Characterization of Hydro-Mechanical Effects of Suction and Clay Minerals on Resilient Modulus, M_r

Abstract

Pavement should be adequately design to sustain repeated load and evenly transfer this load to the subgrade. The response of pavement structure depends on the durability of the subgrade soil, which can be increased through stabilization and compaction, in order to achieve desirable pavement foundation. However, design parameters such as resilient modulus (M_r) is commonly used by design engineers in design of pavement structure. M_r is an important property for mechanistic analysis of pavement response under traffic loading. This study investigated possible effects of clay minerals and matric suction (u_a – u_w) on M_r of three selected Free State Subgrades (FSS). To achieve this objective, three subgrade soils representing typical FSS were selected and tested in the laboratory for M_r. Other basic civil engineering tests were conducted on the soils to determine their geotechnical properties. The specimens were prepared compacted and tested at varying moisture contents and dry densities before and after the addition of 4% and 6% bentonite, and 4% and 6% kaolinite using repeated load triaxial test (RLTT) machine and filter paper in the laboratory. Based on experimental results, M_r exhibited a hysteric loop with moisture variations. The Mr values increases with increase in matric suction on the dry path and the increase varies from one soil to another. The results further revealed that a good bilinear relationship found between M_r – (u_a – u_w) with a linearity coefficient (R²) of 0.7705.