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HomeMy WebLinkAboutCT 80-41; La Costa South Unit 1; Soils Report; 1981-02-25,“I‘,, HCHKlNa .F.NTON C”C.IDEWI . ClYlL 1*e1*mc1 Roy J . Ward Company 1207 Elm Avenue, Suite D Carl&ad, California 92008 BENTON ENGINEERING, A,,LILD sorl. YECHANICS - ,O”NDATIONS ss.0 RlJC,IN ROAD SAN DIL00.CALI,OI1NIA 01111 February 25, 1981 Attention: Gentlemen: Mr. Bob Thompson This is to transmit to you six copies of our report of Project No. El-2-6A entitled, “Soils Investigation, Proposed 14 Unit Condominium, Lot 40 of Lo Costa South Unit No. 1, Navorro Drive, Carlsbad, Colifomio,” doted February 25, 1981. If you should have any questions concerning any of the dota presented in this report, please contact us. Very truly yours, BENTON ENGINEERING, INC. PHB/ir ENBINE&tG$EE~BRARY 2075 Las Palmas Drive Carl&a4 CA 92009459 SOILS INVESTIGATION PROPOSED 14 UNIT CONDOMINIUM LOT 40 OF LA COSTA SOUTH UNIT NO. 1 NAVARRA DRIVE CARLSBAD, CALIFORNIA For the Roy J. Word Compony PROJECT NO. El-2-6A FEBRUARY 25, 1981 TABLE OF CONTENTS SOILS INVESTIGATION Poge No. Introduction ................................................ Field Investigation ........................................... Laboratory Tests ............................................. DISCUSSION COKLUSIONS AND RECOMMENDATIONS Soil Conditions .............................................. 3ond4 Conclusions and Recommendations .............................. 4 Recommendations ............................................ 4 Retoining Walls .............................................. 4ond5 Site Grading ................................................ 5 DRAWING TITLE Dmwing No. Location of Test Borings ...................................... Summory Sheets: Boring No. 1 ......................................... Boring No. 2 ......................................... Boring No. 3 ......................................... Log A- East Slope ............................... Log B - South Slope .............................. Log C - West Slope .............................. Consolidation Curves ......................................... APPENDICES Standard Specifications for Placement of Compacted Filled Ground.. (ASTM D 1557-70 - 90% - 25/5 loyen) Unified Soil Classification Chart . . . . . . . . . . . . . . . . . ..*..‘.....a.. Sampling, etc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 ond 2 2and3 1 AA A B BENTON ENGINEERING. INC. BENTON ENGINEERING. INC. A,,L,ED so,l. YTCHANIC. - ,OUWD*IION* c.B.0 IYIPIN r)OlD ,AW DILGO.C~LIFOINll *11*3 T,LIC”OY, ,,I., SeB-Imss P”lLlP “ENWNG .LNION n1*10(*1. GIYII. 1*01*1.1 SOILS INVESTIGATION introduction This is to present the results of a soils investigation conducted ot the site for ~1 proposed Idunit condominium building located on the south side of Novarra Drive in Carlsbrxf, California. It is understood on underground gomge will be located beneath the proposed buildings ond most of the excavation for the lower level parking area hai already been completed at the time of field exploration on February 4, 1981. The objectives of the investigation were to determine the geneml subsurface soil conditions at the site and sufficient physical characteristics of the soils so that soil pammeten and engineering recommendotionr could be presented for the design of the proposed building foundotions and retaining walls. In order to accomplish the obiectives, three borings were drllled, the soils exposed on the existing banks were logged, and undisturbed samples were obtained for laboratory testing. Field Investigation Three borings were drilled with a truck-mounted rotary bucket-type drill rig at the approximate locations shown on the ottoched Drawing No. 1, entitled “Location of Test I borings. ” The borings were drilled to depths of 8 to 10 feet below the existing ground surface. z . 2 A continuous log of the soils encountered in the borings and exposed on the existing banks 3 .