Evaluation of earth pressure due to deep shield tunnel and its design method

为了评价深埋盾构隧道的土压力，在1G条件下进行了铝棒和干砂人工地基的一系列活门试验。在主动和被动两种状态下，测量了活门上的土压力。还进行了双活门近距离开挖试验，利用专用试验装置测量了地下室土压力的分布情况，并用区域塑性有限元方法对土压力进行了解释，并与试验数据进行了对比。提出了一种考虑应变软化的弹塑性本构模型来模拟Fenner-Pacher曲线所预测的隧道行为。最后，在离心机条件下进行了一系列轴对称活门实验。通过降低土容器底部的高度来降低局部围压，模拟隧道开挖过程。利用激光光学位移传感器测量地面水平沉降量，该传感器在飞行过程中可以径向移动。土壤容器内分别形成干砂、饱和砂和饱和粘土。竖向土压力随着活门位移的增加先减小后逐渐增大。

In order to evaluate the earth pressure acting on a deep shield tunnel, a series of the trap-door experiments were done by using the artificial ground of aluminum bar and dry sand in 1G condition. The earth pressure on the trap-door was measured for the active and passive state. The tests of twin trap-doors under close-excavated condition were also carried out and the distribution of earth pressure at basement were also measured by special experimental equipment.The regid-plastic FEM was applied to explain the earth pressure comparing with the experimental data. Also, an elasto-plastic constitutive model with strain softening was propposed to simulate the tunnel behavior predicted by the Fenner-Pacher curves.Finally, a series of axisymmetric trap door experiments was conducted under centrifugal conditions. The tunneling process was simulated by lowering patrt of the bottom of the soil container to reduce confining stress in the local area. The horizontal profile of settlement at the ground surface could be measured by means of laser-optical displacement sensor which could moved in a radial direction during flight. Dry sand, saturated sand and satulated clay were formed in soil container respectively. The vertical earth pressure decreases with trap door displacement and then tends to increase gradually.