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HomeMy WebLinkAbout; La Costa Vale Unit 3; Soils Report; 1984-05-07SAN MARCOS ENGINEERING CIYIL ENGINLEIIS. 501LS * FOUND*TIOI( Preliminary Soils Investigation & Report for Proposed Residential Pad Lot #432 La Costa Vale, Unit No. 3 SAN MARCOS ENGINEERING ClYlL ENGINLC”I. s011* * rOUND.TlOr.4 May 7, 1984 Mr. Elliott Edelman 2311 Caringa Way No. 46 Carl&ad, CA 92008 Re: Proposed Residential Pad Lot #432, La Costa Vale Unit No. 3 Dear Mr. Edelman, As per your request, we have performed a preliminary soils investigation on the above referenced lot and this report represents our opinion regarding the site soils engineering factors that may affect your proposed project. Summary of Report It is our opinion that the existing site soils can safely support the proposed residential structure planned for the site provided the recommendations presented herein are fol- lowed. Description of Site The site is designated as Lot #432 of La Costa Vale Unit Noi 3 Development and one of the ungraded and unclassified lots per the report of Benton Engineering, Inc. dated Feb- ruary 4, 1977. The lot fronts Piragua Street and is va- cant. It slopes in a Southwesterly direction towards Pi- se0 MULmEFI- DrnWL. ,UIII . SAN MARCOS ENGINEERING ClVlL ENGINEEIIS. SOIL, * FO”ND.TlOr.4 ragua Street at an inclination of about 22%. Plate 1 shows the vicinity map of the project. Prooosed Development The proposed development of site calls for a 2-story resi- dential framed stucco with tile roof house to be sited on a side-hill cut and fill. Portion of the house will be on a slab while a portion will be on raised floors. It is anti- cipated that grading will be necessary to achieve the deve- lopment. Puroose of the Investication The purpose of the prliminary investigation is to determine the following: 1. The physical condition and characteristics of the site soils, 2. Presence of expansive soils, 3. Feasible foundation system, and to make foundation recommendations. Field Soil InvestiqatiDn Program Three test pits were excavated on May 1, 1984 on the project site at the approximate location shown in Plate 2 and marked as T-l, T-2, and T-3 using a backhoe. The field investiga- . -2- ” . 380 MUL.cRm” Dlwr. ,“lll . SAN MARCOS ENGINEERING ClVlL ENG,NLL”S. SOILS * FOUNDITlON tion was conducted under the supervision of a soils engineer. The soils encountered were visually classified according to the Unified Classification System and logged. The soil sam- ples were secured and brought to the lab for testing and clas- sification. The log of the soils are shown as Plates 3, 4, and 5. The subsurface soils can be generally described as about 2 to 3 feet of brown silty to sandy clay, some shale rock and overlying dry to moist light brown to tan sandy clay and shale rock. The shale rock appears to be rippable to an approxima- ted depth of 4 feet but the total depth of rock could not be determined at this time. The excavations were done to a depth of 4 feet. The soils appear to be compact to very compact. Laboratory Soils Testinq A maximum dry density test was performed on the brown silty clay material taken from T-l at 1.5 feet of depth as per ASTM D-1557 and the results indicate the soils to have a maximum dry density of 115 pcf at an optimum moisture content of 12.5%. From our experience of similar type soils in the general area, the,soils can be classified as expansive. -3- 380 MULBC”“” DrnIVri. su,r= . SAN MARCOS ENGINEERING ClWL EHOIHL.... soaL* * F0UND.TIc.N Conclusion and Recommendations ,- 1. It is our opinion that the existing soils can safely support the proposed developmental structures planned for the site. However, the following recommendations need to be observed during the design and construction of the proposed projcet. 2. The existing natural ground surface, which is moderately expansive, can safely support soil bearing pressure of 1800 psf. Footing should be at least 18 inches wide and the bottom of the footing should be at least 24 inches below adjacent finish grade. Wall footings should be continuously reinforced with 1-#5 bar placed 3 inches above the bottom of the footing and 1-#5 bars placed 2 inches below the stem of the footing or floor slab. Isolated footings should be avoided whenever possible. If it is necessary, however, to have isolated footings, the minimum dimension should be 24" square and rein- forced with 344 bars placed both ways. 3. Slabs on grade should have a minimum thickness of 4 inches and reinforced with welded wire mesh placed at mid-depth of the slab. The slab should be underlain by 4 inches of granular material placed over a 6-mil vapor barrier which is underlain by an inch of sand all placed on the subgrade. -4- JBO MUL.TRwT DI1t"r. ,U,Irn I _ _ _ _ _ _ _ . . .