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Home My WebLink AboutPD 2021-0034; TREHAN RESIDENCE; REPORT OF PRELIMINARY GEOTECHNICAL INVESTIGATION; 2021-06-24 REPORT OF PRELIMINARY GEOTECHNICAL INVESTIGATION STARK HOUSE APN 216-160-10-00 LA COSTA AVENUE CARLSBAD, CALIFORNIA PREPARED FOR STARK HOUSE, LLC 290 LANDIS AVENUE, SUITE C CHULA VISTA, CALIFORNIA 91010 PREPARED BY CHRISTIAN WHEELER ENGINEERING 3980 HOME AVENUE SAN DIEGO, CALIFORNIA 92105 CHRISTIAN WHEELER E N G I N E E R I N G 3 9 8 0 H o m e A v e nu e S a n Di e g o , C A 9 2 1 05 6 1 9 -5 5 0- 1 7 00 F A X 61 9 - 55 0 - 17 0 1 June 24, 2021 Stark House LLC CWE 2200253.01 Chula Vista, California 91910 Attention: Ramiro Barajas Subject: Report of Preliminary Geotechnical Investigation Stark House, APN 216-160-10-00, La Costa Avenue, Carlsbad, California Ladies and Gentlemen: In accordance with your request and our proposal dated May 13, 2020, we have completed a preliminary geotechnical investigation for a proposed residential project to be constructed at the subject property. We are presenting herewith a report of our findings and recommendations. It is our opinion and judgment that no geotechnical conditions exist at or in the vicinity of the subject property that would preclude the construction of the proposed residential project provided the recommendations included in this report are implemented. If you have any questions after reviewing this report, please do not hesitate to contact our office. This opportunity to be of professional service is sincerely appreciated. Respectfully submitted, CHRISTIAN WHEELER ENGINEERING Daniel B. Adler, RCE #36037 Daniel J. Flowers, CEG #2686 DBA:dba;djf ec: ramk3@yahoo.com CHRISTIAN WHEELER E N G I N E E R I N G 3 9 8 0 H o m e A v e nu e S a n Di e g o , C A 9 2 1 05 6 1 9 -5 5 0- 1 7 00 F A X 61 9 - 55 0 - 17 0 1 CWE 2200253.01 Stark House APN 216-160-10-00, La Costa Avenue San Diego, California TABLE OF CONTENTS Page Introduction and Project Description ............................................................................................................................. 1 Scope of Services ................................................................................................................................................................ 2 Findings ................................................................................................................................................................................ 3 Site Description ............................................................................................................................................................... 3 General Geology and Subsurface Conditions ............................................................................................................ 3 Geologic Setting and Soil Description .................................................................................................................... 3 Artificial Fill ............................................................................................................................................................. 3 Subsoil ...................................................................................................................................................................... 4 Del Mar Formation ................................................................................................................................................ 4 Groundwater ............................................................................................................................................................... 4 Tectonic Setting .......................................................................................................................................................... 4 General Geologic Hazards ............................................................................................................................................ 5 General ......................................................................................................................................................................... 5 Landslide Potential and Slope Stability ..................................................................................................................... 5 Liquefaction.................................................................................................................................................................. 6 Flooding ....................................................................................................................................................................... 6 Tsunamis ...................................................................................................................................................................... 6 Seiches ........................................................................................................................................................................... 6 Other Potential Geologic Hazards .......................................................................................................................... 6 Conclusions .......................................................................................................................................................................... 6 Recommendations .............................................................................................................................................................. 7 Grading and Earthwork ................................................................................................................................................. 7 General ......................................................................................................................................................................... 7 Pregrade Meeting ........................................................................................................................................................ 7 Observation of Grading ............................................................................................................................................ 8 Clearing and Grubbing .............................................................................................................................................. 8 Site Preparation ........................................................................................................................................................... 8 Fill Slope Keyway ....................................................................................................................................................... 8 Excavation and Backfilling Characteristics ............................................................................................................... 8 Imported Fill ................................................................................................................................................................ 8 Processing of Fill Areas ............................................................................................................................................. 9 Compaction and Method of Filling .......................................................................................................................... 9 Surface Drainage ......................................................................................................................................................... 9 Foundations ................................................................................................................................................................... 10 General ....................................................................................................................................................................... 10 Post-Tensioned Foundations............................................................................................................................... 10 Shallow Foundations ............................................................................................................................................ 10 Dimensions ............................................................................................................................................................ 10 Bearing Capacity ................................................................................................................................................... 10 Footing Reinforcing ............................................................................................................................................. 11 Lateral Load Resistance ........................................................................................................................................... 11 Foundation Excavation Moisture Conditioning ............................................................................................... 11 Foundation Excavation Observation ...................................................................................................................... 11 Settlement Characteristics ....................................................................................................................................... 11 Expansive Characteristics ......................................................................................................................................... 11 Foundation Plan Review ........................................................................................................................................... 12 Soluble Sulfates ......................................................................................................................................................... 12 Seismic Design Factors ................................................................................................................................................ 12 TABLE OF CONTENTS (Cont.) CWE 2200253.01 Stark House APN 216-160-10-00, La Costa Avenue Carlsbad, California Risk Categories............................................................................................................................................................... 13 On-Grade Slabs ............................................................................................................................................................. 14 General ....................................................................................................................................................................... 14 Under-Slab Vapor Retarders ................................................................................................................................... 14 Exterior Concrete Flatwork .................................................................................................................................... 14 Utility Trenches ............................................................................................................................................................. 15 Limitations ......................................................................................................................................................................... 15 Review, Observation and Testing .............................................................................................................................. 15 Uniformity of Conditions ............................................................................................................................................ 15 Change in Scope ............................................................................................................................................................ 16 Time Limitations ........................................................................................................................................................... 16 Professional Standard ................................................................................................................................................... 16 Client's Responsibility .................................................................................................................................................. 17 Field Explorations............................................................................................................................................................. 17 Laboratory Testing............................................................................................................................................................ 