Abstract
Combining multiple tunnels into a single tunnel complex while keeping the surrounding area compact is a complicated procedure. The condition becomes more complex when soft soil is present and the area is prone to seismic activity. Seismic vibrations produce sudden ground shaking, which causes a sharp decrease in the shear strength and bearing capacity of the soil. This results in larger ground displacements and deformation of structures located at the surface and within the soil mass. The deformations are more pronounced at shallower depths and near the ground surface. Tunnels located in that area are also affected and can undergo excessive distortions and uplift. The condition becomes worse if the tunnel area is larger, and, thus, the respective tunnel complex needs to be properly evaluated. In this research, a novel triple tunnel complex formed by combining three closely spaced tunnels is numerically analyzed using Plaxis 2D software under variable dynamic loadings. The effect of variations in lining thickness, the inner supporting structure, embedment depth on the produced ground displacements, tunnel deformations, resisting bending moments, and the developed thrusts are studied in detail. The triple tunnel complex is also compared with the rectangular and equivalent horizontal twin tunnel complexes in terms of generated thrusts and resisted seismic-induced bending moments. From the results, it is concluded that increased thickness of the lining, inner structure, and greater embedment depth results in decreased ground displacements, tunnel deformations, and increased resistance to seismic-induced bending moments. The comparison of shapes revealed that the triple tunnel complex has better resistance against moments with the least amount of thrust and surface heave produced.
Highlights
Tunnels are one of the important means of underground transportation
The literature lacks analytical solutions for it. This shape has resulted from the combination of three closely spaced tunnels into a triplet complex that would carry multiple train tracks for the underground traffic movement and has been discussed with respect to construction arrangements by Naseem and Schotte et al [29]. This unconventional triplet complex in soft soil has been numerically studied in detail using the dynamic module of finite element modeling (FEM) software Plaxis 2D under variable seismic vibrations and embedment depths in order to determine the tunnel distortions, which results in ground settlements, seismically-induced bending moments and axial forces, and make the comparison with the conventional rectangular complex and the equivalent horizontal twin tunnel complex
In order to use in the research, all of them are scaled to 0.4 g unless otherwise stated and named as input motion (IM) 1 and the EC8 The site spectral class A accelerations and their average curve well with
Summary
Tunnels are one of the important means of underground transportation. They are useful in the build-up area where further surface construction in order to accommodate large traffic infrastructure is not possible. Patil and Choudhury et al [16] performed FEM on circular tunnels and studied the lining distortions, bending moments under variable ground vibrations, and different embedment depth and tunnel lining thickness to develop better understanding of tunnel behavior in soft soils. This shape has resulted from the combination of three closely spaced tunnels into a triplet complex that would carry multiple train tracks for the underground traffic movement and has been discussed with respect to construction arrangements by Naseem and Schotte et al [29] This unconventional triplet complex in soft soil has been numerically studied in detail using the dynamic module of FEM software Plaxis 2D under variable seismic vibrations and embedment depths in order to determine the tunnel distortions, which results in ground settlements, seismically-induced bending moments and axial forces, and make the comparison with the conventional rectangular complex and the equivalent horizontal twin tunnel complex. This study would help determine the optimized tunnel parameters and to understand the dynamic behavior of this unique tunnel shape in a better way
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