Water content effects on the strain-rate-dependent dynamic response of fine-grained and coarse-grained sandstones

In deep-mining engineering, water inrush accidents induced by dynamic disturbance were often controlled by the formation of the inrush channel (mainly caused by crack coalescence). It always originated from the microcrack growth and coalescence from the mineral-grain scales and can be influenced by the loading rates. Therefore, this paper selected fine-grained (fine grain) and coarse-grained (coarse grain) sandstones and conducted the dynamic split Hopkinson pressure bar (SHPB) tests with high-speed cameras. Moreover, the microcrack evolution was identified by the optical microscopy that can observe the true microcrack generation and propagation. The results show that water content can weaken the dynamic compressive strength of sandstones and contribute to the rate dependence of strength and energy dissipation, and moreover the coarse grain samples represent a more obvious trend (ε˙ = 40–160s−1). In addition, the box dimension was introduced to calculate the fractal dimension and built the quantitative relationship between mesodamage variable and fractal dimension to identify the microcrack evolution. It can offer a new method to understand the influenced mechanism of water content on the rate dependence of mechanical response from a multi-scale analytical framework. •The water content can contribute to the rate dependence of strength and energy dissipation under dynamic loadings, especially for the CG samples.•Under the lower strain rate (ε ̇=40∼80s-1), the saturated samplessaw a longer rising time of stress-strain curve and a lower peak strength, which was more evident in FG samples. Under the higher strain rate (ε ̇=120∼160s-1), the rising time was shortened and the elastic modulus has an obvious increase, which was more evident in CG samples.•The distributed liquid phase can produce the shorter microcracks in replace of larger microcracks, which can have an obvious effect on CG samples than FG ones.•A quantitative relationship between fractal dimension and the number of microcracks can be built to characterize the mesodamage evolution.