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

本文利用自行研制的TIT和NUS试验系统进行了正常固结软土竖向开挖的离心机模型试验，TIT和NUS系统能较好地模拟双支承墙开挖和矩形开挖在飞行中的施工顺序。得出以下结论：(1)NC粘土在开挖过程中由于剪切作用产生正孔压，可以合理地采用不排水条件的假设。(2)正常固结的粘土在开挖深度很浅时达到朗肯活跃状态，在较低的支承深度之前。试验证实了强度各向异性对评价露天矿稳定性的重要性。开挖底部粘土在开挖深度的一半左右达到被动状态。此深度之后的变形主要由砂土的力学性质决定，即硬度或应力-应变。(3)Pro…多点开挖可以防止沉降量的显著增加，但一旦发生沉降量和变形，很难通过增加支撑力(即预压)来恢复。土的滞回和非线性特性被认为是变形不可恢复的主要原因之一。(4)不同支承条件下的沉降槽的差异主要表现在墙体附近，而远离墙体的沉降槽的差异不大。(5)墙体挠度由两个沿墙体不同高度和应变的激光位移传感器得到。虽然由于挠度计算中不可避免的误差而计入了一些散射，但调动强度与挠度之间存在明显的非线性关系。(6)在无支撑三维开挖中，拐角约束对墙体和地表的移动起着重要的控制作用。增加墙的厚度会减少墙和地面的移动。较少

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