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Home My WebLink AboutMS 01-06; GIBRALTER VIEW TOWNHOMES; UPDATED PRELIMINARY GEOTECHNICAL INVESTIGATION; 2002-09-09BARRY AND ASSOCIATES GEOTECHNICAL ENGINEERING P.O. Box 230348 September 9, 2002 Legacy Development, 6965 El Camino Real Ste. 105-451. Carlsbad, California Encinitas, CA 92023-0348 Inc. (760) 753-9940 92009 Att: Mr Mark Goethals Subject: UPDATED PRELIMINARY GEOTECHNICAL INVESTIGATION Proposed Gibraltar Views 4-Unit Townhomes Gibraltar Street La Costa, California 92009 References: Plans prepared by: TM Engineering, Inc. Dated .5/11/02, and Masson and Associates Dated 11/19/01 Preliminary Geotecbnical Investigation Prepared by Barry and Associates, Dated 4/7/98 Dear Mr. Goethals, In response to your request, we have performed the updated preliminary geotechnical investigation at the subject site for the proposed 4-unit townhomes. The findings of the investigation and recommendations for grading and foundation design are presented in this report. No changes have been.made on the property or adjacent properties since the original geotechnical investigation that would impact the development of the site.The original report is valid unless otherwise recommended in this report. From a geotechnical point of view,-it is our opinion that the site is suitable for the proposed grading and construction of the project, provided the recommendations in this report are implemented during the design and construction phases. If you have any questions, please contact us at (760) 753-9940. This opportunity to be of service is appreciated. Respectfully submitted, A.R.BARY SOCIA Principa rry OFCA A4 UPDATED PRELIMINARY GEOTEC}ICAL INVESTIGATION Proposed 4-Unit Townhomes Gibraltar Street La Costa, California 92009 Prepared For Legacy Development, Inc. 6965 El Camino Real, Suite 105-451 Carlsbad, California 92009 September 9, 2002 W.O. P-1567-2 Prepared By: A.R.-BARRY AND ASSOCIATES P.O. Box 2303.48 Encinitas, CA 92023-0348 - TABLE OF CONTENTS INTRODUCTION................................................ 3 SITE CONDITIONS ............3 PROPOSED ........ . . . . ...... 3 SITE INVESTIGATION ........................................... 3 GEOTEC}ICAL CONDITIONS . . ............. . ......................4 SOIL. . . . .............. . . ......... .................4 EXPANSIVE SOIL ............ . . .4 GROUNDWATER ......................................... 4 D .' SEISMIC ................ . . . . . . .....................4 E . LIQUEFACTION.................. .4 CONCLUSIONS AND RECOMMENDATIONS .............................5 GENERAL ...........................................5 GRADING .................. . .......................... 5 FOUNDATIONS; ................. . ................... 5 SLABS ON GRADE .....................................6 RETAINING WALL . . . . . . . .......... ...................7 DRIVEWAY .......................................... 8 DRAINAGE ...........................................8 FOOTING INSPECTION ................................8 PLAN REVIEW ........................................ 9 LIMITATIONS..................................................9 APPENDICES APPENDIX A See referenced Preliminary Geoteáhnical Investigation APPENDIX B See referenced Preliminary Geotechnical Investigation FIGURE 1 .....................Fault Map FIGURE 2 ......................Liquefaction Map September 9, 2002 W.O. #P-1567-2 Page 3 INTRODUCTION This report presents the results of our preliminary geotechnical investigation. The purpose of this study is to evaluate the nature and characteristics of the earth materials underlying the property and their influence on the proposed project. SITE CONDITIONS The lot is located on the west side of Gibraltar at the terminus of the cul-te-sac street in La Costa, California. The graded lot is elevated approximately three feet •above Street level. The fill slope to the rear of the lot is steeper than 2:1 and several local "pop-outs" have occurred. It appears that the failures are surf icial and can be corrected by cutting the slope back to 2:1 (horiiontàl to vertical) vegetation consists of grass and weeds.. PROPOSED DEVELOPMENT Plans prepared by TM Engineering, Inc. of San Clemente, California, dated 5/11/02 and Masson and Associates of Escondido, California, Dated 11/19/01 provide for a 4 unit 3 story townhomes project. SITE INVESTIGATION See referenced Preliminary Geotechnical Investigation P-1567, prepared by Barry and Associates, dated April '7, 1998. Classification See. referenced Geotechnica]. Investigation. September 9, 2002 W. 0. #P-1567-2 Page 4 GEOTECHNICAL CONDITIONS SOIL See referenced Geotechnica]. Investigation. Expansive Soil .. The potential for 'expansive soils varied from low to moderately expansive. Groundwater Groundwater was not encountered in our test trenches. Groundwater related problems are not anticipated during of after construction. Seismic Parameter Table Symbol Factor Seismic Zone Factor 16-I Z 0.4 Soil Profile Type 16-J - SD Seismic Coefficient . 