% was recorded at the time of drilling and is shown in detail on Dmwing Nos. 2 to 5, Inclusive, I? 0, each entitled “Summary Sheet.” The soils were visually classified by field Identification procedures in accordance -2- with the Unified Soil Clossiflcation Chart. A simplified description of this classification system is presented in the attoched Appendix A at the end of this report. Undisturbed samples were obtained at frequent Intervals, where possible, in the soils ahead of the drilling. The drop weight used for driving the sampling tube into the soils was the “Kelly” bar of the drill rig which weighs 2200 pounds, and the average drop was 12 inches. The general procedures used in fteld sampling are described under “Sompllng” ln Appendix 8. Labomtory Tesk Laboratory tesk were performed on all undisturbed samples of the soils in order to determine the dry density, moisture content, and shearing strength. The msulk of these tesk , ore presented on Drawing Nos. 2 and 3. Consolidatlon tesk were performed on representative samples in order to determine the load-settlement chamcterisita of the soils and the msults of these tesk are presented graphically on Dmwtng No. 6, entitled “Consolidation Curves.” In addition to the above laboratory terk, expansion tesk were performed on the silty cloy soil encountered to determine ik volumetric change chorocteristics with change in moisture content. The recorded expansions of the samples ore presented as follows: Percent Expansion Percent Expansion Under Unit Load of Under Unit Load Depth of 144 Pounds per Square of 500 Pounds per Boring Sample Sample Foot from Field Square Foot from No. No. in Feet Soil Description Moisture to Sotumtion Air Dry to Satumtion 2 2 7.0 Silty clay 0.90 1.82 fi Direct sheor task were performed on selected undkturbed samples that were satumted I z . ond drained prior to testing. The resulk of these tesk ore presented us follows: z” 5 .pi 2 4 BENTON ENGINEERING. INC. -3- Norm01 Sheoring Load in Resistance ki&q ft klps/sq ft Boring: 1, Sample: 1 0.5 0.39 Depth: 1.5 - 2.0 Feet 1 .o 1.40 2.0 2.22 Boring: 2, Sample: 1 0.5 1.02 Depth: 1.5 - 2.0 Feet 1 .o 1 .89 2.0 2.01 Angle of Internal Friction Degrees 40 Apparent Cohesion ft Ib/sq 0 33.5 690 The general procedures used for the preceding loborotory tests ore described brlefiy in Appendix 8. DISCUSSION, CONCLUSIONS AND RECOMMENDATIONS Soil Conditions Medium compact to compact fine to medium sand with scottemd grovel and fine sandy clay nodules WCIS encountered to 6.3 feet in Boring No. 1. This was underloin by compact gravelly fine to medium scmd to 7.0 feet and firm gmvelly clayey Fine to medium sand between 7.0 and 10.0 feet, the depth of exploration. in Boring No. 2 firm clayey fine to medium sand with scattered grovel and cobbles was found to 2.4 feet and was underfoin by firm gmveily clayey fine to medium sand to 5.6 feet, firm silty cloy between 5.6 and 8.5 feet, and firm gravelly clayey fine to medium sand to the limit of bxploration at 10.0 feet. Firm gravelly clayey fine to medium sand was encountered to 8.0 feet, the limit of exploration in Boring No. 3. Free ground water was not encountered in the exploration borings. The soils exposed near the centml portion of the existing slope olong the eost pmperty line were primorily silty sands and slightly silty sands. Fine sandy cloys were observed to a’ depth of 8.0 feet on the south slope area and gmvelly slightly silty fine to coarse sand was found between 8.0 and 10.0 feet, the bottom of the slope. The soils exposed near the middle BENTON ENOINELRING. INC. -4- of the westerly slope consisted of slightly silty fine to medium sand to 1 .O foot, fine to medium sandy cloy between 1 .O and 3.0 feet, silty fine to medium sand from 3.0 to 4.0 feet, and gmveily slightly silty fine to coarse sand to 5.0 feet at the bottom of the slope. Conclusions and Recommendations It is concluded from the field investigotion ond the resulk of loboratory tests that the soils similar to those encountered below o depth of one foot at