Development and Application of Testing System of High Pressure Nitrogen Blasting Experiment for Increasing Permeability

The theories of air jet and quasi-static expansion of high pressure nitrogen have been laid as foundation in this paper. The testing system of high pressure nitrogen blasting experiment is independently developed to get the dynamic variation laws of high pressure nitrogen blasting in coal and rock mass. The experiments in different pressure（5 MPa, 7.5 MPa, 10 MPa）and different volumes（1 L, 2 L, 3 L） have been developed. The results showed that: with the increasing of pressure, it extends from initial longitudinal main crack to longitudinal and transverse two main cracks and the secondary cracks develop more obviously. Besides more cracks, degree of crushing is deeper and the crack propagation regions become bigger. With the expanding of device volume, the main crack becomes longer, while the secondary crack has been inhibited. According to the p-t curve analysis of the high pressure nitrogen blasting experiment, based on different characteristics in each stage, the blasting process can be divided into 3 periods, air jet impingement stage, initiation stage and fracture stage.