Numerical Study on the Effect of Large Deep Foundation Excavation on Underlying Complex Intersecting Tunnels

Abstract

The effect of large deep foundation excavations on the surrounding existing tunnels is a problem that cannot be avoided in the current construction background. This effect is difficult to assess precisely, especially when the geometry of the tunnels and pits is complex. In this paper, a three-dimensional (3D) finite element model has been developed based on a case containing four complex intersecting tunnels and a large deep foundation pit. The model used the hardening soil model with small-strain stiffness (HSS) and the Hoek–Brown (HB) model to describe the mechanical properties of the soil and rock, and various methods including the standard penetration test (SPT) and heavy dynamic penetration test (HDPT) were used to determine the model parameters. The results of the analysis are as follows: the excavation of the foundation pit caused the tunnels to heave and the heave deformation conforms to the normal distribution; the maximum heave of numerical simulation is 3.1 mm which is consistent with the field data; the horizontal displacement, horizontal convergence, and vertical convergence of the tunnels caused by the excavation of the pits are small, and all kinds of deformations meet the control requirements; the intersection of multiple tunnels shows obvious stress concentration when the tunnels were constructed, and the lining stress slightly decreases as excavation progresses.

Numerical Simulation Study on the Impact of Deep Foundation Pit Excavation on Adjacent Rail Transit Structures—A Case Study

“…Meanwhile, Ayasrah et al [27] found that tunneling induces additional axial forces and bending moments as well as increasing axial settlement and lateral deflection after establishing a series of numerical simulations and investigating many parameters, such as tunnel diameter and the distance between the pile and tunnel at different tunnel axes, in deep and shallow tunnels. These studies, including new measurement technologies [28], indicated the regular pattern; namely, that for tunnels at the excavation's base, stress is minimal, with limited displacement observed at monitoring points [4,29,30]. These studies collectively contribute to establishing a theoretical foundation for understanding the impact of excavation on nearby rail transit structures; however, as for the graded excavation of large pits, research has been quite limited in the analysis of the overall performance of the pit.…”

Study on the Impact of Deep Foundation Excavation of Reclaimed Land on the Deformation of Adjacent Subway Tunnels

“…Wu et al [19] studied the influence of deep foundation excavation of soft soil layers on the lower subway tunnel, conducted deformation monitoring of the lower subway tunnel during the deep foundation excavation of a bridge abutment foundation pit, and analyzed the influence of different construction conditions on the displacement and deformation of the subway tunnel through the analysis of accumulated settlement and horizontal displacement data. Zhao et al [20] established a three-dimensional finite element model based on a typical case of foundation pit and tunnel, using various methods to determine the geomechanical properties such as standard penetration tests and heavy dynamic penetration. Zheng et al [21] used a large-scale foundation pit project adjacent to a nearby subway structure as an example to analyze the deformation characteristics of subway structures during foundation pit construction and conducted experiments and practical applications to actively control the horizontal deformation of soil and tunnel by grouting.…”

Numerical Investigation of Existing Tunnel Deformation Induced by Basement Excavation Considering the Unloading Ratio

“…The current research methods for underground structure construction include field monitoring [9][10][11][12][13][14], centrifuge tests [15,16], and numerical simulation [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]. Complex factors such as engineering geological conditions, tunnel structure form, and foundation construction technology can be fully considered in the numerical simulation method, and many scholars have applied this method in their research.…”

“…Shi et al [31][32][33][34] studied the influencing factors of this problem and proposed a calculation method to predict the tunnel deformation through numerical simulation on this basis. Zhao et al [35] compared four tunnels with different positions under the basement and found that the tunnel outside the excavation scope in an area that was twice as large was virtually unaffected. Although the influence of basement excavation above an existing tunnel has been studied by means of numerical simulations, the effects of the rules of basement geometry and tunnel location relative to the basement on the vertical deformation of the tunnel are not yet fully understood.…”