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HomeMy WebLinkAboutCT 79-05; La Costa Greens Lots 6-7; Soils Report Revised; 1979-11-21PHlLlP HENKING BENTON P”lSlDlNT ClYlL 1NGlN1.1 Frederick J. Moyer, A. I.A. Architects 8 Associates 2348 Harcourt Drive San Diego, California 92123 BENTON ENGINEERING. INC. APCLIFD SOIL MLCtl*.NIC* - FO”NDATIOrw ssao RllFFlN ROAD IAN D1EGO. CLLIFORNIA sz, *, November 21, 1979 c7- 74-5 TILIP”OYL ,7!., ~6~-less Attentim: M. Frederick Meyer REv/5L=d Subject : Project No. 79-8-23A Supplemental Subsurface lnfarmatim Reposed Alta Verde Condominiums Lots 6 and 7 of La Costa Greens Subdivision Nath of La Costa Avenue Carl&ad, California Gentlemen: This is to present the findings and recommendations resultirq from drilling six additional borings at selected locations m the subject Foperty. The objectives of drilling six additlmal baings, Borings 2 to 7, inclusive, were to obtain the subsurface soil conditions in the zme of transition near the central area of the site, so that the boundary or demarcation line of the underlying campetent natural soils and the underlying compressible natural soils m the north pcrtim could be mme accurately established. In addition, the information obtained from these additional baings was to be used to estimate the vertical supporting capacities of the piles that are planned to be used to support the structures spanning over the demarcation line. Field Investigation The six additional borings, Barings 2 to 7, inclusive, were drilled, 5.5 inches in diameter, with a truck-mounted rotary auger drill rig at the approximate locations shown m the attached Drawing No. 1, entitled “Location of Test Borings. ” The borings were drilled to depths of 40 to 65 feet below the existing ground surface. The soils encwntered in the six additimal borings and the prcviws boring, Baring No. 1, are shown in detail m Drawiw Nm. 2 to 20, inclusive, each entitled “Summary Sheet. ” Undisturbed samples were obtained at frequent intervals in the soils ahead of the drilli%. The drop weight used for driviq the samplirg tube into the soils was a steel rammer which weighs 140 pounds, and the average drop was 30 inches. Reject No. 79-E23A Frederick J. Meyer, A. I.A. -2- November 21, 1979 Laboratory Tesk Labaratory tests were perfanned m all undisturbed samples of the soils in order to determine the dry density and moisture content. Shearing strengths of the m site natual soils were cbtained by shearing the solls in a saturated and undrained conditim under their existing overburden pressures. The resulk of these tests are presented on Drawing Nos. 2 to 5, TO and 11,and 13 to 15. Cmsolidatim tesk were performed m representative samples in crder to determine the Imd- settlement characteristics of the soils and the results of these tests are presented graphically m Drawing Nos. 21 and 22, each entitled ‘Cmsolidatim Curves. ” Conclusions It is concluded from the results of field expioratims and laboratary tesk that: 1. Soft to medium firm soils, that have in-place dry density less than 104 pcunds per cubic foot, were found in the upper 5.5 feet, 2.5 feet, 2.2 feet, 2.5 feet, 1.5 feet, 3.5 feet and 2.5 feet, respectively of Borings 1 to 7, inclusive. The loose or soft to medium firm existiq fills at the site are cmsidered unsuitable far the support of future building foundations and new compacted fills under present condition. Wherever new compacted fills and buildirqs are to be constructed, these undesirable upper fill soils should be canpletely removed to a horizontal distance equal to 5 feet plus the depth of removal beyond the perimeter footings of the building and/a the daylight line of the new fill soils. Subsequent to the overexcavatim, clean excavated m site soils augmented by select nm-expansive fill import soils should be placed and be uniformly compacted, under continuous engineering inspection and testing, to at least 90 percent of the maximum dry density in accordance with the A. S. T. h+. D 1557-70 method of campactim. This method of ccmpactim requires the use of 25 blows of a 10 pound rammer falling from a height of 18 inches m each of 5 layers in a 4-i& diameter, l/330 cubic foot ccmpclctim mold. Only select non-expansive or slightly expansive soils, such as silty sand, slightly clayey sand cr other sandy soils may be placed in the upper 3.0 feet below final grwnd surface for compaction.’ 