2621 ROCKEFELLER AVE Geotech Report 2022-10-25

I I The use of native glacial g a till soils as structural fill during wet weather should be planned only for areas requiring compaction to 90 percent of MDD, as long as the soils are properly protected from wet weather and not placed during periods of precipitation. The contractor should plan to cover and maintain all fill stockpiles with plastic sheeting if it will be used as structural fill. The reuse of on-site soils is highly dependent on the skill of the contractor and schedule, and we will work with the design 1 team and contractor to maximize the reuse of on-site soils during the wet and dry seasons. Reuse of Concrete Rubble. Existing Portland cement concrete foundations and sidewalks may be I reused as structural fill if properly crushed during demolition. The concrete should be crushed or otherwise ground up and should meet the gradation requirements for gravel borrow as described in Section 9-03.14(1)of the 2006 WSDOT Standard Specifications. 1 Fill Placement and Compaction Criteria. Structural fill should be mechanically compacted to a firm,non-yielding condition. Structural fill should be placed in loose lifts not exceeding 8 to 10 inches in thickness. The actual thickness will be dependent on the structural fill material used and the type and 11 size of compaction equipment. Each lift should be conditioned to the proper moisture content and compacted to the specified density before placing subsequent lifts. Structural fill should be compacted to the following criteria: 1. Structural fill placed behind below-grade walls should be compacted to between 90 to 92 percent of the MDD estimated in accordance with ASTM D 1557. Care should be taken 11 when compacting fill near the face of below-grade walls to avoid over-compaction and hence overstressing the walls. Hand-operated compactors should be used within 5 feet behind the wall. Wall backfill placed within the building footprint should be compacted to between 90 to 92 percent of the MDD within 5 feet of the walls and to at least 95 percent of the MDD beyond 5 feet of the walls. The upper 2 feet of fill below floor slab subgrade should also be compacted to at least 95 percent of the MDD. The contractor should keep all heavy construction equipment away from the top of retaining walls a distance equal to one-half the height of the wall, or at least 5 feet,which ever is greater. 2. Structural fill in hardscape areas, including utility trench backfill, should be compacted to at I least 90 percent of the MDD estimated in accordance with ASTM D 1557,except that the upper 2 feet of fill below final subgrade should be compacted to at least 95 percent of the MDD. 3. Structural fill placed below floor slabs and foundations should be compacted to 95 percent of Ithe MDD estimated in accordance with ASTM D 1557. 4. Non-structural fill, such as fill placed in landscape areas, should be compacted to at least 85 percent of the MDD estimated in accordance with ASTM D 1557. In areas intended for future development, a higher degree of compaction should be considered to reduce the settlement potential of the fill soils. IUtility Trenches Trench excavation, pipe bedding, and trench backfilling should be completed using the general procedures described in the 2006 WSDOT Standard Specifications or other suitable procedures specified by the project civil engineer. The native and fill soils encountered at the site are generally of —i low corrosivity based on our experience in the Puget Sound area. IUtility trench backfill should consist of structural fill and should be placed in lifts of 8 inches or less .,,,r (loose thickness) such that adequate compaction can be achieved throughout the lift. Sand backfill, File No.12547-001-00 Page 6 GEOENGINEER LQ IFebruary 3,2006