Investigation of dynamic characteristics and cumulative plastic strain prediction model of clay-fouled round gravel under cyclic subway loading

This study conducts a series of saturated undrained dynamic triaxial tests using the DYNTTS large triaxial cyclic test system to investigate the dynamic characteristics and cumulative plastic strain evolution of clay-fouled round gravel under cyclic subway loading. The effects of clay fouling level (VCI), confining pressure, and dynamic stress amplitude on round gravel's dynamic properties and cumulative plastic strain are analyzed. In addition, a cumulative plastic strain prediction model is proposed by combining the time hardening theory with clay fouling level, confining pressure, and dynamic stress amplitude. The study's results indicated that with the increase in VCI, the accumulated plastic strain of the specimen tends to increase and then decrease, and the fouled clay changes from lubrication to filling, with the cut-off VCI generally between 20% and 30%. VCI significantly affects the cumulative plastic strain of specimens with small confining pressures and slightly impacts specimens with large confining pressures. With the increase in VCI, the specimen's elastic strain tends to increase and then decrease, while its resilient modulus shows the opposite trend, but both trends are more pronounced with the decrease in the confining pressure and the increase in the dynamic stress amplitude. Generally, the research results can be used as a reference for designing subway roadbed structures and their post-construction settlement predictions.