-._ -. . ^.._ SAN MARCOS ENGINEERING CIYIL ENGIHLIIIS. SOIL. * FouNoIllon .- 4. Prior to the pouring of concrete for the slab, the sub- grade should be wetter at least 1 to 3 percent greater than the optimum throughout the top 3 feet below finish grade. 5. It is possible that rocks will be encountered at site during the grading operations. It is observed from the test pits, however, that the upper 3 to 4 feet is ripp- able. Boulders could likewise be encountered which would require blasting in order to make moving the boul- ders more manageable. 6. It is anticipated that fill will be imported to the site to build up the required building pad as per the grading plans prepared by Schatzmann, Thompson and Associates. The attached Recommended Earthwork Specifications shown in Appendix A is applicable for the filling operations. 7. Footings placed in fill areas shouls be positioned such that the edge of the footing will have at least 5 feet clear horizontal distance from daylight at the slope thus shown: SAN MARCOS ENGINEERING CWlL ENGINrL”,, 301LS * FOUNDITION 8. ~11 surface drainage should be directed away from the foun- dation system positively. 9. The source of borrow for the proposed fill operation has not been determined at this time. The soils engineer should be informed prior to hauling same to the project site so that an evaluation of the material can be made at that time as to its strength and allowable soils bearing pressure placed at site. It is suggested for design purposes of the footings that the value of 1800 psf be used in the design as indicated in paragraph 2 of this recommendations above. 10. Further recommend that the plans show key benching of the slope where fill is proposed to be built up. The typical benching is shown in Appendix A. 11. If during construction soils different from the type mentioned in this report are encountered at the site, the soils engineer should be informed so that the proper evaluation of said soils can be performed. If you have any questions, please call us at (619) 744-0111. Very truly yours, Distribution: (4) - Addressee SME/ck 380 MUL.LRe" DIWr.. s,,,r. . _... .._ --_ _. _---- .-._ -. -... SAN MARCOS ENGINEERING CWL Ef”OINSI”,. ,OIU . FOUHDIIION Project: EH39 n Residential House Pad La Costa Vale No. 3 VICINITY MAP No Scale Reference: Thomas Bros. Map Page 20 D-5 Cadencia/Piragua La Costa, Carlsbad PLATE 1. Location Plan ,eo UUL.C..I O.WI. ,“I’I . SAN MARCOS ENGINEERING CWlL CNOINII”.. se,u a CQ”ND.IlOIl Material d Remarks I I I I I ~~ I ! ! ! ! /I Ycq 1 --, - SAN MARCOS ENGINEERING CWlL LNOINLX”.. SO,” L CO”NO.IIOPI 1ao N”L.I”mv D”WS. SUIT.. Swing No. Fz ,.N HA”CO,. 5. ,ao.. ’ ld,Sl 74..0111 Sheet No./ot/ Material a Remarks . SAN MARCOS ENGINEERING ClYlL LNalNlm”.. SQI” a CC”lrD.IlOlr 3eo M”L.S”mv O”IYS. SUIT. l SAP4 LI.“COS. CA .s0.. 1s191 74..01*1 Boring No.= She.1 No.+.ot+ CONTRACT NO. SAN MARCOS ENGINEERING Civil Enginmr 380 wbc-y or. SUM 8 SAN MARCOS. CAliFORNIA 92069 (619) 744-0111 APPENDIX A RECOMMENDED EARTHWORK SPECIFICATIONS 1. General Description. The objective is to obtain uniformity and adequate internal strength in filled ground by proven engineering procedures and tests so that the proposed structures may be safely supported. The pro- cedures include the clearing and grubbing, removal of existing structures, preparation of land to be filled, processing the fill soils, filling of the land, and the spreading and compaction of the filled areas to conform with - the lines, grades, and slopes as shown on the approved plans. The owner shall retain a Civil Engineer qualified in Soil Mechanics (herein referred to as Engineer) to inspect and test the filled ground as placed to verify the uniformity of compaction of filled ground to the specified 90 percent of maximum dry density. The Engineer shall advise the owner and grading contractor immediately if any unsatisfac- tory conditions are observed to exist and shall have the authority to re- ject the compacted filled ground until such that as corrective measures are taken, necessary to comply with the specifications. It shall be the sole responsibility of the grading contractor to achieve the specified degree of compaction. 