RESILIENT TESTING OF SOILS USING GYRATORY TESTING MACHINE (WITH DISCUSSION AND CLOSURE)

Characterization of soils in terms of resilient behavior is gaining support because of its ready application in mechanistic analysis of pavements and in designing soil-structure systems. Resilient modulus determination, using AASHTO T274-82, has been generally viewed as a complex and time-consuming test. An alternative procedure using the U.S. Army Corps of Engineers Gyratory Testing Machine (GTM) is investigated. Study shows that GTM, developed originally for the design of bituminous mixtures and subsequently used for density control of base and subgrade soils, is likely to be a feasible alternative for resilient modulus testing. The development of the GTM test procedure is described, with special focus on simulating conditions resulting from a moving load. The stress path of GTM loading is compared with that under a passing loaded vehicle to show that the GTM simulates field stress conditions. With due consideration to sample confinement in the mold, a revised equation for kneading resilient modulus is derived. For validating the test procedure, six subgrade soils and three subbase materials are investigated using the GTM and the repeated load triaxial device, and the results are analyzed with respect to material characteristics as well as test variables. Fines content, uniformity coefficient, and stress state (bulk stress) are shown to affect the kneading resilient modulus of soils. The test variables investigated include the stress state of the sample and moisture content during compaction, the latter showing very little effect on the modulus. The important role of sample gyration (shear stress reversal) on kneading modulus is illustrated by the test results. Also included is a regression model for predicting kneading resilient modulus.