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CT 06-06; LA COSTA OAKS NEIGHBORHOOD 3.7; GEOTECHNICAL REPORT; 2007-10-30
ci-0e--°c" UPDATE GEOTECHNICAL REPORT VILLAGES OF LA COSTA - THE OAKS NORTH NEIGHBORHOOD 3.7 LOTS I THROUGH 44 CARLSBAD, CALIFORNIA PREPARED FOR SAN DIEGO NORTH COUNTY NEW HOMES COMMUNITIES C/0 EPPSTEINER & ASSOCIATES SOLANA BEACH, CALIFORNIA OCTOBER 30, 2007 PROJECT NO. 06105-52-23 GEOCON INCORPORATED Michael C. Ertwine Senior Staff Geologist MCE:AS:SW:dmc (6/del) Addressee //, / // Shawn Wecdon GE 2714 i 4i SadrL CEO 1778 GE000N 1-N9 ORFERATE:D GEOTEClcAL;CbNsuLTANTs Project No. 06105-52-23 October 30,2007 San Diego North County New Homes Communities C/0 Eppsteiner & Associates 201 Lomas Santa Fe, Suite 460 Solana Beach, California 92075 Attention: Mr. Stuart M. Eppsteiner Subject: VILLAGES OF LA COSTA - THE OAKS NORTH NEIGHBORHOOD 3.7 LOTS 1 THROUGH 44 CARLSBAD, CALIFORNIA UPDATE GEOTECHNICAL REPORT Dear Mr. Eppsteiner: In accordance with your request and our proposal .(LG-07228) dated October 2, 2007, we have prepared this update geotechnical report for the subject project. The accompanying report presents the results of our study and conclusions and recommendations pertaining to the geotechnical aspects of proposed development of the site. The site was graded as part of the Villages of La Costa - Oaks North development. The grading for Lots 1 through 44 was completed in September 2007. Compacted fill and formational materials of the Santiago Peak Volcanics underlie the site. Provided the recommendations contained in this update report are followed, the site is -considered suitable for construction and support of the proposed residential structures. Should you have questions regarding thisreport,.or if we may be of further service, please contact the undersigned at your convenience. 6960 FlddefDive. an Dió ofrnia21:2l -2974. .• TèIephare(858) -558490O • Fdx(858)5584159 TABLE OF CONTENTS I. PURPOSE AND SCOPE . SITE AND PROJECT DESCRIPTION...........................................................................................1 PREVIOUS SITE DEVELOPMENT..............................................................................................2 SOIL AND GEOLOGIC CONDITIONS ........................................................................................2 4.1 Compacted Fill ......................................................................................................................2 4.2 Santiago Peak Volcanics (Jsp)...............................................................................................3 GROUNDWATER ..........................................................................................................................3 GEOLOGIC HAZARDS .................................................................................................................3 6.1 Faulting and Seismicity .........................................................................................................3 6.2 Liquefaction...........................................................................................................................4 CONCLUSIONS AND RECOMMENDATIONS...........................................................................5 7.1 General...................................................................................................................................5 7.2 Finish Grade Soil Conditions ................................................................................................5 7.3 Seismic Design Criteria.........................................................................................................6 7.4 Future Grading.......................................................................................................................7 7.5 Foundation and Concrete Slabs-On-Grade Recommendations.............................................7 7.6 Retaining Walls and Lateral Loads......................................................................................12 7.7 Slope Maintenance ..............................................................................................................13 7.8 Site Drainage .......................................................................................................................14 LIMITATIONS AND UNIFORMITY OF CONDITIONS FIGURES Vicinity Map Wall/Column Footing Dimension Detail Retaining Wall Drain Detail TABLES Summary of As-Graded Building Pad Conditions and Recommended Foundation Categories Summary of Laboratory Expansion Index Test Results M. Summary of Finish Grade Expansion Index Test Results Summary of Laboratory Water-Soluble Sulfate Test Results Summary of Soil Profile Type UPDATE GEOTECHNICAL REPORT 1. PURPOSE AND SCOPE This report presents the results of the update geotechnical study for Lots I through 44 located at the Villages of La Costa - The Oaks North, Neighborhood 3.7. The purpose of this update report is to provide information regarding the geologic conditions underlying the site and to provide foundation and retaining wall design recommendations. The scope of the study included a review of the following: Update Geotechnical Investigation, Villages of La Costa—The Oaks, Carlsbad, California, prepared by Geocon Incorporated, dated August 3, 2001 (Project No. 06105-12-04). Final Report of Testing and Observation Services Performed During Site Grading, Villages of La Costa - The Oaks North, Neighborhood 3.7, prepared by Geocon Incorporated, in progress (Project No. 06403-52-20). Mass Grading Plans for La Costa Oaks Worth Neighborhood 3.7, prepared by Hunsaker and Associates, City of Carlsbad approval date pending. 