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HomeMy WebLinkAboutCT 77-06; Chestnut Villas; Soil Investigation; 1978-10-11c7 77-6 SOIL INVESTIGATION for CHESTNUT VILLAS Carlsbad, California For ' CASA DEVELOPMENT San Diego, California BY GEOCON, INCORPORATED San Diego, California OCTOBER, 1978 - - GEOCON ENGINEERS AND GEOLOGISTS * CONSULTANTS IN THE APPLIED EARTH SCIENCES - INCORPORATED -_ File No. D-1563-JO1 October 11, 1978 Casa Development 2079 Garnet Street San Diego, California 92109 Attention: Mr. Bob Bryan - Subject: Chestnut Villas Chestnut Avenue Carlsbad, California SOIL INVESTIGATION Gentlemen: - - - In accordance with your request, we have performed a soil investigation of the subject project. We are pleased to submit herewith our report of the investigation. It is our opinion that the site/is suitable for development of the proposed one or two story residential buildings pro- vided the recommendations of this report are carefully followed. This report presents the fIndings of our investigation and includes our conclusions and recommendations based on those findings. If you have any questions regarding this report or if we may be of any further service, please do not hesi- tate to contact our office. Very truly yours, - GERON, INCORPOBATED - - - &$E 17030 _ , \ h &l 49 el S. Ghan II Staff Geologist MSC:JEL:ps copies: (2) addressee (4) Burkett & Wong - m 6645 CONVOY COURT - SAN DIEGO, CALIFORNIA 92111 - PHONE (714) 292-5100 TABLE OF CONTENTS 1 SOIL INVESTIGATION Purpose and Scope. ................ Location and Description of Site and Project ... Field Investigation. ............... Laboratory Tests ................. Figure No. 1, Site Plan ............. Soil Conditions. ................. Groundwater. ................... CONCLUSIONS AND RECOMMENDATIONS General. . . . . . . . . . . . . . . . . . . . . . Grading... . ..O .........O . . . . . Foundations. Concrete Slab;-k:Grade: : : : : : : : : : : : : : Drainage............... ....4. LIMITATIONS AND UNIFORMITY OF CONDITIONS . . . . . . . APPENDIX A / Table I, In-Place Moisture-Density & Direct Shear. Table II, Laboratory Expansion Test Results. . . . Table III, Laboratory Compaction Test Results. . . Figure 2, Log of Test Boring No. 1 , . . . 0 . . . Figure 3, Log of Test Boring Nos. 2 & 3 . . . . . Figure 4, Log of Test Boring No. 4 . . . . . . . . APPENDIX B Page :: : 4 2 10 :I; A-2 t-2 A-5 RECOMMENDED GRADING SPECIFICATIONS . . . . . . . . B-l GEOCON Tr.Ir-o9Po~bTPn File No. D-1563-JO1 October 11, 1978 SOIL INVESTIGATION -- - -- - - Purpose and Scope The purpose of our investigation was to determine the surface and subsurface soil conditions at the site and, based on ~017. conditions encountered, to make recommendations for develop- ment of the site to receive one or two story, wood-frame and masonry residential buildings. The investigation consisted of a site reconnaissance by our staff geologist and the excavation of four exploratory bor- ings to depths varying between l'b and 15 feet. Laboratory tests were performed on samples from the borings to determine various physical properties of the soil types encountered. Recommendations contained herein are based on engineering analysis of data from our field investigation and laboratory tests. Locatl.on and Description of Site and Project 'J!he rectangular-shaped site is located on the south side of Chestnut Avenue approximately 440 feet west of-Highland Drive in Carlsbad, California. -l- GEOCON TT.,PnODnm an-nn File No. D-1563-JO1 October 11, 1978 - .- The site slopes very gently downward to the west and is surrounded by residences and vacant lots. Greenhouses lie to the west of the site. Vegetation consists of sparse native weeds and grasses in addition to several large trees growing near existing struc- tures at the south end of the site. The existing structures are to be removed. It is proposed to develop the site by grading to receive several one or two story residential structures. Field Investigation The field investigation was performed on September 15, 1978 and consisted of a site inspection by our staff geologist and the excavation of four exploratory borings. The borings were drilled to depths ranging from approximately 10 feet to approximately 15 feet below the existing grade. Drilling was accomplished by means of a truck-mounted drill rig equipped with six-Inch dfameter continuous flight auger. As drilling proceeded, samples were taken at various depths in the bor- ings. Undisturbed samples were obtained by driving a three -2- GEOCON ...^-..-,.m .,..-.. File No. D-1563-501 October 11, 1978 - -.