2312 W CASINO RD COMMUNITY TRANSIT Geotech Report 2022-10-25

4.6.1.Structural Fill During wet weather, we recommend that structural fill consist of WSDOT Gravel Borrow with the exception it contains less than 5 percent passing the U.S. No. 200 sieve (based on the material fraction passing the 3/4-inch sieve). We should be provided samples of the proposed imported material for evaluation prior to approving it as acceptable material. During dry weather,structural fill placed at a depth more than 6 inches below slab and pavement subgrade may contain an increased fines content, provided that the minimum compaction criteria is achieved. The maximum particle size of import material for general site grading should be limited to 6 inches. Structural fill should be placed in horizontal lifts which are 12 inches or less in loose thickness when using heavy compaction equipment and 6 inches or less when using hand-operated equipment. Within the new building footprint area, below new stormwater structures, and within 2 feet of the finished subgrade surface for pavement areas, each lift should be uniformly compacted to at least 95 percent of the maximum dry density(MDD)as determined in accordance with the ASTM International (ASTM) D 1557 test method. For fill more than 2 feet below the finished pavement subgrade surface, the compaction criteria may be reduced to 90 percent of the MDD (ASTM D 1557). A representative from our staff should be present at the site to observe and evaluate fill placement and compaction operations, and to complete a representative number of in-place density tests to determine if the compaction criteria are being achieved. 4.6.2.Use of Existing Site Soils The results of our laboratory tests indicate the surficial fill soils are likely within a few percentage points of the optimum moisture content required for compaction. Re-use of on-site soils may be feasible during dry weather conditions provided the soil can be moisture conditioned to within about 2 percentage points of the optimum moisture content. However, on-site soils will not be suitable for re-use during wet weather or on wet subgrades. 4.6.3.Trench Excavations We anticipate trench excavations can be accomplished with conventional excavating equipment.A greater effort will be required where deeper excavations are required that extend into the underlying unweathered glacial till. Occasional cobbles, boulders, and construction debris may also be present at the site. The contractor should be prepared to remove these materials. Since the contractor has control of the construction operations,the contractor should be made responsible for the dewatering methods used, shoring, stability of cut slopes, as well as the safety of the excavations. The contractor is present at the site continuously and is best able to observe changes in site and soil conditions and monitor the performance of excavations.Slope inclinations may need to be modified by the contractor if localized sloughing occurs or if seepage occurs.All dewatering, shoring and temporary slopes should conform to applicable local,state and federal safety regulations. GEOENGINEERs� November 14,2019 Page 8 File No.2095-019-07