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HomeMy WebLinkAboutCT 01-09; LA COSTA TOWN SQUARE COMMERCIAL; UPDATED PRELIMINARY GEOTECHNICAL REPORT; 2000-10-20c-çoi GP1 1:1 Geotechnical • Geologic Environmental 5741 Palmer Way .• Carlsbad California 920081 • (760) 438-3155 • FAX (760) 931-0915 October 20, 2900 W.O. 2938-A-SC Red Crow Properties, Inc. 1947 Camino VidaRoble, Suite 104 Carlsbad, California 92008 Attention: Mr. Bill Shirley Subject: Update Preliminary Geotechnical Report, La Costa Town Center, LA Costa Avenue and Rancho Santa Fe Road, LalCosta, City of Carlsbad, California Reference:. "Preliminary. Geotechnical Study Up Pirrels S.E. 13. and 25 Acres Easterly of La Costa Avenue and Rar Santa Fe Road, La Costa, City of Carlsbad, California," W.O. 1074-SD, d June 6, 1990 by GeoSôils, Inc. Dear Mr. Shirley: . . In accordance with your request, GeoSoils, Inc (GSI) has performed a geotechnical update of the subject site. The purpose of the study was to review existing site conditions relative to the proposed development and the onsite soils and geologic conditions from a geotechnical viewpoint. Unless speôifically suprceded. in the text of this report, recommendations presented inthe above rëferencd report are considered valid and applicable.. . . . . SCOPE OFSERVICES The scope of our services has included the following: Review of the above reMrenáed report: Geologic site reconnaissance General areal seismicity update evaluation. 4; Engineering and geologic analysis of data and preparation of this report. SITE CONDITIONS/PROPOSED DEVELOPMENT 2OOiindicated that site conditions have not substantially changed since the completion Of the referenced report. Noted changes are relatedjto underground utility placement along Rancho Santa Fe Road, which trends through the western portion of the property (Figure 1) It is our understanding that planned site development will consist of site preparation for the construction of single. family residential structures and a commercial' development. Foundation loads are anticipated to be typical for thistype of relatively light construction. Sewage disposal is anticipated to be tied into the regional system. FAULTING AND REGIONAL EISMICITY Failting The' site is situated in a region of active as well as ptentiaIly-active faults. Our review indicates that-there are no known active faults crossing the site within the-areas proposed for development (Jennings, 1994), and the site is not within an Earthquake Fault Zone (Hart and Bryant, 1997). There are a number of faults in the southern California rea that are considered, active and would have an effect on the site in the'form of ground haking, should they be the source of an earthquake (Figure 2). These faults include--but; ire not limited to--the 'San 'Andreas fault, the San Jacinto fault, the Elsinore fault, the Coronado Bank fault zone, and the Newport-Inglewood - Rose Canyon fault zone. 'The possibility of ground. acceleration or shaking at the site may be considered as approximately similar to the. southern California region as a whole. The following table lists the major faults and fault zones in southern California that could have a significant effect on the site should they experience significant activity.. ABBREVIATED FAULT NAME I APPROXIMATE DISTANCE . MILES Coronado Bank-Agua Blanca 22 (75.4) Elsinore , . ' 24 (38.6) ' La Nación ' 17 (27.4) Newport-Inglewood-OffshOre ' . 13 (20.9) Rose Canyon . 7(11.3) San Diego Trough-Bahia Sol. 33 (53.1) Red Crow Properties, Inc. W.O. 2938-A-SC La Costa Town Center October 20, 2000 fi1e:e:\wp7\2900\2938a.upg Page 2 Eiocoiic. Inc 1W 33- -. .