3301 SEAWAY BLVD WHOLE SITE 2025-10-30

Mr. Greg Bertch October 25, 2016 Comment #4 The pavement sections presented in the original geotechnical report seem thin for the areas where heavy trucks will operate. The sections presented for heavy traffic areas are 3 inches of HMA over 6 inches of CRB or 5 inches full -depth HAM. Using a structural coefficient of 0. 42for HMA and 0.14 for CRB results in design AASHTO Structural number of 2.1. Using a subgrade resilient modulus of 10,006psi, typical AASHTO input parameters, and the ESAL value present in the report, we calculate a required structural number of 2.51 using the program Darwin by AASHT(. Response We are not quite sure why the city's reviewer is commenting on the recommended pavement section for a private paved access road and truck parking lot. In any event, we do not agree with the reviewer's assessment. First, the structural coefficient for HMA used by the reviewer is low. Recent studies by WSDOT have shown that the structural coefficient for 14MA is higher and WSDOT has recommended increasing the coefficient from .44 to .5. (See Use of the 1993 AASHTO Guide, MEPDG and Historical Performance to Update the WSDOT Pavement Design Catalog" prepared by the Washington Department of Transportation (WSDOT) dated September 2011). Using this value, the structural number of the recommended pavement section is 2.34. Second, the subgrade resilient modulus assigned by the reviewer is low. Stable and compact subgrade composed of glacial till or outwash soils present at the site will exhibit a resilient modulus of at least 15,000 psi. Using this value along with standard AASHTO inputs and an ESAL of 300,000 the required pavement structural number is 2.14, which is less than the structural number of the recommended section. We trust the information presented is sufficient for your current needs. if you have any questions or require 01Y Project No. T-7342