1400 W MARINE VIEW DR WATERFRONT PLACE APARTMENTS Geotech Report 2022-10-25

• Subgrade Preparation Prior to placing new fills, pavement base course materials or gravel below on-grade floor slabs, subgrade areas should be proof-rolled to locate areas of soft or pumping soils. Proof-rolling can be completed using a heavy piece of tire-mounted equipment such as a loaded dump truck. During wet weather, the exposed subgrade areas should be probed to determine the extent of soft soils. If soft or pumping soils are observed, they should be removed and replaced with structural fill. If deep pockets of soft or pumping soils are encountered outside the building area, it may be possible to limit the depth of over-excavation by placing a woven geotextile separator such as Mirafi 500X (or equivalent) on the over-excavated subgrade prior to placing structural fill. The separation geotextile will provide additional support by reducing fines contamination into the structural fill. After completing the proof-rolling, the subgrade areas should be compacted to a firm condition. We recommend that all subgrade areas be compacted to at least 95 percent of the maximum dry density(MDD) in accordance with ASTM D 1557 test procedure (modified Proctor). Subgrade disturbance or deterioration could occur if the subgrade is wet and cannot be dried. If the subgrade deteriorates during proof-rolling or compaction, it may become necessary to modify the proof-rolling or compaction criteria or methods. Subgrade Protection If construction of the building occurs during the wet weather months, generally October through May, 11111 routing of equipment on the silty subgrade soils will be difficult and the subgrade will likely become disturbed and softened. In addition, a significant amount of mud can be produced. Therefore, to protect the subgrade soils in the building footprint and heavier traffic areas, and to provide an adequate working surface for the contractor's equipment and labor, the contractor should consider protecting exposed subgrade soils with a working pad. In the building footprint, the working pad layer should be 12 inches thick and should consist of 11 -inch minus clean crushed gravel with negligible sand or silt.The working pad layer can be placed in one lift and should be compacted to at least 95 percent of the MDD (per ASTM D 1557). In heavier trafficked areas, temporary roads will be required for access to construction areas during wet weather or wet subgrade conditions. For a project of this size,our experience suggests that 12 to 18 inches of 2-inch minus clean crushed rock will be necessary to provide support for construction equipment haul roads. We recommend that a woven geotextile separator such as Mirafi 500X (or equivalent) be placed between the haul road import material and the silty subgrade soils to minimize mixing of the subgrade and road subbase materials and to reduce pumping. Utility Trenches Trench excavation, pipe bedding,and trench backfilling should be completed using the general procedures described in the 2016 WSDOT Standard Specifications or other suitable procedures specified by the project civil engineer. Utility piping through fill or organic soils should be evaluated by a corrosion expert. • Utility trench backfill should consist of structural fill and should be placed in lifts of 6 inches or less (loose thickness) if on-site soils are used such that adequate compaction can be achieved throughout the lift. GEOENGINEERS May 31,2017 Page 13 File No.22360-003-00