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HomeMy WebLinkAboutCT 73-02; Santa Fe Glens Unit 1-3; Soils Report; 1974-07-16BENTON ENGINEERING. INC. APPLIED SOIL MECHANICS -- FO”NDATIONS 6717 CONVOY COURT **?4 DIEGO. CALIFORNIA S2?11 PYlLlPHENL(ING BENTON FR161DI)IT SIYIL LNGIYILII Rick Engineering Company 509 Elm Avenue Corlsbad, California 92008 Attan tion: Mr. Barry C. Bender July 16, 1974 iELEZnO*IE (7141 565.19s.s Subiect: Project No. 72-8-2BC Supplemental Soil Investigation Santa Fe Glens Unit Nos. 1, 2 and 3 arlsbad Tract No. 73-2 Carl&d, California Gentlemen: In November 1972, we prepared a preliminary sails investigation report for the overall Santa Fe Glens subdivision in San Diega County, California. The report was entitled “Project No. 72-8-2BC, Preliminary Soils Investigation, Santa Fe Glens, San Ciego County, California,” and dated November 14, 1972. Four copies of the report were submitted to Mr. Irving Roston of La Costa Land Company, Ranch0 La Costa, California, on November 14, 1972. The soil lnvestigation found that potentially critical soil zones were encountered in the Borings 1, 2 and 6 drilled within the boundaries of the proposed Santa Fe Glens Unit Nos. 1, 2, and 3, as described in Section 2 on page 2 of that report. We received a copy of the presently proposed grading plans in May of this year ond noted that 1 l/2 horizontal to 1 vertical slopes were proposed for vertical heights of 25 to 36 feet in the areas of Borings 1, 2 and 6. Con- sequently, we proposed to you, on May 15, 1974, to drill additional exploration borings in the arecs of proposed cut slopes in the vicinity of Borings 1, 2 and 6, in order to determine whether any conditions exist which might be detrimental to the long term stability of the pro- posed cuts at the design slope ratio. In order to accomplish this oblective, three additional borings were drilled in the proposed cut are= and bath undisturbed and loose soil samples were obtained for laboratory testing. This additional investigation WQI based on the Reliminary Grading Study Plan (1”~50’ Scale) prepared by Rick Engineering Company of Car&ad, California, and dated May 20, 1974. The three additional borings, Borings lA, 2A and 3A, were drilled either 24 or 30 inches in diameter with a truck-mounted rotary bucket-type drill rig at the approximate locations shown EN6lNEE$N~~EGBt?MY 2075 Las fUmet3 Drive CplfsbsQ CA 92009459 2’ Field Investigation Project No. 72-Z-2BC -2- July 16, 1974 La Costa Land Company, Santa Fe Glen on the attached Drawing No. 1, entitled “Location of Test Borings.” The borings were drilled to depths of 34 to 39 feet below the existing ground surface. A field engineer war lowered into each open boring to determine the degree of dip and direction of slope between bedding planes and to examine the in-place soil layers. A continuous log of the soils encountered in the borlngs WCS recorded at the time of drilling and is shown in detail on Drawing Nos. 28 to 33, inclusive, each entitled “Summary Sheet.” The soils were visually classified by field identification procedures in accordance with the Unified Soils Classification Chart, A simplified description of this classification system is pre- sented 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 Appendlx B. Laboratory Tesk Laboratory tesk were performed on all undisturbed samples of the soils in order to