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Home My WebLink AboutPUD 04-08A; LA COSTA GREENS 1.17; UPDATED GEOTECHNICAL REPORT; 2006-03-10... J.. J.. 111111 .L. .. J. ... J.. ... J. ... ,J. .... J. -I .... J ... J. .... .J -J - ..J - i, UPDATE GEOTECHNICAL REPORT VILLAGES OF LA COSTA THE GREENS -PHASE 2 NEIGHBORHOOD 1.17 CARLSBAD, CALIFORNIA llECEJvB» JUL 25 2008 ENGINEERINC DEPARTMfNr PREPARED FOR WARMINGTON HOMES CARLSBAD, CALIFORNIA MARCH 10, 2006 PROJECT NO. 06403-52-26 ,.. ... ,.. ... .. JIii .... ... .. ... ,... .... -... .. ... -... ... ... .. .... ... ... -.. -- JII .. .. .. .. ... GEOCON INCORPORATED GEOTECHNK:Al CONSULTANTS 0 Project No. 06403-52-26 March 10, 2006 Warmington Homes 701 Palomar Airport Road, Suite 280 Carlsbad, California 92009 Attention: Subject: Gentlemen: Mr. Neal Keating Vll.,LAGES OF LA COSTA -THE GREENS, PHASE 2 NEIGHBORHOOD 1.17 CARLSBAD, CALIFORNIA UPDATE QEOTECHNICAL REPORT In accordance with your authorization of our Proposal No. LG-06079 dated February 27, 2006, 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, GEOCONINCORPORATED 7Yki2. C. {!_-t::,_7 Michael C. Ertwine Senior Staff Geologist MCE:AS:SR:dmc (6/del) (2) Addressee Real Estate Collateral Management Comp C/o Morrow Development Attention: Mr. Tim O'Grady ~~ Shane Rodacker RCE 63291 6960 Flanders Drive ■ Son Diego, California 92121-297 4 ■ Telephone (858) 558-6900 ■ Fox ( 858) 558-6159 -.... .. .. ... ,,. -.. .. .. ... ... ... .... ,.. .... .. -.... ... -- -.... -.. .. -.. .. ... ... ... TABLE OF CONTENTS 1. PURPOSE AND SCOPE ................................................................................................................. 1 2. PREVIOUS SITE DEVELOPMENT .............................................................................................. 1 3. SITE AND PROJECT DESCRIPTION ........................................................................................... 1 4. SOIL AND GEOLOGIC CONDITIONS ........................................................................................ 2 4.1 Compacted Fill (Qcf) ............................................................................................................. 2 4.2 Alluvium (Qal) ...................................................................................................................... 2 4.3 Santiago Formation (Ts) ........................................................................................................ 2 5. GROUNDWATER .......................................................................................................................... 2 6. GEOLOGIC HAZARDS ................................................................................................................. 3 6.1 Faulting and Seismicity ......................................................................................................... 3 6.2 Liquefaction ........................................................................................................................... 4 7. CONCLUSIONS AND RECOMMENDATIONS ........................................................................... 5 7 .1 General. .................................................................................................................................. 5 7.2 Seismic Design ...................................................................................................................... 5 7.3 Finish Grade Soil Conditions ................................................................................................ 6 7.4 Future Grading ....................................................................................................................... 7 7.5 Foundations ........................................................................................................................... 8 7.6 Retaining Walls ................................................................................................................... 12 7. 7 Lateral Loads ....................................................................................................................... 