Groundwater pressure induced failure of sprayed waterproof membrane interface in tunnels

Abstract

Groundwater pressure is the main cause of debonding (i.e. tensile failure) of the sprayed waterproofing membrane interface within composite sprayed concrete lined (SCL) tunnels. It is critical to understand the failure mechanisms, the right approach to numerical simulations of its effects and the practical implications on lining design and membrane interface testing methodology. This paper addresses these issues. The paper first presents a conceptual relationship between the possible groundwater pressure application locations and the stress state, and hence the potential failure mechanisms of the membrane interface in composite SCL tunnels. To quantify stresses in a fully bonded membrane interface, two numerical modelling approaches for the membrane interface with different levels of complexity are introduced. Example numerical analyses of composite beams and whole composite SCL tunnels with a fully bonded membrane interface are provided. The results confirm the conceptual relationship between water application location, the stress state and the potential failure mechanism of the membrane interface. The results also showed that the two numerical modelling approaches proposed are both able to simulate the effects of groundwater pressure on the stress states of the membrane interface and tunnel lining forces. The implications on tunnel design and testing programmes for a sprayed membrane interface are discussed.