2. SITE AND PROJECT DESCRIPTION The subject lots are within the Villages of La Costa - The Oaks North, Neighborhood 3.7 development, located east of the intersection of Rancho Santa Fe Road and Avenida Soledad in the City of Carlsbad, California (see Vicinity Map, Figure 1). Proposed development includes the construction of 44 single-family residential homes and associated improvements. Compacted fill is exposed at grade and is underlain by volcanic rock of Santiago Peak Volcanics. A summary of the as-graded pad conditions for each lot is provided on Table I. In general, the on-site fill materials vary between angular gravels and boulders produced by on-site blasting of hard rock and silty, fine to coarse sand and sandy clay derived from the surficial soils, and weathered formational materials. The locations and descriptions of the site and proposed improvements are based on a site reconnaissance, observations during site grading, a review of the referenced reports and grading plans. and our understanding of project development. If project details vary significantly from those described herein, Geocon Incorporated should be contacted to review and revise of this report. Project No. 06105-52-22 - I - October 30. 2007 3. PREVIOUS SITE DEVELOPMENT The subject lots were graded to the current configuration during mass grading operations for the Villages of La Costa - The Oaks North, Neighborhood 3.7. Grading was performed in conjunction with the observation and testing services of Geocon incorporated. A summary of the observations, compaction test results, and professional opinions pertaining to the grading operations has been presented in the referenced final report of testing and observation services performed during site grading. The majority of the grading operations consisted of removal and recompaction of surficial soil, placing compacted fill, and performing cuts within formational material to the design elevations. Due to the difficult excavation characteristics of the formational materials, cut lots were undercut approximately three to four feet and replaced with compacted fill to the design elevations. In addition, where a cut-fill transition existed within a lot, the lot was undercut approximately three to four feet and replaced with compacted fill. A summary of the as-graded pad conditions for the lots are presented in Table I. 4. SOIL AND GEOLOGIC CONDITIONS The site is underlain by compacted fill and geologic formations of the Jurassic-age Santiago Peak Volcanics. The predominant materials within 3 feet of grade consist of silty sand and gravel and possess a "very low" expansion potential (Expansion Index of 20 or less). The soil type and geologic units are discussed below. 4.1 Compacted Fill In general, structural fill placed and compacted at the site consisted of material that can be classified into three zones: Zone A Material placed within 3 feet from pad grade, 6 feet from parkway grade, and within roadways to at least 1 foot below the deepest utility consisted of "soil" fill with an approximate maximum particle dimension of 6 inches. Zone B Material placed within 10 feet from pad grade and below Zone A consisted of "soil rock" fill with a maximum particle dimension of 12 inches. In addition, material placed on the outer 6 feet of fill slopes and 2 feet below Zone A for fills in roadways and parkways consisted of "soil rock" fill with a maximum particle dimension of 12 inches. Zone C Material placed below Zone B consisted of "soil rock" fill with a maximum particle dimension of 48 inches. It should also be noted that larger rocks with a maximum dimension of approximately 8 feet were buried individually during "rock" fill grading operations. The maximum fill thickness is approximately 44 feet. Fill soil was placed in conjunction with the observation and testing services of Geocon Incorporated which have been summarized in the 4 Project No. 06105-52-23 -2- October 30, 2007 referenced final report of grading. The compacted fill is considered suitable to provide support for the proposed development. 4.2 Santiago Peak Volcanics (Jsp) The Jurassic-aged Santiago Peak Volcanics comprise the majority of the underlying bedrock. These rocks were deposited as an alternating succession of volcanic flows, tuffs, and breccias and typically have an andesite or dacite composition. Subsequently, this sequence of rocks was folded, faulted, and weakly metamorphosed. As encountered during grading, this unit is highly fractured. Closely spaced parallel fractures and joints form "sheeted" zones containing colorful alterations and/or oxidation minerals such as limonite and hematite. Even though the majority of the Santiago Peak Volcanics appears to be highly fractured and altered, the "sheeted" zones typically have steeply dipping, clay- filled fractures. 5. GROUNDWATER We did not encounter groundwater during grading operations. Groundwater is not expected to adversely impact the development of the property. Due to the fractured nature of the formational materials, we encountered some areas of seepage. Subdrains were installed during remedial grading. It is not uncommon for groundwater or seepage conditions to develop where none previously existed. Groundwater elevations are dependent on seasonal precipitation, irrigation, and land use, among other factors, and vary as a result. Proper surface drainage will be important to future performance of the project. 