the boring locations ore suitable for support of the proposed buildings. The rerulk of the expansion task indicate that the silty cloy encountered between 5.6 and 8.5 feet in Boring No. 2 would be considered to hove o low exponsion potential and therefore special design and precautions for exponsive soil conditions will not be required. Recommendations Footings at least one foot in width ond placed at o minimum depth of one foot below the lowest adjacent natural ground surface may be designed using o safe allowobie bearing value of 2,400 pounds per squore foot. This value moy be increased at the rote of 600 pounds per square foot for each additional foot of width and an additlonol rote of 1,000 pounds per squore foot for each additional foot of depth below one foot to a moximum of 4,000 pounds per square foot. These values ore for dead plus live loods and may be increased one-third for combined dead, live, wind and seismic loads. Based on the results of the loaf-consolidation tests, the settlement of a continuous footing 18 inches wide and supporting o uniform lood of 3,600 pounds per lineal foot is estimoted z to be on the order of l/8 inch. z” t Retaining Walls .az a’ The design active pressures for retaining walls with o horizontal surcharge of soil behind the woll ore recommended to be an equivalent fluid pressure of 35 pounds per cubic foot if unrestrained at the top ond ore recommended OS a pressure of 22 “H” pounds per squore foot (where “H” is equal to the height of the wall in feet) in the middle 60 percent eENT.24 ENOINEERING. INC -S- of the wall whara the wall is restrafned. Whpre retafning walls have a sloplng 2 horizontal to 1 vertical surcharge behlnd the wall, then the ecprivalent fluid pressure for the unrestrained wall is recommended to be increased to 45 pounds per cubic foot ond for the pressure on o restmlned wall Is recommended to be 28 “Ii” pounds per rquore foot in the middle 60 percent. These deslgn pressures assume that the backfill solls behind the walls ore silty sand, sand or gravel and thot either weep holes or perforated pipes are installed at the base of the walls in order to prevent hydrostatic pressures from developing behind the walls. The ollowoble passive pressure for footing, cast directly ogalnst the urdlsturbed natural soils is 360 pounds per square foot at the depth of one foot ond this volw may be increased at the rote of 180 pounds per square foot for each addiHonai foot in depth. The allowable friction factor for the dead lood at the bottom of a concrete footing is 0.4. The allowable passive pressure value may be combined with the friction factor to determine the total allowable resistance to lateral movements. Site Grading It is recommended that any additional filled ground placed on the site should be placed under engineering inspection and should be unlformiy compacted to at least 90 percent of maximum dry density in accordance with the applicable sections of the attoched Appendix AA entitled “Standard Specifications for Placement of Compacted Filled Ground.” Respectfully submitted, BEMON ENGINEERING, INC. RCE No. 10332 Dlstributlonr (6) Addressee I-_.-^_. --.-.....v-...m ..r “,I@ 5- 6-g 7- 8- 9- +-- : Cd & 2 ; ; :‘; FT6 . CI’.i .**.pp s s ?+s z %J D a u ti SUMMARY SHEET =.e BOAlNO NO. 1 zg IAt* ELEVATION a= 0 rown, Moist, Medium Compact, ‘ith Scattered Gravel to 3”, Dccasionol Lenses With 15 to 2U% Grovel, Few Nodules of 2.4 ‘ine Sandy Cloy :ompact FINE TO MEDIUM SAN D 5.5 0.32 4.8 9.6 11 .o 0.57 35.7 0.9 rown, Moist, Compact, With GRAVELLY 0 to 50% Gravel and Cobble FINE TO MEDIUM - > 6” SAN D row”, Moist, Firm, With 30 to GRAVELLY ,oo/o Grovel and Cobble to 6” CLAYEY FINE TO MEDIUM SAND - =I 22, rz; &PI - 3.7 4.3 5.7 - - - 1 Indicates Undisturbed Drive Sample PRO,ECT NO DRAWN0 NO. 81-2-6A BENTON ENGINEERING. INC. 2 - - - SUMMARY SHEET BORlNO NO. 2 ELEVATION “, and Cloy Nodules FINE TO MEDIUM Brown, Moist, Firm, With 30% Gravel and Cobble to 6”, Occasional Clay Nodules FINE TO MEDIUM