承压水基坑突涌的水力劈裂

Burst in foundation pit on confined water using hydro-fracturing

突涌是基坑工程施工过程中常遇的主要灾害之一。现有的承压水基坑突涌稳定分析方法均不能反应突涌破坏机理。从水力劈裂的机理入手,建议承压水基坑突涌问题应考虑应力-渗流场耦合作用。在Biot固结理论基础上,建立了基坑突涌分析水力劈裂耦合模型,考虑了土体物理力学性质的动态演化。试图通过分析工作面推进过程中基底土体应力场和渗流场的变化,来判断突涌发生的可能性。研究结果表明:突涌始于基底隔水层所发生的张拉破坏,基底周边是发生突涌的危险位置;渗透弱面(初始张拉裂缝)的水压楔劈效应所导致的水力劈裂为基坑突涌提供了通道;高水压力的存在是突涌发生的前提条件,高水力梯度的产生是基坑突涌的根源。

Burst is one of the main disasters in the foundation pit engineering.However,the current methods for analyzing burst stability of the foundation pit on confined water could not reflect the failure mechanism.According to mechanism of hydro-fracturing,the seepage-stress coupling should be considered when burst is studied.The coupling model for the foundation pit burst in hydro-fracturing process is established based on Biot＇s consolidation theory,and the dynamic evolution of soils permeability and mechanical characteristic are considered.The possibility of burst is explored by analyzing the change of stress field and seepage field during the excavation process.The results show that burst begins in tension failure in aquiclude of foundation base,whilst the periphery of foundation base is where more likely burst occurs;hydro-fracturing caused by water wedge effect of weak surface infiltration（it is the initial tension crack）provides the channel for burst and a confined bed with high pore water pressure is the precondition for burst,but high hydraulic gradient is the root cause for burst.