13 7.8 Slope Maintenance .............................................................................................................. 13 7.9 Site Drainage ....................................................................................................................... 13 LIMITATIONS AND UNIFORMITY OF CONDITIONS FIGURES: 1. Vicinity Map 2. Typical Retaining Wall Drain Detail TABLES: I. Summary of As-Graded Building Pad Conditions and Foundation Category IL Summary of Finish Grade Expansion Index Test Results III. 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 1.17, Lots 1 through 107 and associated improvements located in Phase 2 of the Villages of La Costa -The Greens development. The site is situated south of Poinsettia Lane, north of Dove Lane and west of the existing La Costa Resort and Spa golf course (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: 1. 2. 3. 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 1.17-Lots I through 107 and Lot I I I (Park Site), Carlsbad, California, prepared by Geocon Incorporated, dated February 24, 2006 (Project No. 06403-52-19A). Grading and Erosion Control Plans for: La Costa Greens Neighborhood 1.16 & 1.17, prepared by Hunsaker and Associates, City of Carlsbad approval oated May 10, 2005. 2. PREVIOUS SITE DEVELOPMENT Neighborhood 1.17, Lots 1 through 107, was graded to finish-pad configuration during mass grading operations for Phase 2 of 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 subject area has been completed and consisted of developing 107 single-family residential lots and associated streets. Fill and cut slopes were created with design inclinations of 2: 1 (horizontal:vertical) or flatter, with a maximum height of approximately 40 feet. The maximum thickness of the compacted fill soil is approximately 62 feet. An "As-Graded" Geologic Map is provided in the above-referenced report and depicts the existing geologic conditions and topography . 3 . SITE AND PROJECT DESCRIPTION The development of The Greens -Neighborhood 1.07 consists of 107 single-family residential homes and associated improvements. Compacted fill soil is exposed at grade and underlain by compacted fills placed during the grading of Bressi Ranch, the Santiago Formation, and alluvium. The Santiago Project No. 06403-52-26 -1-March I 0, 2006 .... -... ..... --... ... ... -- ... ... ,,.. ..... -.... ---... -... -----.. ... .. ... Formation is also exposed at grade on cut slopes, cut pads and within some roadways. The "As-Graded" Geologic Map for the project is included in the above-referenced final report of grading. A summary of the as-graded pad conditions for the lots is provided on Table I. In general, the on-site fill materials generally consist of silty to clayey sand . The locations and descriptions of the site and proposed improvements are based on a site reconnaissance, 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 The Santiago Formation, alluvium, and compacted fill soil underlie the site. The predominant materials within 4 feet of grade consist of silty to clayey sand and possess a very low to medium expansion potential. The soil types and geologic unit are discussed below . 4.1 Compacted Fill (Qcf) In general, the fill materials consist of light yellowish brown, silty to clayey sand. The maximum fill thickness is approximately 62 feet. Fill soil was placed in conjunction with the observation and testing services of Geocon Incorporated, which are summarized in the above-referenced final report of grading. 1he compacted fill soil is considered suitable to provide adequate support for the proposed development. 4.2 Alluvium (Qal) A portion of a storm drain easement at the southeastern margin of Neighborhood 1.07 is underlain by alluvium (beneath the compacted fill materials). This area, however, is located outside the zone of influence of any building pads and is not expected to adversely impact any-proposed structures . 4.3 Santiago Formation (Ts) The Eocene-age Santiago Formation, consisting of dense, massive, white to light green, silty, fine to coarse sandstones and hard, greenish-gray to brown claystones and siltstones, is exposed at finish grade on cut lots and underlies the compacted fill at the site and is considered suitable for the support of the proposed development. 