ferrous metals after grading operations. The most common factor in determining soils corrosivity to ferrous metals is electrical resistivity. As soils resistivity decreases, its corrosivity to ferrous metals increases. The tested soils yielded resistivities of 7,700 to 19,000 Ohm-cm, indicating based on the generally adopted corrosion severity ratings, that the soils are moderately to mildly corrosive to ferrous metals. Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 7 Soils and fluids are considered neutral when pH is measured at 7, acidic when pH is measured at <7 and alkaline when measured at >7. Soils are considered corrosive when the pH gets down to around 5.5 or less. Results of the laboratory testing yielded a pH value of 5.4, indicating that the tested soils are slightly acidic and a factor in soil corrosivity to metals. Large concentrations of chlorides will adversely affect any ferrous metals such as iron and steel. Soil with a chloride concentration greater than or equal to 500 ppm (0.05 percent) or more is considered corrosive to ferrous metals. The chloride content of the tested formational materials measured at approximately 30 ppm or 0.003 percent, indicating that chloride content of the tested soils measured is not a factor in corrosion to ferrous metals. The primary cause of deterioration of concrete in foundations and other below ground structures is the destructive attack by soluble sulfates present in the soil and groundwater. The results of water-soluble sulfate testing performed on a representative sample of the formational materials in the general area of the proposed structures, yielded soluble sulfate contents of 60 ppm or 0.006 percent, indicating that the proposed cement/concrete structures that are in contact with the underlying soils are not anticipated to be affected by the on-site soils possessing a sulfate exposure category S0 class per ACI 318-19. As such, based on table 1904.3 of the building code, negligible sulfate exposure requirements for concrete type should be followed. The table below summarizes the laboratory results for chemical testing of the sampled soils: Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 8 Sample Location/ Depth (ft) Soluble Chloride (PPM) Soluble Sulfate (PPM) HP-2 @ 1.5-2.5 30 60 It should be noted that Geotechnical Exploration Inc., does not practice corrosion engineering and our assessment here should be construed as an aid to the owner or owner’s representative. A corrosion specialist should be consulted for the potential attack to buried metal items such as pipes, metal covers, etc. Based on the field and laboratory test data, our observations of the primary soil types, and our previous experience with laboratory shear testing of on-site and similar soils, our Geotechnical Engineer has assigned values for friction angle, coefficient of friction, and cohesion for those soils that will have significant lateral support or load bearing functions on the project. The assumed soil strength values have been utilized in determining the recommended bearing value as well as active and passive earth pressure design criteria for foundations, retaining walls and associated exterior improvements. VI. REGIONAL GEOLOGIC DESCRIPTION San Diego County has been divided into three major geomorphic provinces: the Coastal Plain, the Peninsular Ranges and the Salton Trough. The Coastal Plain exists west of the Peninsular Ranges. The Salton Trough is east of the Peninsular Ranges. These divisions are the result of the basic geologic distinctions between the areas. Mesozoic metavolcanic, metasedimentary and plutonic rocks predominate in the Peninsular Ranges with primarily Cenozoic sedimentary rocks to the west and east of this central mountain range (Demere, 1997). For an extended discussion of Regional Geology, refer to Appendix B. Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 9 VII. SITE-SPECIFIC SOIL & GEOLOGIC DESCRIPTION Our field work, reconnaissance and review of the “Geologic Map of the Oceanside 30’x60’ Quadrangle,” by Kennedy and Tan (2007), indicate that the site is underlain at depth by Quaternary-age Old Paralic Deposits Units 6-7 (Qop6-7), undivided. The encountered old paralic deposits are, in general, overlain by approximately 1 to 1.5 feet of artificial fill (Qaf) at the explored locations within the new development area. Figure No. V, Geologic Map and Legend, presents a plan view geologic map of the general area of the site. Fill Soil (Qaf): Fill soils ranging from 1 to 1.5 feet in thickness were encountered in all of our exploratory excavations. The greatest thicknesses of fill soils (1.5 feet from the existing grade) were encountered in HP-2 in the southeastern area of the property. The encountered fill soils consist of fine- to medium-grained, dry, brown, silty sand (SM). Some landscape roots were observed in the fill soils. The encountered fill soils in general are loose and are classified as having a very low expansion potential. In our opinion, the observed fill soils are not suitable in its current condition for support of new loads from building foundations or additional fill. Refer to Figure Nos. IIIa-e and IVa-b for details. Old Paralic Deposits Units 6-7 (Qop6-7): Old paralic deposits were encountered underlying the fill soils at depths ranging from approximately 1 to 1.5 feet below the existing grade in all exploratory excavations. The formational materials primarily consist of medium dense, moist, light brown, brown and reddish-brown, fine- to medium-grained silty sand (SM). The formational materials are considered to have a very low expansion potential. In our opinion, the nature of the Old Paralic Deposits makes it suitable in its current condition to support loads from new structures or additional fill. Refer to Figure Nos. IIIa-e and IVa-b for details. Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 10 The upper 1 to 1.5 feet of formational soils are considered to be weathered, poorly cemented, moist and have variable density. In our opinion, the upper (weathered) formational materials are not suitable in their current condition (1 to 1.5 feet) to support additional fill or loads from the proposed structures or improvements. Additional observations and evaluation of the exposed formational materials will be required during grading operations by a representative from our firm, and additional recommendations may be required. In our opinion, at least the upper 1 to 1.5 feet of the formational materials should be removed and recompacted. Based on our review of available published information including the “Geologic Map of Oceanside 30’x60’ Quadrangle, CA” by Kennedy and Tan, 2007, the formational materials underlying the site are referred to as “Old paralic deposits, Units 6-7 undivided (Qop2-4), (late to middle Pleistocene) — Mostly poorly sorted, moderately permeable, reddish-brown, interfingered strandline, beach, estuarine and colluvial deposits composed of siltstone, sandstone and conglomerate.” According to the aforementioned map, there are no faults known to pass through the site (refer to Figure No. V, Geologic Map and Legend). VIII. GEOLOGIC HAZARDS The following is a discussion of the geologic conditions and hazards common to the City of Carlsbad and County of San Diego, as well as project-specific geologic information relating to development of the subject site. A. Local and Regional Faults The major active faults nearest to the site are all part of the San Diego section of the Newport-Inglewood-Rose Canyon Fault Zone. This fault zone is formed by several active faults in the San Diego area. The closest mapped fault in this zone is the Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 11 northern portion of the Mount Soledad Fault mapped approximately 19.5 miles south- southeast of the site. Other nearby active faults that form the Rose Canyon fault zone are the Spanish Bight Fault, the Coronado Fault, the Downtown Grabben Fault, and the Silver Strand Fault. Review of the available references indicates that the Rose Canyon Fault Zone system is considered capable of generating an M6.9 earthquake (EERI, 2021). Other fault zones considered active in the general vicinity of the subject site are listed below (distances are to the closest point to the mapped fault):  Newport-Inglewood Fault: Mapped approximately 4 miles west of the site, estimated to be capable of producing a M6.0 to M7.4 earthquake (Grant Ludwig and Shearer, 2004; SCEDC, 2022).  Coronado Bank Fault: Mapped approximately 21 miles west of the site, estimated to be capable of a M7.6 earthquake.  Elsinore Fault: Mapped approximately 25 miles east-northeast of the site, estimated to be capable of a M6.0 to M7.0 (Rockwell et al. 1985) and M7.5 (Greensfelder, 1974).  San Diego Trough Fault Zone: Mapped approximately 29 miles west-southwest of the site. Most recent surface rupture is of Holocene age (SCEDC, 2022).  San Jacinto Fault: Mapped approximately 48 miles northeast of the site, estimated to have a 31 percent probability of a M6.7 or greater earthquake within the next 30 years (Working Group on California Earthquake Probabilities, 2008).  San Clemente Fault: Mapped approximately 54 miles west-southwest of the site (SCEDC, 2022). Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 12 In our explicit opinion, neither an active fault nor a potentially active fault underlies the site. Ground shaking from earthquakes on active southern California faults and active faults in northwestern Mexico is considered the greatest geologic hazard at the site. Further geologic hazards considered in our analysis were ground rupture, landslides, soil liquefaction, tsunamis, seiches, storm surges and flooding. Based on the results of our study, it is our opinion that the conditions at the site are not conducive to any of these other hazards. B. Other Geologic Hazards Ground Rupture: Ground rupture is characterized by bedrock slippage along an established fault and may result in displacement of the ground surface. For ground rupture to occur along a fault, an earthquake usually exceeds M5.0. If a M5.0 earthquake were to take place on a local fault, an estimated surface-rupture length 1 mile long could be expected (Greensfelder, 1974). Our investigation indicates that the subject site is not directly on a known active fault trace and, therefore, the risk of ground rupture is remote. Ground Shaking: Structural damage caused by seismically induced ground shaking is a detrimental effect directly related to faulting and earthquake activity. Ground shaking is considered to be the greatest seismic hazard in San Diego County. The intensity of ground shaking is dependent upon the magnitude of the earthquake, the distance from the earthquake, and the seismic response characteristics of underlying soils and geologic units. Earthquakes of M5.0 or greater are generally associated with significant damage. It is our opinion that the most serious damage to the site would be caused by a large earthquake originating on a nearby strand of the Rose Canyon, Coronado Bank or Newport-Inglewood Faults. Although the chance of such an event is remote, it could occur within the useful life of the structures. Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 13 Landslides: Our investigation indicates that the gentle sloping subject site is not directly on a known recent or ancient landslide. Review of the “Geologic Map of the Oceanside 30’x60’ Quadrangle, California” by Kennedy and Tan (2007) and stereo- pair aerial photographs (4-11-53, AXN-8M-102 and 10), there are no known or suspected ancient landslides located on the site. In our opinion, the property has no potential for landsliding. Slope Stability: Our site reconnaissance and exploratory excavations indicate that the site is underlain by stable and medium dense formational material at depths of 2 to 2.5 feet. The site is located in an area that slopes gently to the west. Our site reconnaissance, review of site conditions, and pertinent documents and geologic maps, indicate that the proposed areas of construction are not affected by any significant slopes, and as such, it is our professional opinion that slope stability is not an issue at this location. Liquefaction: The liquefaction of saturated sands during earthquakes can be a major cause of damage to buildings. Liquefaction is the process by which soils are transformed into a viscous fluid that will flow as a liquid when unconfined. It occurs primarily in loose, cohesionless saturated silt, sand, and fine-grained gravel deposits of Holocene to late Pleistocene age and in areas where the groundwater is shallower than about 50 feet (DMG Special Publication 117) when they are sufficiently shaken by an earthquake. On this site, the risk of liquefaction of soil materials due to seismic shaking does not exist due to the medium dense nature of the underlying formational materials and the lack of shallow static groundwater. In our opinion, the site does not have a potential for soil strength loss to occur due to a seismic event. Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 14 C. Geologic Hazards Summary It is our opinion, based upon a review of the available maps, our research and our site investigation, that no significant geologic hazards are known to exist on the site that would prohibit the construction of the proposed residences. Ground shaking from earthquakes on active Southern California faults and active faults in northwestern Mexico is the greatest geologic hazard at the property. Design of the proposed residential addition in accordance with the current building codes would reduce the potential for injury or loss of human life. Structures constructed in accordance with current building codes may suffer significant damage due to seismic shaking but should not undergo total collapse. In our explicit professional opinion, no active or potentially active faults underlies the site in the area of the proposed construction. IX. GROUNDWATER Free groundwater was not encountered in our exploratory handpits to the maximum depths explored. For a more detailed description of the subsurface materials encountered in our exploratory excavations, refer to Figure Nos. IIIa-e. It should be recognized that minor groundwater seepage problems might occur after development of a site even where none were present before development. These are usually minor phenomena and are often the result of an alteration in drainage patterns and/or an increase in irrigation water. Based on the permeability characteristics of the soil and the anticipated usage and development, it is our opinion that any seepage problems, which may occur, will be minor in extent. It is further our opinion that these problems can be most effectively corrected on an individual basis if and when they occur. We do not anticipate significant groundwater problems Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 15 to develop in the future, if the property is developed as proposed and proper drainage is implemented and maintained. It should be kept in mind that any required grading and/or construction operations will change surface drainage patterns and/or reduce permeabilities due to the densification of compacted soils. Such changes of surface and subsurface hydrologic conditions, plus irrigation of landscaping or significant increases in rainfall, may result in the appearance of surface or near-surface water at locations where none existed previously. The damage from such water is expected to be localized and cosmetic in nature, if good positive drainage is implemented, as recommended in this report, during and at the completion of construction. On properties such as the subject site where dense, low permeability soils exist at shallow depths, even normal landscape irrigation practices on the property or neighboring properties, or periods of extended rainfall, can result in shallow “perched” water conditions. The perching (shallow depth) accumulation of water on a low permeability surface can result in areas of persistent wetting and drowning of lawns, plants and trees. Resolution of such conditions, should they occur, may require site-specific design and construction of subdrain and shallow “wick” drain dewatering systems. Subsurface drainage with a properly designed and constructed subdrain system will be required along with continuous back drainage behind any proposed property line retaining walls, or any perimeter stem walls for raised-wood floors where the outside grades are higher than the crawl space grades. Furthermore, crawl spaces, if used, should be provided with the proper cross-ventilation to help reduce the potential for moisture-related problems. Additional recommendations may be required at the time of construction. Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 16 It must be understood that unless discovered during initial site exploration or encountered during site grading operations, it is extremely difficult to predict if or where perched or true groundwater conditions may appear in the future. When site formational soils are fine-grained and of low permeability, water problems may not become apparent for extended periods of time. Water conditions, where suspected or encountered during grading operations, should be evaluated and remedied by the project civil and geotechnical consultants. The project developer and property owner, however, must realize that post-construction appearances of groundwater may have to be dealt with on a site-specific basis. X. CONCLUSIONS & RECOMMENDATIONS The following recommendations are based upon the practical field investigation conducted by our firm, and resulting laboratory tests, in conjunction with our knowledge and experience with similar soils in the San Diego area. If information concerning the planned development is revised, or any changes in the design and location on the property are modified, new recommendations should be provided and approved in writing by this office. The opinions, conclusions, and recommendations presented in this report are contingent upon Geotechnical Exploration, Inc. being retained to review the final plans and specifications as they are developed and to observe the site earthwork and installation of foundations. Accordingly, we recommend that the following paragraph be included on the grading and foundation plans for the project. If the geotechnical consultant of record is changed for the project, the work shall be stopped until the replacement has agreed in writing to accept responsibility within their area of technical competence for approval upon completion of the work. It shall be the responsibility of Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 17 the permittee to notify the governing agency in writing of such change prior to the recommencement of grading and/or foundation installation work and comply with the governing agency’s requirements for a change to the Geotechnical Consultant of Record for the project. We recommend that the planned residential structures and areas with associated new exterior improvements be supported by conventional, individual-spread and/or continuous footing foundations founded on a minimum 90 percent compacted structural fill soils and dense formational materials. Bearing soils will need to be verified to have the proper moisture content and compaction during grading. A conceptual grading plan has been provided to us for the preparation of this report for the two new 3-story single-family residences (attached at the ground level garages). However, when final construction plans have been completed they should be made available for our review. Additional or modified recommendations for foundation design and construction may be provided as warranted. It is our opinion, based on our current understanding of the proposed construction, that the site is suitable for the planned residences, provided the recommendations herein are incorporated during design and construction. Further, based on our current understanding of the proposed construction, it is our explicit opinion that the proposed site development would not destabilize neighboring properties or induce the settlement of adjacent structures if designed and constructed in accordance with our recommendations. A. Preparation of Soils for Site Development 1. General: Grading should conform to the guidelines presented in the 2022 California Building Code (CBC), as well as the requirements of the City of Carlsbad and our recommendations. Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 18 During earthwork construction, removal and reprocessing of the relatively shallow fills and upper 1 to 1.5 feet approximately of the formational materials, as well as general grading procedures of the contractor, should be observed and the fill placed selectively tested by representatives of the geotechnical engineer, Geotechnical Exploration Inc. If any unusual or unexpected conditions are exposed in the field, they should be reviewed by the geotechnical engineer and if warranted, modified and/or additional remedial recommendations will be offered. The contractor should properly plan the excavations and temporary and/or permanent support necessary to maintain the stability of neighboring structures or adjacent improvements and the excavations needed during construction. 2. Clearing and Stripping: The ground surface vegetated areas should be stripped of existing vegetation within the areas of proposed construction. Holes resulting from the removal of root systems or other buried obstructions that extend below the planned grades should be cleared and backfilled with suitable compacted material compacted to the requirements provided under Recommendation Nos. 4, 5 and 6 below. Prior to any filling operations, the cleared and stripped vegetation and debris should be disposed of off-site. 3. Excavation: After the area of proposed construction has been cleared and stripped, the existing fill and upper 1 to 1.5 feet of formational material should be removed and recompacted. The anticipated depth of loose soil removal is approximately 2 to 2.5 feet below the existing ground surface. Based on the results of our exploratory excavations, as well as our experience with similar materials in the project area, it is our opinion that the existing fill materials can be excavated utilizing ordinary small to medium weight earthmoving equipment. Contractors should not, however, be relieved of Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 19 making their own independent evaluation of excavating the on-site materials prior to submitting their bids. Contractors should also review this report along with the excavation logs in the development areas (HP-1 to HP-5) to understand the scope and quantity of grading required for this project. Variability in excavating the subsurface materials should be expected across the project area. The lateral extent of the excavation and recompaction should be at least 5 feet beyond the edge of any areas to receive improvements, where feasible, or to the depth of excavation or fill at that location, whichever is greater. Special recommendations are presented for areas inside the building footprint where new footings or existing footing modifications are recommended (see Footing Recommendations, Section C). 4. Subgrade Preparation: After the required excavations have been made in the areas of new improvements, the exposed subgrade soils in areas to receive new fill and/or slab on-grade improvements should be scarified to 6 inches in depth, moisture conditioned, and compacted to the requirements for structural fill. Although not anticipated, in the event that planned cuts expose any medium or highly expansive formational materials in the building areas, they should be scarified and moisture conditioned to at least 5 percent over optimum moisture and be placed at least 3 feet below finish grade surface. 5. Material for Fill: Existing on-site very low expansion potential (Expansion Index of 20 or less per ASTM D4829-19) soils with an organic content of less than 3 percent by volume are, in general, suitable for use as structural fill. Any backfill material to be placed behind retaining walls should have a very low expansion potential (EI less than 20), with rocks no larger than 3 inches in diameter. Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 20 6. Fill Compaction: All structural fill, and areas to receive any new structures and improvements, should be compacted to a minimum degree of compaction of 90 percent based upon ASTM D1557-12e1 for very low expansive soils (EI less than 20). Fill material should be spread and compacted in uniform horizontal lifts not exceeding 8 inches in uncompacted thickness. Before compaction begins, the fill should be brought to a water content that will permit proper compaction by either: (1) aerating and drying the fill if it is too wet, or (2) watering the fill if it is too dry. Each lift should be thoroughly mixed before compaction to ensure a uniform distribution of moisture. For any imported very low expansive soils, the moisture content should be within 2 percent of optimum. Soil compaction testing by nuclear method ASTM D6938-17a or sand cone method ASTM D1556-15e1 should be performed a minimum of every 2 feet of fill placement by a representative of Geotechnical Exploration, Inc. Furthermore, our representative should perform necessary observation of fill placement during grading operations throughout the project. In the event that temporary ramps or pads are constructed of uncontrolled fill soils, the loose fill soils should be removed and/or recompacted prior to completion of the grading operation. 7. Chloride and Soluble Sulfate Testing: Imported soils should be tested for chloride and sulphate content if including clays. Soil with a chloride concentration greater than or equal to 500 ppm (0.05 percent) is considered corrosive to ferrous metals. The tested chloride content of the near surface fill and formational materials to be in contact were measured at approximately 30 Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 21 ppm or 0.003 percent, respectively, indicating that chloride content of the tested soils measured is not a factor in corrosion to ferrous metals. Test results should be evaluated by an engineer specializing in soil corrosivity. Cement type recommendations for concrete specifications should be provided by the structural engineer based on the soluble sulfate test results. It is noted that Geotechnical Exploration Inc., does not practice corrosion engineering and our assessment here should be construed as an aid to the owner or owner’s representative. A corrosion specialist should be consulted for any specific design requirement. 8. Trench Backfill: All utility trenches should be backfilled with properly compacted fill. Backfill material should be placed in lift thicknesses appropriate to the type of compaction equipment utilized and compacted to a minimum degree of compaction of 90 percent by mechanical means. Any portion of the trench backfill in public street areas within pavement sections should conform to the material and compaction requirements of the adjacent pavement section, as required by the City of Carlsbad. Our experience has shown that even shallow, narrow trenches, such as for irrigation and electrical lines, that are not properly compacted can result in problems, particularly with respect to shallow groundwater accumulation and migration. Soil compaction testing by a representative of our firm using nuclear method ASTM D6938-17a should be performed every 2 feet of fill placement for both conventional trench backfill areas as well in general fill or backfill areas. On-site soils should be used as compacted backfill top material after the pipe sand bedding material is placed and compacted in utility lines entering the building. Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 22 9. Observations and Testing: As stated in CBC 2022, Section 1705.6 Soils: “Special inspections and tests of existing site soil conditions, fill placement and load-bearing requirements shall be performed in accordance with this section and Table 1705.6 (see below). The approved geotechnical report and the construction documents prepared by the registered design professionals shall be used to determine compliance. During fill placement, the special inspector shall verify that proper materials and procedures are used in accordance with the provisions of the approved geotechnical report.” A summary of Table 1705.6 “REQUIRED SPECIAL INSPECTIONS AND TESTS OF SOILS” is presented below: a) Verify materials below shallow foundations are adequate to achieve the design bearing capacity; b) Verify excavations are extended to proper depth and have reached proper material; c) Perform classification and testing of compacted fill materials; d) Verify use of proper materials, densities and thicknesses during placement and compaction of compacted fill prior to placement of compacted fill, inspect subgrade and verify that site has been prepared properly. Section 1705.6 “Soils” statement and Table 1705.6 indicates that it is mandatory that a representative of this firm (responsible engineering firm) perform observations and fill compaction testing during excavation operations to verify that the remedial operations are consistent with the recommendations presented in this report. All grading excavations resulting from the removal of soils should be observed and evaluated by a representative of our firm before they are backfilled. Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 23 Quality control grading observation and field density testing for the purpose of documenting that adequate compaction has been achieved and acceptable soils have been utilized to properly support a project applies not only to fill soils supporting primary structures (unless supported by deep foundations or caissons) but all site improvements such as stairways, patios, pools and pool decking, sidewalks, driveways and retaining walls, etc. Observation and testing of utility line trench backfill also reduces the potential for localized settlement of all of the above including all improvements outside of the footprint of primary structures. Often after primary building pad grading, it is not uncommon for the geotechnical engineer of record to not be notified of grading performed outside the footprint of the project primary structures. As a result, settlement damage of site improvements such as patios, pool and pool decks, exterior landscape walls and walks, and structure access stairways can occur. It is therefore strongly recommended that the project general contractor, grading contractor, and others tasked with completing a project with workmanship that reduces the potential for damage to the project from soil settlement, or expansive soil uplift, be advised and acknowledge the importance of adequate and comprehensive observation and testing of soils intended to support the project they are working on. The project geotechnical engineer of record must be contacted and requested to provide these services. Failure to comply with this recommendation can result in several costly and time-consuming requirements from the City of Carlsbad engineering department. The geotechnical engineer of record, in this case Geotechnical Exploration, Inc., cannot be held responsible for the costs and time delays associated with the lack of contact and requests for testing services by the client, general Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 24 contractor, grading contractor or any of the project design team responsible for requesting the required geotechnical services. Requests for services are to be made through our office telephone number (858) 549-7222 and the telephone number of the GEI personnel assigned to the project. B. Seismic Design Criteria 10. Seismic Data Bases: The estimation of the peak ground acceleration and the repeatable high ground acceleration (RHGA) likely to occur at the site is based on the known significant local and regional faults within 100 miles of the site. 11. Seismic Design Criteria: The proposed structures should be designed in accordance with the 2022 CBC, which incorporates by reference the ASCE 7- 16 for seismic design. We have determined the mapped spectral acceleration values for the site based on a latitude of 33.1305 degrees and a longitude of -117.3344 degrees, utilizing a program titled “Seismic Design Map Tool” and provided by the USGS through SEAOC, which provides a solution for ASCE 7- 16 utilizing digitized files for the Spectral Acceleration maps. 12. Structure and Foundation Design: The design of the new structures and foundations should be based on Seismic Design Category D, Risk Category II. 13. Spectral Acceleration and Design Values: The structural seismic design, when applicable, should be based on the following values, which are based on the site location, soil characteristics, and seismic maps by USGS, as required by the 2022 CBC. A response Spectrum Acceleration (SA) vs. Period (T) for the site is also included in Appendix C. The Site Class D, Stiff Soil values for this property are: Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 25 TABLE I Mapped Spectral Acceleration Values and Design Parameters SS S1 SMS SM1 SDS SD1 Fa Fv PGA PGAM SDC 1.125 0.404 1.181 0.768 0.788 0.511 1.05 1.9 0.5 0.55 D C. Foundation Recommendations 14. Footings: Footing configuration and reinforcement should be designed by the project Structural Engineer. The following is provided as design minimums. We recommend that the proposed structures be supported on conventional, individual-spread and/or continuous footing foundations bearing on undisturbed medium dense formational materials or on properly compacted fill soils over formational soils. No footings should be underlain by undocumented fill soils. All building footings should be built on formational soils or properly compacted fill prepared as recommended in this report. The footings for the building structures should be founded at least 24 inches below the lowest adjacent finished grade when founded into properly compacted fill as previously described or medium dense to dense formational materials. Site retaining walls shall be embedded at least 18 inches below lowest adjacent grade. Footings located adjacent to utility trenches should have their bearing surfaces situated below an imaginary 1.0:1.0 plane projected upward from the bottom edge of the adjacent utility trench. Otherwise, the utility trenches should be excavated farther from the footing locations. Footings located adjacent to the tops of slopes should be extended sufficiently deep to provide at least 8 feet of horizontal cover between the slope face and outside edge of the footing at the footing bearing level. Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 26 15. Bearing Values: At the recommended depths, footings on formational or properly compacted fill soils may be designed for allowable bearing pressures of 2,400 psf for combined dead and live loads and 3,200 psf for all loads, including wind or seismic. The footings should, however, have a minimum width of 15 inches. An increase in soil allowable static bearing can be used as follows: 1200 psf for each additional foot over 1.5 feet in depth and 600 psf for each additional foot in width to a total not exceeding 5,000 psf. The static soil bearing value may be increased one-third for seismic and wind load analysis. As previously indicated, all of the foundations for the structure should be built on medium dense to dense formational materials or properly compacted fill soils. 16. Footing Reinforcement: All footings should be reinforced as specified by the Project Structural Engineer. However, based on our field investigation findings and laboratory testing, we provide the following minimum recommendations. All continuous footings should contain top and bottom reinforcement to provide structural continuity and to permit spanning of local irregularities. We recommend that a minimum of four No. 5 reinforcing bars be provided in the building continuous footings (two near the top and two near the bottom). All footings should be reinforced as specified by the structural engineer. A minimum clearance of 3 inches should be maintained between steel reinforcement and the bottom or sides of the footing. Isolated square footings should contain, as a minimum, a grid of three No. 4 steel bars on 12-inch centers, both ways. In order for us to offer an opinion as to whether the footings are founded on soils of sufficient load bearing capacity, it is essential that our representative inspect the footing excavations prior to the placement of reinforcing steel or forms. Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 27 NOTE: The project Civil/Structural Engineer should review all reinforcing schedules. The reinforcing minimums recommended herein are not to be construed as structural designs, but merely as minimum reinforcement to reduce the potential for cracking and separations. 17. Lateral Loads: Lateral load resistance for the structure supported on footing foundations may be developed in friction between the foundation bottoms and the supporting subgrade. An allowable friction coefficient of 0.40 is considered applicable. An additional allowable passive resistance equal to an equivalent fluid weight of 260 pounds per cubic foot (pcf) acting against the foundations may be used in design provided the footings are poured neat against the dense properly compacted fill or medium dense to dense formational soils. These lateral resistance value assume a level surface in front of the footing for a minimum distance of three times the embedment depth of the footing and any shear keys, but not less than 8 feet from a slope face, measured from effective top of foundation. 18. Settlement: Settlement under building loads is expected to be within tolerable limits for the proposed residence addition and deck area when foundations are designed as recommended herein for primary structures. For isolated pier foundations bearing into dense formational soils and shallow footings on properly compacted fills designed in accordance with the recommendations presented in the preceding paragraphs, we anticipate that total settlement should be within allowable tolerance and differential angular rotation should be less than 1/240. Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 28 D. Retaining Wall Design We are providing retaining walls design recommendations based on the provided plan showing an interior retaining walls for the proposed residences (retaining approximately 2 feet), the proposed property line retaining walls and for any other potential retaining wall additions to the project plans. 19. Design Parameters – Unrestrained: The active earth pressure to be utilized in the design of any cantilever (free to rotate at its top) retaining walls, utilizing on-site or imported very low expansive soils as backfill should be based on an Equivalent Fluid Weight of 38 pcf (for level backfill only). For 2.0:1.0 sloping backfill, the cantilever retaining walls should be designed with an equivalent fluid pressure of 52 pcf. Unrestrained retaining walls should be backfilled with properly compacted very low expansive soils. Unrestrained retaining walls with level backfill may use a conversion load factor of 0.31 to convert uniform vertical surcharge loads to lateral uniform loads acting on the retaining walls and 0.42 when supporting a sloping 2:1 backfill. 20. Design Parameters – Restrained: Temporary or permanent restrained retaining walls (not able to rotate at its top) supporting very low expansion potential level backfill may utilize a triangular pressure increasing at a rate of 56 pcf for wall design (78 pcf for sloping 2.0:1.0 backfill). The soil pressure produced by any footings, improvements, or any other surcharge placed within a horizontal distance equal to the height of the retaining portion of the wall should be included in the wall design pressure. A conversion factor of 0.47 pcf may be used to convert vertical uniform surcharge loads to lateral uniform pressure behind a restrained retaining wall with level backfill and 0.64 when supporting a 2.0:1.0 sloping backfill. Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 29 Recommended lateral soil pressures are based on the assumption that no loose soils or unstable soil wedges will be retained by the retaining wall. Backfill soils should consist of very low expansion potential soils with an EI of less than 20, and should be placed from the heel of the foundation to the ground surface within the wedge formed by a plane at 30 from vertical, and passing by the heel of the foundation and the back face of the retaining wall. 21. Retaining Wall Seismic Design Pressures: For seismic design of unrestrained walls over 6 feet in exposed height, we recommend that the seismic pressure increment be taken as a fluid pressure distribution utilizing an equivalent fluid weight of 14 pcf. This seismic increment is waived for restrained retaining walls. If the walls are designed as unrestrained walls, then the seismic load should be added to the static soil pressure. 22. Retaining Wall Drainage: The preceding design pressures assume that the walls are backfilled with properly compacted very low expansion potential materials (Expansion Index less than 20) and that there is sufficient drainage behind the walls to prevent the build-up of hydrostatic pressures from surface water infiltration. We recommend that drainage be provided by a composite drainage material such as J-Drain 200/220 and J-Drain SWD, or equivalent. No perforated pipes or gravel are utilized with the J-Drain system. The drain material should terminate 12 inches below the exterior finish surface where the surface is covered by slabs or 18 inches below the finish surface in landscape areas. Waterproofing should extend from the bottom to the top of the wall. A drainage swale should be built behind the retaining wall adjacent or on the south side of the building addition. Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 30 It is not within the scope of our services to provide quality control oversight for surface or subsurface drainage construction or retaining wall sealing and base of wall drain construction. It is the responsibility of the contractor to verify proper wall sealing, geofabric installation, protection board installation (if needed), drain depth below interior floor or yard surfaces, pipe percent slope to the outlet, etc. Geotechnical Exploration, Inc. will assume no liability for damage to structures or improvements that is attributable to poor drainage. In order to improve the potential of maintaining below grade spaces in a dry condition, we recommend that consideration be given to placing lower-level wall subdrains at least 1 foot below the bottom of the lower-level slabs (refer to Figure No. VI, Retaining Wall Drainage Schematic). E. Concrete Slab Performance and Concrete Slab On-Grade Criteria All proposed standard floor slabs on-grade may only be used on new, properly compacted fill or when bearing on medium dense to formational soils with the recommended soil moisture content. Conventional interior floor slabs should be at least 5 inches thick and provided with a minimum reinforcement of No. 4 bars spaced no farther than 18 inches apart. Structural slabs spanning between foundations, if used, should be reinforced as specified by the structural engineer. Shrinkage and isolation joint details should be provided by the structural engineer. Shrinkage joints should be spaced no farther than 20 feet apart and at reentrant corners. 23. Reflective Shrinkage Cracking: We note that shrinkage cracking can result in reflective cracking in brittle flooring surfaces such as stone and tiles. It is imperative that if movement intolerant flooring materials are utilized, the flooring contractor and/or architect should provide specifications for the use of Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 31 high-quality isolation membrane products installed between slab and floor materials. 24. Slab Moisture Emission: Interior slabs on-grade must be sealed in accordance with the manufacturer’s recommendations for the floor coverings that might be utilized. Although it is not the responsibility of geotechnical engineering firms to provide vapor soil moisture protection recommendations, as a service to our clients we are including information and recommended minimum protection criteria as Appendix D. Actual recommendations should be provided by the project architect and waterproofing consultants or product manufacturer. It is recommended to contact the vapor barrier manufacturer to schedule a pre-construction meeting and to coordinate a review, in-person or digital, of the vapor barrier installation. Basement slabs should be protected from soil moisture as specified by the project architect after discussion with the owner about the desired degree of protection desired. 25. Exterior Slab Reinforcement: Exterior concrete slabs such as sidewalks and patios should be constructed on properly recompacted fill soils. Exterior slab reinforcement and control joints should be provided by the project Structural Engineer. As a minimum for protection of on-site improvements, we recommend that all exterior pedestrian concrete slabs be at least 4 inches thick, reinforced with No. 3 bars at 15-inch centers, both ways at the center of the slab, and contain adequate isolation and control joints as well as proper surface drainage. Control joints should be spaced no farther than 8 feet apart and also at re-entrant corners. The performance of on-site improvements can be greatly affected by soil base preparation and the quality of construction. It is therefore important that all improvements be properly designed and constructed for the existing soil Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 32 conditions. The improvements should not be built on loose soils or fills placed without our observation and testing. Slabs on-grade may only be used on medium dense to dense formational soils or properly compacted fill soils as previously discussed. F. Site Drainage Considerations 26. Surface Drainage: Adequate measures should be taken to properly finish- grade the site after the new improvements are in place. Drainage waters from this site and adjacent properties should be directed away from the footings, slabs, and slopes, onto the natural drainage direction for this area or into properly designed and approved drainage facilities provided by the project civil engineer. Proper subsurface and surface drainage will help reduce the potential for waters to seek the level of the bearing soils under the house, wall footings or other improvements. Soils measured from the perimeter foundations of the addition for a distance of 6 feet should drain away from the addition at a minimum 5 percent gradient. Failure to observe this recommendation could result in undermining, soil expansion, and possible differential settlement of the retaining wall or other improvements or cause other moisture-related problems. Currently, the 2022 CBC requires a minimum of 2 percent surface gradient for proper drainage of building pads unless waived by the building official. Concrete pavement may have a minimum gradient of 0.5-percent. The surface gradient adjacent to structures must drain away as indicated in the 2022 CBC. Due to the possible build-up of groundwater (derived primarily from rainfall and irrigation), excess moisture is a common problem behind retaining walls that may be planned. These problems are generally in the form of water Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 33 seepage through walls and mineral staining. In order to minimize the potential for moisture-related problems to develop, the backfill side of all retaining walls must be adequately waterproofed and drained. 27. Erosion Control: Appropriate erosion control measures should be taken at all times during and after construction to prevent surface runoff waters from entering footing excavations or ponding on finished building pad areas. 28. Planter Drainage: Planter areas and planter boxes should be sloped to drain away from the foundations. Planter boxes should be constructed with a closed bottom and a subsurface drain, installed in gravel, with the direction of subsurface and surface flow away from the footings to an adequate drainage facility. G. General Recommendations 29. Cal-OSHA: Where not superseded by specific recommendations presented in this report, trenches, excavations, and temporary slopes at the subject site should be constructed in accordance with Title 8, Construction Safety Orders, issued by Cal-OSHA. Excavations up to 5 feet high should be built at a temporary slope of 1:1 (H:V) due to the on-site cohesionless soils. Temporary grading excavations close to property lines may be excavated and backfilled in alternating A-B-C-D slots no wider than 8 feet. 30. Project Start Up Notification: In order to reduce any work delays during site excavation and development, our firm should be contacted at least 48 hours before any required observation of footing excavations or field density testing of compacted fill soils. If possible, placement of formwork and steel reinforcement in footing excavations should not occur prior to our observations Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 34 of the excavations. If our observations reveal the need for deepening or re- designing foundation structures at any locations, any formwork or steel reinforcement in the affected footing excavation areas would have to be removed before the correction of the observed problem (i.e., deepening the footing excavation, compacting or removal of loose soil in the bottom of the excavation, etc.). 31. Construction Best Management Practices (BMPs): Sufficient BMPs must be installed to prevent silt, mud, or other construction debris from being tracked into the adjacent street(s) or stormwater conveyance systems due to construction vehicles or any other construction activity. The contractor is responsible for cleaning any such debris that may be in the street at the end of each work day or after a storm event that causes a breach in the installed construction BMPs. All stockpiles of uncompacted soil and/or building materials that are left unprotected for a period greater than 7 days are to be provided with erosion and sediment controls. Such soil must be protected each day when the probability of rain is 40% or higher. A concrete washout should be provided on all projects that propose the construction of any concrete improvements that are to be poured in place. All erosion/sediment control devices should be maintained and in working order at all times. All slopes that are created or disturbed by construction activity must be protected against erosion and sediment transport at all times. The storage of all construction materials and equipment must be protected against any potential release of pollutants into the environment. Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 35 XI. GRADING NOTES Geotechnical Exploration, Inc. recommends that we be retained to verify the actual soil conditions revealed during site grading work and footing excavation to be as anticipated in this "Report of Preliminary Geotechnical Investigation” for the project. In addition, the compaction of any fill soils placed during site grading work must be observed and tested by the soil engineer. It is the responsibility of the general contractor to comply with the requirements on the approved plans and the local building ordinances. All/any retaining wall and trench backfill should be properly compacted. Geotechnical Exploration, Inc. will assume no liability for damage occurring due to improperly compacted or uncompacted backfill placed without our observations and testing. XII. LIMITATIONS Our conclusions and recommendations have been based on available data obtained from our field investigation, background review and laboratory analysis, as well as our experience with similar soils and natural ground materials located in the City of Carlsbad. Of necessity, we must assume a certain degree of continuity between exploratory excavations and/or natural exposures. It is, therefore, necessary that all observations, conclusions, and recommendations be verified at the time excavation begins. In the event discrepancies are noted, additional recommendations may be issued, if required. The work performed and recommendations presented herein are the result of an investigation and analysis that meet the contemporary standard of care in our profession within the County of San Diego. No warranty is provided. This report should be considered valid for a period of two (2) years, and is subject to review by our firm following that time. Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 36 As stated previously, it is not within the scope of our services to provide quality control oversight for surface or subsurface drainage construction or retaining wall sealing and base of wall drain construction. It is the responsibility of the contractor to verify proper wall sealing, geofabric installation, protection board installation (if needed), drain depth below interior floor or yard surfaces, pipe percent slope to the outlet, etc. It is the responsibility of the owner and/or developer to ensure that the recommendations summarized in this report are carried out in the field operations and that our recommendations for design of this project are incorporated in the project plans. We should be retained to review the final project plans once they are available, to verify that our recommendations are adequately incorporated in the plans. Additional or revised recommendations may be necessary after our review. This firm does not practice or consult in the field of safety engineering. We do not direct the contractor's operations, and we cannot be responsible for the safety of personnel other than our own. The safety of others is the responsibility of the contractor. The contractor should notify the owner if any of the recommended actions presented herein are considered to be unsafe. The firm of Geotechnical Exploration, Inc. shall not be held responsible for changes to the physical condition of the property, such as addition of fill soils or changing drainage patterns, which occur subsequent to issuance of this report and the changes are made without our observations, testing, and approval. Proposed Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 37 Once again, should any questions arise concerning this report, please feel free to contact the undersigned. Reference to our Job No. 24-14681 will expedite a reply to your inquiries. Respectfully submitted, GEOTECHNICAL EXPLORATION, INC. _______________________________ ______________________________ Jaime A. Cerros, P.E. Leslie D. Reed, President Senior Geotechnical Engineer C.E.G. 999/P.G. 3391 R.C.E. 34422/G.E. 2007 _______________________________ Steve Osetek, Project Geologist REFERENCES JOB NO. 24-14681 June 2024 2007 Working Group on California Earthquake Probabilities, 2008, The Uniform California Earthquake Rupture Forecast, Version 2 (UCERF 2), U.S Geological Survey Open-file Report 2007-1437 and California Geological Survey Special Report 203. Berger, V. and Schug, D.L., 1991, Probabilistic Evaluation of Seismic Hazard in the San Diego-Tijuana Metropolitan Region, Environmental Perils, San Diego Region, Geological Society of America by the San Diego Association of Geologists, October 20, 1991, p. 89-99. City of San Diego, 2008, Seismic Safety Study, Geologic Hazards and Faults, Development Services Department, Grid Tile No. 27. Demere, T.A. 1997, Geology of San Diego County, California, San Diego Natural History Museum, http://archive.sdnhm.org/research/paleontology/sdgeol.html, accessed July 30, 2020. Earthquake Engineering Research Institute (EERI), 2021, San Diego Planning Scenario, Magnitude 6.9 on the Rose Canyon Fault. Grant Ludwig, L.B. and Shearer, P.M., 2004, Activity of the Offshore Newport-Inglewood Rose Canyon Fault Zone, Coastal Southern California, from Relocated Microseismicity, Bulletin of the Seismological Society of America, 94(2), 747-752. Greene, H.G., Bailey, K.A., Clarke, S.H., Ziony, J.I. and Kennedy, M.P., 1979, Implications of fault patterns of the inner California continental borderland between San Pedro and San Diego, in Abbott, P.L., and Elliot, W.J., eds., Earthquakes and other perils, San Diego region: San Diego Association of Geologists, Geological Society of America field trip, November, 1979, p. 21–28. Hart, E.W. and Bryant, W.A., 1997, Fault-Rupture Hazard Zones in California, California Division of Mines and Geology, Special Publication 42. Hart, E.W., Smith, D.P. and Saul, R.B., 1979, Summary Report: Fault Evaluation Program, 1978 Area (Peninsular Ranges-Salton Trough Region), California Division of Mines and Geology, Open-file Report 79-10 SF, 10. Jennings, C.W., and Bryant, W.A., 2010, Fault Activity Map of California, California Geological Survey Geologic Data Map No. 6 Kennedy, M.P. and Tan, S.S., 2007, Geologic Map of Oceanside 30’x60’ Quadrangle, California, California Geological Survey, Department of Conservation. Legg, M., and Agnew, D., 1979, The 1862 Earthquake in San Diego, in Earthquakes and Other Perils: San Diego Region (Abbott, P.L., Elliott, W.J., eds.), San Diego Association of Geologists, San Diego, CA 139-141. Rockwell, T.K., 2010, The Rose Canyon Fault Zone in San Diego, Proceedings of the Fifth International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics. Paper No. 7.06C. tai REFERENCES/Page 2 Rockwell, T.K., Dawson, T.E., Young Ben-Horin, J. and Seitz, G., 2014, A 21-Event, 4,000-Year History of Surface Ruptures in the Anza Seismic Gap, San Jacinto Fault, and Implications for Long-term Earthquake Production on a Major Plate Boundary Fault, Pure and Applied Geophysics, v. 172, 1143– 1165 (2015). Rockwell, T.K., Millman, D.E., McElwain, R.S. and Lamar, D.L., 1985, Study of Seismic Activity by Trenching Along the Glen Ivy North Fault, Elsinore Fault Zone, Southern California: Lamar-Merifield Technical Report 85-1, U.S.G.S. Contract 14-08-0001-21376, 19 p. Ross, Z.E., Hauksson E. and Ben-Zion Y., 2017, Abundant Off-fault Seismicity and Orthogonal Structures in the San Jacinto Fault Zone, Science Advances, 2017; 3(3): e1601946. Published 2017 Mar 15. Singleton, D.M., Rockwell, T.K., Murbach, D., Murbach, M., Maloney, J., Freeman, T., Levy, Y., 2019, Late-Holocene Rupture History of the Rose Canyon Fault in Old Town, San Diego: Implications of Cascading Earthquakes on the Newport-Inglewood-Rose Canyon Fault System, Bulletin of the Seismological Society of America 109, 855-874. Southern California Earthquake Data Center (SCEDC), 2022, Earthquake Information, Fault Name Index, Division of Geological and Planetary Sciences, California Institute of Technology. Toppozada, T.R. and Parke, D.L., 1982, Areas Damaged by California Earthquakes, 1900-1949, California Division of Mines and Geology, Open-file Report. 