7505 SEAWAY BLVD Geotech Report 2022-10-25

November 11, 2016 HWA Project No. 2014-117-21 As an alternative to using imported gravel borrow during periods of wet weather, the existing native soil could be used as structural and/or non-structural fill by mixing with varying amounts of dry concrete or lime. If properly blended, this would have the effect of lowering the moisture content of the soils making them suitable for compaction. This process would involve stockpiling the material and setting up a mixing plant that would be capable of processing the volumes required. If this alternative is desirable, further evaluation and testing should be completed to determine appropriate mixing ratios. 4.8.4 Pipe Bedding and Trench Backfill The soils at, or near, the bottoms of structures and where utility pipes will be placed, typically consist of silty gravelly sand. To provide suitable support and bedding for the pipe,we recommend the utilities be founded on suitable bedding material consisting of clean sand and/or gravel. Soils which are loosened or disturbed by excavation should be compacted or removed prior to placement of pipe bedding material. Pipe 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 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 meeting the specifications for"Gravel Backfill for Pipe Zone Bedding" in Section 9-03.12(3) of the WSDOT Standard Specifications (WSDOT, 2016) should be used as pipe zone backfill and placed in layers and tamped around the pipes to obtain complete contact. To protect the pipe,bedding material should extend at least 12 inches above the top of the pipe. Where perched ground water exists it may collect in the trench during construction. Trench excavations should be planned to minimize the accumulation of water during trenching. Trench backfill should consist of clean, free-draining, granular soils free from organic matter or other deleterious materials. Such materials should be less than 4 inches in maximum particle dimension, with less than 7 percent fines (portion passing the U. S. Standard No. 200 sieve), as specified for"Gravel Borrow" in Section 9-03.14(1) of the WSDOT Standard Specifications (WSDOT, 2016). The fine-grained portion of structural fill soils should be non-plastic. 4.8.5 Compaction Structural backfill,trench backfill, CSBC, and CSTC should be densely compacted in a systematic manner. The contractor should develop compaction methods that consistently produce adequate compaction levels. Structural fill soils should be moisture conditioned and compacted to the requirements specified in Section 2-03.3(14)C, Method C, of the WSDOT Standard Specifications (WSDOT, 2016); except the standard of compaction achieved shall not be less than 95% of the maximum dry density(MDD) determined for the fill material by test 2014-117 Final Geotechnical Report 14 HWA GEOSCIENCES INC.