600 RIVERSIDE RD Geotech Report 2022-10-25

Landau Associates subgrade for the proposed access roads should be prepared in accordance with the recommendations presented in Section 3.4 of this report. Assuming a design California Bearing Ratio (CBR) of about 5 percent (which would be a reasonable value for a properly prepared pavement subgrade at the project site), the recommended pavement section would support about 1,900,000 ESALs (18-kip equivalent single axle loads) during a 20 year performance period. If it is anticipated that the traffic loading conditions at the project site will generate more than about 1,900,000 ESALs during a 20 year performance period, LAI should be contacted for additional recommendations. Asphalt concrete should meet the requirements in Section 5-04 of the 2016 WSDOT Standard Specifications and consist of HMA Class 1/2-inch, PG 64-22. CSBC should meet the gradational requirements in Section 9-03.9(3) of the 2016 WSDOT Standard Specifications, and be placed, spread, shaped, and compacted in accordance with Section 4-04 of the 2016 WSDOT Standard Specifications. 3.8.2 Trail Segments -- For the proposed trail, except as noted in the next paragraph of this report section, we recommend a pavement section that consists of 3 inches of HMA over 4 inches of CSBC that meets the gradational requirements in Section 9-03.9(3) of the 2016 WSDOT Standard Specifications. The recommended pavement section can be used where the proposed trail crosses Containment Area A-2 (see below for additional information related to crossing Containment Area A-2). The upper two inches of CSBC may be replaced by two inches of CSTC. Prior to placement of the recommendation pavement section, the subgrade for the proposed trail should be prepared in accordance with the recommendations presented in Section 3.4 of this report. It is our understanding that a portion of the proposed trail will be constructed below the 100-year flood plain elevation, which is elevation +12.7 ft. Along the portion of the trail that will be constructed below the 100-year flood and roughly parallel to the Snohomish River (i.e., not along the portion of the trail proposed between the 8tn Street cul-de-sac and the Snohomish River), we recommend a pavement section that is more robust than the pavement section recommended above. For the portion of the trail that will be constructed below the 100-year flood elevation and along the Snohomish River, we recommend a pavement section that consists of 3 inches of hot mix asphalt over 2 inches of CSBC. The 2 inches of CSBC should be underlain by an additional 10 inches of CSBC, for a total of 12 inches of CSBC. Along the river side of the trail, the lower 10 inches of the CSBC should be wrapped with geotextile. The geotextile should overlap the top and bottom of the lower CSBC by a minimum of 3 ft. To provide additional erosion protection along the river side of the trail, a 2-ft wide shoulder, the top of which should be flush with the top of the trail, should be installed. The shoulder should be constructed using CSBC and the CSBC should extend to the bottom elevation of the pavement section for a total thickness of 15 inches measured from the top of the trail. Geotechnical Engineering Report 0121030.010.011 Riverside Business Park March 22, 2018 Public Access Trails and Roadway Improvements 3-12