determine the dry density and moisture content. The results of these tests ure presented on Drawing Nos. 28 to 33, inclusive. Consolidotion tesk were performed on one representative sample in order to determine the loal-settlement characteristics of the soils and the resulk of these tesk are pre- sented graphically on Drawing No. 34, entitled “Consolidation Curve.” In addition to the above laboratory tesk, expansion tesk were performed on some of the clayey soils encountered to determine their volumetric change characteristics with change in moisture content. The recorded expansions of the samples are presented ce follows: Percent Expansion Under Unit Load of Depth of 500 Pounds per Squore Boring Sample Sample, Soil Foot from Air Dry to No. No. In Feet Description Saturation 2A 1 3.0 C layey fine sand 1.28 2A 2 5.0 Fine sandy cloy 2.78 2A 3 10.0 C I ayey fine sand 0.81 2A 4 15.0 Clayey fine to medium sand 1.99 3A 2 6.0 Clayey fine scmd with clay seams 3.29 3A 4 15.0 Silty fine sand 0.3 The general procedures used for the laboratory tesk are described briefly in Appendix 8. Compaction tests were performed on representative samples of the soils to be excavated to establish compaction criteria. The soils wem tested according to the A.S.T.M. D 1557-70 method of compaction which uses 25 blows of a 10 pound rammer dropping 18 inches on each of Project No. 72-D-2BC Lo Costa Land Company, Sonta Fe Glen -3- July 16, 1974 5 layers in a 4 inch diameter l/30 cubic foot mold. The resulk of the tests are presented as follows: Maximum Boring Bag Depth Soil Dry Density No. Sample in Feet Description Ib/cu ft 1A 2 5.0-6.0 Slightly silty fine sand and silty 113.0 ffne sand with clay seams 2A 2 2.0-3.0 Clayey fine sand 111.2 2A 4 14.5-15.5 Clayey fine to medium sand 116.6 3A 1 3.0-4.0 Slightly silty fine sand 113.3 Optimum Mois- ture Content % dry wt 15.5 15.3 11.3 14.2 In order better to classify the finer grained soils, Attorberg Limit tesk were performed on certain samples in accordance with A.S.T.M. Designations D 423-61T ond D 424-59. The resulk of these tests and the group symbols for the soil classifications are presented as follows: &I Boring Sample Depth Soil Liquid Plastic Plasticity Group No. No. in Feet Description Limit Limit Index Symbol 1A 4 14.0-15.0 Clay 55.2 25.2 30.0 CH 2A 5 20.0 Clay 59.7 24.2 35.5 CH 3A 6 29.0-30.0 Clay 60.4 21.2 39.2 CH Mechanical analysis tesk were performed on a representative soil sample to aid in soil clas- sifications. Tb soil sample was washed through the No. 200 sieve in order to determine the fraction of fine grained soils with particles smaller than No. 200 sieve size. The rasulk of the task are presented below: U.S. Sieve Size No. 200 Soil Classification: Boring 2A, Bag 2 Depth: 9.5-10.0 Feet Percent Finer By Weight 36.7 Clayey fine sand sENTON ENGINEERING. INC. Project No. 72-C-2BC La Costa Land Company, Santa Fe Glen -4- July 16, 1974 Direct shear tests were performed on selected undisturbed clay samples from the previously slickensided zones ,that were all saturated before testing and sheared in undrained condition. In order to simulate the perviously tectonic movemenk, the samples were sheared repeatedly using differen.t surcharge loads during the tesk. The resul k of these tesk are presented below: Boring lA, Sample 3 Depth: 10.0 Feet * Boring 1 A, Sample 5 Depth: 20.0 Feet Boring 2A, Sample 5 Depth: 