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June 13, 2023 <br />HWA Project No. 2022-188-21 <br />Table 6. Recommended Pavement Layer Thickness for the Northwest Area <br />Material <br />Description <br />Minimum Pavement Layer Thickness <br />(inches) <br />WSDQT Standard <br />Specification <br />HMA' <br />4.0* <br />9-02.1(4) <br />CSBC2 <br />6.0 <br />9-03.9(3) <br />Select Borrow <br />12.01 <br />9-03.14(2) <br />*Note: Thickness does not account for potential surface damage by repetitive equipment <br />movement and scraping by loader bucket, etc. <br />HMA: Hot Mix Asphalt: Binder Grade PG64H-28. HMA shall be placed in 2 lifts. <br />�5> CSBC: Crushed Surfacing Base Course, compacted as specified. <br />(6) Thickness of Select Borrow may be reduced if base of over -excavation and replacement with <br />CSBC is at least 22 inches below the top of new roadway. <br />4.11.4 HMA Design Considerations <br />The following design considerations should be noted and implemented: <br />• Pavement design using a reliability level of 90% can be interpreted as meaning that prior <br />to the end of the design period, about 10% of the pavement will require reconstruction <br />because of structural failure. Therefore, as the design life is approached, the <br />serviceability of the pavement should be critically viewed to determine the need for and <br />extent of any overlay application that may be required. <br />• The pavement will likely require a thin functional overlay after about 10 to 14 years <br />because of non-structural associated distress caused by environmental factors such as <br />degradation of the asphalt surface and rutting. Areas subject to surface abrasion by heavy <br />equipment operation may require repair more frequently. <br />HMA pavements are susceptible to shoving and rutting from heavy trucks particularly at <br />intersections. In these areas, more frequent maintenance and even premature <br />reconstruction of the pavement may be required. <br />• It is essential to the satisfactory performance of the pavement that good drainage is <br />provided to prevent water ponding alongside the pavement and saturation of the <br />pavement and subgrade layers. The base layers should be configured to prevent water <br />from being trapped within the layer. <br />2022-188-21 KCTS — Final Geotechnical Report 20 HWA GEOSCIENCES INC. <br />