- - - 7f_ •- --- - - -N331 CreeL- ------•-- • •./ '• t-=l )j rt' : NU _ To Cant \1 335-- • - - -. f•i • •-'j/-- OWAII - ,_' ,Iç :l \- H "- • - \ - 4 6---- - ) N33 A. jiXr P ' r' A11r -4 A W _V' 'I NV . - Base Map: Rancho Santa Fe Quadrangle, California--San Diego Co., 7.5 Minute Series (Topographic) 1968 (photo revised 1983), by USGS, 1":2000' 0 1/2 1 Il/ Scale ' Miles Reproduced with permission granted by Thomas Bios. Maps. This map is 'copyrighted by Totnas Bros. Maps. it Is unlawful to copy or reproduce all or any part thereof, whether for personal use or resale, without permission. All W.O. "Ij SITE LOCATION MAP -' Figure 1 - IIis_;. - I I SAN FRANCISCO LCES SITE LOCATION (+): Latitude -• 33.0817 N Longitude - 117.2333 W La Costa Town Center W.O. 2938-A-SC • CALIFORNIA FAU'L Figure 2 tpoSniic. Inc. I, Seismicity The acceleration-attehuation.reiations of .Joyner' and Boore (1982), Campbell and Bozorgnia (1994); and Sadigh and others (1987) have been incorporated into EQFAULT (Blake, 1997). For this study, peak horizontal ground accelerations anticipated at the site were determined based on the random mean and mean plus 1 sigma attenuation curves developed by Joyner and Boore (1982), Campbell andB'ozorgnia (1994); and Sadigh and others (1987). These acceleration-attenuation relations have been incorporated in EQFAULT, a computer program by Thomas F. Blake (1997), which performs deterministic seismic hazard analyses using up to 150 digitized .Calif prnia faults as earthquake sources: The program estimates the closest distance between each fault and the subject site. If a fault is found to be within a user-selected radius, the brogram estimates peak horizontal ground acceleration that may oc cur :t,1he site from the upper bound ("maximum credible") and "maximum probable" earthquakes on that fault. Site acceleration, as a percentage of the acceleration df gravity (g), is computed 'by any of the 14 user-selected acceleration-attenuation relations that are contained in EQFAULT. Based on the above, and using a radius of 100 mites ¶or search, peak horizontal ground accelerations from an upper bound 'earthquake may be on the order of 0.480g to 0.561g. However, peak probable horizontal ground acceieratioi may be on the order of 0.279g to 0.314g. ' Seismic Shaking Parameters Based on the site conditions, Chapter 16 of the Uniform Building Code (International Conference of Building Officials, 1997), the following seismic parameters are provided Seismic zone (per Figure 16-2') ' ' ' ' ' 4 Seismic Zone Factor, (per Table 16-1*) ., ' ' '0.40 Soil Profile Type (per Table 16-J*) ' SD**** 'Seismic Coefficient C. (per Table 16Q*)' ' ' " 0.40 N8, 0.40 N8, 0.44 Na Seismic Coefficient C,, (per Table 16.R*) , ' ' :0.40 N,,, 0.56 N, 0.64 N,, Near Source Factor N. (per Table 16.S*) , 1.0 Near Source Factor N,, (per Table 16T*) ' ' ' 1.0 Seismic Source Type (per Table 16-U') ' , B Distance to Seismic Source . .. ' '. 7 ml. (11.2 km) Upper Bound Earthquake M 6.9 Red Crow Properties, Inc. W.O. 2938-A-SC, La Costa Town Center October 20, 2000 li1e:e:\wp7\2900\2938a.upg Page 5 GeoSo us, Inc. * Figure and table references from Chapter 16 of the Uniform Building Code (1997). ** SB may be used for lots underlain by bedrock (Santiago PeakVolcanics) Sc-may be used for lots underlain by bedrock (Santiago Pek.Volcanics), where fills are more than 10 feet below the bottom of the footings.' '• S0 may be used for lots underlain byformational sedimentsl (Delmar/Lusardi Formations), or for lots where fills have been placed on formational sediments. It should be noted that the parameters above are provided for the average soil properties for the top 100 feet 'of the soil profile. The SB parameters are reasonably and conservatively justified for competent -rock with moderate fracturing and weathering based on an estimated 'shear wave velocity (a ."S" wave) of greater than 2,500 feet per second (fps) in the top 100 feet of the soil profile, as contrated to the velocities used in our seismic refraction studies. (a "P" wave). The estimated wave velocities, are about 0.58 of P wave velocities measured in our seismic refractions studies ,(Das, 1992; Hunt, 1986; and Griffiths and King, 1976). Accordingly, in accordance with the 1997 UBC, it is reasonably estimated that the shear wave, velocity for the average 6oil profile of the top 100 feet of the soil profile exceeds 2,500 fps in granitic/volcanic bedrock. ' EARTHWORK RECOMMENDATIONS