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Home My WebLink AboutCT 04-03; LA COSTA RIDGE NEIGHBORHOODS 2.3 & 2.4; UPDATE GEOTECHNICAL REPORT; 2005-09-20Ii! In.' UPDATE GEOTECHNICAL REPORT . VILLAGES OF LA COSTA - THE RIDGE NEIGHBORHOODS 2.3 AND 2.4 (SOUTH) LOTS I THROUGH 48 •. CARLSBAD, CALIFORNIA PREPARED FOR WARMINGTON HOMES CARLSBAD, CALIFORNIA :. SEPTEMBER 20, 2005 PROJECT NO. 07290-52-04 GEOCON' ' INCORPORATED I - GEOTECHNICAL CONSULTANTS Project No 07290-52-04 1 September 20, 2005 1 Warminton Homes V 701 Palomar Airport Road, Suite 280 . I Carlsbad, California 92009 - Attention: Mr. Chuck Isbell S Subject VILLAGES OF LA COSTA - THE RIDGE NEIGHBORHOODS 2.3 AND 2.4 (SOUTH), LOTS 1 THROUGH 48 I V CARLSBAD, CALIFORNIA: V UPDATE GEOTECFINICAL REPORT 1 Gentlemen I VV In accordance with your verbal authorization of our Proposal No. LG-05374 dated September 2, 2005, we have prepared this update geotechnical report for the subject project. The accompanying Vreport presents the results of our study and contains conclusions and recommendations pertaining to I the geotechnical aspects of the proposed development of the site. Provided that the recommendation - contained in this update report are followed, the site is considered suitable for onstruction and: -: - support of the proposed structures and improvements as presently planned.. - V - - Should you have any questions regarding this report, or if we may be of further service, please - V VI - contact the undersigned at your cOnvenience. .1 Very truly yours, V GEOCON INCORPORATED RCE 63291 Up. 6130/06 M G 1524 I No. 6329. ftInill, OF C CA I (6/del) Addressee (Iv®r) oo bs (2) . Morrow Development V - . Attention: Mr. Tim O'Grady V 6960 Flanders Drive • San Diego, California 92121.2974 U Telephone (858) 558-6900 U Fax (858) 558-6159 I T fVV - V V VV V TABLE OF CONTENTS • PURPOSE AND SCOPE ...................... ................................................................... ................ ......... 1 1 PREVIOUS SITE DEVELOPMENT ...................................................... ......................................... 1 I 3 4 SITE AND PROJECT DESCRIPTION 1 SOIL AND GEOLOGIC CONDITIONS 2 I 4.1 Compacted Fill (Qcf):. ..., ..2 4.2 San Marcos Gabbro (Kg[sm]) ..............................................................................................3 4.3 Escondido Creek Granodiorite (Kg [e]).................................................................................3 I 4.4 Bonsall Tonalite (Kg [b])........................................................................................................3 4.5 Santiago Peak Volcanics (Jsp)........ ....................................................... ................... . ............... 3 S. GROUNDWATER ...........................................................................................................................3 1 GEOLOGIC HAZARDS ...................................................................................................................4 • 6.1 . Faulting and Seismicity ........................................................................................................4 1 6.2 Liquefaction ................................ ................................................................. . .............. .. ............ 5 CONCLUSIONS AND RECOMMENDATIONS .... ............. ............................................................ 5 I 7.1 General... .......................................................................................................... ........ .................. 5 7.2 Seismic Design ......................................................................................................................s 7.3 Finish Grade Soil Conditions ................................................................................................6 .7.4. -Future- Grading:.............................................. .........................................................................7 7 5 Foundations 7 7.6 Retaining Walls 11 1 7 7 Lateral Loads T8 Slope Maintenance - 12 13 7.9. Site Drainage 13 1 LIMITATIONS AND UNIFORMITY OF CONDITIONS I MAPS AND ILLUSTRATIONS Figure 1, Vicinity Map .