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Home My WebLink AboutPD 2019-0015; CARLSBAD INN MITIGATION PHASE 2-4; RESPONSE TO GEOTECHNICAL REVIEW COMMENTS (SECOND REVIEW); 2019-07-05CHRISTIAN WHEELER ENGINEERING July 5, 2019 Grand Pacific Resorts, Carlsbad Inn 3075 Carlsbad Boulevard Carlsbad, California 92008 Attention: Keith Whaley CWE 2190062.03 Subject: Response to Geotechnical Review, Project ID GR2019-020 Proposed Parking Garage Shoring Carlsbad Inn, 3075 Carlsbad Boulevard, Carlsbad, California References: 1) Hetherington Engineering, Inc., Third-Party Geotechnical Review (First), Carlsbad Inn Mitigation Phases 2-4, June 18, 2019, Project No. 8894.1 Grading Plans For: Carlsbad Inn Water Intrusion Mitigation Project, Phase 2-4, prepared by Excel Engineering, undated (Sheets I through 9) Temporary Shoring Plans for Carlsbad Inn Water Intrusion Mitigation Plan, prepared by Shoring Design Group, dated April 8, 2019 (Sheets 10 through 19) Report of Limited Geotechnical Investigation, Proposed Parking Garage Shoring, Carlsbad Inn, 3075 Carlsbad Boulevard, Carlsbad, California, CWE Report 2190062.01, dated March 19, 2019. Ladies and Gentlemen: In accordance with your request, we have prepared this report to present additional information required by the City of Carlsbad regarding the geotechnical issues at the site. The comments in the referenced geotechnical review letter and our responses to the comments in the referenced memorandum within our purview are presented below. Reviewer Comment 1: The Consultant should review the project grading and temporary shoring plans, provide any additional geotechnical analyses/recommendations considered necessary, and confirm that the plans have been prepared in accordance with the geotechnical recommendations. 3980 Home Avenue + San Diego, CA 92105 + 619-550-1700 + FAX 619-550-1701 CWE 2190062.03 July 5, 2019 Page No. 2 CWE Response: We have performed a limited geotechnical review of the referenced grading and temporary shoring plans. Our review indicates that the grading plans are, from a geotechnical standpoint, in accordance with our recommendations. In addition, we reviewed the referenced temporary shoring plans to determine whether the following elements of our referenced report appear to be incorporated into the plans. The plans reference our geotechnical report. The recommended lateral pressure is on the plans. The recommended ultimate lateral bearing (passive) value is on the plans. The recommended maximum deflection is on the plans. The intent of our limited plan review was to verify that the plans submitted for construction reflect the described minimum geotechnical recommendations, and that no additional investigation or recommendations are required due to changes made in the project since our investigation was performed. It is not our intent to provide a third party review of the shoring calculations or shoring design. The design engineer is responsible for properly designing the temporary shoring and other structural elements based on the requirements of the shoring and considering the information presented in our report. Based on our review, it is our opinion that our recommendations have been adequately implemented and no additional analysis and/or recommendations are needed. Reviewer Comment 2: The Consultant should specify the sulfate exposure category based on the soluble sulfate testing and provide recommendations for sulfate resistant concrete, if necessary. CWE Response: The water soluble sulfate content of a selected soil sample from the site was determined in accordance with California Test Method 417. The results of this test indicate that the soil sample had a soluble sulfate content of 0.002 percent. Soils with a soluble sulfate content of less than 0.1 percent are considered to be negligible. Reviewer Comment 3: The Consultant should address the impacts to adjacent property and improvements as the result of the proposed work. CWE Response: It is our opinion that the proposed development will not destabilize or result in settlement of adjacent property or improvements, given the recommendations contained in the above- referenced Limited Geotechnical Report are followed. CWE 2190062.03 July 5, 2019 Page No. 3 Reviewer Comment 4: The Consultant should provide the site Seismic Design Category. CWE Response: The site Seismic Design Category is D. Reviewer Comment 5: The Consultant should provide recommendations for backdrains, backfill placement, compaction, and geotechnical testing for the site work and proposed improvements. CWE Response: All grading should conform to the guidelines presented in the current edition of the California Building Code, the minimum requirements of the City of San Diego, and the recommended Grading Specifications and Special Provisions attached hereto, except where specifically superseded in the text of this report. SITE PREPARATION: All excavated areas should be approved by the geotechnical engineer or his representative prior to replacing any of the excavated soils. The exposed soils underlying concrete flatwork should be scarified to a depth of about 12 inches, watered thoroughly, and compacted to at least 90 percent relative compaction. Retaining wall backfill soils should be compacted to at least 90 percent relative compaction. Expansive or clayey soils should not be used for