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Home My WebLink AboutCT 02-24; VILLAGES OF LA COSTA GREENS 1.11, 1.13, 1.14; UPDATE GEOTECHNICAL REPORT; 2004-07-28UPDATE GEOTECHNICAL REPORT VILLAGES OF LA COSTA - THE GREENS NEIGHBORHOODS 1.119 1.139 AND 1.14 CARLSBAD, CALIFORNIA PREPARED FOR JOHN LAING HOMES CARLSBAD, CALIFORNIA JULY 289 2004 GEOCON INCORPORATED GEOTECHNICAL CONSULTANTS 0 Project No. 06403-52-16 July 28, 2004 John Laing Homes 6193 Paseo Del Norte, Suite 160 Carlsbad, California 92009 Attention: Ms. Liz Albano .Subject: VILLAGES OF LA COSTA - THE GREENS NEIGHBORHOODS 1. 11, 1. 13, AND 1.14 CARLSBAD, 'CALIFORNIA UPDATE GEOTECHNICAL REPORT Dear Ms. Albano: In accordance with your authorization of our Proposal No. LG-04 165 dated April 14, 2004 we have prepared this update geotechnical report for the subject project. The accompanying report presents the results of our study and contains conclusions and recommendations pertaining to the geotechnical aspects of the proposed development of the site. Provided that the recommendations contained in this update report are followed, the site is considered suitable for construction and support of the proposed structures and improvements as presently planned. Should you have any questions regarding this report, or if we may be of further service, please contact the undersigned at your convenience. Very truly yours, GEOCON INCORPORATED 7rl.Q2. Michael C. Ertwine Staff Geologist ASh a! dacker " RCE 63291 MCE:SR:AS:dmc (6/del) Addressee 6960 Flanders Drive 0 San Diego, California 92121-2974 U Telephone (858) 558-6900 U Fax (858) 558-6159 TABLE OF CONTENTS PURPOSE AND SCOPE .1 PREVIOUS SITE DEVELOPMENT 1 SITE AND PROJECT DESCRIPTION ........................................................................................... 1 SOIL AND GEOLOGIC CONDITIONS ......................................................................................... 2 4.1 Compacted Fill (Qcf) ..............................................................................................................2 4.2 Undocumented Fill (Qudf).....................................................................................................3 4.3 Alluvium (Qal).......................................................................................................................3 4.4 Santiago Formation (Ts) ........................................................................................................3 4.5 Santiago Peak Volcanics (Jsp)...............................................................................................3 tISSJiL7U4L..- GEOLOGIC HAZARDS .............................. ....................................................................................4 6.1 Faulting and Seismicity ........................................................................................................... 4 6.2 Liquefaction ......................................................................................................................... ..5 6.3 Landslides..............................................................................................................................5 CONCLUSIONS AND RECOMMENDATIONS...........................................................................6 7.1 General...................................................................................................................................6 7.2 Seismic Design.......................................................................................................................6 7.3 Finish Grade Soil Conditions.................................................................................................7 7.4 Future Grading ............................... . ....................................................................................... 8 7.5 Foundations ............................................................................................................................. 8 7.6 Retaining Walls....................................................................................................................12 7.7 Lateral Loads ........................................................................................................................13 7.8 Slope Maintenance ............................................................................................................... 13 7.9. Site Drainage ......................................................................................................................... 