3800 RIVERFRONT BLVD Geotech Report 2023-05-04

I March 26, 2019 HWA Project No. 2015-061-21 Task 600-7 IWhere the fill soils are competent and do not require over-excavation, bedding material should be placed directly on the undisturbed fill soils. Trench bottoms should be free of debris and standing water. If subgrade soils are disturbed, the disturbed material should be Iremoved down to undisturbed soil and replaced with properly placed and compacted bedding material. To minimize trench subgrade disturbance during excavation, the excavator should use a smooth-edged bucket rather than a toothed bucket. Utilities Founded within Refuse IRefuse encountered at the pipe invert elevation during excavation should be over-excavated to a depth of at least 12 inches below the base of the proposed pipe bedding(2 feet below the I base of the pipe). Over-excavation should extend the full width of the trench. Over excavated areas should be backfilled with foundation material Class A, as described in Section 9-03.17 of the WSDOT Standard Specifications (WSDOT, 2018). The foundation I material should be compacted to the maximum extent possible prior to placing the pipe zone bedding. 4.4.7 Pipe Bedding Pipe bedding beneath the utilities should consist of gravel backfill for pipe zone bedding as I specified in Section 9-03.12(3) of the WSDOT Standards and specification (WSDOT, 2018). Based on the results of the laboratorytestingpro gam for this stud the onsite soils encountered p �' Y� at the site generally do not meet the requirements for pipe bedding. IPipe bedding should provide a firm uniform cradle for support of the pipes. A minimum 12-inch thickness of bedding material beneath the pipe should be provided. Prior to installation of the I pipe, the pipe bedding should be shaped to fit the lower part of the pipe exterior with reasonable closeness to provide uniform support along the pipe. Pipe bedding material should be used as pipe zone backfill and placed in layers and tamped around the pipes to obtain complete contact. ITo protect the pipe,bedding material should extend at least 12 inches above the top of the pipe. 4.4.8 Trench Backfill Recommendations IThe fill soils and refuse encountered in the explorations along the proposed utility alignments are not suitable for reuse as trench backfill for this project. Imported trench backfill will be required I for all utility installations. For most utility applications, Gravel Borrow meeting the WSDOT specifications is standard imported utility trench backfill material. However, Gravel Borrow can be difficult to impossible to compact in periods of wet weather. As the utility installations are Iexpected to take place during the wet spring months, we recommend Crushed Surfacing Base Course(CSBC)meeting the requirements of Section 9-03.9(3) of the WSDOT standard specifications (WSDOT, 2018)be used as trench backfill for all utility installations. 1 I Geotechnical Report Revision 3 26 2019.doc 1 7 HWA GEOSCIENCES INC.