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HomeMy WebLinkAboutCT 72-32; Chinquapin & Stella Maris Ln; Soils Report; 1973-05-25BENTON ENGINEERING, INC. APPLIED SOIL MEC”*NICS - FOLtND*TIclNS 5787 CONVOY COURT SAN DIEGO. C*L,FORNI* 82111 PHlLlP HENKINCI BENTON PILBIDENT ClVlL LNGlNLEIl S.L. 8 B. Service Corporation 14022 Romona Boulevard, Suite E Baldwin Park, California 91706 May 25, 1973 Subject: Project No, 73-5-4BF Preliminary Soils Investigation Royal Homes of Carlsbad Chinquapin Avenue and Stella Maris Lane Co&bad, California Gentlemen: TELEPHDHE ,714, 56s.,855 ENGINEERING DEPT. LiBRAflY City of Carl&ad 2075 Las Palmas Drive Carlsbad, CA92009-4859 CONCLUSIONS It is concluded from the field investigation and laboratory test results that: 1. The firm to very firm natural soils existing below the loose to medium firm topsoils are suitable for use as supporting materials for the proposed fills and residential stnrctures. Where- ever the comoressibie loose to medium firm upper soils exist below finished grade, it is recommended that these be removed and be replaced with fill soils uniformly compacted to at least 90 percent of maximum dry density. For example at Boring 2, the upper 2.7 feet of soils are at approximately 73 percent of maximunl dry density and exhibit considerable consolidation when subjected to increased moisture conditions as evidenced by the load-consolidation test results on Drawing No. 5. Where such soil conditions are found to exist below finished grade and beneath proposed fill areas, it is recommended that these soils be removed and be replaced as filled ground, uniformly compacted to at least 90 percent of maximum dry density, during the grading of the subdivision. 2. It is concluded from the results of laboratory tests that the firm to very firm natural soils have a safe bearing value of at least 2000 DO@ oer sauare foot for one foot wide continuous footings placed at a depth of one foot below the firm undisturbed natural ground surface. The settIp- ment of a one foot wide continuous footing so placed and loaded to 2000 pounds per square foot is estimated to be less than l/4 inch. 3. The result of the laboratory expansion test indicates that the clayey fine to medium sand encountered between 2.5 and 5.5 feet /II Boring 3, would be considered as a “low to non- expansive” type soil. It is therefore concluded that the soils encountered in the exploration bor- ings are of sufficiently low potential expansion that special design for expansive soil conditions will not be required. Project No. 73-5-4BF Royal Homes of Carlsbad -2- May 25, 1973 4. All of the soils may be satisfactorily compacted in fill oreas and, when properly compacted to ot least 90 percent of maximum dry density, hove o safe bearing value of 2000 pounds per square foot for one foot wide continuous footings placed at a depth of one foot below the compacted ground surface. Th e settlement of a one foot wide continuous footing placed on fill soils, uniformly compacted to 90 percent of maximum dry density ond loaded to 2000 pounds per square foot, is estimated to be less than T/8 inch. Prior to placing filled ground, it is recommended that oil loose to medium firm compressible soils be removed and that the fi!led ground be placed on approved firm to very firm undisturbed natural soils as described in Section 1 on page 1. Recommendations for the placement of filled ground are presented in the attached Appendix AA, entitled “Standard Specifications for Placement of Compacted Filled Ground. ” 5. Slope stability analyses, based on the results of the laboratory tests, indicate that the proposed I l/2 bpriZpptal ta 1 vertical cut slopes and the 2 horizontol to 1 vertical compacted filled ground slopes will be stable with a factor of safety greater than 1.5 for heights up to 20 feet. It is recommended that suitable erosional control and proper drai?$ be provided to prevent water from running over the top of exposed slopes. 