82-17. U.S. Dept. of Agriculture, 1953, Aerial Photographs AXN-8M-102 and 103. Mi VICINITY MAP Proposed Carlsbad Boulevard Homes 5211 Carlsbad Boulevard Carlsbad, CA. Figure No. I Job No. 24-14681 SITE Thomas Bros. Guide San Diego County, pg 1126-F2 Carlsbad State Beach PACIFIC OCEA AGUA HEDJONA L GOON Geotechnical Exploration, Inc. INF-3 Approximate Location of Infiltration Test INF-2 INF-1 INF-3 HP-1 HP-2 HP-3 Approximate Location of Exploratory Handpit HP-3 Approximate Location of Proposed Structure HP-4 HP-5 Qaf Qop Artificial Fill Old Paralic Deposits, unit 6-7 GEOLOGIC LEGEND 6-7 QafQop6-7 Qaf Qop6-7 24-14681-P2.ai NOTE: This Plot Plan is not to be used for legal purposes. Locations and dimensions are approximate. Actual property dimensions and locations of utilitiesmay be obtained from the Approved Building Plans or the “As-Built” Grading Plans. LEGEND PLOT PLAN AND SITE SPECIFIC GEOLOGIC MAP Proposed Carlsbad Boulevard Homes 5211 Carlsbad Boulevard Carlsbad, CA. Figure No. II Job No. 24-14681 June 2024 GRAPHIC SCALE 1” = 20’ (approximate) N 0 10 20 3020 REFERENCE: This Plot Plan was prepared from a CONCEPTUAL SITE PLAN by PLSA ENGINEERING dated 05/01/2023 and from on-site field reconnaissance performed by GEI. CARLSBAD BOULEVARD 5211 Carlsbad Blvd PLSA I Pl.SA ENGINEERING.COM ----------------------------------------______ .,.,.. '------------------------,_ ...... -----_________ , -..... -----------....., ..,--------.,,.. EXISTING FIRE l('(()RNff -------..... G --G --G --G --G --G ----G --G --G --G --G'--~ G ~--------...,,, __ EXISTINGliACWATERIIAJ/1 '.._,, _., ..... ..._ -----..... ,.,,--' . / ............ ________ ,,,, ..... -----.. w--w--w--w--:W--------=-w--w--w--w __L.w--w--w--w--w..---'"'--C-w--w--w--w--w------.;;:;-w--\\ ('-, /EXIST/IIG/iVCPSEWfflllAJ/1 - ~ S --~ --fa _L S --S ::,-;--~~ , --S S _/S ---S ~G-::RCPS~DRAJ/1 .,; ----S --S --.5 ~S \ s -------f ---------~s ___ ---,, --s --s --s --,, --6 --s --s --s ----.,;--s--s--s--~-----s--::-:::;..s -- I ----, .1----1--------------------------~---------------------.. ---------- -e w EXISl'IIIG N; PAVBl.flff EDGE EXISTING GRAVEi. SHOUIDER w--w -X ---- EXJS ------- LOT34 MAP 2696 -....... --, , --,I I I I ---- ... ...._ EXISTING WOOO ~NCE.-:.-::...:-~-!lr"',l PROPOSED-----s-...,;...~1:1 RETAJ/1//IG WALL MAliH•~5FT -----1 l-- I ------ t T27 ~AP 2696 UNIT1 FF= 50.6 PAD=49.8 WALL s SITE PLAN SC/4E -1' • 10' ERA!. AJN -X/Sl'ING SEI\ER MAIN 1 EXISTING 6' VCP 51:Wl:R MAJ!/ --5 --s--S -.5 --s S--S--:,--S--5-4.1_9jE@i:Ar____ --~rEXIST~6'vc:PWAJEII~ C /5:IZ!/FS ~ I W--1--W--W--W--W--\\ /- / _,. EXISTI/IG 4' Cl WAl!:IUIA~ ,_,,,_.--.,,..,,,. (ABAMJONfD) w --1w --w --_w_ . ---1.i_ ...... nNG ..,_ FENCf -- ---~-------~-- EXISTING FREE STANDING MASOHlY WALL CEHrfllED 0/'I PROPffflY Ui'I£ (4933}B\vcrFSOOl?TII /"9 •9! a~s so urn LOT32 MAP 2696 ---~---------------------s ----- -LOT29---- 'AP-c 6~ D Geotechnical Exploration, Inc. SY M B O L SA M P L E BL O W S / 6" SM SM 8.6 8 127.6 0 5.1 94.2 74 20 SM 4.3 22 1 H IN-PLACE SAMPLE Proposed Carlsbad Blvd Homes MODIFIED CALIFORNIA SAMPLE SITE LOCATION: FIGURE NO. IIIaIN-PLACE HAND-DRIVE SAMPLE 5211 Carlsbad Blvd. Carlsbad, CASTANDARD PENETRATION TEST 24-14681PERCHED WATER TABLE LOG NO.HP-1BULK BAG SAMPLE JOB NAME: FOOTING * DISTURBED BLOWCOUNT JOB NUMBER: 10 9 8 7 6 - mild to moderate cementation OLD PARALIC DEPOSITS (Qop6-7) 4 Bottom of Excavation at 4 ft. No Groundwater, No Caving, Backfilled with Cuttings 5 2 3 MA X I M U M D R Y DE N S I T Y ( p c f ) DE N S I T Y ( % of MD D ) EX P A N ( + % ) CO N S O L ( - % ) 1 1 EX P A N S I O N I N D E X % P A S S I N G # 2 0 0 SI E V E SA M P L E O . D . ( i n ) DE P T H (f e e t ) SA M P L E DESCRIPTION AND REMARKS (Grain Size, Density, Moisture, Color) EQUIPMENT: Hand Tools DIMENSION & TYPE OF EXCAVATION: 2' x 2' x 4' DATE LOGGED: May 8, 2024 LOGGED BY: SO SURFACE ELEVATION: ± 47' Above Mean Sea Level SILTY SAND, fine- to medium-grained, loose, dry, brown. - abundant roots ARTIFICIAL FILL (Qaf) SILTY SAND, fine- to medium-grained, loose to medium dense, moist, light-brown and brown - poorly cemented OLD PARALIC DEPOSITS (Qop6-7) - becomes medium dense, moist, brown and reddish- brown 2 3 REVIEWED BY: LDR/JAC GROUNDWATER/SEEPAGE DEPTH: Not Encountered FIELD DESCRIPTION AND CLASSIFICATION U. S . C . S IN - P L A C E MO I S T U R E ( % ) IN - P L A C E D RY DE N S I T Y ( p c f ) OP T I M U M MO I S T U R E ( % ) -~~f ~ 1 Geotechnical Exploration, Inc. ~ - - - !·: \ J X - - - - - -·--·-·--·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-· ·-·--·-·-·-·-·-·-·-· ·-·-·--·-·-·-· ·-·-· ·-·-· ·-·-· ·-·-·-· ·- - -- - --- - - - - - - - - - - - - - - - - - - - - - - - - - - ii LC SY M B O L SA M P L E BL O W S / 6" SM SM 6.9 109.6 18 1 H SA M P L E 2 EQUIPMENT: Hand Tools DIMENSION & TYPE OF EXCAVATION: 2' x 2' x 3' DATE LOGGED: May 8, 2024 LOGGED BY: SO SURFACE ELEVATION: ± 49' Above Mean Sea Level SA M P L E O . D . ( i n ) DE P T H (f e e t ) DESCRIPTION AND REMARKS (Grain Size, Density, Moisture, Color) REVIEWED BY: LDR/JAC GROUNDWATER/SEEPAGE DEPTH: Not Encountered FIELD DESCRIPTION AND CLASSIFICATION U. S . C . S IN - P L A C E MO I S T U R E ( % ) IN - P L A C E D RY DE N S I T Y ( p c f ) MA X I M U M D R Y DE N S I T Y ( p c f ) DE N S I T Y ( % o f MD D ) EX P A N ( + % ) CO N S O L ( - % ) No Groundwater, No Caving, Backfilled with Cuttings Bottom of Excavation at 4 ft. - mild to moderate cementation EX P A N S I O N I N D E X % P A S S I N G # 2 0 0 SI E V E OP T I M U M MO I S T U R E ( % ) 5 6 1 4 3 8 7 9 10 MODIFIED CALIFORNIA SAMPLE FIGURE NO. IIIbIN-PLACE HAND-DRIVE SAMPLE STANDARD PENETRATION TEST PERCHED WATER TABLE BULK BAG SAMPLE IN-PLACE SAMPLE SITE LOCATION: 5211 Carlsbad Blvd. Carlsbad, CA JOB NUMBER: 24-14681 JOB NAME: Proposed Carlsbad Blvd Homes LOG NO.HP-2 FOOTING * DISTURBED BLOWCOUNT OLD PARALIC DEPOSITS (Qop6-7) SILTY SAND, fine- to medium-grained, loose, dry, brown. - abundant roots ARTIFICIAL FILL (Qaf) 2 1 SILTY SAND, fine- to medium-grained, loose to medium dense, moist, light-brown and brown - poorly cemented OLD PARALIC DEPOSITS (Qop6-7) - becomes medium dense, moist, brown and reddish- brown -~~f ~ 1 Geotechnical Exploration, Inc. ~ - -- - -- - jI . ·! ·--·-·-.,--·--·-·-·-·-·-·-·-· ·-·-·--·-·-·-· ·-·-· ·-·-· ·-·-· ·-·-·-· ·- -\ -·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-' - - X - - - - - - - - - - - - - - - - - - - - - - - - - - - - ii LC SY M B O L SA M P L E BL O W S / 6" SM SM 3.6 102.9 81 21 SM 1 H EQUIPMENT: Hand Tools DIMENSION & TYPE OF EXCAVATION: 2' x 2' x 3' DATE LOGGED: May 8, 2024 LOGGED BY: SO SURFACE ELEVATION: ± 46' Above Mean Sea Level SA M P L E O . D . ( i n ) DE P T H (f e e t ) SA M P L E DESCRIPTION AND REMARKS (Grain Size, Density, Moisture, Color) REVIEWED BY: LDR/JAC GROUNDWATER/SEEPAGE DEPTH: Not Encountered FIELD DESCRIPTION AND CLASSIFICATION U. S . C . S IN - P L A C E MO I S T U R E ( % ) IN - P L A C E D RY DE N S I T Y ( p c f ) OP T I M U M MO I S T U R E ( % ) MA X I M U M D R Y DE N S I T Y ( p c f ) DE N S I T Y ( % o f MD D ) EX P A N ( + % ) CO N S O L ( - % ) SILTY SAND, fine- to medium-grained, loose, dry, brown. - abundant roots 1 ARTIFICIAL FILL (Qaf) SILTY SAND, fine- to medium-grained, loose to medium dense, moist, light-brown and brown - poorly cemented EX P A N S I O N I N D E X % P A S S I N G # 2 0 0 SI E V E 3 2 OLD PARALIC DEPOSITS (Qop6-7) 2 4 Bottom of Excavation at 3 ft. No Groundwater, No Caving, Backfilled with Cuttings 5 7 6 8 9 FOOTING * DISTURBED BLOWCOUNT JOB NUMBER: 10 FIGURE NO. IIIcIN-PLACE HAND-DRIVE SAMPLE 5211 Carlsbad Blvd. Carlsbad, CASTANDARD PENETRATION TEST 24-14681PERCHED WATER TABLE LOG NO.HP-3BULK BAG SAMPLE JOB NAME: 1 - becomes medium dense, moist, brown and reddish- brown - mild to moderate cementation OLD PARALIC DEPOSITS (Qop6-7) IN-PLACE SAMPLE Proposed Carlsbad Blvd Homes MODIFIED CALIFORNIA SAMPLE SITE LOCATION: -~~f ~~ Geotechnical Exploration, Inc. ~~ - - ! .. ' .. --::-1- -.. - - - - - - - - - - - - - - - - ii \ J i I ------------j 1---·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-; \ I LC __________ _____._____ SY M B O L SA M P L E BL O W S / 6" SM SM SM 6.4 21 1 H EQUIPMENT: Hand Tools DIMENSION & TYPE OF EXCAVATION: 2' x 2' x 3' DATE LOGGED: May 8, 2024 LOGGED BY: SO SURFACE ELEVATION: ± 45' Above Mean Sea Level 2 % P A S S I N G # 2 0 0 SI E V E SA M P L E O . D . ( i n) DE P T H (f e e t ) SA M P L E DESCRIPTION AND REMARKS (Grain Size, Density, Moisture, Color) REVIEWED BY: LDR/JAC GROUNDWATER/SEEPAGE DEPTH: Not Encountered FIELD DESCRIPTION AND CLASSIFICATION U. S . C . S IN - P L A C E MO I S T U R E ( % ) IN - P L A C E D RY DE N S I T Y ( p c f ) OP T I M U M MO I S T U R E ( % ) MA X I M U M D R Y DE N S I T Y ( p c f ) DE N S I T Y ( % o f MD D ) EX P A N ( + % ) CO N S O L ( - % ) SILTY SAND, fine- to medium-grained, loose, dry, brown. - abundant roots 1 ARTIFICIAL FILL (Qaf) SILTY SAND, fine- to medium-grained, loose to medium dense, moist, light-brown and brown - mild cemented1 EX P A N S I O N I N D E X - becomes medium dense, moist, brown and reddish- brown 3 - mild to moderate cementation 2 OLD PARALIC DEPOSITS (Qop6-7) OLD PARALIC DEPOSITS (Qop6-7) 4 Bottom of Excavation at 3 ft. No Groundwater, No Caving, Backfilled with Cuttings 5 7 6 8 9 10 24-14681PERCHED WATER TABLE LOG NO.HP-4BULK BAG SAMPLE JOB NAME: FOOTING * DISTURBED BLOWCOUNT JOB NUMBER: IN-PLACE SAMPLE Proposed Carlsbad Blvd Homes MODIFIED CALIFORNIA SAMPLE SITE LOCATION: FIGURE NO. IIIdIN-PLACE HAND-DRIVE SAMPLE 5211 Carlsbad Blvd. Carlsbad, CASTANDARD PENETRATION TEST -~~f ~~ Geotechnical Exploration, Inc. ~~ - - ! .. ' .. -.. -.. - - - - - - - - - - - - - - - - ii \ J i I ------------j 1---·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-; \ I LC __________ _____._____ SY M B O L SA M P L E BL O W S / 6" SM SM SM 1 H EQUIPMENT: Hand Tools DIMENSION & TYPE OF EXCAVATION: 2' x 2' x 3' DATE LOGGED: May 8, 2024 LOGGED BY: SO SURFACE ELEVATION: ± 44' Above Mean Sea Level % P A S S I N G # 2 0 0 SI E V E SA M P L E O . D . ( i n) DE P T H (f e e t ) SA M P L E DESCRIPTION AND REMARKS (Grain Size, Density, Moisture, Color) REVIEWED BY: LDR/JAC GROUNDWATER/SEEPAGE DEPTH: Not Encountered FIELD DESCRIPTION AND CLASSIFICATION U. S . C . S IN - P L A C E MO I S T U R E ( % ) IN - P L A C E D RY DE N S I T Y ( p c f ) OP T I M U M MO I S T U R E ( % ) MA X I M U M D R Y DE N S I T Y ( p c f ) DE N S I T Y ( % o f MD D ) EX P A N ( + % ) CO N S O L ( - % ) 1 SILTY SAND, fine- to medium-grained, loose, dry, brown. - abundant roots and some trash 1 ARTIFICIAL FILL (Qaf) SILTY SAND, fine- to medium-grained, loose to medium dense, moist, light-brown and brown - poorly cemented 2 EX P A N S I O N I N D E X - becomes medium dense, moist, brown and reddish- brown 3 - mild to moderate cementation 2 OLD PARALIC DEPOSITS (Qop6-7) OLD PARALIC DEPOSITS (Qop6-7) 4 Bottom of Excavation at 3 ft. No Groundwater, No Caving, Backfilled with Cuttings 5 7 6 8 9 10 24-14681PERCHED WATER TABLE LOG NO.HP-5BULK BAG SAMPLE JOB NAME: FOOTING * DISTURBED BLOWCOUNT JOB NUMBER: IN-PLACE SAMPLE Proposed Carlsbad Blvd Homes MODIFIED CALIFORNIA SAMPLE SITE LOCATION: FIGURE NO. IIIeIN-PLACE HAND-DRIVE SAMPLE 5211 Carlsbad Blvd. Carlsbad, CASTANDARD PENETRATION TEST -~~f ~~ Geotechnical Exploration, Inc. ~~ - - ! .. ' .. -.. -.. - - - - - - - - - - - - - - - - ii \ J i I ------------j 1---·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-·-; \ I LC __________ _____._____ Source of Material Handpit HP-1 Depth 1-2.5ft U.S.C.S.SILTY SAND (SM) Maximum Dry Density (PCF)127.6 Optimum Moisture Content (%)8.0 Coarse Material +No. 4. Sieve (%) Corrected Maximum Dry Density (pcf) Corrected Optimum Moisture Content (%) Curves of 100% Saturation for Specific Gravity equal to: 2.80 2.70 2.60 TEST RESULTS ASTM D1557-12(2021) Method ATest Method LABORATORY TEST RESULTS FIGURE NO. IVa JOB NAME: Proposed Carlsbad Blvd Homes SITE LOCATION: 5211 Carlsbad Blvd. Carlsbad, CA MOISTURE-DENSITY RELATIONSHIP JOB NUMBER: 24-14681 90 95 100 105 110 115 120 125 130 135 140 145 150 0 5 10 15 20 25 30 Dr y D e n s i t y ( p c f ) Moisture Content (%) Standard Test Method for Laboratory Compaction Charaterisitics of Soil Using Modified Effort \ \ \ \ \ \ \ 1 \ \ 1 \ \ ' ' ' \ ' ' \ \ ..... , ). \ ... 