6. GEOLOGIC HAZARDS 6.1 Faulting and Seismicity We used the computer program EQFA ULT (Blake, 2000) to approximate the distance of known faults to the site. Within a search radius of 50 miles from the site, 12 known active faults were identified. The results of the seismicity analyses indicate that the Rose Canyon Fault is the dominant source of potential ground motion at the site. Earthquakes on the Rose Canyon Fault having a maximum magnitude of 7.2 are considered to be representative of the potential for seismic ground shaking within the property. The "maximum earthquake" is defined as the maximum earthquake that appears capable of occurring under the presently known tectonic framework (California Geologic Survey Notes, Number 43). We calculated the estimated maximum ground acceleration expected at the site to be approximately 0.30g, using the Sadigh, et al. (1997), acceleration-attenuation relationship. The earthquake events and site accelerations for the faults considered most likely to subject the site to ground shaking are presented on Table 6.1. The seismic risk at the site is not considered significantly greater than that of the surrounding developments or the Carlsbad area in general. 4 Project No. 06105-52-23 - 3 - October 30, 2007 TABLE 6.1 DETERMINISTIC SITE PARAMETERS FOR SELECTED ACTIVE FAULTS Fault Name Distance From Site (miles) Maximum Credible Magnitude Maximum Credible Site Accelerations (g) Rose Canyon 8 7.2 0.30 Newport-lnglewood (Offshore) 13 7.1 0.21 Elsinore-Julian 23 7.1 0.13 Elsinore-Temecula 23 6.7 0.10 Coronado Bank 23 7.6 0.17 Earthquake Valley 38 6.5 0.05 Elsinore-Glen Valley 38 6.8 0.06 San Joaquin Hills 43 6.6 0.05 Palos Verdes 43 7.3 0.07 San Jacinto-Anza 46 7.2 0.06 San Jacinto-San Jacinto Valley 48 6.9 0.05 San Jacinto-Coyote Mountain 48 6.6 1 0.04 In the event of a major earthquake along any of the referenced faults or other faults in the Southern California region, the site could be subjected to moderate to severe ground shaking. With respect to seismic shaking, the site is considered comparable to others in the general vicinity. While listing of peak accelerations is useful for comparison of potential effects of fault activity in the region, other considerations are important in seismic design including the frequency and duration of motion and the soil conditions underlying the site. The seismic design of structures should be performed in accordance with the Uniform Building Code (UBC) or California Building Code (CBC) currently adopted by the City of Carlsbad. 6.2 Liquefaction Liquefaction typically occurs when a site is located in a zone with seismic activity, on-site soils are cohesionless, groundwater is encountered within 50 feet of the surface, and soil relative densities are less than about 70 percent. If the four previous criteria are met, a seismic event could result in a rapid pore water pressure increase from the earthquake-generated ground accelerations. Due to the dense nature of the compacted fill and formational materials and the lack of a permanent groundwater table, the potential for liquefaction occurring at the site is considered to be very low. Project No. 06105-52-23 -4- October 30, 2007 7. CONCLUSIONS AND RECOMMENDATIONS 7.1 General 7.1.1 No soil or geologic conditions were encountered during previous geotechnical investigations or grading operations, which in our opinion would preclude the continued development of the property as presently planned, provided that the recommendations of this report are followed. 7.1.2 The site is underlain by compacted fill and formational materials of the Santiago Peak Volcanics. We observed the placement of compacted fill during mass grading operations and performed in-place density tests to evaluate the dry density and moisture content of the fill material. In general, the in-place density test results indicate that the fill soil has a dry density of at least 90 percent of the laboratory maximum dry density near to slightly above optimum moisture content at the locations tested. 7.1.3 The site is considered suitable for the use of conventional foundations and slab-on-grade and/or a post-tensioned foundation system. We understand that a post-tensioned foundation system is being considered and recommendations are included herein. 7.1.4 Excavations within the fill materials should generally be possible with moderate to heavy effort using conventional heavy-duty equipment. Excavations below the fill and into the Santiago Peak Volcanic may require localized blasting and may generate oversize rocks. 7.2 Finish Grade Soil Conditions 7.2.1 Observations and laboratory test results indicate that the prevailing soil conditions within the upper approximately three to four feet of finish grade pads have an Expansion Index (El) of 20 or less and are classified as having a "very low" expansion potential as defined by Uniform Building Code (IJBC) Table 18-I-B. Table II presents a summary of the expansion index laboratory test results. Table Ill presents a summary of the indicated expansion index of the prevailing subgrade soil conditions for each lot. 7.2.2 We tested some samples of the site materials to check the percentage of water-soluble sulfate. Results from the laboratory water-soluble sulfate tests are presented in Table IV and indicate that the on-site materials possess "negligible" sulfate exposure to concrete structures as defined by UBC Table 19-A-4. Project No. 06105-52-23 - 5 - October 30, 2007 7.2.3 Geocon Incorporated does not practice in the field of corrosion engineering. Therefore, if improvements that could be susceptible to corrosion are planned, further evaluation by a corrosion engineer should be performed. 