Productivity and working costs of modern trench-cutters for the construction of concrete diaphragms in an urban environment

Abstract

In the excavation of shallow underground works in an urban environment using the ‘cut and cover’ method, the choice is often made to use concrete diaphragms in order to support the side walls, before proceeding with the excavation of the ground. When these diaphragms exceed a depth of about 20 m, trench-cutters are generally used to excavate the panels, using a supply of bentonite mud. A remarkable development of trench-cutters has taken place over the last 30 years and these machines today allow panels to be excavated in any type of ground whatsoever, even when it is highly cemented. The experience that has been gained in Turin (Italy) in recent years can be considered interesting, because of the huge number of diaphragms that have been completed and the varying characteristics of the ground in the urban area, which ranges from loose sand and gravel to highly cemented ones. On the basis of detailed analysis of the in situ behaviour of trench-cutters in Turin and of laboratory investigations on the effects of wear on the tools, it has been possible to make a preliminary estimation of the construction costs and the productive times of the concrete diaphragms for the different types of geology.