3620 BROADWAY VERIZON 2019-01-11

Geotechnical Engineering Evaluation NGA File No.983917 Stadium.Flowers Addition March 10,2017 Everett,Washington Page 11 Permanent drainage should be installed for retaining walls. Where the retaining walls are constructed against the shoring walls, a drainage composite should be placed against the lagging prior to pouring the foundation wall. Weep pipes should be connected to the drainage composite and tightlined through the foundation walls into the proposed drainage system. Recommendations for these systems are found in the Subsurface Drainage subsection of this report. We recommend that we be retained to evaluate the proposed wall drain backfill material and drainage system installation. Slab-on-Grade Slabs-on-grade should be supported on subgrade soils prepared as described in the Site Preparation and Grading subsection of this report. We recommend that all floor slabs be underlain by at least six inches of free-draining gravel with less than three percent by weight of the material passing Sieve #200 for use as a capillary break. We recommend that the capillary break be hydraulically connected to the footing drain system to allow free drainage from under the slab. A suitable vapor barrier, such as heavy plastic sheeting(6-mil minimum), should be placed over the capillary break material. An additional 2-inch thick moist sand layer may be used to cover the vapor barrier. This sand layer is optional and is intended to protect the vapor barrier membrane during construction. Site Drainage Surface Drainage: Stormwater handling plans were not developed at the time this report was prepared. We should be retained to evaluate drainage plans prior to construction. Final site grades should allow for drainage from the planned and existing structures. We suggest that the finished ground be sloped at a minimum gradient of three percent for a distance of at least 10 feet away from the building. All runoff generated on this site, including roof downspouts, yard and footing drains, and hard surfaces, should be collected and routed into a permanent discharge system. Water should not be allowed to collect in any area where footings or slabs are to be constructed. Subsurface Drainage: We do not anticipate that groundwater will likely be encountered during construction, but if so, we recommend that the contractor slope the bottom of the excavation and collect the water into ditches and small sump pits where the water can be pumped out of the excavations and routed into a suitable outlet. We recommend that all down spouts and footing drains be tightlined to an appropriate discharge location. NELSON GEOTECHNICAL ASSOCIATES, INC.