Site grading should be performed in accordance with the minimum standards of the City of Carlsbad, the Uniform Buildi,ng Code (1' 997 edition) and the grading guidelines presented in the appendix. Due to the anticiDated rock Ihardness, consideration should be to at1ét 12 inths below Inwpct utility invrt elevation. Overexcaation within parkways should also be considered with respect to utility laterals. Overexdavation for rock hardness is not a geotechnical requirement. FOUNDATION RECOMMENDATIONS General The foundation design and: construction recommendations presented herein are preliminary in nature and will be:finalizéd at the completion of grading. Recommendations for residential conventional .foundation systems are provided in the following sections. The foundation systems may be used to support the prop9sed structures, provided they are founded in competent' bearing material and should be 'designed and constructed in accordance with the guidelines contained in the Udiform Building Code. All footing designs should be reviewed by the project structural engineer. The use of conventional and/or post tensioned slab foundations will be determirhed in accordance'with the criteria presented in the attached Table 1 and Table.. Red Crow Properties, Inc.. W.O. 2938-A-SC La Costa Town Center October 20, 2000 fi1e:e:\wp7\2900\2938a.upg Page 6 GeoSo its, Inc. Conventional Foundation Design Conventional spread and continuous footings my beused to support the proposed residential structures provided they are founded entirely in properly compacted fill or other competent bearing material (i.e., bedrock). Footings should not simultaneously bear directly on bedrock and fill soils. 2. Analyses indicate that an allowable bearing vake of 1500 pounds per square foot may be used for design of continuous footings per Table 1, and for design of isolated pad footings 24 inches square and 18 inches deep into properly compacted fill or bedrock. The bearing value ¶nay be increased by one--third for- seismic or other temporary loads. This value n1ay. be increased by 20 percent for each additional 12 inches,,.in depth, to a max,mu1n of 2500 pounds per square foot No increase, in bearing, for footing width is recommended. 3 For lateral'sliding resistance, a 0.35 coefficient of friction may utilized for a concrete to soil contact when multiplied by the dead load. Passive earth pressure may be computed as anequivalent fluid having a density of 200 pounds per cubic foot with a maximum earth pressure of 2500 pounds per square foot. . . When combining passive pressure and friction 61 resistance, the passive pressure component should be reduced by one-third. . . . Footings should maintain a horizontal distanc- or setback between any adjacent slope face and the bottom outer edge of the footing The horizontal distance may be calculated by usin 11/3, ?vhere (h) is the height of the slope The horizontal setback should not be less than 7 feet, nor heed to be greater than 40 feet (per code). The setback rii'ay b-riiaihtainèd b simply deepening the- footings. Flatwork, utilities orother.impróvements within a zone of h/3 from the top of slope may be subject to lateral distortion. Footings,fltwork, and utilities setbacks should be constructed in accordance with distances itjidicated in this section, .and/or the approved plans. . . . Conventional Foundation/Concrete Slab Construction The following foundation construction recommendations are presented as a minimum criteria from a soils engineering standpoint. The onite soils expansion potentials are generally in the very low to very high range, based on test results from the 1990 reference report. However, new soil samples-,should be collected and tested according to the current standards. Red Crow Properties, Inc W.0. 