1707 SCENIC DR SNO CO PUD Geotech Report 2022-10-25

l ,}�, . �..�._{ �/ �;1'� •' ) l� 1 `C�1 �� t rl'��l L�``'�� GU"��✓' i �vZ� � � i111 (��/�L V'�'� 5�'��C ��1/ ( .,� � -�: � � - . � % Imported structurai fill placed during wet weather, under structures, and to construct slopes should consist of gravei borrow per WSDOT standard specification section 9-03.14(1). Imported structural fill placed during dry weather should meet the criteria for Common Borrow as specified in Section 9-03.14(3) of the 2014 WSDOT Standard Specifications. Common Borrow will be suitable for use as structural fill during dry weather only and in areas not on the slopes and under structures. Crushed rock surfacing should be in accordance with the District's standard for substation design. The 12-inch thick crushed rock subbase should meet the criteria for crushed surfacing base course as specified in Section 9-03.9(3) of the 2014 WSDOT Standard Specifications. The clean crushed gravel should meet the gradation requirements of Section 9-03.1(4)C Grading No. 67 ofthe WSDOT Standard Specifications. On-site Soils The fill and glacial till soils contain significant fines (material passing the U.S. Standard No. 200 sieve) ^ ' and will be highly moisture-sensitive and susceptible to disturbance, especially when wet. Ideally, � earthwork should be undertaken during extended periods of dry weather when the soils will be less susceptible to disturbance and provide better support for construction equipment. Dry weather construction will help reduce earthwork costs and increase the potential for usingthe native soils as fill. The on-site soils are moisture sensitive and generally have natural moisture contents higher than the anticipated optimum moisture content for compaction; typically 2 to 7 percent and as high as 15 percent over optimum moisture content. As a result, the on-site soils will likely require moisture conditioning (drying) in order to meet the required compaction criteria during dry weather conditions and will not be suitable for reuse during wet weather. Trafficability on the site is not expected to be difficult during dry weather conditions. However, the native soils will be susceptible to disturbance from construction equipment during wet weather conditions and pumping, rutting and generation of mud from the exposed soils under equipment loads may occur. Reuse of Existing Concrete Rubble Existing Portland cement concrete (PCC) rubble may be reused as structural fill if properly crushed during demolition and approved by the District. Recycled PCC rubble may be used as structural fill throughout the project, except: (1) within 3 feet of landscape areas or as determined by the civil engineer, and (2) within the infiltration facilities or water collection trenches. For use as structural fill, the concrete rubble should be crushed or otherwise ground up and should meet the gradation requirements for Gravel Borrow per WSDOT Standard Specifications Section 9-03.14(1). Fill Placement and Compaction Criteria Structural fill should be mechanically compacted to a firm, non-yielding condition. In general, structural fill should be placed in loose lifts not exceeding 12 inches in thickness when compacted using heavy equipment. Loose lifts should be reduced to 4 inches or less when using hand operated equipment. Each lift should be conditioned to the proper moisture content and compacted to the specified density before placing subsequent lifts. Structural fill placed �vithin the substation should be compacted to at least 95 percent of the MDD estimated in accordance with ASTM D 1557 under all structures and behind retaining walls, and within 2 feet of planned grade. Structural fill should be compacted to at least 90 percent of the MDD elsewhere on the site. CiEOENGINEER� October24,2014 Page8 � File No.0482-027-02