16-0 Ca 0.44Na Seismic, Coefficient 16-R Cv 0.64Nv Near Source Factor 16-S Na 1.0 Near Source Factor 16-T Nv 1.0 Seismic Source Type - B. Maximum Moment Magnitude ..........6.9 Slip Rate, SR......................1.5 mm/yr. Liauef action The soils on the site are not considered subject to seismically induced liquefaction due to such factors as soil density, sand particle size, and lack of groundwater. Liquefaction September 9, 2002 W.O. #P-1567-2 Page 5 CONCLUSIONS AND RECOMMENDATIONS General The on site soils are suitable for the proposed grading project and for the support of the proposed structures, provided the recommendations in this report are implemented during the design, grading, and construction phase. Grading General Grading will consist of •the removal and exportation of approximately 4 feet of loose fill that capes the lot. The underlying soil will be removed and re-compacted to a depth of approximately 3 feet, scarified to 18" and, re-compacted. Final depth of removal will be determined by a representative of this firm during the grading operation. It is our understanding that the City of Carlsbad will not permit any alteration of the existing fill slopes, even though they are steeper than 2 horizontal to 1 vertical and show signs of surface failure. See Grading Specifications, Appendix B Foundation Footings for the proposed project should be a minimum of 15 inches wide and founded a minimum of 18" below grade. A 12-inch-by-12-inch grade beam should be placed across the garage opening. Footings September 9, 2002 W.O; #P-1567-2 Page 6 founded a minimum of 18" below grade may be designed for a bearing value of 1500 psf. The.bearing value indicated above is for the total of dead and applied live loads. This value may be increased by 33 percent for short durations of loading, including the effects of wind and seismic forces. Resistance to lateral load may be provided by friction acting at the base of foundations and passive earth pressure. A coefficient of friction of 0.3 should be used with dead-load forces. A passive earth pressure of 250 pounds per square foot, per foot of depth of fill penetrated to a maximum of 1500 pounds should be used in the design. Steel reinforcement should consist of 4-#4 bars, 2 placed 3" from the bottom of the footing and 2 placed 2" below the top of the footing. Footings located near the edge of fill slopes must maintain a horizontal distance of 7 feet from the outside edge of the footing to the edge of the fill slope. Slabs on grade If slab on grade is planned it should be a minimum of 4..0 inches thick and reinforced in both directions with No. 3 bars, placed 18 inches on center. The slab should be underlain by a minimum 4-inch September 9, 2002 W.O. #P-1567-2 Page 7 sand blanket which incorporates a minimum 6.0-mil Visqueen or equivalent moisture barrier in its center, for moisture sensitive floors. Utility trenches underlying the slab should be bedded in clean sand to at least one foot above the top of the conduit, then backfilled with the on-site granular materials, compacted to a minimum of 90 percent of the laboratory maximum dry density. However, sufficiently compacting the backfill deposits may damage or break shallow utility lines. Therefore, minor settlement of the backfill in the trenches is anticipated in these shallow areas. To reduce the possibility of cracks occurring, the slab should be provided with additional reinforcement to bridge the trenches. Retaining Walls Retaining walls should be designed in accordance with the following soil perimeters: Soil Type Equivalent Fluid Pressure (.PCF) (Unrestrained Walls) Native Soil 33 (Level Backfill) Additional Uniform Pressure (PSF) (Restrained Walls) 6xH* *H= Height of wall in feet Walls should be adequately drained to prevent build-up of hydrostatic pressures. Footings should be designed in accordance with the previous foundation recommendations. September 9, 2002 W.O. #P-1567-2 Page 8 Driveway The following recommendations are submitted as preliminary guidelines for pavement construction and are based on a .non- expansive soils condition in the upper 12" of subgrade. Asphalt Concrete The driveway section should consist of 4.0 inches of asphalt over 8.0 inches of Class II base. The Class II base and the upper 12 inches of the subgrade deposits should becompactéd to a minimum of 95 percent of the laboratory maximum dry density. The upper 12" of subgrade should consist of non-expansive soil. Paved areas should be protected from moisture migrating under pavement. Drainage All roof water should be collected and conducted to a suitable location via non-erodible devices. Roof gutters are recommended. Pad water should be directed away from foundations and around the residence to a suitable location. Pad