2: Clearing, Grubbing, and Preparing Areas to be Filled. (a) All brush, vegetation, and any biodegradable refuse shall be re- moved, piled, and burned or otherwise disposed of so as to leave the areas to be filled free of vegetation and debris. Any uncompact- ed filled ground or loose compressible natural ground, shall be removed unless the report recommends otherwise. Any unstable, swampy, or otherwise unsuitable areas shall be corrected by draining or removal, or both. (b) The natural ground which is determined to be satisfactory for the support of the filled ground shall then be plowed or scarified to a depth of at least six inches (6”). and until the surface if free from ruts, hummocks, or other uneven features which would tend to prevent uniform compaction by the equipment to be used. (c) After the natural ground has been prepared, it shall then be brought to the proper moisture content and compacted to not less then 90 percent of maximum density in accordance with the A. S. T. M. D1557-70 method which uses 25 blows of a 10 pound rammer falling 18 inches on each of 5 layers in a 4 inch diameter 1139 cubic foot ,cylindrical mold. - Page 2 RECOMMENDED EARTHWORK SPECIFICATIONS (CONT.) (d) Where fills are made on hillsides or exposed slope areas, with gradients greater than 10 percent, horizontal benches shall be cut into firm undisturbed natural ground in order to provide both lateral and vertical stability. This is to provide a horizontal base so that each layer is placed and compacted on a horizontal plane. The initial bench at the toe of the fill shall be at least 10 feet in width on firm undisturbed natural angle of repose or de- sign slope. The Engineer shall determine the width and frequency of all succeeding benches which will vary with the soil conditions and the steepness of slope. 3. Materials and Special Requirements. The fill soils shall consist of select materials free from vegetable matter, and other deleterious substances, and shall not contain rocks or lumps greater than 6 inches in diameter. This may be obtained from the excavation of banks, borrow pits or any other approved sources and by mixing soils from one or more sources. If excessive vegetation, rocks, or soils with inadequate strength or other unacceptable physical characteristics are encountered, - these shall be disposed of in waste areas as shown on the plans or as directed by the Engineer. If, during grading operations, soils are found which were not encountered and tested in the preliminary investigation, tests on these soils shall be performed to determine their physical characteristics. Any special treatment recommended in the preliminary or subsequent soil reports not covered herein shall become an addendum to these specifications. The testing and specifications for the compaction of subgrade, subbase, and base materials for roads, streets, highways, or other public property or rights-of-way shall be in accordance with the standards of the governmental agency having jurisdiction. 4. Placing, Spreading, and Compacting Fill Materials. (a) 62) (d) When the moisture content of the fill material is below that spe- cified by the Engineer, water shall be added in the borrow pit until the moisture content is near optimum to assure uniform mix- ing and effective compaction. When the moisture content of the fill material is above that spe- cified by the Engineer, resulting in inadequate compaction or un- stable fill, the fill material shall be aerated by blading and scarifying or other satisfactory methods until the moisture con- tent is near optimum as specified. After processing, the suitable fill material shall be placed in layers which, when compacted, shall not exceed six inches (6”). Each layer shall be spread evenly and shall be throughly mixed during the spreading to insure uniformity of material and mois- ture in each layer. After each layer has been placed, mixed and spread evenly, it shall be