Structural damage and dynamic failure mechanism of granite residual soils under impact loading

A series of impact tests with various frequencies and amplitudes are performed to study the influences of impact loading on the mechanical behaviors of granite residual soils, particularly for the development of deformation and excess pore water pressure. Similar critical values for amplitude and frequency are observed. Once the amplitude and frequency exceed their critical values, the soil is damaged severely and its strength decreases. Under the impact loading with low frequency or ultra-high frequency, higher pore water pressure is generated, resulting in a decrease of the effective stress and strength. Three quantitative parameters of the morphological features of the hysteresis curve are proposed to evaluate the dynamic damage of granite residual soils. Furthermore, three modes of impact damage and their characteristics are suggested. The structural damage caused by impact energy dissipation and accumulation of plastic deformation is proved to be the dominant cause of soil failure. The influence degree of impact loading on the granite residual soils depends on the natural structure strength and the amount of micro-cracks of the soil, as well as the propagation of cracks and plasticity strain induced by impact loading. Based on test results, it is suggested that the critical value for amplitude and frequency of the soils be ascertained before construction and impact loading with high-amplitude and low or ultra-high frequency be avoided. This study can enhance the understanding of the mechanical response of soils under impact loading and provide technical guidance for construction.