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HomeMy WebLinkAboutCT 82-09-2A; La Costa Meadows Unit 2; Soils Report; 1982-09-20PHlLlP HENKINO eENTON P”ES,O~.d, C,“lL TNGI”ILI ‘BENTON ENGINEERING, INC. *PPLcED 50iL MECHANICS ~~ FOUNDATIONS 5540 RUFFlN ROAD SAN DIEGO.CALIFOHNIA 92!23 September 20, 1982 TFLE,“DHL 1714, S(lB-I*,, P 8 M Investment, Ltd. % Richard Armstrong 267-F El Camino Real Encinitas, CA 92024 Gentlemen: This is to transmit to you two copies of our report of Proiect No. 82-9-2A entitled “Soils investigation, Proposed Colonial House Condominiums, Lots 396 and 397 of La Costa Meadows Unit No. 2, Carlsbad, California, ” dated September 20, 1982. ’ We ore also sending, under separate cover, two copies of this report to Mr. Richard Armstrong and one copy of this report to Mr. Brian Smith, Civil Engineer. If you should have any questions concerning any of the doto contained in this report, please contact us. Very truly yours, BENTON ENGINEERING, INC. Pi-B/jr ENGINEEAfNG DEFT. LlBRARY City of Carlsbad 2075 Las Palmas Drive Carfsbad CA92009459 SOILS INVESTIGATION PROPOSED COLONIAL HOUSE CONDOMINIUMS LOTS 396 AND 397 Cf LA COSTA MEADOWS UNIT NO. 2 CARLSBAD, CALiFORNlA For P and M Investment, Ltd. PROJECT NO. 82-9-2A SEPTEMBER 20, 1982 ^-.. _^L. r.,r..,CrOl.lc ,-r TABLE OF CONTENTS SOILS INVESTIGATION No. Page Introduction ________________-_--------------- - ------- -------_ 1 Field Investigation - _____________________ -___--_-_-___--__--_-- 1 and 2 Laboratory Tests ________________________-________________-__ 2 DISCUSSION, CONCLUSIONS AND RECOMMENDATIONS Soil Conditions ____--______------_--_-_--_------__--------- Conclusions - ___-_--_-______-- --- --_-----_ -------- _--- ---e-_-- Footing ~commen&tions _------e-m ------- ------_------------- Retaining Walls ______ - ______ -__-___-___-_--__----------------- Special Design for Expansive Soil Conditions ---------------------- 3 3 and 4 3 4 and 5 5and6 DRAWING TITLE Location of Test &rings ------------------------ ------ ---------_ Summary Sheets: bring No, 1 -_--_------------------------------------ Boring No. 2------------------------------------------ Boring No. 3 ___________---_--_------------------------ Boring No. 4 ---- c____----_-__------_----------------- bring Noa 5 -------------me ----w-v - ---__----- --_-m-s Boring No. 6------------------------------------------ Consolidation Curves --------------_-------------------------- 24 APPENDICES Unified Soi, Classification Chart-------------------------------- Sampling, Shear Tests, Consolidation Tests and Expansion Tests----------------------------------------------- 1 2 3 4 5 6 7 8 and 9 A B BENTON ENGINEERING. INC BENTON ENGINEERING. INC. APPLIED 60CL MECHANICS ~~~- FO”NDATlONS 55.40 R”FF,N ROAD SI\N DIECO.CALIFORNIA 92123 PHlLlP HENKINO eENTOH PIISIDIN, ClYlL E’(TIYEEII introduction SOILS INVESTIGATION This is to present the results of o soils investigation conducted on the site for the proposed Colonial House Condominiums, bk 396 and 397 of La Costa Meadows Unit No. 2, in Carl&ad, California. It is understood that the proposed three story buildings will be primarily of wood frame construction with interior masonry walls. Retaining walls are to be constructed on the east and north sides of the proiect. The objectives of the investigation were to determine the general subsurface soil conditions at the site and sufficient physical chorocteristics of,the soils so that soil parameters and engineering recommendations could be presented for the design and construction of the proposed buildings and retaining wall foundations. In order to accomplish these objectives, six borings were drilled