throughly compacted to not less than the density set forth . Page 3 RECOMMENDED EARTHWORKSPECIFICATIONS (CONT.) in paragraph 2 (c) above. Compaction shall be accomplished with sheepsfoot rollers, multiple-wheel pneumatic-tired rollers, or other approved types of compaction equipment, such as vib- ratory equipment that is specially designed for certain soil types. Rollers shall be of such design and maintained to such a level that they will be able to compact the fill material to the specified density. Tamping feet of sheepsfoot rollers shall be maintained such that the soil will be compacted rather than sheared by the roller. Rolling shall be accomplished while the fill material is at the specified moisture content. Rolling of each layer shall be continuous over its entire area and the roller shall make sufficient trips to insure that the specified density has been obtained. Rolling shall be accomplished in a planned procedure such that the entire areas to be filled shall receive uniform compactive effort. (e) The surfaces of the fill slopes shall be compacted by means of _ sheepsfoot rollers or other suitable equipment. Compacting operations shall be continued until the slopes are stable and until there is no appreciable amount of loose soil on the slopes. Com- pacting of the slopes shall be accomplished by backrolling the slopes~ in increments of 3 to 5 feet in elevation gain or by other methods producing satisfactory results. (0 Field density tests shall be taken for approximately each foot in elevation gain after compaction, but not to exceed two feet in vertical height between tests. Field density tests may be taken at intervals of 6 inches in elevation gain if required by the Engineer. The location of the tests in plan shall be so spaced to give the best possible coverage and shall be taken no farther apart than 100 feet. Tests shall be taken on corner and terrace lots for each two feet in elevation gain. The Engineer may take additional tests as considered necessary to check on the uniformity ofcompaction. Where sheepsfoot rollers are used, the tests shall be taken in the compacted material below the disturbed surface, No additional layers of fill shall be spread until the field density tests indicate that the specified density has been obtained. (g) The fill operation shall be continued in six inch (6”) compacted layers as specified above, until the fill has been brought to the finished slopes and grades as shown on the accepted plans. 5. Inspection. Sufficient inspection by the Engineer shall be maintained aurmg the filling and compacting operations so that he can verify that the fill was constructed in accordance with the accepted specifications. 6. Seasonal Limits No fill material shall be placed, spread, or rolled if weather conditibns increase the moisture content above permissible limits. When the work is interrupted by rain, fill operations shall not be resumed until field tests by the soils engineer indicate that the moisture content and density of fill are as previously specified. - Page 4 RECOMMENDED EARTHWORK SPECIFICATIONS (CONT.) 7. Limiting Values of Nonexpansive Soils. Those soils that expand 3.0 percent or less from air dry to saturation under a unit load of 150 pounds per square foot are considered to be nonexpansive. a. All recommendations presented in the attached report are a part of these specifications. SAN MARCOS ENGINEERING CIWL ENOINrxms. SielL, a FeUNDATlON Natural Ground Surface Stripping Depth: Remove All Topsoil Notes: 1. Width W should be at Ieast 10’ . 2. The outside edge of bottom key shall be below topsoil or loose surface material. 3. Keys are required where the natural slope is steeper than 10 percent gradient or 10 horizontal to 1 vertical. TYPICAL KEY BENCHING FOR SLOPES No Scale ,eo MULmC’I*” DIWIC. ,“lTl . _ _ - . ^ SAN MARCOS ENGINEERING ClYlL LNQI?4CL”,. S01L, a cou*o.TIoI. APPENDDZ B. RECOMMENDATIONS FOR EXPANSIVE SOILS For soils that are expansive with respect to change in volume with change in moisture content, there is no economical way to absolutely prevent movement if there is a change in soil moisture content. Insofar as it is practicable, a stable soil moisture content should be established and maintained throughout the life of the structures. It is usually not practical to maintain