Study on the mechanical behavior of silt-clay transition soils under cyclic loading

Abstract

To better understand the mechanical behavior of cohesive soils under repetitive loads, a series of consolidated undrained (CU) cyclic triaxial tests on normally consolidated silt-clay transition soils were performed. The tested soils were created by mixing kaolin clay with non-plastic silt at different proportions. All testing procedures and conditions of the axisymmetric triaxial compression tests were kept consistent. Only the silt content of these soils was systematically varied. Cyclic stress ratios (CSR) of 0.30, 0.45, 0.60, 0.75, and 0.90 with cyclic loading frequencies of 0.05 Hz and 0.10 Hz were employed in these tests. It has been observed that the CSR has a significant effect on the accumulation of plastic strains of the soil specimens. The plastic strains increase with higher CSR values. The specimens eventually fail when the CSR values are equal and greater (ควรเป็น equal to or greater) than 0.75. As the silt content increases, the transition cohesive soils start to exhibit ratcheting responses even with low CSR values. For similar numbers of load cycles, the observed excess pore water pressures tend to increase more rapidly with increasing silt content. It has also been observed that the values of undrained resilient modulus of the tested silt-clay soils decrease as the silt content increases. This contradicts the well-observed trend of monotonic triaxial tests in that an increase in silt content generally renders an increase in undrained stiffness of fine-grained cohesive soils.