This report looks at the effect of gravel size particles on the maximum dry density of granular soils. The procedures which the Washington State Department of Transportation use for determination of maximum dry density sometimes produce density standards which cannot be obtained in the field.
Eight soil samples were tested to determine the influence of angularity of rock particles on the density. The samples were selected to provide a variation of rounded to angular particles. The method (WTM 606) WSDOT uses to determine maximum density curve was found to overpredict the maximum dry density test results as compared to one point maximum density tests (Modified Proctor).
It is recommended that modifications be made to the current WSDOT Method (WTM 606) and that gravel size correction method, described in the report, be added to WSDOT procedures for soils with gravel contents above 50 percent.