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Home My WebLink AboutCT 13-03; Robertson Ranch West Village; GEOTECHNICAL RECOMMENDATION FOR THE FILL PLACEMENT OPERATION, PLANNING AREA PA-1, ROBERTSON RANCH; 2016-05-05May 5, 2016 Mr. Kevin Brickley Toll Brothers LGC Valley, Inc. Geotechnical Consulting 725 Town and Country Road, Suite 200 Orange, California 92868 ~-... -..·.-r..,-~ I 2 '11'~ .t 0 y-~. :' .. : •' ~·~;_~. ;~·'f', Project No. 133023-03 Subject: Geotechnical Recommendations for the Fill Placement Operations, Planning Area PA-l, Robertson Ranch, Carlsbad Tract No. 13-03, Carlsbad, California, California References: LGC Valley, Inc., LGC Valley, Inc., 2014, Geotechnical and Environmental Recommendations for Robertson Ranch, Carlsbad Tract No. 13-03, Carlsbad, California, Project Number 133023-03, dated April29, 2014. Introduction O'Day Consultants, 2015, Grading Exhibit Planning Area A-1, Robertson Ranch, 1 Sheet, dated November 13, 2015 In accordance with your request, LGC Valley, Inc., (LGC) has prepared this letter to provide our geotechnical recommendations concerning the placement of fiB within Planning Area PA-l of the Robertson Ranch project located at 4980 El Camino Real, in Carlsbad, California. We understand that PA-l will be used as a disposal site for approximately 72,000 cubic yards of soil that is currently stockpiled on PA-11. The soil was generated during the grading of the Robertson Ranch project and temporarily stockpiled on PA-11. We also understand that PA-l will remain an open space area and that no development or placement of structures or other settlement improvements are planned. Based on our evaluation, it is our professional opinion that the site design is suitable from a geotechnical perspective provided the fmdings, conclusions, opinions, and recommendations contained within this report are implemented during site development. Site and Project Description Planning Area PA-l is located in the western portion of Robertson Ranch northeast of the intersection ofEl Camino Real and Tamarack Avenue. The roughly triangular-shaped site is bounded by El Camino Real and Planning Area PA-2 on the southwest, Tamarack Avenue on the northwest, a SDG&E Easement on the east. Existing minor drainages are present along the western and eastern sides of the proposed fill area. The site was previously farmed and currently consists of a tilled gently-sloping area with elevations ranging from approximately 75 feet mean sea level (msl) on the northwest to approximately 55 feet msl on the southeast. An approximately 10-to 15-foot tall fill slope ascending to Tamarack Avenue is present along the northwest side of the site. 2420 Grand Avenue, Suite F2 • Vista • CA 92081 • (760) 599-7000 • Fax (760) 599-7007 I \ The proposed fill area will consist of a relatively flat-topped mound with the top located on the northwest side ofPA-1 at an elevation of approximately 90 feet msl. Slopes up to approximately 20 to 30 feet in height, at a slope inclination of 2.5:1 (horizontal to vertical) or flatter, are planned on the east and southwest sides. The street easement along the south side of Tamarack will be widening and a meandering sidewalk potentially placed in the easement at a later date. Recommendations The recommendations provided in the referenced report (LGC, 2014) are considered applicable and remain valid, unless otherwise stated below, in which case the recommendations included in the referenced report are superseded by those included in this report. We anticipate that earthwork during the Planning Area PA-l fill placement operations will consist of processing the area to receive fill, construction of a fill slope key along the proposed toe-of-slope, trucking of fill onto the site, placement and moderate compaction of the fill, and benching of the existing fill slope along Tamarack A venue as fill is placed. Site Preparation Prior to the grading operations, the area to receive fill should be scarified to a minimum depth of 12 to 24 inches, moisture-conditioned, and recompacted. Fill Slope Key A fill slope key should be constructed along the outer downhill side of the fill area in Planning Area PA-l. The fill slope key should be excavated at least 2 feet deep along the toe-of-slope and constructed approximately 15 feet wide with the key bottom angled a minimum of 2 percent into-the-slope. The anticipated fill slope key location is presented on the Geotechnical Map (Figure 1 ). Fill Placement and Compaction The fill soils placed in PA-l should have a near-optimum moisture condition and be wheel-rolled as the fill is placed. The outer 15 feet of the slope around the majority of the fill area, should be moisture conditioned to at least optimum-moisture content and compacted in uniform lifts to at least a 90 percent relative compaction based on the laboratory maximum dry density (ASTM D1557). The optimum lift thickness required to produce a uniformly compacted fill will depend on the type and size of compaction equipment used. In general, fill should be placed in lifts not exceeding 8 inches in compacted thickness. Placement and compaction of the fill should be performed in general accordance with the current City of Carlsbad grading ordinances, sound construction practices, and the recommendations presented herein. Slope Maintenance To reduce the potential for erosion and slumping of the proposed fill slope, the slope should be planted with ground cover and deep-rooted vegetation as soon as practical upon completion of grading. Proper maintenance of vegetation, including regular irrigation, should be performed. Project iVa. 133023-03 Page2 May5, 2016 Limitations Our services were performed using the degree of care and skill ordinarily exercised, under similar circumstances, by reputable engineers and geologists practicing in this or similar localities. No other warranty, expressed or implied, is made as to the conclusions and professional advice included in this report. Changes in conditions must be evaluated by the project soils engineer and geologist and design(s) adjusted as required or alternate design( s) recommended. Closure This report is issued with the understanding that it is the responsibility of the owner, or of his/her representative, to ensure that the information and recommendations contained herein are brought to the attention of the architect and/or project engineer and incorporated into the plans, and the necessary steps are taken to see that the contractor and/or subcontractor properly implements the recommendations in the field. The contractor and/or subcontractor should notify the owner if they consider any of the recommendations presented herein to be unsafe. If you should have any questions, please do not hesitate to contact us. The undersigned can be reached at (760) 215-5540 or (661) 702-8474. Respectfully submitted, LGC Valley, Inc. Randall Wagner, CEG 1612 Senior Project Geologist RKW/BIH Distribution: (1) Addressee (via E-mail) Basil Hattar, GE 2734 Principal Engineer Attachments: Figure 1 -Planning Area PA-l Geotechnical Map Project No. 133023-03 Page3 May5, 2016 " I j§iUi I !lit!! ~''-----'--~