14 LIMITATIONS AND UNIFORMITY OF CONDITIONS Figures: Vicinity Map Typical Retaining Wall Drain Detail Tables: Summary of As-Graded Building Pad Conditions and Foundation Category (Neighborhood 1.11) Summary of As-Graded Building Pad Conditions and Foundation Category (Neighborhood 1.13) Summary of As-Graded Building Pad Conditions and Foundation Category (Neighborhood .1.14). Summary of Laboratory Water-Soluble Sulfate Test Results .. . .. . UPDATE GEOTECHNICAL REPORT 1. PURPOSE AND SCOPE This report presents the results of the update geotechnical study for the proposed residential development of Neighborhood 1.11, Lots 58 through 92, Neighborhood 1.13, Lots 97 through 129, Neighborhood 1. 14, Lots 1 through 57 and 93 through 96 and associated improvements located in the Villages of La Costa - The Greens development. The site is situated north of Alga Road, and east of a La Costa Resort and Spa in Carlsbad, California (see Vicinity Map, Figure 1). The purpose of this update report is to provide foundation and retaining wall design recommendations. The scope of the study included a review of the following: Update Soil and Geological Investigation, Volume I and II, Villages of La Costa - The Greens, Carlsbad, California, prepared by Geocon Incorporated, dated June 25, 2001 (Project No. 06403-12-03). Final Report of Testing and Observation Services Performed During Site Grading, Villages of La Costa - The Greens, Neighborhoods 1. 11, 1. 13, and 1.14 and Alicante Road Station 10+00 to 31+25, Carlsbad, California, prepared by Geocon Incorporated, dated July 27, 2004 (Project No. 06403-52-09). Grading Plans for: La Costa Greens Neighborhood 1.11, 1.13 and 1.14, prepared by Hunsaker and Associates, City of Carlsbad approval dated May 6, 2004. 2. PREVIOUS SITE DEVELOPMENT Neighborhoods 1.11, 1.13, and 1.14 were graded to a finish-pad configuration during mass grading operations for the Villages of La Costa - The Greens development. 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 are presented in the above-referenced final report of grading. Mass grading for the site has been completed and consisted of developing single-family residential lots and associated streets. Fill slopes were constructed with design inclinations of 2:1 (horizontal: vertical) or flatter, with a maximum height of approximately 40 feet. Maximum thickness of the fill soils is approximately 86 feet. An "As-Graded" Geologic Map is provided in the above-referenced final report of grading and depicts the existing geologic conditions and topography. 3. SITE AND PROJECT DESCRIPTION The development of The Greens - Neighborhoods 1. 11, 1. 13, and 1.14 consists of 129 single-family residential homes, and associated improvements. Compacted fill soils and the Santiago Formation are exposed at grade throughout the site. A summary of the as-graded pad conditions for the lots is Project No. 06403-52-16 July 28, 2004 provided on Tables I through ifi. In general, the on-site fill materials generally vary between angular gravels and boulders produced by onsite blasting of hard metavoicanic rock to clayey, fine sands, sandy to silty clay, and sandy to clayey gravels derived from excavations within surficial soils and the Santiago Formation. The locations and descriptions of the site and proposed improvements are based on a site recon- naissance, a review of the referenced grading plans, and our understanding of project development. If project details vary significantly from those described above, Geocon Incorporated should be contacted to determine the necessity for review and revision of this report. 4. SOIL AND GEOLOGIC CONDITIONS Santiago Peak Volcanics, Santiago Formation, undocumented fill, alluvium and compacted fill soils underlie the site. The predominant materials within 4 feet of grade generally consist of clayey to silty sand and sandy gravels and possess a low to medium expansion potential. The soil type and geologic unit are discussed below. 4.1 Compacted Fill (Oct) In general, structural fill placed and compacted at the site consisted of material which 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 a 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 and "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 86 feet and was placed in conjunction with the observation and testing services of Geocon Incorporated and reported in the above-referenced final report of grading. The compacted fill soils are considered suitable to provide adequate support for the proposed development. Project No. 06403-52-16 - 2 - July 28, 2004 4.2 Undocumented Fill (Qudf) Undocumented fill was encountered near the intersection of Alga Road and Alicante Road. This material was apparently placed during the grading for Alga Road. The lateral extent of remedial grading in this area was limited due to the presence of Alga Road and, therefore, some undocumented fill was left in place. The removal and resulting excavation was replaced with properly compacted fill. 4.3 Alluvium (Qal) Alluvium was encountered at the base of the removal adjacent to Alga Road. Due to suitable moisture density relationship and granular characteristics, the alluvium was left in place. 