5109 SEAHURST AVE 2025-12-12 - Laserfiche WebLink

COBALT GEOTECHNICAL INVESTIGATION NGEOSCIENCES EVERETT,WASHINGTON November 16,2018 bearing materials can be reduced by pouring concrete as soon as possible after completing the footing excavation and evaluating the bearing surface by the geotechnical engineer or his representative. 8.1.5 Stormwater Management The site is underlain by very fine-grained,dense glacial deposits. These soils have a very low permeability which decreases with depth. It is likely that there will be shallow perched groundwater throughout the property that further limits infiltration suitability. We performed an in-situ infiltration test in H13-1 at a depth of 3 feet below grade. Following testing and application of correction factors for site variability, testing, and influent control,the infiltration rate was 0.25 inches per hour,which is lower than what the Department of Ecology considers to be feasible. We do not recommend utilizing infiltration trenches or drywells at the site. We recommend routing runoff from impervious surfaces into City infrastructure. 8.1.6 Slab-on-Grade We recommend that the upper 18 inches of the 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 Institutes ACI 360R-06 Design of Slabs on Grade and ACI 302AR-04 Guide for Concrete Floor and Slab Construction are recommended references for vapor barrier selection and floor slab detailing. Slabs on grade may be designed using a coefficient of subgrade reaction of 18o pounds per cubic inch(pei) assuming the slab-on-grade base course is underlain by structural fill placed and compacted as outlined in Section 8.1. A perimeter drainage system is recommended unless interior 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 from the building and preferably with a relatively impermeable surface cover immediately adjacent to the building. 8.1.E Groundwater Influence on Construction Groundwater was not encountered in the hand borings. There is a slight chance that perched groundwater could be encountered in excavations greater than about 6 feet in depth during the late winter and early spring. 7 PO Box 82243 Kenmore,WA 98028 cobaltgeo"amail.com 2o6-331-1097