Abstract

Damage of tunnels often occurs in Japan caused by swelling smectite rockmass. For an effective countermeasure against the damage, mechanical interaction between tunnel lining and swelling rock mass are analyzed by a two-scale analysis based on a homogenization theory in this study. In the microscopic scale, swelling of smectite minerals and damage process of surrounding intact rocks induced by the swelling of smectite minerals are analyzed by a 3D continuous damage model. This microscopic analysis provides the averaged volumetric change and the damaged macroscopic stiffness of the representative volumetric element (RVE) of rock mass. In the macroscopic scale, therefore, stress distribution within/around the tunnel lining can be reasonably analyzed by using the averaged secant stiffness and its volumetric strain of the RVE. The mechanical interaction between the tunnel lining and swelling rock mass is discussed and examined as some case studies are carried out.

1. Introduction

In recent years, a problem that ground expansion by swelling clay minerals destroys the roadbed of a mountainous tunnel has occurred in various regions. The expansion of these clay minerals comes with the process of water-absorption. These clay minerals are called 'smectite' or 'smectite group'. Whereas swelling clay minerals has come to be known for their weird mechanical behavior, a method to evaluate and/or predict the amount of their hygroscopic expansion has yet to be established, especially from a practical viewpoint. One of the reasons is that swelling clay minerals generally consist of minerals with size of about 100 nm, namely, it is too small to deal with. In addition, it is reported that the hygroscopic expansion, which is based on a thermo-chemical phenomena, degrades the macroscopic material stiffness of the ground caused by its own microscopic damage. The complicated mechanical behavior of the ground involving swelling clay minerals comes from a kind of phenomena based on multi-physics, due to the hygroscopic expansion.

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