Brown, Moist, Firm, With 3G% Boring No. 3 FINE TO MEDIUM BENTON ENGINEERING INC. SUMMARY SHEET LIGHTLY SILTY FINE TO MEDIU SLIGHTLY SILTY FINE TO COARSE Log B South Slope 2 WLL E 0’; i i$ n l- 2- 3- 4- r: ‘ f z Gd $g SUMMARY SHEET Log C 9” West Slope m \ ~\ .._ Brown, Very Moist, Compact, SLIGHTLY SILTY With Occasional Gravel FINE TO MEDIU SAND n, With FINE TO MEDIUM raw urovel SANDY CLAY PROJECT NO. 81-2-6A BENTON ENGINEERING. INC. 0 1 2 3 4 0 1 2 3 0 1 2 3 0 1 2 3 4 CONSOLIDATION CURVES LOAD IN KIPS PER SQUARE FOOT 0.2 0.4 0.6 0.6 I 2 4 6 6 IO I I NT CONSOLIDATION AT FIELD MO . INDICATES PERCENT CONSOLIOATION AFTER SATURATION PROJECT NO. I DRAWINO NO. Ql-7_XA BENTON ENGINEERING INC. I BENTON ENGINEERING, INC. *,cL,TD .O,L YIc”ANlcm - FOUIIDATIONS ns.0 R”FPl” ROAD *AN DILOO. CALl,ORNll *2lP1 PHlLlP HENI(INa BENTON r”L*IOINT. C,“ll LNrlWlll T.LIP”ON. ,714, sss-less APPENDIX AA STANDARD SPECIFICATIONS FOR PLACEMENT OF COMPACTED FILLED GROUND 1. General Description. The objective is toattain uniformity and adequate internal strength in filled ground by proven engineering procedures and tests so that the proposed structures may be safely supported. The procedures include the clearing and grubbing, removal of existing structures, preparation of land to be filled, filling of the land, the spreading, ond compaction of the filled areas to conform with the lines, grodes, and slopes os shown on the accepted plans. The owner shall employ a qualified soils 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 soils engineer shall advise the owner and grading contractor immediately if any unsatisfactory conditions ore observed to exist and shall have the authority to reject the compacted filled ground until such time that 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 rubbish shall be removed, piled, and burned or other- wise disposed of so as to leave the areas to be filled free of vegetation and debris. Any soft, swompy or otherwise unsuitable oreos 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 is free from ruts, hummocks, or other uneven features which would tend to prevent uniform compaction by the equipment to be used. (4 Where fil Is are made on hi I lsides or exposed slope areas, 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 o horizontal plane. The initial bench at the toe of the fill shall be at least 10 feet in width on firm undisturbed natural ground at the elevo- tion of the toe stake placed at the natural angle of repose or design slope. The soils engineer shall determine the width and frequency of all succeeding benches which will vary with the soil conditions and the steepness of slope. APPENDIX AA -2- (d) After the natural ground has been prepared, It shall then be brought to the proper mois- ture content and compacted to not less than ninety percent of maximum density in accordance with A.S.T.M. D-1557-70 method that uses 25 blows of a 10 pound hammer falling from 18 inches on each of 5 layers in a 4” diameter cylindrical mold of a 1/3Oth cubic foot volume. 3. Materials and Special Requirements. The fill soils shall consist of select materials so graded that at least 40 percent of the material passes a No. 4 sieve. This may be obtained from the excavation of banks, borrow pits of any other approved sources and by mlxirg soils from one or more sources. The material used shall be free from vegetable matter, and other de- leterious substances, and shall not contain rocks or lumps of greater than 6 inches in diameter. 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 soils engineer. If during grading operations, soils not encountered and tested in the preliminary investigation are found, 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 those of the governmental agency havig jurisdiction. 