5306 EAST DR 2023-05-31 - Laserfiche WebLink

COBALT GEOTECHNICAL INVESTIGATION �.a a s c i EN Cs EVERETT, WASHINGTON December 5, 2019 8.1.5 Stormwater Management The site is underlain by glacial till. Infiltration is typically not feasible in the areas underlain by glacial till. We performed a small-scale pilot infiltration test in TP-3 at a depth of 4 feet below grade. Following testing and application of correction factors for site variability (0.33), testing (0.4), and influent control (0.9),, the -infiltration. rate was:. determined to be'o.24 inches per hour. This rate is lower than what is considered to be feasible for widespread infiltration.. Depending on the final site layoutand grading, it may be possible to utilize permeable pavements for new driveways. We understand that there is a detention vault in place within the existing driveway area that will be utilized for stormwater. We can provide additional options for stormwater management upon request. We should be provided with final plans for review to determine if the intent of our recommendations has been incorporated or if additional modifications are needed. 8a.6 Slab -on -Grade We recommend that the upper 18 inches of the existing fill and/or native soils within slab areas be re - compacted to -at least 95-percent of the modified proctor (ASTM D1557 Test Method). Often, a vapor barrier is considered below concrete slab areas. However, the usage of a vapor barrier could result in curling of the concrete slab at joints. Floor covers sensitive to moisture typically requires the usage of a vapor barrier. A materials or structural engineer should be consulted regarding the detailing of the vapor barrier below concrete slabs, Exterior slabs typically do not utilize vapor barriers. The American Concrete'Insfitates ACI'36oR-o6'Design of Slabs-on"Grade andACI'302.1R-04 Guide -for Concrete Floor and Slab Construction are recommended references for vapor barrier selection and floor slab detailing. A minimum 4 inch thick capillary break should be placed over the prepared subgrade. This may consist of pea gravel or 5/8 inch clean angular rock. Slabs on grade may be designed using a coefficient of subgrade reaction of i8o pounds per cubic inch (pci) assuming the slab -on -grade base course is underlain by structural fill placed and compacted as outlined in Section 8.1. A 4 inch thick capillary break material should be placed over the prepared subgrade. This could include pea gravel or 5/8 inch clean angular rock. -A•perimeter--drainage•-ssystemii&xecommended unlessinterior slab areas are elevated a minimum of 12 inches above adjacent exterior grades. If installed, a perimeter drainage system should consist of a 4 inch diameter perforated drain pipe surrounded by a minimum 6 inches of drain rock wrapped in a non -woven geosynthetic filter fabric to reduce migration of soil particles into the drainage system. The perimeter drainage system should discharge by gravity flow to a suitable stormwater system. Exterior grades surrounding buildings should be sloped at a minimum of one percent to facilitate surface water-. flow ,away .; mm,-the,,build ng-and ..preferably with .a.,.,relatively impermeable surface cover immediately adjacent to the building. 9 PO Box 82243 Kenmore, WA 98028 cobaltge Ogmail.com 206-331-1097