Mechanical Response of Granite Residual Soil Subjected to Impact Loading

When constructing subway tunnels, blasting is commonly used to deal with granite boulders in weathered granite formations. It is, therefore, crucial to evaluate how the blasting-induced impact loading affects surrounding granite residual soil. By means of laboratory impact tests at different conditions, this paper presents the mechanical responses of granite residual soil. High-speed impact loading affects the soil in two ways, namely, (1) increasing the shear resistance; and (2) damaging the soil structure. Cyclic impact tests reveal the critical peak stress Acr, which approaches soil apparent preconsolidation pressure. When the peak stress exceeds Acr, the soil is severely damaged and the accumulative deformation increases sharply, indicating that the cementation of soil is destroyed. Besides, the soil is most resistant to impact loading at a threshold value of the loading frequency fth and exhibits better resistance under high confining pressures. A framework was proposed that reflects soil structural damage and within which the failure mechanism under impact loading is explained. The damage to the soil structure generated with energy dissipation is the decisive factor in soil failure, and the accumulation of permanent deformation is the direct reason why soil fails. Three response modes were proposed for studied soil under impact loading. This research provides parameters for subway tunnel construction and enhances the understanding of granite residual soil under impact loading.