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Home My WebLink AboutCDP 16-26; TABATA RANCH LOT 4; GEOTECHNICAL RECOMMENDATIONS - RETAINING WALLS; 2019-05-21,, ~ CT~c Construction Testing & Engineering, Inc. Inspection I Testing I Geotechnical I Environmental & Construction Engineering I Civil Engineering I Surveying May 21 , 2109 Tabata Family Trust C/O: WMC General Contractors, Inc. Attention: Mr. Bruce Wiegand 760 Garden View Ct., Suite 200 Encinitas, California 92024 Telephone: (760)803-2427 CTE Project No. 10-13292G CEIVE JUN 18 2019 LA~DNDEVELOPMENT GI NEER ING Via Email: bruce@wncommunities.com Subject: Update Geotechnical Recommendations for Retaining Walls Proposed Tabata Ranch Subdivision Lot-4 6764 Strawberry Place Carlsbad California References: At end of document Mr. Wiegand: As requested, Construction Testing & Engineering, Inc. (CTE) has completed a review of the previously prepared geotechnical reports and documentation for Lot 4 at the subject site, as referenced herein, in order to provide retaining wall design recommendations. We also recently visited the site to confirm current conditions. Recommendations are based on prior site documentation referenced herein, new and/or updated regulatory requirements, review of current site conditions, and the scope of work we agreed to perform at this time. Based on project improvement plans the proposed improvements are to consist of retaining wall construction. CTE has found the recommendations in the referenced geotechnical documents to be in compliance with common geotechnical engineering practices and should be considered valid unless revised herein. However, CTE reserves the right to further modify recommendations and/or provide additional recommendations based on the actual conditions encountered at the site during earthwork and/or construction. Design parameters in CTE's referenced geotechnical report for walls below grade wall are considered appropriate for retaining wall design and are reiterated herein for convenience. 1441 Montiel Road, Suite 115 I Escondido, CA92026 I Ph (760) 746-4955 Fax (760) 746-9806 I www.cte-inc.net ~ Update Geotechnical Recommendations for Retaining Walls Page 2 Proposed Tabata Ranch Subdivision Lot-4 6764 Strawberry Place, Carlsbad California May 21, 2019 CTE Job No. 10-13292G 1.0 WALLS BELOW GRADE For retaining walls to be constructed in association with the proposed development, the following parameters are anticipated to be applicable. Walls should be designed using the recommended equivalent fluid pressures in Table 1.0 below. Walls below the water level are not anticipated for the subject site. In addition to the recommended earth pressure, subterranean structure walls adjacent to traffic loads should be designed to resist a uniform lateral pressure of 100 psf. This is the result of an assumed 300- psf surcharge behind the walls due to normal street traffic. If the traffic is kept back at least 10 feet or a distance equal to the retained soil height from the subject walls, whichever is less, the traffic surcharge may be neglected. The project architect or structural engineer should determine the necessity of waterproofing retaining walls to reduce moisture infiltration. Retaining wall backfill located within a 45-degree wedge extending up from the heel of the wall should consist of soil having an Expansion Index of 30 or less (ASTM D 4829) with less than 30 percent passing the No. 200 sieve. The upper 12 to 18 inches of wall backfill should consist of lower permeability soils, in order to reduce surface water infiltration behind walls. The project structural engineer and/or architect should detail proper wall backdrains, including gravel drain zones, fills, filter fabric and perforated drain pipes. Design Parameters: • Retaining footings and reinforcing design should be based on an allowable vertical bearing capacity of 2500psf for retaining walls founded on properly compacted fill material. • Passive soil pressure for lateral bearing capacity lateral capacity of 200 psf per foot of depth (not to exceed l 200psf) is appropriate for design. • A coefficient of friction for concrete on properly compacted fill soils is 0.30. • The internal friction angle of 30 degrees is considered appropriate for design. TABLE 1.0 EQUIVALENT FLUID UNIT WEIGHTS (pounds per cubic foot) SLOPE BACKFILL WALL TYPE LEVEL BACKFILL 2:1 (HORIZONTAL: VERTICAL) CANTILEVER WALL 35 45 (YIELDING) RESTRAINED WALL 60 80 \\ESC _SERVER\Projects\l 0-13000 to I 0-13999 Projects\! 