Dynamic responses and failure modes of stratified sedimentary rocks

Understanding the dynamic responses and failure modes of stratified sedimentary rocks is critical to predict ground motion in sedimentary rock formations during underground excavation. We experimentally investigated the dynamic properties of sandstone specimens, siltstone specimens, and composite specimens with sealed sandstone-siltstone interfaces using a split Hopkinson pressure bar system. We also numerically examined the effects of rock type, strain rate, particle size, and interface cementation degree on the dynamic properties of sedimentary rock specimens using the discrete element method. Our results show that the dynamic strengths of sandstone and siltstone increase with higher strain rate in a similar manner, but the dynamic strength of sandstone is larger than that of siltstone at the same strain rate. Although the size of deposited particles may not affect the dynamic strength of lithified rocks, the fracture surface of sandstone with large particle size is relatively rough. The degree of cementation at the interface between siltstone and sandstone has a negligible effect on the dynamic strength of sedimentary rocks, but remarkably affects the failure modes. Micro-cracks first initiate in the low-strength siltstone, and coalesce with those subsequently developed in the sandstone and at the sealed interface to form meso-fractures.