17 ATTACHMENTS TABLES Table I Seismic Design Factors - 2019 CBC FIGURES Figure 1 Site Vicinity Map PLATES Plate 1 Site Plan & Geologic Map Plate 2 Geologic Cross Section A-A’ Plate 3 Fill Slope Keyway Detail APPENDICES Appendix A Subsurface Explorations Appendix B Laboratory Test Results Appendix C References Appendix D Recommended Grading Specifications-General Provisions PRELIMINARY GEOTECHNICAL INVESTIGATION STARK HOUSE LA COSTA AVENUE CARLSBAD, CALIFORNIA INTRODUCTION AND PROJECT DESCRIPTION This report presents the results of a preliminary geotechnical investigation performed for a proposed residential project to be located adjacent to and north of La Costa Avenue, California. The following Figure No. 1 presents a vicinity map showing the location of the property. Although no development plans are presently available, we assume that the subject project will consist of the construction of a two-story residential structure. It is anticipated that the proposed structure will be of wood- frame construction, supported by shallow foundations and incorporate conventional concrete on-grade floor slabs and raised floors. Grading to accommodate the proposed construction is expected to consist of cuts and fills up to about 2 feet from existing grades. To assist in the preparation of this report, we were provided with miscellaneous architectural plans prepared by Studio Uno Architecture, dated June 11, 2021. A copy of the site plan included in the architectural plan set was used as a base map for our Site Plan and Geologic Map, and is included herein as Plate No. 1. We have also included a copy of the building section on sheet A-7 of the plan set, modified to depict the site geology and included herein as Plate No. 2. This report has been prepared for the exclusive use of Stark House LLC, and its design consultants, for specific application to the project described herein. Should the project be modified, the conclusions and recommendations presented in this report should be reviewed by Christian Wheeler Engineering for conformance with our recommendations and to determine whether any additional subsurface investigation, laboratory testing and/or recommendations are necessary. Our professional services have been performed, our findings obtained and our recommendations prepared in accordance with generally accepted engineering principles and practices. This warranty is in lieu of all other warranties, expressed or implied. CHRISTIAN WHEELER E N G I N E E R I N G 3 9 8 0 H o m e A v e nu e S a n Di e g o , C A 9 2 1 05 6 1 9 -5 5 0- 1 7 00 F A X 61 9 - 55 0 - 17 0 1 STARK HOUSE LA COSTA AVENUE CARLSBAD, CALIFORNIA DATE:JUNE 2021 BY: SRD JOB NO.: 2200253.01 FIGURE NO.: 1 CHRISTIAN WHEELER E N G I N E E R I N G SITE VICINITY 2SHQ6WUHHW0DSFRQWULEXWRUV PROJECT SITE a arra Driv L anr rt' CWE 2200253.01 June 24, 2021 Page No. 2 SCOPE OF SERVICES Our preliminary geotechnical investigation consisted of surface reconnaissance, subsurface exploration, obtaining representative soil samples, laboratory testing, analysis of the field and laboratory data, and review of relevant geologic literature. Our scope of service did not include assessment of hazardous substance contamination, recommendations to prevent floor slab moisture intrusion or the formation of mold within the structures, evaluation or design of storm water infiltration facilities, or any other services not specifically described in the scope of services presented below. More specifically, the intent of our proposed investigation was to:  Excavate 5 test pits and 1 hand-augured boring to explore the existing soil conditions and collect representative soil samples.  Backfill the test pits with the removed soil. It should be noted that the soil was not compacted and will have to be removed and replaced as compacted fill during the future site grading.  Evaluate, by laboratory tests and our past experience with similar soil types, the engineering properties of the various soil strata that may influence the proposed construction, including bearing capacities, expansive characteristics and settlement potential.  Describe the general geology at the site including possible geologic hazards that could have an effect on the proposed construction, and provide the seismic design parameters in accordance with the 2019 edition of the California Building Code.  Discuss potential construction difficulties that may be encountered due to soil conditions, groundwater or geologic hazards, and provide geotechnical recommendations to mitigate identified construction difficulties.  Provide site preparation and grading recommendations for the anticipated work.  Provide foundation recommendations for the type of construction anticipated and develop soil engineering design criteria for the recommended foundation designs.  Provide earth retaining wall design recommendations.  Provide a preliminary geotechnical report presenting the results of our investigation, including a plot plan showing the location of our subsurface explorations, excavation logs, laboratory test results, and our conclusions and recommendations for the proposed project. Although a test for the presence of soluble sulfates within the soils that may be in contact with reinforced concrete was performed as part of the scope of our services, it should be understood Christian Wheeler Engineering does not practice corrosion engineering. If a corrosivity analysis is considered necessary, we recommend that the client retain an engineering firm that specializes in this field to consult with them on this CWE 2200253.01 June 24, 2021 Page No. 3 matter. The results of our sulfate testing should only be used as a guideline to determine if additional testing and analysis is necessary. FINDINGS SITE DESCRIPTION The subject site consists of a vacant, rectangular-shaped lot located adjacent to and north of La Costa Avenue in the City of Carlsbad, California. The lot is identified as Lot 10 of La Costa-South Unit #1 and APN 216- 160-10-00. The property is bounded on the south by La Costa Avenue, on the east by a private access drive, and is otherwise bounded by single-family residential properties. A 5 foot-wide sewer easement is located along the westerly property line. Topographically, the southern portion of the lot is near flat-lying, whereas the rest of the lot slopes gently down to the north. Retaining walls less than about 5 feet high exist at the northern and eastern property lines. These walls retain the subject site. According to site plan by Uno Architecture, site elevations range from about 100 feet along La Costa Avenue to about and 75 feet at the northwest corner of the property. In reviewing the referenced report by Benton Engineering, Inc. and the photographs for available years, it appears that the subject site was graded in the late 1960’s with the development of La Costa-South Unit #1. Grading and earthwork at the subject site appear to have consisted of terracing the once gently sloping hillside and placing the majority of the fills in the northerly portion of the site. GENERAL GEOLOGY AND SUBSURFACE CONDITIONS GEOLOGIC SETTING AND SOIL DESCRIPTION: The subject site is located in the Coastal Plains Physiographic Province of San Diego County. Based upon the findings of our subsurface explorations it was determined that the property is underlain by artificial fill, subsoil, and Delmar Formation. These materials are described below in order of increasing age: ARTIFICIAL FILL (Qaf): The lot was found to be underlain be artificial fill. As encountered in the subsurface explorations, these materials extend to a maximum depth of about 4¾ feet below existing grade (test pit P-2). However, deeper fill soils may exist in areas of the lot not investigated. The artificial fill generally consisted of olive brown to grayish-brown, brown, and light brown, damp, soft to medium stiff, sandy clayey (CL). The fill soils encountered within test pits P-4, P-5, and within a portion of test pits P-3 consisted of light yellowish-brown, moist, medium dense, silty sand (SM). The clayey fill soils CWE 2200253.01 June 24, 2021 Page No. 4 (CL) were found have high expansion potential (EI=98), whereas the sandy fill soils (SM) were judged to have a low expansive potential (EI between 21 and 50). SUBSOIL (Unmapped): A relatively thin subsoil layer with a maximum thickness of about 2 feet was encountered underlying the artificial fill in test pits P-1, P-2, P-3, and HA-1. However, thicker subsoil may exist in areas of the lot not investigated. The subsoil generally consisted of grayish-brown and dark brown, moist, medium stiff and stiff, fat clay (CH). The subsoil was judged to have very high expansion potential (EI=139). DELMAR FORMATION (Td): Tertiary-age sedimentary deposits of the Delmar Formation were encountered underlying the surficial soils throughout the site. As encountered in our subsurface exploration, the formational soils consisted of interbedded light yellowish brown, moist, dense, silty sand (SM), olive brown, moist, stiff, fat clay (CH)., and olive brown, moist, dense, clayey sand (SC). The sandy materials (SM) were judged to have a very low Expansion Index (EI<20). The sandy clayey materials (SC) were judged to have a low to medium Expansion Index (EI between 21 and 90), whereas the fat clay (CH) was found to have a very high expansion Index (EI=141). GROUNDWATER: No groundwater or seepage was encountered in our subsurface explorations. However, it should be recognized that minor groundwater seepage problems might occur after construction and landscaping are completed, even at a site where none were present before construction. 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 anticipated construction and the permeability of the on-site soils, it is our opinion that any seepage problems that 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. TECTONIC SETTING: No faults are known to traverse the subject site. However, it should be noted that much of Southern California, including the San Diego County area, is characterized by a series of Quaternary-age fault zones that consist of several individual, en echelon faults that generally strike in a northerly to northwesterly direction. Some of these fault zones (and the individual faults within the zone) are classified as “active” according to the criteria of the California Division of Mines and Geology. Active fault zones are those that have shown conclusive evidence of faulting during the Holocene Epoch (the most recent 11,000 years). The Division of Mines and Geology used the term “potentially active” on Earthquake Fault Zone maps until 1988 to refer to all Quaternary-age (last 1.6 million years) faults for the purpose of evaluation for possible zonation in accordance with the Alquist-Priolo Earthquake Fault Zoning Act and identified all Quaternary-age faults as “potentially active” except for certain faults that were presumed to be inactive based on direct geologic evidence of inactivity CWE 2200253.01 June 24, 2021 Page No. 5 during all of Holocene time or longer. Some faults considered to be “potentially active” would be considered to be “active” but lack specific criteria used by the State Geologist, such as sufficiently active and well-defined. Faults older than Quaternary-age are not specifically defined in Special Publication 42, Fault Rupture Hazard Zones in California, published by the California Division of Mines and Geology. However, it is generally accepted that faults showing no movement during the Quaternary period may be considered to be “inactive”. A review of available geologic maps indicates that the nearest active fault zone is the Newport-Inglewood- Rose Canyon Fault Zone (RCFZ), located approximately 6 miles to the west of the site. The offshore location of the RCFZ near the site is based on marine geophysical surveys and according to the USGS the slip rate is not fully constrained, but appears to be approximately 1.0±0.5 mm/yr in the north, increasing to 1.5±0.5 mm/yr in the south. The County of San Diego Seismic Safety Element also indicates that the RCFZ could produce up to a magnitude 7.1 event. With these attributes the site can be considered a Near-Fault Site in accordance with the CBC 2019. Other active fault zones in the region that could possibly affect the site include the Coronado Bank Fault Zone to the southwest, the San Diego Trough and San Clemente Fault Zones to the west; the Palos Verdes Fault Zone to the northwest; and the Elsinore, San Jacinto and San Andreas Fault Zones to the northeast. GENERAL GEOLOGIC HAZARDS GENERAL: The site is located in an area where the risks due to significant geologic hazards are relatively low. No geologic hazards of sufficient magnitude to preclude the construction of the subject project are known to exist. In our professional opinion and to the best of our knowledge, the site is suitable for the proposed improvements. LANDSLIDE POTENTIAL AND SLOPE STABILITY: As part of this investigation, we reviewed the publication, “Landslide Hazards in the Northern Part of the San Diego Metropolitan Area" by Tan, 1995. This reference is a comprehensive study that classifies San Diego County into areas of relative landslide susceptibility. The subject site is located in Area 4-1, which is considered to be “most susceptible” to slope failures. Subarea 4- 1 includes slopes considered to be outside the limits of known landslides but contains observably or notably unstable slopes consisting of materials such as the Delmar Formation. Although most slopes within Subarea 4-1 do not currently contain landslide deposits, there is