Analysis on improvement effect of subgrade by dynamic compaction

To evaluate the quality of the subgrade reinforcement by dynamic compaction (DC), a dynamic finite element model was established based on the soil cap yield hardening model. A subroutine was performed to simulate the parameters (e.g., modulus of soil) changing with drop numbers. The numerical results agreed well with the results of the field test, which validated the reliability of the proposed numerical method. The optimal drop number, the degree of compaction in different zones, and density contour of the silty subgrade under 1500kN·m were analyzed by both numerical simulations and field tests. Results indicate that the multi-point tamping mainly improves the degree of compaction between adjacent impact points, producing a “dumbbell-shaped” soil spatial distribution pattern. The ironing compaction can effectively improve the soil within the depth of 1.2 ~ 1.3 m for the shallow soil layer, which makes the density of soil more uniform. Through field test, the static resilience modulus of silty subgrade reinforced by DC is around 50 MPa. The post-construction settlement of the subgrade constructed by DC is less than that by layered filling, indicating that the quality of subgrade treated by DC is reliable.