The tunnel construction in a densely populated city requires tunneling below or near to sub-surface structure or foundation of existing structures. The design of these tunnels requires the study of interaction of tunnel excavations driven underground with the ground surface. The day-to day practice is based on experienced based thumb rule and linear analysis. This provides very limited information for understanding the interaction. This article presents the analysis of effects of two tunnels driven in soft rock on the surface settlement using 2D finite element analysis. The numerical results are compared with the field observation and empirical relations.

In the course of study, parameters varied during analysis were spacing between the tunnels, orientation alignments of tunnels, size of tunnel, ground properties and in-situ stresses. The observation of surface settlement has been made with respect to these parameters. The effect on zone of plastic strain has also been studied to understand behavior of failure in soil. The finite element analysis results are compared with the results obtained from four different software.

1. Introduction

The increase in population and growth of city has pushed the need to shift various facilities underground to create space on ground surface available other basic utilities which can be shifted underground. Need is the source of innovation and innovation brings in new challenges to be dealt with. One of the challenges that modern tunneling industry has brought to us is ground movement upon earth excavation. Which in turn effects the existing structures nearby the tunnel alignment. The challenge is more critical in densely populated regions of city beneath which the tunnel passes. A huge care is required to be taken during excavation process and regular monitoring of tunnel convergence is part of it even then the tunneling induces ground settlement despite all the protective measures adopted for the controlling the volume loss during tunneling. In this paper a study is presented showing method of pre-estimation of ground behavior due to excavation of twin tunnels.

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