- - - -- - - - inch O.D. split tube sampler 12 inches into the undisturbed soil mass with blows from a 140 pound hammer falling 30 inches. The sampler was equipped internally with one-inch high by 2-3/8 inch diameter brass sample rings to facilitate sample removal and testfng. Disturbed bulk samples were also taken from the borings. The samples were returned to our laboratory for testing. The approximate locations of the test borings are shown on the attached Plot Plan, Figure 1. Logs of the borings are presented on Figures 2 through 4. / The logs depict the soil types encountered and show the ap- proximate depths at which samples were taken. Laborat0r.y Tests All 1aborator.y tests were performed in accordance with gen- erally accepted test methods of the American Society for Testing and Materials (ASTM) and other suggested procedures. . Relatively undisturbed drive samples were tested for their in-place dry density, moisture content, shear strength, and expansive potential. - -3- GEOCON TY.Tc.n~xzn~ amnn File No. D-1563-501 A., --s- -3 n+n - - - PROPoSED BUl!L Dhv~ APPROXIHAT.. LOCATION ff ?-EW BORhVG c-1 EX/SmJG sr7?ucruRE S~&T,O~NOF'&STB~ CHESTNUT VILLAS Carlsbad, California FIGURE W Tf?4GE Iu* 1 GEOCON 8 INCORPORATED 4 GEOCON TNcnRPnRATFn File No. D-1563-501 October 11, 1978 - -- - - - - - - A disturbed bulk sample of the near surface material was tested for fts maximum dry density and optimum moisture con- tent in accordance with ASTM Test Method D1557-70. The results of our laboratory tests are summarized in tabular form in Appendix A. In-place moisture density relationships are also presented on the Logs of Test Borings. Soil Conditi.ons Soil conditions at the site were found to be quite uniform. The entire site is underlain by Pleistocene Marine Terrace Deposits and associated topsoils: The surficial soils typically consist of medium dense, moist, silty and slightly clayey sands. Expansive soils were not encountered during our investigation, however, if such soils are encountered during grading of the site, every effort should be made to place expansive soils deeper than two feet below finish grade. If expansive soils exist within two feet of finish grade at the completion of grading, footing depths should be increased at the discretion of the project soils engineer. -50 GEOCON TNcORPnR*TR" File No. D-1563-501 October 11, 1978 -- - - Soils encountered at the site possess good foundation bearing characteristics both in the natural state and as' properly compacted fill. Groundwater No groundwater was encountered during the course of this investigation. Each of the geologic units and surficial deposits encountered on the site have permeability characteristics and/or ancient fracture systems that could be susceptible under certain con- ditions to subsurface water seeiage. Inasmuch as no springs, seeps, or groundwater occurrences were observed, or are known to occur on the site, it is our opinion that the seepage po- tential is relatively low. It is our recommendation, however, that periodic inspection be made by either our soil engineer or engineering geologist during grading for the presence of unknown and unpredictable groundwater occurrences. Remedial measures, if any, will than be recommended. - - -6- GEOCON TwcnRPowATPn - File No. D-1563~JO1 October 11, 1978 _.- -_ - - CONCLUSIONS AND RECOMMENDATIONS General 1. The site is suitable for development of the proposed one or two story, wood-frame and masonry residential buildings, provided the recommendations of this report are carefully followed. Grading 2. All grading should be performed in accordance with the "Recommended Grading Specifications" contained in Appendix B. 3. Site preparation should begin with the removal and ex- portation of existing structures, trash, debris, and vege- tation designated for removal. 4. All concrete slabs, footings, septic tanks, and leach lines should be removed in their entirety. Depressions re- sulting from the removal of such items should be properly backfilled and compacted. 5. The natural ground should then be scarified to a depth -70 GEOCON INCORPORATED - File No. D-1563-JO1 October 11, 1978 c- -_ of 12 inches, moisture conditioned to near optimum moisture content, and recompacted. 6. Fill should then be placed and compacted in layers until final elevations are reached. Layers of fill should be no thicker than will allow for adequate bonding and compaction. A thickness of six to eight inches may be assumed to be sat- isfactory for this project. 