基于离散元的高内水压下水力劈裂机理研究

Study on Hydraulic Fracturing Mechanism Under High Internal Water Pressure Based on DEM

本文针对高水压导致隧洞水力劈裂问题,运用PFC2D离散元模拟软件从细观力学角度出发,考虑水岩耦合条件建立水力劈裂数值模型,研究高内水压下围岩水力劈裂机制,获取水力劈裂发展过程,并分析大主应力对裂缝发展规律影响。研究表明:在高内水压作用下,洞壁处围岩首先劈裂,进入裂缝中的水对裂纹侧壁产生水压力,进而使裂纹尖端产生拉应力,进一步引起裂纹扩展;高内水压随裂纹扩展距离逐渐衰减,当裂纹扩展至一定距离后由于水压力小于围岩抗拉强度而趋于稳定;黏聚力增大会对裂缝发展起抑制作用,而内摩擦角对劈裂效果影响甚微;水力劈裂方向与地应力大主应力方向一致,大主应力对开裂起促进作用,小主应力对开裂起抑制作用。研究结果可为抽水蓄能电站等高压隧洞工程设计与施工提供依据。

Aiming at the hydraulic fracturing problem of tunnel caused by high water pressure,starting from micromechanics and considering the H-M coupling conditions,a hydraulic fracturing numerical model is established using PFC2 D.The hydraulic fracturing mechanism of surrounding rock under high internal water pressure is studied,the development process of hydraulic fracturing is obtained,and the influence of large principal stress on the law of crack development is analyzed.It is found that under the action of high internal water,the surrounding rock at the tunnel wall first splits,and the water entering the crack produces water pressure on the side wall of the crack,which then produces tensile stress at the crack tip and further causes the crack propagation.The high internal water gradually decreases with the crack propagation distance.When the crack extends to a certain distance,it tends to be stable because the water pressure is less than the bearing capacity of the surrounding rock.It is found that the increase of cohesion will inhibit the crack development,and the internal friction angle has little effect on the splitting effect.The hydraulic splitting direction is along the direction of large principal stress,the large principal stress promotes the cracking,and the small principal stress prevents the cracking.The results can provide a basis for the design and construction of pumped-storage power stations and other high pressure tunnel engineering.