Evaluating Influence of Microscopic Properties on Mechanical Behavior of Gravelly Soils by Using Discrete-Element Method

Amidst the rapid development of the metropolitan area in Taichung, Taiwan, the mass rapid transit system (MRT) exemplifies a green public transportation project that helps minimize road traffic and reduce greenhouse gas emissions. However, managing the engineering of gravelly soils during MRT construction is challenging. This study adopted the discrete-element method software PFC2D to investigate the influence of microscopic properties on the mechanical performance of gravelly soils. Triaxial test data relating to gravelly soils with pure shear stress paths were analyzed to realize the mechanical behavior. The specimens were classified into Groups A and B based on the matrix properties, with and without cohesion. The simulation adopted two types of contact models to reflect gravelly soil matrix properties, which demonstrated reasonable agreement with the test results. After validating the proposed numerical model with a series of triaxial tests of gravelly soil under different confining pressures, this study investigated the influences of the micro parameters of porosity, friction coefficient, bond strength, and normal and shear stiffness of gravels and matrix on the mechanical behavior of gravelly soils. The results indicated that the main factors for Group A were the friction coefficient and effective modulus between particles. For Group B, the friction coefficient and bonding effective modulus were the main factors. The shear strength of gravelly soils increased when the friction coefficient, effective modulus, and bonding effective modulus increased.