5. GROUNDWATER Groundwater was encountered during grading operations in the alluvial soils but is not anticipated to adversely impact the development of the property. Due to the variable nature of the Santiago Project No. 06403-52-26 -2 -March 10, 2006 -... --... ... .. .... ... .. ... -... ... -... -------.... --- - --- --.... Formation, which consists of interbedded sandstone and claystone/siltstone, seepage was encountered in several cut slopes and subsequently mitigated during remedial grading by the construction of drained stability fills. 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. 6 . GEOLOGIC HAZARDS 6.1 Faulting and Seismicity Our review of pertinent geologic literature, the previously referenced geotechnical investigation report dated June 25, 2001, and our experience with the soil and geologic conditions in the general area indicate that no known active, potentially active, or inactive faults are located within the 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. Portions of the Rose Canyon Fault have been included in a Special Study Earthquake Fault Zone. A maximum seismic event of Magnitude 7.2 is postulated for the Rose Canyon Fault with an estimated maximum 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 Maximum Maximum Site (miles) Earthquake 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 Project No. 06403-52-26 -3 -March 10, 2006 -----.... ... .... ... ---- ""' -.. ,,. - -- ---- ----- --... .. In the event of a major earthquake along any of the above-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 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. 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 soil is 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 formational materials and compacted fill and the fine-grained characteristic of the alluvium, the potential for liquefaction occurring at the site is considered to be very low. Project No. 06403-52-26 -4-March 10, 2006 -... ,. ... ... -... -... --- ... ,. ... ... .... -.... """ '-- -... ---... --... .. 7 . CONCLUSIONS AND RECOMMENDATIONS 7.1 General 7.1.1 7.1.2 7.2 7.2.1 No soil or geologic conditions were encountered during previous geotechnical investigations 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. 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. Seismic Design The site is located within Seismic Zone 4 according to UBC Figure 16-J. Compacted fill soil 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 So Seismic Zone Factor 0.40 0.40 Table 16-I Soil Profile Sc So Table 16-J Seismic Coefficient, c. 0.40 0.44 Table 16-Q Seismic Coefficient, Cv 0.56 0.64 Table 16-R Near-Source Factor, Na 1.0 1.0 Table 16-S Near-Source Factor, Nv 1.0 1.0 Table 16-T Seismic Source B B Table 16-U Project No. 06403-52-26 -5 -March 10, 2006 - -... ----... --.... - -.... ...., -------... ------ -.. .. 7.2.2 7.3 7.3.1 Based on a review of the as-graded conditions presented in the as-graded report referenced below, as well as the seismic setting, the lots are assigned the seismic design parameters as indicated in the following table. TABLE 7.2.2 SUMMARY OF SOIL PROFILE TYPE Lot Nos. UBC Classification 1 So 2 through 4 Sc 5 through 9 So 10 Sc 11 through 16 So 17 and 18 Sc 19 through 21 So 22 and 23 Sc 24 through 29 So 30 through 33 Sc 34 through 38 So 39 and 40 Sc 41 through 44 So 45 through 51 Sc 52 and 53 So 54 through 56 Sc 57 through 59 So 60 through 71 Sc 72 through 78 So 79 through 97 Sc 98 through 107 So Finish Grade Soil Conditions Observations and laboratory test results indicate that the prevailing soil conditions within the upper approximately 3 feet of finish grade have an expansion potential of "very 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. Project No. 06403-52-26 -6-March 10, 2006 ... ,.. -... ... ... -.. --... ... .. .... ,. ... ,.. ... ,.. -.. -... ... -,.. -.. ,,. -.. .. 