7.3 Seismic Design Criteria 7.3.1 Table 7.3.1 summarizes site-specific seismic design parameters obtained from the 1997 Uniform Building Code (UBC) Table 16-J for soil profile types Sc and SD which are prevalent on this project. The values listed in Table 7.3.1 are for the Rose Canyon Fault, which is identified as a Type B fault and is more dominant than the nearest Type A fault due to its proximity to the site according to the computer program UBCSEJS. Table V presents a Summary of Soil Profile Types for each lot and the corresponding values listed on Table 7.3.1 should be used for seismic design. TABLE 7.3.1 1997 UBC SEISMIC DESIGN PARAMETERS Parameter Value UBC Reference Fill Thickness, T (feet) T<20 T>20 -- Soil Profile Sc SD Table 16-J Seismic Zone Factor 0.40 0.40 Table 16-I Seismic Coefficient, Ca 0.40 0.44 Table 16Q Seismic Coefficient, C,, 0.56 0.64 Table 16-R Near-Source Factor, Na 1.0 1.0 Table 16-S Near-Source Factor, N,, 1.0 1.0 Table 16-T Seismic Source B B Table 16-U 7.3.2 We used the computer program Seismic Hazard Curves and Uniform Hazard Response Spectra, provided by the USGS to calculate the seismic design criteria. Table 7.3.2 summarizes site-specific design criteria obtained from the 2007 CBC, Chapter 16 Structural Design, Section 1613 Earthquake Loads. The short spectral response has a period of 0.2 second. Project No. 06105-52-23 -6- October 30, 2007 TABLE 7.3.2 2007 CBC SEISMIC DESIGN PARAMETERS Parameter Value IBC-06 Reference Site Class C D Table 1613.5.2 Spectral Response - Class B (short), Ss 1.079g 1.079g Figure 1613.5(3) Spectral Response - Class B (1 sec), S1 0.406g 0.406g Figure 1613.5(4) Site Coefficient, Fa 1.000 1.069 Table 1613.5.3(1) Site Coefficient, F 1.394 1.594 Table 1613.5.3(2) Maximurrf Considered Earthquake Spectral l.079g l.153g Section 1613.5.3 (Eqn 16-37) Response Acceleration (short),_SMS Maximum Considered Earthquake Spectral 0.566g 0.647g Section 1613.5.3 (Eqn 16-38) Response Acceleration —(1_see),_5M1 5% Damped Design Spectral Response 0.719g 0.769 Section 1613.5.4 (Eqn 16-39) Acceleration (short),_SDS 5% Damped Design Spectral Response 0.377g 0.431 Section 1613.5.4 (Eqn 16-40) Acceleration (1 see), s0, 7.3.3 Based on a review of the as-graded conditions presented in the referenced as-graded report, the lots are assigned the seismic design parameters as indicated in Table V. 7.3.4 Conformance to the criteria for seismic design in Tables 7.3.1 and 7.3.2 does not constitute any kind of guarantee or assurance that significant structural damage or ground failure will not occur if a maximum level earthquake occurs. The primary goal of seismic design is to protect life and not to avoid damage, since such design may be economically prohibitive. 7.4 Future Grading 7.4.1 Additional grading performed at the site should be accomplished in conjunction with our observation and compaction testing services. Grading plans for future grading should be reviewed by Geocon Incorporated prior to finalizing. Trench and wall backfill should be compacted to a dry density of at least 90 percent of the laboratory maximum dry density near to slightly above optimum moisture content. This office should be notified at least 48 hours prior to commencing additional grading or backfill operations. 7.5 Foundation and Concrete Slabs-On-Grade Recommendations 7.5.1 The following foundation recommendations are for proposed one- to three-story residential structures. The foundation recommendations have been separated into three categories based on either the maximum and differential fill thickness or Expansion Index. The foundation category criteria are presented in Table 7.5.1. Projcct No. 06105-52-23 - 7 - October 30, 2007 TABLE 7.5.1 FOUNDATION CATEGORY CRITERIA Foundation Category Maximum Fill Thickness, T (Feet) Differential Fill Thickness, D (Feet) Expansion Index (El) I T<20 -- EI<50 H 20<T<50 10<D'c20 50<E1<90 111 T>50 D>20 90<131<130 7.5.2 Table 7.5.2 presents minimum foundation and interior concrete slab design criteria for conventional foundation systems. TABLE 7.5.2 CONVENTIONAL FOUNDATION RECOMMENDATIONS BY CATEGORY Foundation Minimum Footing Embedment Continuous Footing Interior Slab Category Depth (inches) Reinforcement Reinforcement I 12 Two No. 4 bars, 6 x 6 - 10/10 welded wire mesh one top and one bottom at slab mid-point II 18 Four No. 4 bars, No. 3 bars at 24 inches two top and two bottom on center, both directions III 24 Four No. 5 bars, No. 3 bars at 18 inches two top and two bottom on center, both directions 7.5.3 The embedment depths presented in Table 7.5.2 should be measured from the lowest adjacent pad grade for both interior and exterior footings. The conventional foundations should have a minimum width of 12 inches and 24 inches for continuous and isolated footings, respectively. A wall/column footing dimension detail is presented in Figure 2. 7.5.4 The concrete slab-on-grade should be a minimum of 4 inches thick for Foundation Categories I and 11 and 5 inches thick for Foundation Category Ill. The concrete slabs-on- grade should be underlain by 4 inches and 3 inches of clean sand for 4-inch thick and 5-inch-thick slabs, respectively. Slabs expected to receive moisture sensitive floor coverings or used to store moisture sensitive materials should be underlain by a vapor inhibitor covered with at least 2 inches of clean sand or crushed rock. If crushed rock will be used, the thickness of the vapor inhibitor should be at least 10 rail to prevent possible puncturing. 7.5.5 As an alternative to the conventional foundation recommendations, consideration should be given to the use of post-tensioned concrete slab and foundation systems for the support of the proposed structures. The post-tensioned systems should be designed by a structural 4 Project No. 06105-52-23 - 8 - October 30. engineer experienced in post-tensioned slab design and design criteria of the Post- Tensioning Institute (UBC Section 1816). Although this procedure was developed for expansive soil conditions, we understand that it can also be used to reduce the potential for foundation distress due to differential fill settlement. The post-tensioned design should incorporate the geotechnical parameters presented on Table 7.5.3 for the particular Foundation Category designated. TABLE 7.5.3 POST-TENSIONED FOUNDATION SYSTEM DESIGN PARAMETERS Post-Tensioning Institute (PTI) Design Parameters Foundation Category Thornthwaite Index -20 -20 -20 Clay Type - Montmorillonite Yes Yes Yes Clay Portion (Maximum) 30% 50% 70% Depth to Constant Soil Suction 7.0 ft. 7.0 ft. 7.0 ft. Soil Suction 3.6 ft. 3.6 ft. 3.6 ft. Moisture Velocity 0.7 in./mo. 0.7 in./mo. 0.7 in./mo. Edge Lift Moisture Variation Distance 2.6 ft. 2.6 ft. 2.6 ft. Edge Lift 0.41 in. 0.78 in. 1.15 in. Center Lift Moisture Variation Distance 5.3 ft. 5.3 ft. 5.3 ft. Center Lift 2.12 in. 3.21 in. 4.74 in. 7.5.6 UBC Chapter 18, Div. III, §1816 uses interior stiffener beams in its structural design procedures. If the structural engineer proposes a post-tensioned foundation design method other than UBC Chapter 18, Div. 111, §1816, the following recommendations apply: The deflection criteria presented in Table 7.5.3 are still applicable. Interior stiffener beams should be used for Foundation Categories 11 and III. The embedment depth and width of the perimeter foundations should be at least 12 inches. The perimeter footing depth should be at least 18 inches and 24 inches for foundation categories II and Ill, respectively. 7.5.7 Our experience indicates post-tensioned slabs are susceptible to excessive edge lift, regardless of the underlying soil conditions. Placing reinforcing steel at the bottom of the perimeter footings and the interior stiffener beams may mitigate this potential. Current PT! design procedures primarily address the potential center lift of slabs but, because of the Project No. 06105-52-23 - 9 - October 30, 2007 placement of the reinforcing tendons in the top of the slab, the resulting eccentricity after tensioning reduces the ability of the system to mitigate edge lift. The structural engineer should design the foundation system to reduce the potential of edge lift occurring for the proposed structures. 7.5.8 During the construction of the post-tension foundation system, the concrete should be placed monolithically. Under no circumstances should cold joints form between the footings/grade beams and the slab during the construction of the post-tension foundation system. 7.5.9 Category I, II, or ifi foundations may be designed for an allowable soil bearing pressure of 2,000 pounds per square foot (psf) (dead plus live load). This bearing pressure may be increased by one-third for transient loads due to wind or seismic forces. 7.5.10 Isolated footings, if present, should have the minimum embedment depth and width recommended for conventional foundations for a particular foundation category. The use of isolated footings, which are located beyond the perimeter of the building and support structural elements connected to the building, are not recommended for Category III. Where this condition cannot be avoided, the isolated footings should be connected to the building foundation system with grade beams. 7.5.11 For Foundation Category III, consideration should be given to using interior stiffening beams and connecting isolated footings and/or increasing the slab thickness. In addition, consideration should be given to connecting patio slabs, which exceed 5 feet in width, to the building foundation to reduce the potential for future separation to occur. 7.5.12 Special subgrade presaturation is not deemed necessary prior to placing concrete; however, the exposed foundation and slab subgrade soil should be moisture conditioned, as necessary, to maintain a moist condition as would be expected in any such concrete placement. 7.5.13 Where buildings or other improvements are planned near the top of a slope steeper than 3:1 (horizontal: vertical), special foundations and/or design considerations are recommended due to the tendency for lateral soil movement to occur. For fill slopes less than 20 feet high, building footings should be deepened such that the bottom outside edge of the footing is at least 7 feet horizontally from the face of the slope. Project No. 06105-52-23 _10- October 30, 2007 When located next to a descending 3:1 (horizontal: vertical) fill slope or steeper, the foundations should be extended to a depth where the minimum horizontal distance is equal to H13 (where H equals the vertical distance from the top of the fill slope to the base of the fill soil) with a minimum of 7 feet but need not exceed 40 feet. The horizontal distance is measured from the outer, deepest edge of the footing to the face of the slope. An acceptable alternative to deepening the footings would be the use of a post-tensioned slab and foundation system or increased footing and slab reinforcement. Specific design parameters or recommendations for either of these alternatives can be provided once the building location and fill slope geometry have been determined. If swimming pools are planned, Geocon Incorporated should be contacted for a review of specific site conditions. Swimming pools located within 7 feet of the top of cut or fill slopes are not recommended. Where such a condition cannot be avoided, the portion of the swimming pool wall within 7 feet of the slope face be designed assuming that the adjacent soil provides no lateral support. This recommendation applies to fill slopes up to 30 feet in height, and cut slopes regardless of height. For swimming pools located near the top of fill slopes greater than 30 feet in height, additional recommendations may be required and Geocon Incorporated should be contacted for a review of specific site conditions. Although other improvements, which are relatively rigid or brittle, such as concrete flatwork or masonry walls, may experience some distress if located near the top of a slope, it is generally not economical to mitigate this potential. It may be possible, however, to incorporate design measures which would permit some lateral soil movement without causing extensive distress. Geocon incorporated should be consulted for specific recommendations. 