2. Based m the findiryls in additional borings and laboratory tests, the line of demarcation as defined m page 5 of wr October 2, 1979 repmt, has been relocated as shown m the attached Drawing No. 1. Where proposed buildings are to span over the line of demarcation withwt Fovisim for structural separation, it is considered feasible to provide pile foundation support fa that portion of each structure immediately north of the demarcation line, so that potential adverse differential settlemenk within that building can be minimlzed. The piles would serve to distribute the upper structural loads by sheariw resistance into the deeper, firm natural soils in contact with the perimeter surface of the piles. The allowable vertical supporting capacities of a 12-inch square concrete pile or a 12-i& wide steel H-pile are pre- sented m the attached Drawing No. A. The allowable vertiwl supporting capacities af the piles are based m the minimum shearing resistance of the deeper and less compressible natuml soils times the surface area of the pile in cantact with these soils divided by a factor of safety of 2. If other types of pile are to be used, their supporting capacities may be derived by applying a correction based m a direct proportion of the values shown m Drawiw No. A in accordance with the respective perimeter swface areas of the piles. The safe uplift * It should be noted, that wherever expansive sandy clay, silty clay or clay type soils exist in the upper 3 feet below finished grade, as determined during field inspectim, these hwld be removed and should be replaced with non-expansive compacted fill rolls. Project No. 7%8-23A Frederick J. Meyer, A. I.A. -3- November 21, 1979 resistance of each pile may be assumed to be me-half of the downward supparting capacity. In order to minimize adverse effeck of,possible downdrag forces caused .by the settlement of the canpressible soil layers on the upper pation of the driven piles, it is recommended that a 24-inch diameter hole be pre-drilled to Elevation -10.0 feet for piles to be driven in the vicinity of Boring 4 area and to Elevation -15.0 feet in the vicinity of Borings 2 and 7. After pre-drilling, a (cordboard) sonotube should be installed. Piles should then be driven to the design tip elevations. Loose fine sand may then be poured between the sonotubes and the driven piles. It is recommended that the driven vertical piles should not be relied on for lateral support. Any lateral forces should be resisted by grade beams that are designed to transmit the loads to continuous footings located 10 feet or more southerly of the demarcation line. The suggested soil parameters to estimate the lateral resistance are as follows: Grade beams and continuous footings located perpendicular to the direct:m of lateral force: An equivalent fluid density of 200 pounds [r?r cubic foot may be assumed to estimate the passive resistance of soils in contact with the side faces of the grade beams and continuous footings. In order to Fovide an adequate lateral support for the future foundation systems, it is recommended that the grade beams and/or footings be embedded at least 2 feet below the undisturbed final ground surface. If these are reinfcrced to tie in with concrete slabs and/or footings resting on capacted fill without structural support provided by driven piles and located more than 10 feet south of the demarcation line, a friction Factor of 0.4 may be assumed to estimate the sliding resistance of the soils. It is concluded from the