2938 -A -SC La Costa Town Center ,. • - October 20, 2000 fiIe:e:\wp729OO\2938a.upg . • Page 7 GeoSoils. Inc. Recommendations by the project's design-structuralengineer or architect, which may exceed the soils engineer's recommendations, should take precedence over .the ,following minimum requirements. Final foundation design will be provided based on the expansion potential of the near surface soils encountered duripg grading, and/or depths at fills constructed'.....:, .. Very Low to Low ExDansive Soils:(.ExDanslon Index 0-50 Exterior footings should be founded at a minimum.depth of 12 inches for one story, and 18 inches below the lowest adjacent ground surface for two story residential structures. Interior footings maybe founded t a depth of 12 inches below the lowest adjacent ground surface. All.footings should be reinforced with two No. '4 reinforcing bars, one placed near the top and 6ne placed near the bottom of the footing. . . . . ; A grade beam, reinforced as above, and at least 12 inches wide should be provided across large(e;g. garage) entrances. The base of the-grade beam-should be at the same elevation as the bottom of'adjoining footings. Concrete slabs, where moisture condensation i is undesirable, should be underlain by a vapor. barrier consisting of .a minimum df ten mil (or ten-mil for rocky fills) polyvinyl chloride or eqUivalè?it membrane with all laps sealed. This membrane should be laid over a mihimuthbf two inches of sand and covered with a minimum of two inches of sand (total four-inches) to aid in uniform curing of the concrete, and to protect the membrane from puncture. Concrete slabs should be a minimum of 4 inches thick, and should be reinforced with No. 3 rebar at 18 inches on center, each way. All slab reinforcement should be supported to ensure. placement near the vertical midpoint of the concrete "Hooking" is not considered an acceptable methd of positioning the reinforcement. Garage slabs should be poured separately from the residence footings and quartered with expansion joints or saw cuts. A Oositive separation from the footings should be maintained with expansion joint material to permit relative movement. Premoistening/presaturation is necessary for tiese soil conditions; hoWever, the moisture content of the subgrade soils should be equal to or greater than optimum moisture to a depth of 12 inches below gradein the slab areas Prior to placing visqueen or reinforcement, soil présaturation should be verified by this office within 72 hours of pouring slabs. Red Crow Properties, Inc. W.O. 2938-A-SC La Costa Town Center October 20, 2000 fi1e:e:\wp7\2900\2938a.upg Page 8 ;nçni1.c. Inc. Medium Expansive Soils (Expansion Index 51-9O 1, Exterior footings should. be founded at a minimum depth of 18 inches for both one- and two-story residential structures, below the lowest adjacent ground surface. Interior footings may be founded at a depth of 15 inches below the lowest adjacent ground surface. All footings should be reinforced with two No.. 4 reinforcing bars, one placed near the top and two placed near the bottom of the footing. isolated interior or exterior piers and columns are not ecommended. A grade beam, reinforced as above, and at least; 12 inches wide by 18 inches deep should.be provided across large (e.g garagé),entrances. The base of the grade beam should be at the same elevation as the bottom of adjoining footings. Concrete slabs, where moisture condensation is undesirable, should be underlain by a vapor barrier consisting of a minimum of ten mil (or ten-mil for rocky fills) polyvinyl chloride or equivalent membrane wit ti all laps sealed This membrane should be laid over a mini'mui bf two inches of sand and covered with a minimum of two inches of sand (total four inches) to aid in Uniform curing of the concrete, and to protect the membrane from puncture. . . . . •... Concrete slabs should be a minimum of 4 inches thick, and should be reinforced with No. 3. rebar at 18 inches on center, each way. All slab reinforcement should be supported to ensure placement near the vertical midpoint of the 'concrete. "Hooking" the wire.rnesh is not considered an adceptable method-of positioning theY reinforcement. . . . •. . . . . . Garage slabs should be poured separately from the residence footings and quartered with