and both undisturbed and loose bulk samples were obtained for laboratory testing. Q ‘;’ Field Investigation T cy co Six borings were drilled with a truck-mounted rotary bucket-type drill rig at the 1 approximate locations shown on the attached Drawing No. 1 , entitled “Location of Test Borings. ” IL 2 + The borings were drilled to depths of 9.5 tb 15.0 feet below the existing ground surface. A continuous 2 log of the soils encountered in the borings was recorded at the time of drilling and is shown in detail 2 on Drawing Nos. 2 to 7, inclusive, each entitled “Summary Sheet. ” 3 .% 2 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 droo weight used for driving the sampling tube into the soils was the “Kelly” bar of the drill -2- rig which weighed 2040 pounds, rmd the average drop was 12 inches. The general procedures used in field sampling are described under “Sampling” in the attached Appendix B. Laboratory Terk Laboratory tesk were performed on oil undisturbed samples of the soils in Boring Nos. 1 to 4, inclusive,, in order to determine the dry density ond moisture content., The results of these task ore presented on Drawing Nos. 2 to 5, inclusive. Consolidation tests were performed on representative sampies in order to determine the load-settlement charmcteristics of the soils and the resulkof these tests are presented graphically on Dmwing Nos..8and9, each entitled “Consolidation Curves.” ln addition to the above laboratory tests, expansion tests 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 ore presented as follows: Percent Expansion Under Unit Load of Depth of 500 Pounds per Square Boring Somple Sample Foot from Air Dry No. No. in Feet Soil Description to Saturotion 1 1 2.5 Silty cloy 5.44 2 ’ 1 2.5 Clayey fine sand 1.23 ,3 1 2.5 Fine sandy clay 4.66 Q Y The general procedures used for the preceding laboratory tests ore described briefly in Appendix B. 9 % Direct shear tests were performed on selected undisturbed samples that were saturated ond 3 IL drained prior to testing. The results of these tests ore presented below: c-4 7 r Angle of z Normal Shearing Intern01 Lad in Resistance Friction c!x:;:A . 2 kipsjsq ft kipdsq ft Degrees ft Ib/sq _ 5 0.5 0.32 20.5 130 2 Boring: 1, Sample: 1 e Depth: 2.5 feet 1 .o 0.51 0. 2.0 1.12 Boring: 2, Sample: 1 0.5 0.35 29 70 Depth: 2.5 feet 1.0 0.63 2.0 1.51 -3- DISCUSSION, CONCLUSIONS AND RECOMMENDATIONS Soil Conditions Filled ground was encountered to depths of 8.0, 11 .O, 2.5, 4.2, and 5.8 feet, respectively, in Borings 1,2,3,4, and 5. Firm natural fine sandy cloy was encountered ot the surface in Boring 6. The upper fill soils were loose to medium loose to depths varying from 0.4 to 1 .O foot below the existing ground surface. The fill soils below these depths consisted primorily of compact silty clays, fine sondy cloys, clays and clayey fine sands. The natural soils underlying the fill consisted of clay, silty cloy, grwcl1.y clay, clayey fine to medium sond, clayey fine to coarse sand, fine sandy clay, and gmvelly fine to medium sandy cloy. These natural soils were medium firm to very firm except between 4.2 and 6.5 feet in Boring 4 where the silty clay was loose and porous. Free ground water was not encountered in the exploration borings, drilled on Moy 25, and September 8, 1982. Conclusions The existing compacted filled ground is suitable for footings placed at least 2.0 feet below the existing ground surface and designed using cm allowable beoring value of 1500 pounds 3 + per squore foot. However, a layer of loose noturol soil was encountered below the fill, between fz -$i 4.2 and 6.5 feet, in Boring 4 and it is recommended that footings in the vicinity of Boring 4, the :: central portion along the east side of the building on Lot 397, should be deepened through this T; ‘? LY loose layer and be founded at one foot into the underlying medium firm clay. It is recommended co . 