3003 W CASINO RD BLDG 40-58 Geotech Report 2022-10-25

3.13 BELOW-GRADE UTILITY CONSTRUCTION Buried utility construction associated with the project will include abandonment of portions of existing lines within the proposed building footprint and re-routing of utilities to new locations outside of the building footprint. The recommendations in this section are intended for relatively small utility construction—utility conveyances on the order of 24 inches in diameter or less. For construction of larger utilities and for re-routing of a large utility tunnel to Building 40-57(a separate part of the 777X project), utility/tunnel-specific geotechnical design recommendations will need to be developed. Based upon the conditions encountered during subsurface exploration, we expect that utility excavations would occur primarily in existing fill or new fill,which could include discontinuous zones of perched water. The likely volume of water from perched zones and utility trench backfill is anticipated to be small controllable through proper sloping of the trench subgrade to sump areas and the use of`trash' pumps. Trench excavations should be sloped or benched, or shored, in accordance with local, state, and federal safety requirements and in accordance with the recommendations in Section 3.5. We anticipate that soil exposed at any utility trench subgrade should exhibit a medium dense condition or better at the time of excavation. Where loose soils, wet soils or soils exhibiting an appreciable organic content are encountered, the trench subgrade should be overexcavated at least 12 inches. Granular fill meeting the requirements for Gravel Backfill for Pipe Zone Bedding in Section 9- 03.12(3) of the 2014 WSDOT Standard Specifications should be placed and compacted to a dense condition to restore the planned trench subgrade elevation. Where suitable existing fill or native soils are encountered at the subgrade elevation,any loose soil or debris should be removed and the utility subgrade compacted to a dense condition. After pipe or conduit placement, compacted Backfill for Pipe Zone Bedding should be placed around the pipe and to a depth extending above the pipe crown in accordance with pipe manufacturer recommendations. Above the bedding zone, backfill meeting the material requirements for Bank Run Gravel for Trench Backfill in Section 9-03.19 of the 2014 WSDOT Standard Specifications should be placed and compacted to within 12 inches of the pavement or concrete apron subgrade. Within 12 inches of the pavement or apron subgrade, CSBC should be used. Excavation and backfilling of buried utilities should be accomplished in accordance with Section 7-08.3 of the 2014 WSDOT Standard Specifications. 5/16/14 P:\I423\002\010\PileRm\R\Draft Bldg 40-58 Report\Bldg 40-58_draft rpt.docx INTERIM DRAFT 3-12