1 I\ ,, I\ I ' \ .\ ~ I '\ \ \ ' I/ 'Ii i I\ \ ' ' \ I\ \ I\ I\ \ I\ \ ' I\ I\ I\ \ \ I\ \ \ \ -, I\ I\ ' I\ \ II\ I'\ II\ ' ' " I'\_ ' I'\ I\ I\ I\ ' '\ \. I\ \ \ 4~~= G e ote chnical Exploration, Inc. ~ LABORATORY TEST RESULTS FIGURE NO. IVb JOB NAME: Proposed Carlsbad Blvd Homes SITE LOCATION: 5211 Carlsbad Blvd. Carlsbad, CA DIRECT SHEAR JOB NUMBER: 24-14681 U.S.C.S.SILTY SAND (SM) Cohesion (psf)0 Symbol Source of Material HP - 1 Depth 1-2.5ft Friction Angle ᶲ (degrees)32.8 Test Method ASTM D3080, Saturated, Peak, Remolded to 90% of Max Dry Density -1000 0 1000 2000 3000 4000 5000 0 500 1000 1500 2000 2500 3000 3500 4000 4500 Sh e a r S t r e n g t h ( p s f ) Normal Load (psf) Standard Test Method for Direct Shear Tests of Soils ---.-- 4~~= Geotechnical Exploration, Inc. ~ Figure No. V Job No. 24-14681 CARLSBAD-BLVD-HMS-GEO-OC.ai Proposed Carlsbad Boulevard Homes 5211 Carlsbad Boulevard Carlsbad, CA. DESCRIPTION OF MAP UNITS June 2024 Qop Very Old Paralic Deposits, Unit 11 6-7 Tsa Santiago Formation PACIFIC OCEAN SITE EXCERPT FROM ONSHORE MAP SYMBOLS Contact - Contact between geologic units; dotted where concealed. Fault - Solid where accurately located; dashed where approximately located; dotted where concealed. U = upthrown block, D = downthrown block. Arrow and number indicate direction and angle of dip of fault plane. Anticline - Solid where accurately located; dashed where approximately located; dotted where concealed. Arrow indicates direction of axial plunge. Syncline - Solid where accurately located; dotted where concealed Arrow indicates direction of axial plunge. Landslide - Arrows indicate principal direction of movement. Quired where existence is questionable Strike and dip of beds Inclined Inclined Inclined Strike and dip of igneous foliation Strike and dip of metamorphic foliation Old Paralic Deposits, Unit 2-4Qop Kgp - Granite pegmatite dike. Overturned Vertical Horizontal Vertical Strike and dip of igneous joints Inclined Vertical Strike and dip of sedimentary joints Vertical 2-4 bseMip Onshora ba!Ml ,,..~p.sogrephy, f'!ydrography, .and •en,poru,IIOn) (""'1 U,S.G.S, d~~81 line 9"'Ph (01.G) OBIS. OCGiilrtStd& JO' .11. 60' rnt!!IOC. quadranok!t,. Shaded .lcpographic basa froll} U,S_G.S.. dlgil:BI eieYeBl:m modeh (OEM's) Orf11hore l)tlllh~"'°'rfc CCMtclU,S •l'KI 'lh■ded bolh)'n,Blry ltom N,0,1,), ""9"' and m-m -· ProjecHon l!. UTM, 'Zone 11, North Amelican Datum 1921 Ttli! map was h.11\dad lJ\ pert ~ the u_s_ GeologJcBI SU"'"'! No1ro..al Coopoa,ritllt Goolo9!< ~ P_, STATEMAP A-" 00, OINOAG0092 1he Oapartmonc 01 CORICf'l/81Mln INllkn no WarJanllel: a lo the -ityolm i<Pi'nc!Ud !or ony ponll:IJJor purpooe. 70 GEOLOGIC MAP OF THE OCEANSIDE 30' x 60' QUADRANGLE, CALIFORN.IA Compiled by Michael P. Kennedy1 and Siang S. Tan 1 2007 Digital preparation by Kelly R. 8ovard2, Rachel M. Alvarez2, Michael J. Watson2, and Ca ~los I. Guti.erre-z1 ,1. Otc>al1'M~li,l~U°", G;iJIJomlo Giooloalcal:trUNoy Z, IJ.S.. Goologg! Su,vay, °"llllltmtlf11 ol l:a~h --UnMlrlllly ol Cllllamlo, Rt,or>l(jo _L _ _l!_ ___ _ D 70 _L_ 70 -Ir- -+- EB -+- 6D ---l3- 55 ----"---- --- Geotechnical Exploration, Inc. FOUNDATION REQUIREMENTS NEAR SLOPES TOP OF COMPACTED FILL SLOPE Proposed Structure Concrete Floor Slab \ Setback (Any loose soils on the slope surface shall not be considered to provide lateral or vertical strength for the footing or for slope stability. Needed depth of embedment shall be measure from competent soil.) Reinforcement of Foundations and Floor Slabs Following the Recommendations of the Architect or Structural Engineer. Concrete Foundation 18" Minimum or as Deep as Required for Lateral Stability COMPACTED FILL SLOPE WITH MAXIMUM INCLINATION AS PER SOILS REPORT. Total Depth of Footing Measured from Finish Soil Subgrade COMPACTED FILL ' ~ ' ' ' Outer Most Fac'e-----8'-----' of Footing TYPICAL SECTION ( Showing Proposed Foundation Located Within 8 Feet of Top of Slope) 24-14681-Vl.dwg E a., 0 Q. it: 0 Q) V') (.)'+-c 0 0 Q. 1no i:5 I- 18" FOOTING/ 8' SETBACK Total Depth of Footing * 1.5: 1.0 SLOPE 2.0: 1.0 SLOPE 0 82" 66" 2' 66" 54" 4' 51" 42" 6' 34" 30" 8' 18" 18" * when applicable Figure No. VI Job No. 24-14681 41i~,. Geotechnical .-, Exploration, Inc. ~ June2024 RECOMMENDED SUBGRADE RETAINING WALL DRAINAGE SCHEMATIC Proposed Retaining Wall . • ..• •·. i,. ..• . . . ' . ..• ~ .": .•·· .. •:~ . . . ._ ·, .•... . . ' :. ► •• : • • •• :~ •. "· .. 1,,..,• •• i---.-,.,.............,.,.....,......,.,...........,..,..,...............,.............,.. ............ .,.,...............,...............,,...........,..................,.,...--«<~~~~~~~~~ ' ~~»>~~,«,," <✓-1/ //✓ /// J-Drain 2~ or Equival;~f ---\_ Properly Compacted Backfill Waterproofing Membrane To Top Of Wall ------J-Drain SWD Sealant NOTTO SCALE NOTE: As an option to Miradrain 6000, Gravel or Crushed rock 3/4" maximum diameter may be used with a minimum 12" thickness along the interior face of the wall and 2.0 cu.ft/ft. of pipe gravel envelope. 24-14681-Vll.dwg Figure No. VII Job No. 24-14681 ~~ Geofechnlcal ~1,-,lirll Exploration, Inc. ~ ~ June 2024 APPENDIX A UNIFIED SOIL CLASSIFICATION SYSTEM (U.S.C.S.) SOIL DESCRIPTION Coarse-grained (More than half of material is larger than a No. 200 sieve) GRAVELS, CLEAN GRAVELS GW Well-graded gravels, gravel and sand mixtures, little (More than half of coarse fraction or no fines. is larger than No. 4 sieve size, but smaller than 3”) GP Poorly graded gravels, gravel and sand mixtures, little or no fines. GRAVELS WITH FINES GC Clay gravels, poorly graded gravel-sand-silt mixtures SANDS, CLEAN SANDS SW Well-graded sand, gravelly sands, little or no fines (More than half of coarse fraction is smaller than a No. 4 sieve) SP Poorly graded sands, gravelly sands, little or no fines. SANDS WITH FINES SM Silty sands, poorly graded sand and silty mixtures. SC Clayey sands, poorly graded sand and clay mixtures. Fine-grained (More than half of material is smaller than a No. 200 sieve) SILTS AND CLAYS Liquid Limit Less than 50 ML Inorganic silts and very fine sands, rock flour, sandy silt and clayey-silt sand mixtures with a slight plasticity CL Inorganic clays of low to medium plasticity, gravelly clays, silty clays, lean clays. OL Organic silts and organic silty clays of low plasticity. Liquid Limit Greater than 50 MH Inorganic silts, micaceous or diatomaceous fine sandy or silty soils, elastic silts. CH Inorganic clays of high plasticity, fat clays. OH Organic clays of medium to high plasticity. HIGHLY ORGANIC SOILS PT Peat and other highly organic soils Ii APPENDIX B Regional Geologic Descriptions In the Coastal Plain region, where the subject site is located, the “basement” consists of Mesozoic crystalline rocks. Basement rocks are also exposed as high relief areas (e.g., Black Mountain northeast of the subject property and Cowles Mountain near the San Carlos area of San Diego). Younger Cretaceous and Tertiary sediments lap up against these older features. These sediments form a “layer cake” sequence of marine and non-marine sedimentary rock units, with some formations up to 140 million years old. Faulting related to the La Nación and Rose Canyon Fault zones has broken up this sequence into a number of distinct fault blocks in the southwestern part of the county. Northwestern portions of the county are relatively undeformed by faulting (Demere, 1997). The Peninsular Range forms the granitic spine of San Diego County. These rocks are primarily plutonic, forming at depth beneath the earth’s crust 140 to 90 million years ago as the result of the subduction of an oceanic crustal plate beneath the North American continent. These rocks formed the much larger Southern California batholith. Metamorphism associated with the intrusion of these great granitic masses affected the much older sediments that existed near the surface over that period of time. These metasedimentary rocks remain as roof pendants of marble, schist, slate, quartzite and gneiss throughout the Peninsular Ranges. Locally, Miocene-age volcanic rocks and flows have also accumulated within these mountains (e.g., Jacumba Valley). Regional tectonic forces and erosion over time have uplifted and unroofed these granitic rocks to expose them at the surface (Demere, 1997). The Salton Trough is the northerly extension of the Gulf of California. This zone is undergoing active deformation related to faulting along the Elsinore and San Jacinto Fault Zones, which are part of the major regional tectonic feature in the southwestern portion of California, the San Andreas Fault Zone. Translational movement along these fault zones has resulted in crustal rifting and subsidence. The Salton Trough, also referred to as the Colorado Desert, has been filled with sediments to depth of approximately 5 miles since the movement began in the early Miocene, 24 million years ago. The source of these sediments has been the local mountains as well as the ancestral and modern Colorado River (Demere, 1997). The San Diego area is part of a seismically active region of California. It is on the eastern boundary of the Southern California Continental Borderland, part of the Peninsular Ranges Geomorphic Province. This region is part of a broad tectonic boundary between the North American and Pacific Plates. The actual plate boundary is characterized by a complex system of active, major, right-lateral strike-slip faults, trending northwest/southeast. This fault system extends eastward to the San Andreas Fault (approximately 70 miles from San Diego) and westward to the San APPENDIX B/Page 2 Clemente Fault (approximately 50 miles off-shore from San Diego) (Berger and Schug, 1991). In California, major earthquakes can generally be correlated with movement on active faults. As defined by the California Division of Mines and Geology, now the California Geological Survey (CGS), an "active" fault, described by CGS (2018) as a Holocene-Active fault, is one that has had (ground) surface displacement within Holocene time, the last 11,700. In addition, “potentially active fault” has been amended to Pre-Holocene fault: a fault whose recency of past movement is older than 11,700 years, and thus does not meet the criteria of Holocene-Active fault as defined in the State Mining and Geology Board regulations. A three-tier fault classification is used as follows: • Active Faults: Faults that have demonstrable surface displacement during Holocene time. • Potentially Active Faults: Faults with Quaternary displacement but Holocene surface displacement is indeterminate. • Inactive Faults: Pre-Quaternary faults. During recent history, prior to April 2010, the San Diego County area has been relatively quiet seismically. The youngest paleoearthquake that cuts the early historical living surface is likely the 1862 San Diego earthquake that had an estimated magnitude of M6 (Legg and Agnew, 1979; Singleton et al., 2019). Paleoseismic trenches at the Presidio Hills Golf Course on the main trace of the Rose Canyon Fault contained evidence for historical ground rupturing earthquakes as recently as 1862 and the mid-1700s. Results of the study also suggest the Rose Canyon Fault has a ~700-800-year recurrence interval (Singleton et al., 2019). On June 15, 2004, a M5.3 earthquake occurred approximately 45 miles southwest of downtown San Diego (26 miles west of Rosarito, Mexico). Another widely felt earthquake on a distant southern California fault was a M5.4 event that took place on July 29, 2008, west-southwest of the Chino Hills area of Riverside County. Several earthquakes ranging from M5.0 to M6.0 occurred in northern Baja California, centered in the Gulf of California on August 3, 2009. A M5.8 earthquake followed by a M4.9 aftershock occurred on December 30, 2009, centered about 20 miles south of the Mexican border city of Mexicali. On April 04, 2010, a large earthquake occurred in Baja California, Mexico. It was widely felt throughout the southwest including Phoenix, Arizona and San Diego in California. This M7.2 event, the Sierra El Mayor earthquake, occurred in northern Baja California, approximately 40 miles south of the Mexico-USA border at shallow depth along the principal plate boundary between the North American and Pacific APPENDIX B/Page 3 plates. According to the U.S. Geological Survey this is an area with a high level of historical seismicity, and it has recently also been seismically active, although this is the largest event to strike in this area since 1892. The April 04, 2010, earthquake appears to have been larger than the M6.9 earthquake in 1940 or any of the early 20th century events (e.g., 1915 and 1934) in this region of northern Baja California. This event's aftershock zone extends significantly to the northwest, overlapping with the portion of the fault system that is thought to have ruptured in 1892. Ground motions for the April 04, 2010, main event, recorded at stations in San Diego and reported by the California Strong Motion Instrumentation Program (CSMIP), ranged up to 0.058g. On July 07, 2010, a M5.4 earthquake occurred in Southern California at 4:53 pm (Pacific Time) about 30 miles south of Palm Springs, 25 miles southwest of Indio, and 13 miles north-northwest of Borrego Springs. The earthquake occurred near the Coyote Creek segment of the San Jacinto Fault. The earthquake exhibited right lateral slip to the northwest, consistent with the direction of movement on the San Jacinto Fault. It was followed by more than 60 aftershocks of M1.3 and greater during the first hour. In the last 50 years, there have been four other earthquakes in the magnitude M5.0 range within 20 kilometers of the Coyote Creek segment: M5.8 in 1968, M5.3 on 2/25/1980, M5.0 on 10/31/2001, and M5.2 on 6/12/2005. The biggest earthquake near this location was the M6.0 Buck Ridge earthquake on 3/25/1937. 