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Home My WebLink AboutCT 00-06; BRESSI RANCH; GEOTECHNICAL REVIEW OF MECHANICALLY STABILIZED RETAINING WALL; 2003-11-26Cf oovo1: 4. Leighton and Associates, Inc. 4 LEIGHTON GROUP COMPANY November 26, 2003 Project No. 971009-009 To: Leimar Communities 5780 Fleet Street, Suite 320 Carlsbad, California 92008-4700 San Diego, California 92108 Attention: Ms. Kristine Zortman Subject: Geotechnical Review of Mechanically Stabilized Retaining Wall, South side of Poinsettia Lane Between Station Nos. 84+25 and 85+44; Bressi Ranch, Carlsbad, California Introduction In accordance with the requirements of the City of Carlsbad, we have performed a geotechnical review of the proposed Mechanically Stabilized Retaining Wall along the south side of Poinsettia Lane between Station Nos. 84+25 and 85+44 within the Bressi Ranch development located in Carlsbad, California. The reviewed plans and calculations, entitled Verdura 40 Wall Design, Station 84+25 to 85+44, were designed and prepared by Southern California Geotechnical (SCG) for Soil Retention Systems, Inc., (SCG, 2003). The results our or geotechnical review of the proposed retaining wall is presented below. Retaining Wall Plan Review Findings The purpose of our review is to review the plans and geotechnical soil parameters utilized in the design calculations for conformance with the recommendations provided in the referenced geotechnical documents (Appendix A). Geotechnical review of. the Verdura retaining wall design methodology was not performed as part of our review. However, we did perform a global stability analysis of the slope containing the proposed Verdura retaining wall. Based on our review, we have prepared the following comments that should incorporated into the design and construction of the proposed retaining wall: 3934 Murphy Canyon Road, Sue B205 • San Diego, CA 92123-4425 858.292.8030 • Fax 858.292.0771 . www.leightongeo.com 971009-009 Supporting Calculations: The supporting calculations for the proposed reinforced retaining wall does not include a surcharge for the vehicular traffic on Poinsettia Lane as recommended in the segmental retaining wall recommendations (Leighton, 2003). An appropriate surcharge should be included in the calculations. Supporting Calculations: The interaction factors for pullout used in the calculations appear applicable to a well-graded sand and gravel backfill material. If the existing on-site soil is planned to be used as backfill, should be noted that geotechnical observation and testing during the current grading operations indicates that the majority of the on-site soils consist of silty fine sands or silty clay to clayey silts. Therefore, according to the technical notes on Mirafi's web site (Mirafi, 2002), the appropriate factors for a Miragrid 5XT are presented below if the on-site soil is used as backfill. The reinforced wall engineer should verify the assumptions associated with the determination of these parameters. Ci=0.8to0.9 Cds=O.8 (not O.9t0 0.94) Verdura Wall Plans Sheets 1 through 3: Construction Note No. 8 under "Subsurface Drainage System Installation" states "extend non-perforated piping to drainage piping as shown on drawings". However, the drawings (Sheets 2 and 3) do not show the proposed locations of the non-perforated pipe, or state a maximum horizontal spacing for the non- perforated pipe. The drawings should be revised to show the locations of the proposed non- perforated pipes on Sheet 2. . Verdura Wall Plans Sheet 1. Materials. Geocirid and Geosvnthetic Reinforcina Notes: The Long Term Design Strength (LTDS) for the Miragrid 5XT is shown as 1,733 lbs/fl, however in the supporting calculations the allowable tensile strength is calculated as 1,729 lbs/ft. The reinforced retaining wall engineer should verify