Stability of deep excavation in soft clay deposits-Deformation and interaction with adjacent structure-

本研究利用新近开发的TIT和NUS试验系统，对正常固结软粘土中的竖向开挖进行了离心模型试验，TIT和NUS试验系统分别能较好地模拟双支撑墙明挖和矩形开挖的施工顺序。得出了以下结论。(1)NC粘土在开挖过程中由于剪切作用产生正孔压，可合理采用不排水条件假设。(2)正常固结粘土在较低支撑之前在非常浅的开挖深度达到朗肯活跃条件。试验结果证实了强度各向异性对明挖边坡稳定性评价的重要性。基坑底部的粘土在开挖深度的一半左右达到了被动状态。该深度之后的变形主要由砂的力学性质决定，即，刚度或应力应变。(3)Pro ...更多信息 支撑可以防止沉降的显著增加;然而，一旦发生沉降和变形，通过增加支撑力（即，预加载）。土体的滞回和非线性特性被认为是引起土体不可恢复变形的主要原因之一。(4)不同支护条件下沉降槽的差异主要表现在近墙处，而远离墙处沉降槽的差异不大。(5)壁面挠度由两个激光位移传感器在不同高度和沿壁面沿着应变的数据导出。虽然由于挠度计算中不可避免的误差而包括了一些散射，但在动员强度和挠度之间清楚地获得了非线性关系。(6)在无支撑三维开挖中，角点约束在控制墙和地面移动方面起着重要作用。增加墙的厚度可以减少墙和地面的移动。少

In this study centrifuge model tests on vertical excavation in normally consolidated soft clay was carried out using a newly developed test systems in TIT and NUS.By TIT and NUS systems construction sequence in double propped wall open excavation and rectangular shape excavation can be properly simulated in flight respectively. The following conclusions were drawn.(1) The assumption of undrained condition can be reasonably adopted for NC clay during excavation because of positive pore pressure generation due to shearing.(2) Normally consolidated clay reached Rankine's active conditions at very shallow excavation depth before lower propping. The importance of strength anisotropy for the stability evaluation in open excavation was confirmed in the tests. The clay in the bottom of excavation reached its passive condition around the half of excavation depth. The deformation after this depth was mainly determined by the mechanical properties of sand, i.e., stiffness or stress-strain.(3) Pro … More pping can prevent marked increase in the settlement ; however, it is very difficult to recover the settlement and deformation once it occurs by increasing the strutting force (i.e., preloading). Hysteretic and non-linear behavior of soil is considered to be one of the main reasons of the irrecoverable deformation.(4) Difference in the settlement trough with different propping conditions mainly revealed near the wall, while for far away from the wall no much difference in the trough could be seen.(5) The wall deflection was derived from the data of two laser displacement transducers at different heights and strains along the wall. Although some scattering was included due to the inevitable error in the deflection calculation, a non-linear relation was clearly obtained between mobilized strength and deflection.(6) The corner constraint plays an important role in controlling wall and ground movement in an unstrutted 3D excavation. Increasing the thickness of the wall reduces the wall and ground movement. Less