4.4 Santiago Formation (Ts) The Eocene-aged Santiago Formation, consisting of dense, massive, white to light green, silty, fine to coarse sandstones and hard, greenish-gray to brown, claystones and siltstones are exposed at finish grade on cut lots and underlie the compacted fill at the site and are considered suitable for the support of the proposed development. 4.5 Santiago Peak Volcanics (Jsp) Jurassic-aged Santiago Peak Volcanics ôomprise a portion of the underlying bedrock within the Neighborhood 1.13 and 1.14 and are considered suitable for support of the existing and proposed site development. This unit is not anticipated to be encountered during foundation and utility excavations within the pads and roadways. However, if excavations exceed 3 to 4 feet for homeowner improvements such as pools, hard rock will be encountered and very difficult excavation and refusal should be anticipated. 5. GROUNDWATER Groundwater was encountered during grading operations but is not anticipated to adversely impact the development of the property due to the installations of canyon subdrains. Due to the variable nature of the Santiago Formation, which consists of interbedded sandstone and claystone/siltstone, and the contact between the Santiago Formation and Santiago Peak Volcanics, seepage was encountered and consequently mitigated during remedial grading by subdrain installations. During grading, minor seepage was encountered on the metavolcanic cut slope at the back of Lot 97 within Neighborhood 1.13. The seepage has reduced in volume; however, if seepage continues, remedial measures may be necessary. 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 of irrigation and rainwater will be important to future performance of the project. Project No. 06403-52-16 - 3 - July 28, 2004 6.. GEOLOGIC HAZARDS 6.1 Faulting and Seismicity Our review of pertinent geologic literature and the previously referenced geotechnical investigation report dated June 25, 2001, and our observations during grading of the site, and our experience with the soil and geologic conditions in the general area indicate that noknown active, potentially active, or inactive faults are located within the subject site. The nearest known "active" faults are the Rose Canyon Fault and the Newport-Inglewood (offshore) located approximately 7 and 10 miles, respectively,, to the west and the Coronado Banks Fault Zone, which lies approximately 22 miles to the southwest. The California Geological Survey (CGS) has included portions of the Rose Canyon Fault in an Earthquake Fault Zone. A Maximum Credible seismic event of Magnitude 7.2 is postulated for the Rose Canyon Fault with an estimated Maximum Credible peak site acceleration of 0.32 g based on the Sadigh, et al. (1997) acceleration-attenuation relationship. The seismicity of the site is influenced by both local and regional fault systems within the southern California and northern Baja California region. Table 6.1 lists the fault zones that present the greatest seismic impact to the site. TABLE 6.1 FAULT SYSTEMS WITHIN THE SOUTHERN CALIFORNIA AND NORTHERN BAJA CALIFORNIA REGION Fault Name Distance from Site (miles) Maximum Credible Earthquake Maximum Credible Site Acceleration (g) Rose Canyon 7 7.2 0.32 Newport-Inglewood (Offshore) 10 7.1 0.25 Coronado Banks Fault Zone 22 7.6 0.17 Elsinore-Julian 23 7.1 0.13 Elsinore-Temecula 23 6.8 0.10 Palos Verdes 41 7.3 0.08 Elsinore-Glen Ivy 37 6.8 0.06 San Jacinto-Anza 49 7.2 0.06 In the event of a major earthquake along any of the above-referenced faults or other faults in the SouthernCalifornia 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 peak accelerations is useful for comparison of potential effects of fault activity in the region, Project No. 06403-52-16 - 4 - ' July 28, 2004 other considerations are important in seismic design including the frequency and duration of motion and the soil conditions underlying the site. We recommend that seismic design of structures be performed in accordance with the Uniform Building Code (UBC) currently adopted by the City of Carlsbad. 6.2 Liquefaction Liquefaction typically occurs when a site is located in a zone with seismic activity, onsite soils are cohesionless, groundwater is encountered within 50 feet of the surface, and soil relative densities are less than about 70 percent. If all 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. 