the LTDS for the Miragrid 5XT and revise the plans or calculations, accordingly. . Verdura Wall Plans Sheet 2. Profile: Poinsettia Lane. and Surmortina Calculations: The supporting calculations do not include a calculation for the portion of proposed retaining wall between Station Nos.. 84+25 and 84+62, where the plans show only two layers of reinforcement. A calculation supporting the reduction of reinforcement should be included with the supporting calculations. Global Slope Stability Findings Based on the current design of the Verdura Retaining Wall (SCG, 2003) and the anticipated geotechnical conditions, it is our professional opinion that the proposed slope in the vicinity of the proposed retaining wall will have a factor-of-safety of 1.50 or greater following the completion of the project provided the site is graded and constructed in accordance with the -2- Leighton 971009-009 project geotechnical recommendations and that unforeseen geotechnical conditions are not encountered. The results of our global or overall slope stability analysis are presented in Appendix B of this letter. If unforeseen geotechnical conditions are encountered, the project geotechnical consultant should evaluate the conditions and provide appropriate recommendations to ensure that the global stability of the slope and retaining wall have a factor-of-safety of at least 1.50. If you have any questions regarding this letter, please contact this office. We appreciate this opportunity to be of service. Respectfully submitted, 0cSSlo4 2 45283 . ( WA Exp. No )rn LEIGHTON AND ASSOCIATES, INC. 'iiLñ&L William D. Olson, RCE 45283 Senior Project Engineer n KW Randall K. Wagner, C!E 1612 Director of Geology Attachment: Appendix A - References ,*YkED GE K. Appendix B - Global Slope Stability Analysis .No. 161-2i * CERTIFIED * Distribution: (4) Addressee ENGINEERING GEOLOGIST . (2) Lennar Communities, Attention: Mr. Jim Urbina OF CAOf (2) City of Carlsbad, Attention: Mr. Casey Arndt (1) Soil Retention Systems, Attention: Mr. Bob Edwards -3- Leighton 971009-009 APPENDIX A References Leighton and Associates, Inc., 1997, Preliminary Geoteclmical Investigation, Bressi Ranch, Carlsbad, California, Project No. 4971009-002, July 29, 1997. , 2003, Geotechnical Recommendations Concerning Revised Grading and Placement of a Segmental Retaining Wall along the Existing 24-Inch Forced Sewer Main, Poinsettia Lane Station No. 84+00 to 85+50, Bressi Ranch, Carlsbad, California, Project No. 971009-009, August 11, 2001 Mirafi, 2002, Technical Note, Determination of the Long Term Properties for Miragrid Reinforcement Geogrids by NCMA Guidelines, dated January 1, 2000, revised September 1, 2002 Southern California Geotecimical (SCG), 2003, Verdura 40 Wall Design, Station 84+25 to 85+44, Poinsettia Lane at Bressi Ranch, Carlsbad, California, Project No. 03G236-1, dated September 25, 2003. A-i Bressi Ranch Poinsettia Lane Sta. 84+25.11 to 85+44.17 File Name: Nov. wall static lb.slz Analysis Method: Bishop Direction of Slip Movement: Right to Left Factor of Safety: 1.61 Surcharge = 250 psf S S 5555••••SSS S. S S • •• S. •SS •SS•S•S••• S S •SSS S. •S S S S • S S S • S S S S S S S • S S.........S.......... .•,• S • S • S S S S • S S S • S S • S • S ..............S.SS... a . . . . . . . . . . S S S S S S S S S S. S S S S S S • S • S S S S • S S S S S S 5 • • • S 1.61 • • • • • • • • S • • S 5,5 • • S S S S • S S S S • •5•S • S S •S 0 1 0 0 •0 0 5 S S S 5•. 51555555•••S S S S S S St.. S • S S 5500•09SS S • S • .5 • • 5 5 5 5 • S S S S S S S S • S • . S • S • S S S S • S S • S S S • • S S a,& 0,0 5S 55555 •SSSSS S 555555555... S SSSSSSS • ••tSSSSSSSSS 55555.555 .5. • • S.. 5555555555.. SSfSI S SSSSSSSSSSSSSSS 5*5555.55 •SSSSS •SSSSS 60 55 50 45 PU 15 10 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 Horizontal Distance (ft)