20.0 Feet Boring 3A, Sample 6 Depth: 25.0 Feet * Remolded to field density Normal Load in kidsq ft 0.5 0.5 1.0 2.0 0.5 0.5 1.0 2.0 0.5 2.02 32 130 0.5 0.42 1.0 0.78 2.0 1.40 0.5 1.0 2.0 2.0 0.66 23 70 0.72 0.94 1.61 Maximum Shear Load kips/sq ft 1.26 0.64 0.66 1.17 Angle of Internal Friction Degrees 20 Apparent Cohesion Ib/sq ft 300 0.66 42 200 1.17 2.08 2.09 In order to evaluate the shearing resistance and cohesive strength of the clay soils along the previous slide planes, unconfined compression tesk were performed on hvo clayey samples and the resul k of these tests are presented below: Boring Sample Depth No. No. (Feet) 1A 3 10.0 1A 6 25.0 Unconfined Compressive Strength W/xi ft) 4720 1970 Apparent Cohesion (Wsq ft) 2360 985 BENTON ENGINEERING. INC. Project No. 72-8-2BC La Costa Land Compcmy, Santa Fe Glen -5- July 16, 1974 Conclusions and Recommendations Based on the results of laboratory strength tesk conducted on the slickensided clayey soils found in the exploration borings, and in reference to the strength parameters of the similar cluyey soils in the general areas at the time of incipient failure, the following factors of safety have been obtained for both 36 feet and 20 feet height of slopes at different slope ratios: APumed Height of Slopes (Feet) 36 26 Slope Ratio (Horizontal to Vertical) 1 l/2:1 2:l 2 l/2:1 2:l Factors of Safety Against Shearing Failum Including 10 Percent for Seismic Loading 1.08 1.28 1.86 157 It is therefore concluded and recommended that the proposed excavation slopes in the areas of Borings lA, 2A and 3A be made no steeper than 2 horizontal to 1 vertical for slopes less than 26 feet ins height. For slopes between 2aand 36 feet, the slopes should be made no steeper than 2 l/2 horizontal ta 1 vertical. It is recommended that proper drainage devices be provided at the top and the bottom of the proposed cut slopes; 50 that sheet flow of surface run off over the slope surface, and the possible scouring of the toe of slope crm be mlnimized. Down drains over the proposed cut slopes may be ne.eded. Water seepage found between.19 and 24 feet in Boring 2A moy also need special dminage provisions. ,, .~ _ ~- . .._~._ .-~ Respectfully submitted, BENTON ENGINEERING, INC: Reviewed by SHS/PHB/pk Distr: (4) Addressee (1) La Costo Land Compcmy Attention: Mr. Irving Roston BENTON ENOINEERING. INC. > ut SUMMARY WEEI’ SUMMARY WEEI’ E’t CKJH’NG NO.LllB_-~.- CKJH’NG NO.LllB_-~.- ELEVATION 260.0’ * ELEVATION 260.0’ * $Y pc: r¶ - - 7 .c - Z3.l IE.! -.---__- Dark Brown, Dry, Medium Soft CLAYEY FINE SANDY CLAY Light Brown and Light Gray- green, Slightly Moist, Medium Firm, Thin Bedded - 03.’ 00.4 cu.2 - - - - I , / : / ; I Light Brown and Groy-brown, Slightly Moist, Very Firm, Many Sea Shells, Contact Dips 4’ at S 350 qV Light Brown and Gray-brown, Slightly Moist, Very Firm, Clay Seams ta 2 Inches, Layers WManv Sea Shells Green With Red-brown and Yellow, Slightly Moist, Very Firm, Many Thin Silt Veins With Some Gypsum Crystals, SI ickensided, Fractured t SLIGHTLY SILTY / -INE SAND AND jlLTY FINE SANC nl - - / - 9.7 19.5 CLAY PROJECT NO. 72-8-2BC Continued o Drawing No. 29 8 - Indicates Loose Bag Sample - Indicates Undisturbed Drive Sample * - Elevations shown were obtained by interpolation Between Contour Lines on the Preliminary Grading Study Plan (1”=50’ Scale) prepared by Rick Engineering Company of C&bad, Cal ifornia, dated May 20, 1974 I-- .I_.,.