7.3.2 7.3.3 7.3.4 7.4 7.4.1 It should be noted that although rocks larger than 6-inch-diameter were not intentionally placed within the upper 3 feet of pad grades, some larger rocks may exist at random locations. In addition, concretionary lenses or layers may exist within the cut lots that may cause difficult excavation . Random samples obtained throughout the subject neighborhoods were subjected to water-soluble sulfate testing to evaluate the amount of water-soluble sulfates within the finish-grade soil. 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" to "severe" sulfate exposure ratings as defined by UBC Table 19-A-4. The results of the soluble-sulfate tests are summarized on Table III. Table 7 .3 presents a summary of concrete requirements set forth by UBC Table 19-A-4 . Sulfate Exposure Negligible -Moderate Severe Very Severe TABLE 7.3 REQUIREMENTS FOR CONCRETE EXPOSED TO SULFATE-CONTAINING SOLUTIONS Water-Soluble Cement Maximum Water Sulfate Percent Type to Cement Ratio by Weight by Weight 0.00-0.10 ---- 0.10-0.20 II 0.50 0.20-2.00 V 0.45 >2.00 V 0.45 Minimum Compressive Strength (psi) -- 4000 4500 4500 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 . Future Grading 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 . Project No. 06403-52-26 . 7 . March 10, 2006 ! .. ---- ---... .. --.. ... ... ... ,,. -- ------.. ------,.. -- 7.5 Foundations 7.5.1 7.5.2 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 soil as well as the Expansion Index (EI) of the prevailing subgrade soil of a particular building pad. Finish-grade Expansion Index test results are presented on Table II, attached. The category criteria are summarized herein. 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 III: Fill thickness exceeds 50 feet, or variation in fill thickness exceeds 20 feet, or Expansion Index exceeds 90 but is 130 or less . 1. 2. 3. 4. 5. All footings should have a minimum width of 12 inches. Footing depth is measured from lowest adjacent subgrade. These depths apply to both exterior and interior footings. All interior living area concrete slabs should be at least 5 inches thick. This applies to both building and garage slabs-on-grade. All interior 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 recommended in No. 4 above. The post-tensioned systems should be designed by a structural engineer experienced in post-tensioned slab design and the design criteria of the Post-Tensioning Institute (UBC Section 1816). Although this procedure was developed for expansive soil, 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 the Table 7.5 for the particular foundation category designated for each lot as presented on Table I. Project No. 06403-52-26 -8 -March 10, 2006 -------------.... -------------.... -------... ... ... 7.5.3 7.5.4 TABLE 7.5 POST-TENSIONED FOUNDATION SYSTEM DESIGN PARAMETERS Post-Tensioning Institute (PTI) Foundation Category Design Parameters I II III 1. Thornthwaite Index -20 -20 -20 2. Clay Type -Montmorillonite Yes Yes Yes 3. Clay Portion (Maximum) 30% 50% 70% 4. Depth to Constant Soil Suction 7.0 ft. 7.0 ft. 7.0ft. 5. Soil Suction 3.6 ft. 3.6 ft. 3.6ft. 6. Moisture Velocity 0.7 in.Imo. 0.7 in.Imo. 0.7 in.Imo. 7. Edge Lift Moisture Variation Distance 2.6 ft. 2.6 ft. 2.6ft. 8. Edge Lift 0.41 in. 0.78 in. 1.15 in. 9 . Center Lift Moisture Variation Distance 5.3 ft. 5.3 ft. 5.3 ft. 10. Center Lift 2.12 in. 3.21 in. 4.74 in. 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. III, §1816, the following recommendations apply: • The deflection criteria presented in Table 7.5 are still applicable . • Interior stiffener beams be used for Foundation Categories II and III. • The depth of the perimeter foundation should be at least 12 inches for Foundation Category I, 18 inches for Foundation Category II, and 24 inches for Foundation Category III. Geocon Incorporated should be consulted to provide additional design parameters as required by the structural engineer. Our experience indicates post-tensioned slabs are 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 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. Project No. 06403-52-26 -9 -March 10, 2006 ------.. ---.... ---.... -------------------..., ,,.. -.. .. 7.5.5 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. 