400 RIVERSIDE RD SEPA 016 - 039 - RIVERSIDE BUSINESS PARK Geotech Report 2025-04-14

December 8, 2016 Project No. T-7388-1 5.9 Pavements ' Pavement subgrades should be prepared as described in Section 5.2 of this report. Regardless of the degree of relative compaction achieved, the subgrade must be firm and relatively unyielding before paving. The subgrade ' should be proofrolled with heavy rubber tired construction equipment such as a loaded 10 yard dump truck to verify this condition. ' The pavement design section is dependent upon the supporting capability of the subgrade soils and the traffic conditions to which it will be subjected. We expect traffic at the facility will consist of cars and light trucks, along with heavy traffic in the form of tractor-trailer rigs. For design considerations, we have assumed traffic in parking and in car/light truck access pavement areas can be represented by an 18-kip Equivalent Single Axle Loading (ESAL) of 50,000 over a 20-year design life. For heavy traffic pavement areas, we have assumed an ' ESAL of 300,000 would be representative of the expected loading. These ESALs represent loading approximately equivalent to 3 and 18, loaded (80,000 pound GVW) tractor-trailer rigs traversing the pavement daily in each area, respectively. With a stable subgrade composed of the existing on-site granular fill prepared as recommended, we recommend the following pavement section options: Light Traffic and Parking: • Two inches of hot mix asphalt(HMA) over four inches of crushed rock base(CRB) • Full depth HMA—3 ''/ inches Heavy Traffic: • Three inches of HMA over six inches of CRB • Full depth HMA— 5 inches ' Soil cement stabilization or constructing a soil cement base for support of the pavement section can also be considered as an alternate to the above conventional pavement sections. Assuming a properly constructed soil ' cement base having a minimum thickness of 12 inches and a minimum 7-day compressive strength of 100 pounds per square inch (psi), a minimum HMA pavement thickness of 3 inches would be required for the heavy traffic areas. The design of the soil cement base should be completed using samples of the subgrade exposed at the time of construction. The paving materials used should conform to the Washington State Department of Transportation (WSDOT) specifications for '/2-inch class HMA and CRB. Long-term pavement performance will depend on surface drainage. A poorly-drained pavement section will be ' subject to premature failure as a result of surface water infiltrating the subgrade soils and reducing their supporting capability. For optimum performance, we recommend surface drainage gradients of at least two percent. Some degree of longitudinal and transverse cracking of the pavement surface should be expected over time. Regular maintenance should be planned to seal cracks as they occur. ' Page No. 10