Measuring stress and strength of coal by drilling cutting torque method

The feasibility of judging the stress and strength of coal by drilling pipe torque and drilling thrust is given through mechanical analysis during the drilling process. On this basis, the way to judge the risk of rock burst by testing drilling pipe torque and drilling thrust is put forward. The drilling experiments on the prefabricated similar coal specimens are performed under different stresses and strengths of coal and advance speeds. A torque-thrust testing device is designed for these tests. The results show that: (1) Under the influence of a single factor, the drilling pipe torque linearly increases with the stress of coal, while the drilling thrust reduces linearly with the stress of coal. The variation rules of drilling pipe are consistent with those of the stress of coal and drilling volume. (2) Both the drilling pipe torque and the drilling thrust linearly increase with the increasing strength of coal. (3) For the same coal and rock materials under the same pressure, the faster the drilling speed, the larger the drilling cutting torque, and vice versa. The results are important for the forecast of dynamic disasters in coal mines.