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HomeMy WebLinkAboutCDP 2016-0006; MFD-01; REVISED PICP CONSTRUCTION PROCEDURE ALTERNATIVE; 2017-04-10APR 11 2017 / Project No. Gl-15-12-50 April 10,2017 Ohms Collaborative Mr. Hector Aramburo 536 Sears Avenue San Diego, California 92114 6116 GEOTECHNICAL SOLUTIONS. INC. Consulting Geotechnical Engineers & Geologists 5931 Sea Lion Place, Suite I 09 Carlsbad, California 920 l 0 760-602-7815 smsgeosol.inc@gmail.com REVISED PICP CONSTRUCTION PROCEDURE ALTERA TIVE, PROPOSED ARELLANO 4-UNIT APARTMENTS, 2637 JEFFERSON STREET, CARLSBAD We understand undisturbed ("uncompacted") sub grade soils will be necessary under the PICP pavement section to promote infiltration for onsite storm water retention, and avoiding a Priority Development Project (PDP). We further understand that the project design requires to eliminate the perforated underdrain pipe, having the stormwater infiltrate into the undisturbed ("uncompacted") subgrade, due to inability to gravity discharge subsurface water onto any nearby storm drainage system or the neighboring properties. Consequently, the purpose of this effort was to provide a feasible revised construction alternative for the proposed PICP paving section for accommodating the project design requirements. Reference is made to the following pertinent reports prepared by this office: I. "Alternative PICP Construction Procedure, Proposed Arellano 4-Unit Apartments, 263 7 Jefferson Street, Carlsbad, California," dated February 14, 2017. 2. "Geotechnical Plan Review Update, Proposed Arellano 4-unit Apartments, 2637 Jefferson Street, Carlsbad, California,'' dated October 24, 2016. 3. "'Geotechnical Investigation, Proposed 3-story 4-Unit Residence, 2637 Jefferson Street, Carlsbad, California," dated January 11, 2016. The proposed new design revisions to the PICP system, is generally considered feasible from a geotechnical viewpoint. However, the following recommendations are appropriate and should be considered in the final designs and implemented during the construction phase, where appropriate Ohms Collaborative Revised PICP Construction Procedure Alternative April 10, 2017 Page2 and as applicable: 1. Suitable undisturbed ("uncompacted") subgrade soils may be considered for the PICP pavement section. Based on our site study (see references), suitable undisturbed ("uncompacted") subgrade soils (native Terrace Deposits) occur at depths ranging from 2 to 2.5 feet below the existing ground surfaces (BGS). For this purpose, pavement section ground preparations should consist of removals of upper fill/topsoil section to expose the underlying undisturbed ("uncompacted") native Terrace Deposits. An increased pavement base section (ASTM No. 57 stone base course) should then be placed over the exposed undisturbed ("uncompacted") native Terrace Deposits. The increased pavement base section will also provide a lager storage capacity for the planned BMP facility. Remainder of the PICP pavement structural section will stay unchanged. 2. The perforated underdrain pipe may also be eliminated, provided an adequate storage capacity (with a proper safety factor) is considered in the design of the project BMP facility. Additionally, all foundations bearing and sub grade soils underneath the planned new building should be compacted to minimum 95% compaction levels. 3 All southern building foundations adjacent to the PICP should be extended a minimum of24 inches below the bottom of the paver base section (ASTM No. 57 stone base course), or at least 42 inches below pad finish rough grade, whichever is more. A concrete slurry cut-off wall (deepened edge restraint) extending a minimum of24 inches below the bottom of the pavement section base course should also be consider to protect adjacent site improvements and structures, where necessary and as appropriate, as previously specified (see references). LIMITATIONS The future performance ofthe PICP pavement BMP facility, as ctm-ently planned at the project site is difficult to predict with certainty due to numerous unpredictable factors, such as amount of seasonal and annual rainfall, infiltration rates, irrigation and maintenance of drainage systems. In order to reduce potential impacts on the adjacent building foundations, structures, improvements, or problems associated with the planned BMP facility, the following recommendations are presented: -Provide periodic maintenance of the PICP pavement BMP facility, as necessary, and monitor nearby structures and improvements. Should any saturated ground or related conditions occur, the project civil engineer and geotechnical consultant should be immediately notified. Mitigation recommendations may become necessary, and cannot be ruled out. Provide landscaping consisting of drought resistant plants and monitor the amount of irrigation water. Irrigation should be limited to the amount of water necessary to sustain plant Ohms Collaborative Revised PICP Construction Procedure Alternative April 10, 2017 Page3 life. A landscape architect should be consulted, in this regard. The performance and impact of the newly required private P ICP pavement BMP drainage infiltration facilities can only be evaluated through time. Additional recommendations or future repairs and modifications to the system may be necessary, in the event adverse or consequential conditions manifest themselves. This will require proper disclosure to any owners and all interested/affected parties. However, in no respect do we guarantee or warrant the performance of the private PICP pavement BMP drainage infiltration facilities. We appreciate this opportunity to be of service to you. again. Should any questions arise concerning this report, please do not hesitate to contact this office. Reference to our Project No. GI-5-12-20 will help to expedite our response to your inquiries. SHS Geotechnical Solutions, Inc. Distribution: Addressee (2, e-mail) NJ/6 GEOTECHN1CAL SOLUTIO:'\S. INC.