承压水基坑突涌机制离心模型试验与数值模拟

软土地区的深基坑工程,在承压水作用下容易发生管涌、流土和隔水层整体顶升等形式的突涌破坏.结合紧邻地铁枢纽深大基坑工程,设计了基坑突涌离心模型试验,模拟不同承压水位作用下黏性土体隔水层突涌状态,并建立有限元数值模型,分析试验水位压力下坑底土体的应力应变机制.离心模型试验和数值模拟结果表明,在承压水压力作用下,坑底隔水层产生向上的隆起变形,并且基坑中间位置变形量大,随着水位的升高,土体变形曲率增大;基坑围护墙附近的隔水层土体剪切应变大于体积应变,而隔水层与承压含水层的界面处体积应变较大,产生水压楔裂作用并形成有效应力为零的区域;黏性土体隔水层在剪切效应与界面楔裂效应的共同作用下,发生整体顶升破坏.

Centrifugal Model Tests and Numerical Simulation on Hydraulic Heave Mechanism in Excavation with Confined Water

In soft ground with lower confined aquifer, the bottom of an excavation may appear hydraulic heave like erosion, piping, bottom heave and hydraulic uplift at high hydraulic gradient. Combined with deep and large excavation engineering immediately adjacent to a subway hub, centrifugal model test was designed to simulate hydraulic heave in high cohesive aquiclude, at different hydraulic loads. In addition, numerical model was established to analyze soil stress strain mechanism at the hydraulic loads of centrifugal model test. Centrifugal model test and numerical simulations results show that under the effect of confined water, aquiclude uplift large in the central of foundation pit while small around the retaining wall, and aquiclude deformation curvature increase when confined water level become higher; the soil shear strain is greater than volume strain in aquiclude adjacent to retaining wall, but volume strain is greater at interface between aquiclude and confined aquifer, which produces discrete crack and wedge failure, and also make the effective stress in the region becomes zero; the low permeability cohesive aquiclude appears hydraulic uplift under the combination of shear failure mechanism and interface wedge failure mechanism.