7. All fill and backfill should be compacted to at least 90 percent of maximum dry density as determined by ASTM Test Method D1557-70. / Foundations 8. The proposed project is well suited for the use of con- tinuous strip footings or isolated spread footings. All footings should be a minimum of 12 inches wide and 12 inches deep for single story structures. Footings for two story structures should be at least 12 inches wide and 18 inches deep. We recommend minimum footing reinforcement to consist of two continuous No. 4 steel reinforcing bars placed hori- zontalky in the footing, one placed near the top of the foot- ing and one placed near the bottom. -8- GEOCON INCORPORATED File No. D-1563-JO1 October 11, 1978 - - 9. Foundations constructed as above may be designed for an allowable soil bearing pressure of 2500 psf for dead plus live loads. Loads may be increased by one-third for short-time loading. Concrete Slabs-on-Grade 10. Concrete slabs-on-grade, if used, should be at least four inches thick. The slabs should be underlain by four inches of crushed gravel or clean sand and a visqueen mois- ture barrier to act as a capillary break. 11. Minimum slab reinforcement should consist of 6x6-10/10 welded w%re mesh throughout. Drainage 12. Adequate drainage provisions are imperative. Under no circumstances should water be allowed to pond adjacent to footings. The site should be graded such that storm waters and irrigation excess drain away from structures and into swales or other controlled drainage facilities. - 13. Roof downdrains should empty into splashblocks and be directed away from the structure into controlled drainages, - -9- GEOCON INCORPORATED - .- - - ‘- - File No. D-1563-501 October 11, 1978 LIMITATIONS AND UNIFORMITI OF CONDITIONS 1. The 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 dis- closed in the borings. If any variations or undesirable conditions are encountered during construction, or if the proposed construction will differ from that planned at the present time, Geocon, Incorporated should be no- tified so that supplemental recommendations can be given. 2. This report is issued with the understanding that it is the responsibility of the owner, or of his representa- tive, to ensure that the information and reconxnendations contained herein are brought to the attention of the arch- itect 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. 3. The findings of this report are valid as of the pres- ent date. However, changes in the conditions of a property -lO- GEOCON TNCORPORATED r- File No. D-1563-501 October 11, 1978 - - - - - - - - - can occur with the passage of time, whether they be due to natural processes or the works of man on this or adjacent properties. In addition, changes in applicable'or appro- priate standards may occur, whether they result from leg- islation or the broadening of knowledge. Accordingly, the findings of this report may be invalidated wholly or par- tially by changes outside our control. Therefore, this report is subject to review and should not be relied upon after a period of three years. -ll- - GEOCON TNcnRPoRATRn - File No. D-1563-JO1 October 11, 1978 TABLE I Summary of In-Place Moisture-Density and Direct Shear Test: Results Angle of Dry Moisture Unit Shear Sample Depth Density Content Cohesion Resistance No. ft. pcf % psf Degrees 1-2 2 111.9 6.6 180 31 l-3 5 118.4 9.2 1-5 10 119.6 6.7 2-1 2 123.1 4.3 TABLE II - Summary of Laboratory Exbansion Test Results Moisture Content Expansion (+) Betore Alter Test Test Sample Description Depth Dry . Settii;;;k;;i Density No. ft. % % pcf % psf l-3 Or-brn, slightly 5 -k1.2(9.2) 13.8 118.4 -0.6 150 Clayey, Silty SAND - *Sample air-dried before test-as received moisture content in parentheses. A-l GEOCON j INCORPORATED File No. D-1563-JO1 ' October 11, 1978 TABLE III _- Summary of Laboratory Compaction Test Results A.S.T.M. D1557-70 Max. Dry Optimum Sample Depth Density Moisture Number Peet Description pcf X dry wt. 1-l o-2 Dark brown, Silty 129.9 8.5 SAND A-2 File No. D-1563-JO1 nrtrrhar 11 1475? - - - - “bC”YbL &I, .&.I,” IN-PLACE mm SAU#x LO6 a mwYrahon OESCR/PTfON IN NlAdhVR LOUNON &s,#m,v DRY MO/STURI mr Of eibdt DENSITY cwmr WPLE P.c.f % W ei BORING NO. 1 BULK SAMPL dense, moist, dark brown, medium SAND es light brown, humid 111.9 6.6 dG,moist, orange-brown, slightly Clayey, Silty, medium 118.4 9.2 BULK SAMPL 119.6 6.7 L2- * /. w . .,. : / BORING TERMINATED AT 15.0 FEET Figure Z - Log of Test Boring No. 1 A-3 GEOCON INCORPORATED File No. D-1563-JO1 - October 11, 1978 IN-PLACE mvf SAMfiE LOG a /+7&0tlm DEscufPrfo.4 /N NuMbFff War~oN Ro$lst0na DRY MOCVURE mr Of e/aryl, DENSITY cwmvr SAMPAE AC.f % dry ti 0 -I BORING NO. 2 .' . ., . . TOPSOIL, 2_ :w: _ medium dense, moist, dark brown, 2-1 I:I'I: 5o '~~ff~~&m~~~~ E$&, humid 123.1 4.3 4 +I: ------ '.I; 1 :I:, dense, moist, or-brown, Silty, medium SAND 6, 8 - jl'*[ :I : ;j:I: u lomv 'l:l:l. BORING TERMINATED AT 10.0 FEET 0 _ BORING NO. 3 , ; . ,' TOPSOIL, 2, medium dense, moist, dark brown, --- , Silty, medium SAND *. I l-becomes light brown --- 4 - or-brown, slightly medium SAND 6 - 8 - 1." ,ki+ . $/ ' BORING TERMINATED AT 10.0 FEET Figure 3 - Log of Test Boring Nos. 2 & 3 A-4 GEOCON INCORPORATED - File No. D-1563-JO1 na-d-nhnr 11 1 a7s2 - - - - - - IN-PLACE wrN SAMPLE LOG m !beaftal IN wmm iocwmv tb~ cETr OF et@ SAMPLE i?ESCf?lPlION DRY uo/snm DENSITY cavmr AC.f % dv v) 0 .. 