2 ot the time of excavation for the footings along this side of the project, that a soils engineer be 3 2. on the iob to examine the trench and footing excavation and probe the sides and bottom to determine e o- the horizontal limits of the porous natural soils in a north-south and east-west direction so that the extent of the required deepened footings may be determined. lt is concluded from the laboratory tests that the silty cloy soil, similar to that encountered to 3.5 feet in boring 1, and the mixture of cloy and fine sandy cloy, encountered to 2.5 feet in BENTON ENGINEERING. INC. -4- Boring 3, would be considered “expansive” type soils. Fine sandy cloys and silty clays were also encountered in the upper portion of Borings 5 and 6. Therefore, special design ond precautions will be required to minimize possible detrimental effects caused by these potentiolly expansive soils. Footing Recommendations The upper portions of four out of the six exploratory borings consisted of the expansive soil conditions, therefore, oil footings should be placed at least 2.0 feet below the lowest adjacent ground surface. Footings at least one foot in width and placed at a minimum depth of 2.0 feet moy be designed using on allowable bearing value of 1.500 pounds per square foot. This value is for dead plus live loods ond moy be increased one-third for dead, live, wind ond seismic loodings. The depths of footings in the vicinity of Boring 4 must be deepened one foot below the porous natural soils in thot area. A system of deepened piers and reinforced concrete grade beams may be on economical clternative to continuous footings in that area of the site. Based on the results of the load-consolidation tests, the settlements of continuous footings 2 feet wide, supporting a uniform load of 3OW pounds per lineal foot, are estimated to be on the order of l/4 to l/2 inch. 5 Retaining Walls 4 Contilever type retaining walls with o horizontal surcharge of soil behind the wall may a 3 be designed using cm equivalent fluid pressure of 45 pounds per cubic foot. Walls supporting o &I. 2 1 l/2 horizontol to 1 vertical slope should be designed for on equivalent fluid pressure of 85 + 2 pounds per cubic foot. These design pressures assume that no hydrostatic pressures will develop 2 behind the walls and thot no significant surcharge loads ore placed within o horizontal distance ;; .E equol to the height of the wall. Either weep holes or perforoted drain pipes bockfilled with grovel e p. behind tht stem wall should be provided to prevent hydrostatic pressures from developing behind the walls. For lateral resistonce, on allowable passive pressure of 300 pounds per square foot may be used at o depth of one foot into the compacted filled ground or suitable undisturbed notuml ground BENTON ENGINEERING. INC. -5 and this value moy be increased at the rote of 100 pounds per squore foot for each additional foot in depth below one foot. A coefficient of 0.3 is recommended for the frictional resistance between the bottom of the footing and either the compacted fill or suitable natural soil. This value may be combined with the allowable passive pressure to determine the total ollowoble resistonce to lateral movements. Special Design for Expansive Soil Conditions In order to minimize possible detriment01 effects caused by the potentiolly expansive soil conditions, the following minimum special design and Rrecoutions ore recommended. Additional steel reinforcement and greater depths of footings moy be needed ond may be specified by the Architect and/or Structural Engineer. 