a possibility of failure even in the absence of activities of man (Tan, 1995). No evidence of landsliding or deep-seated slope failures were noted during our reconnaissance of the site or during review of the referenced geotechnical literature. It is our professional opinion and judgement that the on-site slopes will demonstrate minimum factors-of-safety of 1.5 or greater against global CWE 2200253.01 June 24, 2021 Page No. 6 and surficial slope failures once the recommended remedial grading has been completed. It is also our opinion that the proposed construction will not destabilize the neighboring properties. LIQUEFACTION: The near-surface soils encountered at the site are not considered susceptible to liquefaction due to such factors as soil density, grain-size distribution, plasticity and the absence of shallow groundwater conditions. FLOODING: As delineated on the Flood Insurance Rate Map (FIRM), panel 06073C1034H prepared by the Federal Emergency Management Agency, the site is in Zone X which is considered to be an “area of minimal flood hazard.” Areas of minimal flood hazards are located outside of the boundaries of both the 100-year and 500-year flood zones. TSUNAMIS: Tsunamis are great sea waves produced by a submarine earthquake or volcanic eruption. Review of the referenced Tsunami Inundation Map of the Encinitas Quadrangle indicates that the site is located outside of the projected tsunami inundation area (CalEMA, 2009). SEICHES: Seiches are periodic oscillations in large bodies of water such as lakes, harbors, bays or reservoirs. Due to the site’s location, it should not be affected by seiches. OTHER POTENTIAL GEOLOGIC HAZARDS: Other potential geologic hazards such as, volcanoes or seismic-induced settlement should be considered to be negligible or nonexistent. CONCLUSIONS In general, it is our professional opinion and judgment that the subject property is suitable for the construction of the subject project provided the recommendations presented herein are implemented. The main geotechnical condition affecting the proposed project consists of potentially compressible artificial fill and subsoil, expansive soils, and a cut/fill transition. The subject site is underlain by artificial fill and subsoil. As encountered in the subsurface explorations, the artificial fill and subsoil extend to a combined maximum depth of about depth of about 6 feet below existing grade (test pit P-3). However, deeper fill soils may exist in areas of the lot not investigated. It is our opinion that these materials are unsuitable, in their present condition to support settlement sensitive improvements. CWE 2200253.01 June 24, 2021 Page No. 7 In order to mitigate this condition, it is recommended that the fill soils and subsoil be removed and replaced as compacted fill. The prevailing foundation soils were found to have a very highly expansive potential (EI=141). The recommendations contained herein reflect this condition. It should be recognized that the intent of this report is to provide cost-effective site preparation and foundation recommendations to mitigate the potential detrimental effect of the on-site expansive soils on the proposed structure. However, soils with very high expansion potential may detrimentally affect light-weight exterior improvements such as site walls, sidewalks, and driveways. Select grading consisting of replacing the expansive soils with a soil that has a low expansive potential is one of the best ways to mitigate for expansive soil conditions. However, this may be cost prohibitive for the subject project. If select grading is infeasible, consideration should be given to utilizing materials that are tolerant to movement, implementing drought tolerant landscaping, providing positive drainage away from exterior improvements, and providing concrete surfaces with appropriate weakened plane joints. Regardless of these or other similar measures, some distress to exterior improvements requiring future maintenance or even replacement should be anticipated, due to expansive soils. The site is located in an area that is relatively free of geologic hazards that will have a significant effect on the proposed construction. The most likely geologic hazard that could affect the site is ground shaking due to seismic activity along one of the regional active faults. However, construction in accordance with the requirements of the most recent edition of the California Building Code and the local governmental agencies should provide a level of life-safety suitable for the type of development proposed. RECOMMENDATIONS GRADING AND EARTHWORK GENERAL: All grading should conform to the guidelines presented in the current edition of the California Building Code, the minimum requirements of the City of Carlsbad, and the recommended Grading Specifications and Special Provisions attached hereto, except where specifically superseded in the text of this report. PREGRADE MEETING: It is recommended that a pregrade meeting including the grading contractor, the client, and a representative from Christian Wheeler Engineering be performed, to discuss the recommendations of this report and address any issues that may affect grading operations. CWE 2200253.01 June 24, 2021 Page No. 8 OBSERVATION OF GRADING: Continuous observation by the Geotechnical Consultant is essential during the grading operation to confirm conditions anticipated by our investigation, to allow adjustments in design criteria to reflect actual field conditions exposed, and to determine that the grading proceeds in general accordance with the recommendations contained herein. CLEARING AND GRUBBING: Site preparation should begin with the removal of any existing vegetation and other deleterious materials in areas to receive proposed improvements or new fill soils. SITE PREPARATION: It is recommended that fills soils and subsoil underlying the proposed structure, fill soils, and associated improvements be removed in their entirety. Based on our findings these materials extend to combined maximum depth of about depth of about 6 feet below existing grade (test pit P-3). The anticipated removals are depicted on Plate No. 2. Deeper removals may be necessary in areas of the site not investigated or due to unforeseen conditions. Lateral removals limits should extend across the entire lot. No removals should be performed beyond property lines. All excavated areas should be approved by the geotechnical engineer or his representative prior to replacing any of the excavated soils. The excavated materials can be replaced as properly compacted fill in accordance with the recommendations presented in the “Compaction and Method of Filling” section of this report provided that they are free of roots. FILL SLOPE KEYWAY: A keyway should be constructed at the toe of the fill slope along the northerly property line. The keyway should be at least 5 feet wide. The keyway should be sloped back into the hillside at least 2 percent and should extend at least 1 foot into the competent materials of the Delmar formation. Where the existing ground has a slope of 5:1 (horizontal to vertical) or steeper, it should be benched into as the fill extends upward from the keyway. A keyway detail is provided on Plate No. 3. EXCAVATION AND BACKFILLING CHARACTERISTICS: : The prevailing foundation soils consist of fat clays (CH). Although these materials will be relatively easy to excavate with conventional grading and trenching equipment, backfilling operations with these materials will be difficult due to their high in-situ moisture contents and clayey composition. Consideration should be given to importing sandy materials to blend with the on-site materials. IMPORTED FILL: Imported fill should consist of low expansive (EI between 21 to 50) silty sands or clayey sands free of rocks or lumps over 3 inches in maximum dimension. Imported fill should be approved by this office prior to delivery to the site in order to establish compatibility with the on-site soils and project requirements. Laboratory tests will be needed prior to import fill approval. A minimum 5 business days lead time should be assumed. CWE 2200253.01 June 24, 2021 Page No. 9 PROCESSING OF FILL AREAS: Prior to placing any new fill soils or constructing any new improvements in areas that have been cleaned out to receive fill, the exposed soils should be scarified to a depth of about 12 inches, moisture conditioned, and compacted to at least 90 percent relative compaction. COMPACTION AND METHOD OF FILLING: In general, all structural fill placed at the site should be compacted to a relative compaction of at least 90 percent of its maximum laboratory dry density as determined by ASTM Laboratory Test D1557. Retaining wall backfill underlying settlement sensitive improvements should be compacted to at least 95 percent. Fills should be placed at or slightly above optimum moisture content, in lifts six to eight inches thick, with each lift compacted by mechanical means. Fills should consist of approved earth material, free of trash or debris, roots, vegetation, or other materials determined to be unsuitable by the Geotechnical Consultant. Fill material should be free of rocks or lumps of soil in excess of 6 inches in maximum dimension. Utility trench backfill within 5 feet of the proposed structure and beneath all concrete flatwork or pavements should be compacted to a minimum of 90 percent of its maximum dry density. SURFACE DRAINAGE: The drainage around the proposed improvements should be designed to collect and direct surface water away from proposed improvements and the top of slopes toward appropriate drainage facilities. Rain gutters with downspouts that discharge runoff away from the structure into controlled drainage devices are recommended. The ground around the proposed improvements should be graded so that surface water flows rapidly away from the improvements without ponding. In general, we recommend that the ground adjacent to structure slope away at a gradient of at least 5 percent for a minimum distance of 10 feet. If the minimum distance of 10 feet cannot be achieved, an alternative method of drainage runoff away from the building at the termination of the 5 percent slope will need to be used. Swales and impervious surfaces that are located within 10 feet of the building should have a minimum slope of 2 percent. It is essential that new and existing drainage patterns be coordinated to produce proper drainage. Pervious hardscape surfaces adjacent to structures should be similarly graded. Drainage patterns provided at the time of construction should be maintained throughout the life of the proposed improvements. Site irrigation should be limited to the minimum necessary to sustain landscape growth. Over watering should be avoided. Should excessive irrigation, impaired drainage, or unusually high rainfall occur, zones of wet or saturated soil may develop. CWE 2200253.01 June 24, 2021 Page No. 10 FOUNDATIONS GENERAL: Based on the findings and engineering judgment, it is recommended that the proposed structures be supported by post-tensioned foundation system or conventional shallow foundations. The following minimum recommendations are based on the anticipated soil conditions, and are not intended to be used in lieu of structural considerations. All foundations should be designed by a qualified engineer. POST TENSIONED FOUNDATIONS Post- Tensioned foundations may be utilized for the support of the subject structures. The post tension related design parameters from the Post Tensioning Institute, 3rd edition, are provided below. TABLE II: POST-TENSIONED FOUNDATIONS Post-Tensioning Institute (PTI) – 3rd Edition Thornthwaite Index -20 Edge Moisture Variation, em Center Lift (ft) 9.0 Edge Lift (ft) 5.3 Differential Soil Movement, ym Center Lift (in) 0.65 Edge Lift (in) 1.93 An allowable soil bearing pressure of 2,000 pounds per square foot (psf) may be assumed for post- tensioned foundations. This value may be increased by one-third for combinations of temporary loads such as those due to wind or seismic loads. Perimeter footings for post-tensioned foundations should extend at least 30 inches below finish pad grade. SHALLOW FOUNDATIONS DIMENSIONS: Spread footings supporting the proposed structure and associated exterior improvements should extend to a minimum depth at least 30 inches below lowest adjacent finish pad grade. Continuous and isolated spread footings should have a minimum width of 12 inches and 24 inches, respectively. BEARING CAPACITY: Spread footings with a minimum embedment described in the previous paragraph may be designed for an allowable soil bearing pressure of 2,000 pounds per square foot CWE 2200253.01 June 24, 2021 Page No. 11 (psf). The bearing value may also be increased by one-third for combinations of temporary loads such as those due to wind or seismic loads. FOOTING REINFORCING: Reinforcement requirements for foundations should be provided by a structural engineer. However, based on the existing soil conditions, we recommend that the minimum reinforcing for continuous footings consist of at least 2 No. 5 bars positioned near the bottom of the footing and 2 No. 5 bars positioned near the top of