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Home My WebLink AboutMS 2018-0006; BREAKERS VIEW BEACH HOMES; PRELIMINARY GEOTECHNICAL INVESTIGATION; 2016-07-25COAST GEOTECHNICAL CONSULTING ENGINEERS AND GEOLOGISTS July 25, 2016 Marc Kovens 18 Via Burrone Newport Coast, CA 92657 Subject: REVISED CITY OF CARLSBAD RESPONSE Proposed Twin Home Development 3648 Carlsbad Boulevard Carlsbad, California RE C F11"WED OCT 192020 Reference: PRELIMINARY GEOTECHNICAL INVESTICLAARb DEVELOPMENT Proposed Twin Home Development 3648 Carlsbad Boulevard ENGINEERING Carlsbad, California Prepared by Coast Geotechnical Dated February 11, 2016 Dear Mr. Kovens: This report is in response to the city of Carlsbad request for additional information regarding the Preliminary Geotechnical Report on the above referenced project. Site Location The subject property is located at 3648 Carlsbad Boulevard, north of Juniper Avenue, along the east side of Carlsbad Boulevard, in the city of Carlsbad. Expansive Soils Based on laboratory testing of selected samples, the residual soil and Pleistocene terrace deposits reflect an expansion potential in the very low range (El. 4). P.O. BOX 230163 * ENCINITAS, CALIFORNIA 92023 (858) 755-8622 Coast Geotechnical July 25, 2016 W.O. P-6541115 Page 2 of S Cross Section The enclosed Cross Section A-A' deicts the general subsurface geologic conditions, approximate current proposed development, existing structures and approximate limits of proposed remedial grading. Permeable Payers - Infiltration It is nearly impossible to direct infiltrated water vertically in narrow walkway areas, driveways and areas adjacent to foundations. Infiltrated water will likely flow along utility line backfill and other avenues which provide less resistance to lateral flow. Walkways, driveways and areas adjacent to structural foundations should be provided with an impermeable liner such as a minimum 15 mil Stego impervious membrane or equivalent. Pavement underdrains are recommended and should be incorporated in the design for adequate collection and disposal of filtrated storm water. Infiltration (Alternative) The following alternative is provided that will allow infiltration in the western portion of the site, as proposed in the patio pervious paver area on the grading plans. Infiltration is also possible in the rear pervious paver driveway area, as discussed with bHA, Civil Engineering. However, the following approach is considered less desirable from a geotechnical viewpoint than lining the sections with an impervious liner. Coast Geotechnical July 25, 2016 W.O. P-6541115 Page 3 of 5 A minimum 6.0 inches thick concrete slurry cutoff wall should be constructed adjacent to the western foundation line. The cutoff wall should extend to the northern and southern property lines. The wall should continue westward along both the southern and northern property lines to the western property line. The cutoff wall should extend vertically a minimum of 3.0 feet below the base of the proposed structure footing and/or pavement section, whichever is deeper. The rear drive should also be provided with a cutoff wall that extends along the edge of the carport slab to the property lines. The cutoff wall should extend along the north, south and eastern property lines to create a box for vertical infiltration. The cutoff walls should be continuous with no gaps for water to migrate laterally. No infiltration should be allowed along the narrow northern and southern side yard areas. The cutoff walls may be poured with a lean concrete mix (2-sack slurry). The walls should be a continuous pour and should not have any cold joints. All penetrations and any future penetrations through the concrete slurry cutoff wall will need to be sealed with slurry. The cutoff walls need to be water tight and any avenues through the walls will allow concentrated drainage flow into foundation and slab areas that could result in moisture problems and possibly foundation/slab distress. The approximate locations and limits of the proposed subsurface cutoff walls are shown on the enclosed revised grading plan by bHA, Civil Engineering. Coast Geotechnical July 25,2016 W.O. P-6541115 Page 4 of 5 Permeable Interlocking Concrete Payers (PICP) PICP pavement structural section (Driveways) should consist of 31/8 inch PICP, over a minimum of 2.0 inches of ASTM No. 8 bedding course/choke stone, over a minimum of 12 inches of ASTM No. 57 stone base course, over a minimum of 12 inches of 95 percent compacted subgrade. Bedding course/choke stone and base course stone should also be well compacted, consolidated and interlocked (avoid crushing the underdrain pipes) with heavy construction equipment. ASTM No. 8, No. 9 or No. 89 should be used for joint materials, depending on the joint size and per manufacturer recommendations. The above stone base section may be reduced from 12 inches to a minimum of 6.0 inches for walkways, if desired. Gradation requirements for ASTM No. 57, No. 8, No. 89 and No. 9 are as follows: Sieve Size Percent Passing I No. 57 No. 8 No. 89 No. 9 1'/2" 100 1' 95to100 1/2 ! 25to60 100 100 85 to 100 90 to 100 100 No.4 OtolO 10to30 20to55 85 to 100 No.8 0to5 OtolO 5to30 10to40 No. 16 0 to 5 0 to 10 0 to 10 No. 50 0to5 0to5 This is the minimum structural section and is suitable for the anticipated traffic load. Coast Geotechnical July 25, 2016 W.O. P-6541115 Page 5 of 5 Site Exploration Based on our experience on projects in close proximity to the site, the underlying Pleistocene terrace deposits are anticipated to be relatively uniform across the site. Minor variations within the depth of fill deposits may be addressed during the remedial grading phase. Additional exploratory borings are unnecessary. LIMITATIONS Infiltration, even with subsurface cutoff walls, increases the risk of saturated soils that support foundations, slabs and exterior improvements on the subject property and adjacent properties. Water will seek the least path of resistance. The developer should consider these risks should this option be chosen. It is the responsibility of the owner and contractor to ensure that the cutoff walls are water tight for the life expectancy of the structure. If you have any questions, please do not hesitate to contact us at (858) 755-8622. This opportunity to be of service is appreciated. 2109 EN.j GEOLOGIS1 1 V G. Cross Section Grading Plan (showing subsurface cutoff walls) Respectfully submitted, COAST GEOTECHNI( ~4d4awl - Mark Burwell, C.E.O. Engineering Geologist Enclosure: I II[tiJIJJtU CROSS SECTION A-A' A A' I Proposed Structure --7--~, _ n Exist. Residence IT L Fit I - - - Proposed Gd - -50, - __L ni'_' - • -. '- •-. 1:1 Tøinp. • REMEDIAL GRADING - ----- ----------.-- —45 - Slop. • * Qt - 4O GEOLOGIC UNITS af ARTIFICIAL FILL Qs SOIL Qt TERRACE DEPOSITS Coast Geotechnical P-6541 115 SECTION A-A TENTATIVE PARCEL MAP BREAKERS VIEW CONDOMINIUMS MS 16-03 CDP 16-20 PUD 16-01 SDP 16-11 2M 6'SMRM a' SECT. ION 8-il MT- r ----i SUBSURFACE CUTOFF WALL A CL\" \\ CARLSBAD BLVD. z \ \ \\ BASIN O(ffLET DETAIL OT AP.iJ. 2O4-232-11.-' ". 1' 0 ) S ' ' A P2O —2 VV NOTES- SHEET20F