3214 BROADWAY SEPA 017 - 004 Geotech Report 2025-04-14

American Property Develot:. rent ES-0599.05 January 16, 2015 Page 6 Updated January 22, 2015 Where structural fill is utilized outside of the foundation areas, a suitable granular soil with a moisture content that is at or near the optimum level should be used. The native silty sand soils can be considered for use as structural fill provided the soil is at or near the optimum level at the time of placement. The native soils have a moderate sensitivity to moisture, and will become unstable if exposed to excessive moisture. If the native soils cannot be successfully compacted, the use of an imported soil may be necessary. Imported soil intended for use as structural fill should consist of a well graded granular soil with a moisture content that is at or near the optimum level. During wet weather conditions, imported soil intended for use as structural fill should consist of a well graded granular soil with a fines content of five percent or less defined as the percent passing the #200 sieve, based on the minus three-quarter inch fraction. Structural fill is defined as compacted soil placed as wall backfill and in slab-on-grade, utility trench, and roadway areas. Soils placed in structural areas should be compacted to a relative compaction of ninety percent, based on the maximum dry density as determined by the Modified Proctor Method (ASTM D-1557-02) and placed in maximum twelve inch lifts. In pavement areas, the upper twelve inches of the structural fill should be compacted to a relative compaction of at least ninety five percent. As previously mentioned, structural fill below foundations should consist of a suitable crushed rock material. Erosion Control In general, control of off-site erosion for this project will likely be limited to construction entrances. Silt fencing should be installed as appropriate, and as needed along the site perimeter. Construction entrances should consist of quarry spalls underlain by a non-woven filter fabric. Quarry spall thickness will depend on subgrade stability at the entrance, but should typically be at least six inches. Shoring Recommendations We anticipate cuts of up to approximately 15 feet will be required to construct the below grade garage levels. Where sufficient space is available, a portion of the garage level excavations may be completed using open cuts. Temporary shoring or a combination of shoring and temporary slopes will be necessary where the building will be sited in close proximity to the property limits. In our opinion, where shoring is necessary, the use of a conventional cantilever or tieback shoring system is feasible for temporary support of excavations. In our opinion, soil nailing is also a feasible alternative for excavation shoring. For purposes of this study, we have provided recommendations for soil nailing, and recommendations for cantilever and tieback shoring. It is important to note that if tiebacks or soil nails are utilized, appropriate easements will be required from adjacent property owners to accommodate the tendons and nails, as appropriate. Earth Solutions NW,LLC