Experimental investigation into the interface properties of composite concrete lined structures

Composite shell linings, consisting of a layer of permanent sprayed concrete to form a primary lining, a layer of spray applied waterproofing membrane and a further layer of sprayed or cast secondary concrete lining, represent the latest development in the tunnelling industry. While demand for the composite shell method is increasing, there are still some unknowns associated with it. One of the biggest areas of uncertainty for the composite shell method is the extent of composite action in the interfaces between the sprayed waterproofing membrane and the primary and the secondary linings. A research programme is in progress at the University of Southampton, UK, to investigate the behaviour of composite shell SCL tunnels. As part of the testing programme, a series of short-term direct tension and direct shear tests have been carried out on samples cut from panels built up from a sprayed primary layer, spray applied waterproofing membrane and sprayed secondary layer. The aim of the tests has been to understand the fundamental properties of sprayed concrete-membrane bonding systems, especially the impact of the interface roughness on strength and stiffness. This paper will report some of the test results obtained and their significance.