a completely stable soil moisture content. Therefore, in order to minimize the undesire- able effects of the expansive soils on the structures. if these soils are placed or allowed to remain within the upper three feet below finish grade, it is re- commended that the following special precautions be exercised in design and construction of slabs and foundations. a. b. C. d. e. f. f. 1 , g. Avoid the use of isolated interior piers where possible. Continuous interior and exterior footings should be used throughout and these should be placed at a minimum depth of 2 feet below the lowest adja- cent exterior final ground surface. Reinforce and interconnect continuously with steel bars all interior and exterior footings with 2-#4 bars at 3 inches above the bottom of all footings and 2-#4 bars placed 1 l/2 inches below the top of the foundation stems for frame floors or top of slab for slab-on-grade construction. Insofar as practicable, maintain the moisture at 1 to 4 percent greater than optimum in the soil below the building to a depth of 3 feet below finish grade prior to placing concrete. It is to be noted that large amounts of moisture should not be added immediately prior to placing the concrete. This will result in expansion of the soil against the uncured concrete which could cause possible damage. In buildings where it is practicable to permit independent movement of slabs with respect to foundations , such as in garages and warehouses, these slabs should be separated from the foundations by l/2 inch thick- ness of construction felt or equivalent. Special care should be exer- cised to assure that the separation extends to the full depth of the thick- ened edges of slabs and that door stops sttached to the building clear the slab by at least one inch. Use raised self-supporting floors that span between continuous footings or reinforce all concrete slabs on grade with 6x6-10/10 welded wire fabric. Provide a minimum of 4 inches of clean sand beneath all concrete slabs. Provide a moisture barrier 2 inches below slabs in areas that receive flooring which might be adversely affected by capillary moisture. As an alternate to paragraph (d) above, if the project loan is to be guaranteed by the Federal Housing Administration, provide 4 inches of gravel overlain by a moisture barrier which in turn is overlain by 1 inch of sand under concrete slabs on grade., Provide positive drainage from all perimeter footings to a horizontal distance of at least 5 feet outside the building walls. SAN MARCOS ENGINEERING Cl”lL ENOIPILTIS. SOILS a FOYNDITlON 380 M”L.L!-PI ODWC. s- 7r. S.N HAICOS. CA 9zos* ,dlDl 74a.0111 APPENDIX. E UNIFIED SOIL CLASSIFICATION’ MAJOR OI”ISIONS HlG”LY ORGANlCSO,LS GW - GP - GM - GC - SW - SP - SM - SC - - ML - CL - OL - MH - CH - OH - Pt - FlELD lOENTlFlCAT!ON PROCEDURES TYPICAL NAMES ,E.c!“ding oar:,c,a large, !*a11 3 l”Che¶ and barxng !IXlli,“~ 30 IIilrrlled we.gn:rl Silty pravd,. p<abd.wnd~ill mirur”. NO”PlllliC fine3 0, r;nn ,wth 101 Jlafticlw ,101 &nr,fiu,ion grocedures in ML ,LIOll aa”*” gnrch. pvclwnd4a” ml*t”res. Plartic line, ,‘.a, ,dcnrif~o~~on ,%oced”rns l” CL bClOd. 1 Wcllgradc.2 lands. gravcw sands. !illlL w Wide range-n grain size and iubrranrial am*““” no lines. 01 111 :nrrmwd*re DlliiClC ram. Pwrl”qadcd San*, grarell” Id”dl. :htrl. or Plcdaminanlf” on, lim or a 3”‘la Of j.in no ‘inas. wtk mm* Inlermed,aM flln .~~wng. S,lr# $a”&, sa.nd*ilt ml.t”In I :.‘: NOnOlaltlC ‘I”CS J, he3 WlIk !JI DIas:,cIry ,tor d*nlifloc on procrdurlr se. ML b.b.4, rnorganic 1111, and v*,y fin* smd,. ~oclc %“,. r,!n/ or ciarey fine San*, or ClWCY IillS nlrh Ilkah, m.ticiw. / None 10 rl’gkl ( G”#ck IO 1!ow ( None Inorgmc Cl.“, of low to medium Pl.lliC,I”, gravelly ClW% randy Cl.“,, IlIlY ClW,. Medium IO klgh None co itry I,oyl Medium ICI” clays. orglmc fllU and organic Iill” clay, Of IO*I Plal*~cilY. ) ‘n:y: ) slow ) SWl lnotprnic 11111. mlcaCeO”I or d~alomac~o”, Sllgkl :o Sllghl to tine Iand” 3, 1111* IOil& elaltlc IllIs rnLdl”rn Slw. to non* mca,um ,norgan;c Ci.“l Of high Plasticity. 1.1 clays. 1 ++~~*h:;;-* r Non* 1 HiO” Orgm’c CII”l 0‘ medd;um IO hlgk PIas1Iclry. NO”L :3 rery org*ntc 1’1.1. Medium !O LIqll SLght (0 l,o~ mMi”m . Peat and 0lh.C highly organic IOilS. Readil” dcntlfled DY CoIor. c&x. roangy ‘eel d”d freQr*“tly by Ilb,O”l IlilirlC,