7.5.6 7.5.7 7.5.8 7.5.9 7.5.10 Foundations for Category I, II, or III 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 . The use of isolated footings that are located 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 connected to the building foundation system with grade beams . No special subgrade presaturation is 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. 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. 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 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 H/3 ( 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 Project No. 06403-52-26 -IO -March 10, 2006 --- -... - ... ,.. -l' --.... ------------... --,,,. --... ,.. -... ... 7.5.11 7.5.12 7.5.13 7.5.14 • 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. 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. 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. 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 settlement or minor heave of the flatwork. Dowelling details should be designed by the project structural engineer. The recommendations of this report are intended to reduce the potential for cracking of slabs due to expansive soil (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 the placement of crack-control joints at periodic intervals, particularly where re-entrant slab comers occur. Project No. 06403-52-26 -11 -March 10, 2006 -.... -------... ---.... ----------------,.. --- -... - 7.6 Retaining Walls 7.6.1 7.6.2 7.6.3 7.6.4 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 to 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. For those lots with finish-grade soil having an Expansion Index greater than 90 and/or where backfill materials do not conform to the above criteria, Geocon Incorporated should be consulted for additional recommendations. 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 distance equal to two-thirds of the wall height, a surcharge equivalent to 2 feet soil should be added. All retaining walls should be provided with a drainage system adequate to prevent the b_Eildup 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 less than 90) backfill material with no hydrostatic forces or imposed surcharge load. If conditions different than those described are anticipated, or if specific drainage details are desired, Geocon Incorporated should be contacted for additional recommendations. 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 7.5.10. Project No. 06403-52-26 -12 -March 10, 2006 -... ,,. --.... ---... ,,. -- -.... ,,. --.... ,,. ---... ... - -,,. ... -.... --... 7.7 Lateral Loads 7.7.1 7.7.2 7.8 7.8.1 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 soil or undisturbed natural 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. 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. 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 (such as crib-type walls) are planned, Geocon Incorporated should be consulted for additional recommendations . Slope Maintenance 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 3 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 soil, 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 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 Project No. 06403-52-26 . 13. March 10, 2006 -------------... ---------------,.. -... ..., --- 7.9.2 7.9.3 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. 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. 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. 06403-52-26 -14 -March 10, 2006 -.... ---... --... ------------------------... -.. .... 1. 2. 3. 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. 06403-52-26 March 10, 2006 - -------- --... ----- ----,,. -------- ... -.. ... LAGOON SOURCE: 2006 THOMAS BROTHERS MAP SAN DIEGO COUNTY, CALIFORNIA REPRODUCED WITH PERMISSION GRANTED BY THOMAS BROTHERS MAPS. THIS MAP IS COPYRIGHT BY THOMAS BROS. MAPS. rT IS UNLAWFUL TD COPY OR REPRODUCE ALL OR Nff PART TliEREOF, WHETHER FOR PERSONAL USE OR RESALE, WITHOUT PERMISSION. GEOCON INCORPORATED GEOTEOINICAL CONSULT ANTS 6960 FLANDERS DRIVE· SAN DIEGO, CALIFORNIA 92121 • 297 .4 PHONE 858 558-6900 • FAX 858 558-6159 MCE/MM I I DSK/GTYPD IXM03-52·26_MM_Ma._\llCNTY VICINITY MAP 1PAS£0 P.\SED P.\SED 6IWffll ~~ PASEOEIISIWR P.