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Home My WebLink AboutCT 04-14A; TRAILS END; ADDENDUM TO THE GEOTECHNICAL REVIEW OF MECHANICALLY STABILIZED EATHR (MSE) WALLS; 2017-11-08RE061V17Ei3 _o.i NOV2OZOl7I - LAND DEVELOPMEN5ith ENGINEERING Date Geotechnical e Geologic a Coastal o Environmental 5741 Palmer Way a Carlsbad, California 92010 • (760) 438-3155 • FAX (760) 931-0915 • www.geosoilsinc.com TECHNICALMEMO RAN DUM DATE: November 8, 2017 W.O. 6635-F-SC TO: Donna Drive, LLC 5505 Canca De Golf t4 Rancho Santa Fe, California 92091 .' Attention: Mr. Brian Dorman VY No. 19' c..' Li fl ( No. RCE 477 " rflQfflg / *Exp. IL Geologist From: Robert G. Crisman, CEG 1934 or C David W. Skelly, RCE 47857 SUBJECT: Addendum to the Geotechnical Review of Mechanically Stabilized Earth (MSE) Walls, Trails End Development, CT 04-14, Carlsbad, California References: 1. "Geotechnical Review of Mechanically Stabilized Earth (MSE) Walls, Trails End Development, CT 04-14, Carlsbad, California," W.O. 6635-F-SC, Dated November 2, 2017, by GeoSoils, Inc. "Keystone Retaining Walt Plans for: Trails End Development, CT 04-14," Sheet KW1, Job No. 17201 dated September 25, 2017, by ABl Engineering Consultants, Inc. 'Precise Grading Plans For: Trails End Development, CT 04-14," 5 Sheets, DWG No. 481 ZE - 1A, Job No. 13136, dated June 28, 2017 (City Approval date), by Masson &Associates, Inc. "Geotechnical Update and Plan Review, Trails End Development, Carlsbad, California," W.O. 6635-Al-SC, dated June 6, 2016, by GeoSoils, Inc. "Geotechnical Update Evaluation, Proposed Trails End Development, Northwest Corner of the Donna Drive and Carlsbad Village Drive Intersection, Carlsbad, San Diego County, California," W.C. 6635-A-SC, dated November 27, 2013, by GeoSoils, Inc. In accordance with your requestand authorization, GeoSoils, Inc. (GSl) has reviewed the referenced wall plan with respect to site soil conditions and the geotechnical reports. Based on our review, this addendum to the geotechnical review, dated November 2, 2017 (see Reference No. 1) was prepared. The MSE wall (per Reference No. 2) does not appear to have reinforcing grid in it. The design guidelines prepared by Keystone Retaining Wall Company (available online) appear to indicate that gravity walls are only allowed up to 4.67 feet for a 2:1 sloping surcharge and a select backfill type (i.e., siltysand, phi = 30, c= 50, unit weight = 120 pcf). There is currently no testing of onsite soil to support the 30 degree phi angle used in the design. An evaluation of shear strength for soils within the foundation zone for the wall indicated a phi angle of 20 degrees, a cohesion of 317 psf, and a density of 130 pcf. Recommend that the wall engineer revise design to account for actual foundation zone conditions. Soil to be used for wall backfill, i.e., retained zone and/or reinforced zone soils are not currently present onsite. As such, GSI will need to obtain soil sample of potential backfill and evaluate shear strength prior to use. Our experience suggests that a select soil with a phi angle of 30 degrees, and a cohesion of 50 psf (i.e. silty sand) will exhibit as-built densities on the order of 130 pcf, not the 120 pcf used. in design. As such, GSI recommends a unit weight of 130 pcf be used in design with respect to the reinforced and retained zones. An evaluation of global stability (static and seismic) was performed for the current plan slope configuration and MSE wall (per Reference No. 3), using known parameters for foundation zone soils, as well as anticipated parameters for reinforced and retained zone soils, our