3620 36TH PL NE 2018-01-02 MF Import

The pavement section requires a high structural number due to the soft native soils that exist at the site and the heavy loads from the front-end loader traffic. As shown in Table 3, Options 3 and 4 incorporate geogrid reinforcement layers that provide increase base course strength (Option 3) and subgrade improvement (Options 3 and 4). Inclusion of tha geogrid reinforcement effectively reduces the required base thickness for Option 3 and the subbase thickness for Options 3 and 4. The pavement sections shown for Options 3 and 4 are based on preliminary analyses and are included to illustrate the potential benefits of incorporating geogrid materials into the pavement design. The benefits may include decreased import of crushed surfacing base course and subbase materials, decreased earthwork for subgrade preparation including excavation and handling of cut materials. We recommend that Options 3 and 4 be evaluated further if considered beneficial to the project. The pavement sections presented in Table 3 are for areas where the front-end loader traffic will be routed. It may be possible to reduce the pavement section requirements in areas where the front-end loaders will not be operating. For other pavement areas we evaluated the traffic loads and required pavement section based on 75 trucks, including about 50 residential route trucks and 25 semi -trucks per day. The required pavement section is shown in Table 4. Table 4. Recommend Asphalt Concrete Pavement Sections (truck traflic!cars) 4 " "Pavement Section Thickpess (inches) OPT10,V 5 Orr1o) v 6 - AC', Class B 4 4 ATBZ 4 - CSBN s Sand/Gravel Subbase 22 or 12 w/geogrid 22 or 12 w/geognd 1AC = Asphalt Concrete Pavement, Class B per WSDOT Specifications 5-04 and 9.03. 2ATB = Asphalt Treated Base, per WSDOT Specifications 4-06 and 9.03. 3CSBC = Crushed Surfacing Base Course, per WSDOT Specifications 9-03.9(3). Geogrid reinforcement may also be incorporated to reduce the subbase thickness for Ortions 5 and 6 in the truck tr tiic areas. A layer of Tensar BX1200 geogrid reinforcement incorporated at the bottom of the subbase layer can effectively reduce the subbase thickness to 12 inches. 4.9 DRAINAGE CONSIDERATIONS We recommend that all surfaces be sloped to drain away from the proposed building areas. Pavement surfaces and open space areas should' sloped such that the surface water is collected and routed to suitable discharge points. Roof drains should be connected to tightlines hat discharge into the storm sewer disposal system. Based on the soil conditions observed in the borings and test pits, we anticipate that groundwater in temporary excavations can be controlled by pumping the water from shallow sumps. The contractor should have the responsibility to determine what dewatering measures are needed. C7J G e o E n g in e e r s 22 File No. 10625-001-OM23W3