2 _ BORING NO. 4 : + TOPSOIL, iiil* _ medium dense, moist, red-brown, :i:l:l: ! Silty, medium SAND L-becomes light brown, humid 4 _ dense, moj_st, or-brown, slightly Clayey, Silty, medium SAND 6 _ .(‘. 8 - if.1 ;1? ‘/,.’ ;fpJ 10 ;rq. L# BORING TERMINATED AT 10.0 FEET Figure 4 - Log of Test Boring No. 4 A-5 GEOCON INCORPORATED File No. D-15630JO1 October 11, 1978 RECOMMENDED GRADING SPECIFICATIONS for CHESTNUT VILLAS Carlsbad, California 1.1 1.11 1.12 1.13 2.1 2.11 General Description These specifications have been prepared for grading and site development of Chestnut Villas located on the south side of Chestnut Avenue in Carlsbad, California. Geocon, Incorporated, hereinafter described as the soil engineer, should be consulted prior to any site work connected with site development to wnsure compliance with these specifications. These specifications shall only be used in conjunctiop with the soil report of which they are a part. This item shall consist of all clearing and grubbing, preparation of land to be filled, filling of the land, spreading, compaction and control of the fill, and all subsidiary work necessary to complete the grading of the filled areas to conform with the lines, grades, and slopes as shown on the accepted plans. In the event that any unusual conditions not covered by the special provisions are encountered during grad- ing operations, the soil engineer shall test and ob- serve all grading operations. Tests The standard test used to define maximum density of all compaction work shall be the ASTM Test Procedure D1557-70. All densities shall be expressed as a relative compaction in terms of the maximum density obtained in the labora- tory by the foregoing standard procedure-. - - - B-l GEOCON INCORPORATED File No. D-1563-JO1 October 11, 1978 3.1 Clearing, Grubbing, and Preparing Areas to be Filled 3.11 Any trees not utilized in landscaping, structures, weeds, and other rubbish shall be removed, piled, or otherwise disposed of so as to leave the areas that have been dis- turbed with a neat and finished appearance, free from unsightly debris. 3.12 Any septic tanks, if encountered, and debris must be removed from the site prior to any building, grading or fill operations. Septic tanks, including all connecting drain fields and other lines, must be totally removed and the resulting depressions properly reconstructed and filled to the complete satisfaction of the super- vising soil engineer. 3.13 All water wells on the site shall be capped according to the requirements of the San Diego County Health De- partment. The strength of the cap shall be at least equal to the adjacent soil. The final elevation of the top of the well casing must be a minimum of 36 inches below any adjacent grade prior to any grading of fill operations. / 3.14 All buried tanks, if encountered, must be totally removed and the resulting depressions properly recon- structed and filled to the complete satisfaction of the supervising soil engineer. 3.15 All vegetable matter and soil designated as unsuitable by the soil engineer shall be removed under the direc- tion of the soil engineer. The then exposed surface shall then be plowed or scarified to a depth of at least eight inches and until the surface is free from ruts, hummocks, or other uneven features which would tend to prevent uniform compaction by the equipment to be used. 3.16 The original ground upon which the fill is to be placed shall be plowed or scarified deeply, and where the slope ratio of the original ground is steeper than 6.0 hori- zontal to 1.0 vertical, the bank shall be stepped or benched. At the toes of the major fills and on the side- slope fills! the base key shall be, as described else- where in this report, at least 10 feet-in width, cut at B-2 GEOCON INCORPORATED FUe No. D-15630JO1 October 11, 1.978 3.17 4.1 4.11 4.12 5.1 5.11 5.12 least three feet into the undisturbed or native 'soil, and sloped back into the hillside at a gradient of not less than two percent. Subsequent keys should be cut into the hillside as the fill is brought up the slope. The construction of subsequent keying operations shall be determined by the soil engineer during grading oper- ations. Ground slopes which are flatter than 6 to 1 shall be benched when considered necessary by the soil engineer. After the foundation for the fill has been cleared, plowed, or scarified, it shall be disced or bladed un- til it is uniform and free from large clods; brought to the proper moisture content by adding water or aer- ating;. and compacted to relative density of not less than 90 percent. Materials Native soil, free of organic material and undesirable deleterious material, may be used