6.3 Landslides Examination of aerial photographs in our files, review of available geotechnical reports for the site vicinity, our field investigation and observations during site grading indicate that no landslides are present at the property or at a location that could impact the site. Project No. 06403-52-16 - 5 - . July 28, 2004 7. CONCLUSIONS AND RECOMMENDATIONS 7.1 General 7.1.1 No soil or geologic conditions were encountered during previous geotechnical investiga- tions or grading operations that 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 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 will be used throughout the project. Therefore, conventional footing recommendations are not included in this report, but can be provided upon request. Design criteria for post-tensioned slabs are provided in Section 7.5. 7.2 Seismic Design 7.2.1 The site is located within Seismic Zone 4 according to UBC Figure 16-J. Compacted fill soils and formational materials underline the proposed buildings. For seismic design, the site is characterized as soil types Sc and SD. Table 7.2.1 summarizes site design criteria. The values listed in Table 7.2.1 are for the Rose Canyon Fault, which is identified as a Type B fault. The Rose Canyon Fault is located approximately 7 miles west of the site. Table 7.2.2 presents a summary of soil profile type for each building and the corresponding values from Table 7.2.1 should be used for seismic design. TABLE 7.2.1 SITE SEISMIC DESIGN CRITERIA Parameter Soil Profile Type UBC Reference Sc SD Seismic Zone Factor 0.40 0.40 Table 16-I Soil Profile S SD Table 16-J Seismic Coefficient, C, 0.40 0.44 Table 16-Q 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 Project No. 06403-52-16 -6- July 28, 2004 7.2.2 Based on review of the as-graded conditions presented in the as-graded report referenced above, as well as the seismic setting, the lots are assigned the seismic design parameters as indicated below in Table 7.2.2. TABLE 7.2.2 SUMMARY OF SOIL PROFILE TYPE Unit Building Pad UBC Classification 1.11 58 and 59 Sc 1.11 60 and 61 SD 1.11 62 through 69 Sc 1.11 70 and 71 SD 1.11 72 through 92 Sc 1.13 97 through 104 Sc 1.13 105 through 110 SD 1.13 111 through 113 Sc 1.13 114 through 129 SD 1.14 l through 6 SD 1.14 7 through 15 Sc 1.14 16 through 36 SD 1.14 37 through 44 Sc 1.14 45 through 47 SD 1.14 48 through 53 Sc 1.14 54 SD 1.14 55 Sc 1.14 56 SD 1.14 57, 93 through 96 Sc 7.3 Finish Grade Soil Conditions 7.3.1 Observations and laboratory test results indicate that the prevailing soil conditions within the upper approximately 4 feet of finish grade have an expansion potential of "low" to "medium" (Expansion Index of 90 or less) as defined by Uniform Building Code (UBC) Table 18-I-B. Expansion Index test results for each lot are included on Table I. 7.3.2 It should be noted that although rocks larger than 6 inch diameter were not intentionally placed within the upper 4 feet of pad grades, some larger rocks may exist at random locations. • Project No. 06403-52-16 - 7 - July 28, 2004 7.3.3 Random samples obtained throughout the neighborhoods were subjected to water-soluble sulfate testing to evaluate the amount of water-soluble sulfates within the finish grade soils These test results are used to determine the potential for sulfate attack on normal Portland Cement concrete. The test results indicate sulfate contents that correspond to "negligible" and "severe" sulfate exposure ratings as defined by UBC Table 19-A-4. The results of the soluble sulfate tests are summarized on Table IV. Table 7.3 presents a summary of concrete requirements set forth by UBC Table 19-A-4. It is recommended that the concrete used in the subject neighborhoods meet the requirements for "severe" sulfate ratings as provided in Table 7.3. TABLE 7.3 REQUIREMENTS FOR CONCRETE EXPOSED TO SULFATE-CONTAINING SOLUTIONS Sulfate Water-Soluble Cement Maximum Water Minimum Exposure Sulfate Percent Type to Cement Ratio Compressive by Weight by Weight Strength (psi) Negligible 0.00-0.10 -- -- -- Moderate 0.10-0.20 II 0.50 4000 Severe 0.20-2.00 V 0.45 4500 Very Severe > 2.00 V 0.45 4500 7.3.4 Geocon Incorporated does not practice in the field of corrosion engineering. Therefore, if improvements that could be susceptible to corrosion are planned, it is recommended that further evaluation by a corrosion engineer be performed. 7.4 Future Grading 7.4.1 Any additional grading performed at the site should be accomplished in conjunction with our observation and compaction testing services. Grading plans for any future grading should be reviewed by Geocon Incorporated prior to finalizing. All trench and Wall backfill should be compacted to a dry density of at least 90 percent of the laboratory maximum dry density at or slightly above optimum moisture content. This office should be notified at least 48 hours prior to commencing additional grading or backfill operations. 