Testing Methodology for Resilient Modulus of Base Materials

Resilient moduli of base and subgrade materials are important parameters in the new pavement design method adopted by AASHTO and many state agencies. Several testing protocols for determining the resilient moduli of subgrade soils have been proposed and evaluated in the technical literature. Unfortunately, less effort has been focused on developing protocols appropriate for base materials. The main objective was to describe a resilient modulus testing procedure that has been developed for the Texas Department of Transportation. The proposed procedure contains the main steps of the AASHTO T294-92 procedure, with several exceptions. Namely, the loading sequence of the T294-92 procedure was modified to avoid subjecting the specimens to high devi-atoric stresses at low confining pressures. The conditioning cycles were replaced by a procedure in which the specimen was grouted to the platens to minimize disturbance to the specimen during stage testing. The effects of end restraint on the vertical strains were minimized by measuring the deformations of the middle one-third of the specimen. To avoid well-known problems with mounting linear variable differential transformers on the specimen, noncontact probes were used to measure deformations. To maximize the amount of information gained, the lateral deformations were also measured with noncontact probes to determine the Poisson's ratio. On the basis of tests on nine synthetic specimens with known properties and nine different base materials from different parts of Texas, it was concluded that the proposed methodology yields accurate and repeatable results.