4. Placiw, Spreading, and Compactirlg Fill Materials. (a) 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 moisture in each layer. (b) When the moisture content of the fill material is below that specified by the soils engineer, water shall be added until the moisture content is near optimum as specified by the soils engineer to assure thorough bonding during the compactly process. (c) When the moisture content of the fill material is above that specified by the soils engineer, the fill material shall be aerated by bladirg and scarifying or other satls- factory methods until the moisture content is near optimum as specified by the soils engineer. (d) After each layer has been placed, mixed and spread evenly, It shall be thoroughly compacted to not less than ninety percent of maximum density in accordance with A.S.T.M. D-1557-70 modified as described in 2 (d) above. Compaction shall be accomplished with sheepsfoot rollers, multiple-wheel pneumatic-tired rollers, or other approved types of compaction equipment, such as vibratory equipment that Is specially designed for certain soil types. Rollers shall be of such design that they will be able BENTON CNOINLLRINO. INC. APPENDIX AA -3- to canpact the fill material to the specified density. Rolling shall be acccmplished 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 desired density has been obtained, The entire areas to be filled shall be compacted. (e) Fill slopes shall be compacted by means of sheepsfoot rollers or other suitable quip- ment. Compacting operations shall be continued until the slopes are stable but not too dense for planting and until there is no appreciable amount of loose soil on the slopes. Ccmpacting of the slopes shall be accanplished 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 by the soils engineer for approximately each foot in elevation gain after ccmpaction, 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 soils 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 eleva- tion gain. The soils engineer may take additional tests as considered necessary to check on the uniformity of canpaction. Where sheepsfoot rollers are used, the tests shall be taken in the canpucted 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. (9) The fill operation shall be continued in six inch (6”) ccmpacted layers, as specified above, until the fill has been brought to the finished slopes and grades as shown on the accepted plans. 5. 6. 7. Inspection. Sufficient inspection by the soils engineer shall be maintained during the fill- ing and compacting operations so that he ccm certify that the fill was constructed in occord- ante with the accepted specifications. Seasonal Limits. No fill material shall be placed, spread, or rolled if weather conditions increase the moisture content above permissible limits. When the work is fnterrupted by rain, fill operations shall not be restsned until field tests by the soils engineer indicate that the moisture content and density of the fi II are as previously specified. All recommendoticns presented in the “Conclusions” section of the attached report are a part of these specifications. BENTON ENGINEERING, INC. *C?.L,LD SOIL MLCHAN,C* - COUNDATIONS *Da0 l”.FlN ROAD 5*?4 q ILGO. CALIFORNIA **,*a PHlLlP HENKING BENTON PI)EBIDINT ClVll. LNGIWILR APPENDIX A Unified Soil Classification Chart* SOIL DESCRIPTION GROUP SYMBOL I. COARSE GRAINED, More than half of material is h than No. 200 sieve size .** GRAVELS CLEAN GRAVE LS MowiF;;;n half of coarse fraction is larger than No. 4 sieve size but smaller GRAVELS WITH FINES than 3 inches (Appreciable amount of fines) SANDS CLEAN SANDS Gtmn half of coarse fraction is smaller than No. 4 sieve size SANDS WITH FINES (Appreciable amount of fines) II. FINE GRAINED, More than half of material is smaller than No. 200 sieve size.