backfill material. COMPACTION AND METHOD OF FILLING: In general, all structural fill placed at the site should be compacted to a relative compaction of at least 90 percent of its maximum laboratory dry density as determined by ASTM Laboratory Test Di 557. Fills should be placed at or slightly above optimum moisture content, in lifts six to eight inches thick, with each lift compacted by mechanical means. Fills should consist of approved earth material, free of trash or debris, roots, vegetation, or other materials determined to be unsuitable by the Geotechnical Consultant. Fill material should be free of rocks or lumps of soil in excess of 3 inches in maximum dimension. Utility trench backfill within 5 feet of the proposed structure and beneath all concrete flatwork or pavements should be compacted to a minimum of 90 percent of its maximum dry density. WALL DRAINAGE SYSTEMS: Groundwater was not observed during our subsurface investigation and is not expected to be encountered within the excavation; therefore, backdrains are not considered necessary for this project. If required, the retaining wall engineer should provide a detail for a wall drainage system. Typical retaining wall drain system details are presented as Plate No. 1 of this report for informational purposes. Additionally, outlets points for the retaining wall drain system should be coordinated with the project civil engineer. CWE 2190062.03 July 5, 2019 Page No. 4 Reviewer Comment 6: The Consultant should provide recommendations for unshored temporary excavaions (slope ratios, height, etc.), if necessary CWE Response: As provide in the referenced geotechnical report, we anticipate that the existing on- site soils will consist of Type B material, meaning that temporary cut slopes can be excavated at a maximum inclination of 1:1 (horizontal to vertical) for a maximum height of 20 feet. Our firm should be contacted to observe all temporary cut slopes during grading to ascertain that no unforeseen adverse conditions exist. No surcharge loads such as foundation loads, or soil or equipment stockpiles, vehicles, etc. should be allowed within a distance from the top of temporary slopes equal to half the slope height. Reviewer Comment 7: The Consultant should provide recommendations for hardscape subgrade preparation, minimum hardscape thickness, reinforcement and joint spacing from a geotechnical standpoint. CWE Response: Providing recommendations for exterior fiatwork was not within the scope of our services. However, the contractor can use the following recommendations as a guide: EXTERIOR FLATWORK: Exterior concrete slabs on grade should have a minimum thickness of 4 inches. All slabs should be provided with weakened plane joints in accordance with the American Concrete Institute (ACT) guidelines. Special attention should be paid to the method of concrete curing to reduce the potential for excessive shrinkage cracking. It should be recognized that minor cracks occur normally in concrete slabs due to shrinkage. Some shrinkage cracks should be expected and are not necessarily an indication of excessive movement or structural distress. Prior to placement of concrete, the exposed subgrade soils should be scarified to a depth of about 12 inches, watered thoroughly, and compacted to at least 90 percent relative compaction. Reviewer Comment 8: The Consultant should provide a list of recommended geotechnical observation and testing during grading and construction. CWE Response: The geotechnical observation and testing recommended during construction consist of the following: Observation of drilling for shoring piers 0 Observation of all temporary cut slopes SCC:scc;djf ec: kwhaley@kmcgroup-llc.com GE2748 0 CH OF C r 7EER/A,Q TROY S. \9. i I WILSON \ 0 No. 2551 ca 0 OF CAt-°./ CWE 2190062.03 July 5, 2019 Page No. 5 Observation and testing of any fill placement, including retaining wall backfill and subgrade soil. If you have any questions regarding this letter, please do not hesitate to contact this office. Christian Wheeler Engineering appreciates this opportunity of providing professional services for you for the subject project. Respectfully submitted, CHRISTIAN WHEELER ENGINEERING Shawn Cap, R.G.E. # 48 roy S. Wilson, C.E.G. 42551 a 3 6" MIN. 12" MIN. 2 T2 _ A DETAIL LII_DETAIL 6" MIN. 6" MIN. 6 41 rI A A 4- DETAIL DETAIL NOTES AND DETAILS GENERAL NOTES: THE NEED FOR WATERPROOFING SHOULD BE EVALUATED BY OTHERS. WATERPROOFING TO BE DESIGNED BY OTHERS (CWE CAN PROVIDE A DESIGN IF REQUESTED). EXTEND DRAIN TO SUITABLE DISCHARGE POINT PER CIVIL ENGINEER. 4 DO NOT CONNECT SURFACE DRAINS TO SUBDRAIN SYSTEM. DETAILS: O 4 -INCH PERFORATED PVC PIPE ON TOP OF FOOTING, HOLES UNDERLAY SUBDRAIN WITH AND CUT FABRIC BACK FROM POSITIONED DOWNWARD (SDR 35, SCHEDULE 40, OR EQUIVALENT). 6 DRAINAGE PANELS AND WRAP FABRIC AROUND PIPE. ® 3% INCH OPEN-GRADED CRUSHED AGGREGATE. COLLECTION DRAIN (TOTAL DRAIN OR EQUIVALENT) LOCATED GEOFARBRIC WRAPPED COMPLETELY AROUND ROCK. AT BASE OF WALL DRAINAGE PANEL MANUFACTURER'S RECOMMENDATIONS. PER () PROPERLY COMPACTED BACKFILL SOIL. WALL DRAINAGE PANELS (MIRADRAIN OR EQUIVALENT) PLACED PER MANUFACTURER'S REC'S. CANTILEVER RETAINING WALL DRAINAGE SYSTEMS PROPOSED PARKING GARAGE SHORING CARLSBAD INN, 3075 CARLSBAD BOULEVARD, CARLSBAD, CA DATE: JULY 2019 1 JOB NO.: 2190062.03 Or- CHRISTIAN WHEELER ENGINEERING