• • • . . • Figure 2, Typical Retaining Wall Drain Detail- TABLES . - • . • .. Table I, Summary of As-Graded Building Pad Conditions and Foundation Category . • Table II, Summary of Laboratory Water-Soluble Sulfate Test Results ~ I H I HI ~ I I I 7- I UPDATE GEOTECHNICAL REPORT 1. PURPOSE AND SCOPE I This report presents the results of the update geotechnical study for the proposed residential development of Neighborhoods 2.3 and 2.4 (South) Lots 1 through 48 and associated improvements I located in the Villages of La Costa - The Ridge development. The site is situated east of ElF.uerte: Street and south bf Corihtia Street in Carlsbad, California (see Vicinity Map, Figure 1). The purse' of this update report is to provide foundation and retaining wall design recommendations The scope of the study included areview of the following: Update Geotechnical Investigation, Villages of La Costa - The Ridge, Carlsbad, California, I prepared by Geocon Incorporated, dated August 27, 2001 (Project No. 06105-12-05). Final Report of Testing and Observation Services Performed During Site Grading, Villages I of La Costa - The Ridge, Neighborhoods 2.3 and 2.4, Carlsbad, California, prepared by Geocon Incorporated, dated September 16, 2005. (Project No. 07290-52-01). 'Grading and Erosion Control Plans for. La Costa Ridge Neighborhood 2.3 and 2.4, prepared I by Hunsaker and Associates, with the City of Carlsbad approval dated August 23, 2005. • I .. 2. PREVIOUS SITE DEVELOPMENT - Neighborhoods 2 3 and 2 4 (South), Lots I through 48 were graded to finish pad configuration during I mass grading operations for the Villages of La Costa - The Ridge development Grading was - performed in conjunction with the obervation and testing services of Geocon Incorporated A summary of the observations, compaction test results, and professional w.opinions pertaining to the I grading are presented in the above-referenced final report of grading Mass grading for the subject area has been completed and consisted of developing 48 single-family residential lots and associated I . streets. Fill slopes were created with design inclinations of 2:1 (hôrizOntal:vertical) or flatter, with a maximum height of approximately 70 feet. The maximum thickness of the fill soil is approximately 41 feet. An "As-Graded" Geologic Map has been provided in the above-referenced final report and I depicts the existing geologic conditions and topography. I - 3. SITE AND PROJECT DESCRIPTION The development of The Ridge - Neighborhoods 2.3 and 2.4 consists of 104 single-family residential I homes and associated improvements. However, only the southern portion (lot numbers 1 through 48) is the subject of this report. Compacted fill soil is exposed at grade and is underlain by volcanic and I granitic rock consisting of the Santiago Peak Volcanics, Bonsall Tonalite, San Marcos Gabbro, and Escondido Creek Granodiorite. A. summary of the as-graded pad conditions for each lot is provided on Table I. In general, the on-site fill materials generally vary between angular gravels and boulders Project No. 07290-52-04 • - 1- September 20, 2005 I 1 .: .., H I produced by onsite blasting of hard rock to silty, fine to coarse sands and sandy to clayey gravels derived from the surficial soils and weathered formational materials. . . I 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 I . . project details vary significantly from those described above, Geocon Incorporated should be oiitted to determine the necessity for review and revision of this report. ,. I . . •' .4. SOIL AND GEOLOGIC CONDITIONS . The site is underlain by compacted fill and geologic formations of the Jurassic-age Santiago Peak Volcanics and Cretaceous-age Bonsall Tonalite, San Marcos Gabbro, and Escondido Creek Granodiorite. The predominant materials within 3 feet of grade consist of silty sand and gravel and I possess a "very low" to "low" expansion potential. The. soil type and geologic units are discussed below. . .. . . 