钻孔和巷硐周围流体压力变化对围岩变形及应力状态的影响

Influence of Fluid Pressure Change on the Deformation and Stress State of Surrounding Rockmass of Boreholes and Caverns

钻孔、巷硐周围流体压力的分布和变化对围岩变形和应力状态有着显著影响。但这是一个涉及多个变量、多种响应的动态耦合过程 ,尚无法用解析法解算。孔硐周围的流体压力的动态变化又难以实现物理模拟。以钻孔排放瓦斯为例 ,通过数值模拟 ,结合宏观观测结果和微观机制的分析 ,对其规律和一些工程现象与措施的机理作了初步分析。

The distribution and change of fluid pressure have significant influence on the deformation and stress state of surrounding rockmass of the boreholes and caverns, which is related to many engineering phenomena. However, this is a dynamic coupling process involving several variables and responses, and has not been solved by analytical method yet. Also, study of the dynamic variation of fluid pressure can hardly be approached by physical model. In this article, we will, taking the discharging gas through borehole as an example, analyze the mechanism of some related engineering phenomena and appropriate countermeasures by applying numerical simulation and using the outcomes of experiments which were carried out on both macro and micro scales. There are two basic findings: 1) During the process of gas discharge, pressure gradient of gas near the borehole wall decreased greatly, the Mohr's stress circle enlarged, the stress state deteriorated and the plastic range expanded. 2) Outside the above area, both the maximum principle stress and the minimum principle stress increased, so did the effective stress and the influence range of stress redistribution. Based on the two findings described above, the following mechanisms for the deformation of surrounding rockmass in the process of gas discharge are proposed: in the area where the pressure gradient of gas decreased greatly, shear and tensile failure occurred. Just outside this area, the stress increased and its influence range enlarged, the deformation of surrounding rockmass accumulated accordingly. Furthermore, decrease of gas pressure against the grain surface could lead to the development of internal off load crevice. These mechanisms has been illustrated by many related engineering phenomena. When gas pressure decreased, the conductivity coefficient of coal increased accordingly, and deformation of surrounding rockmass accumulated. Finally, we believe that gas discharge can release not only gas expansion energy, but also deformation energy of surrounding rockmass. Consequently, it is obviously helpful to reduce the possibility of outburst.