6. Both cutting and filling are required for the development of the site. Residences may be constructed partly in cut ond partly in fill provided the load-settlement characteristics of the natural soils and the compacted filled ground are comparable. If any soil types are encountered during grading operations that were not tested in this investiga- tion, additional laboratory testswill be conducted in order to determine their physical character- istics, and supplemental reports and recommendations will automatically become a part of the specifications. Pages 1 to 5, inclusive, and Drawing Nos. 1 ta 6, inclusive, are a part of this report. Respectfully submitted, .,.r . . BENTON ENGINEERING, INC. BY z@k?& R. C. Remer Reviewed by Philip H. $ enton, Civil Engineer Distr: (5) Addressee RCR/‘PHB/ew BENTON ENGINEERING. INC. Project No. 73-5-4BC Royal Homes of Carlsbad -3- May 25, 1973 DISCUSSION A preliminary soils investigation has been completed on the proposed “Roy01 Homes of Carlsbad” subdivision located on the southeast side of Ch)nquapin Avenue near Stello Maris Lane in Carlsbad, California. The objectives of this investigation were to determine the existing soil conditions at the site, to develop sufficient information about the physical properties of the soils so that recom- mendations could be made for grading and foundation design, and to provide information to comply with the requiremenk of the City of Carlsbad. In order to acccmplish these objectives, three borings were drilled, undisturbed and loose bag samples were obtained, and laboratory tesk were performed on these samples. The general topography of the site may be described as gently sloping to the southwest. Future drainage will be into the streets and storm drains. An avocado grove exists on the north portion of the site and the remainder of the area is covered with weeds and tomato plants. Several structures exist on the easterly portion of the site. According to the “Soil Map” prepared by the U. S. Department of Agriculture, the upper soils in the area are described as Elkhorn loamy sand. The soils encountered in the exploration borings, as described according to the Unified Soil Classification Chart, consisted primarily of silty and slightly silty sands, clayey sand, and slightly clayey sand. Field Investigation Three borings were drilled with a truck-mwnted rotary bucket-type drill rig at the approximate locations shown on the attached Drawing No. 1, entitled “Location of Test Borings. ‘I The bor- ings were drilled to depths of 10 to 12 feet below the existing ground surface. A continuous log of the soils encountered in the borings was recorded at the time of drilling and is shown in detail on Drawing Nos. 2, 3, and 4, each entitled “Summary Sheet.” The soils were visually classified by field identification procedures in accordance with the Unified Soil Classification Chart. A simplified description of this classification system is presented in the attached Appendix A at the end of this report. Undisturbed samples were obtained at frequent intervals 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 1623 pounds, and the average drop was 12 inches. The general procedures used in field sampling are described under “Sampling” in Appendix B. Laboratory Tests Laboratory tests were performed on all undisturbed samples of the soils in order to determine the dry density and moisture content. The results of these tests are presented on Drawing Nos. 2, 3, and 4. Consolidation tests were performed on representative samples in order to determine the load-settlement chamcteristics of the soils and the results of these tests are presented graphically on Drawing Nos. 5 and 6, each entitled “Consolidation Curves.” BENTON ENGINEERING. INC. Project No. 73-5-4BC Royal Homes of Carlsbad -4- May 25, 1973 In addition to the above laboratory tests, an expansion test was performed on a representative sample of the clayey fine to medium sand encountered to determine its volumetric change chorac- teristics with change in moisture content. The recorded expansion of the sample is presented as follows: Percent Expansion Under Unit Load of Depth of 150 Pounds per Square Boring Sample Sample, Sai I Foot from Air Dry No. No. in Feet