the footing. LATERAL LOAD RESISTANCE: Lateral loads against foundations may be resisted by friction between the bottom of the footing and the supporting soil, and by the passive pressure against the footing. The coefficient of friction between concrete and soil may be considered to be 0.25. The passive resistance may be considered to be equal to an equivalent fluid weight of 250 pounds per cubic foot. This assumes the footings are poured tight against undisturbed soil. If a combination of the passive pressure and friction is used, the friction value should be reduced by one-third. FOUNDATION EXCAVATION MOISTURE CONDITIONING: It is recommended that foundation excavations not be allowed to dry out during the construction process. However, due to the clayey nature of the foundation materials, this operation should be done carefully. Excessive moistening of the soils will result in a sloppy foundation bottom. FOUNDATION EXCAVATION OBSERVATION: All footing excavations should be observed by Christian Wheeler Engineering prior to placing of forms and reinforcing steel to determine whether the foundation recommendations presented herein are followed and that the foundation soils are as anticipated in the preparation of this report. All footing excavations should be excavated neat, level, and square. All loose or unsuitable material should be removed prior to the placement of concrete. SETTLEMENT CHARACTERISTICS: The anticipated total and differential settlement is expected to be less than about 1 inch and 1 inch over 40 feet, respectively, provided the recommendations presented in this report are followed. It should be recognized that minor cracks normally occur in concrete slabs and foundations due to concrete shrinkage during curing or redistribution of stresses, therefore some cracks should be anticipated. Such cracks are not necessarily an indication of excessive vertical movements. EXPANSIVE CHARACTERISTICS: The prevailing foundation soils are assumed to have a very high expansive potential (EI=141). The recommendations within this report reflect these conditions. CWE 2200253.01 June 24, 2021 Page No. 12 FOUNDATION PLAN REVIEW: The final foundation plan and accompanying details and notes should be submitted to this office for review. The intent of our review will be to verify that the plans used for construction reflect the minimum dimensioning and reinforcing criteria presented in this section and that no additional criteria are required due to changes in the foundation type or layout. It is not our intent to review structural plans, notes, details, or calculations to verify that the design engineer has correctly applied the geotechnical design values. It is the responsibility of the design engineer to properly design/specify the foundations and other structural elements based on the requirements of the structure and considering the information presented in this report. SOLUBLE SULFATES: The water-soluble sulfate content of a selected soil sample from the site was determined in accordance with California Test Method 417. The results of this test indicate that the soil sample had a soluble sulfate content of 0.016 percent. Soils with a soluble sulfate content of less than 0.1 percent are considered to be negligible. However, it should be recognized that the sulfate content of surficial soils may increase with time due to soluble sulfate in the irrigation water or fertilized use. It should be understood Christian Wheeler Engineering does not practice corrosion engineering. If a corrosivity analysis is considered necessary, we recommend that the client retain an engineering firm that specializes in this field to consult with them on this matter. The results of our corrosion testing should only be used as a guideline to determine if additional testing and analysis is necessary. SEISMIC DESIGN FACTORS The seismic design factors applicable to the subject site are provided below. The seismic design factors were determined in accordance with the 2019 California Building Code. The site coefficients and adjusted maximum considered earthquake spectral response acceleration parameters are presented in the following Table I. TABLE I: SEISMIC DESIGN FACTORS Site Coordinates: Latitude Longitude 33.088° -117.257° Site Class C Site Coefficient Fa 1.2 Site Coefficient Fv 1.5 Spectral Response Acceleration at Short Periods Ss 0.992 g Spectral Response Acceleration at 1 Second Period S1 0.36 g SMS=FaSs 1.19 g SM1=FvS1 0.54 g CWE 2200253.01 June 24, 2021 Page No. 13 SDS=2/3*SMS 0.794 g SD1=2/3*SM1 0.36 g Probable ground shaking levels at the site could range from slight to moderate, depending on such factors as the magnitude of the seismic event and the distance to the epicenter. It is likely that the site will experience the effects of at least one moderate to large earthquake during the life of the proposed improvements. RISK CATEGORIES The project structural engineer and architect should evaluate the appropriate Risk Category and Seismic Design Category for the planned structures. The values presented herein assume a Risk Category of II and a Seismic Design Category D. Table II presents a summary of the risk categories in accordance with ASCE 7- 16. TABLE II ASCE 7-16 RISK CATEGORIES Risk Category Building Use Examples I Low risk to Human Life at Failure Barn, Storage Shelter II Nominal Risk to Human Life at Failure (Buildings Not Designated as I, III or IV) Residential, Commercial and Industrial Buildings III Substantial Risk to Human Life at Failure Theaters, Lecture Halls, Dining Halls, Schools, Prisons, Small Healthcare Facilities, Infrastructure Plants, Storage for Explosives/Toxins IV Essential Facilities Hazardous Material Facilities, Hospitals, Fire and Rescue, Emergency Shelters, Police Stations, Power Stations, Aviation Control Facilities, National Defense, Water Storage CWE 2200253.01 June 24, 2021 Page No. 14 As discussed in our referenced geotechnical report no faults are known to traverse the subject site and our review of available geologic maps indicates that the nearest active fault zone is the Newport-Inglewood - Rose Canyon Fault Zone (RCFZ), located approximately 6½ miles to the west of the site. The off shore location of the RCFZ near the site is based on marine geophysical surveys and according to the USGS the slip rate is not fully constrained, but appears to be approximately 1.0±0.5 mm/yr in the north, increasing to 1.5±0.5 mm/yr in the south. The County of San Diego Seismic Safety Element also indicates that the RCFZ could produce up to a magnitude 7.1 event. With these attributes the site can be considered a Near-Fault Site in accordance with the CBC 2019. ON-GRADE SLABS GENERAL: It is our understanding that the floor system for proposed structure may consist of concrete slab-on-grade. The slab should be designed by the project structural engineer based on the findings of this report. A design coefficient of subgrade reaction, Kv1, of 50 pounds per cubic inch (pci) may be used for slab-on-grade design. UNDER-SLAB VAPOR RETARDERS: Steps should be taken to minimize the transmission of water vapors from the subsoil through the interior slabs where it can potentially damage the interior floor coverings. Local industry standards typically include the placement of a vapor retarder, such as polyethylene liner, in a layer of coarse sand, placed directly beneath the concrete slab. Two inches of sand are typically used above and below the liner. The vapor retarder should at least consist of 15-mil thick Stegowrap® or similar material with sealed seams, and extend to a depth of at least 12 inches along the sides of the interior and perimeter footings. The sand placed around the liner should have a sand equivalent of at least 30, contain less than 10% material passing the No. 100 sieve, and less than 5% material passing the No. 200 sieve. The membrane should be placed in accordance with the recommendations and considerations contained in American Concrete Institute (ACI) 302, “Guide for Concrete Floor and Slab Construction” and ASTM E1643, “Standards Practice for Installation of Water Vapor Retarder Used in Contact with Earth or Granular Fill Under Concrete Slabs.” It is the flooring contractor’s responsibility to place floor coverings in accordance with the flooring manufacturer specifications. EXTERIOR CONCRETE FLATWORK: Exterior concrete slabs on grade, including driveways, should have a minimum thickness of 6 inches and be reinforced with at least No. 4 bars placed at 12 inches on center each way (ocew). Driveway slabs should be provided with a thickened edge at least 30 inches deep and 6 inches wide. All slabs should be provided with weakened plane joints in accordance with the ACI guidelines. Special attention should be paid to the method of concrete curing to reduce the potential for excessive CWE 2200253.01 June 24, 2021 Page No. 15 shrinkage cracking. It should be recognized that minor cracks occur normally in concrete slabs due to shrinkage. Some shrinkage cracks should be expected and are not necessarily an indication of excessive movement or structural distress. However, it should be recognized that soils with very high (EI=133) expansion potential may detrimentally affect light weight exterior improvements such as site walls, sidewalks, and driveways. Some distress to exterior improvements requiring future maintenance or even replacement should be anticipated due to expansive soils. UTILITY TRENCHES It is anticipated that utility trenches will be backfilled with materials much more permeable than the surrounding clayey soils. In order to mitigate the potential for these trenches to act as conduits for water under the proposed structure, it is recommended that a cutoff concrete plug be constructed at minimum distance of at least 3 feet from the structure to act as a dam. The plug should extend at least 12 inches beyond the edges and the bottom of the trench and should be at least 12 inches high or 6 inches above any bedding material, whichever is more. LIMITATIONS REVIEW, OBSERVATION AND TESTING The recommendations presented in this report are contingent upon our review of final plans and specifications. Such plans and specifications should be made available to the geotechnical engineer and engineering geologist so that they may review and verify their compliance with this report and with the California Building Code. It is recommended that Christian Wheeler Engineering be retained to provide continuous soil engineering services during the earthwork operations. This is to verify compliance with the design concepts, specifications or recommendations and to allow design changes in the event that subsurface conditions differ from those anticipated prior to start of construction. UNIFORMITY OF CONDITIONS The recommendations and opinions expressed in this report reflect our best estimate of the project requirements based on an evaluation of the subsurface soil conditions encountered at the subsurface exploration locations and on the assumption that the soil conditions do not deviate appreciably from those encountered. It should be recognized that the performance of the foundations and/or cut and fill slopes may CWE 2200253.01 June 24, 2021 Page No. 16 be influenced by undisclosed or unforeseen variations in the soil conditions that may occur in the intermediate and unexplored areas. Any unusual conditions not covered in this report that may be encountered during site development should be brought to the attention of the geotechnical engineer so that he may make modifications if necessary. CHANGE IN SCOPE This office should be advised of any changes in the project scope or proposed site grading so that we may determine if the recommendations contained herein are appropriate. This should be verified in writing or modified by a written addendum. TIME LIMITATIONS The findings of this report are valid as of this date. Changes in the condition of a property can, however, occur with the passage of time, whether they be due to natural processes or the work of man on this or adjacent properties. In addition, changes in the Standards-of-Practice and/or Government Codes may occur. Due to such changes, the findings of this report may be invalidated wholly or in part by changes beyond our control. Therefore, this report should not be relied upon after a period of two years without a review by us verifying the suitability of the conclusions and recommendations. PROFESSIONAL STANDARD In the performance of our professional services, we comply with that level of care and skill ordinarily exercised by members of our profession currently practicing under similar conditions and in the same locality. The client recognizes that subsurface conditions may vary from those encountered at the locations where our borings, surveys, and explorations are made, and that our data, interpretations, and recommendations be based solely on the information obtained by us. We will be responsible for those data, interpretations, and recommendations, but shall not be responsible for the interpretations by others of the information developed. Our services consist of professional consultation and observation only, and no warranty of