expansion jointéor saw cuts. A p:ositive separation from the footings should be maintained with expansion joint material to permit relative movement 6 Presaturation is recommndedfor these soil conditions The moisture content of the subgrade soils should be equal to or greater than optimum moisture to a depth of 18 inches below gadeiYthé slab areas. Prior to placing visqueen or reinforcement, soil presaturatior'should be verified by this office. within 72 hours of pouring slabs. . . Post-Tensioned Slab Foundation Systems Post-tensioned (PT) slabs'-may be utilized for coistruction of typical one (1) and two (2) story residential structures onsite. The information and recommendations presented in this section are not meant to supersede design by' a registered structural engineer or civil engineer familiar with post-tensioned slab design or corrosion engineering consultant.' Red Crow Properties, Inc. W.O. 2938-A-SC La Costa Town Center October 20, 2000 fi1e:e:\wp7\2900\2938a.upg Page 9 GeóSoils, Inc. 2. From a soil expansion/shrinkage standpoint, a fairly common contributing factor to. distress of structures using post-tensioned slaEs is a significant fluctuation in the moisture content of soils underlying the perimter of the slab, compared to the center, causing a "dishing" or "arching" of the! slabs. To mitigate this possible phenomenon, a combination of soil presaturatioh (if necessary, or after the project has been dormant for a period of time).and consruction of a perimeter "cut oft.wall grade beam may be employed. 3 For very low to low (E I = 0 through 50) expansive soils, perimeter and mid span beams .should be a minirnurn.12 inches deep below lowest adjacent pad grade. Perimeter beams should be a.riiinirhum of 18 inches deep for medium expansive and 24 inches deep for highly expansive soil conditions. The perimeter foundations may be integrated into the slab design or independent of the slab. The perimeter .beams should be a. minimum of 12 inches in wiith. . . . A vapor barrier should be utilized and be of sufficient thickness to provide an adequate separation of foundation from soils 1(10-mil -thick). The vapor barrier should be lapped and adequately sealed to prvide a continuous water-resistant barrier under the entire slab. The vapor barrier should be sandwiched' between. two 2-inch thick. layers Of sand (SE>30) for a total df 4 inches of sand. 4.. Isolated piers should not be incorporated into the post tension .slab system. Specific soil presatu ration for slabs is not reqiiired for very. low, expansive soils; however, the moisture contertqf the subgrade sbils should be at or above the soils' optimum moisture content to' a minimum dpth of 18 inches below grade depending on the footing embedment. . . Post-tensioned slabs should be designed using sound engineering practice and be in accordance with the Post-Tension lnstitute(PTl), local and/or national code criteria and the recommendations of a structural or civil 'engineer qualified in post- tension slab design. Alternatives to P11 methdology. may be-used if equivalent systems can be proposed which accommodate iihe angular distortions, expansion. parameters, and settlements. noted for this project. If alternatives to PTI are suggested by the structural consultant, consideration should be given for additional review by a .qualified structural PT-designer. ISoil related parameters for post- 'tensiohed slab design, are presented in Table 2. Recommendations for the, total and differential settlement will be provided when the project grading plans an (further geotechnical information) become available In accordance with guidelines presented in the Uniform Building Code, improvements, and/or footings should maintainj a horizontal distance, X, between any adjacent descending slope face and the bottom outer edge of the improvement Red Crow Properties, Inc. . . W.O. 2938-A-SC La Costa Town Center . October 20, 2000 file:e:\wp7\2900\2938a.upg Page 10 GeoSol is Inc. and/or footing. The horizontaVdistance,.X, It ay be calculated by using X = h/3, where h is the height of the slope. .X should be less than 7 feet, nor need to be greater than 40 feet. X may be. maintained by deepening the footings. Improvements constructed within a distance Of h/3 from the top of slope may be subject to lateral distortion. . Foundations for any adjacent structures, ,including retaining walls, should be deepened (as necessary) to below a 1:1 projection upward and away from any proposed lower foundation system. This recommendation may not be considered valid, if the additional surcharge imparted by the upper foundation on the lower foundation has been incorporated into the desin .of the lower foundation.. Additional setbacks, not discussed or superseded herein, and presented in the UBC are considered. valid. ddARosloN Laboratory testing for soluble sulfates, pH, and corrosion to metals have not been completed. Based upon our experience in the site vicinity, however site materials may have a moderate to severe potential for corrosion to cpncrete (i.e., sulfate content) and a severely high potential for corrosion to - exposed steel (i.e.; saturated resistivity). Preliminary testing should be completed prior to grading. Upon completion of aradinçi. additional tctinp of soils (including import. materials) is recommended prior to the construction of utilities and foundations. Further evaluation by a qualified corrosion engineer may be considered. Accordingly, the use of Type V concrete with a modified'water/cement ratio cannot be precluded. DEVELOPMENT CRITERIA Landscape Maintenance and Planting Water has been shown to weaken the inherent strength of soil and slope stability is. significantly reduced by overly wet conditions. Positive'surface drainage away from graded slopes should be maintained and only the amount of irrigation necessary to sustain plant life should be provided for planted slopes. Overwateing should be avoided. Graded slopes constructed within and utilizing onsite materials would be erosive. Eroded debris may be minimized and surficial slope stability enhanced by establishing and maintaining a suitable vegetation cover soon after construction. Plants selected for landscaping should be light weight, deep rooted types which require little water and are capable of surviving the prevailing climate. Compaction to the face of fill slopes would Red Crow Properties, Inc. W.O. 2938-A-SC La Costa Town Center October 20, 2000 fi1e:e:\wp7\2900\2938a.upg Page 11 C.P-nSails. liw. tend to minimize short term erosion until vegetation. is established. In order to minimize erosion on a slope face, an erosion control fabric (i.e. jutle matting) should be considered. From a geotechnical standpoint leaching is not recommended for establishing landscaping. If the surface soils area 'processed for the,purpose. of adding amendments. they should'be reoompacted tô95 percent relative corrpaction; . . Additional Site Improvements Recommendations for additional grading, exterior concrete flatwork design and construction, including driveways, can be provided upon request. If in the future, any additional improvements are planned for the site, recommendations concerning the geological orgeotechnical aspects of design and construction of said improvements could be provided upon request.. 0 , Trenching All footing trench excavations fortrt36tures and walls si ould be. observed and approved by a representative of this office prior, to placing reinfor ement. Footing trench spoil and any excess soils generated from utiIitLtrench. excava ions should be compacted to a minimum relative compaction of 90'peràent if not remo ed from the site; All excavations should be observed by one of our representatives and conform to CAL-OSHA and local safety codes. GSI does not consult 'iii the area of safét engineers. . . In addition, the potential for encountering hard spots'.during footing and utility tre nch excavations should be anticipated. If these Ooncretions are encountered within, the proposed footing trench, they should be removed, which, could prodUce larger excavated areas