4.1 Compacted Fill (Qcf) . . . . . I In gneral, structural fill placed and compacted at the site consisted of material which can be classified into three zones: . . •• . . . I Zone A Material placed within 3 feet from pad grade, 6 feet from parkway grade, and within roadways to at least 1 foot below the deepest utility consisted of "soil" fill with an I approximate maximum particle dimension of 6 inches - I Zone B Material placed within 10 fe&t from pad grade and below Zone A consisted of "soil rock" fill with a m maximum particle diension 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 I 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 I . • • with a maximum dimension of approximately 8 feet were buried individually during "rock" fill grading operations.. • The maximum fill thickness is approximately 41 feet. Fill soil was placed in conjunction with the • - - I observation and testing services of Geocon Incorporated which have been summarized in the above-referenced final report of grading. The compacted fill soil is considered suitable to proylde adequater support for the proposed development. . • I • •• Project No. 07290-52-04 - 2 - September 20, 2005 I I 4.2 San Marcos Gabbro (Kg [Sm]) . The Cretaceous-'aged San Marcos Gabbro was encountered within the north- and south-central I portions of the project. This unit is typically characterized as moderately weathered, fractured, fine- to medium-grained, dark gray gabbro. 1 .4.3 Escondido Creek Granodiorite (Kg [e]) - I' In published literature, this unit is described as a "leucogranodicrite" because of the overall light color, but averages of composition are typically gianodiorite. This rock type was encountered within the central and northern portions of. the project and generally consists of slightly to moderately .1 weathered, light brown to olive, medium- to coarse-grained granodiorite. I 4.4 Bonsall Tonalite (Kg [b]) .. . The Bonsall Tonalite was mapped as resistant, quartz-rich diorite bodies that were commonly. 1 . associated with the contact between Escondido Creek Granodiorite and the San Marcos Gabbio or Santiago Peaks Volcanics. This rock type was encountered in central and northern portions of the - project, and formed resistant ridges and outcrops prior to grading. The Bonsall Tonalite is fine- to I 'medium-grained, slightly to moderately weathered, and contained gabbro or, volcanic inclusions. Fine-grained and unweathered portions of the Bonsall Tonalite required heavy ripping effort, blasting or 'breaker hammers to excavate. .••• .. :. .. - . . I 4 5 Santiago Peak Volcanics (Jsp) T-he Jurassic aged Santiago Peak Volcanics, with the exception of the central portion of the site, I comprise the majority of the underlying bedrock These rocks were deposited as an alternating succession of volcanic flows, tuffs, and breccias and typically have an andesite or dacite composition Subsequently, this sequence of rocks was folded, faulted, and weakly metamorphosed As I encountered during grading, this unit is highly fractured. Closely spaced parallel fractures and joints form "sheeted" zones containing colorful alteration and/or oxidation minerals such as limonite and. .I • hematite. Even though the majority of the Santiago Peak Volcanics appears to behighly fractured and - altered, the "sheeted" zones typically have steeply dipping, tight clay-filled fractures. 1 5. GROUNDWATER . Groundwater was not encountered during grading operations and is not anticipated to adversely I impact the development of the, property. Due to the fractured nature of the formational materials, some areas of seepage were encountered and contained during remedial grading by subdrains. It is I . 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 I Project No. 07290-52-04 • -3 - September, 20, 2005 I • • .,• •. - H ' other factors, and vary as a result. Proper surface drainage of irrigation and rainwater will be important to future performance of the project. I 6. GEOLOGIC HAZARDS I 6.1 Faulting and Seismicity Our review of pertinent geologic literature, :thpreviously referenced geotechnical investigation I report dated August 3, 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 at the site. I The nearest known "active" faults are the Rose Canyon Fault and the Newport-Inglewood (offshore) located approximately 8 and 12 miles, respectively, to the west and the Elsinore Fault Zone, which I lies approximately 23 miles to the northeast. Portions of the Rose Canyon Fault have been included in an Alquist-Priolo Earthquake Fault Zone. A Maximum Credible seismic event of Magnitude 7.2 is postulated for the Rose Canyon Fault with an estimated MaximumCredible peak site acceleration of I 0.35 g based on the Sadigh, et cii. (1997) acceleration-attenuation relationship. I 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 presentthe greatest. seismic impact to the site 4. TABLE 6 1 I FAULT SYSTEMS WITHIN THE SOUTHERN CALIFORNIA AND NORTHERN BAJA CALIFORNIA REGION - Fault Name . Distance from Site (miles) Maximum . .. : Credible Earthquake'Site Maximum Credible . :Site Acceleration (g) Rose Canyon - '. . . 