This paper focuses on the optimization of uplift piles for a base plate considering local anti-floating stability. According to the force characteristics of the base plate subjected to buoyancy, a bi-directional evolutionary structural optimization (BESO) process is proposed. The optimization process takes the pile length as the design variable and the pile end displacement as the sensitive coefficient. The proposed process is conducted with FLAC3D to optimize the length of each uplift pile, including two cases with different pile diameters and spacing. The optimization process shows that the deformation degree of the base plate is significantly reduced when the piles are adopted with large diameters and sparse spacing, and oscillates at a low level when the piles are adopted with small diameters and dense spacing. Consequently, the design method of uplift piles considering the local anti-floating stability is proposed by referring to the optimization results of two cases. Finally, the proposed design method is applied to a practical project, and the original design of the uplift piles is optimized. The comparison results show that the deformation degree of the base plate of optimization designs is significantly lower than the original design.

In this study, we explore the stability of shield tunnel faces excavated entirely within confined aquifers through a combined physical investigation. A series of orthogonally designed model tests were performed to examine how the hydraulic head difference (Δh) and aquitard thickness (M) jointly influence face stability and seepage behavior. Our results reveal a distinct concave-downward pore-pressure profile and a steep hydraulic gradient immediately ahead of the excavation face. Excavation-induced stress redistribution was largely restricted to the aquifer, whereas the overlying aquitard exhibited negligible disturbance due to its low permeability and higher strength. The evolution of stress disturbance followed a three-stage process encompassing initial disturbance, progressive development, and large-scale destabilization. Deformation contours exhibited a conical failure zone with normalized width and height ranging from 0.7D to 1.0D and 1.7D to 1.86D. Surface settlements remained within ±1 mm, confirming that deformation was effectively confined below the aquitard. Numerical simulations reproduced the overall hydro-mechanical response, validating the experimental observations but slightly overpredicting support pressures due to the absence of arching effects. The findings highlight Δh/M as the dominant control parameter, with aquitard thickness exerting a moderating influence.

This paper is aimed at the problem of inaccurate calculation of the water inflow of a foundation pit with a suspended water-proof curtain in a confined water stratum. According to the groundwater hydraulics principle, the theoretical model of the seepage field of the foundation pit is established, and the analytical formula of the water inflow for the circular, strip, and rectangular foundation pits is deduced. The seepage path influence coefficient α related to the water-proof curtain insertion ratio, the thickness of the confined aquifer, and the radius of the foundation pit is proposed and obtained by the positive and negative analysis of numerical simulation. The coefficient is used to correct the equivalent seepage length in the pit and directly affect the calculation result of water inflow. Finally, based on the calculation results of the analytical solution of water inflow, the relationship between the scale of the foundation pit and the water control effect is discussed. The research results show that the theoretical analysis results in this paper are in good agreement with the numerical results and the measured data in the field: when the size of the foundation pit is too large, it is not suitable to use the suspended water-proof curtain as the water control measure.