先存断裂对抽水沉降及地裂缝活动影响的数值模拟

Numerical Simulation of the Effect of Preexisting Fault on Land Subsidence and Ground Fissures During Pumping

过度抽取地下水对断层构造型地裂缝的加剧作用是很明显的,但具体的作用机制却很复杂,过去的研究多是简单的定性分析,数值模拟和定量计算少有报道。笔者采用比奥(Biot)固结渗流理论和基于A、B面接触判断的库仑滑动和张裂的接触面单元,对抽水作用下地裂缝的活动进行了数值模拟,初步探讨了抽水活动引发和加剧地裂缝活动的机制。结果表明:抽水作用下抽水井周围水平应力场发生近井区挤压、远井区拉张的变化,当拉张区内的拉应力超过土体抗拉强度时将会出现自上而下的张裂缝;先存断裂的存在将影响应力变化的模式,同时由于断裂的软弱性,使得地层容易沿其发生滑动或拉裂,从而加剧地裂缝的活动;先存断裂对地面沉降和地裂缝具有诱导、隔离和放大的作用。

The effect of pumping on ground fissures caused by fault is obvious, but its mechanism is rather complicated. Most of the previous corresponding researches are simple qualitative analysis, while numerical simulation and quantitative analysis are few. A new method was adopted to simulate the fault effect on ground fissures during pumping, which is based on Biot seepage and consolidation theory and contact surface element considering the contact relationship of side A and B. The results indicate that pumping could arouse stress change around pumping well, the horizontal earth stress near the well ascend while descend far away from it, causing cracks come into being from above to below when horizontal stress exceed the tensile strength. Additionally, preexisting fault affect the stress redistribution distinctly. Due to the low strength of fault surface, it is easy for stratum to be tore apart or slide along the fault, promoting the activity of ground fissures. In general, the effect of preexisting fault on ground subsidence and fissures includes induction, segregation and amplification.