any kind whatsoever, express or implied, is made or intended in connection with the work performed or to be performed by us, or by our proposal for consulting or other services, or by our furnishing of oral or written reports or findings. CWE 2200253.01 June 24, 2021 Page No. 17 CLIENT'S RESPONSIBILITY It is the responsibility of the Client, or its representatives, to ensure that the information and recommendations contained herein are brought to the attention of the structural engineer and architect for the project and incorporated into the project's plans and specifications. It is further their responsibility to take the necessary measures to ensure that the contractor and his subcontractors carry out such recommendations during construction. FIELD EXPLORATIONS Six subsurface explorations were excavated on June 27, 2020 at the locations indicated on the Existing and Proposed Site Plan and Geotechnical Maps included herewith as Plate Nos. 1 and 2. These explorations consisted of 5 hand-dug test pits and 1 hand-augured boring. The fieldwork was conducted under the observation and direction of our engineering geology personnel. The explorations were carefully logged when made. The logs are presented on Appendix A. The soils are described in accordance with the Unified Soils Classification. In addition, a verbal textural description, the wet color, the apparent moisture, and the density or consistency is provided. The density of granular soils is given as very loose, loose, medium dense, dense or very dense. The consistency of silts or clays is given as either very soft, soft, medium stiff, stiff, very stiff, or hard. Chunk samples and bulk samples of the earth materials encountered were collected. Samples were transported to our laboratory for testing. LABORATORY TESTING Laboratory tests were performed in accordance with the generally accepted American Society for Testing and Materials (ASTM) test methods or suggested procedures. A brief description of the tests performed and the subsequent results are presented in Appendix B. P-2 P-1 P-3 P-5 P-4 HA-1 Qaf Td Qaf Td A A' P-5 Approximate Test Pit Location Approximate Hand Auger Test Location Artificial Fill over Delmar Formation Geologic Cross Section Qaf Td CWE LEGEND HA-1 Note: Subsoils Not Mapped DATE: JUNE 2021 BY: SD JOB NO.: 2200253.01 PLATE NO.: 1 SITE PLAN AND GEOTECHNICAL MAP STARK HOUSE LA COSTA AVENUE CARLSBAD, CALIFORNIA CHRISTIAN WHEELER E N G I N E E R I N G 00 20'40' SCALE: 1" = 20' w ~ ~ 0 () <( ...J c::, c::, EXIST 8" VC SEWER PROPOCED 3 -CAR GARAGE 901 SQF GARAGE PROPOSED NEW "TWO STORY RESIDENCE 2005 F.F. 2293 SECOND F. ~u01J@D@ ==ir= UNO ARCHITECTURE + DESIGN + PLANNING ~ -$- 130 120 110 90 80 A :'i" (P P-5 LAUNDRY WALK-IN CLOSET 2 ' 2'-6" LimmmfBE=D=RO=O=M=2 ==============::::::::::::=== J:- □--"''°'000 1 R-131ffSUl.'.TlON 3CARGARAGE Anticipated Removals _ ____, Td P-3 Projected West 15' rn D Td TERRACE I GRILL Projected East 8' DECK P-1 Projected est 13' A' 130 120 110 100 90 80 - 70 L_ ____ ___L. _____ L_ ____ ---1.,_ _____ ..,L_ ____ ___i_ _____ ...,L_ ____ ----1 _____ ....1,_ _____ L.-____ ---1... _____ ..__ ____ __,__ _____ _.__ ____ __,_ __ __,70 o ro w ~ ~ w @ w M w ~ m ~ ~ ~ m CWELEGEND Qaf Artificial Fill Td Delmar Formation GEOLOGIC CROSS SECTION A-A' DATE: BY: STARKHOUSE LA COSTA AVENUE CARLSBAD, CALIFORNIA JUNE2021 JOB NO.: 0 2200253.01 SD PLATE NO.: 2 10' 20' SCALE: 1" = 10' CHRISTIAN WHEELER ENGINEERING Existing Ground Surface _ - _ -Compacted Fill _-_ - _ - _ -_ -_ - Existing Ground Surface j _L 2:1 (H:V) Proposed Grade -------------- ---2%Min.-- 1 Foot Minimum Into Ji-I-■ __ ·----cr_ii;=_ .. ["T"iii'i=_iii=-_K_e_,yw'----'ay,__ __ -i, I L Bench Height (4 Feet Typical) Competent Material 5 Foot Minimum for Slopes <10' High 12 Foot Minimum for Slope >10' High NO SCALE FILL SLOPE KEYWAY DETAIL DATE: STARKHOUSE LA COSTA AVENUE CARLSBAD, CALIFORNIA JUNE2021 JOB NO.: 2200253.01 BY: SD PLATE NO.: 3 ?A CHR.ISTIAN WHEELER. ENGINEER.ING Appendix A Subsurface Explorations g ::c: E-s ll-< ~ A 0 - - 1-- - - 2-- -- 3-- -- 4-- -- 5-- -- 6-- -- 7-- -- 8-- -- 9-- -- 10-- -- 11-- -- 12-- -- 13-- -- 14-- -- 15-- LOG OF TEST PIT P-1 Date Logged: Logged By: Existing Elevation: Finish Elevation: g ~ ~ z s 0 0 i:Q .... u ~ E-s 5= ~ ~ rJ'J ~ u rJ'J ~ ~ 0 1/,; CL CH SM 6/29/20 DJF ±83' ±83' Equipment: Hand tools Auger Type: N/A Drive Type: N/A Depth to Water: N/A SUMMARY OF SUBSURFACE CONDITIONS (based on Unified Soil Classification System) Artificial Fill (Qaf): Olive brown to grayish-brown, damp, soft to medium stiff, SANDY CLAY. _j __J_'_ Subsoil: Grayish-brown, moist, medium stiff,_![AT CLAY. Del Mar Formation (fd): Light yellowish-brown, moist, dense, ~ery fine-to medium-grained, SILTY SAND "?th orangish iron staining, upper 12" moderately weathered with trace clay and wNte precipitate deposi~s. Very dense. Test pit terminated at 5.~ feet. No groundwater or seepage encountered. Notes: Symbol Legend STARK HOUSE y Groundwater Level During Drilling LA COSTA A VENUE '! Groundwater Level After Drilling CARLSBAD, CALIFORNIA '' Apparent Seepage DATE: JUNE 2021 JOB NO.: * No Sample Recovery ** Non-Representative Blow Count BY: SRD APPENDIX: (rocks present) SamI!le Tree and Laborato!)'. Test Legend Cal Modified California Sampler CK Chunk SPT Standard Penetration Test DR Drive Ring ST ShdbyTube MD Max Density DS Direct Shear S04 Soluble Sulfates Con Consolidation SA Sieve Analysis El Expansion Index HA Hydrometer R-Val Resistance Value SE Sand Equivalent Chi Soluble Ch1orides Pl Plasticity Index Res pH & Resistivity CP Collapse Potential SD Sample Density Z,::-~ ,-.. z ~ ~ 0 0 ~ ~~ 0 i::.s ;;,.t~ ~~ 0 ~[ ~ oZ ~ ~ ~ ii,:: rJ'J (J tl ; ll-< ~ A~,e, E-s:Jll-< 0~ ZS ~ .... z A ~,-.. 3~ ~ ,tl 0 Oo ~o~ ll-< '-' i:Q ~u us:.., " 2200253.01 CHRISTIAN WHEELER. ENGINEEIUNG A-1 LOG OF TEST PIT P-2 SamI!le Trl!e and Laborato!)'. Test Legend Cal Modified California Sampler CK Chunk SPT Standard Penetration Test DR Drive Ring ST ShdbyTube Date Logged: 6/29/20 Equipment: Hand tools MD Max Density DS Direct Shear Logged By: DJF Auger Type: N/A S04 Soluble Sulfates Con Consolidation SA Sieve Analysis El Expansion Index Existing Elevation: ±96' Drive Type: N/A HA Hydrometer R-Val Resistance Value SE Sand Equivalent Chi Soluble Ch1orides Finish Elevation: ±96' Depth to Water: N/A Pl Plasticity Index Res pH & Resistivity CP Collapse Potential SD Sample Density g ~ ~ Z,::-~ ,-.. z ~ ~ z s 0 0 0 ~ ~~ 0 g 0 i:Q i::.s ;;,.t~ ~~ 0 .... u ~ SUMMARY OF SUBSURFACE CONDITIONS ~[ oZ ~ ::c: E-s 5= (based on Unified Soil Classification System) ~ ii,:: Cl) (J E-s ~ ~ Cl) tl ; ~ ~ ~ ~ o~,e, E-s:J~ 0~ ~ ~ u ZS ~ .... z A ~,-.. 3~ ~ Cl) 0 Oo ~o~ A ~ ~ 0 ~ ,tl i:Q ~u ~ '-' us:.., 0 1/,; I CL Artificial Fill (Qaf): Olive brown to light brown, damp, soft to medium stiff, - -SANDY CLAY with sandstone/ claysione fragments of Del Mar Formation. 1---l - - 2-- - -~ 3--I CH Subsoil: Dark brow_e,_moist, stiff, FAT CLAY. - - 4--I - - 5--~ CH Del Mar Formation (Td): Olive brown, moist, stiff, FAT OLA"¥, highly - -weathered. l L 6-- - - Test pit terminated at 6 feet. No groundwater or seepage encountered. 7-- - - 8-- - - 9-- - - 10 -- - - 11-- - - 12-- - - 13-- - - 14-- - - 15-- Notes: Symbol Legend STARK HOUSE y Groundwater Level During Drilling LA COSTA A VENUE " '! Groundwater Level After Drilling CARLSBAD, CALIFORNIA '' Apparent Seepage DATE: JUNE 2021 JOB NO.: 2200253.01 CHRISTIAN WHEELER. * No Sample Recovery ENGINEEIUNG ** Non-Representative Blow Count BY: SRD APPENDIX: A-2 (rocks present) g ::c: E-s ll-< ~ A 0 - - 1-- -- 2-- -- 3-- -- 4-- -- 5-- -- 6-- -- 7-- -- 8-- -- 9-- -- 10-- -- 11-- -- 12-- -- 13-- -- 14-- -- 15-- LOG OF TEST PIT P-3 Date Logged: Logged By: Existing Elevation: Finish Elevation: g ~ ~ z s 0 0 i:Q .... u ~ E-s 5= ~ ~ rJ'J ~ u rJ'J ~ ~ 0 1/,; CL SM CH CH SC 6/29/20 Equipment: Hand tools DJF Auger Type: N/A ±99' Drive Type: N/A ±99' Depth to Water: N/A SUMMARY OF SUBSURFACE CONDITIONS (based on Unified Soil Classification System) Artificial Fill (Qaf): Brown, damp, soft to medium stiff, SANDY CLAY with concrete debris-up to 2' fu diameter. _J Expansion Ind9< = 98 (Iiigh) Light yellowish-brown, moist, medium den~e, vbry fine-to mbdium-grained, SILTY SAND L th fragments ofDelf ar Sariclstone. Subsoil: Dark brown, nioist,I stiff, FAT CLAY. Expansion Inclex = J 39 (VerJHigh) -t Del Mar Formation (fd): Olive brown, moist, stiff to very stiff, FAT CUAY with reddish iron staining, highly-weathered to 7.5'. Expansion Index= 141 (Yery High) I Olive brown, moist, dense, very fine-to medium-grained, CLAYEY SAND. Test pit terminated at 9.5 feet. No groundwater or seepage encountered. Notes: Symbol Legend STARK HOUSE y Groundwater Level During Drilling LA COSTA A VENUE '! Groundwater Level After Drilling CARLSBAD, CALIFORNIA '' Apparent Seepage DATE: JUNE 2021 JOB NO.: * No Sample Recovery ** Non-Representative Blow Count BY: SRD APPENDIX: (rocks present) SamI!le Tree and Laborato!)'. Test Legend Cal Modified California Sampler CK Chunk SPT Standard Penetration Test DR Drive Ring ST ShdbyTube MD Max Density DS Direct Shear S04 Soluble Sulfates Con Consolidation SA Sieve Analysis El Expansion Index HA Hydrometer R-Val Resistance Value SE Sand Equivalent Chi Soluble Ch1orides Pl Plasticity Index Res pH & Resistivity CP Collapse Potential SD Sample Density ,-. z ~ ~ ~~ 0 ;;,.t~ ~~ 0 oZ ~ ~ ~ ii,:: rJ'J (J ~ A~,e, E-s:Jll-< 0~ .... z ~,-. 0 Oo A ~o~ 3~ i:Q ~u us:.., HA lEI MD PI CK ~04 _OS CK El CK El " 2200253.01 CHRISTIAN WHEELER. ENGINEEIUNG A-3 LOG OFTEST PIT P-4 SamI!le Trl!e and Laborato!)'. Test Legend Cal Modified California Sampler CK Chunk SPT Standard Penetration Test DR Drive Ring ST ShdbyTube Date Logged: 6/29/20 Equipment: Hand tools MD Max Density DS Direct Shear Logged By: DJF Auger Type: N/A S04 Soluble Sulfates Con Consolidation SA Sieve Analysis El Expansion Index Existing Elevation: ±100' Drive Type: N/A HA Hydrometer R-Val Resistance Value SE Sand Equivalent Chi Soluble Ch1orides Finish Elevation: ±100' Depth to Water: N/A Pl Plasticity Index Res pH & Resistivity CP Collapse Potential SD Sample Density g ~ ~ Z,::-~ ,-.. z ~ ~ z s 0 0 0 ~ ~~ 0 g 0 i:Q i::.s ;;,.t~ ~~ 0 .... u ~ SUMMARY OF SUBSURFACE CONDITIONS ~[ oZ ~ ::c: E-s 5= (based on Unified Soil Classification System) ~ ii,:: Cl) (J E-s ~ ~ Cl) tl ; ~ ~ ~ ~ o~,e, E-s:J~ 0~ ~ ~ u ZS ~ .... z A ~,-.. 3~ ~ Cl) 0 Oo ~o~ A ~ ~ 0 ~ ,tl i:Q ~u ~ '-' us:.., 0 SM Artificial Fill (Qaf): Light brown, damp, medium dense, very fine-to - - .. medium-grained, SILTY SAND with trace clay. 1--.. - - .. CKj 2-- SM Del Mar Formation (fd): Light yellowish-brdwn, moi~t, very dense,J"ery fine-- - .. CK 11.5 116.6 to medium-grained, SILTY SAND-with orangish iron staining. I 3--.. - - 4--Test pit terminated at 3j_ feet. No groundwater or seepage encountered. - - 5-- - - 6-- - - 7-- - - 8-- - - 9-- - - 10 -- - - 11-- - - 12-- - - 13-- - - 14-- - - 15-- Notes: Symbol Legend STARK HOUSE y Groundwater Level During Drilling LA COSTA A VENUE " '! Groundwater Level After Drilling CARLSBAD, CALIFORNIA '' Apparent Seepage DATE: JUNE 2021 JOB NO.: 2200253.01 CHRISTIAN WHEELER. * No Sample Recovery ENGINEEIUNG ** Non-Representative Blow Count BY: SRD APPENDIX: A-4 (rocks present) LOG OFTEST PIT P-5 SamI!le Trl!e and Laborato!)'. Test Legend Cal Modified California Sampler CK Chunk SPT Standard Penetration Test DR Drive Ring ST ShdbyTube Date Logged: 6/29/20 Equipment: Hand tools MD Max Density DS Direct Shear Logged By: DJF Auger Type: N/A S04 Soluble Sulfates Con Consolidation SA Sieve Analysis El Expansion Index Existing Elevation: ±100' Drive Type: N/A HA Hydrometer R-Val Resistance Value SE Sand Equivalent Chi Soluble Ch1orides Finish Elevation: ±100' Depth to Water: N/A Pl Plasticity Index Res pH & Resistivity CP Collapse Potential SD Sample Density g ~ ~ Z,::-~ ,-.. z ~ ~ z s 0 0 0 ~ ~~ 0 g 0 i:Q i::.s ;;,.t~ ~~ 0 .... u ~ SUMMARY OF SUBSURFACE CONDITIONS ~[ oZ ~ ::c: E-s 5= (based on Unified Soil Classification System) ~ ii,:: Cl) (J E-s ~ ~ Cl) tl ; ~ ~ ~ ~ o~,e, E-s:J~ 0~ ~ ~ u ZS ~ .... z A ~,-.. 3~ ~ Cl) 0 Oo ~o~ A ~ ~ 0 ~ ,tl i:Q ~u ~ '-' us:.., 0 SM Artificial Fill (Qaf): Light brown, damp, medium dense, very fine-to - - .. medium-grained, SILTY SAND with trace concrete and AC debris. 1--.. - - .. 2-CK -.. - -SM Del Mar Formation (fd): Light yellowish-brdwn, moist, very dense,h ry fine-CK 3--.. to meilium-grained, SII:11Y SAND with orangish iron staining . I - - 4--Test pit terminated at 3j_ feet. No groundwater or seepage encountered. - - 5-- - - 6-- - - 7-- - - 8-- - - 9-- - - 10 -- - - 11-- - - 12-- - - 13-- - - 14-- - - 15-- Notes: Symbol Legend STARK HOUSE y Groundwater Level During Drilling LA COSTA A VENUE " '! Groundwater Level After Drilling CARLSBAD, CALIFORNIA '' Apparent Seepage DATE: JUNE 2021 JOB NO.: 2200253.01 CHRISTIAN WHEELER. * No Sample Recovery ENGINEEIUNG ** Non-Representative Blow Count BY: SRD APPENDIX: A-5 (rocks present) LOG OF HAND AUGER HA-1 SamI!le Trl!e and Laborato!)'