Abstract
The antifloating property of underground structures in areas with high underground water levels is a key design aspect. Evaluating the buoyancy forces acting on underground structures is complicated, particularly in the presence of confined water beneath the structures. Herein, the effects of the permeability coefficient of layered soil, hydraulic gradient, and embedment depth of the aquiclude on the buoyancy force acting on underground structures are investigated through three model tests:(1)calibration of the test system,(2)buoyancy force acting on a structure located in homogeneous soil considering vertical direction seepage, and(3)buoyancy force acting on a structure located in layered soil considering vertical seepage of confined water. The results show that the pore pressure along the structure and the buoyancy force acting on the underground structure considering seepage are greater than those obtained under hydrostatic conditions. The raising ratios of the pore pressure and buoyancy force are equal to the vertical hydraulic gradient when seepage occurs in homogeneous soil. In the presence of confined water, the raising ratio is significantly greater than the hydraulic gradient. In the cases studied herein, the raising ratio is approximately twice the hydraulic gradient. Simplified equations are proposed to calculate the buoyancy force acting on underground structures considering the vertical seepage of confined water. Finally, a finite element analysis is carried out to verify the conclusions obtained from the model test and the rationality of the proposed equations.
Highlights
The antifloating design of underground structures is an important aspect in underground engineering
The results show that the pore pressure along the structure and the buoyancy force acting on the underground structure considering seepage are greater than those obtained under hydrostatic conditions
We study the influence of vertical seepage of confined water on the buoyancy force acting on underground structures in different soil configurations and hydraulic gradients through model tests
Summary
The antifloating design of underground structures is an important aspect in underground engineering Large underground structures, such as underground garage of highrise buildings and underground pipe galleries, in high-level underground water level are exposed to high buoyancy forces, which may uplift underground structures [1–3], those located in confined water. The reasonable estimation of the buoyancy forces acting on underground structures in complex geological and hydrological conditions is important to the safety of such structures. The buoyancy force without considering the effect of seepage can be calculated in two steps: (1) reasonably determining the underground water level and (2) calculating the buoyancy force based on Archimedes’ principle. Many researches showed that the measured buoyancy forces acting on underground structures are lower than those obtained based on the Archimedes’ principle [4–7]. The pore water pressure in soil, which changes the magnitude of the buoyancy force acting
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