Rate effect on the burst tendency of coal-rock combined body under low loading rate range

Uniaxial compression tests with four different orders of magnitude under low loading rate range (10-3 -100 MPa / s) were conducted for coal-rock combined body. The influence of loading rate on the burst tendency of coal- rock combined body was investigated by using compressive strength,elastic modulus,impact energy index,elastic ener- gy index and normalized dynamic failure time. The results show that with the increase of loading rate,the bearing fail- ure structure of coal-rock combined body is converted from coal to coal-rock combined body,and the critical loading rate is obvious. The compressive strength and elastic modulus of coal-rock combined body remains at a relatively low value under the critical loading rate,and changes to a high level above the critical loading rate. The impact energy in- dex increases first and then decreases with the increase of loading rate,and reaches the maximum value near the criti- cal loading rate. The elastic energy index increases with the increase of loading rates. The corrected dynamic failure time decreases rapidly before the critical loading rate,and then decreases slowly and tends to be stable after the critical loading rate. It can be concluded that the burst tendency of coal-rock combined body can be divided into two distinct levels with the increase of loading rate,and the mutation rate of burst tendency near the critical load rate is very obvi- ous. The critical loading rate effect has a certain guiding significance for determining the suitable working face advan- cing speed in the field condition.