. Test Legend Cal Modified California Sampler CK Chunk SPT Standard Penetration Test DR Drive Ring ST ShdbyTube Date Logged: 6/29/20 Equipment: Hand tools MD Max Density DS Direct Shear Logged By: DJF Auger Type: N/A S04 Soluble Sulfates Con Consolidation SA Sieve Analysis El Expansion Index Existing Elevation: ±94' Drive Type: N/A HA Hydrometer R-Val Resistance Value SE Sand Equivalent Chi Soluble Ch1orides Finish Elevation: ±94' Depth to Water: N/A Pl Plasticity Index Res pH & Resistivity CP Collapse Potential SD Sample Density g ~ ~ Z,::-~ ,-.. z ~ ~ z s 0 0 0 ~ ~~ 0 g 0 i:Q i::.s ;;,.t~ ~~ 0 .... u ~ SUMMARY OF SUBSURFACE CONDITIONS ~[ oZ ~ ::c: E-s 5= (based on Unified Soil Classification System) ~ ii,:: Cl) (J E-s ~ ~ Cl) tl ; ~ ~ ~ ~ o~,e, E-s:J~ 0~ ~ ~ u ZS ~ .... z A ~,-.. 3~ ~ Cl) 0 Oo ~o~ A ~ ~ 0 ~ ,tl i:Q ~u ~ '-' us:.., 0 0 SC Artificial Fill (Qaf): Light brown, damp, medium stiff, SANDY CLAY. - - 1-- Cal - - 2-- - -~ 3--~ CH Subsoil: Dark brown, mbist, stiff, FAT CLAY. - - 4-- ~ - -I CH DelMar_Form~on (fd): Olive br?w~, '[':1Y ~?iJt, stifftof=ry stiff, FAT Cal 21.8 103.2 5--CLAY, highly weathered to 6.5', reddir irol_stauung. - -I 6--Gradational contact. - -Ii SC Olive brown, moist, very dense, ve1ry fine-to medium-grain3 CLAYEY SAND. Cal 7-- - - 8-- Terminated at 8 feet. - -No groundwater or seepage encountered. 9-- - - 10 -- - - 11-- - - 12-- - - 13-- - - 14-- - - 15-- Notes: Symbol Legend STARK HOUSE y Groundwater Level During Drilling LA COSTA A VENUE " '! Groundwater Level After Drilling CARLSBAD, CALIFORNIA '' Apparent Seepage DATE: JUNE 2021 JOB NO.: 2200253.01 CHRISTIAN WHEELER. * No Sample Recovery ENGINEEIUNG ** Non-Representative Blow Count BY: SRD APPENDIX: A-6 (rocks present) Appendix B Laboratory Test Results STARK HOUSE LA COSTA AVENUE, CARLSBAD, CALIFORNIA LAB SUMMARY BY: DBA DATE: JUNE 2021 REPORT NO.:2200253.01 FIGURE NO.: B-1 E n g i n e e r i n g CHRISTIAN WHEELER Laboratory tests were performed in accordance with the generally accepted American Society for Testing and Materials (ASTM) test methods or suggested procedures. Brief descriptions of the tests performed are presented below: a) CLASSIFICATION: Field classifications were verified in the laboratory by visual examination. The final soil classifications are in accordance with the Unified Soil Classification System and are presented on the exploration logs in Appendix A. b) MOISTURE-DENSITY: MOISTURE-DENSITY: In-place moisture contents and dry densities were determined for a selected soil sample in accordance with ATM D 1188. The results are summarized in the test pit log presented in Appendix A. c) MAXIMUM DENSITY & OPTIMUM MOISTURE CONTENT: The maximum dry density and optimum moisture content of typical soils were determined in the laboratory in accordance with ASTM Standard Test D1557, Method A. d) DIRECT SHEAR: A direct shear test was performed on selected samples of the on-site soils in accordance with ASTM D3080. e) EXPANSION INDEX TEST: Expansion index tests were performed on selected remolded soil samples in accordance with ASTM D 4829. f) GRAIN SIZE DISTRIBUTION: The grain size distribution of a selected sample was determined in accordance with ASTM C136 and/or ASTM D422. g) ATTERBERG LIMITS: The Liquid Limit, Plastic Limit and Plastic Index of a selected soil sample were determined in accordance with ASTM D424. h) SOLUBLE SULFATE CONTENT: The soluble sulfate content of a selected soil sample was determined in accordance with California Test Methods 417. :. I I I CWE 2200253.01 June 24, 2021 Appendix B-2 LABORATORY TEST RESULTS STARK HOUSE APN 216-160-10-00 LA COSTA AVENUE CARLSBAD, CALIFORNIA MAXIMUM DRY DENSITY AND OPTIMUM MOISTURE CONTENT (ASTM D1557) Sample Location Test Pit P-3 @ 0-2½ Sample Description Brown Very Clayey Sand with Silt (SC) Maximum Density 120.0 pcf Optimum Moisture 11.5 % DIRECT SHEAR (ASTM D3080) Sample Location Test Pit P-3 @ 0-2½’ Sample Type Remolded to 90% Friction Angle Cohesion 15° 500 psf EXPANSION INDEX TESTS (ASTM D4829) Sample Location Test Pit P-3 @ 0-2½’ Test Pit P-3 @ 4½’-6’ Test Pit P-3 @ 6’-7½’ Initial Moisture: 12.0 % 12.7 % 14.4 % Initial Dry Density 100.9 pcf 98.5 pcf 95.8 pcf Final Moisture: 26.9 % 31.6 % 33.8 % Expansion Index: 98(High) 139 (Very High) 141(Very High) GRAIN SIZE DISTRIBUTION (ASTM D422) Sample Location Test Pit P-3 @ 0-2½’ Sieve Size Percent Passing #4 100 #8 99 #16 98 #30 94 #50 87 #100 72 #200 58 0.05 mm 52 0.005 mm 25 0.001 mm 15 ATTERBERG LIMITS (ASTM D424) Sample Location Test Pit P-3 @ 0-2½’ Liquid Limit 43 Plastic Limit 19 Plasticity Index 24 (CL) CWE 2200253.01 June 24, 2021 Plate No. B-3 LABORATORY TEST RESULTS (CONT.) SOLUBLE SULFATES (CALIFORNIA TEST 417) Sample Location Test Pit P-3 @ 0-2½ Soluble Sulfate 0.016 % (SO4) Appendix C References CWE 2200253.01 June 24, 2021 Appendix E-1 REFERENCES American Society of Civil Engineers, ASCE 7 Hazard Tool, https://asce7hazardtool.online Benton Engineering, Inc., Final Report on Compacted Filled Ground, LA Costa South Unit No.1, Rancho La Costa, CA, dated June 23, 1969. California Emergency Management Agency – California Geological Society – University of Southern California, 2009, Tsunami Inundation Map for Emergency Planning, Encinitas Quadrangle, scale 1:24,000, dated June 1, 2009. Compaction Labs, Inc. Report of Certification of Compacted Fill Ground, Proposed Single Family Dwelling 2440 La Costa Avenue, La Costa, CA, dated August 26, 1986. Federal Emergency Management Agency, 2019, San Diego County, California and Incorporated Areas Flood Insurance Rate Map, Map Panel Number 06073C1034H Historic Aerials, NETR Online, historicaerials.com Jennings, C.W. and Bryant, W. A., 2010, Fault Activity Map, California Geological Survey, Geologic Data Map No. 6, http://www.quake.ca.gov/gmaps/FAM/faultactivitymap.html Kennedy, Michael P. and Tan, Siang S., 2007, Geologic Map of the Oceanside 30’x60’ Quadrangle, California, California Geologic Survey, Map No. 2 Tan, S.S., 1995 and Giffen, D.G., Landslide Hazards in the Northern Part of the San Diego Metropolitan Area, San Diego County, California, California Division of Mines and Geology Open-File Report 95-04 Studio Uno Architecture, Architectural Plans, Stark Residence, La Costa Avenue, Carlsbad, California, dated June 11, 2021. U.S. Geological Survey, Quaternary Faults in Google Earth, http://earthquake.usgs.gov/hazards/qfaults/google.php Appendix D Recommended Grading Specifications – General Provisions CWE 2200253.01 June 24, 2021 Appendix D, Page D-1 RECOMMENDED GRADING SPECIFICATIONS - GENERAL PROVISIONS STARK HOUSE APN 216-160-10-00 LA COSTA AVENUE CARLSBAD, CALIFORNIA GENERAL INTENT The intent of these specifications is to establish procedures for clearing, compacting natural ground, preparing areas to be filled, and placing and compacting fill soils to the lines and grades shown on the accepted plans. The recommendations contained in the preliminary geotechnical investigation report and/or the attached Special Provisions are a part of the Recommended Grading Specifications and shall supersede the provisions contained hereinafter in the case of conflict. These specifications shall only be used in conjunction with the geotechnical report for which they are a part. No deviation from these specifications will be allowed, except where specified in the geotechnical report or in other written communication signed by the Geotechnical Engineer. OBSERVATION AND TESTING Christian Wheeler Engineering shall be retained as the Geotechnical Engineer to observe and test the earthwork in accordance with these specifications. It will be necessary that the Geotechnical Engineer or his representative provide adequate observation so that he may provide his opinion as to whether or not the work was accomplished as specified. It shall be the responsibility of the contractor to assist the Geotechnical Engineer and to keep him appraised of work schedules, changes and new information and data so that he may provide these opinions. In the event that any unusual conditions not covered by the special provisions or preliminary geotechnical report are encountered during the grading operations, the Geotechnical Engineer shall be contacted for further recommendations. If, in the opinion of the Geotechnical Engineer, substandard conditions are encountered, such as questionable or unsuitable soil, unacceptable moisture content, inadequate compaction, adverse weather, etc., construction should be stopped until the conditions are remedied or corrected or he shall recommend rejection of this work. CWE 2200253.01 June 24, 2021 Appendix D, Page D-2 Tests used to determine the degree of compaction should be performed in accordance with the following American Society for Testing and Materials test methods: Maximum Density & Optimum Moisture Content - ASTM D1557 Density of Soil In-Place - ASTM D1556 or ASTM D6938 All densities shall be expressed in terms of Relative Compaction as determined by the foregoing ASTM testing procedures. PREPARATION OF AREAS TO RECEIVE FILL All vegetation, brush and debris derived from clearing operations shall be removed, and legally disposed of. All areas disturbed by site grading should be left in a neat and finished appearance, free from unsightly debris. After clearing or benching the natural ground, the areas to be filled shall be scarified to a depth of 6 inches, brought to the proper moisture content, compacted and tested for the specified minimum degree of compaction. All loose soils in excess of 6 inches thick should be removed to firm natural ground which is defined as natural soil which possesses an in-situ density of at least 90 percent of its maximum dry density. When the slope of the natural ground receiving fill exceeds 20 percent (5 horizontal units to 1 vertical unit), the original ground shall be stepped or benched. Benches shall be cut to a firm competent formational soil. The lower bench shall be at least 10 feet wide or 1-1/2 times the equipment width, whichever is greater, and shall be sloped back into the hillside at a gradient of not less than two (2) percent. All other benches should be at least 6 feet wide. The horizontal portion of each bench shall be compacted prior to receiving fill as specified herein for compacted natural ground. Ground slopes flatter than 20 percent shall be benched when considered necessary by the Geotechnical Engineer. Any abandoned buried structures encountered during grading operations must be totally removed. All underground utilities to be abandoned beneath any proposed structure should be removed from within 10 feet of the structure and properly capped off. The resulting depressions from the above-described procedure should be backfilled with acceptable soil that is compacted to the requirements of the Geotechnical Engineer. This includes, but is not limited to, septic tanks, fuel tanks, sewer lines or leach lines, storm drains and water lines. Any buried structures or utilities not to be abandoned should be brought to the attention of the Geotechnical Engineer so that he may determine if any special recommendation will be necessary. CWE 2200253.01 June 24, 2021 Appendix D, Page D-3 All water wells which will be abandoned should be backfilled and capped in accordance to the requirements set forth by the Geotechnical Engineer. The top of the cap should be at least 4 feet below finish grade or 3 feet below the bottom of footing whichever is greater. The type of cap will depend on the diameter of the well and should be determined by the Geotechnical Engineer and/or a qualified Structural Engineer. FILL MATERIAL Materials to be placed in the fill shall be approved by the Geotechnical Engineer and shall be free of vegetable matter and other deleterious substances. Granular soil shall contain sufficient fine material to fill the voids. The definition and disposition of oversized rocks and expansive or detrimental soils are covered in the geotechnical report or Special Provisions. Expansive soils, soils of poor gradation, or soils with low strength characteristics may be thoroughly mixed with other soils to provide satisfactory fill material, but only with the explicit consent of the Geotechnical Engineer. Any import material shall be approved by the Geotechnical Engineer before being brought to the site. PLACING AND COMPACTION OF FILL Approved fill material shall be placed in areas prepared to receive fill in layers not to exceed 6 inches in compacted thickness. Each layer shall have a uniform moisture content in the range that will allow the compaction effort to be efficiently applied to achieve the specified degree of compaction. Each layer shall be uniformly compacted to the specified minimum degree of compaction with equipment of adequate size to economically compact the layer. Compaction equipment should either be specifically designed for soil compaction or of proven reliability. The minimum degree of compaction to be achieved is specified in either the Special Provisions or the recommendations contained in the preliminary geotechnical investigation report. When the structural fill material includes rocks, no rocks will be allowed to nest and all voids must be carefully filled with soil such that the minimum degree of compaction recommended in the Special Provisions is achieved. The maximum size and spacing of rock permitted in structural fills and in non-structural fills is discussed in the geotechnical report, when