Water infiltration estimation in tunnels: with reference to the Melbourne underground

Understanding the potential for water flow into a tunnel through the surrounding rock mass and the tunnel lining is essential for tunnel design and assessment. Typically, water penetrates through a lining along discrete paths such as joints and cracks. However, the hydraulic conductivity can be non-uniform through the lining for a range of reasons. A method describing the flow through a lining with progressively changing hydraulic conductivity is presented. When the hydraulic conductivity of the outer surface of the lining is higher than that of the inner surface, the water inflow rate can be several times higher compared to a homogenous lining with hydraulic conductivity equal to the inner surface. The inhomogeneity of the lining could also affect the water pressure on the tunnel, which could be an important factor for the stability study. A water seepage factor chart for engineering applications, incorporating inhomogeneous hydraulic conductivity, is presented.