A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Geotechnical and Earth Resources Engineering

Thesis (M. Eng.) - Asian Institute of Technology, 2023

This study investigated the behavior of clayey soil under cyclic triaxial loading conditions in both fully saturated and partially saturated states. The soil samples were prepared and tested in a custom-built triaxial apparatus. The cyclic loading was applied at a constant confining pressure while varying the deviator stress amplitude. The effects of saturation level, stress amplitude, and number of cycles on the soil's behavior were analyzed by measuring the soil's cyclic resistance ratio and deformation characteristics. This study used testing manuals from ASTM, AASHTO, and previous case studies to perform initial testing on saturated and partially-saturated soils. The excess pore water pressure for soils under different conditions showed similar trends, with a non-linear relationship between excess PWP and matric suction. Axial strain decreased with increasing matric suction, and all soils with the same confining pressure showed similar trends of axial strain with an increase in the number of cycles. Higher matric suction resulted in lower strain due to an increase in compressional resistance. The stress path for all soil specimens showed a similar trend, with an increase in excess PWP causing the effective stress path to move towards the left and ultimately failing after reaching the failure line. The strength of the soil increased with increasing initial matric suction, and the shear modulus value also increased with an increase in matric suction. Soil specimens with similar confining pressure and varying matric suction showed similar behavior, with the shear modulus for soil with matric suction of 100 kPa and 50 kPa higher than the soil with matric suction of 0 kPa. The results showed that the cyclic resistance ratio decreased with increasing stress amplitude and number of cycles for both saturated and partially saturated soil. Further research can be carried out to perform tests on reconstituted samples and to find the effect and compare results with different initial conditions on properties of soil.