applicable. Field observation and compaction tests to estimate the degree of compaction of the fill will be taken by the Geotechnical Engineer or his representative. The location and frequency of the tests shall be at the Geotechnical Engineer's discretion. When the compaction test indicates that a particular layer is at less than the required degree of compaction, the layer shall be reworked to the satisfaction of the Geotechnical Engineer and until the desired relative compaction has been obtained. CWE 2200253.01 June 24, 2021 Appendix D, Page D-4 Fill slopes shall be compacted by means of sheepsfoot rollers or other suitable equipment. Compaction by sheepsfoot roller shall be at vertical intervals of not greater than four feet. In addition, fill slopes at a ratio of two horizontal to one vertical or flatter, should be trackrolled. Steeper fill slopes shall be over-built and cut- back to finish contours after the slope has been constructed. Slope compaction operations shall result in all fill material six or more inches inward from the finished face of the slope having a relative compaction of at least 90 percent of maximum dry density or the degree of compaction specified in the Special Provisions section of this specification. The compaction operation on the slopes shall be continued until the Geotechnical Engineer is of the opinion that the slopes will be surficially stable. Density tests in the slopes will be made by the Geotechnical Engineer during construction of the slopes to determine if the required compaction is being achieved. Where failing tests occur or other field problems arise, the Contractor will be notified that day of such conditions by written communication from the Geotechnical Engineer or his representative in the form of a daily field report. If the method of achieving the required slope compaction selected by the Contractor fails to produce the necessary results, the Contractor shall rework or rebuild such slopes until the required degree of compaction is obtained, at no cost to the Owner or Geotechnical Engineer. CUT SLOPES The Engineering Geologist shall inspect cut slopes excavated in rock or lithified formational material during the grading operations at intervals determined at his discretion. If any conditions not anticipated in the preliminary report such as perched water, seepage, lenticular or confined strata of a potentially adverse nature, unfavorably inclined bedding, joints, or fault planes are encountered during grading, these conditions shall be analyzed by the Engineering Geologist and Geotechnical Engineer to determine if mitigating measures are necessary. Unless otherwise specified in the geotechnical report, no cut slopes shall be excavated higher or steeper than that allowed by the ordinances of the controlling governmental agency. ENGINEERING OBSERVATION Field observation by the Geotechnical Engineer or his representative shall be made during the filling and compaction operations so that he can express his opinion regarding the conformance of the grading with acceptable standards of practice. Neither the presence of the Geotechnical Engineer or his representative or CWE 2200253.01 June 24, 2021 Appendix D, Page D-5 the observation and testing shall release the Grading Contractor from his duty to compact all fill material to the specified degree of compaction. SEASON LIMITS Fill shall not be placed during unfavorable weather conditions. When work is interrupted by heavy rain, filling operations shall not be resumed until the proper moisture content and density of the fill materials can be achieved. Damaged site conditions resulting from weather or acts of God shall be repaired before acceptance of work. RECOMMENDED GRADING SPECIFICATIONS - SPECIAL PROVISIONS RELATIVE COMPACTION: The minimum degree of compaction to be obtained in compacted natural ground, compacted fill, and compacted backfill shall be at least 90 percent. For street and parking lot subgrade, the upper six inches should be compacted to at least 95 percent relative compaction. EXPANSIVE SOILS: Detrimentally expansive soil is defined as clayey soil which has an expansion index of 50 or greater when tested in accordance with the Uniform Building Code Standard 29-2. OVERSIZED MATERIAL: Oversized fill material is generally defined herein as rocks or lumps of soil over 6 inches in diameter. Oversized materials should not be placed in fill unless recommendations of placement of such material are provided by the Geotechnical Engineer. At least 40 percent of the fill soils shall pass through a No. 4 U.S. Standard Sieve. TRANSITION LOTS: Where transitions between cut and fill occur within the proposed building pad, the cut portion should be undercut a minimum of one foot below the base of the proposed footings and recompacted as structural backfill. In certain cases that would be addressed in the geotechnical report, special footing reinforcement or a combination of special footing reinforcement and undercutting may be required. July 21, 2022 Stark House LLC CWE 2200253.02 Chula Vista, California 91910 Attention: Ramiro Barajas Subject: Additional Recommendations Stark House, APN 216-160-10-00, La Costa Avenue, Carlsbad, California Reference: Christian Wheeler Engineering, Report of Preliminary Geotechnical Investigation, Stark House, APN 216-160-10-00, La Costa Avenue, Carlsbad, dated June 24, 2021, CWE Report No. 2200253.01 Ladies and Gentlemen At your request, we have prepared this report to present additional recommendations for the subject project. information required by the City of Carlsbad regarding the geotechnical issues at the site. The comments in the city review letter and our responses to the comments in the referenced memorandum are presented below. EARTH RETAINING WALLS FOUNDATIONS: Foundations for any proposed retaining walls should be constructed in accordance with the foundation recommendations presented in the referenced report. PASSIVE PRESSURE: The passive pressure for the anticipated foundation soils may be considered to be 250 pounds per square foot per foot of depth. The upper foot of embedment should be neglected when calculating passive pressures, unless the foundation abuts a hard surface such as a concrete slab. The passive pressure may be increased by one-third for seismic loading. The coefficient of friction for concrete to soil may be assumed to be 0.25 for the resistance to lateral movement. When combining frictional and passive resistance, the friction should be reduced by one-third. ACTIVE PRESSURE: The active soil pressure for the design of “unrestrained” and “restrained” earth retaining structures with level backfill may be assumed to be equivalent to the pressure of a fluid weighing 40 CHRISTIAN WHEELER E N G I N E E R I N G 3 9 8 0 H o m e A v e nu e S a n Di e g o , C A 9 2 1 05 6 1 9 -5 5 0- 1 7 00 F A X 61 9 - 55 0 - 17 0 1 CWE 2200253.02 July 21, 2022 Page No. 2 and 60 pounds per cubic foot, respectively. These pressures do not consider any other surcharge. If any are anticipated, this office should be contacted for the necessary increase in soil pressure. These values are based on a drained backfill condition. Seismic lateral earth pressures may be assumed to equal an inverted triangle starting at the bottom of the wall with the maximum pressure equal to 7.8H pounds per square foot (where H = wall height in feet) occurring at the top of the wall. WATERPROOFING AND WALL DRAINAGE SYSTEMS: The need for waterproofing should be evaluated by others. If required, the project architect should provide (or coordinate) waterproofing details for the retaining walls. The design values presented above are based on a drained backfill condition and do not consider hydrostatic pressures. The retaining wall designer should provide a detail for a wall drainage system. Typical retaining wall drain system details are presented as Plate No. 1 of this report for informational purposes. Additionally, outlet points for the retaining wall drain system should be coordinated with the project civil engineer. BACKFILL: Retaining wall backfill and fills underlying the proposed structure should be compacted to at least 95 percent relative compaction. All other backfills should be compacted to at least 90 percent relative compaction. Expansive or clayey soils should not be used for backfill material. Due to the clayey nature of the on-site soils import soils will likely be needed for use in wall backfill operations. The wall should not be backfilled until the masonry has reached an adequate strength. If gravel is used for backfill, it should be wrapped in filter fabric and capped with at least 24 inches of compacted fill. INFILTRATION RESTRICTIONS Based upon the soil conditions observed in our test pits, the site is underlain by soils with a very high expansive potential (EI=141). We anticipate that wetting the on-site soils through infiltration could result in heave, slope instability, and distress to the proposed structure and nearby improvements. This coupled with setbacks from property lines, existing slopes, retaining walls, and fills greater than 5 feet in depth will make infiltration at the site restricted. In order to mitigate the risk to acceptable levels, liners and underdrains are recommended in the design and construction of the proposed BMP basin. The liners should be impermeable (e.g. High-density polyethylene, HDPE, with a thickness of about 30 mil or equivalent Polyvinyl Chloride, PVC). The underdrains should be perforated within the liner area, installed at the base and above the liner, be at least 3 inches in diameter and consist of Schedule 40 PVC pipe. The underdrains outside of the liner should consist of solid pipe. The CWE 2200253.02 July 21, 2022 Page No. 3 penetration of the liners at the underdrains should be properly waterproofed. The underdrains should be connected to a proper outlet. The devices should also be installed in accordance with the manufacturer’s recommendations. If you have any questions regarding this report, please do not hesitate to contact this office. Christian Wheeler Engineering appreciates this opportunity of providing professional services for you for the subject project. Respectfully submitted, CHRISTIAN WHEELER ENGINEERING Daniel B. Adler, RCE #36037 Daniel J. Flowers, CEG #2686 DBA:dba:djf encl: Plate No.1 ec: ramk3@yahoo.com 1 3 5 5 5 1 1 3 2 2 3 4 NOTES AND DETAILS 1 GENERAL NOTES: 1) THE NEED FOR WATERPROOFING SHOULD BE EVALUATED BY OTHERS. 2) WATERPROOFING TO BE DESIGNED BY OTHERS (CWE CAN PROVIDE A DESIGN IF REQUESTED). 3) EXTEND DRAIN TO SUITABLE DISCHARGE POINT PER CIVIL ENGINEER. 4) DO NOT CONNECT SURFACE DRAINS TO SUBDRAIN SYSTEM. 4 2 3 4 5 UNDERLAY SUBDRAIN WITH AND CUT FABRIC BACK FROM DRAINAGE PANELS AND WRAP FABRIC AROUND PIPE. COLLECTION DRAIN (TOTAL DRAIN OR EQUIVALENT) LOCATED AT BASE OF WALL DRAINAGE PANEL PER MANUFACTURER'S RECOMMENDATIONS. 4 3 6 4 4 4 4 4 4 7 4-INCH PERFORATED PVC PIPE ON TOP OF FOOTING, HOLES POSITIONED DOWNWARD (SDR 35, SCHEDULE 40, OR EQUIVALENT). 34 INCH OPEN-GRADED CRUSHED AGGREGATE. GEOFARBRIC WRAPPED COMPLETELY AROUND ROCK. PROPERLY COMPACTED BACKFILL SOIL. WALL DRAINAGE PANELS (MIRADRAIN OR EQUIVALENT) PLACED PER MANUFACTURER'S REC'S. DETAILS: 6 7 12" 12"12" 12" 12" MIN. 6" MIN. 6" MIN.6" MIN. 1 DETAIL 2 2 DETAIL DETAIL DETAIL STARK HOUSE APN 216-160-10-00, LA COSTA AVENUE CARLSBAD, CALIFORNIA DATE: JULY 2022 BY: SD JOB NO.: 2200253.02 PLATE NO.: 1 CANTILEVER RETAINING WALL DRAINAGE SYSTEMS CHRISTIAN WHEELER E N G I N E E R I N G □----- i~~~~ 4 . cl 4 • /•~' ,, ' ~/, ~~ cl cl ~ ~ ~---------~~ □----- 0 Q; 0 0 0 □----- ~~~~ 4 cl /a · ,,;z« / ~ ~" /~ cl □----- 0 0 ;, January 16, 2023 Stark House LLC CWE 2200253.03 Chula Vista, California 91910 Attention: Ramiro Barajas Subject: Response to 2nd Round of City of Carlsbad Third-Party Geotechnical Review Stark House, APN 216-160-10-00, La Costa Avenue, Carlsbad, California References: 1) Christian Wheeler Engineering, Report of Preliminary Geotechnical Investigation, Stark House, APN 216-160-10-00, La Costa Avenue, Carlsbad, dated June 24, 2021, CWE Report No. 2200253.01 2) Snipes-Dye Associates, Grading Plans For: Stark Residence, 2436 La Costa Avenue, Carlsbad, California, 92009, undated 3) Lamar Engineering, Structural Plans, Stark House, Sheets SN1, S1, S4, and SD2, dated January 12, 2023 4) Christian Wheeler Engineering, Additional Recommendations, Stark House, APN 216-160-10-00, La Costa Avenue, Carlsbad, dated July 21, 2022, CWE Report No. 2200253.02 5) Ninyo & Moore, Second Round of Third-Party Geotechnical Review, Proposed Stark Residence on APN 216-160-10, La Costa Avenue, Carlsbad, CA, Project ID PD2021-0034, La Costa Avenue, Carlsbad, California, dated September 28, 2022 Ladies and Gentlemen At your request, we have prepared this report to present additional information required by the City of Carlsbad regarding the geotechnical issues at the site. The comments in the city review letter and our responses to the comments in the referenced memorandum are presented below. Remaining City Comment 1: The geotechnical consultant should review the project grading and foundation plans and provide any additional geotechnical recommendations, as