as fill. Native soil which is expansive shall not be placed on the top two feet of building pads without the approval of the soil engineer. The materials for fill shall be approved by the soil engineer before commencement of grading operations. Any imported material must be approved for use before being brought to the site. The materials used shall be free from vegetable matter and other deleterious material, and be nonexpansive, Expansive soil Fs defined as soil which expands more than 3.0 percent when saturated at 90 percent relative compaction and optimum moisture content under a surcharge of 150 psf. Placing, Spreading, and Compacting Fill Material The selected fill material shall be placed in layers which when compacted shall allow adequate bonding and compaction. Each layer shall be spread evenly and shall be thoroughly blade mixed during the spreading to ensure uniformity of material in each layer. When the moisture content of the fill material is be- low that specified by the soil engineer, water shall - B-3 GEOCON INCORPORATED File No. D-1563-JO1 October 11, 1978 - - - - - 5.13 5.14 5.15 5.16 5.17 5.18 be added until the moisture content is as specified to assure thorough bonding during the compaction process. When the moisture content of the fill mat&rial is above that specified by the soil engineer, the fill material shall be aerated by blading or other satisfactory methods until the moisture content is as specified. After each layer has been placed, mixed, and spread evenly, it shall be thoroughly compacted to a relative compaction of not less than 90 percent. When fill material includes rock, no rocks will be allowed to nest, and all voids must be carefully filled with small stones or earth and properly compacted. No rocks larger than six inches in diameter will be permitted in the fill. Compaction shall be by sheepsfoot rollers, multiple- wheel pneumatic-tired rollers, or other types of acceptable compacting rollers. Rollers shall be of such design that they will be able to compact the fill to the specified moisture.content range, Rolling of each layer shall be conti/nuous over its entire area and until the required density has been obtained. Field density tests shall be made by the soil engineer. Where sheepsfoot rollers are used, the soil may be disturbed to a depth of several inches. Density tests shall be taken in compacted material below the disturbed surface. When these tests indicate that the density of any layer of fill or portion thereof is below the required 90 percent density, the particular layer or portion shall be reworked until the required density has been obtained. The fill operation shall be continued in compacted layers, as specified above, until the fill has been brought to the finished slopes and graded as shown on the accepted plans. Fill slopes shall be compacted by means of sheepsfoot rollers or other suitable equipment. Compaction opera- tions shall be continued until the slopes are stable. B-4 GEOCON INCORPORATED File No. D-1563-501 October 11, 1978 5.19 All earthmoving and working operations shall be con- trolled to prevent water from running into excavated areas. All water shall be promptly removed and the site kept dry. 6.1 Disposal of Oversize Rock 6.11 Oversize rock shall be either exported from the site, used for landscaping purposes, or placed in designated nonstructural fill areas. 6.12 Prior to grading, the soil engineer shall be consulted to approve any proposed nonstructural fill areas. In general, nonstructural fill areas will be acceptable if located outside of the “zone of influence” of proposed .structures; e.g. rear yard fills at least 15 feet from structures and beneath street areas (deeper than pro- posed utility lines). 6.13 Oversize rock shall not exceed four feet in greatest dimension, shall be placed in lifts not exceeding four, and shall be placed in a manner that will not produce “nesting” of the rock. ;The voids between the rock8 shall be completely filled with fine granular material. 6.14 No oversize rock shall be placed within four feet of finish lot grade nor within the anticipated depth of utility lines, whichever is deeper. 7.1 Engineering Observation 7.11 Field observations by the soil engineer shall be made during the fill and compaction operations 80 that he can express his opinion regarding the conformance of the grading with the accepted specifications. 8.1 Seasonal Limits 8.11 No fill material shall be placed, spread, or rolled while it is at an unsuitable high moisture content, nor during unfavorable weather conditions. When the work is interrupted by heavy rain, fill operations shall not be resumed until field tests by the soil engineer indicate that the moisture coritent and den- sity of fill are as previously specified. B-5 GEOCON INCORPORATED