7.5 Foundations 7.5.1 The foundation recommendations that follow are for one- or two-story residential structures and are separated into categories dependent on the thickness and geometry of the underlying fill soils as well as the Expansion Index (El) of the prevailing subgrade soils of a particular building pad. The category criteria are summarized herein. Project No. 06403-52-16 - 8 - July 28, 2004 Category I: Maximum fill thickness is less than 20 feet and Expansion Index is less than or equal to 50: Category II: Maximum fill thickness is less than 50 feet and Expansion Index is less than or equal to 90, or variation in fill thickness is between 10 feet and 20 feet. Category m: Fill thickness exceeds 50 feet, or variation in fill thickness exceeds 20 feet, or Expansion Index exceeds 90 but is less than 130. Notes: All footings should have a minimum width of 12 inches. Footing depth is measured from lowest adjacent subgrade (including topsoil, if planned). These depths apply to both exterior and interior footings.. All building concrete slabs should be at least 5 inches thick. This applies to both building and garage slabs-on-grade. All building concrete slabs should be underlain by at least 4 inches of clean sand. All slabs expected to receive moisture sensitive floor coverings or used to store moisture sensitive materials should be underlain by a vapor barrier placed at the midpoint of the clean sand. - 7.5.2 The post-tensioned systems should be designed by a structural 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 soils, it is understood 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 in Table 7.5 entitled for the particular foundation category designated for each lot as presented on Tables I through ifi. TABLE 7.5 POST-TENSIONED FOUNDATION SYSTEM DESIGN PARAMETERS Post-Tensioning Institute (PT!) Design Parameters Foundation _Category i ii . iii 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 1 2.12 in. 3.21 in. 4.74 in. Project No. 06403-52-16 - 9 - -. July 28, 2004 7.5.3 UBC Section 1816 uses interior stiffener beams in its structural design procedures. If the structural engineer proposes a post-tensioned foundation design method other than UBC Section 1816, it is recommended that interior stiffener beams be used for Foundation Categories II and ifi. The depth of the perimeter foundation should be at least 12 inches for Foundation Category I. Where the Expansion Index for a particular building pad exceeds 50 but is less than 91, the perimeter footing depth should be at least 18 inches. Geocon Incorporated should be consulted to provide additional design parameters as required by the structural engineer. 7.5.4 Our experience indicates post-tensioned slabs may be susceptible to excessive edge lift, regardless of the underlying soil conditions, unless reinforcing steel is placed at the bottom of the perimeter footings and the interior stiffener beams. Current PTI design procedures primarily address the potential center lift of slabs but, because of the placement of the reinforcing tendons in the top of the slab, the resulting eccentricity after tensioning may reduce the ability of the system to mitigate edge lift. The foundation system should be designed to reduce the potential for edge lift to occur. 7.5.5 Foundations for Category I, II or 111 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 such as wind or seismic forces. 7.5.6 The use of isolated footings that are boated beyond the perimeter of the building and support structural elements connected to the building is not recommended for Category III. Where this condition cannot be avoided, the isolated footings should be con- nected to the building foundation system with grade beams. 7.5.7 No special subgrade presaturation is deemed necessary prior to placing concrete; however, the exposed foundation and slab subgrade soils should be moisture conditioned, as necessary, to maintain a moist condition as would be expected in any such concrete placement. 7.5.8 Consideration should be given to connecting, patio slabs that exceed 5 feet in width to the building foundation to reduce the potential for future separation to occur. 7.5.9 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. Project No. 06403-52-16 _10 - July 28, 2004 For cut and fill slopes, 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. Where the height of the fill slope exceeds 20 feet, the minimum horizontal distance should be increased to 1-113 (where H equals the vertical distance from the top of the slope to the toe) but need not exceed 40 feet. For composite (fill over cut) slopes, H equals the vertical distance.from the top of the slope to the bottom of the fill portion of the slope. An acceptable alternative to deepening the footings is 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. Swimming pools located within 7 feet of the top of cut or fill slopes are not recommended. Where such a condition cannot be avoided, it is recommended that the portion of the swimming pool wall within 7 feet of the slope face be designed with the assumption 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 that 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 that would permit some lateral soil movement without causing extensive distress. Geocon Incorporated should be consulted for specific recommendations. 