高水压条件下泥水盾构开挖面稳定离心模型试验研究

开挖面稳定是越江跨海盾构隧道工程安全的关键,尤其是高水压条件下,开挖卸荷导致开挖面稳定控制更加困难。以越江跨海盾构隧道为背景,研制了一套包含材料和设备的高水压泥水支护形式的开挖面稳定模拟试验装置,通过大型离心模型试验研究了高水压下开挖面坍塌失稳破坏模式和土、水应力变化规律。研究结果表明:①高水压条件下开挖面失稳具有突发性,土体呈现由局部-整体形式急速发展破坏,极小的泥水压力变化幅度即可导致土体迅速发展为整体破坏并传至地表,失稳过程中可观测到滑移倾角减小、破坏范围扩张;②随着泥浆压力的降低,开挖面前方土压力呈现先减小后增大最终趋于稳定值,开挖面失稳可以划分为微观变形、局部破坏、土拱形成、整体失稳四个阶段;③开挖面发生主动破坏时,孔隙水压会发生突然降低现象,这是由于高应力条件下密砂具有剪胀效应,从而引起负孔压导致孔隙水压力急剧下降。这种孔压波动会对开挖面失稳带来不利影响,加速开挖面失稳进程、导致失稳区域的扩大。研究成果对越江海水下隧道工程具有指导意义。

Centrifugal model tests on face stability of slurry shield tunnels under high water pressures

With the development of the national marine strategy and economy in China, more and more cross-sea and cross-river shield tunnels are to be built. The face stability of the shield tunnels is a key problem for the project safety. It will be more difficult to control the face stability under a high water pressure because of the unloading and seepage condition. A device for centrifugal model tests on face stability of shield tunnels is designed. The collapse patterns of the tunnel face and the surrounding soil pressures are investigated through the centrifugal model tests. Some important conclusions are drawn as follows: (1) The collapse of the tunnel face can be divided into four stages. At the first stage, the soil is still in an elastic state and the tunnel face presents a micro deformation. At the second stage, a local collapse happens to the tunnel face and the damaged area is located at the top of the tunnel face. At the third stage, the soil arch is formed, and the limit support pressure is reached. At the last stage, general collapse occurs and the collapse extends to the ground surface. (2) With the decrease of the slurry pressure, the soil pressure first decreases then increases, and a relative stable value is kept at last. The suggested support pressure ratio is 0.98 in this study. (3) The pore water pressure around the tunnel face decreases evidently. The seepage force acting on the soil contributes to the damage of the tunnel face. The conclusions obtained in this study may be useful for the similar projects.