Static and Dynamic Interaction Between Soil and Underground Tunnel: Fid-Bau Portal

Static and Dynamic Interaction Between Soil and Underground Tunnel

Shakya, Rahul / Singh, Manendra

The interaction between soil and tunnel lining is an important factor affecting the performance of underground tunnels. In numerical analysis, interface elements are used between different materials to analyze soil-structure interactions and to capture normal and shear stress transfer across discontinuities between two dissimilar material components. PLAXIS software uses “zero-thickness” interface elements between the soil and structural components to simulate soil-structure interactions. These elements introduce a factor that reduces the strength and stiffness of the soil at the contact point. In this paper, plane-strain analysis of a typical section of Delhi-Metro underground tunnels has been performed. Interaction between tunnel and surrounding soil has been considered using interface element. The static and dynamic responses of the soil-tunnel system were evaluated in terms of induced displacement in the soil -tunnel system, induced forces, and bending moment in the tunnel liner. For dynamic analysis, the earthquake’s transverse component (horizontal component) was applied at the base of the model. Viscous absorbent boundary conditions were used to represent the displacement conditions along the vertical boundaries. The interface condition between the soil and tunnel plays a significant role in seismic analysis. The strength parameter of the interface and soil is related to the reduction factor (Ri). The value of Ri varies from 0 to 1. Ri is 0 for the full-slip condition and 1 for the no-slip condition. If Ri is between 0 and 1, relative slip is allowed between the tunnel and the surrounding soil. After analysis, it can be concluded that axial force in the tunnel liner increased with increase in value of Ri, whereas an increase in the value of Ri leads to a reduction in shear force and bending moment. Similarly, displacements, both in soil and RC liners, have decreased with an increase in the value of Ri, and maximum values of displacement have occurred for full slip condition (Ri = 0).