7.5.10 Exterior slabs not subject to vehicle loads should be at least 4 inches thick and reinforced with 6 x 6-W2.9 x W2.9 (6 x 6-6/6) 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 a dry density of at least 90 percent of the laboratory maximum dry density. 7.5.11 All concrete slabs should be provided with adequate construction joints and/or expansion joints to control unsightly shrinkage cracking. The design of joints should consider criteria of the American Concrete Institute when establishing crack-control spacing patterns. 7.5.12 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 intended to reduce the potential for differential elevations that could result from differential Project No. 06403-52-16 - 11 - July 28, 2004 settlement or minor heave of the flatwork. Dowelling details should be designed by the project structural engineer. 7.5.13 The recommendations of this report are intended to reduce the potential for cracking of slabs due to expansive soils (if present), differential settlement of deep fills, or fills of 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, particularly where re-entrant slab corners occur 7.6 Retaining Walls 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, an active soil pressure of 45 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 less than 90. Where backfill materials do not conform to the above criteria, 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 wall portion of the wall in feet) 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 above active soil pressure. For retaining walls subjected to vehicular loads within a horizontal distatice equal to two-thirds of the wall height, a surcharge equivalent to 2 feet soil should be added. 7.6.3 All retaining walls should be provided with a drainage system adequate to prevent the buildup of hydrostatic forces and should be waterproofed as required by the project architect. The use of drainage openings through the base of the wall (weep holes, etc.) is not recommended where the seepage could be a nuisance or otherwise adversely impact the property adjacent to the base of the wall. A typical retaining wall drainage system is presented as Figure 2. The above recommendations assume a properly compacted granular (Expansion Index 90 or less) backfill material with no hydrostatic forces or imposed surcharge load. If conditions different than those described are anticipated, or if specific Project No. 06403-52-16 -12- July 28, 2004 drainage details are desired, Geocon Incorporated should be contacted for additional recommendations. 7.6.4 In general, wall foundations having a minimum depth and width of one foot 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 less than 90. 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 anticipated. The location of the wall footings, however, should comply with the recommendations presented in Section 7.5.9. 7.7 Lateral Loads 7.7.1 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 granular fill soils or undisturbed natural soils. The allowable passive pressure assumes a horizontal surface extending at least five 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. An allowable friction coefficient of 0.4 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. 7.7.2 The recommendations presented above are generally applicable to the design of rigid concrete or masonry retaining walls having a maximum height of 8 feet. In the event that walls higher than 8 feet or other types of walls are planned, such as crib-type walls, Geocon Incorporated should be consulted for additional recommendations. 7.8 Slope Maintenance 7.8.1 Slopes that are steeper than 3:1 (horizontal: vertical) may, under conditions that 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 recommended that, to the maximum extent practical: (a) disturbed/loosened surficial soils be either Project No. 06403-52-16 -13 - July 28, 2004 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 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 project's slopes in the future. 7.9 Site Drainage 7.9.1 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 that carry runoff away from the proposed structure. 7.9.2 All 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. 7.9.3 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 recommend 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. 