Modeling layered composite rock with excavated tunnels subjected to ground loads

Abstract

Tunnels excavation in layered composite rock subjected to ground loads to make the best of underground space is an important engineering problem in more and more mega-cities. Such a three-dimensional case, layered composite rock with excavated tunnels, is usually simplified as a two-dimensional plane strain problem in mechanics. The present study reports a Semi-Analytical Method (SAM) to predict elastic field of an excavated layered composite rock with the assistance of the Equivalent Inclusion Method (EIM) that can handle elastic field of the layers and tunnels simultaneously. In the EIM, the layer and tunnel are considered as inhomogeneities of different elastic moduli from the base rock, and the inhomogeneities are further equivalent to inclusions of identical elastic modulus to the base rock but including eigenstrains. Effectiveness of the SAM is examined by the Finite Element Method (FEM) through comparing their results. Moreover, a yield approximate index (YAI) is introduced to evaluate safety of excavated layered composite rock and acoustic emission (AE) event is used to count the number of plastic yield elements. Finally influences of depth of and distance between the tunnels, thickness, elastic modulus, number of the layer, range of ground load on principal stress, YAI, plastic zones are discussed, which may have potentials to provide guidance for practical engineering applications of tunnel excavation.