water should not pond. Footing Inspections Structural footing excavations should be inspected by a representative of this firm prior to the placement of reinforcing steel. September 9, 2002 W.O. #P-1567-2 Page 9 Plan Review A copy of the final building plans should be submitted to this office for review, prior to the initiation of construction. Additional recommendations may be necessary at that time. moderately LIMITATIONS This report is presented with the provision that it is the responsibility of the owner or the owner's representative to bring the information and recommendations given herein to the attention of the project's architects and/or engineers so that they may be incorporated into the plans. If conditions encountered during construction appear to differ from those described in this report, our office should be notified so that we may consider whether or not modifications are needed. No responsibility for construction compliance with design concepts, specifications or recommendations given in this report is assumed unless on-site review is performed during the course of construction. The conclusions and recommendations of this report apply as of the current date. In time, however, changes can occur on a property whether caused by acts of man or nature on this or adjoining properties. Additionally, changes in professional standards may be brought about by legislation or the expansion of knowledge. Consequently, the conclusions and recommendations of this report September 9, 2002 W.O. #P-1567-2 Page 10 may be rendered wholly or partially invalid by events beyond our control. This report is therefore subject to review and should not be relied upon after the passage of three years. The professional judgments presented herein are founded partly on our assessment of the technical data gathered, partly 0n our understanding of the proposed construction and partly on our general experience in the geotechnical field. If you have any questions, please do not hesitate to contact our office at 753-9940. Respectfully submitted, ) A.R. BA Y tu G00119 Principal' Enginee MA 71 1 PL A N NING M For a Major Earthquake, San Diego Tijuana Metropolitan Area F 11 I 1 1 , I9 4 l : 04 1990 :::::::;:::::::1:, obddod) ag//rj/blo hi buildings of good design end construction, alight to nodnrata in S . !t,.u. \ .... •/ .. . - I - . 4 ... / / •. .. i wa//boll ordlmsybul/dinga ona/dorabieia poorly built orbadtydos/gnodbuildings, roil of piaster iii onidrat,le to large amount,also some stucco Broke numerous windows furniture to sums extent Broke week chimneys at roof line (sometimes Damage 1 1 / / / I' 1 / / 1 /t 1 c/ I ) / ( damaging roofs) fail of cornices from towers and high buildings. Damage alight In atluctoroS (brick) bu/11oopo0a11y10 withstand earthquakes. Consider- , able ill Ordinary substantial huiid/nge partial collapse ractkvsd tumbled down w0000n houses in Some caaas throw off panel walls Is frame structures, Fall of walls twisting fiI of cl/imnoya columns rr/onumellls also (salary alaska towers s. ISdicetes the I /[ upper range of damage associated with Intons/ly VIII — Indicates 11,0 lower range Damage considerable in at,vcturas (masonry) built especially to wit/Island earth . quakes throw out of plumb some wood frame houses ba/il especially to withstand / / ;7 / I r — I / I ) r (.0 ( j.t .' N ' auayross substantial (masomy) buildings, sonya colap large part; or hks sometimes broken. f-h •i• -•- I /; .. :d11 . - . : .. ingly, Intensities ~IX can be anticipated along the fault zone and whatever ground failure aucurs, ;/--./iJ'" I//lonoinosIxa,egoneranyaitribareblolosudaoafasIllngatddoroendrsiiureAccord D DAMAGE ASSESS - GROUND FAILURE ct~) Area with vary high 10 f//gIl potential for ground la//urn, notably liquefect/on, soil/n- menl and similar a/fools. It Area sub)26t to ssisni/col/y Induced ianduid/ng. 1/13 9 THEY ARE BASED UPON IHE. FOLLOWING HYPOTHETI CAL CIIAN OF EVE -S IN THE PLANNING AREA EX- 2 VARIOUS LOCALITIC v ACILITIES AFIE HYPODIETICAL AND NOT TO BE Ism CONSTFIU OAS SITE-SPECIFIC ENGINEERING EVALUA- -OR THE MOST PART, DAMAGE ASSESSMENTS -1) FOR THIS PARTICU r 4/ill SCENARIO PAATHQUAKI/ THPFIP IS L)l$AORU MIINT AMONG INVESTIGATORS Pb TO THE ( 4 4 / / / / / 1 / •' I / / / / I / .4 n t/( 1 I / - I I? .L5 MOST REALISTIC MODEL FOR PREDICTING SEISMIC IN- EN /. / / I 1 °)k - - 1 1 r is / I / 1/ /4d4?i 1/I — TESNEDAN SENSITIVE TO EMEFI(K-NCY FIE. OUAI<EPLA I EACH WOULD NNIN/S YIELOADIFFERENT zf', PARTICULARLY h — /PrClIIC SCENARIO AN EARTHQUAKE or S/GRill \ / / / / FACILITIES 7HAT ARE -T IF DAMAGE ASSESSMENT$ ARE BASED UPON THIS Isf ;"v 1 V i / / I //is ( / / / /7 \ / / 1 / / 5 VN CANTLY DIFFERENT MAGNITUDE ON THIS (DR ANY ONE I N- 0 MANY OTHER FAUL "S IN THE PLANNING AREA WILL MILE FEE F 7 SIL VER STRAND PA IlL T Planning 177 71 If CD J Area 4 Over Strand Fault At- / 44 4 3 4-S RECEIVED DEC 09 2005 ENGINEERING DEPARTMENT