06403-52-16 -14 - July 28, 2004 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 that 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. Project No. 064035216 July 28, 2004 II \ - V KMUW )IA 7 PVSEO VALLE -.------ 8 1I04O 84 9 PASED SALINEED I I '12, J ', -p P 1V IAIIA 1PA1 VIA 51147 1TE ii , p - i__-._ -- - ii I I V—':p•. I o _- VIDA B :\-. -1 - - - ./4 -mom c0N0jS008 LAS - - - - 74t - -- - - ORcr No I_'" -- • - ..-- - ..- r AS p4 \_' I AVVCH0 BA8_ - --------- VIA PATIS 34 PAM CT Rik Tim Im 23 V ill' Qc 9 - —RLIA RITA BEL st • POITTSE.\ T2 A SITE CUM r45 III, (--- ( 8 CAN 80 VALENCIA ' ___ 100 ::•:. NlOA ..- PlAZA PAS.. EST BLUFF PLAZA a i 1.LUCERV ' 25 Y,L S . , PO VA IARA IPKWY ALGA ) .5 ETNA I 30 cl PINE- left 1900 RD cc: cr .1 VIA PELICN 44 CR HI NGE FS /YEA TOS LAGOON RD I --- / - PIES #5 • 11/ IA rnTA ••• ' •t MKVPWOFVAth ..- l?i \•V \' SOURCE: 2004 THOMAS BROTHERS MAP SAN DIEGO COUNTY, CALIFORNIA REPRODUCED WITH PERMISSION GRANTED BY THOMAS BORThERS MAPS. I flitS MAP IS COPYRIGHT BY THOMAS BROS. MAPS. if IS UNLAWFUL TO COPY NO SCALE DR REPRODUCE ALL OR ANY PART THEREOF, WHETHER FOR PERSONAL USE OR RESALE. WITHOUT PERMISSION. GE000N 0 INCORPORATED GEOTECHNICAL CONSULTANTS 6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121 —2974 PHONE 858558-6900— FAX 858 558-6159 MCE I MM • DSK/E0000 MVWT.&Gd,l%,it.M I VICINITY MAP I VILLAGES OF LA COSTA - THE GREENS NEIGHBORHOOD 1. 11, 1. 13, & 1.14 CARLSBAD, CALIFORNIA DATE 07-28-2004 1 PROJECT NO. 06403 - 52 - 16 1 FIG. I GROUND SURFACE 1.5 CONCRETE BROWDITCH PROPOSED RETAINING WALL COMPACTED 7/7 BACKFILL GROUND SURFACE - •. .:... //-.._ APPROVED . •Y, FILTER FABRIC 4 . , • 2/3 H . . .;— ,.. I OPEN GRADED - . r MAX. AGGREGATE 3MAX. FOOTING IN.J 4 DIA. PERPORATED PVC PIPE MIN. 1/2% FALL TO APPROVED OUTLET NO SCALE TYPICAL RETAINING WALL DRAIN . DETAIL I GE000N INCORPORATED GEOTECHNICAL CONSULTANTS 6960 FLANDERS DRIVE - SAN DIEGO, CAUFORNIA 92121-2974 PHONE 858 558-6900 - FAX 858 558-6159 — MCE /MM DSKJE000D Mo.4.fl l.iWd2 VILLAGES OF LA COSTA - THE GREENS NEIGHBORHOOD 1. 11, 1. 13, & 1.14 CARLSBAD, CALIFORNIA DATE 07-28-2004 IPROJECT NO. 06403-52- 16 FIG.2 TABLE I SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS AND FOUNDATION CATEGORY FOR NEIGHBORHOOD 1.11 LOTS NOS. 58 THROUGH 92, VILLAGES OF LA COSTA - THE GREENS Approximate Approximate Lot Pad Condition Maximum Maximum Depth Expansion Foundation No. Depth of Fill of Differential Fill Index Category (feet) (feet) 58 Undercut due to 17 13 53 II cut-fill transition 59 Undercut due to 16 12 53 II cut-fill transition 60 Undercut due to 26 22 53 III cut-fill transition 61 Undercut due to 28 23 53 ffl cut-fill transition 62 Undercut due to 4 1 53 II cut-fill transition 63 Undercut due to 4 1 53 II claystone 64 Undercut due to 16 12 41 II cut-'fill transition 65 Undercut due to 16 12 41 II cut-fill transition 66 Undercut due to 15 11 41 II cut-fill transition 67 Undercut due to 9. 5 41 cut-fill transition 68 Undercut due to 15 11 41 II cut-fill transition . 69 Undercut due to 8 4 41 I cut-fill transition 70 Undercut due to 24 20 65 III cut-fill transition 71 Undercut due to 22 18 65 II cut-fill transition 72 Undercut due to 14 10 65 II cut-fill transition . 73 Undercut due to 14 10 65 II cut-fill transition 74 Cut N/A N/A 31 I 75 Undercut due to 4 .1 66 II claystone 76 Undercut due to 4 1 66 II claystone Project No. 06403-52-16 July 28, 2004 TABLE I (Continued) SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS AND FOUNDATION CATEGORY FOR NEIGHBORHOOD 1.11 LOTS NOS. 58 THROUGH 92, VILLAGES OF LA COSTA - THE GREENS Lot No. Pad Condition Approximate Maximum Depth of Fill (feet) Approximate Maximum Depth of Differential Fill Expansion Index Foundation Category Undercut due to (feet) 77 claystone 1 ' 66 II 78 Cut N/A N/A 31 I 79 Cut N/A N/A 31 I 80 Undercut due to claystone 1 66 II 81 Cut N/A N/A 61 II 82 Cut N/A N/A 61 II 83 Cut N/A N/A 61 II 84 Cut N/A N/A 61 II 85 Cut N/A N/A 61 II 86 Cut N/A N/A 61 II 87 Cut N/A N/A 52 II 88 Cut 'N/A N/A 52 II 89 Cut N/A N/A 52 ' II 90 Cut N/A N/A 52 II 91 Cut N/A N/A 52 II 92 Cut 'N/A N/A 52 II TABLE II SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS AND FOUNDATION CATEGORY FOR NEIGHBORHOOD 1.13' LOT NOS. 97 THROUGH 129, VILLAGES OF LA COSTA - THE GREENS Approximate Approximate Lot Pad Condition Maximum Maximum Depth Expansion Foundation No. Depth of Fill of Differential Index Category (feet) Fill (feet) 97 Undercut due to rock 9 6 55 ' II 98 Undercut due to rock ' 9 ' 6 ' 55 II 99 Undercut due to rock 4 1 55 II 100 1 Undercut due to rock 4 1 55 II Project No. 06403-52-16 ' July 28, 2004 TABLE II (Continued) SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS AND FOUNDATION CATEGORY FOR NEIGHBORHOOD 1.13 LOT NOS. 97 THROUGH 129, VILLAGES OF LA COSTA - THE GREENS Lot No. Pad Condition Approximate Maximum Depth of Fill (feet) Approximate Maximum Depth of Differential Fill (feet) Expansion Index Foundation Category 101 Undercut due to rock 4 1 71 II 102 Undercut due to cut- fill transition 13 7 71 II 103 Undercut due to 8 cut-fill transition 4 71 II 104 Undercut due to 4 claystone 1 71 II 105 Fill . .29 9 54 II 106 Fill 36 28 54 III 107 Fill 51 44 54 .108 Fill 46 32 54 III 109 Fill 34 22 54 110 Fill. 22 14 54 II 111 Undercut due to rock 4 1 40 I 112 Undercut due to cut-fill transition 10 6 40 I 113 Fill 18 14 40 II 114 Fill 30 17 40 II 115 Fill 36 24 35 116 Fill 37 24 35 117 Fill 40 . 