Analysis of stress wave effect during coal breakage process by high pressure gas jet

In terms of the shortcomings of hole collapse and the suppression of gas desorption and migration caused by using hydraulic anti-reflection measures in soft and low permeable coal seam,this paper put forward a technical meth- od of using high pressure gas jet to break coal,relieve pressure and anti-reflection. According to thermodynamics corre- lation theory,the critical local velocity and pressure of stress wave caused by gas jet breaking coal were calculated and analyzed and the high pressure gas jet breaking coal experiment was carried out. When high pressure gas jet impacted coal body,the quasi-static load and dynamic load acted on it and caused the coal body surface to form some erosion pits. In the way of stress wave,the coal body could be cut through by cracks loading which resulted in rupture. By es- tablishing the dispersion equation of stress wave propagation in coal body,the influence of porosity and permeability on stress wave propagation in coal was analyzed. The result shows that the porosity has a significant effect on the wave velocity. With the increase of the porosity,the attenuation of stress wave shows an obvious tendency,and the attenuation of stress wave becomes more obvious in high frequency. At a low frequency,the permeability has little influence on the wave velocity. At a high frequency,the wave velocity increases with the increase of permeability when the permeability is low. In addition,the wave velocity attenuation shows a tendency of increasing first and decreasing later. When the permeability is greater than 10-11 ,the wave velocity is not affected by the permeability,and the stress wave is not atten- uated.