Dynamic Behavior of Stone Column–Improved Soft Clay under Three-Stage Traffic Loads

This paper presents the results of a laboratory investigation into the response of stone column–improved soft clay under dynamic traffic load conditions. Six reduced-scale model tests were performed with vertical traffic load composed of three consecutive stages: initial static load, cyclic load, and postcyclic load. The principal parameters were comprehensively investigated, such as loading frequency (1, 3, and 5 Hz), bearing stratum, and reinforcement conditions. The results show that dynamic settlement of a floating geosynthetic-encased stone column (F-ESC) increases rapidly with the increase in the time of cyclic loading at high loading frequency (5 Hz), accounting for 36.8% of total settlement. The geogrid encasement showed great benefits to the settlement improvement of stone columns under traffic loading. High-frequency traffic load generally decreased the bearing capacity and load transfer efficiency of F-ESC. Excess pore-water pressure (EPWP) is sensitive to the load frequency, and the value in F-ESC under the 5 Hz cyclic load is 1,420.5% larger than that under 1 Hz cyclic load. Rapid increase and accumulation of EPWP may cause significant foundation settlement at high loading frequency. The end-bearing geosynthetic-encased stone column shows a high strain increment ratio (up to 96.2%) under cyclic loads, which should be duly considered in the selection and design of reinforcement materials.