Micromechanics analysis and mechanical characteristics of water-saturated coal samples under coupled static-dynamic loads

Contrast experiments between static and dynamic loadings on water-saturated coal samples from Yima min- ing area was conducted by using the improved SHPB and the RMT-150 test systems. The effect of mechanical proper- ties of coal samples under different loading conditions was obtained. Results show that the stress-strain relationship un- der static and dynamic loadings is obviously different. The peak strength and elastic modulus reduce gradually with the increase of saturation time under static loading,and the softening coefficient of compressive strength is 0. 66 and 0. 52 respectively for three days and seven days saturation. Meanwhile,the peak strength of coal samples under dynamic loading similarly reduces with saturation dynamic loading. And the softening coefficient of three days and seven days becomes 0. 65 and 0. 60,but the elastic modulus increases with the coefficients of 1. 15 and 1. 37 respectively,which is different from the common results of sandstone test. Water has a significant effect on the dynamic failure of coal sam- ples,and the particle size of failure coal samples decreases with water saturation time under static and dynamic loading combination. Based on the compressive wing crack propagation mechanism,the calculation formula of water-saturated coal samples' dynamic compressive strength was obtained in coupled static-dynamic loads. The strength of coal samples under combined dynamic loading condition was improved 10-30 percents comparing to static loading,and the increase of elastic modulus was obvious,which indicates that the deformation and strength characteristics of coal samples under middle strain rate are related to structure,water content and loading mode.