evaluation indicated a factor of safety (FOS) of at least 1.5 (static), however, the FOS for the seismic, analysis was less than the minimum criteria of FOS 2~ 1.15. Additional analysis, including the use of geotextile grid behind the MSE wall was performed, based on our analysis, an adequate factor of safety for both static and seismic conditions is achieved when a minimum two (2) layers of Miragrid 5XT (or equivalent), with a minimum length of 18 feet, are used within the walls "reinforced" zone. Printouts of the stability analysis for the reinforced wall conditions are attached. The conclusions and recommendations presented in the referenced reports remain pertinent and applicable and should be appropriately implemented during project planning, design, and construction. The conclusions and recommendations presented herein are professional opinions. These opinions have been derived in accordance with current standards of practice, and no warranty, either express or implied, is given. Standards of practice are subject to change with time. GSI assumes no responsibility or liability for work or testing performed by others, or their inaction; or work performed when GSI is not requested to be onsite, to evaluate if our recommendations have been properly implemented. Use of this report constitutes an agreement and consent by the user to all the limitations outlined above, notwithstanding any other agreements that may be in place. In addition, this report may be subject to review by the controlling authorities. Attachments: Stability Analysis for Reinforced MSE Wall Conditions Donna Drive, LLC W.O. 6635-B-SC Trails End, CT 04-14, Carlsbad November 8, 2017 File* e:\wpl2\6600\6635fatt.memo GeoSoils, h. Page 2 230 210 190 0 6635-F-SC Trails End - Static, Mirafi 5XT @ 18' rf,'I df d,,nn 'I'i".I'.&,,ro thflihA1i ..7.17'-f-r. m wII - thIir - ytnrir - 1R n12 Run By: GeoSoits. Inc. 11/8/2017 01:31 PM # FS Soil Soil Total Saturated Cohesion Friction Pore Ptez. Load Value Intl Points: 36. to 36.2 a 1.586 Desc. Type Unit WI. Unit WI. Intercept Angle Pressure Surface LI 2000 Term Limits: 78. to IOU. b 1.587 No. (pci) (pci) (psi) (dog) Param. No. L2 500 psf c 1.588 cot 1 120.0 125.0 317.0 20.0 0.03 0 d 1.589 all 2 130.0 135.0 50.0 30.0 0.01 0 o 1.591 a12 3 130.0 135.0 317.0 20.0 0.01 0 I 1.591 Tsa 4 120.0 125.0 500.0 30.0 0.00 0 gl.592 a h 1.593 i 1.594 r— Wt IL j 1.594 I -- - ..... ... ............. .///f.. ...... -3.i 2 7 2 - .22_T0T__,_ : L.._ . Lb/f, : ._. 2 13 3 3 : 3 H 20 40 60 80 100 120 GSTABL7 v.2 FSmin=1 .586 Safety Factors Are Calculated By The Modified Bishop Method 6635-F-SC Trails End - Seismic, Mirafi 5XT @ 18' x:\shared\word perfect data\carlsbad\6600\6635 donna drive, llc\slope stability\11-7-17\6635-f-se mse wall -seismic - 5xtgrid - 2.p12 Run By: GeoSoils, Inc. 11/8/2017 01 :3OPM I_:....f. # FS Soil Soil Total Saturated Cohesion Friction Pore Piez. Load Value nit Points: 36. to 36.2 a 1.158 Desc. Type UnitWt. UnitWt. Intercept Angle Pressure Surface LI 2000psf Term Limits: 78. to 100. b 1.159 No. (pcI) (pcI) (psf) (deg) Param. No. L2 500psf C 1.159 col 1 120,0 125.0 317.0 20.0 0.03 0 Peak (A) 0,460(g) d 1.159 all 2 130.0 135.0 50.0 30.0 0.01 khCoef. 0.15Og< e 1.160 a12 3 130.0 135.0 317.0 20.0 0.01 0 V oe. 0.10 g 1 1.160 Isa 4 120.0 125.0 500.0 30.0 0.00 0 gl.160 a h 1.161 —h i 1.161 LIIe'cP 1 .161 .................................................... ,.._... _3J.. 7/ 'I . --------- _.. .. 1N 2 3"2 3,3 3 3 I 1 Ia 3 1 1 I 4 . i6 H I Ii 20 40 60 80 100 120 GSTABL7 v.2 FSmin=1.158 Safety Factors Are Calculated By The Modified Bishop Method 230 210 190 L 0