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

Abstract:

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.

Key words:excavation; confined water; hydraulic heave mechanism; stress strain state; centrifugal model test; numerical simulation