600 RIVERSIDE RD Geotech Report 2022-10-25

I U I Landau Associates 3.6.6 Reuse of Site Soils The onsite soils consist primarily of alluvial sands and dredged sand fill. The alluvial sands and dredged sand fill typically consist of fine to medium sand with varying silt content. This soil will be suitable for use as structural fill under most conditions assuming that it is handled in accordance with the Soil and Groundwater Management Plan (LAI 2017). The alluvial sands and dredged sand are not expected to be especially moisture sensitive and should be compactable under a variety of weather conditions. However, if the optimum moisture content of the soil is exceeded, moisture conditioning could be required. Moisture conditioning will also be required if onsite soil is obtained from excavations that encounter groundwater. If onsite soils cannot be reused as trench backfill, the onsite soils should be disposed of at a suitable offsite location in accordance with the Soil and Groundwater Management Plan (LAI 2017). 3.6.7 Wet Weather Earthwork If construction is accomplished during wet weather and it is not possible to properly compact the onsite soil, or if a sufficient amount of fill material is not available onsite, we recommend that structural fill consist of Bank Run Gravel for Trench Backfill in Section 9-03.19 of the 2016 WSDOT Standard Specifications, except the amount of fines should be limited to 5 percent or less, based on a wet sieve analysis of that portion passing the %-inch sieve. In addition, if fill is to be placed or earthwork is to be performed in wet weather or under wet conditions, the contractor may reduce soil disturbance by: • Accomplishing earthwork in small sections • Limiting construction traffic over unprotected soil • Sloping excavated surfaces to promote runoff • Limiting the size and type of construction equipment used • Providing gravel "working mats" over areas of prepared subgrade • Removing wet surficial soil prior to commencing fill placement each day • Sealing the exposed ground surface by rolling with a smooth drum compactor or rubber -tired roller at the end of each working day • Providing upgradient perimeter ditches or low earthen berms and using temporary sumps to collect runoff and prevent water from ponding and damaging exposed subgrades. 3.7 Below -Grade Pump Stations The subgrade soil beneath the proposed pump stations is anticipated to consist of very soft to soft silt. The subgrade soil is expected to provide adequate foundation support, provided the upper 12 inches of subgrade soil is overexcavated and replaced with foundation material meeting the requirements for Bank Run Gravel for Trench Backfill in Section 9-03.19 of the 2016 WSDOT Standard Specifications. Geotechnical Engineering Report 0121030.010.011 Riverside Business Park March 22, 2018 Public Access Trails and Roadway Improvements 3-10