within the footing or utility trenches. Drainage Positive site drainage should be maintained at all times; Drainage should not flow uncontrolled down, any descending.sIope. Water 'Should be directed away from foundations and not allowed to pond and/or seep into the ground Pad drainage should be directed toward the street o'r'oth0'r approved area Roof gutters and down spouts should. be considered to control roof dainage. Down spouts should outlet a minimum of 5 feet from.the proposed structure or into a subsurface drainage system. We would recommend that any proposed open bottom planters ac jacent to proposed structures be eliminated for a minimum distance of 10 feet. As an alternative, closed bottom type planters could be utilized. An outlet placed in-the bottorii of the planter, could be installed to direct drainage away from structures or any exterior iconcrete flatwork. Red Crow Properties, Inc. W.O. 2938-A-SC La Costa Town Center October 20, 2000 fi1e:e:\wp7\2900\2938a.upg Page 12 t2ncg)flc hit' PLAN REVIEW Project grading plans should be reviewed by'this office as they become available. Based., on our review, supplemental recommendations and fuçther geotechnical studies specific to the proposed grading configuration (s) will ' likely. be teàommended. Further fieldwork will require disturbance and removal of vegetation LIMITATIONS' The materials observed on the project site and the referenced reports reviewed are believed to be generally representative of the area; however, soil and bedrock materials vary in character between excavations and natural outcrops or conditions exposed during mass grading. site conditions may vary due to seasonal changes or other factors. GSl assUmes no responsibility or liability for work, testing or recommendations performed or provided by others. The scope of' work was perfornped within the limits of a budget.' "Inasmuch as our' study is based upon the site materials observed, selective laboratory testing and engineering analysis, the conclusion and recommendations are professional opinions These opinions have been derived in accordance with current standards of practice and no warranty is expressed or implied. Standards of practice are subject to change'with time Red Crow Properties, inc. W.O. 2938-A-SC. La Costa Town Center October 20, 2000 fi1e:e:\wp7\2900\2938a.upg Page 13 GeoSoils, Inc. The opportunity to be of service is sincerely appreciated. If you should have any questions, please do not hesitate to contact the underigned at 760/438-3155. Respectfully submitted, GeoSolls, Inc. Saadyt,41(arhan, Ph.D. P 10. Project Engineer Edward lip LUMP Engineering Geologist, CEG 192 OFci.7 SSF/EPL/JPF/DWS/sw Reviewed b C. avid W. Skelly V Civil Engineer, ACE 4785. Attachments: Table 1.- Conventional Foundation Recommendations Table 2 - Post Tensioned Foundation Reàornmendations Appendix - References Distribution: (4) Addressee Red Crow Properties, inc. W.O. 2938-A-SC La Costa Town Center October 20, 2000 file:e:\wp7\2900\2938a.upg Page 14 GeoSOIls. Inc. TABLE 1 Preliminary Conventional Perimeter Footings and Slab Recommendations for La Costa Town Square FOUNDATION MINIMUM .. INTERIOR. REINFORCING - INTERIOR SLAB UNDER-SLAB CATEGORY. FOOTING.. SLAB.... STEEL REINFORCEMENT TREATMENT. SIZE . 1 THICKNESS . . .. .-. . - I 12" Wide 4 "Thick 1- #4 Bar Top #3 Bars 2" Sand Over 10- x . and Bottom @ Mil Polyvinyl 12' Deep : 18" o.c. Membrane Over Both Directions 2" Sand Base II 12" Wide 4" Thick 2- #4 Bars Top #3 Bars 2" Sand Over 10- • x . and Bottom @ Mil Polyvinyl 18' Deep 18" o.c. Membrane Over Both Directions 2" Sand Base ill Use Post-Tensioned Slab, see Table .