5211 Carlsbad Boulevard, Carlsbad, CA Latitude, Longitude: 33.1305, -117.3344 Date 6/17/2024, 9:34:13 AM Design Code Reference Document ASCE7-16 Risk Category II Site Class D - Stiff Soil Type Value Description SS 1.125 MCER ground motion. (for 0.2 second period) S1 0.404 MCER ground motion. (for 1.0s period) SMS 1.181 Site-modified spectral acceleration value SM1 null -See Section 11.4.8 Site-modified spectral acceleration value SDS 0.788 Numeric seismic design value at 0.2 second SA SD1 null -See Section 11.4.8 Numeric seismic design value at 1.0 second SA Type Value Description SDC null -See Section 11.4.8 Seismic design category Fa 1.05 Site amplification factor at 0.2 second Fv null -See Section 11.4.8 Site amplification factor at 1.0 second PGA 0.5 MCEG peak ground acceleration FPGA 1.1 Site amplification factor at PGA PGAM 0.55 Site modified peak ground acceleration TL 8 Long-period transition period in seconds SsRT 1.125 Probabilistic risk-targeted ground motion. (0.2 second) SsUH 1.268 Factored uniform-hazard (2% probability of exceedance in 50 years) spectral acceleration SsD 1.5 Factored deterministic acceleration value. (0.2 second) S1RT 0.404 Probabilistic risk-targeted ground motion. (1.0 second) S1UH 0.448 Factored uniform-hazard (2% probability of exceedance in 50 years) spectral acceleration. S1D 0.6 Factored deterministic acceleration value. (1.0 second) PGAd 0.608 Factored deterministic acceleration value. (Peak Ground Acceleration) PGAUH 0.5 Uniform-hazard (2% probability of exceedance in 50 years) Peak Ground Acceleration CRS 0.888 Mapped value of the risk coefficient at short periods CR1 0.902 Mapped value of the risk coefficient at a period of 1 s CV 1.325 Vertical coefficient APPENDIX C Proposed Carlsbad Boulevard HomesJob No. 24-14681 0.768 0.511 D 1.9 ' Carlsbad Tide Pool ' Go gle OS HPD Teak & Deck Professionals Q Map data ©2024 Google APPENDIX D SOIL MOISTURE INFORMATION AND VAPOR BARRIER MEMBRANES Soil moisture vapor can result in damage to moisture-sensitive floors, some floor sealers, or sensitive equipment in direct contact with the floor, in addition to mold and staining on slabs, walls and carpets. The common practice in Southern California is to place vapor retarders made of PVC, or of polyethylene. PVC retarders are made in thickness ranging from 10- to 60-mil. Polyethylene retarders, called visqueen, range from 5- to 10-mil in thickness. These products are no longer considered adequate for moisture protection and can actually deteriorate over time. Specialty vapor retarding and barrier products possess higher tensile strength and are more specifically designed for and intended to retard moisture transmission into and through concrete slabs. The use of such products is highly recommended for reduction of floor slab moisture emission. The following American Society for Testing and Materials (ASTM) and American Concrete Institute (ACI) sections address the issue of moisture transmission into and through concrete slabs: ASTM E1745-09 Standard Specification for Plastic Water Vapor Retarders Used in Contact Concrete Slabs; ASTM E1643-18a Standard Practice for Selection, Design, Installation, and Inspection of Water Vapor Retarders Used in Contact with Earth or Granular Fill Under Concrete Slabs; ACI 302.2R-06 Guide for Concrete Slabs that Receive Moisture-Sensitive Flooring Materials; and ACI 302.2R- 06 Guide to Concrete Floor and Slab Construction. Based on the above, we recommend that the vapor barrier consist of a minimum 15- mil extruded polyolefin plastic (no recycled content or woven materials permitted). Permeance as tested before and after mandatory conditioning (ASTM E1745 Section 7.1 and subparagraphs 7.1.1-7.1.5) should be less than 0.01 perms (grains/square foot/hour/per inch of Mercury) and comply with the ASTM E1745-09 Class A requirements. Installation of vapor barriers should be in accordance with ASTM E1643-18a. The basis of design is 15-mil StegoWrap vapor barrier placed per the manufacturer’s guidelines. Reef Industries Vapor Guard membrane has also been shown to achieve a permeance of less than 0.01 perms. We recommend that the slab be poured directly on the vapor barrier, which is placed directly on the prepared properly compacted smooth subgrade soil surface. Common to all acceptable products, vapor retarder/barrier joints must be lapped at least 6 inches. Seam joints and permanent utility penetrations should be sealed with the manufacturer’s recommended tape or mastic. Edges of the vapor retarder should be extended to terminate at a location in accordance with ASTM E1643-18a or to an alternate location that is acceptable to the project’s structural engineer. All terminated edges of the vapor retarder should be sealed to the building foundation APPENDIX D/Page 2 (grade beam, wall, or slab) using the manufacturer’s recommended accessory for sealing the vapor retarder to pre-existing or freshly placed concrete. Additionally, in actual practice, stakes are often driven through the retarder material, equipment is dragged or rolled across the retarder, overlapping or jointing is not properly implemented, etc. All these construction deficiencies reduce the retarder’s effectiveness. In no case should retarder/barrier products be punctured or gaps be allowed to form prior to or during concrete placement. Vapor barrier-safe screeding and forming systems should be used that will not leave puncture holes in the vapor barrier, such as Beast Foot (by Stego Industries) or equivalent. Vapor retarders/barriers do not provide full waterproofing for structures constructed below free water surfaces. They are intended to help reduce or prevent vapor transmission and/or capillary migration through the soil and through the concrete slabs. Waterproofing systems must be designed and properly constructed if full waterproofing is desired. The owner and project designers should be consulted to determine the specific level of protection required. Following placement of any concrete floor slabs, sufficient drying time must be allowed prior to placement of floor coverings. Premature placement of floor coverings may result in degradation of adhesive materials and loosening of the finish floor materials. 18 June 2025 Mr. John Norum Job No. 24-14681 KMJ Real Estate 2888 Locker Avenue East, Suite 200 Carlsbad, CA 92010 Subject: Grading and Foundation Plans Review Carlsbad Boulevard Homes 5211 Carlsbad Boulevard Carlsbad California Dear Mr. Norum: As requested, we have reviewed the latest civil grading plans (undated) for the subject project, and prepared by Pasco Laret and Suiter (PLSA) showing details for the driveway and pedestrian walkways to be constructed with pavers, and other details for runoff water infiltration and site drainage. The undated reviewed plans include six sheets that we have reviewed from a geotechnical engineering viewpoint to verify adequate conformance with our geotechnical recommendations presented in our preliminary geotechnical report for the project dated June 17, 2024 (revised June 18, 2025). We have also reviewed the structural plans for the project with signature date May 30, 2025 prepared by Gouvis Engineering, including sheets SN1.1, SN1-SN3, S-1.1- S-1.5, SD1, SD1A, SD2-SD4. The structural plans details and specifications have been found to be in compliance with our recommendations presented in our Preliminary Geotechnical Report for the project, dated June 17, 2024; and Revised Preliminary Geotechnical Report, dated June 18, 2025. The referenced and reviewed grading plans and also the structural foundation plans have been found to be in compliance with our recommendations. A copy of our revised preliminary geotechnical report and this letter should be provided to all pertinent contractors involved with the soil preparation and foundation construction. Any grading should be performed per the city approved plans and grading ordinance, and per the recommendations presented in our geotechnical report. 4~~-Geotechnical Exploration, Inc. SOIL AND FOUNDATION ENGINEERING • GROUNDWATER • ENGINEERING GEOLOGY 7420 TRADE STREET• SAN DIEGO, CA. 92121 • (858) 549-7222 • FAX: (858) 549-1604 • EMAIL: geotech@gei-sd.com Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 2 Should you have any questions, please feel free to call our office. Reference to our Job No. 24-14681 will expedite a response to your inquiries. Respectfully submitted, GEOTECHNICAL EXPLORATION, INC. _____________________________________ Jaime A. Cerros, P.E. R.C.E. 34422/G.E. 2007 Senior Geotechnical Engineer 18 June 2025 Mr. John Norum Job No. 24-14681 KMJ Real Estate 2888 Locker Avenue East, Suite 200 Carlsbad, CA 92010 Subject: Response to City of Carlsbad Geotechnical Report Review Carlsbad Boulevard Homes 5211 Carlsbad Boulevard Carlsbad California City Project ID: MS2024-0006 Grading Permit No:GR2025-0007 Dear Mr. Norum: As requested by your project civil engineer Mr. Bryan Knapp with Pasco Laret Suiter & Associates (PLSA), and as required by the City of Carlsbad reviewer, we are issuing this response letter in regards to City of Carlsbad geotechnical review comments to our “Report of Preliminary Geotechnical Investigation, Proposed Carlsbad Boulevard Homes, 5211 Carlsbad Boulevard, Carlsbad, California” dated June 17, 2024. The city geotechnical reviewer’s document is dated February 05, 2025. 1. Please review the most current grading plan for the project and provide any additional recommendations or modifications to the geotechnical report if necessary. GEI Response to Comment 1: We have reviewed the most current grading plans for the project prepared by PLSA and we are providing a revised geotechnical report with a revision date of June 18, 2025. The revisions made in the report indicate that all imported soils are to consist of soils with very low expansion potential. 2. The strength (direct shear) testing of the on-site soils that is presented in the geotechnical report indicates the values c=0 and φ=32.8. Please confirm and 4~~-Geotechnical Exploration, Inc. SOIL AND FOUNDATION ENGINEERING • GROUNDWATER • ENGINEERING GEOLOGY 7420 TRADE STREET• SAN DIEGO, CA. 92121 • (858) 549-7222 • FAX: (858) 549-1604 • EMAIL: geotech@gei-sd.com Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 2 provide the calculations to support the recommended bearing capacity of 2,400 psf for conventional continuous footings that is provided in the report. GEI Response to Comment 2: The bearing equation for continuous footings is 𝑄௕ =𝐶∗𝑁௖ +𝛾∗𝐷௙ +ଵ ଶ ∗𝛾∗𝐵∗𝑁ఊ; where C=the soil cohesion, is equal to zero in this case; 𝛾=120 pcf, soil unit weight; Nc, Nq, and Nγ soil bearing coefficients based on the soil friction angle using Vesic values (from Geotechnical Engineering Techniques and Practices by Roy Hunt) as follows: Nc=35.49; Nq=23.18; Nγ=30.22 corresponding to continuous footings at least 6 feet in length, and Df=1.5 feet in depth, and B=1.25 feet in width. Substituting our soil parameter values in the equation yielded the following ultimate bearing capacity: Qb=(0 x 35.49) + (120x 1.5 x 23.18) +(0.5 x 120 x 1.25 x 30.22) = 6438.9 psf We used a factor of safety of 2, which yielded an allowable bearing capacity of 3,219.45 psf. We recommended in our report an allowable soil bearing capacity of 2,400 psf. 3. The “Material for Fill” (pages 19/20), “Fill Compaction” (page 20), and Retaining Wall Design (pages 28/29) sections of the report indicate soils used as fill should have an Expansion Index below 50 (“Low”). However, other pages of the report indicate the on-site soils possess an Expansion Index of 0 (Very Low) per the laboratory testing (which the reviewer assumes was used as the basis for the foundation and slab recommendations provided in the report for the proposed structure). As soils with an Expansion Index over 20 are considered expansive and require mitigation in accordance with Sections Section 1803.5.3 and 1808.6 of the 2022 California Building Code, please revise the “Material for Fill” (pages 19/20), “Fill Compaction” (page 20), and “Retaining Wall Design” (pages 28/29) sections of the report as necessary to provide requirements for soil to have an Expansion Index below 20 (Very Low) and not 50. If soils with an Expansion Index up to 50 are recommended for use, please provide updated foundation/slab recommendations for the expansive soils as necessary to satisfy the requirements of Section 1808.6 of the 2022 California Building Code. Please provide the parameters (Effective Plasticity Index, etc.) as necessary for the structural engineer to apply the requirements of Section 1808.6 and indicate the specific method of Section 1808.6 (1808.6.1 through 1808.6.4) that GEI is recommending to satisfy the Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 3 requirements for expansive soils and Section 1808.6 and for slab-on-ground floor design. GEI Response to Comment 3: The on-site soils have a very low expansive index of zero. We are modifying our recommendations in our Preliminary Geotechnical Report for the project (Job No. 24-14681) dated June 17, 2024 and revised it as shown in the Revised Geotechnical Report dated June 18, 2025 to indicate that any imported soils to be used at the site to have a similar expansion index to the on-site soils, that is to have an expansion index classification of very low, EI equal to 20 or less. 4. Please provide the amount of anticipated total settlement that should be anticipated for design for the proposed development. GEI Response to Comment 4: We anticipate that the total settlement for the design of the proposed development will be less than 1 inch for properly compacted soils or dense natural soils, which is within the acceptable settlement tolerance for this type of project. 5. Please provide recommendations (allowed vertical height, angle of inclination, slot cutting/construction in section, shoring, etc.) for the temporary cuts anticipated for the construction of the proposed site walls located immediately adjacent to and along the north, south, and west property boundaries. Please provide the allowed time exposure for the foundation excavations prior to foundation/wall stem construction and backfilling. Recommendations should be provided as necessary to prevent any adverse impact to the existing adjacent off-site improvements and property. GEI Response Comment 5: All of the site retaining walls located within the project will be retaining new fill soils placed for the project inside the property. The new walls will not retain soils from adjacent properties. The foundation excavations may be exposed any normal time needed for construction after they are inspected to be in founded in suitable/firm soils prior to placing the steel reinforcing. If rainstorms occur prior to concrete placement in the footing excavations, the footing bearing soils will need to be re-inspected for adequacy. The backfill behind the stem of the retaining walls may only occur after the concrete inside the stem has cured sufficiently to comply with the specifications of the structural engineer. The new retaining walls construction will not have any adverse impact on the off-site improvements and property. 