Description to Saturation 3 2 4.0 Clayey fine to medium sand 1.17 J The general procedures used for the preceding laboratory tests are described briefly in Appendix B. Compaction tesk were performed on representative samples of the soils ta be excavated to establish compaction criteria. The soils were tested according to the A.S.T.M. D 1557-66T method of compaction which uses 25 blows of a 10 pound rammer dropping 18 inches on each of 5 layers in a 4 inch diameter l/30 cubic foot mold. The results of the tests are presented as follows: Boring Bag No. Sample 1 1 1 2 2 1 Maximum Optimum Mois- ‘Wh Soi I Dry Density ture Content in Feet Description Ib/cu ft % dry wt 0.5-l .5 Slightly silty fine to 133.0 7.4 medium sand 2.0-3.0 Slightly silty fine to 133.4 6.9 medium sand 3.0-4.0 Slightly silty fine to 129.7 9.3 medium sand with clay binder Direct shear tests were performed on selected soil samples remolded to 90 percent of maximum dry density and on selected undisturbed samples that were all saturated and drained prior to testing. The results of these tests are presented below: Boring 2, Sample 1 Depth: 1 .O feet Normal Load in kips/sq ft 0.5 1.0 2.0 Maximum Shear Load kips/sq ft 0.34 0.63 1.27 Angle of Internal Friction Degrees 32.5 * Apparent Cohesion Ib/sq ft 0* Boring 2, Sample 2 0.5 0.67 37 290 Depth: 3.0 feet , 1.0 1.17 2.0 1.93 * This upper zone of soil is to be removed and recompacted so that these values do not apply to bearing value calculations. BENTON ENGINEERING. INC. Project No. 73-5-4BC Royal Homes of Carlsbad -5- Normal Load in kips/sq ft Boring 1, Bag 1 ** 0.5 0.65 Depth: 0.5-l .5 feet 1.0 1.11 2.0 1.71 Boring 2, 8ag 1 ** 0.5 0.72 Depth: 3.0-4.0 feet 1.0 1.26 2.0 2.05 Shear Load kips/sq ft May 25, 1973 Angle of Internal Friction Degrees 31 Apparent Cohesion Ib/sq ft 350 38 330 ** Tests were performed on samples molded to 90 percent of maximum dry density Using the lower values far the internal angle of friction and apparent cohesion of the suitable bearing solIs, and the Tsnaahi Formula for local shear failure{ the safe allowable bearing pressures for the soils are determined as follows: Local Shear Formula: Assumptions: Q’~ = 2/3 C Nlc + Y Df Nlq + Y BN’y (1) Continuws footing 1 foot wide = 28 (2) Depth of footing = 1 .O foot = Df Undisturbed Natural Soils 0=3P C = 290 Ib/sq ft Y = 106 Ib/cu ft N’C = 27.5 Nlq = 16.5 N’y = 13.0 Q’~ = (2/3 x 290 x 27.5) + (106 x 1.0 x 16.5) + (106 x 0.5 x 13.0) = 7,759 Ib/sq ft Q’d Safe = Q’d 4: (Factor of Safety) 2,586 Ib/sq ft Fill Soils Compacted to 90 Percent of Maximum Dry Density 0=31° C = 350 Ib/sq ft Y = 129 Ib/cu ft N’, = 19.5 Nlq = 10.0 N’y = 6.0 Q’d = (2/3 x 350 x 19.5) + (129 x 1.0 x 10.0) + (129 x 0.5 x 6.0) = 6,227 Ib/sq ft Qld Safe = Qld +,3 (Factor of Safety) = 2,076 Ib/sq ft BENTON ENGINEERING. INC. SUMMARY SHEET BORlNO NO. 1 ELEVATlON 145.8’* SILTY FINE TO MEDIUM SAND - Indicates Loose Bag Sample - Indicates Undisturbed Drive Sample - Elevations shown were obtained by interpolation between contour lines on Browne and Vogt Inc., groding plan. PROJECT NO. DRAWN0 NO. BENTON ENGINEERING INC. G. .z< g; SUMMARY SHEET 6 at5 ZL =zy 25 5E 52: BORlNO NO. 2 ;$; zy $Y ES.0 ,tA ELEVATION 131 .o’ 5% 89 ze$ $ :;i 8.1 3.7 94.6 6.5 4.3 101.7 Very Firm, Slight Cl Slightly Micaceous SILTY FINE TO MEDIUM SAND 8.1 7.8108.5 16.2 9.6 114.8 PROJECT NO. DRAWN0 NO. 7%5-4BF BENTON ENGINEERING, INC. 3 SUMMARY SHEET BORlNG NO. ELEVATION_1Z)9.1’ CLAYEY FINE PROJECT NO. DRAWING NO. 73-5-4BF BENTON ENGINEERING, INC. 4 : .I ” ? (z r 1 ? : P CONSOLIDATION CURVES LOAD IN KIPS PEN SOUARE FOOT 5 7 E e $ 8. 