高压气体射流破煤应力波效应分析

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

针对松软低透煤层中水力化增透措施存在的塌孔、抑制瓦斯解析及运移等缺点,提出采用高压气体射流破煤卸压增透的技术方法。根据热力学相关理论,计算分析了气体射流破煤应力波产生的临界当地声速及压力;并进行了高压气体射流破煤实验,高压气体射流冲击煤体时,以准静态载荷和动态载荷作用于煤体,在煤体表面形成冲蚀坑,并以应力波加载的方式在煤体内形成贯穿裂纹导致煤体破裂。通过建立应力波在煤体内传播的弥散方程,分析了孔隙率和渗透率对应力波在煤体内传播的影响。结果表明孔隙率对波速有明显的影响,应力波的衰减随孔隙率增大呈增大趋势,且在高频时应力波衰减变化更为明显;低频时渗透率对波速的影响不大,高频时,在渗透率较低时波速随着渗透率的增大逐渐增大,且波速衰减呈现先增大后减小的趋势;当渗透率大于10-11时,波速不受渗透率的影响,同时应力波也未出现衰减。

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 method of using high pressure gas jet to break coal,relieve pressure and anti-reflection. According to thermodynamics correlation 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 establishing 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 ve-locity. 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 attenuated.