## 1 Introduction  
During the mining process, the stability of coal pillars is the premise of safe and efficient mining. Empirical formula [1; 2; 3] and numerical simulations [4; 5; 6] are widely used to study the strength and stability of pillars. However, pure compression load is assumed to be applied to coal pillars in these studies. In engineering, coal pillars often have certain inclination angles and are subjected to combined compression and shear loading. The shear stress component is conducive to the initiation and expansion of pillar cracks, which is one of the important reasons for shear instability of inclined pillars. In laboratory tests, uniaxial compression [7; 8; 9; 10; 11; 12], biaxial compression [13; 14], triaxial compression [15; 16; 17; 18; 19], Brazilian splitting [20; 21] and shear tests [22; 23; 24] are widely employed to study the deformation and failure behavior of rock samples under different loading conditions. However, these studies have certain limitations, namely the actual situation of the coupled compression-shear loading on inclined pillars cannot be effectively simulated. Besides, as an important factor affecting the structural stability of inclined pillars, mining strength has a certain mapping relationship with the loading rate in the laboratory loading process of coal samples [25]. Therefore, it is important to study the effect of loading rate on the mechanical property and failure behavior of coal samples under the coupled compression-shear loading to reveal the instability mechanism of the inclined pillar under the mining. Studies have shown that the strain rate has an important impact on the mechanical properties of coal rock [26]. Based on the triaxial compression test (under the fixed confining pressure of 50 MPa), [PERSON] et al. [27] conducted a study on the mechanical and failure behavior of shale under different strain rates (\(5\times 10^{-6}\) s\({}^{-1}\)-\(1\times 10^{-3}\) s\({}^{-1}\)). The results showed that with the increase of strain rate, the peak strength of the sample increases gradually; when the strain rate is less than \(1\times 10^{-5}\) s\({}^{-1}\), the single shear failure mode is presented on the failure surface, and when the strain rate is greater than \(1\times 10^{-5}\) s\({}^{-1}\), the surface cracks are crisscross and interlinked and distributed in a complex form. [PERSON] et al. [28] concluded that the influence of strain rate on the strength of ductile salt rock is more significant than that of brittle limestone. [PERSON] et al. [29] and [PERSON] et al. [30] studied the strain rate sensitivity of sandstone with different sizes under the uniaxial compression, and proposed an empirical equation correlating the dynamic increment factor with the applied strain rate. [PERSON] et al. [31] conducted uniaxial compression tests on type I and type II rock, and concluded that the peak strength of type II rock increases with the increase of strain rate. [PERSON] et al. [32] and [PERSON] et al. [33] carried out the uniaxial compression tests of coal samples under different loading rates. However, different results were obtained. [PERSON] et al. [32] reported that the uniaxial compressive strength first increases and then decreases with the increase of loading rate, while [PERSON] et al. [33] claimed that the uniaxial compressive strength tends to increase gradually. However, in the above research, the influence of coupled compression-shear loading mode on the mechanical response of coal samples are ignored. Besides, research on the dynamic impact failure behavior of rock or non-rock materials under the coupled compression-shear loading has been widely studied. [PERSON] and [PERSON] [34] studied the pure shear failure behavior of rock under the dynamic loading by using an improved torsional split Hopkinson bar (TSHB) experimental system; [PERSON] and [PERSON] [35] introduced the modified TSHB test system into the field of rock mechanics to study the dynamic friction and shear effects of closed cracks.