8 . . 7.2 . 0.35 Newport—Inglewood (Offshore) 12 7.1 . . 0.24 Coronado Banks Fault Zone 23 . 7.6 0.16 Elsinore—Julian . 23 7.1 0.12 Elsinore—Temecula . 23 . 6.8 , 0.10 Elsinore—Glen Ivy 38 . 6.8 0.05 Earthquake Valley 38 . 6.5 . 0.04 San Joaquin Hills 42 6.6 0.04 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 Project No. 07290-52-04 . . . - .4 - September 20, 2005 I I I Li 1 U I 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 I performed in accordance with the Uniform Building Code (UBC) currently adopted by the City of Carlsbad. 6.2 Liquefaction.... ., I Liquefaction typically occurs. 'Ihen '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 I 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 absence of a permanent groundwater table, the potential for I liquefaction occurring at the site is considered to be very low. I 7. CONCLUSIONS AND RECOMMENDATIONS 7.1 General I 7.1.1 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 reommndations of this report are followed 7.1.2-,. -The site is cnsidered 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 underline the proposed buildings. For seismic design, the site is characterized by soil profile 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 8 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. ' Project No. 07290-52-04 - 5 - September 20, 2005 TABLE 7.2.1 SITE SEISMIC DESIGN CRITERIA Parameter - Soil Profile Type UBC Reference Sc S0 Seismic Zone Factor 0.40 ' 0.40 Table 16-I Soil Profile Sc S0 Table 164 Seimic Coefficient Ca 0.40 0.44 Table 16 Q Sèismic Coefficient, C 0.56 0.64 Table..16-R. Near-Source Factor, Na -1.0 1.0 Table 16-S Near-Source Factor, N 1.0 1.0 Table 16-T Seismic Source B . B Table 16-U 7.2.2 Based on review of the as-graded conditions presented in the referenced as-graded report, as well as the seismic setting, the lots are assigned the seismic design parameters as indicated below in 7.2.2. TABLE 7.2.2 SUMMARY OF SOIL PROFILE TYPE 7 3 Finish Grade Soil Conditions 7.3. 1' Observations and laborafory, test results indicate that the prevailing soil conditions within the upper approximately 4 feet of finish grade have an expansion potential of "very low" ' to "low" (Expansion Index 'of 50 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 3 feet' of pad grades, some larger rocks may exist at random locations: ' 7.3.3 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 soils. These test results are used to determine the potential for sulfate attack on -Project No. 07290-52-04 - 6 - ' ' - September 20, 2005 I I •normal Portland Cement concrete. The-test results indicate sulfate' contents that correspond to "negligible" sulfate exposure ratings as defined by UBC Table 19-A-4. The results of the water-soluble sulfate tests are summarized on Table II. I. .. . 7.3.4 Geocon Incorporated does not practice in the field of corrosion engineering, Therefore, if. I 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 I 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' I 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 I least 48 hours prior to commencing additional grading or backfill operations I 75 Foundations 7.5.1 The foundation recommendations that follow are for one- or two-story residential I 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 Finish grade Expansion Index test results are presented on I Table I, attached.The category criteria are summarized herein I Category I Maximum fill thickness Is less than 20 feet and Expansion Index is less than or equal to 50 I 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 less than 130. I I I I September 20, 2005 Notes: 1. All footings should have a minimum width of 12 inches. 2. 