The Effects of True Triaxial Loading and Unloading Rates on the Damage Mechanical Properties of Sandstone

Coal is the main energy source in China. In the process of coal resource mining, the surrounding rock of roadways is often in the complex stress environment of “three heights and one disturbance”. At the same time, rocks in the stratum are often in a three-way unequal pressure state under the action of geological structure, and conventional rock mechanics tests cannot study the mechanical properties of rocks under actual stress conditions; thus, this is based on the self-developed true triaxial multifunctional fluid–structure coupling test system to study the damage mechanical Properties of Sandstone. The results are shown as follows: With an increase in loading rate, the peak damage D cr of sandstone decreases, but the initial damage D a increases in the elastic stage, and the brittleness of sandstone weakens. With the increase in the unloading rate, D cr increases, but D a decreases in the elastic stage, and the sandstone brittleness increases first, then decreases. In addition, the peak maximum principal strain ε 1max first decreases rapidly and then slowly; the peak minimum principal strain ε 3max increases first, then decreases slowly, and increases slowly; the peak intermediate principal strain ε 2max decreases slowly; and the peak volume strain ε vmax increases rapidly first and then slowly with increases in the loading rate. With an increase in the unloading rate, ε 1max increases rapidly first, then decreases slowly, then increases rapidly and finally increases slowly; ε 3max first decreases slowly, then increases slowly, and finally decreases slowly; and ε 2max increases slowly then decreases slowly. ε vmax decreases rapidly first and then increases slowly with increasing loading rate.