ABSTRACT
Tunnelling in swellable soils is a challenging procedure with high risk of damage into the tunnel structure. To minimize the risk of damage to the tunnel support, a rigid or ductile principle of tunnel structure design are often applied to hinder or tolerate deformation in the ground upon swelling, respectively. Considering the coupled interactions between tunnel structure and the swelling rock, prediction of hydration process in swelling clay shales requires investigation of the water retention behaviour of shale under different tunnelling relevant boundary conditions. In this study, the main focus lies on the volumetric boundary conditions. For this purpose, the soil-water retention curves (SWCCs) of both intact and reconstituted Opalinus clay shale (OPA) were determined experimentally. This was carried out for each of the two materials under constant volume conditions in microcells, representing stiff tunnel lining, as well as without volumetric constraints, representing unsupported tunnels, where the intermediate states (deformation tolerant tunnel linings) can be fairly defined through interpolated. In contrast to bentonite that exhibits a noticeable influence of the volumetric boundary conditions, experiments on Opalinus indicated a rather smaller or eventually no influence in case of intact and reconstituted OPA, respectively. This phenomenon is believed to be attributed to mineralogy and fabric of samples.
