钻孔施工围岩破坏过程模拟研究

Simulation study on the failure of surrounding rock in borehole

地下钻孔围岩破坏会导致塌孔、卡钻、挤毁套管等工程事故。为探讨钻孔围岩的破坏机理和过程,文章建立了尺寸为800 mm×800 mm×200 mm(长×宽×厚)、中心为φ160 mm的钻孔物理模型,向模型施加逐步增大的边界荷载从而模拟钻进过程中围岩的破坏过程;在此基础上,考虑到围岩的应变软化特性,利用FLAC^(3D)中的应变软化模型建立钻孔数值模型并进行求解。物理和数值模拟结果显示:边界荷载加至3.88 MPa时,围岩塑性区开始发育,孔壁出现微小裂纹;到3.94 MPa时,塑性区快速扩展,裂纹扩展到整个孔壁;随后塑性区扩展速率减缓,围岩破坏相对稳定;当荷载加至4.44 MPa时,在较短时间和应力区间内,塑性区和残余区迅速扩展,裂纹迅速增加、贯通,孔壁出现明显破裂带,围岩破坏显著;此后荷载加至4.88 MPa的过程中,塑性区和残余区扩展缓慢,无明显破坏发生。该数值模拟与物理模拟结果和淮北青东矿839工作面的钻孔电视观测结果较为吻合,研究成果能够为区内勘探孔、水文孔的选址及钻进方案设计提供一定的理论依据和实践指导。

The failure of surrounding rock in borehole will lead to engineering accidents such as borehole collapse,drill sticking and casing collapse.In order to explore the failure mechanism and process of surrounding rock during borehole drilling,a physical model with a size of 800 mm×800 mm×200 mm and aφ160 mm circular cavern was established and a gradually increasing boundary load was applied to it.On this basis,considering the strain-softening characteristics of surrounding rock,a borehole numerical model was established and solved by the strain-softening model in FLAC^(3D).The results of physical and numerical simulation show that when the load reaches 3.88 MPa,the plastic zone of surrounding rock begins to develop,and micro cracks appear on the borehole wall;when the load reaches 3.94 MPa,the plastic zone expands rapidly,and the crack extends to the whole borehole wall,followed by the growth rate of plastic zone slowing down and the failure of surrounding rock being relatively stable;when the load reaches 4.44 MPa,the plastic zone and residual zone expand rapidly,the cracks increase quickly,an obvious fracture zone appears,and the surrounding rock is damaged significantly in a short time and stress range;in the process of the load reaching 4.88 MPa,the plastic zone and residual zone expand slowly,and no obvious damage occurs on the borehole wall.The results of numerical and physical simulation are in good agreement with the borehole television results of 839 working face in Qingdong coal mine,Huaibei City.The research results can provide theoretical basis and practical guidance for the site selection and drilling scheme design of exploration holes and hydrological holes in the area.