10200 19TH AVE SE COSTCO FUEL STATION Geotech Report 2022-10-25

GEOTECHNICAL ENGINEERING STUDY Costco Wholesale c/o Barghausen Consulting Engineers E-8556 January 13, 1999 Page 11 Pavement Areas - The adequacy of site pavements is related in part to the condition of the underlying subgrade. To provide a properly prepared subgrade for pavements, the subgrade should be treated and prepared as described in the "Site Preparation and General Earthwork" section of this report. Pavement subgrade should be in a firm and unyielding condition when proofrolled, and fill areas should meet the requirements of structural fill. In localized areas of soft, wet, or unstable subgrade, a greater thickness of structural fill or crushed rock may be needed to stabilize these localized areas. Cement treatment and cement kiln dust treatment may also be considered for stabilizing wet areas of subgrade. The following flexible pavement section for lightly-loaded areas can be used: • Two inches of asphalt concrete (AC) over four inches of crushed rock base (CRB) material, or • Two inches of AC over three inches of asphalt treated base (ATB) material. Heavier truck-traffic areas will require thicker sections depending upon site usage, pavement life and site traffic. As a general rule, the following flexible pavement sections can be considered for truck-trafficked areas: • Three inches of AC over six inches of CRB, or • Three inches of AC over four and one half inches of ATB. These pavement thicknesses may be modified based on anticipated traffic loads and frequency. In areas where rigid pavement is planned, the modulus of subgrade reaction of the subbase can be used in the design. For rigid pavements supported on at least two feet of structural fill that is in a firm and unyielding condition when proofrolled, a modulus of subgrade reaction of 250 pounds per cubic inch (pci) can be used for the subbase. If requested, ECI can provide subgrade reaction values for asphalt or cement treated subbase materials. Earth Consultants, Inc.