An investigation of the effect of erosion voids on existing tunnels.

摘要

Much of our subsurface infrastructure suffer from aging and is becoming more susceptible to damage due to the deterioration of either the buried structure or the surrounding ground. A known mode of deterioration in tunnels is the formation of erosion voids on the outer surface of the tunnel linings. These are usually caused by the ingress of groundwater through cracks in the tunnel lining that slowly erode the soil surrounding the crack by transporting soil particles. This process may lead to pressure redistribution on the lining and progressive deterioration that could lead to eventual failure. A greater understanding of the impact of these erosion voids can aid in the maintenance of aging infrastructure.A review of the literature regarding this topic showed that little research has been done beyond numerical analysis and site investigations of failed tunnels. This study presents the results of the experimental investigation that has been conducted to examine the effect of erosion voids on the earth pressure distribution acting on the tunnel liner. The experimental setup allowed for the simulation of the two-dimensional tunnelling process and the tunnelling-induced pressure that results from shield tunnelling. A model tunnel was constructed out of segmented steel pipe to simulate a machine bored tunnel. A controlled contraction of the tunnel diameter was used to simulate a tail void closure and soil movement needed to establish initial conditions. Pressure sensors were placed at various locations along the lining and fine sand was used as the soil medium. A void of known size was then introduced at different locations around the tunnel and the contact pressure on the lining was measured before and after the void introduction. Results indicated significant changes in the magnitude of earth pressure in the close vicinity of the void. The changes in earth pressure differed greatly depending on the placement of the erosion void. Voids placed at a 45° angle between the springline and the invert showed the greatest increase at +29%, whereas voids placed near the springline measured the most change at -60%. This showed considerable change in pressure with the introduction of a relatively small void.