~ DRAWING NO. BENTON ENGINEERING, INC. 28 I PROJECT rm 72-8-2BC Green With Red-brown and Yellow, Slightly Moist, Very Firm, Many Thin Silt Veins With Some Gyosum Crystals Irregular but Generally Continuous l/2 Inch to 3/4 lncl Gypsum Vein Dips 3’ at S 600 E, Highly Fractured and SI ickensided Dark Brown With Yellow, Slightly Moist, Very Firm, Thinly Interbedded, Contact Dips 70 at N 700 W Dark Green With Yellow, Slightly Moist, Very Firm, Slightly Slickensided, 6 Inches any Gypsum Veins 30S7fNNO411 - Occasional Gypsum Veins II---m__II Ix-_- =, SUMMARY SHEET rrt BORING No.-j_A_&ont.) $2 UP YY ?G cc= 0 CLAY / I 16.2 Dark Green With Red-brown, Very Slickensided, Fractured, Water in Slickensides to 29.8 Feet i’ CLAY 4 1 1 I , ‘ 1 ‘0.8 10.8 8.3 26 .’ 97. + I -I--- ORAWNG NU. BENTON ENGINEERING, INC. 29 r-i-r-i-- 2 E g .;:: :.‘. 2 L:. 3 . 1 . . . . . . . . ~ a ;;;;; . . . . . . . . . . . . . . . 6 SlJMMARY SHEET BOH,NG NO. 2,4 Red-brown, Dry, Loose CLAYEY FINE SAND SILTY FINE SAND Red-brown. Dry. Loose rown +v-brown Jght Gray With Yellow Streaks, jlightly Moist, Firm 7.8 3. - .ight Groy , CLAYEY FINE SAND I Inch Thick Red-brown Pocket m Southwest Half of Boring t inch Thick Red-brown Pocket m One Side of Boring 14.6 '1 3 zl 4 3 4 :~ ,. ,. p 5= 3; 5- ron Oxide Stains 3ray With Red-brown, Slightly noist, Firm L -- SILTY CLAY &- 17.8 :LAYEY FINE TO AEDIUM SAND , ! INE TO MEDIUM SANDY CLAY ; - 6. &ht Brown, Moist, Firm ‘ei low-brown 3yosum >ray-brown, Very Moist, Soft 3 Inch Layer of Gypsum at Ilive and Light Red-brbwn m tark Green ond Light Yellow, ‘cry Moist, Firm, Gypsum, later Seepage d “0 v, 3, I PROJECT NO. Continued on Drawing No. 31 .- DRAWN0 NO. BENTON ENGINEERING, INC. 30 SUMMARY St-iEE~I tlOHlNG NO. 2A LCont . ) _----,~ 21 22 23 ’ ” -H- ll----_ Green, Very Moist, Very Firm 24 25 26 27 28 29 30 31 32 33 - !- c-- 3 /- I( 1~~ Groy, Very Moist, Very Firm, ented- ght Yellow-green, Moist, 34 I i1 ~9.6!108. 12 CLAY (Merges) j , 18.3 FINE SANDY MY (Merges) :LAYEY FINE TO AEDIUM SAND --- SILTY CLAY (Merges) FINE SANDY CLAY 127.5 cry Moist, Very Finn 16.t - 13.r - 11 .; - 37 38 39 PROJECT NO. 72-8-2BC BENTON ENGINEERING, INC. -- ” TT --h,“mxI-.e ,---_I- ~_ ..---. -._~_---- z ; w(I r-2 : -lY -4 5$ 60 ? iv, ocz ; mz ; "L$ * ~~~N~y2~~q---~-~ T--~ ..:y+ Dark Brown, Dry, Medium Firm, SILTY FlNE . . Rootlets SAND (Merges) I- : Light Brown and Light Gray, 3 -,’ IF 4 Slightly Moist, Very Firm 3.9 ?5.1 , . . 7 ,.I fJ;Jeo~;~nw;sWlth Partially Llght Groy With Light Red- ./ j brown, Slightly Moist, Very ; 16.2 1 11 .S 08. . I- !-- ( L r-[ i-- i-( I- i- :II / 9. 14.6 12.1 I 1 I 1 : : 1 1 c ; t 5 1C 11 12 13 14 15 16 17 I8 19 !O - CLAYEY FINE SAND ‘T: \ pi .I ‘I ( Light Gray With Light Yellow j and Black, Slightly Molst,~ Very Firm, 1 to 2 inch Lens of Light Gmy Cl,oy and Red-brown \ Clayey Fine Sand at Contact Plane, Contact Dips 3O at PF 6.2 35.. 2 to 5 Inch Lens of Slightly Silty Fine to Medium Sand and &$\qThin Light Green Clay Seams, iron Cemented Nodules Sill-Y FINE SAND j ; 3.2 13.7 10.5 1 k3.t - Continued on Drawing No. 33 PROJECT NO. 72-B-28(3 I BENTON ENGINEERING, INC. I DRNVING NO 32 SUMMARY SHEET BOHING fd0.-~&~nt.) Red-brown and Dark Green, C Soft, Sea Shells Red-brown and Dork Green, + - - 04. 