7.5.14 Exterior slabs not subject to vehicle loads should be at least 4 inches thick and reinforced with 6x6-W2.9/W2.9 (6x6-6/6) welded wire mesh. The mesh should be placed within the upper one-third of the slab. Proper mesh positioning is critical to future performance of the slabs. It has been our experience that the mesh must be physically pulled up into the slab after concrete placement. The contractor should take extra measures to provide proper mesh placement. Prior to construction of slabs, the subgrade should be moisture conditioned to at least optimum moisture content and compacted to at least 90 percent of the laboratory maximum dry density. 7.5.15 Concrete slabs should be provided with adequate construction joints and/or expansion joints to control unsightly shrinkage cracking. The structural engineer should consider criteria of the American Concrete institute when establishing crack-control spacing patterns. 7.5.16 Where exterior flatwork abuts the structure at entrant or extant points, the exterior slab should be dowelled into the structure's foundation stemwall. This recommendation is Project No. 06105-52-23 - II - October 30. 2007 intended to reduce the potential for differential elevations that could result from differential settlement or minor heave of the flatwork. Dowelling details should be designed by the project structural engineer. 7.5.17 The recommendations of this report are intended to reduce the potential for cracking of slabs due to expansive soil (if present), differential settlement of existing soil or soil with varying thicknesses. However, even with the incorporation of the recommendations presented herein, foundations, stucco walls, and slabs-on-grade placed on such conditions may still exhibit some cracking due to soil movement and/or shrinkage. The occurrence of concrete shrinkage cracks is independent of the supporting soil characteristics. Their occurrence may be reduced and/or controlled by limiting the slump of the concrete, proper concrete placement and curing, and by the placement of crack control joints at periodic intervals, in particular, where re-entrant slab corners occur. 7.5.18 Geocon Incorporated should be consulted to provide additional design parameters as required by the structural engineer. 7.6 Retaining Walls and Lateral Loads 7.6.1 Retaining walls not restrained at the top and having a level backfill surface should be designed for an active soil pressure equivalent to the pressure exerted by a fluid density of 35 pounds per cubic foot (pcf). Where the backfill will be inclined at no steeper than 2:1 (horizontal: vertical), an active soil pressure of 50 pcf is recommended. These soil pressures assume that the backfill materials within an area bounded by the wall and a 1:1 plane extending upward from the base of the wall possess an expansion index of 50 or less. For those lots with finish-grade soils having an expansion index greater than 50 and/or where backfill materials do not conform to the criteria herein, Geocon Incorporated should be consulted for additional recommendations. 7.6.2 Unrestrained walls are those that are allowed to rotate more than 0.001H (where H equals the height of the retaining portion of the wall) at the top of the wall. Where walls are restrained from movement at the top, an additional uniform pressure of 7H psf should be added to the active soil pressure. For retaining walls subject to vehicular loads within a horizontal distance equal to two-thirds the wall height, a surcharge equivalent to 2 feet of fill soil should be added. 7.6.3 Retaining walls should be provided with a drainage system adequate to prevent the buildup of hydrostatic forces and waterproofed as required by the project architect. The use of drainage openings through the base of the wall (weep holes) is not recommended where the seepage could be a nuisance or otherwise adversely affect the property adjacent to the base Project No. 06105-52-23 - 12 - October 30, 2007 of the wall. The above recommendations assume a properly compacted free-draining backfill material (El of 50 or less) with no hydrostatic forces or imposed surcharge load. Figure 3 presents a typical retaining wall drainage detail. If conditions different than those described are expected, or if specific drainage details are desired, Geocon Incorporated should be contacted for additional recommendations. 7.6.4 In general, wall foundations founded in properly compacted fill or formational materials should possess a minimum depth and width of one foot and may be designed for an allowable soil bearing pressure of 2,000 psf, provided the soil within 3 feet below the base of the wall has an expansion index of 90 or less. The proximity of the foundation to the top of a slope steeper than 3:1 could impact. the allowable soil bearing pressure. Therefore, Geocon Incorporated should be consulted where such a condition is expected. 7.6.5 For resistance to lateral loads, an allowable passive earth pressure equivalent to a fluid density of 300 pcf is recommended for footings or shear keys poured neat against properly compacted fill soil. The allowable passive pressure assumes a horizontal surface extending at least 5 feet or three times the surface generating the passive pressure, whichever is greater. The upper 12 inches of material not protected by floor slabs or pavement should not be included in the design for lateral resistance. A friction coefficient of 0.35 may be used for resistance to sliding between soil and concrete. This friction coefficient may be combined with the allowable passive earth pressure when determining resistance to lateral loads. 