\SED PICMXII \ •W'· RNDll POSTA I • "-"" YAW, I t N NO SCALE VILLAGES OF LA COSTA-THE GREENS NEIGHBORHOOD 1 . 17 CARLSBAD, CALIFORNIA DATE 03-10-2006' I PROJECT NO. 06403-52-26 I FIG.1 ---------.. .. -... -----... -------------.... .. --.... PROPOSED RETAINING WALl GROUND SURFACE \ CONCRETE LINE DRAINAGE DITCH 2/3H ~ ::·:.: ,. .... >:~>-~) ' •··•· • ·•·. _:·. MIRAFI 140FILTER FABRIC OR EQUIVALENT OPEN GRADED 1" MAX. AGGREGATE 4" DIA. PERPORATED PVC PIPE MIN. 1/2% FALL TO APPROVED OUTLET NO SCALE RETAINING WALL DRAIN DETAIL GEOCON INCORPORATED 0 GEOTEOiNICAL CONSULT ANTS 6960 FLANDERS DRIVE -SAN DIEGO, CALIFORNIA 92121-297 .4 PHONE 858 558-6900 -FAX 858 558-6159 MCE/MM I I DSK/GTYPD 06A03-52•26_11M_/o/a_llETWJoJJ.. VILLAGES OF LA COSTA-THE GREENS NEIGHBORHOOD 1 . 17 CARLSBAD, CALIFORNIA DATE 03-10-2006 I PROJECT NO. 06403 -52 -26 I FIG. 2 -------.... -... ---.... ,,,. -... -.... ---... - -... -... .. ... ... ... .. .. ... Lot No . 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 TABLEI SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS AND FOUNDATION CATEGORY FOR NEIGHBORHOOD 1.17, LOT NOS.1 THROUGH 107 Approximate Approximate Pad Condition Maximum Maximum Depth Expansion Depth of Fill of Differential Fill Index (feet) (feet) Undercut due to 23 20 65 cut-fill transition Undercut due to 13 10 65 cut-fill transition Undercut due to 11 8 65 cut-fill transition Undercut due to 9 6 65 cut-fill transition Undercut due to 26 22 65 cut-fill transition Undercut due to 25 22 78 cut-fill transition Undercut due to 25 22 78 cut-fill transition Undercut due to 26 22 78 cut-fill transition Fill 24 20 78 Fill 14 10 78 Fill 27 11 76 Fill 30 22 76 Fill 34 20 76 Undercut due to 34 30 76 cut-fill transition Undercut due to 30 27 86 cut-fill transition Undercut due to 20 16 86 cut-fill transition Undercut due to 13 10 16 cut-fill transition Cut NIA NIA 33 Undercut due to 24 21 16 cut-fill transition Undercut due to 24 20 16 cut-fill transition Project No. 06403-52-26 Foundation Category III II II II III III III III III II II III III III III II II I III III March 10, 2006 ------------------------------- -----.. Ill Lot No. 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 TABLE I (Continued) SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS AND FOUNDATION CATEGORY FOR NEIGHBORHOOD 1.17, LOT NOS.1 THROUGH 107 Approximate Approximate Pad Condition Maximum Maximum Depth Expansion Depth of Fill of Differential Fill Index (feet) (feet) Undercut due to 23 20 16 cut-fill transition Cut NIA NIA 33 Cut NIA NIA 33 Undercut due to 23 20 54 cut-fill transition Fill 32 7 63 Fill 39 21 63 Undercut due to 38 35 63 cut-fill transition Undercut due to 35 32 63 cut-fill transition Undercut due to 25 21 58 cut-fill transition - Undercut due to 18 15 58 cut-fill transition Undercut due to 14 11 58 cut-fill transition Undercut due to 19 16 58 cut-fill transition Undercut due to 17 14 58 cut-fill transition Undercut due to 21 18 61 cut-fill transition Fill 22 17 61 Fill 26 15 61 Fill 46 28 61 Fill 44 23 61 Cut NIA NIA 51 Undercut due to 10 7 51 cut-fill transition Undercut due to 32 28 51 cut-fill transition Project No. 06403-52-26 Foundation Category III I I III II III III III III II II II II II II II III III II II III March 10, 2006 ---------------------------------... - - Lot No. 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 TABLE I (Continued) SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS AND FOUNDATION CATEGORY FOR NEIGHBORHOOD 1.17, LOT NOS.1 THROUGH 107 Approximate Approximate Pad Condition Maximum Maximum Depth Expansion Depth of Fill of Differential Fill Index (feet) (feet) Fill 47 35 51 Fill 48 38 51 Undercut due to 34 31 51 cut-fill transition Cut NIA NIA 89 Cut NIA NIA 16 Cut NIA NIA 16 Cut NIA NIA 16 Cut NIA NIA 16 Cut NIA NIA 16 Undercut due to 14 10 82 cut-fill transition Undercut due to 30 26 82 cut-fill transition Undercut due to 28 25 82 cut-fill transition Undercut due to 12 9 66 cut-fill transition Undercut due to 12 9 66 cut-fill transition Undercut due to 18 15 66 cut-fill transition - Undercut due to 24 20 66 cut-fill transition Undercut due to 27 24 66 cut-fill transition Undercut due to 32 29 66 cut-fill transition Undercut due to 4 1 54 concretions Undercut due to 4 1 54 concretions Undercut due to 4 1 54 concretions Project No. 06403-52-26 Foundation Category III III III II I I I I I II III III II II II III III III II II II March 10, 2006 ---------... --------- ------------- ---.. Lot No. 