6. Please evaluate and discuss the potential for storm water infiltration at the subject site as part of the proposed project. Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 4 GEI Response Comment 6: On May 8, 2024 we performed percolation testing at three locations considered feasible for potential storm water infiltration BMPs at depths ranging from 36 to 42 inches per the requirements of the City of Carlsbad BMP Design Manual, in accordance with Appendix D. Our infiltration testing was conducted northeast, southeast and west of the proposed development. Testing at the three locations revealed falling head rates ranging from 2.667 to 2.857 minutes/inch. The percolation test rate results were converted to an infiltration rate using the Porchet Method, and indicates infiltration rates with temperature correction of 1.793-inch/hour, 1.854-inch/hour and 2.004- inch/hour. Applying the minimum factor of safety of 2.0, the infiltration rates were reduced to 0.8965-inch/hour, 0. 927-inch/hour and 1.002-inch/hour. Based on our review of USDA Web Soil Survey, the site has been assigned to hydrologic soil group (HSG) B. Hydrologic soil group B indicates “…soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture.” It is our opinion that the USDA’s assigned hydrologic soil group of B is representative of the encountered sandy surface soils on the project site. Based on the results of our percolation testing and evaluation of the infiltration rates, and the results of the percent soil passing No. 200 sieve, it is our professional opinion that the site has relatively favorable geologic and soil conditions, along with the measured soil infiltration rates, for the design of full infiltration at this time, and is therefore suitable at current ground elevations for infiltration of storm water discharge on the proposed permeable paver driveway areas shown on the most current grading plan. 7. Please provide a detailed summary list of the geotechnical observations/testing services that should be provided during the construction of the proposed development (grading residential structure, site walls, hardscape, etc. GEI Response Comment 7: During grading, we should observe the bottom of the excavation of removed soils to determine the suitability of the excavation bottom bearing soils. After establishing the suitable bottom, the grading contractor will place horizontal soil lifts not exceeding 8-inches in vertical height and compact the soil by mechanical means. Field density tests of placed and compacted soils will be tested at approximately every 2 feet in vertical thickness, verifying the adequacy of soil moisture content and relative compaction. Soil samples will be collected during the grading to verify the maximum dry density of the soils being placed as fill material, and verify the adequacy of the imported soils by performing sieve test analysis and expansion Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 5 index tests as well as maximum dry density and optimum moisture tests. In addition, we will need to verify the adequacy of the final footing excavation bottom soils and embedment depth, soil moisture content and compaction of on-site soils being used for any trench and retaining wall backfill, and moisture content of subgrade soils to receive pavement or flatwork improvements. In public street areas, our firm should obtain soil samples and perform R-value tests in areas to receive pavement (if required) to verify adequacy of pavement cross section as well as compaction of base layer and asphalt concrete, gradation of base material and determination of maximum dry density in the laboratory as well as relative compaction in the field. Should you have any questions, please feel free to call our office. Reference to our Job No. 24-14681 will expedite a response to your inquiries. Respectfully submitted, GEOTECHNICAL EXPLORATION, INC. _______________________________ ______________________________ Jaime A. Cerros, P.E. Richard A. Cerros, P.E. R.C.E. 34422/G.E. 2007 R.C.E. 94223 Senior Geotechnical Engineer chard A. Cerros, P. E. r F q47:n 06 August 2025 Mr. John Norum Job No. 24-14681 KMJ Real Estate 2888 Locker Avenue East, Suite 200 Carlsbad, CA 92010 Subject: Response to City of Carlsbad Geotechnical Report Review Carlsbad Boulevard Homes 5211 Carlsbad Boulevard Carlsbad California City PROJECT ID: MS2024-0006 GRADING PERMIT No:GR2025-0007 Dear Mr. Norum: As requested by Mr. Bryan Knapp with Pasco Laret Suiter & Associates (PLSA), and as required by the City of Carlsbad reviewer, we are issuing this response letter regarding City geotechnical comments to our Report of Preliminary Geotechnical Investigation dated June 17, 2024. The geotechnical reviewer’s document is dated June 30, 2025. 1. The strength (direct shear) testing of the on-site soils that is presented in the geotechnical report indicates the values C=0 and Φ=32.8. Please confirm and provide the calculation to support the recommended bearing capacity of 2,400 psf for conventional continuous footings that is provided in the report. (repeat comment – in the response to this comment presented in the recently submitted “Response to City of Carlsbad Geotechnical Report Review, Carlsbad Boulevard Homes…,” the consultant indicates a factor of safety of 2 was used to determine the allowable bearing capacity value of 2,400 psf. With respect to the calculation for the allowable bearing capacity, please provide the basis and justification for the use of a factor of safety of 2 in the calculation versus the customary industry standard factor of safety value of 3. Please provide references as necessary to support the use of a factor of safety of 2 for allowable bearing capacity.) 4~~-Geotechnical Exploration, Inc. SOIL AND FOUNDATION ENGINEERING • GROUNDWATER • ENGINEERING GEOLOGY 7420 TRADE STREET• SAN DIEGO, CA. 92121 • (858) 549-7222 • FAX: (858) 549-1604 • EMAIL: geotech@gei-sd.com Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 2 GEI Response: We are providing 4 references as follows: 1.) Geotechnical Engineering Techniques and Practices by Roy B. Hunt, McGraw Hill 1984, page 303; 2.) The Engineering of Foundations, by Rodrigo Salgado, McGraw Hill, 2008, page 29; 3.) Foundation Design Principles and Practices by Donald P. Coduto, Prentice Hall, 1994, page 185; and 4.) The Foundation Engineering Handbook by Manjriker Gunaratne, CRC Taylor and Francis Group, 2006, Page 104, Table 3.4 C. To apply a factor of safety to the soil bearing capacity, several factors need to be considered, including the structure type category, the degree of confidence of the soil conditions and the adequacy of the soil data, and the likelihood of total loads to occur. There are three structural categories used for factors of safety classification: Type A structures which are railway bridges, warehouses, blast furnaces, hydraulic retaining walls, silos, highway bridges, etc. where maximum design loads may occur occasionally; and consequences of failure could be serious, or the loads may occur often and the consequences of the failure could be disastrous. Type B structures are for light industrial public buildings and Type C structures are for apartment and office buildings, where the maximum design load are unlikely to occur. A factor of safety of 2 in calculating the soil/foundation bearing capacity may be used where the soil conditions are well defined and will be closely controlled and monitored during grading/construction, and where the structure type category is C (i.e. apartment or office). In our professional opinion, the site soil conditions are known and well defined on this project. The dead loads in the structural design are calculated very close to real loads but design live loads, per code, are estimated high and not likely to occur in real life. A factor of safety of 3 applies when soil conditions are well defined, and the structure type category is A, and full design loads are likely to occur. A factor of safety of 4 applies when soil conditions are not well defined and limited on the soil exploration, the structure is type category A, and full design loads are likely to occur. In Donald P. Coduto’s, Foundation Design Principles and Practices, page 185 indicates that a higher factor of safety is used when the soil exploration is very limited and the project structure type category A. In our geotechnical report for the subject project, we calculated the soil bearing capacity for a continuous footing using the bearing equation for continuous footings of the encountered soil parameters, stratigraphy well defined: Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 3 𝑄௕ =𝑐𝑁௖ +𝛾𝐷௙𝑁௤ +1 2 𝛾𝐵𝑁ఊ where C=soil cohesion (equal to zero in this case); γ=120 pcf, soil unit weight; and Nc, Nq, and Nγ are soil bearing coefficients using Vesic values (from Geotechnical Engineering Techniques and Practices by Roy Hunt). Therefore, for a friction angle of 32.8°, Nc=35.49; Nq=23.18; and Nγ=30.22 for continuous footings at least 6 feet in length; and Df=1.5 feet in depth; and B=footing width of 1.25 feet. Substituting the values into the equation results in the following: Qb=(0 x 35.49)+(120x 1.5 x 23.18)+(0.5 x 1.25 x 120 x 30.22) = 6438.9 psf If we use a factor of safety of 2, the calculation is 3219.4 psf. We conservatively adjusted the bearing capacity and recommended an allowable soil bearing capacity of 2,400 psf, which translates to an actual factor of safety of 6,438.9/2,400 which equals 2.68. 2. Please provide recommendations (allowed vertical height, angle of inclination, slot cutting/construction in section, shoring, etc.) for the temporary cuts anticipated for the construction of the proposed site walls located immediately adjacent to and along the north, south, and west property boundaries. Please provide the allowed time exposure for the foundation excavations prior to foundation/wall stem construction and backfilling. Recommendations should be provided as necessary to prevent any adverse impact to the existing adjacent off-site improvements and property. (repeat comment – please provide recommendations for the temporary cuts associated with the proposed remedial grading and footing excavations (reportedly up to approximately 2.5’ below existing grade) along the property boundaries.) GEI Response: Based on the property line locations of the proposed retaining walls and their heights, it may be preferable to construct the retaining walls before the rough grading of the building pads is initiated. In doing so, the retaining wall excavation will be approximately 2 feet in depth and the foundation can be constructed, followed by retaining wall construction. The maximum differential between the adjacent properties and the project site will not be more than 2.5 feet and will not require shoring. Once the foundations are poured, the stems of the retaining walls can be constructed. Once the retaining wall concrete is cured and wall drainage and waterproofing is in place, the walls can be backfilled and the grading for the building pads can be performed at the same time. All new retaining walls will be retaining new fill soils placed for the project. The new walls will not retain soils from adjacent properties. The foundation excavations may be exposed at any time after they have been inspected and found to be in adequate bearing soils prior to placement of steel Carlsbad Blvd. Homes Job No. 24-14681 Carlsbad, California Page 4 reinforcement. If rain events occur prior to concrete placement of the footing excavations, the footing bearing soils will need to be re-inspected. The backfill behind the stem of the walls may only occur after the concrete inside the stem has cured sufficiently to comply with the structural engineer’s specifications. 3. Please provide a detailed summary list of the geotechnical observations/testing services that should be provided during the construction of the proposed development (grading, residential structure, site walls, hardscape, etc.). (repeat comment – please add temporary cuts associated with site grading, footings, and utility trenches to the list of geotechnical services to be performed during construction.) GEI Response: During grading, the geotechnical representative should observe the adequacy of the building pad excavation bottom bearing soils, perform field density tests of placed and recompacted soils to verify the adequacy of the soil moisture content and degree of relative compaction at least every 2 feet in vertical thickness, collect and verify the maximum dry density of the soils being placed as fill material, and verify the adequacy of imported soils by performing sieve tests and expansion index tests as well as maximum dry density and optimum moisture tests. In addition, adequacy of the footing excavation bottom bearing soils and depth should be verified. Adequacy of the soil moisture content and compaction of on-site or import soils being used for utility trench and retaining wall backfill, and the subgrade soils to receive pavement or flatwork improvements, should also be verified. In public street areas, soil samples should be collected to perform R-value tests to verify the adequacy of pavement cross section. The adequacy of compaction for the base layer and asphalt concrete, including verifying the adequacy of gradation of the base material and determine the laboratory maximum dry density, as well as relative compaction in the field, should also be performed. We do not anticipate temporary cuts to be required for this project. Should you have any questions, please feel free to call our office. Reference to our Job No. 24-14681 will expedite a response to your inquiries. Respectfully submitted, GEOTECHNICAL EXPLORATION, INC. _______________________________ ______________________________ Richard A. Cerros, P.E. Jaime A. Cerros, P.E. R.C.E. 94223 R.C.E. 34422/G.E. 2007 Senior Geotechnical Engineer R.C.E. 94223 .. !nior Geotechn