appropriate, and indicate if the plans have been prepared in accordance with the geotechnical recommendations provided in the referenced geotechnical report. CHRISTIAN WHEELER E N G I N E E R I N G 3 9 8 0 H o m e A v e nu e S a n Di e g o , C A 9 2 1 05 6 1 9 -5 5 0- 1 7 00 F A X 61 9 - 55 0 - 17 0 1 CWE 2200253.03 January 16, 2023 Page No. 2 CWE Response: We have performed a limited geotechnical review of the referenced grading plans for the subject project in order to ascertain that the recommendations presented in our referenced reports have been implemented, and that no additional recommendations are needed due to changes in the proposed construction. Based on this review, it is our opinion that, that the recommendations provided in this report and contained in the referenced reports are sufficient and that no additional recommendations are necessary. We have also performed a limited geotechnical review of the referenced foundation plans (Sheets SN1, S1, S4 and SD2) to determine whether the following elements of our referenced report appear to be incorporated into the plans. • The plans reference our geotechnical reports. • The recommended soil design bearing capacity is on the plans. • The recommended seismic design factors are on the plans. • The recommended minimum foundation dimensions and reinforcing steel are reflected on the plans. The intent of our limited plan review was to verify that the plans submitted for construction reflect the described minimum geotechnical recommendations, and that no additional investigation or recommendations are required due to changes made in the project since our investigation was performed. It is not our intent to provide a third-party review of the structural calculations or structural design. The design engineer is responsible for properly designing the foundations and other structural elements based on the requirements of the structure and considering the information presented in our report. Based on our review, it is our opinion that our recommendations have been adequately implemented and no additional analysis and/or recommendations are needed. Remaining City Comment 2: The geotechnical consultant should provide an updated geotechnical map/plot plan that utilizes the latest grading plan for the project to clearly show the lateral limits of the recommended remedial grading. CWE Response: See attached Plate No.1. Closed City Comment 3: The 8th bullet on Page 2 of the referenced geotechnical report indicates that the intent of the report was to “Provide earth retaining wall design recommendations” for the project. However, such recommendations are not included. The Geotechnical Consultant should provide recommendations for the design and construction of new retaining walls. Furthermore, the Geotechnical Consultant should indicate if soils derived for onsite excavations are suitable for reuse as retaining wall construction. CWE Response: Comment closed. CWE 2200253.03 January 16, 2023 Page No. 3 Remaining City Comment 4: The “Landslide Potential and Slope Stability” section on Page 5 of the referenced geotechnical report indicates that the slopes on site “do not currently contain landslide deposits, there is a possibility of failure even in the absence of activities of man”. Although the Geotechnical Consultant does conclude that no indications of landsliding are present at the site, the Geotechnical Consultant should provide a recommendation to observe temporary backcuts during construction for signs of instability, such as adverse bedding. CWE Response: As discussed on Page No. 8 of our report (CWE, 2021) “Continuous observation by the Geotechnical Consultant is essential during the grading operation to confirm conditions anticipated by our investigation, to allow adjustments in design criteria to reflect actual field conditions exposed, and to determine that the grading proceeds in general accordance with the recommendations contained herein.” In addition, we recommend that our firm be contacted to have an engineering geologist observe the cut slopes during grading to ascertain that no unforeseen adverse geotechnical conditions exist such as slope instability, adverse bedding or seepage. If adverse conditions are identified, additional recommendations will be provided, as necessary. Remaining City Comment 5: The “Site Preparation” section on Page 8 of the referenced report indicates that remedial grading removals of existing fills and subsoils should be performed and extend across the lateral limits of the lot. As noted in this section, these removals may extend to depths of 6 feet or more. The Geotechnical Consultant should comment on and graphically depict how these removals will impact the existing sewer line at the western edge of the lot and the existing retaining walls at the northern and eastern edges of the lot. CWE Response: Removals should not encroach into utility easements or within 2 feet of the existing improvements to remain. Where lateral removals cannot be achieved due to existing improvements or utility easements deepened foundation recommendations will be warranted. Deepened foundation recommendations will be provided once remedial grading operations have been completed and the extent of removals determined. If these setbacks and our grading recommendations are implemented it is our opinion that the proposed grading operations will not destabilize the existing improvements or neighboring properties. See attached Plate Nos.1 through 3 of this report for graphic illustrations of the anticipated removal limits. Remaining City Comment 6: As noted in the “Site Preparation” section on Page 8 of the referenced geotechnical report, removals of 6 feet or deeper are anticipated. Additionally, Plate 2 depicts potential temporary cuts up to approximately 8 feet in height. The geotechnical consultant should provide recommendations for the inclinations of temporary slopes to be cut at the site. CWE Response: We anticipate that temporary excavation slopes up to about 8 feet high may be required during the recommended site preparation operations as well as retaining wall construction. In general, cut slopes can be excavated at an inclination of 1:1 (horizontal to vertical) if founded in the Delmar Formation and at a CWE 2200253.03 January 16, 2023 Page No. 4 1.5:1 (horizontal to vertical) if founded in fill materials. For removals adjacent to the existing sewer easement slot removals can be implemented as necessary. Slot excavations should be performed in cuts no more than 8 feet wide. The 8-foot-wide slot removals should be excavated and backfilled in the same day and no personal should be allowed in or near the excavations. We recommend that our firm be contacted to have an engineering geologist observe the temporary cut slopes during grading to ascertain that no unforeseen adverse conditions requiring revised recommendations are encountered. If adverse conditions are identified, it may be necessary to flatten the slope inclination. No surcharge loads such as soil or equipment stockpiles, foundations, etc. should be allowed within a distance from the top of temporary slopes equal to half the slope height. Remaining City Comment 7: The “Lateral Load Resistance” section on Page 11 of the referenced geotechnical report recommends the use of a coefficient of friction between soil and concrete of 0.25. The Geotechnical Consultant should indicate how this value was developed using friction angle of 15 degrees as indicated in the laboratory test results presented in Appendix B. CWE Response: It is our opinion that the coefficient of friction recommended in the referenced geotechnical report is appropriate based on our engineering judgment and the anticipated as-graded conditions. If needed, revised recommendation will be provided after grading is performed. Remaining City Comment 8: The “On-Grade Slabs-General” section on Page 14 of the referenced geotechnical report recommends the use of slabs-on-grade for the building floor system. The Geotechnical Consultant should clarify if the floor slabs for the building are to be standard concrete slabs-on-grade or to be post-tensioned slabs-on-grade. CWE Response: The referenced structural plans detail slab-on-grade floor systems for the building. Remaining City Comment 9: The “Exterior Concrete Flatwork” section on Pages 14 and 15 of the referenced geotechnical report recommends that exterior flatwork be 6 inches thick and reinforced with No.4 rebar. It also recommends that the driveway slab be constructed with thickened edges. With these mitigation measures, the Geotechnical Consultant indicates that these types of surface improvements may be detrimentally impacted by the underlying expansive soils, which suggests these improvements may be subjected to soil movement of the expansive soils. The Geotechnical Consultant should comment on whether or not additional recommendations are needed to address potential differential soil movement at transition areas between these types of improvements and adjacent buildings, such as driveway to garage and flatwork to front door transition areas. CWE Response: Any exterior flatwork adjacent to door openings should be doweled as recommended by the project structural engineer. CWE 2200253.03 January 16, 2023 Page No. 5 Remaining City Comment 10: The referenced grading plans depict a detention basin with slopes at inclinations of 2:1 (horizontal to vertical) to be constructed at the northern end of the lot. The Geotechnical Consultant should provide recommendations for the inclinations of engineer fill slopes and slopes within the interior of detention basins. CWE Response: Engineered fill slopes including the slopes within the interior of the detention basin should be constructed at a 2:1 (horizontal to vertical) or flatter inclination. The slopes for the interior of the detention basin will incorporate an impermeable liner approximately 12 inches to 2 feet below proposed grades and multiple outlet drains. The liner will extend up to the proposed ponding elevation and be backfilled with on-site clayey soils. Based our discussions with the projects civil engineer, the detention basin is designed to accommodate storm water from the 100-year flood and water is not intended to pond. However, the outer soils within the basin maybe exposed to inundation and routine inspection and maintenance of the basin will be necessary. A maintenance plan should be specified for the basin by the designer and followed by the owner during the entire lifetime of the basin. If you have any questions regarding this report, please do not hesitate to contact this office. Christian Wheeler Engineering appreciates this opportunity of providing professional services for you for the subject project. Respectfully submitted, CHRISTIAN WHEELER ENGINEERING Daniel B. Adler, RCE #36037 Daniel J. Flowers, CEG #2686 DBA:dba:djf encl: Plates 1, 2 and 3 ec: ramk3@yahoo.com P-2 P-1 P-3 P-5 P-4 HA-1Qaf Td Qaf Td LA COSTA AVENUE B'B A' A P-5 Approximate Test Pit Location Approximate Hand Auger Test Location Cross Section Artificial Fill over Delmar Formation Qaf Td CWE LEGEND HA-1 Note: Subsoils Not Mapped DATE: JANUARY 2023 BY: SD JOB NO.: 2200253.03 PLATE NO.: 1 SITE PLAN AND GEOTECHNICAL MAP STARK HOUSE LA COSTA AVENUE CARLSBAD, CALIFORNIA CHRISTIAN WHEELER E N G I N E E R I N G W+E 00 20'40' SCALE: 1" = 20' ANTICIPATED LIMITS OF REMEDIAL GRADING ) 8 <;/ l (70.00 RIM) ... L D -r 11 .. ·· / ~'>, ') -r ,.;)\ ~t / \ (56.7511::> ~. 216-160~;; • ········•·•••• .·~ : ... ' ",( §~k:;rr:·~~-w • : \ ~: ~~~Jr > \i ... ,·, ··············• I • ........... --... ·--r -~ ·.·~ '',<.,,.~ ~ PN0.611 r.a·vds )WG. Nb.1· Zl TO $1A ~ ~~\ rel~ g~ -: ii1 ' .,,c"; •f> J, .. s1: PL f--------, 70 80 90 100 110 120 130 0 10 20 30 40 50 60 70 80 90 100 110 A 70 80 90 100 110 120 130 120 A' 130 140 145 P-5 P-3 Projected West 15' P-2 Projected East 8' P-1 Projected West 13' Qaf Qaf Qaf Subsoil Subsoil Subs o i l Td Td Td Anticipated Removals Artificial Fill Delmar Formation CWE LEGEND Qaf Td DATE: JANUARY 2023 BY: SD JOB NO.: 2200253.03 PLATE NO.: 2 GEOLOGIC CROSS SECTION A-A' STARK HOUSE LA COSTA AVENUE CARLSBAD, CALIFORNIA CHRISTIAN WHEELER E N G I N E E R I N G SCALE: 1" = 10' 00 10'20' l ~ 1F -jL--Ciimiiiiizc=~==::;::~~m:==:;::::::;;::::::~~===~~mim:=~=:iiiimii~r----,-~I -l" 'f "'"''"-· WALK-IN CLOSET ,F-BEDROOM 2 -11,j D ~mssrn,ooM BALCONY ~ _,.,. I -1"', I TERRACE/ GRILL ~CAR GARAGE -11 =Tr -......c;;;;::;J -L..LJ==:.IJ - --c: 2 "C ~ '< ~-r, - 70 80 90 100 110 120 130 0 10 20 30 40 50 60 70 80 90 100 B 70 80 90 100 110 120 130B' P-2 Manhole to Remain EL=94.1 IE=85.08 Existing Grade QafQaf TdTd Td Anticipated Removals Qaf Qaf Proposed Grade Proposed Building Sewer Easement PL PL Existing Wall Proposed Stairway Qaf Td Artificial Fill Delmar Formation CWE LEGEND Qaf Td DATE: JANUARY 2023 BY: SD JOB NO.: 2200253.03 PLATE NO.: 3 GEOLOGIC CROSS SECTION B-B' STARK HOUSE LA COSTA AVENUE CARLSBAD, CALIFORNIA CHRISTIAN WHEELER E N G I N E E R I N G SCALE: 1" = 10' 00 10'20' ----. --~ - ... I· -1 ... - I ..._ ...._ ..._ -.... t ...._ 1 --------._ ...._ ---...._ ..._ ..._ \J/~ ..._ T - I ..._ ..._ --..._ -- I / ------ - I I I I I I I I I I I ' I - ~~~ •