1910 MERRILL CREEK PKY 2018-11-15

Mr. Danen Peugh January 19, 2004 Pavements Pavement subgrades should be prepared as described in the Site Preparation and Grading section 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 construction equipment 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. For traffic consisting mainly of light passenger and commercial vehicles with only occasional heavy traffic, and with a stable subgrade prepared as recommended, we recommend the following pavement sections: • Two inches of asphalt concrete (AC) over four inches of crushed rock base (CRB} • Two inches of AC over three inches of asphalt-treated base (ATB) For heavy truck traffic areas, we recommend the following pavement sections be used: • Three inches of AC over six inches of CRB • Three inches of AC over four inches of ATB The paving materials used should conform to the Washington State Department of Transportation (WSDOT) specifications for Class B asphalt concrete, ATB, and CRB. As an alternative to using ATB or CRB, consideration can be given to constructing the pavement base using soil cement. For this process, the native soils would be uniformly blended with Portland cement, moisture conditioned as necessary, and then compacted. The AC pavement section would then be constructed over the soil cement base (SCB). On a preliminary basis, for constructing the SCB, Type I Portland cement should be blended uniformly with the native soils at a rate of 0.65 pounds of cement per inch of compacted depth per square foot of area. Prior to mixing, the soil's moisture content should be above optimum moisture. If required, water should be added during mixing to maintain this moisture conditioning. Once blended and moisture conditioned, initial compaction of the mixture should be accomplished with a sheep's foot compactor. Following this initial compaction, the soil cement can be graded with final compaction then achieved with a static smooth drum roller. The soil cement should be compacted to a minimum relative compaction of 95 percent in accordance with ASTM Test Designation D-698 (Standard Proctor). Grading and final compaction of the soil cement should occur within three hours of initial mixing. Once completed, traffic should be kept to a minimum and the SCB allowed to cure a minimum of three days pnior to paving. During this time, the surface of the soil cement should be kept moist and not be allowed to dry excessively. For the light and heavy duty pavement sections, we recommend a minimum SCB thickness of 8 and 12 inches, respectively, be used as an alternative to the ATB or CRB. Project No. T-5471 Page No. 9