load-consolidation test data that the northern portion of the subject property is still undergoing settlement since placement of existing fills in 1969, and it is anticipated that some protrusions of grade beams and pile caps or piles will occur as the soils settle relative to the driven piles. The mwnitudes of differential settlement will thus depend m the thicknesses of the ccmpressible soil strata that increase in thickness northerly of the demarcation line. 3. In accordance with the request made by the Project Structural Engineer, Mr. Abe Salameh of Cmeer Engineering of San Diego, California, we have re-evaluated the bearing value of soils as shown m page 4 of our original soils investigatin report datedOctober 2, 1979 for the subject project. As a result of the re-evaluation, it is our opinion that the originally reccmmended bearing value of 1,000 pounds per square foot, as described on pclge 4 of the October 2, 1979 report, may be increased to 1,500 pounds per square foot if the soft to medium firm existing fills in the upper portion of the site arc all removed and recompacted to at least 90 percent of the maximum dry density in accordance with the procedures described under Section 1 m page 2 of the ‘Conclusions” of this report. BENTON ENGINEERING. INC Project No. 79-8-23A Frederick J. Meyer, A. I.A. -4- November 21, 1979 Respectfully submitted, BENTON ENGINEERING, ILK. By Ad-.&-~ -.~- . . Civil Engineer RCE No. “;9913 Reviewed b RCE No. 10332 Dishibutica:(3) Addressee (1) Coneer Engineering, Attention: h. Abe Salameh SH S/PH B/c BENTON ENGINEERING. INC. I .i .! I : I f c i : .! ; PROJECT NO. 79-8-23A SUMMARY SHEET BDRINQ NO. 1 ELEVATION 22.0’ (*) Light Brown to Light Gray Brown, Dry, Laos; to Msdium Compact, Some Asphaltic Concrete Fragments tight Brown and Gray Brown, Moist, Firm to Very Firm .enses of Dark Gray Fine jandy Clay With Scattered 3rganlc Material SILTY -INE TO MEDIUA SAND :INE TO MEDIUA SANDY CLAY 7.7 - 12.’ 2.3 10.2 - 12.: 18.1 17.6 00.: - 18.i 03.1 lo.t 0.61 - 4.28 I .16 Z.32 Continued On Drawing No. 3 1 Indicates Undisturbed Drive Soil Sample II Indicates Loose Bag Sample 3 Indicates Sample Not Recovered * Elevations were Obtained From 1” = 10’ Scale Grodlng Plan prepared by R 8, R Engineering Co., and signed by Allen D. Ring DNAWING NO. BENTON ENGINEERING, INC. 2 1 .: s I : $ i 4 . ! 2 16- 17 19- 2(r 211 22 23 24- 25 26 27 28 29- 3c- 3t 32- 33- 34- 35 - 0 @ J - PROJECT NO. 79-a-23A SUMMARY SHEET BORINQNO. 1 (Cont.) E Dark Groy, Saturated, Medium ,. z Firm e - - v Light Gray and Olive Gray, Mottled, Saturated, Medium Firm ~ ,, Pockits and LeAses of Clayey ’ - w - ere 9 - rr*r - w e w 3; - w - .,,.. z Dark Gray and Groy ‘INE TO MEDIUA SANDY CLAY FINE SANDY CLAY ‘. ;t SE YY >’ zit 0 - - 7.0 CLAYEY FINE SAND 4.9 FINE SANDY CLAY Continued On Drawing No. 4 9.5 3.9 i.2 7.6 8.3 14.: I .3: .lC :.41 I DRAWING NO. BENTON ENGINEERING, INC. R SUMMARY SHEET BORINQ NO. 1 (Cwt.) 7 Dark Groy and Gray, 36- ,. Saturated, Medium Firm v rrrrr - 37- +++ Dark Blue Gray and Dark Olive Gray, Mottled, Saturated, Medium Firm to Firm 5.3 25.1 99.7 1.11 FINE SANDY 6.3 23.9 100.9 0.37 8.8 22.9 101.5 1.77 10.5 27.0 97.8 2.23 Continued On Drawing No. 5 PROJECT NO. I DRAWING NO. 79-8-23A BENTON ENGINEERING, INC. 4 SUMMARY SHEET BORINQ NO. 1 (CO”t .) Light Blue Gray and Dark Gray Brown, Marbled, Satumted, Very Firm Amounts of Claystone and Sil tstone Fragments I I I PRO>ECT NO. ORAWINQ NO. 79-8-23A BENTON ENGINEERING, INC. 5 1 2, 3' 4. 5 6 7 8 9 '0 11’ 12, 13. :4- 15' 16, ;7. 18. i9, !O SUMMARY SHEET BORINQ NO. 2 ELEVATION 29.3' ~~~ .‘.‘~. ‘;; Gray Brown With Rusty Streaks, Thin Layer of Gray Brown Silty n with Rusty Streaks, 3 Old Topsoil, Dark Brown, Very Moist, Firm, Rootlets, Organic Matter FINE TO MEDIUM SANDY CLAY SILTY FINE TO MEDIUM SAND FINE SANDY CLAY FINE SANDY CLAY Continued On Drawing No. 7 7.4 z 4.6 6.0 Z! 52: YW{ ‘PI - 13.1 13, - 19.' 7.6 6.2 03 08. - 10. 34. 10. E: j!; % - -- - -- - -- -- -!