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工况下，采用铝筋和干砂人工地基进行了一系列活板门试验。对活板门主动和被动状态下的土压力进行了测量。同时进行了双活板门在封闭开挖条件下的试验，并利用专用的试验装置测量了地下室的土压力分布，并将试验数据与区域塑性有限元法进行了对比分析。提出了考虑应变软化效应的弹塑性本构模型，模拟了Fenner-Pacher曲线预测的隧道行为。最后，进行了离心条件下的轴对称活板门试验。采用土箱底部下沉的方式来减小局部区域的围压，模拟了隧道开挖过程。利用激光-光学位移传感器在飞行过程中沿径向移动，可以测量地面沉降的水平分布。在土容器中分别形成干砂、饱和砂和饱和粘土。竖向土压力随活门位移的增大而减小，然后逐渐增大。

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.