1. Use continuous interconnected reinforced concrete footings, where possible, and place these at a minimum depth of 2.0 feet below the lowest adjacent exterior finol ground surface. If isolated interior column footings ore required, these should be placed ot o depth of 2.5 feet below the lowest odjocent ground surface. 2. Reinforce and interconnect continuously with steel bors oil interior ond exterior footings with one #5 bor at 3 inches above the bottom of the footings ond one #5 bar placed 1 l/2 inches below the top of the stems of the footings. 3. Raised wooden floors that spon between continuous footings that hove o clearance of 18 inches above the expansive soils ore best. If slobs are placed on grode these should be reinforced with ot least 6 x 6 - lO/lO welded wire fabric. A minimum of 4 inches of crushed rock 3/4 to 1 inch in size should be ploced beneoth oil concrete slobs and covered with o moisture barrier . Two inches of clean sand should*then be placed over the moisture barrier and below the bottom of the slob. 4. Separate garage slobs From perimeter footings by o l/2 inch thickness of construction felt or equivalent, to allow independent movement of garage slobs relotive to perimeter footings. Assure complete seporotion by extending the felt over the full depth of the front thickened edge BENTON ENGINEERING. INC. -6- of the garoge slob. Also, cut off the garage door stops at least l/2 inch above the slob. 5. Exercise every effort to assure that the soil under the foundations ond slobs has o uniform moisture content, 3 percent to 4 percent greoter thon optimum throughout the top 3 feet below finished grade of the time of placing foundations and slabs. 6. It is recommended that positive drainage, 6 inches of vertical foll in 6 feet horizontally, should be provided around the perimeter of the buildings in landscaped oreas. Droinage systems should also be provided to collect oil runoff from rrwfs and conduct the woter in wotertight pipes either into the streets or storm drains. All surfoce drainage should be prevented from ponding adjacent to or running over the tops of slopes. Inlet boxes and wotertight pipes should be instolled when necessary to comply with the above requirements. Respectfully submitted, BENTON ENGINEERING, INC. BY C Remkr I . . Reviewed by $4 RCE No. 10332 Distribution: (2) Addressee -i (2) Mr. Richard Armstrong (1) Mr. Brion Smith, Civil Engineer k Li RCR/PHs/jr i4 BENTON ENGINEERING. INC. I I I 1 I I I I I I I 1 - 3 of LOT 396 ilooe !jope 83--l LOT d 397 4 I I I LUCIERNAGA STREEI - LEGEND @Xotes Approximate Location of Test bring Drawn.bv: R.C. Remer Dote: 6-11-1982 LOCATION OF TEST BORINGS Scale: 1 ” = 80’ PROPOSED COLONIAL HOUSE CONDOMINIUh4S LOTS 396 AND 397 OF LA COSTA MEADOWS~ UNIT NO. 2 CARLSBAD, CAlIFORNlA PROJECT NO. 82-5-l2F BENTON ENGINEERING, INC. I DRAWING NO. 1 I SUMMARY SHEET eanINQNa. 1 of Clayey Fine Sand 0 Indicates Undisturbed Drive Sample A Indicates Loose Bulk Sample ,RoJEcl Ma. DRAWIWQ No. 82-5-12F; BENTON ENGINEERING, INC. -- 2 I 1; 3* -1 D-. 4 il !f 3-l ? 1J i L i l- 2- 3- 4- s- 6- 7- 8‘ SUMMARY SHEET OONINONO. 2 1 Light Brown, Dry, Loose, Mixe With Some Clayey Fine Sand Slightly Moist to Moist, Compact Light Brown, Slightly &lst to Moist, Compact, With Scattered Rock Fragments to 6” Dark Brawn, Slightly Erbist, Medium Firm, Porous 1 Very Firm . Slightly Moist, a I [lark Brown,Slightly Moist,’ L SILTY CLAY MLXTURE OF CLAYEY FINE SAND AND SILTY CLAY SILTY CLAY CLAY it 8 Ia= Lc X’ - 4. - 4. 4. 