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 for all categories. This applies to both buildii:ând garage slabs-on-grade. All interior concrete slabs should be uñierlain by at least 3 inches of clean sand or crushed rock. All slabs expected to receive moisture sensitive floor coverings or used to store moisture sensitive materials should be underlain by a vapor inhibitor covered with at least 2 inches of the clean sand recommended in No. 4 above. 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 can also be used to reduce the potential for foundation distress due to differential fill settlement. The post-tensioned design should incorporate the geotechnicál parameters presented in Table 7.5 entitled Post-Tensioned Foundation Systems Design Parameters for the particular foundation category designated TABLE 7 5 POST-TENSIONED FOUNDATION SYSTEM DESIGN PARAMETERS Post-Tensioning Institute (PT!) Design Parameters Foundation Category i H HI .1. •Thornthwaite Index ' S ' -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 ' 212 iii. 121-in V ..VV4.:74i_VV.. Project No. 07290-52-04 September 20, 2005 7.5.3 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. ifi, §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 thp perirneter foundation should be at least 12 inches for Foundation Category I, 18 in-ches 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: , 7.5.4 'During the construction of the post-tensioned 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 -. 7.5.5 , Foundations for Category I, .11, or III may be designed for an allowable soil bearing pressure ,of 2,000 pounds per square foot (ps (dead plus live load). This bearing pressure ' may be increased by one third for transient loads such as wind or seismic forces 1.5.6' - 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 I Where this condition cannot be avoided, the isolated footings should be connected to the building foundation system with grade beams I ' 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. 1 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.' I I Project No. 07290-52-04 ' - 9 - . September 20, 2005 H I 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. 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. Whe?e the height of the fill slope exceeds 20 feet, the minimum horizontal distanc I . shdüld be increased to H13 (where H equals the vertical distance from the top,.pf V:1i. tlièslope 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 I .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 I have been determined. Swimming pools located within 7 feet of the top of cut or fill slopes are not I 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 I recommendation applies to fill slopes up to 30 feet in height and cut slopes V . 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 I 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 I consulted for specific recommendations I 7.5.10 Exterior slabs not subject to vehiële 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 V I mesh placement. Prior to construction of slabs, the subgrade should be moisture conditioned to at least optimum moisture content and compacted to at least 90 percent of the laboratory maximum dry density. 7.5.11 All concrete slabs should be provided with adequate construction joints and/or expansion I . • joints to control unsightly shrinkage cracking. The design of joints should consider criteria of the American Concrete Institute when establishing crack-cOntrol spacing patterns. I • V , •, V V Project NOV 07290-52-04 • . - 10- • - V September 20, 2005 I -. LI I 7.5. 12 Where exterior fiatwork abuts the structure at entrant or extant points, the exterior slab should be dowelled into the structure's foundation stemwall. This recommendation is I intended to reduce the potential for differential elevations that could result from differential settlement or minor heave of the flatvork. Dowelling details should be designed by the project structural engineer., . The recommendations of this report are intended to reduce the potentilfor cracking of slabs due to expansive soils (if present), differential settlement of.de.ep, 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 I 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 I . 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. 