0-13292O\Ltr_ Update Recommendations Lot 4 -Retaining Wall.doc Update Geotechni.cal Recommendations for Retaining Walls Proposed Tabata Ranch Subdivision Lot-4 6764 Strawberry Place, Carlsbad California Page 3 May21,2019 CTE Job No. 1 O-l 3292G Lateral pressures on cantilever retaining walls (yielding walls) due to earthquake motions may be calculated based on work by Seed and Whitman (1970). The total lateral thrust against a properly drained and backfilled cantilever retaining wall above the groundwater level can be expressed as: For non-yielding ( or "restrained") walls, the total lateral thrust may be similarly calculated based on work by Wood (1973): Where PA= Static Active Thrust (given previously Table 1.0) PK= Static Restrained Wall Thrust (given previously Table 1.0) ~p AE = Dynamic Active Thrust Increment= (3/8) kh yH2 ~PKE = Dynamic Restrained Thrust Increment= kh yH2 kh = 2/3 Peak Ground Acceleration= 2/3 (PGAM) H = Total Height of the Wall y = Total Unit Weight of Soil:::::: 135 pounds per cubic foot The increment of dynamic thrust in both cases should be distributed triangularly with a line of action located at H/3 above the bottom of the wall (SEAOC, 2013). These values assume non-expansive backfill and free-draining conditions. Measures should be taken to prevent moisture buildup behind all retaining walls. Drainage measures should include free-draining backfill materials and sloped, perforated drains, as designed and detailed by the wall engineer or architect of record. These dra_ins should discharge to an appropriate off-site location. Any necessary waterproofing should be as specified by the project architect. 2.0 LIMITATIONS As indicated, the updated recommendations herein are based on our evaluation performed to date and could require modification as project improvement plans further progress and/or based on conditions encountered during construction. The field evaluation and geotechnical analysis referenced in our geotechnical documents was conducted according to current engineering practice and the standard of care exercised by reputable Geotechnical Consultants performing similar tasks in this area. No other warranty, expressed or implied, is made regarding the conclusions, recommendations and opinions expressed. Variations may exist and conditions not observed or described may be encountered during construction. Our conclusions and recommendations are based on an analysis of the observed conditions. If conditions different from those described are encountered, our office should be notified and additional recommendations, if required, will be provided upon request. \\ESC_SERVER\Projects\l 0-13000 to I 0-13999 Projects\) 0-l 3292G\Ltr_ Update Recommendations Lot 4 -Retaining Wall.doc Update Geotechnical Recommendations for Retaining Walls Proposed Tabata Ranch Subdivision Lot-4 6764 Strawberry Place, Carlsbad California Page4 May 21, 2019 CTE Job No. 1 0-l3292G We appreciate the opportunity to be of service on this project. Should you have questions, please contact the undersigned at your convenience. Respectfully submitted, CONSTRUCTION TESTING & ENGINEERING, INC. Dan T. Math, GE #2665 Principal Engineer Rodney J. Jones, RCE #84232 Project Engineer RJJ/JFL/DTM References: Update Geotechnical Recommendations for Proposed Tabata Ranch Subdivision Lot-4 Lemon Leaf Drive, Carlsbad California CTE Job No. 10-l3292G, dated August 26, 2016 (Revised March 5, 2018) Update Geotechnical Recommendations for Proposed Tabata Ranch Subdivision Lemon Leaf Drive, Carlsbad California CTE Job No. 10-l3292G, dated August 26, 2016 Interim As-Graded Geotechnical Report Proposed Tabata Ranch Subdivision Lemon Leaf Drive, Carlsbad, California CTE Job No. 10-12101G, dated July 6, 2015, Modified August 2, 2015 Geotechnical and Update Report and Grading Plan Review Proposed Tabata Ranch Subdivision Lemon Leaf Drive, Carlsbad, California Vinje & Middleton Engineering Job# 01-364-P, dated August 2, 2006 Preliminary Geotechnical Investigation Proposed 4-Lot Subdivision, Tabata Ranch Off Camino De Las Ondas and Lonicera Street, Carlsbad, California Vinje & Middleton Engineering Job# 01-364-P, dated October 24, 2001 \\ESC _SERVER\Projects\J 0-13000 to I 0-13999 Projects\10-13292O\Ltr_ Update Recommendations Lot 4 -Retaining Wall.doc