12. - 12. :LAYEY FINE TO MEDIUM SAND, FINE SANDY cL&rges) 1 !5.8 5.8 7.5 - 1 .d I---- Slickensided CLAY Dark Gray-green, Slightly ; Moist, Very Firm, Occasional i Cemented Modules 2 I 3 CLAYEY FINE TC MEDIUM SAND (Merges) CLAY 4 I - - CB. - - - 1.6 8.r - _-- i PROJECT NO. DR.wvING NU. ! 72-G-20C BENTON ENGINEERING, INC. 33 CONSOLIDATION CURVE LOAD 111 KIPS PER SQUARE FOOT +50.2 0.4 06 0.8 LO 2 / / ~ -T-j-+$ I0 I6 o indicates percent consolidation at field moisture l Indicates percent cons01 idotion after saturation PROJECT NO. 73sL7Rc- I BENTON ENGINEERING, INC. I DRAWlNO NO ?A BENTON ENGINEERING. INC. APPLIED SOIL MECHANIC* - ~O”NDAT,ONS 6737 CONYO” CO”lT 8.N DIEGO. CALlFdRNlA e7.111 .“lLIP YENKING BENTON C”*sIDI*T. ClViL LYGIYLErn APPENDIX A Unified Soil Classification Chart* SOIL DESCRIPTION GROUP SYMBOL I. COARSE GRAINED, More than holf of -- moteriai is w than No. 200 sieve size.** GRAVELS CLEAN GRAVE LS More ho!f of coarse fraction is larger than No. 4 sieve size but smallerGRAVELS WITH FINES than 3 inches (Appreciable amount of fines) SANDS CLEAN SANDS More than holr or 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 than 50 III. HIGHLY ORGANIC SOILS GW GP GM GC SW SP SM SC ML CL OL MH CH OH PT TYPICAL NAMES TLLL.“OUL ,714, sss-less Well graded gravels, gravel-sand mixtures, little or no fines. Poorly graded gravels, gravel-sand mixtures, little or no fines. Silty grovels, poorly graded gravel- sand-silt mixtures. Clayey gravels, poorly graded grovel- sand-clay mixtures. 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-cloy mixtures. 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 clays, silty clays, lean clays. Organic silts ond organic silty-clays of low plasticity. Inorganic silts, micaceous or diatomoceous fine sandy or silty soils, elastic silts. Inorganic clays of high plasticity, fat clays. Organic cloys of medium to high plasticity Peat and other highly organic soils. * Adopted by the Corps of Engineers and Bureau of Reclamation in Jonuary, 1952. l * AI, .1_.~_ -1--. __ LL!. -I-.* ^.p I, < <+,,J,,A BENTON ENGINEERING, INC. APPLIEO 801L MECHANICS - FO”ND*TIONS 6717 CONVOY COURT *AN DIEGO. CALIFORNIA 8211, PHlLlC HENKINO BENTON C”I.IDIN, ClYlL LNG,NELR APPENDIX B TILLPYONI ,,I., S(IS.,OES 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 a double ball valve on the other, and with ct 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 token 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 calculated OS the average 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 shear 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 made without removing the samples from the brass liner rings in which they are 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 conditions. Consolidation Tests The apparatus used for the consolidation tests is designed to receive one of the one inch high rings of soil as it comes from the field. Loads are applied in several increments to the upper surface of the test specimen and the resulting deformations are recorded at selected time intervals for each increment. Generally, each increment of load is maintained on the sample until the rote of deformation is equal to or less than l/10000 inch per hour. Porous stones are 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 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 made until downword movement stops. The dial reading is recorded and expansion is recorded until the rate of upward movement is less than 1/10000 inch per hour.