Numerical analysis for prediction of optimum deformation of long tunnel crown stability with respect to excavation depth

Lawal Ezekiel Abiodun

Abstract

Optimum stability of tunnel structures and ground movements are influenced by excavation, and these are issues of greater concern as far as the stability of any underground structure is concerned. The critical area of concern is the stability of the tunnel crown which requires special attention to ensure the stability of the tunnel structures and the safety of both man powers and the equipment used. Before the advent of powerful design aids tools such as numerical analysis software, the tunnel’s design was primarily based on experience. The use of numerical analysis software has made it possible to model and predict the actual site conditions to achieve safer and more economical designs. This study aims to understand and predict the stability of the tunnel crown with respect to excavation depth by using Plaxis 2D v8 finite element analysis software and East Coast Railway, Malaysia tunnel project as a case study. The site condition was modeled and excavated at various tunnel depths of 0.5D,1.0D,1.5D,2.0D,2.5D to 3.0D which are around 7 m to 42 m depths, where D is the tunnel diameter. Based on the output results, both vertical and horizontal displacements show appreciable increases as the tunnel depths get deeper due to overburden. The result confirmed that there is a clear relationship between the tunnel excavation depth and the stability of the tunnel crown.

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