4. 14. - zi & L-0 PL - 15.; - 9.2 3.5 8.2 9.0 - - - ,4.0 - ?9.4 Q8.8 ‘4.8 13.1 & $1 ri - - IRmEcl No. %:2r?iF. I DNAWNQ NO. BENTON ENGINEERING, INC. 3 SUMMARY SHEET eoNINQN0. 3 Brown, Slightly Moist, Very Firm,With Scattered Rock FINE TO MEDIUM INE TO MEDIUM PROJECT NO. ONAWINQ NO. 82-5-l F,, 9 2i BENTON ENGINEERING, INC. 4 -- SUMMARY SHEET eonlwoNo. 4 MWFCT NO. ORAWINO NO. BENTON ENGINEERING, INC. 5 . F: E ; B 5 E 5 b s i 3- 6- 8- t- SUMMARY SHEET eoN,NaNo. 5 and Rusty Brown Spots, With Few Fractured Rock to 4” Dark Brown, Moist, Firm, PROJECT NO FINE SANDY CLAY SILTY CLAY SILTY CLAY - 2.c 0.2 - 4.1 6.1 - -- -- - -- -- - - -- - -- ma - - -- -- -- - f Fil - BENTON ENGINEERING, INC. OnAwlNa No. .6 . 5 t i? z ,” r E d L Y i B SUMMARY Y(EET OORWONO. 6 With Interbeds of Yellow Brown, Fractured Rock, Slightly Porous CLAYEY FINE TO COARSE SAND MOJECT No. DRAWING No. 82-5-l% BENTON ENGINEERING, INC. 7 - - CONSOLIDATION CURVES LOAD IN KIPS PER SQUARE FOOT 0.4 0.6 0.6 I 2 4 6 6 IO 0.2 0 1 ( ( / 2 3 4 6 6 8 0 INDICATES PERCENT CONSO’LIDATION AT FIELD MOISTURE l INDICATES PERCENT CONSOLIDATIDN AFTER SATURATION PROJECT NO. ORAWINB NO. 82-5-12F BENTON ENGINEERING INC. 82-9-2&~_ 8 +1 0 1 2 0 6 8 9 11 12 CONSOLIDATION CURVES LOAD IN KIPS PER SQUARE FOOT 0.2 0.4 0.6 0.6 I 2 4 6 6 IO I6 1 0 INDICATES PERCENT CONSOLIDATIDN AT FIELD MOISTURE 0 INDICATES PERCENT CONSOLIDATION AFTER SATURATION PROJECT NO. 82-5-12F I ORAWINQ NO. BENTON ENGINEERING INC. Q9-o-76. ' 9 PHlLlP HENKlNCI BENTON ,llSlDLNT ClYlL INcTINEErl BENTON ENGINEERING, INC. APPLIED *ml. MECHINlCO - FO”HD*TION* se40 R”i=FlN ROID SAN DIECiO,CALIFORNIA 92113 APPENDIX A Unified Soil Classification Chart* SOIL DESCRIPTION GROUP SYMBOL I. COARSE GRAINED, More than half of material is w than No. 200 sieve size.** GRAVELS CLEAN GRAVELS = half 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 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 than 50 Ill. HIGHLY ORGANIC SOILS GW GP GM GC SW SP SM SC ML CL OL MH CH OH PT TELEPHONE (714, S18S-l~~S TYPICAL NAMES Well graded gravels, gravel-sand mixtures, little or no fines. Poorly groded gravels, gravel-sand mixtures, little or no fines. Silty gravels, poorly graded gravel- sand-silt mixtures. Clayey gravels, poorly graded gravel- 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-clay mixtures. Inorganic silts and very fine sands, rock flour, sandy silt or clayey-silt-sand mixtures with slight plasticity. Inorganic cloys of low to medium plas- ticity, gravelly clays, sandy clays, silty clays, lean clays. 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 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 January, 1952. ** All sieve sizes on this chart ore U. S. Standard. BENTON ENGINEERING, INC. *.PPLIED *on. YEC”ANICB - FOtJND*TION* ss.0 R”m=lN ROAD SIN DIEGO, CALIFORNIA 92123 PHll.lP HENKING eENTON PlEILlDm4T ClVlL LNrlNsll APPENDIX B Sampling The undisturbed soil samples are 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 o 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 CI 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 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 as 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 I 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 ore made without removing the samples from the brass liner rings in which they are secured. Each sample is sheared under CI 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 ore 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 crs 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 rate 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 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.