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Home My WebLink AboutCUP 2022-0010; CARLSBAD DESALINATION PLANT; PAVEMENT RECOMMENDATIONS AT CARLSBAD AQUAFARM TEMPORARY DRIVEWAYS; 2022-09-19Technical Memorandum Date: Monday, September 19, 2022 Project: Carlsbad Desalination Plant (CDP) Intake Phase 2 To: Janelle Moyer, PE (HDR Internal) From: Jim Starick, PE and Matthew Dennerline, PE, GE Subject: Pavement Recommendations at Carlsbad Aquafarm Temporary Driveways We have developed this technical memorandum to summarize our recommendations for the construction of the temporary driveway entrances planned for access to the Carlsbad Aquafarm. We understand that the existing access to the Aquafarm facility will be restricted during the CDP Phase 2 Intake construction. Two temporary access driveways will be installed to provide vehicular access to the Aquafarm from Carlsbad Boulevard during construction. Once construction on the CDP Intake project is completed (approximately 12 months), the curb, gutter, and sidewalk will be returned to match existing conditions. A preliminary plan sheet has been attached at the end of this memo to show conceptual proposed paved areas. These temporary driveways will be similar in design to the driveway that was previously constructed for Phase I, now removed. We understand that the Phase I design included a 4-inch section of hot mix asphalt (HMA) over 4 inches of Class 2 aggregate base. Background geotechnical information in relation to the main CDP Intake project has been provided in a draft geotechnical design report dated May 2022 (HDR, 2022). This memo serves to add information pertaining to the temporary driveways and does not otherwise modify recommendations in that report. Geotechnical Data Typical upper surface soils consist of clayey or silty sands, and existing parking lot pavements generally consist of about 3 inches of asphalt concrete (AC) over 4 inches of aggregate base. Pavements are summarized below based on our review of existing data. See CDP Intake Project geotechnical report (HDR, 2022) for boring logs. Boring Name Pavement (inches) Location Apex B-2 5.5 AC over 6.5 Base End of eastern dock paved area GeoLogic B-16 3 AC over 3 Base Central parking lot area GeoLogic B-17 3 AC over 4 Base Central parking lot area GeoLogic B-18 3 AC over 4 Base Central parking lot area NM NMB-7 3.5 AC over 3 Base Central parking lot area NM GHD-2 6 AC over 4 Base Drive area behind existing intake structure / crane access NM GHD-3 2 AC over 6 Base Parking area near shore/existing access road HDR R-22-004 6 AC over 5 Base Levee road ~p ~ . \ ~ FJ£LLL'J ·01 HDR R-22-005 3 AC over 4 Base Eastern shoreline drive area Pavement supporting capacity of the upper soils was measured by resistance (R-value) during previous phases of the project. R-value testing performed by Geo-Logic (2008) is presented below. R-value testing performed by Ninyo and Moore (2013) is presented below. Conclusions and Recommendations We understand that the driveways are intended to serve only for the duration of construction which is temporary in nature. However, we also understand that the City of Carlsbad prefers the driveways to meet a permanent driveway construction standard. Construction traffic is not anticipated to use these driveways which serve only the Aquafarm with vehicular traffic and occasional delivery vehicle access. Based on the guidance provided