循环冷冲击作用下煤的渗透性变化规律试验研究

为了研究循环冷冲击处理对煤体增透作用的影响,利用SLX-80型高低温处理系统对原煤煤样进行多次循环冷冲击处理,并利用电子天平和三轴瓦斯渗流实验系统分别测定了煤样冷冲击处理前后的质量变化和渗透率增加幅度,对比分析了冷冲击处理前后煤样表面的裂纹分布情况。试验研究结果表明,循环冷冲击处理所产生的热应力超过煤体抗拉强度时会在煤体内部形成新的裂缝,增加原始裂缝的有效宽度,从而提高了煤体内部裂缝连通的有效性,有效改善了煤体渗透性;循环冷冲击处理后煤体渗透率的平均增幅为16%～215%,煤体渗透率增幅大小与处理后的裂纹增加数量及其连通性紧密相关;煤岩材料的非均质性、外部应力载荷及“负损伤”效应的影响使得循环冷冲击处理后的煤体渗透率增幅具有明显的随机性,并呈现出非均匀波动变化特征;循环冷冲击处理所产生的收缩-膨胀效应会引起煤体部分碎块脱落,最终导致煤体质量减小,循环冷处理后煤体的平均质量减幅为0.151%。

Experimental Study on the Change Rule of Coal Permeability under Cyclic Cold Impact

To investigate the influence of cyclic cold impact treatments on improvement of coal permeability, the SLX-80 high and low temperature treating system was utilized to conduct the cyclic cold impact treatments on raw coal, then the change of mass variation and permeability increment before and after cyclic cold impact were measured respectively by the electronic balance and the triaxial gas seepage experimental system. At the same time, the distribution of cracks on the surface of coal samples were comparatively analyzed before and after cyclic cold impact treatment. The experimental results indicate that when the thermal stress caused by cyclic cold impact exceeding the tensile strength of coal, several new cracks will be generated in coal body and the effective width of original cracks will increase, which can improve the efficiency of crack connectivity and usefully improve the permeability of coal. The average growth of coal permeability after cyclic cold impact is 16%～215% and the increasing magnitude of coal permeability is closely related to the quantity of the newly generated cracks and their connectivity. The influence of the heterogeneity of coal, the external loads and the “negative damage effect” will lead to the obvious randomness of the growth of coal permeability after cyclic cold impact. And the growth of coal permeability will present a characteristic of inhomogeneous fluctuating. The effect of shrinking and swelling caused by cyclic cold impact will lead to the breaking-off of part of coal fragments, which eventually results in the reduction of coal mass. The average mass reduction of coal after cyclic cold impact was 0.151%.