** SILTS AND CLAYS Liquid Limit Less thon 50 SILTS AND CLAYS Liquid Limit Greoter than 50 III. HIGHLY ORGANIC SOILS GW GP GM GC Well graded gravels, gravel-sand mixtures, little or no fines. Poorly graded grovels, grovel-sand mixtures, little or no fines. Silty gravels, poorly groded gravel- sand-silt mixtures. Clayey gravels, poorly graded gravel- sand-cloy mixtures. SW SP SM SC Weil graded sand, gravelly sands, little or no fines. Poorly graded sands, gravelly sands, little or no fines. Silty sands, poorly graded sand-silt mixtures. Clayey sands, poorly graded sand-clay mixtures. ML CL OL MH CH OH Inorganic silts and very fine sands, rock flour, sandy silt or clayey-silt-sond mixtures with slight plasticity. Inorganic cloys of low to medium plas- ticity, gravelly cloys, sondy cloys, silty cloys, lean cloys. Organic silts and organic silty-clays of low plasticity. Inorganic silts, micaceous or diatomaceous fine sandy or silty soils, elastic silts. Inorganic cloys of high plasticity, fat cloys. Organic cloys of medium to high plasticity PT Peat and other highly organic soils. TYPICAL NAMES TELlPHONE ,714) S6S.IDSS * Adopted by the Corps of Engineers and Bureau of Reclamation in January, 1952. ** AI, .:,?.\.a -:.,a* mn *l.:c rL..* “la 1 I c ttnnrlnrrl BENTON ENGINEERING. INC. APPLIED (IOIL “ECWANICB - FOUNDATIONS *s.o R”rFlN ROAD SAN DIEGO. CIL.lFORNll 9117.3 PHlLlP HENKINCI BENTON PRESIDENT. Cl”lL ENG,NELI TELEPllOLlE 1714, tx5.,8S5 APPENDIX B Sampling The undisturbed soil samples ore obtained by forcing a special sampling tube into the undisturbed soils at the bottom of the boring, at frequent intervals below the ground surface. The sampling tube consists of a steel barrel 3.0 inches outside diameter, with a special cutting tip on one end and o double ball valve on the other, and with a lining of twelve thin brass rings, each one inch long by 2.42 inches inside diameter. The sampler, connected to a twelve inch long waste barrel, is either pushed or driven approximately 16 inches into the soil and a six inch section of the center portion of the sample is taken for laboratory tests, the soil being still confined in the brass rings, after extraction from the sampler tube. The samples are taken to the laboratory in close fitting waterproof containers in order to retain the field moisture until completion of the tests. The driving energy is calcu!ated as the average energy in foot-kips required to force the sampling tube through one foot of soil at the depth at which the sqmple is obtained. Shear Tests The shear tests ore run using o direct sheor machine of the strain control type in which the rate of deformation is approximately 0.05 inch per minute. The machine is so designed that the tests are mode without removing the samples from the brass liner rings in which they are secured. Each somple is sheared under o normal load equivalent to the weight of the soil above the point of sampling. In some instances, samples are sheared under various normal loads in order to obtain the internal angle of friction and cohesion. Where considered necessary, samples are saturated and drained before shearing in order to simulate extreme field moisture conditions. Consolidation Tests The apparatus used for the consolidation tests is designed to receive one of the one inch high rings of soil OS it comes from the field. Loads ore applied in sevenal increments to the upper surface of the test specimen ond the resulting deformations ore recorded at selected time intervals for each increment. Generally, each increment of load is mointained on the sample until the rote of deformation is equal to or less than l/10000 inch per hour. Porous stones ore placed in contact with the top and bottom of each specimen to permit the ready addition or release of water. Expansion Tests One inch high samples confined in the brass rings ore permitted to air dry at 105” F for at least 48 hours prior to placing into the expansion apparatus. A unit load of 500 pounds per square foot is then applied to the upper porous stone in contact with the top of each somple. Water is permitted to contact both the top and bottom of each sample through porous stones. Continuous observations ore mode until downward movement stops. The dial reading is recorded and expansion is recorded until the rote of upward movement is less than l/10000 inch per hour.