9900 19TH AVE SE Geotech Report 2018-01-02 MF Import

Geatechnical Engineering Report Home Base Warehouse - Everett July 31, 1997 NCA File No. 213497 Page 10 All backfill for subsurface walls that is used as non-structural fill should be compacted to between 90 and 92 percent of the maximum dry density as determined in accordance with ASTM D 1557. Care should be taken to prevent the buildup of excess lateral soil pressures due to overcompaction of the backfill behind the wall. This can be accomplished by placing the backfill located within 18 to 24 inches of the wall in lifts not exceeding 8 inches in loose thickness, and compacting this zone with hand operated compaction equipment. Site Drainage Surface Drainage: The finished ground surface should be graded such that storm water is directed to an appropriate storm water collection system. Water should not be allowed to stand in any area where footings, slabs or pavements are to be constructed. Final site grades should allow for drainage away from the building. We suggest that the finished ground be sloped at a gradient of 3 percent minimum for a distance of at least 10 feet away from the building. Surface water should be collected by permanent catch basins and drain lines, and be discharged into a storm drain system. Subsurface Drainage: Perched ground water seepage was encountered in one of our explorations. Should ground water seepage be encountered or excessive rainfall occur during construction, we recommend that the contractor slope the bottom of excavation during construction and collect the water to ditches and sump pits, from which the water can be pumped and discharged into a storm drain system. A drainage system should be planned behind all retaining walls and around exterior footings. An IS - inch -wide blanket of free -draining sand or pea gravel should be installed behind all retaining walls and on the outside of perimeter footings. A perforated pipe should be placed in the free -draining material at the base of the wall or footing. The pipe should be routed to an appropriate discharge point. Slabs -on -Grade Slabs -on -grade should be supported on subgrade soils prepared as described in the Site Preparation and Grading and Structural Fill sub -sections of this report. Where moisture control is important, we recommend that all floor slabs be underlain by at least 6 inches of free -draining sand or gravel, for use as a capillary break. We recommend that the capillary break be hydraulically connected to the footing drain to allow free drainage from under the slab. A suitable vapor barrier, such as heavy plastic sheeting, NELSON-COUVRETTE & ASSOCIATES, INC.