Day by day the call to solve traffic congestion problems is increasing. Subway tunnels and high-speed railway are commonly used for transportation. Therefore, tunnel construction induces soil movement, which in turn affects the stability and integrity of adjacent existing buildings. A series of numerical simulations have been established to investigate the effects of tunnel construction of the Greater Cairo Metro–Line 3-Phase-1 on adjacent pile cap foundations of Garage El-Attaba building. Many parameters have been investigated such as tunnel diameter and the distance between pile and tunnel at different tunnel axis and deep and shallow tunnel. After thorough analysis of the results’ simulation, it was found that the tunneling induces additional axial forces and bending moment as well as increasing axial settlement and lateral deflection. Moreover, the results obtained from the parametric study for the shallow and deep tunnel show that the tunnel depth has a much significant effect on piles responses. Finally, the tunnel diameter has an impact on pile responses as well as the pile cap foundation influenced by the tunnel when the tunnel is in very close vicinity of the pile, and its effect is modest to negligible if located far away from the buildings.

Deep foundations are frequently built close to existing tunnels in the urban environment. Tunnels can only withstand very small movements. The construction of bored piles and/or the subsequent loading of the piles may result in unbearable movements or stresses that could result in cracking of the tunnel linings, which worries obstacles to the tunnel structure. This research presents an understanding of the interaction issue and investigates and evaluates various geometric factors that determine the effect of the construction of the pile on the existing tunnel. However, numerical modeling was established utilizing a modified Mohr-Coulomb constitutive model for the soil strata. Numerous factors have been examined, including different locations of the pile tip to the tunnel centerline as well as variable pile diameters and lengths. The numerical analysis results revealed that the bending moment decreases as the distance from the tunnel increases from 8 to 12 m and then remains constant, while the shear stress is not affected considerably. In addition, the shear stress and bending moment increase with pile diameter and length due to the increased confinement caused by the pile. The spacing has a considerable effect on the horizontal displacement with very little effect on the vertical displacement. Moreover, there is an increase in the shear force developed in the tunnel lining with pile diameter for different spacings between the tunnel and pile. This increase becomes smaller as the pile length increases. At small spacing between the pile and tunnel (8.3 m and 12.5 m), the bending moment in the tunnel lining decreases as the pile length increases. Doi: 10.28991/CEJ-SP2023-09-016 Full Text: PDF

An inclined straight combination support pile can play a better role in deep foundation pit support, especially for the protection of adjacent structural pile foundations. We take a section of the construction of a deep foundation pit project in Wuhan City, Hubei Province as the research object. This paper studies the influence of inclined and straight combination support piles on the bending moment and displacement behavior of adjacent pile foundations during the construction of foundation pits under the influence of different factors such as distance from the excavation surface, pit angle effect, inclined pile tilt angle, pit depth to width ratio, and construction conditions on the adjacent pile foundation using a three-dimensional finite element model. According to the research results, as the distance from the excavation surface increases, the bending moment of the adjacent pile foundation decreases, and the closer the pile is to the foundation pit, the greater the horizontal displacement of the pile; the bending moment and displacement of the pile foundation are supported by the pit angle effect. Moreover, the pile bending moment increases with the increase of the pit depth–width ratio, and the maximum displacement point of the pile body gradually moves down from the middle of the pile body to the bottom of the pile foundation as the excavation depth of the pit increases. In addition, the minimum displacement of the adjacent pile foundation is at the top of the pile, and the maximum displacement is at the middle of the pile. Finally, compared with the static analysis, the whole process of dynamic simulation can reflect the dangerous working conditions in the project construction process, and make a more complete safety control construction plan for the project construction process.

Tunnel construction will inevitably change the surrounding soil’s original stress and displacement fields, affecting the surrounding piles. In addition, the lateral displacement of the soil at the subway tunnel’s face is symmetrically distributed along the tunnel’s central axis, which is greater in the center and smaller on both sides. Therefore, the protection of existing piles and providing a reasonable reinforcement plan have become the focus of attention. Taking a section of Tianjin Metro Line 3 as the research object, this paper studies the influence of the shield tunnel excavation process on the existing pile foundation through three-dimensional finite element simulation. The model has been verified through field monitoring data. Then, parameter analysis has been carried out for two reinforcement measures: grout reinforcement and isolation pile construction. According to the research results, the impact of shield construction on the pile foundation is mainly within the range of twice tunnel diameter to the pile foundation from the front and back of the tunnel face. In addition, the grouting reinforcement has better control of the vertical displacement of the existing pile foundation. The construction of isolation piles can better control the lateral displacement of the existing pile foundation. Have certain reference significance for similar projects.

In the construction of mountain tunnels, biased and water-rich strata are often encountered. During tunnel excavation, the fluid–solid coupling has a great influence on the stability of the surrounding rock. This effect will be more severe when the terrain is biased. The bias tunnel points out the asymmetric load of the rocks which are surrounding the tunnels through the drilling or construction process due to the topographic situation. These loads can cause inverse actions during tunnel construction. Therefore, the effect of fluid–solid coupling on the displacement field, stress field, and seepage field of the tunnel surrounding rock under different biased terrains are studied in this paper. In the context of the Youzishu tunnel project, the numerical model is established to define the degree of terrain bias. Besides, the concept of bias coefficient is introduced. To achieve what is needed, 10 sets of increasing bias coefficients are obtained, by changing the inclination of the terrain to study the influence of formation bias degree on tunnel excavation in water-rich formations. After an in-depth analysis of the simulation results, it is found that the influence of fluid–structure interaction cannot be ignored. By analyzing ten groups of data under different working conditions, the biased terrain will aggravate this effect. As far as the displacement field of the surrounding rock is concerned, the biased formation has a greater impact on the deeply buried side than on the shallow-buried side, and has a greater impact on the vault than on the arch bottom. In addition, by analyzing the stress field and seepage field of the surrounding rock, a similar result can be obtained: the influence of formation bias on the deeply buried side is greater than that on the shallow-buried side, and the biased terrain will increase the pore pressure outside the tunnel lining and increase the water inflow. Finally, the locations where the displacement, stress, water pressure, and water inflow are the largest during the tunnel excavation process are found by the simulations and analyzed. Thus, attention can be paid to these locations, permitting a focus on protection during the construction process.