- Fill PROJECT NO. 79-8-23A DRAWING NO. BENTON ENGINEERING, INC. 6 I .I *! I : I c : i c ! ? SUMMARY SHEET 8ORlNQ NO. 2 (Cont.) FINE SANDY and Organic Matter -II I Continued On Drawing No. 8 5.3 4.2 4.2 3.9 !l.! 14.2 5.2 il .9 1 1. I PROJECT NO. 79-8-23A ORAWINQ NO. EENTON ENGINEERING, INC. 7 4 SUMMARY SHEET EORINQ NO. 2 (Cold .) 2 Gray Brown, Very Moist, Medium Firm, Some Organic Matter, Firm Below 44’, Small Amount of Ground Water at Bottom of the Hole FINE SANDY CLAY / 8.8 124.51100.91 I PROJECT NO. 79-8-23A BENTON ENGINEERING, INC. DRAWING NC.. 8 I .I .! I : I c ; 2 . ! 2 SUMMARY SHEET BORINQ NO. 3 ELEVATION 29.9’ 1 Brown, Dry, Loose FINE TO MEDIUM Continued On Drawing No. 10 79-3-23A I BENTON ENGINEERING, INC. 9 8 z SUMMARY SHEET if i BORINQ NO. 3 (ConI.) t E w Dark Grey Brown, Moist, @ m Medium Firm, Organic . . ,,~ ,...., ~ Roohets 6.7 21.7 104.8 1.06 Older Formation, Saturatedi 5.6 20.2 106.2 1.26 FINE SANDY 6.3 23.0 104.6 1.62 4.9 27.0 97.3 1.08 Continued On Drawing No. 11 PROJECT NO. ORAWINQ NO. BENTON ENGINEERING, INC. SUMMARY SHEET BORINQ NO. 3 (Cont. ) CLAYEY FINE SAND u- 3 . . . ifj- .a 4.9 24.3 101.3 3.64 PROJECT NO. DRAWING NO. 79-&23A BENTON ENGINEERING, INC. 11 SUMMARY SHEET FINE SANDY Layer of Clayey Fine to Medium Sand at 6’ Organic, Rootlets Continued on Drawing No. 13 79-&23A BENTON ENGINEERING, INC. I 12 I .I .! I 7 t t : i * ! 2 SUMMARY SHEET BORINQ NO. 4 (Cont. ) FINE SANDY Firm,Organic,Rootlets PROJECT NO. ORAWINQ NO. 79-8-23A BENTON ENGINEERING, INC. 13 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 ~ ..,...... j eg town and Green,Moist, 1 ::“” ,... Medium FIrm,Mixed withclayey , :::.::: . . . fine Sand, Fmgments of Silt- 6.7 stone and Claystone x yz 5 iog SUMMARY SHEET :p $Ez q ORINQ NO. 5 $2 82 2 ELEVATION 27.2 ,.., .k Light &own,Moist,Soft &own and Green,Moist, INE TO MEDIUM FINE SANDY CLAY 6.0 9.8 6.0 9.8 Continued on Drawing No. 15 =I pi z-1 0, - 1.61 I I I PROJECT NO. DRAWING NO. 79-8-23A BENTON ENGINEERING, INC. I 14 .: I I ‘I I L : 4 c ! ; ,lL..I I.“. .R?RA I SUMMARY SHEET BORING NO. 5 (Cont. ) ~Brown,Moist,Medium Firm, White and Rusty Streaks - ic .~. ith Brown Rusty Streaks -rr I-c v w - ,. -3- s w iir .~. ,~,. c*l e M i .,‘~,..., *i m +a+ w FINE SANDY CLAY 1.9 I.9 5.3 24. : 13.4 12.6 1.14 0.8; BENTON ENGINEERING, INC. I DRAWING NO. 15 SUMMARY SHEET BORING NO. 6 ELEVATION 32.0 Light Brown,Moist,Soft to FINE SANDY CLAYEY FINE Continued on Dmwing No. 17 PROJECT NO. 7%&23A I BENTON ENGINEERING, INC. I 16 i .i .! i 4 4 4 5 ;i SUMMARY SHEET BORING NO. 6 (Cont. ) Medium Firm,Rootlets,Organic Sand and Fine Sandy Clay Continued on Drawing No. 18 SUMMARY SHEET BORING NO. 6 (C or& ) -I PROJECT NO. DRAWING NO. 79-8-23A BENTON ENGINEERING, INC. 18 SUMMARY SHEET EORINQ NO. 7 FINE SANDY Grayish White,Moist,Firm FINE TO MEDIUM Moist,Mdium Firm CLAYEY FINE Brown,Greenish Gray Continued on Drawing No. 20 PROJECT NO. DRAWING NO. BENTON ENGINEERING, INC. i .: .! 1 : : 4 r J 2 SUMMARY SHEET GORING NO. 7 (cont. ) CLAYEY FINE PROJECT NO. DRAWING ~0. 79-B-23A BENTON ENGINEERING, INC. 20 0 1 2 6 CONSOLIDATION CURVES LOAD IN KIPS PER SQUARE FOOT l INDICATES PERCENT CONSOLIDATION AFTER SATURATION t PROJECT NO. 79-&23A I DRAWING NO. BENTON ENGINEERING INC. 21 1 0.2 0.4 0.6 0.6 I 2 4 6 6 IO I6 I I I III I I I 0 0 INDICATES PERCENT CONSOLIDATION AT FIELD MOISTURE CONSOLIDATION CURVES LOAD IN KIPS PER SQUARE FOOT 0.6 I 2 4 6 6 IO IE III I I1111111 III1 6 ,,, ,,, ,,, ,,,,, ~ ,,,,,, ,,, II: ,,4 '~' I ,,f ::: q ;_,,:-,:,,,- ,,,,, _: ,,,, ,: Rnrirm I L-7. 8 5 lllpe: 0 INDICATES PERCENT CONSOLIDATION AT FIELD MOISTURE l INDICATES PERCENT CONSDLlDfiTlON AFTER SATURATION PROJECT NO. 79-8-23A DRAWING NO. BENTON ENGINEERING INC. 22 Elev. +lO Elev. 0 Elev. -10 Elev. -20 Elev. -30 Elev. -40 Elcv. -50 ALLOWABLE VERTICAL SUPPORTING CAPACITY OF A IklNCH SQUARE COKRETE PILE OR STEEL H-PILE (‘F. S. -?) k&J 0 30 60 90 120 150 181 - ..__ -- ____ ._ - PROJECT NO, DRAWING NO BENTON ENGINEERING. INC.