7.7 Slope Maintenance 7.7.1 Slopes that are steeper than 3:1 (horizontal: vertical) may, under conditions which are both difficult to prevent and predict, be susceptible to near surface (surficial) slope instability. The instability is typically limited to the outer three feet of a portion of the slope and usually does not directly impact the improvements on the pad areas above or below the slope. The occurrence of surficial instability is more prevalent on fill slopes and is generally preceded by a period of heavy rainfall, excessive irrigation, or the migration of subsurface seepage. The disturbance and/or loosening of the surficial soils, as might result from root growth, soil expansion, or excavation for irrigation lines and slope planting, may also be a significant contributing factor to surficial instability. It is, therefore, recom- mended that, to the maximum extent practical: (a) disturbed/loosened surficial soils be either removed or properly recompacted, (b) irrigation systems be periodically inspected and maintained to eliminate leaks and excessive irrigation, and (c) surface drains on and adjacent to slopes be periodically maintained to preclude ponding or erosion. It should be noted that although the incorporation of the above recommendations should reduce the Project No. 06105-52-23 - 13 - October 30, 2007 potential for surficial slope instability, it will not eliminate the possibility, and, therefore, it may be necessary to rebuild or repair a portion of the projects slopes in the future. 7.8 Site Drainage 7.8.1 Adequate drainage is critical to reduce the potential for differential soil movement, erosion and subsurface seepage. Under no circumstances should water be allowed to pond adjacent to footings or behind retaining walls. The site should be graded and maintained such that surface drainage is directed away from structures and the top of slopes into swales or other controlled drainage devices. Roof and pavement drainage should be directed into conduits which carry runoff away from the proposed structure. 7.8.2 Underground utilities should be leak free. Utility and irrigation lines should be checked periodically for leaks for early detection of water infiltration and detected leaks should be repaired promptly. Detrimental soil movement could occur if water is allowed to infiltrate the soil for a prolonged period of time. 7.8.3 Landscaping planters adjacent to paved areas are not recommended due to the potential for surface or irrigation water to infiltrate the pavement's subgrade and base course. We recommend that drains to collect excess irrigation water and transmit it to drainage structures, or impervious above-grade planter boxes be used. In addition, where landscaping is planned adjacent to the pavement, we recommended construction of a cutoff wall along the edge of the pavement that extends at least 6 inches below the bottom of the base material. Project No. 06105-52-23 -14 - October 30. 2007 LIMITATIONS AND UNIFORMITY OF CONDITIONS Recommendations of this report pertain only to the site investigated and are based upon the assumption that the soil conditions do not deviate from those disclosed in the investigation. If any variations or undesirable conditions are encountered during construction, or if the proposed construction will differ from that anticipated herein, Geocon Incorporated should be notified so that supplemental recommendations can be given. The evaluation or identification of the potential presence of hazardous or corrosive materials was not part of the scope of services provided by Geocon Incorporated. This report is issued with the understanding that it is the responsibility of the owner, or of his representative, to ensure that the information and recommendations contained herein are brought to the attention of the architect and engineer for the project and incorporated into the plans, and the necessary steps are taken to see that the contractor and subcontractors carry out such recommendations in the field. The findings of this report are valid as of the present date. However, changes in the conditions of a property can occur with the passage of time, whether they are due to natural processes or the works of man on this or adjacent properties. In addition, changes in applicable or appropriate standards may occur, whether they result from legislation or the broadening of knowledge. Accordingly, the findings of this report may be invalidated wholly or partially by changes outside our control. Therefore, this report is subject to review and should not be relied upon after a period of three years. Projcct No. 06105-52-23 October 30, 2007 . MELRO OR " av •*' , uny p COSTA 's R -r ----'- .. 04 ARCHER %,LLEARV1W 1t 'kt SAGEW000 ; t.t,t 0v> - - . ... AR ,. 4•,j• - O41 > tcô EL lier 29 - I PA& ' , SAN - FOR \- £'O .. MID , 'N NC EN —.-----------.--I —tA--- p I Pt 2FALLSVi.4 I RD SITE CHERIDA \ I . , tEMNI iG T.. ej DR J. , ._...\ I / — i I / iir'o I -01i3 4QA . ....'----- .----- ........----,----------.-.---------..--.---....'.-.-----._. IIMI 4 PTOP;1RT0't.".cC' c4ro .t0Otcs ..".Ô4, '-- - . -. . / .,-..... <' i.Ac)N 113S R11- S3A0 P .f•O t .• ,IDLt.O\i . ,. -.1' . CTE CA lop,0 - — - .j,- %OOCN Ct SOURCE: 2007 THOMAS BROTHERS MAP SAN DIEGO COUNTY, CALIFORNIA MAP © RAND MCNALLY, R.L.07-S-82, REPRODUCED WITH PERMISSION. NO SCALE IT IS UNLAWFUL TO COPY OR REPRODUCE ALL OR ANY PART THEREOF. WHETHER FOR PERSONAL USE OR RESALE, WITHOUT PERMISSION* GEOCON (low) INCORPORATED GEOTECHNICAL CONSULTANTS 6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121-2974 PHONE 858 558-6900 - FAX 858 558-6159 ME I DW DSKIGTYPD \I'y MW I VICINITY MAP I VILLAGES OF LA COSTA - THE OAKS NORTH NEIGHBORHOOD 3.7 LOTS 1 THROUGH 44 CARLSBAD, CALIFORNIA bATE 10-30-2007 I PROJECT NO. 06105-52-23 I FIG. 1 I WALL FOOTING CONCRETE SLAB .O I SAND / PAD GRADE VISaUEEN_J z 1-0. • p—a. OW OW O z: .