ABSTRACT
Unlined underground pressure tunnels and shafts have been the standard design in Norway since the 1960s, and in some cases, shotcrete is used as both temporary and permanent support. For low-porosity rocks in such an environment, the geomechanical response of the host rock with respect to water saturation under unconfined and confined loading remains ambiguous, and so does the long-term stability of these infrastructures. Researchers have investigated the effect of saturation on the unconfined strength and stiffness, but little literature exists on the confined conditions. To address this gap, this research examines the effect of saturation and confinement on the response of two low-porosity rocks: Cobourg limestone and Point du Bois granite. In this paper, stress-strain analyses are presented to investigate saturation effects in tension, compression, and confined shear. Geomechanical laboratory testing results are applied to simple numerical simulations to compare failure extent and long-term stability predictions, for unsaturated and saturated mechanical properties of these rocks, around a deep pressure tunnel.
