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

为了评估深埋盾构隧道的土压力，在1G条件下，采用铝条和干砂人工地基进行了一系列活板门试验。测量了活板门在主动和被动状态下的土压力。对双活板门进行了封闭开挖条件下的试验，并利用专用试验设备测量了地下室的土压力分布。采用区域塑性有限元法对土压力进行了解释，并与试验数据进行了比较。同时，提出了考虑应变软化的弹塑性本构模型来模拟Fenner-Pacher曲线预测的隧道行为。最后，在离心条件下进行了一系列轴对称活板门实验。通过降低部分土容器底部以减小局部围应力来模拟隧道掘进过程。激光光学位移传感器在飞行过程中可沿径向移动，可测量地表沉降水平剖面。在土容器中分别形成干砂、饱和砂和饱和粘土。竖向土压力随活板门位移减小，后呈逐渐增大的趋势。

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.