(2) for design parameters. Category Criteria Category I: Max. Fill Thickness is less than 20' and Expansion Index Is less.than or equal to 50 and Differential Fill Thickness is less- than 10' (see note- FT-Category Ii: Max. Fill Thickness is less than 50 and Expansion Index is less than or equal to-90 or Differential Fill Thickness is between 10 and 20'. (see note 1). Category Ill: Max. Fill Thickness exceeds 50', or Expansion Index exceeds 90 but is less than 130, or Differential Fill Thickness exceeds 20' (see note 1). Notes: 1. Post tension (PT) foundations are required where maximum fill exceeds 50', or the ratio of the maximum fill thickness to the minimum fill thickness exceeds 3:1 Consideration should be given to using post tension foundations where the expansion Index exceeds 90. Footing depth measured from lowest adjacent subgrade. . . . Maximum allowable soil bearing pressure is 2,000 PSF (see notes of Table 2). Concrete for slabs and footings shall have a minimum compressive strength of 2,000 PSI-(2,500 PSI for exterior flatwork), or adopted UBC mm., at 28 days, using 5 sacks of cement. Maximum Slump shall be 5'. . • Visqueen vapor barrier not required under garage slab. However, consideration should be given to future uses of the slab area, such as room conversion and/or storage of moisture-sensitive materials. . Isolated footings shall be connected to foundations with grade beams. Sand used for base under slabs shall be very low expansive, and have SE > 30. • - •• All slabs should be provided with weakened plane joints to control cracking. Joint spacing should be In accordance with correct industry standards and reviewed by the project structural engineer. . . • 1' TABLE 2 PRELIMINARY POST TENSION SLAB lION RECOMMENDATIONS, LA COSTA TOWN SQUARE Expansion Index . .. ............. . Foundation Category* I (PT) Very Low to Low .:_:..'(050) . 11 (PT) Medium (51-90) . :. III (PT) High (>90) . ... Perimeter footing embedment - . . . .12" . . 18" (w/premoistening) (24". (w/premoistening) Allowable bearing value 1200 pf** . 1 2Ô0. psf** 1200 psf**. Modulus of subgrade reaction 100 pci/inch •. 75 pci/inch . 75 pci/inch Coefficient of friction 0.35 . 0.35 0.35 Passive pressure 200 pcf 200 pcf . 200 pcf: Soil suction (Pt) . 3.6 . 3.6 3.6 Depth to constant soil suction 5 feet 5 feet . 5 feet Thornthwaite moisture index -20.0 inches/year -20.0 inches/year . -20.0 inches/year em edge . 2.5 feet 2.7 feet 3.0 feet em center . . 5.0.feet 5.5 feet .5.5 feet ym edge 0.35 inches 0.5 inches 0.75 inches Ym center . . 1.1 inches 2.0 inches . . 2.5 inches. *Preliminary values. for differential settlement A re included in the text of this report. **Intemal bearing values within the perimeter of the Post-tension slab may be increased by 20 percent for each additional foot of embedment (beyond 6" surface subgrade for perimeter footings adjacent to landscape areas) to a maximum value of 2500 psf. •. . • APPENDIX REFERENCE Blake, Thomas F. 1997, EQFAULT computer program and users manual for the deterministic prediction of horizontal acceleratibns from digitized California faults. Campbell, K.W. and Bozorognia, Y.' 1994, "Near-Sburce Attenuation of Peak Horizontal Acceleration from Worldwide AcceIerograms Recorded from. 1857 to. 1993," Proceedings, Fifth U.S. National Conference oh, Earthquake Engineering, Vol. III, Earthquake Engineering Research Institute, pp. 283292: . Das,.B.M., 1993, Principles of soil dynamics, published.by PWS-Kent Publishing Company. GrensfeIder, R. W., 1974, Maximum credible rock acceleration from earthquakes in California: California Division of Mines and Geàlogy; Map Sheet 23. Griffiths, D.H. and King, R.F., reprinted 1976, Applied geophysics for engineers and geologists, published by Pergamon Press. Hart, E. W. and Bryant W.A., 1997, Fault rupture hazard zones in California, Alquist-Priolo earthquake fault zoning act with index to earthquake fault zone maps, California Division of Mines and Geology, Special Publication 42, undated Housner, G. W. 1 970, Strong ground motion in Earthquake Engineering, Robert Wiegel, ed., Prentice-Hall. . . Hunt, R.E.,. 1986, Geotechnical engineering analysis and evaluation, published by McGraw-Hill Book Company. Idriss, I. M. 1994, Attenuation Coefficients for Deep and Soft Soil Conditions, personal communication. • • 0 • • 0 International Conference of Building Officials, 1997, Uniform building code: Whittier, California. 0 GeoSoils Inc.