Seepage flow around tunnels in swelling rock

Abstract

The swelling phenomenon in tunneling is numerically modelled as a coupled hydraulic-mechanical process. The present communication focuses on the significance of the constitutive seepage flow equations, as well as on the importance of the hydraulic boundary conditions. The observed absence of swelling deformations at the tunnel walls and the crown can be explained as a consequence of varying hydraulic boundary conditions along the excavation boundary. According to the presented numerical results, the non-linearity of the unsaturated flow equations has a decisive qualitative influence on the predicted deformation field.

Study of the soil–atmosphere moisture exchanges through convective drying tests in non‐isothermal conditions

“…with a v and v the vapour density, respectively, in the surroundings and at the boundary of the sample and a vapour mass transfer coefficient, which can be expressed as a function of the degree of saturation at the surface of the sample S r,w , the drying temperature or the air velocity [15,22,[24][25][26]. It can be assumed that the mass transfer coefficient is maximal when the boundary layer is saturated and decreases with its desaturation.…”

On boundary condition in tunnels under partial saturation

“…Each of them is using a mass transfer coefficient which can be expressed as a function of the degree of saturation, the porosity or the air windspeed in the gallery [Dracos, 1980;Anagnostou, 1995;Zhongxhuan et al, 2004]. To obtain the evaporation flow, this mass transfer coefficient can be multiplied by the difference of relative humidity [Anagnostou, 1995], vapour pressure [Zhongxhuan et al, 2004] or vapour potential [Kowalski, 1997] between air gallery and the geological formation. As proposed by Ben Nasrallah & Pere [1998], we choose to express vapour exchanges as the difference of volumetric vapour mass between the tunnel atmosphere and rock mass:…”

“…Vapour exchanges occur when the relative humidities of air gallery and rock mass are different. Several formulations of the vapour flows can be found in the literature, which usually assume that the flow is proportional to the difference of relative humidity [Anagnostou, 1995], vapour pressure [Zhongxhuan et al, 2004], the vapour potential [Kowalski, 1997] or the volumetric vapour mass [Ben Nasrallah & Pere, 1998]. …”

Tunnel stability and deformations in water-bearing ground

“…This contradicts the facts and leads to unsafe predictions concerning the resulting stresses in the lining (overestimated axial forces, underestimated bending moments). Realistic predictions of the observed deformation pattern are possible only when taking into account the seepage flow and the hydraulic-mechanical coupling (Anagnostou 1995a). In a coupled analysis, the displacement field depends on the porewater pressures prevailing around the tunnel and, consequently, on the hydraulic boundary conditions.…”