11831 AIRPORT RD WHOLE SITE FILE Geotech Report 2022-10-25

Pavement Design Subgrade Preparation We recommend that the subgrade soils in new pavement areas be prepared and evaluated as described in the "Earthwork" section of this report. We recommend that the subgrade be compacted to at least 95 percent of the MDD per ASTM D 1557 prior to placing pavement section materials. If the subgrade soils are loose or soft, it may be necessary to excavate the soils and replace them with structural fill. A layer of suitable woven geotextile fabric may be placed over soft subgrade areas to limit the thickness of structural fill required to bridge soft,yielding areas. New Hot-Mix Asphalt Pavements At a minimum we recommend that new pavement sections be designed to meet the minimum design sections required in each jurisdiction.We do not have specific traffic data for design of the bus lanes. Based on the conditions encountered in our explorations and our experience on previous Community Transit projects, we recommend a minimum pavement section of 12 inches of asphalt overlying 6 inches of crushed rock base course. For driveway approaches subject to heavy truck or tanker traffic,we recommend a minimum asphalt pavement section of 12 inches of Class B asphalt overlying 4 inches of crushed rock base. Where concrete pavement is used, we recommend a minimum pavement section of 10 inches of portland cement concrete (PCC) overlying 4 inches of crushed rock base. For driveways the concrete thickness can be reduced to 8 inches. Thinner sections may be appropriate where limited bus traffic is expected as discussed below. New pavement sections outside heavy bus traffic can be designed in accordance with the WSDOT Pavement Policy. Table 12, presents the WSDOT minimum requirements for HMA and PCC pavement sections for Design Period ESALs less than 5,000,000.We can provide additional pavement analyses using actual traffic data if available. TABLE 11 WSDOT RECOMMENDED MINIMUM PAVEMENT SECTION (DESIGN PERIOD ESALS < 5,000,000) Flexible Pavement Rigid Pavement HMA CSBC PCC Slab CSBC 6 inches 6 inches 8 inches 4 inches Erosion and Sedimentation Control Potential sources or causes of erosion and sedimentation depend upon construction methods,slope length and gradient, amount of soil exposed and/or disturbed, soil type, construction sequencing and weather. The project impact on erosion-prone areas can be reduced by implementing an erosion and sedimentation control plan.The plan should be designed in accordance with applicable county standards.The plan should incorporate basic planning principles including: • scheduling grading and construction to minimize soil exposure, ■ retaining existing vegetation whenever feasible, ■ revegetating or mulching denuded areas, GEOENGINEERS April 14,2017 Page26 File No.2095-032-00