-.. O LL :. FOOTING WIDTH COLUMN FOOTING CONCRETE SLAB AL r 4 4 4 SAND / / 1 VISQUEEN s / 00 LL 4 4 4 q 4 FOOTING WIDTH NO SCALE *SEE REPORT FOR FOUNDATION WITDH AND DEPTH RECOMMENDATION I WALL/ COLUMN FOOTING DIMENSION DETAIL I GEOCON Q INCORPORATED GEOTECHNICAL CONSULTANTS 6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121-2974 PHONE 858 558-6900 - FAX 858 558-6159 ME/AML DSK/E0000 C0LFC072DWG/wrJ VILLAGES OF LA COSTA - THE OAKS NORTH NEIGHBORHOOD 3.7 LOTS 1 THROUGH 44 CARLSBAD, CALIFORNIA DATE 10-30-2007 I PROJECT NO. 06105 - 52 - 23 1 FIG.2 GROUND SURFACE / 2 / / CONCRETE BROWDITCH 1 PROPOSED - PROPERLY RETAINING WALL -.- COMPACTED / BACKFILL / BACKCUT ./ / APPROVED / FILTER FABRIC - . ( 2/3H •d - OPEN GRADED V MAX. AGGREGATE GROUND SURFACE - I - FOOTING 4' DIA. PERPORATED SCHEDULE 40 PVC PIPE. MIN. 1/2% FALL TO APPROVED OUTLET NOTES: 1 ...... PREFABRICATED DRAINAGE PANELS, SUCH AS MIRADRAIN 7000 OR EQUIVALENT, MAYBE USED IN LIEU OF PLACING GRAVEL TO HEIGHT OF 2/3 THE TOTAL WALL HEIGHT 2......DRAIN SHOULD BE UNIFORMLY SLOPED AND MUST LEAD TO A POSITIVE GRAVITY OUTLET 3 ...... TEMPORARY EXCAVATION SLOPES SHOULD BE CONSTRUCTED AND/OR SHORED IN ACCORDANCE WITH CAL-OSHA REGULATIONS NO SCALE RETAINING WALL DRAIN DETAIL GE000N 0 INCORPORATED GEOTECHNICAL CONSULTANTS 6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121-2974 PRONE 858 558-6900 - FAX 858 558-6159 ME/AML DSKJE0000 .WALWWG/, VILLAGES OF LA COSTA - THE OAKS NORTH NEIGHBORHOOD 3.7 LOTS 1 THROUGH 44 CARLSBAD, CALIFORNIA I DATE 10-30- 2007 1 PROJECT NO. 06105-52-23 1 FIG. 3 TABLE I SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS AND RECOMMENDED FOUNDATION CATEGORIES FOR VILLAGES OF LA COSTA - THE OAKS NORTH, NEIGHBORHOOD 3.7 LOTS 1 THROUGH 44 Approximate Approximate Maximum Maximum Expansion Recommended Lot No. Pad Condition Depth of Fill Depth of Fill Index Foundation (feet) Differential Category (feet) I Undercut due to rock 8 1 1 I Undercut due to cut/fill 2 20 15 0 ii transition Undercut due to cut/fill 3 20 15 0 II transition Undercut due to cut/fill 4 20 14 0 II transition Undercut due to cut/fill 5 20 15 0 11 transition Undercut due to cut/fill 6 6 1 0 I transition 7 Undercut due to rock 9 2 0 I 8 Undercut due to rock 9 1 0 I 9 Undercut due to rock 5 1 1 1 10 Undercut due to rock 9 4 1 1 11 Undercut due to rock 5 1 0 i 12 Undercut due to rock 5 1 0 I 13 Undercut due to rock 5 1 0 I 14 Undercut due to rock 6 1 0 I 15 Undercut due to rock 6 1 0 1 16 Undercut due to rock 6 1 0 I 17 Undercut due to rock 7 2 0 I 18 Undercut due to rock 13 9 0 1 19 Undercut due to rock 14 8 0 1 20 Undercut due to rock 14 8 0 I 21 Undercut due to rock 15 9 1 1 22 Undercut due to rock 9 3 0 I 23 Undercut due to rock 7 3 0 I 24 Undercut due to rock 5 2 0 1 25 Undercut due to rock 5 1 0 i 26 Undercut due to rock 5 2 0 1 Project No. 06105-52-23 October 30. 2007 IV TABLE I (Continued) SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS AND RECOMMENDED FOUNDATION CATEGORIES FOR VILLAGES OF LA COSTA - THE OAKS NORTH, NEIGHBORHOOD 3.7 LOTS 1 THROUGH 44 Approximate Approximate Maximum Maximum Expansion Recommended Lot No. Pad Condition Depth of Fill Depth of Fill Index Foundation (feet) Differential Category (feet) 27 Undercut due to rock 5 1 0 I 28 Undercut due to rock 5 1 0 I 29 Undercut due to rock 5 1 0 i 30 Undercut due to rock 5 2 0 I 31 Undercut due to rock 12 8 0 I 32 Undercut due to rock 5 1 3 I Undercut due. to cut/fill 33 7 1 3 . I transition 34 Fill Lot 8 2 3 I 35 Fill Lot 19 10 3 II 36 Fill Lot 31 16 2 II 37 Fill Lot 33 14 2 II Undercut due to cut/fill 38 18 14 2 II transition Undercut due to cut/fill 39 25 20 2 III transition Undercut due to cut/fill 40 22 17 0 II transition Undercut due to cut/fill 41 18 10 0 II transition Undercut due to cut/fill 42 12 7 0 I transition Undercut due to cut/fill 43 16 7 0 1 transition Undercut due to cut/fill 44 30 24 0 III transition Project No. 06105-52-23 October 30. 2007 TABLE II SUMMARY OF LABORATORY EXPANSION INDEX TEST RESULTS ASTM D 4829-03 Sample No. Moisture Content Dry Density (pci) Expansion Index UBC Classification Before Test (%) After Test (%) El-H 8.2 13.3 118.1 0 Very Low El-1 8.1 14.1 117.9 2 Very Low EI-J 7.7 14.2 118.4 3 Very Low El-K 7.8 13.8 118.4 0 Very Low EI-L 7.8 14.2 118.3 2 Very Low El-M 7.9 13.7 118.4 0 Very Low El-N 8.7 15.8 113.4 1 Very Low El-0 7.4 13.0 118.7 0 Very Low El-P 7.8 12.8 118.7 0 Very Low El-Q 8.0 13.3 118.3 1 Very Low El-T 8.2 14.7 114.9 0 Very Low El-U 8.6 16.1 113.9 1 0 Very Low El-V 8.6 13.9 113.7 1 0 Very Low TABLE III SUMMARY OF FINISH GRADE EXPANSION INDEX TEST RESULTS VILLAGES OF LA COSTA -THE OAKS NORTH, NEIGHBORHOOD 3.7 LOTS 1 THROUGH 44 Lot No Sample at Finish Grade Expansion Index UBC Classification Lot 1 El-N I Very Low Lots 2 through 4 El-L 0 Very Low Lots 5 through 8 EI-M 0 Very Low Lots 9 and 10 El-N 1 Very Low Lots 11 through 14 EI-T 0 Very Low Lots 15 through 17 El-V 0 Very Low Lots 18 through 21 El-Q 1 Very Low Lots 22 through 24 El-P 0 Very Low Lots 25 through 28 El-0 0 Very Low Lots 29 through 31 El-K 0 Very Low Lots 32 through 35 E1-J 3 Very Low Lots 36 through 39 El-1 2 Very Low Lots 40 through 43 El-H 0 Very Low Lot 44 El-U 0 Very Low Project No. 06105-52-23 October 30, 2007 TABLE IV SUMMARY OF LABORATORY WATER-SOLUBLE SULFATE TEST RESULTS CALIFORNIA TEST 417 Sample No. Water-Soluble Sulfate (%) Sulfate Exposure El-H 0.008 Negligible El-J 0.006 Negligible El-L 0.015 Negligible El-0 0.007 Negligible El-Q 0.004 Negligible El-T 0.019 Negligible El-V 0.015 Negligible TABLE V SUMMARY OF SOIL PROFILE TYPE Lot Nos. 1997 UBC Classification 2007 CBC Classification SC C 2 through 5 SD D 6 through 35 Sc C 36 and 37 SD D 38 . Sc C 39 and 40 5D D 41 through 43 Sc C 44 SD D A, Project No. 06105-52-23 . . October 30, 2007