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 TABLE I (Continued) SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS AND FOUNDATION CATEGORY FOR NEIGHBORHOOD 1.17, LOT NOS.1 THROUGH 107 Approximate Approximate Pad Condition Maximum Maximum Depth Expansion Depth of Fill of Differential Fill Index (feet) (feet) Undercut due to 4 1 54 concretions Undercut due to 4 1 54 concretions Undercut due to 4 1 71 concretions Undercut due to 4 1 71 concretions Undercut due to 4 1 71 concretions Undercut due to 4 1 71 concretions Cut NIA NIA 28 Cut NIA NIA 28 Cut NIA NIA 28 - Undercut due to 32 29 61 cut-fill transition Fill 48 40 61 Fill 42 20 61 Fill 24 8 47 Fill 26 8 47 Fill 23 8 47 Fill 20 10 47 Fill 8 2 47 Fill 9 3 42 Undercut due to 10 6 52 cut-fill transition Undercut due to 10 7 82 cut-fill transition Fill 11 4 60 Fill 8 5 38 Fill 8 4 47 Fill 4 1 47 Project No. 06403-52-26 ______ . ..,,.,~-..... ,------··· Foundation Category II II II II II II I I I III III III II II II II I I II II II I I I March 10, 2006 ---... -----------------------.. --------,. ... Lot No. 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 TABLE I (Continued) SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS AND FOUNDATION CATEGORY FOR NEIGHBORHOOD 1.17, LOT NOS.1 THROUGH 107 Approximate Approximate Pad Condition Maximum Maximum Depth Expansion Depth of Fill of Differential Fill Index (feet) (feet) Fill 7 4 47 Fill 8 5 47 Fill 15 8 58 Fill 12 10 58 Fill 7 4 58 Fill 8 4 58 Fill 7 3 44 Fill 8 3 44 Fill 5 1 44 Undercut due to 8 6 44 cut-fill transition Undercut due to 19 16 44 cut-fill transition Undercut due to 25 22 53 cut-fill transition Fill 51 24 53 Fill 27 18 53 Fill 23 16 53 Fill 48 23 53 Fill 54 24 66 Fill 54 19 o6 Fill 54 4 66 Fill 58 17 66 Fill 62 23 66 Project No. 06403-52-26 Foundation Category I I I II II II I I I I II III III II II III III III III III III March 10, 2006 ----- --------- ---.... --- - .... ---... ---- TABLE II SUMMARY OF FINISH GRADE EXPANSION INDEX TEST RESULTS VILLAGES OF LA COSTA; THE GREENS NEIGHBORHOOD 1.17, LOTS 1 THROUGH 107 Lot Numbers Sample at Expansion UBC Finish Grade Index Classification 1 through 5 EI-Q 65 Medium 6 through 10 EI-R 78 Medium 11 through 14 EI-S 76 Medium 15 and 16 EI-T 86 Medium 17 EI-AG 16 Very Low 18 EI-AH 33 Low 19 through 21 EI-AG 16 Very Low 22 and 23 EI-AH 33 Low 24 EI-AI 54 Medium 25 through 28 EI-Y 63 Medium 29 through 33 EI-X 58 Medium 34 through 38 EI-Z 61 Medium 39 through 44 EI-AF 51 Medium 45 EI-AD 89 Medium 46 through 50 EI-AB 16 Very Low 51 through 53 EI-AA 82 Medium 54 through 59 EI-W 66 Medium 60 through 64 EI-V 54 Medium 65 through 68 EI-U 71 Medium 69 through 71 EI-AC 28 Low 72 through 74 EI-K 61 Medium 75 through 79 EI-J 47 Low 80 EI-AE 42 Low 81 EI-lb 52 Medium 82 EI-le 82 Medium 83 EI-Id 60 Medium 84 EI-le 38 Low 85 through 88 EI-P 47 Low 89 through 92 EI-O 58 Medium 93 through 97 EI-N 44 Low 98 through 102 EI-L 53 Medium 103 through 107 EI-M 66 Medium Project No. 06403-52-26 March 10, 2006 ----------... --... -.... -------- ..... .... -... .. ... .. Ill 1111 Ill .. .. TABLE Ill SUMMARY OF LABORATORY WATER-SOLUBLE SULFATE TEST RESULTS CALIFORNIA TEST 417 Sample No. Water-Soluble Sulfate(%) Sulfate Exposure UBC Table 19-A-4 EI-lb 0.092 Negligible EI-le 0.240 Severe EI-Id 0.225 Severe EI-le 0.132 Moderate EI-J 0.495 Severe EI-K 0.156 Moderate EI-L 0.138 Moderate EI-M 0.380 Severe EI-N 0.520 Severe EI-O 0.720 Severe EI-P 0.540 Severe EI-Q 0.675 Severe EI-R 0.555 Severe EI-S 0.585 Severe EI-T 0.585 Severe EI-U 0.690 Severe EI-V 0.675 Severe EI-W 0.270 Severe EI-X 0.375 Severe EI-Y 0.195 Moderate EI-Z 0.720 Severe El-AA 0.765 Severe EI-AB 0.100 Moderate EI-AC 0.720 Severe EI-AD 0.765 Severe EI-AE 0.435 Severe EI-AF 0.051 Negligible EI-AG 0.255 Severe El-AH 0.345 Severe EI-AI 0.255 Severe Project No. 06403-52-26 March 10, 2006