Abstract: Traffic loading from trains or vehicles will cause damages in transportation infrastructure constructed on silt soil, and consequently result in reduction of transportation infrastructure’s availability. In order to investigate cumulative deformation and dynamic behaviors of silt soil under large cycles of traffic loading, a series of dynamic triaxial tests have been conducted on Qiantang River silt soil. Effect of soil’s physical properties, such as relative compaction(RC), water content and loading features, and loading frequency, confining pressure and cyclic stress ratio(CSR) on soil’s axial strain, dynamic modulus, damping ratio have been discussed based on the test data. The results show that the critical cyclic stress ratio(CSR) of Qiantang River silt soil is about 0.11. When the applied dynamic stress is below the critical dynamic stress, silt soil’s dynamic modulus shows very little reduction; and the cumulative axial strain is very small. When dynamic stress exceeds the critical dynamic stress, soil’s dynamic modulus reduces quickly, and the residual dynamic modulus can reach about 20% of the initial elastic modulus. Meanwhile, the dynamic modulus and damping ratio change significantly with the axial strain. The test data on silt soil’s dynamic modulus and damping ratio show a uniform conclusion after normalization on the data. Silt soil’s dynamic modulus almost keeps constant when the axial strain (or the normalized cycle number) is less than a threshold value, and decreases exponentially when beyond it and reaches a stable value ultimately. The damping ratio develops exponentially with the axial strain (or the normalized cyclic number).

Key words: silt soil, cyclic loading, cumulative deformation, dynamic modulus, damping ratio