600 RIVERSIDE RD Geotech Report 2022-10-25

Landau Associates of the site soil was variable. Seasonal variation in the moisture content of shallow site soil is also expected. The onsite soil consists 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. 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 contents 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 import soil is to be used for filling activities, the soil must be selected and tested per the recommendations of the Soil and Groundwater Management Plan (LAI 2017). If practical, recycled concrete materials can be considered for use as structural fill. Recycled concrete materials used as structural fill should meet the requirements set forth in Section 9-03.21 of WSDOT's 2016 Standard Specifications for Road, Bridge, and Municipal Construction (Standard Specifications), with the exception that they also must meet the minimum gradation criteria for Select Borrow outlined in Section 9-03.14(2) of the 2016 WSDOT Standard Specifications. Use of recycled concrete should comply with current environmental policies. Structural fill placed to raise site grades for the proposed access road and trails should be placed in loose, horizontal lifts less than 8 to 10 inches in thickness and thoroughly compacted. All structural fill under future building and paved areas (including the proposed trails) should be compacted to at least 95 percent of the maximum dry density, as determined using test method ASTM D 1557. Fill placed within landscaped areas should be compacted to a minimum of 85 percent of its maximum dry density to reduce the potential for excessive settlement. Compaction criteria for utility trench backfill are presented in Section 3.6.5 of this report. 3.6 Utility Construction The following sections provide geotechnical recommendations for design and construction of new utility structures. The following recommendations are based on our understanding that the maximum depth of the structures will be about 13.5 ft bgs. 3.6.1 Construction Dewatering At the time of our subsurface investigation in March 2017, groundwater was observed at depths ranging from about 4.5 to 7.5 ft bgs. If trench excavations are completed in the summer and early fall months and the excavations do not extend deeper than about 4 ft below existing grades, it is anticipated that the proposed utilities could be installed without encountering significant groundwater. However, groundwater may be encountered within the trench zone, particularly during winter and spring months. If groundwater is encountered during shallow trench excavation, we expect that open sump pumping will be adequate to control groundwater flow into the trench. Geotechnical Engineering Report 0121030.010.011 Riverside Business Park March 22, 2018 Public Access Trails and Roadway Improvements 3-5 1 1 1 1 1 1 1 1 1 1