7.5.14 If Dost-tensioned systems are used, they should be designed to resist the amount of edge lift I indicated in Table 75. Our experience ,indicates that, unless reinforcing steel is placed at the bottom of the perimeter footing and interior stiffener beams, post-tensioned slabs are susceptible to excessive edge lift, regardless of underlying soil conditions. Current PTI design procedures primarily address the potential for center lift of slabs but, because of the placement of reinforcing tendons in the top of the slab, the resulting stress eccentricity after tensioning reduces the ability of the system to mitigate edge lift I ; ..... - 7.6':"' Retaining Wails, 7.6.1 Retaining walls not restrained at the top and having a level backfill surface should be I . designed-for an 'active soil presure equivalent to the pressure exerted by a fluid'density of. 35 pounds per cubic foot (pet): 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 50: For those lots with I .finish grade soils having 'an Expansion Index greater than 50 and/or 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 0.00IH (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 , Project No. 07290-52-04 - I I - ' September 20, 2005 loads within a horizontal distance 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 less than 50) 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. 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 90 or less. The proximity of the foundation to the top of a slope steeper than 3:1 could impact the allowable soil bearing pressure. Therefore, Geocon Incorporated should be consulted where such a condition is anticipated; The location of the wall footings, however, should comply with the - recommendations presented in Section 7.5.9. Lateral Loads'-,- 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' 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. I 7.72 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. Project No, 07290-52-04 -12 - ' September 20, 2005 H I I / 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' he'dVy rainfall, excessive irrigation or the migration of subsurface sepage. Thb disturbanc'ç 'áhd/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 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. I 7.9 Site Drainage I 7.9.1. Adequate drainage is cri9cal to reduce the potential for differential soil movement, erosion, and subsurface seepage Under no circumstances should water be allowed to pond adjacent I to footings or behind retaining walls The site should be graded and maintained such that S urface 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 I 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 ôutoff wall along the edge of the pavement that extends at least 6 inches below the bottom of the base material. Project No. 07290-52-04 ,. - 13 - September 20, 2005 I I I I I: I El 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. 07290-52-04 HI '' — RD 'VVV% \ $EUiT8ll8 / 'o I ESTWO EEWH:\aD RORVL COSTIOS II I 2 6' J 3 PASEO-6U1168 BAN*1 '-'o 4> mATS C#IAAS ' 4> 1\ P65W GIWITO I;VIA mAT) S4V '.,, 2 VIA SHAPATIA V II V 1 / 4 - / 5 '-- 6 P45W ENSIILW PATES PICADOR T's5A RAn GIPOSTA 8 I0A ... 1 I' DR / 9 P4360 SAU8EW -' CARRJLLO PARK 0 VV. V - US - \ \ / V EVAS\VVV - 7 ,, cWCHO ' /'_.ATpA06 c0V<O\ II APA ( flfl V V . EVV ..V:VVV. V - -- - / VI ,AV V 'jAO 49,.. ç\- GYT' •I mn/A 'LA4stO\ II .VVV_VVV\'V . S 6H -- I VIA PATAnIA kT- ojoCORThS eo 23 - • V VS ' 24 / / V• JVVVVS4) X/ 7VV.._3 o: / LA COSTA V - RESORT S53/ c' ' 17-44 12760 '& ST sI ØS. 3J\ rl / VtI V 5JV 'cI/1l UI 5, ELT/ 036 5' V1 SV Ll BEL ST V V V ," <SS /•P4 I V'• \_V fIQ % r.-j IAARAJ ILA PL t; 2 VIA CALDRON ZODIAC ycDERO h\ \) J/ CIE T Co 6 ASS TOW/GA siJ V 20 AOJAIAOVALENCIA 2(OSSO4>c.) OIET zr VIAI/OA / S .V77SSV S4 EST BLUFF \ 1L0C 25 = V ER8IA /0A l :PKWY ALGA - 30. Ci TI ao CT ~ARINGA 31 CANfE LA COSTA RESORT SPA VISTA- 'I So PAW 4 I All I V / SOURCE: 2005 THOMAS BROS. MAP • SAN DIEGO COUNTY, CALIFORNIA REPRODUCED WITH PERMISSION THIS MAP IS COPYRIGHT BY THOMAS GRANTED BY THOMAS BROS. MAPS. BROS. MAPS. IT IS UNLAWFUL TO COPY NO SCALE OR REPRODUCE ALL OR ANY PART THEREOF, WHETHER FOR PERSONAL USE OR RESALE, WITHOUT PERMISSION. GEOCON INCORPORATED GEOTECHNICAL CONSULTANTS 6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121-2974 PHONE 858 558-6900 - FAX 858 558-6159 JH/AML 7 osii0000 6/GEOT4JPtATfl/GVKMP.DWG,4 VICINITY MAP VILLAGES OF LA COSTA - THE RIDGE NEIGHBORHOOD 2.3 AND 2.4 (SOUTH) CARLSBAD, CALIFORNIA DATE 09-20-20057 0JEcTN0.072905204 1 FIG.1 GROUND. - SURFACE. RETAINING WALL - - . . 