A Numerical Investigation of the Deformation Mechanism of a Large Metro Station Foundation Pit under the Influence of Hydromechanical Processes

Abstract

Considering the unique conditions of deep and large subway foundation pit excavation affected by heavy rainfall in soil-rock composite strata, this paper employs finite element numerical simulation methods to study foundation pit instability under the influence of heavy rainfall. According to the hydraulic coupling conditions caused by rainfall, a fluid-solid coupling numerical model for a deep and large subway foundation pit in soil-rock composite strata is established in this paper. By selecting the Anshan road station of Qingdao subway line 4 as the engineering background, various parameters related to foundation pit excavation affected by heavy rainfall at different excavation depths were analyzed. The study found that after the foundation pit was excavated, the surrounding pore water pressure decreased and the pore water pressure near the ground surface increased rapidly due to rainfall. As the horizontal distance from the foundation pit increased, the pore water pressure at the same depth also increased. The excavation of the foundation pit caused uplift of the bottom of the pit. After rainfall, the uplift value decreased compared with that before rainfall. With increasing excavation depth, the decreased value of the bottom uplift decreased and then increased. The rainfall caused the horizontal displacement of the pit walls on both sides of the pit to increase. When the excavation depth was 10 m, the horizontal displacements on both sides of the pit were equivalent. When the excavation depth was 20 m, the horizontal displacement was concentrated in the first 10 m; when the excavation depths were 30 m and 40 m, the horizontal displacement was concentrated in the first 13 m. This finding shows that when the foundation pit was affected by rainfall, the sidewall collapsed at a distance of 13 meters from the ground. As the excavation depth increased, the depth of excavation instability was closer to the bottom of the pit. The research in this paper can provide a reference for the construction of deep and large foundation pits in similar composite ground conditions that are affected by rainfall.

Analysis of Influencing Parameters of the Improved Model for Rainfall Infiltration in Unsaturated Tailings Soil

“…where q is the magnitude of rainfall intensity; t p � (θ s − θ i )S f /q(q/k s − 1); k s is the saturated permeability coefficient of unsaturated slope soils; and S f is the substrate potential head of the unwetted layer relative to the saturated layer. e substrate potential head is taken as half of the water potential corresponding to the inlet pressure value of the soil [17,20,29].…”

“…Richa et al [16] found an analytical expression for the effective saturated hydraulic conductivity and analyzed the infiltration rate of unsaturated soils and the evolutionary characteristics of soil surface moisture under rainfall conditions. Wang et al [17] established a numerical model of flow-solid coupling on the slope of foundation pits with soil-rock composite strata to analyze the change law of hydraulic coupling caused by rainfall. Guo et al [18] analyzed the effect of inhomogeneous initial water content on the improved GA model in conjunction with the field monitoring results.…”

Study on the Characteristics of Self‐Stabilizing Height Distribution for Deep Foundation Pit Vertical Sidewall in Binary Strata of Upper Soil and Lower Rock

“…e following conclusions can be drawn from Table 5 and Figure 7: (1) FOS of foundation pit vertical soil sidewall decreases with the increase of soil wall excavation height. According to the criterion of F ST �1.35, Hs 0 is 6.92 m. (2) According to the relationship between Hs and Hs 0 , the stable state of the vertical soil wall can be quickly determined: when Hs ≤ Hs 0 , soil wall excavation meets the self-stability requirements. On the contrary, when Hs > Hs 0 , soil wall excavation cannot meet the requirements of self-stability.…”

“…With the accelerating process of urbanization in China, a type of deep foundation pit whose bottom is above the interface between soil stratum and rock stratum comes into being. e unique feature of this deep foundation pit type is that the strata within its excavation depth are composed of soil and rock from top to bottom, and the difference of the main mechanical parameters such as cohesion and elastic modulus between the two strata is almost thousands of times, such as Wusi Square Station foundation pit of Qingdao Metro Line 3 [1], Anshan Road Station foundation pit of Qingdao Metro Line 4 [2,3], and Chashan station foundation pit of Shenzhen Metro Line 7 [4]. In this paper, this type of deep foundation pit is uniformly called deep foundation pit in the binary strata of upper soil and lower rock.…”

Causation Identification and Control Measures of Deformation by Integrated Dewatering-Excavation Process Simulation of a T-Shaped Deep Foundation Pit

“…Previous studies have shown that the excavation of foundation pits always induced settlement of the surrounding buildings and influenced adjacent subway tunnels [1][2][3]. There are many factors, such as excavation unloading [4][5][6], groundwater drawdown [7][8][9], unloading modulus, excavation method [10,11], space-time effect [12,13], and other factors that are related to the surrounding deformation of the foundation pit. These factors pose great challenges to the safety of the surrounding environment and the foundation pit itself.…”