9 1 0 INDICATES PERCENT CONSDLIDATION Al FIELD MOISTURE . INDICATES PERCENT CONSOLIDATION AFTEN SATURATION PROJECT NO. DRAWINQ NO. 73-5-4BF BENTON ENGINEERING, INC. 5 CONSOLIDATION CURVES LOAD IN KIPS PER SOUARE FOOT !!I 5 a 0 INDICATES PERCENT CONSOLIDATION Al FIELD MOISTURE . INDICATES PERCENT CONSDLIDATION AFTER SATURATION PROJECT NO. 73-5-4BF I BENTON ENGINEERING, INC. DRAW17 NO. 1 BENTON ENGINEERING, INC. APPLIED SOIL MECH*NICS - FOUNDATIONS 6717 CONYOY COURT EAN DIEGO. CALIFORNIA 82111 PHlLlP “ENKING BENTON C”LIl,DLHI ClVlL FNGINLEI APPENDIX AA TELEPIIOWE ,7,4, SB~-1rnSS STANDARD SPECIFICATIONS FOR PLACEMEN OF COMPACTED FILLED GROUND 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 procedures include the clearing and grubbing, removal of existing structures, preparation of land to be filled, filling of the land, the spreading, and compaction of the filled areas to conform with the lines, grades, and slopes as 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 are observecl 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, 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 is free from ruts, hummocks, or other uneven features which would tend to prevent uniform compaction by the equipment to be used. (c) Where fills are made on hillsides 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 a 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. (4 APPENDIX AA -2- After the naiural ground has been prepared, it shall then be brought to the proper mois- ture content and compacted to not less than ninety percent of maxlmum density in accordance with A.S.T.M. D-1557-66T 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 Dosses a No. 4 sieve. This mav be obtained from I the excavation of banks, borrow pits of any other approved sources and by mixing soils from one or more sources. The material uses 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 stret-gth 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 gradiw 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 having jurisdiction. 4. Placillg, Spreading, and Compactir\g Fill Materials. (a) 6) (4 (4 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. When the moisture content of the fill material is below that specified by the soils er\gineer, water shall be added until the moisture content is near optimum as specified by the soils engineer to assure thorough bonding during the compactiw process. When the moisture content of the fill material is above that specified by the soils ewineer, the fill material shall be aerated by blading and scarifyiw or other satis- factory methods until the moisture content is near optimum as specified by the soils ewineer. 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-1557-66T 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 5. _. 6. 7. a. (4 (9 (9) APPENDIX AA -3- to compact the fill material to the speclfled denslty. Rolling shall be acccmplished while the fill material is ot the specified moisture content. Rolli~ of each layer shall be continuous over Ik entire area and the roller shall make sufficient trips to insure that the desired dens1 ty has been obtained. The entire areas ta be A lled shall be compacted. Fill slopes shall be compacted by means of sheepsfoot rollers or other suitable equipment. Compacting operations shall be continued until the slopes are stable but not tot dense for plantlq and until there is no appreciable amount of loose soil on the slopes. Compacting of the slopes shall be accomplished by backrolliw the slopes ln increments of 3 to 5 feet in elevation gain or by other methods producing satisfactory results. Field density tests shall be taken by the soils ewineer for approximately each foot in elevation gain after compaction, but not to exceed two feet in vertical height between tests. Field density tesk may be taken at intervals of 6 inches in elevation gain if required by the solls engineer. The location of the tests In plan shall be so spaced to give the best possible coverage and shall be takena farther qp& than 100 feet. Tesk shall be taken on corner and terrace lok for each two feet In elevation gain. e sol Is erglneer may take oddltional tests as considered necessary ta check on the unlformity of compactfon. Where sheepsfoot rollers are used, the tests shall be taken In the com- pacted material below the disturbed surface. No additional layers of fill shall be spread until the fleld density tests indicate thot the specified density has been obtained. The fTll operation shall be continued In SIX Inch (6”) compacted layers, as specified above, until the ffll has been brought to