3/4CRUSHED .-V GRAVEL H F MIRAFI 140 IN FILTER FABRIC 14. 4 . . - . . 2/3 H - . - .. ' .;. 4.4 .• \ - I - ' 4< : 4 DIA. PERFORATED SCHEDULE 4O PVC PIPE - - . -. - T - - -. NOTES: . 1......PVC PIPE TO DRAIN AT A MINIMUM GRADIENT OF 1% AND CONNECT TO A SUITABLE OUTLET. 2......WALL DRAINAGE PANELS SUCH AS MIRADRAIN OR EQUIVALENT MAY BE * USED IN LIEU OF EXTENDING GRAVEL TO TWO-THIRDS THE WALL HEIGHT. NO SCALE RETAINING WALL DRAINAGE DETAIL GEOCON .;. Qi INCORPORATED GEOTECHNICAL CONSULTANTS 6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121- 2974 PHONE 858 558-6900 - FAX 858 558-6159 JH/AML - DSKIE0000 VILLAGES OF LA COSTA - THE RIDGE NEIGHBORHOOD 2:3 AND 2.4 (SOUTH) CARLSBAD, CALIFORNIA DATE 09-20-2005 1 PROJECT NO. 07290 -52 -04 1 FIG. 2 U RE1WALLDWG/ - - 1 . . - .*,-•- TABLE I. SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS AND FOUNDATION CATEGORY, THE RIDGE, NEIGHBORHOODS 2.3 AND 2.4 (SOUTH), LOT NOS. I THROUGH 48 Lot Approximate Approximate Expansion Foundation No. Pad Condition Maximum Depth of . Index Category Depth of Fill Differential Fill Fill .17 '- 9 23 I 2 Fill 22 6 23 II 3 Fill 18 . 2 23 I 4 Fill 20 7 23 II 5 Fill 22 8 23 II 6 'Fill 19 7 15 I 7 Fill ' 20 10 15 II 8 Undercut due to 18' 12 15 11 cut/fill transition 9 Undercut due to 6 15 I cut/fill transition 10 Undercut due to. 8 ' 5 26 'I cut/fill transition . 11 Undercut due to 14 10 26 II cut/fill transition 12 Undercut due to 23 - 17 26 II cut/fill transition 13 Undercut due to 23 17 26 II cut/fill transition 14 Undercut due to 3 0 I cut/fill transition ' : •' ' 15 Undercut due to . ' .10 0 cut/fill transition 16 Fill . 14 . 8 0 I 17 Fill' 18 7 0 I 18 Undercut due to 16 ' 12 0 'I cut/fill transition . 19 ' Undercut due to 15 12 0 II cut/fill transition 20 Undercut-due o ' ö" 27 cut/fill transition . 21 Fill . 30 ' 13 4 . II 22 Fill' 30 . 13 Project No. 07290-52-04 . September 20, 2005 TABLE I (Continued) SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS AND FOUNDATION CATEGORY THE RIDGE, NEIGHBORHOODS 2.3 AND 2.4 (SOUTH), LOT NOS. I THROUGH 48 Lot Approximate Approximate Expansion Foundation Pad Condition Maximum Depth of No. Depth of Fill ' .' Differential Fill Index Category 23 Fill 4L'30. 15 4 II Undercut due to 24 cut/fill transition 14 11 4 II - Undercut due to . 25 cut/fill transition 14 ' 9 4 . I Undercut due to 26 cut/fill transition 24 18 0 II Undercut due to 27 cut/fill transition 21 17 0 II Undercut due to 28 cut/fill transition 13 10 . 0 II 29 Fill 16 -. 4 0 I 30 Fill '16 4 1 I 31 Fill 14 1 1 I 32 Fill 19 5 1 I 33 Fill 20 .''16..- .34 Fill 41 17 0 II 35 Fill 30 12 0 II 1 36 , Fill .. 25 ' . - 8' ' ' 0 II. . 37 - . Fill. 27 11' 0 38 . . Fill 28 , 11 . ' 0 . II '39 Fill 28 . 13.' ' 0 , ' JJ 40 " Fill 24 8 . 0 II 41 Fill 25 10 '0 II 42 Fill , 29 14 . 0 II 43 . Fill 30 ' . 12 0 ' II 44 Undetcutdue.to 17 -'--- cut/fill transition --1-4--'-'--I ----II Project No. 07290-5,2-04 September 20, 2005 TABLE I (Continued) SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS - AND FOUNDATION CATEGORY THE RIDGE, NEIGHBORHOODS 2.3 AND 2.4 (SOUTH), LOT NOS. I THROUGH 48 Lot Approximate Approximate Expansion Foundation No. Pad Condition Maximum Depth of Index Category. Depth of Fill Differential Fill Uñderiidite to 45 cut/fill transition 12 9 1 I 46 Undercut due to 11 1 I cut/fill transition 47 Fill ' 20 8 1' II 48 Fill 26 15 1 II / TABLE II SUMMARY OF WATER-SOLUBLE SULFATE LABORATORY TEST RESULTS CALIFORNIA TEST 417 Sample No. Water-Soluble Sulfate (%) , Sulfate Exposure Lot Nos. -.El 2 0 005 Negligible 1 through 5 El 3 010 04 Negligible 6 through 9 El 4 :'0.006. Negligible 10 through 13 El 5 0 020 Negligible 21 thr oug4 25 E1,6 .0.004- Negligible 14 through 17 E17 ' , ,0.005 ".-. '' 'Negligible ' , 18 through 20 El 8 , ' 0.018 ' , ' Negligible ' '26',through'29 El 9 " 0.005 ' - ' Negligible 30 through 33 El 10 , ' 0.010 'Negligible ' 34 through 38 El 11 , 0.004 ' ' Negligible 39 through 43 El 12 ' ' 0.002 ' ' ' Negligible , 44 through 48 Project No. 07290-52-04 ' September 20, 2005