by the City of Carlsbad Engineering Standards (2022, Section 4.6 B), parking lots and driveways should be designed to a minimum Traffic Index of 4.5, with a minimum asphalt section of 4 inches. Using Caltrans gravel factor calculations for a 20-year design life (Caltrans, 2020), we calculated minimum pavement sections required using the lowest R- value (15) of the data presented above for conservatism. Based on these calculations a pavement section of 4 inches of asphalt over 4 inches of Class II aggregate base is sufficient, and is similar to the existing parking lot areas. Beneath the base section, the upper 1 foot of subgrade should be compacted to 95% of maximum density per ASTM D 1557 test methods. Portland Cement concrete (PCC) used in the driveway transition strips or similar should confirm to the City of Carlsbad Engineering Standards (2022, Section 3.15) using 7.5 inches PCC over 6 inches of aggregate base, with the upper 1 foot of subgrade compacted as described above. References City of Carlsbad, 2022, Engineering Standards Volume 1 General Design Standards, accessed via https://www.carlsbadca.gov/home/showpublisheddocument/330/637425982505630000 Caltrans, 2020, Highway Design Manual. GeoLogic Associates, 2008, Geotechnical/Environmental Report, Proposed Carlsbad Desalination Project, Reconfigured Site, Encina Generating Station, Carlsbad, California, dated September 22. 1hYa1u : Resistn:nce ''R" value w;ts ootainecl for th!;ee ~llmples. Testii1g wa~ perf<lTme-d in acoorda:nce wit:h Califomfa Test 301. Tihc test resa I s are p.1;e:sentcd below. Sam_p.le Location R-V;alue -B-9-. 2-4• 38 B-14, 1-3' 47 S/\l'IIPL..E L:0CA TION I SAM-le DSPTH SOil TYPE lfll 6·6 J,0-!i.O 'J!i/'e/¥ SANO (SC) fl.\/Alll - 15 HDR, 2022, Geotechnical Design Report – DRAFT, Carlsbad Deslaination Plant Intake Phase 2, Poseidon Water, Carlsbad, CA, May. Ninyo & Moore, 2013, Geotechnical Evaluation, Carlsbad Seawater Desalination Plant (Intake Pump Station Site), 4600 Carlsbad Boulevard, Carlsbad, California, dated August 20. Ninyo & Moore, 2016, Geotechnical Evaluation, New Intake/Discharge Structure, Carlsbad Seawater Desalination Plant, 4600 Carlsbad Boulevard, Carlsbad, California, dated November 30. PROPOSED TEMPORARY FISH FARM ACCESS DRIVEWAYS & RAMPS LAGOON CARLSBAD BLVD EC-2 EC-2 SE-1 10% 25 . 0 ' 10% EC-2 EC-2 10% 25 . 0 ' 10% APN 210-010-45-00 EXISTING ROW EXISTING BACK OF WALK EXISTING CURB & GUTTER EXISTING C&GEXISTING ROWEXISTING BACK OF WALK EXISTING BARBED WIRE FENCING 10 % 2% 25 % 10 % 2% 25 % EXISTING CATCH BASIN SE-10 TR-1 x x xx x x x x x x x x xx x xx TR-1 OF 280 B 2 ISSUE DESCRIPTION PROJECT MANAGER PROJECT NUMBER 0 1"2"FILENAME SCALE SHEET DATE C D A 1 3 4 5 6 7 8 CARLSBAD DESALINATION PLANT PHASE 2 INTAKE MODIFICATIONS PRELIMINARY DESIGN S. FRIEDMAN 10341720 DESIGNED BY CHECKED BY DRAWN BY J. MOYER C. TYNES D. CELAYA 60% SUBMITTAL NOT FOR CONSTRUCTION CIVIL EROSION CONTROL PLAN - TEMPORARY DRIVEWAYS 00C08.dwg 1" = 20'00C08-- - LEGEND SURFACE FLOW SILT FENCE INLET PROTECTION STABILIZED CONSTRUCTION INGRESS / EGRESS CLASS II BASE ASPHALT CONCRETE CONCRETE SILT FENCE SE-1 393 LF INLET PROJECTION SE-10 1 EA STABILIZED CONSTRUCTION TR-1 2 EA INGRESS / EGRESS PRESERVATION OF EXISTING VEGETATION EC-2 QTYBMP NO.DESCRIPTION 38 • ---------------------- " -------- " ----18 L13.B4 POSEIDON CHANNELSIDE a Poseidon Water company - ---- SCALE: 1"=20' □ □ 0 1. --- □ ---0 20 40 60