30 35 . lB 118 Fill 38 33 35 III 119 Fill 54 25 71 120 Fill 61 14 71 121 Fill 63 13 71 lB 122 Fill 60 11 71 lB 123 Fill 64 17 . 71 124 Fill 60 13 71 lB 125 Fill 47 17 65 II 126 Fill 44 16 65 II 127 Fill 32 20 65 III 128 Fill 26 14 65 II 129 Fill 25 17 65 II Project No. 06403-52-16 July 28, 2004 TABLE III SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS AND FOUNDATION CATEGORY FOR NEIGHBORHOOD 1.14 LOTS NOS. 1 THROUGH 57 AND LOTS 93 THROUGH 96 VILLAGES OF LA COSTA - THE GREENS Approximate Approximate Lot Maximum Maximum Depth Expansion Foundation No. Pad Condition Depth of Fill of Differential Fill Index Category (feet) (feet) 1 Fill. 23 10 87 II 2 Fill 24 10 87 II 3 Fill 32 15 87 II 4 Fill 38 24 87 'ifi 5 Fill' 37 31 63 ifi Undercut due to 6 cut-fill 22 18 _transition 63 II Undercut due to 7 cut-fill 16 12 _transition 63 II Undercut due to 8 cut-fill 12 8 _transition 63 II 9 Undercut due to 9 cut-fill _transition 4 62 II Undercut due to 10 19 cut-fill transition 15 62 II. Undercut due to 11 cut-fill 5 1 _transition 62 II Undercut due to 12 4 claystone 1 62 II Undercut due to 13 4 claystone 1. 62 II Undercut due to 14 4 claystone 1 70 II Undercut due to 15 4 claystone 1 70 II Undercut due to 16 cut-fill transition 24 20 111 70 Undercut due to 17 cut-fill 36 32 _transition 48 III 18 Fill 36 32 48 19 Fill ' 46 40 48 Undercut due to 20 cut-fill 38 34 _transition 48 ifi Undercut due to 21 cut-fill transition 26 22 111 51 Project No. 06403-52-16 ' July 28, 2004 TABLE III (Continued) SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS AND FOUNDATION CATEGORY FOR NEIGHBORHOOD 1.14 LOTS NOS. 1 THROUGH 57 AND LOTS 93 THROUGH 96 VILLAGES OF LA COSTA - THE GREENS Approximate Approximate Lot Pad Condition Maximum Maximum Depth Expansion Foundation No. Depth of Fill of Differential Fill Index Category (feet) (feet) 22 Fill .45 36 51 ifi 23 Fill 63 27 51 UI 24 Fill 69 28 51 ifi 25 Fill 43 25 59 III 26 Fill 60 .35 59 UI 27 Fill 74 30 59 28 Fill 79 .28 59 29 Fill 74 18 59 30 Fill - Alluvium 67 21 52 III 31 Fill - Alluvium 81 5 52 UI 32 Fill - Alluvium 86 19 52 ifi 33 Fill - Alluvium 86 19 52 ifi 34 Fill 75 34 52 In 35 Fill 71 55 . 45 UI 36 Fill 42 35 45 . UI 37 Undercut due to cut-fill transition 18 14 45 II 38 Undercut due to cut-fill transition 17 13 45 II 39 Undercut due to cut-fill transition 14 10 45 II 40 Undercut due to cut-fill transition 15 11 54 II 41 Undercut due to 14 cut-fill transition 10 . 54 II Undercut due to 42 4 claystone 1 . 27 I 43 Undercut due to cut-fill transition 7 2 27 I 44 Fill 11 3 54 II 45 Fill 24 1 18 54 II 46 Fill 32 22 54 .UI Project No. 06403-52-16 July 28, 2004 TABLE Ill (Continued) SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS AND FOUNDATION CATEGORY FOR NEIGHBORHOOD 1.14 LOTS NOS. 1 THROUGH 57 AND LOTS 93 THROUGH 96 VILLAGES OF LA COSTA - THE GREENS Approximate Approximate Lot Pad Condition Maximum Maximum Depth Expansion Foundation No. Depth of Fill of Differential Fill Index Category (feet) (feet) 47 j Fill 26 10 27 II 48 Fill 18 13 27 II 49 Undercut due to 10 5 27 I cut-fill _transition 50 Undercut due to cut-fill transition 9 4 49 I Undercut due to 51 cut-fill transition 12 8 49 I Undercut due to 52 cut-fill _transition 16 .10 49 II Undercut due to 53 - 19 cut-fill transition 14 49 II 54 Undercut due to 21 cut-fill _transition 17 49 II 55 Undercut due to 15 cut-fill _transition 10 32 II 56 Undercut due to 22 cut-fill _transition 18 32 II 57 Undercut due to . cu 18 14 32 II 93 - Undercut due to 4 claystone 1 80 Il Undercut due to 94 4 claystone 1 80 II Undercut due to 95 4 claystone 1 80 II 96 Undercut due to 4 claystone 1 80 II Project No. 06403-52-16 July 28, 2004 fr t TABLE IV SUMMARY OF WATER-SOLUBLE SULFATE LABORATORY TEST RESULTS NEIGHBORHOODS 1.14, 1.13, AND 1.11, LA COSTA GREENS CALIFORNIA TEST 417 Sample No. Water-Soluble Sulfate (%) Sulfate Exposure UBC Table 19-A-4 El-A 0.175 Moderate El-B 0.175 Moderate El-C 0.028 Negligible EI-D 0.035 Negligible EI-E 0.049 Negligible El-F 0.115 Moderate EI-G 0.041 Negligible - El-H 0.027 Negligible El-I 0.046 Negligible El-AR 0.375 Severe El-Al 0.080 Negligible El-AK 0.207 Severe El-AM 0.030 Negligible EI-AO 0.315 Severe El-AP 0.600 Severe EI-AQ 0.129 Moderate El-AS 0.405 Severe Li Project No. 06403-52-16 July 28, 2004