the finished slopes and grades as shown on the accepted plans. ?FT- Sufflclent Inspection by the soils ergineer.shall be maintained during the tT lrg an compacting operations so that he can certify that the fill was constructed in accordance with the accepted specifications. seasonal Lfmfk. No fill material shall be placed, spread, or rolled if weather conditions 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 the fill are as previously specified. Limiting Values of Nonexpansive Soils. Those soils that expand_25 percent or less frgm air dry to saturation under a unit load of 500 pounds per square foot are considered to be nonexponslve . All recommendations presented in the “Conclusions ” section of the attached report are a part of these speciflcotions. q LNTON LNeIHLmINO. INC. BEtiTON ENGINEERING, INC. APPLIED 001L MECHANIC* - FOUNDATIONS 6717 CONVOI COURT *AN OIEGO. C*LIFORN,* 92,,1 P”IL,P HENKING BENTON C”ISIDII(I ClWL INCTINIL” APPENDIX A Unified Soil Classification Chart* SOIL DESCRIPTION GROUP SYMBOL I. COARSE GRAINED, More than half of material is b thon No. 200 sieve size.** GRAVELS CLEAN GRAVELS z 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 More than 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 than 50 SILTS AND CLAYS Liquid Limit Greater thon 50 Ill. HIGHLY ORGANIC SOILS GW GP GM GC Well graded gravels, grovel-sand mixtures, little or no fines. Poorly graded grovels, gravel-sand mixtures, little or no fines. Silty gravels, poorly graded gravel- sand-silt mixtures. Clayey gravels, poorly graded gravel- sand-clay mixtures. SW SP SM SC Well 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-sand mixtures with slight plasticity. Inorganic clays of low to medium plas- ticity, gravelly clays, sandy cloys, silty cloys, lean cloys. Organic silts and organic silty-clays of low plasticity. Inorganic silts, micoceous or diatomoceous fine sandy or silty soils, elastic silts. Inorganic cloys of high plasticity, fat clays. Organic cloys of medium to high plasticity PT Peat and other highly organic soils. TYPICAL NAMES TELEPHONZ ,714, 5(1s.,oss * Adopted by the Corps of Engineers and Bureau of Reclamation in January, 1952. ** All sieve .i~ec nn this rhnrt ore U. 5. Standard. BENTON ENGINEERING, INC. APPLIED SOIL MECH*NICS - ,=O”ND*T,ONs 6717 CONYOY COURT **I4 DIEGO. CALIFORNIA 82111 PHlLlP “ENKING BENTON P”sslornT. ClYlL LHClHLL” APPENDIX B Sampling The undisturbed soil samples ore obtained by forcing o 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 o special cutting tip on one end ond o double boll valve on the other, and with o 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 18 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 ore token to the laboratory in close fitting waterproof containers in order to retain the field moisture until completion of the tests. The driving energy is calculated as the overage energy in foot-kips required to force the sampling tube through one foot of soil at the depth at which the sample is obtained. Shear Tests The shear tests are run using a direct sheor machine of the stroin control type in which the rote 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 ore secured. Each sample is sheared under a 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 condttrons. 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 are applied in several increments to the upper surface of the test specimen and the resulting deformations ore recorded at selected time intervals for each increment. Generally, each increment of load is maintained on the sample until the rate of deformation is equal to or less than l/l0000 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. Exoansion Tests One inch high samples confined in the brass rings are 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 sample. Water is permitted to contact both the top and bottom of each sample through porous stones. Continuous observations are mode until downward movement stops. The dial reading is recorded and expansion is recorded until the rate of upward movement is less than l/10000 inch per hour.