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.

Exploring the criteria influencing construction productivity of diaphragm walls in underground stations in Egypt

“…In contrast, this study did not account for the effect of breakdowns time, operator experience, maneuvering area, damping area availability, type of panel (successive-primary-closed), shift type, site condition, cage type (fiber/or steel), storage area, connection type (welding/or mechanical) and the arrival time of the concrete car mixer. Cardu and Oreste provided a detailed analysis of the in situ behavior of trench cutters and of laboratory investigations on the effects of wear on the tools [5]. This study concluded that the cutting tools wear rate is significantly influencing the excavation rate.…”

“…The underground construction in urban areas is usually conducted by the 'cut and cover' method, in which concrete construction is built around the underground structure before carrying out the site excavation. If the diaphragm walls' (DWs) depth exceeded 20 m, the trench cutters are usually employed in the panels' excavation [5][6][7][8][9][10]. The common use of trench cutters for the excavation of DWs led to the advancement of the 'cut and cover method.'…”

“…The common use of trench cutters for the excavation of DWs led to the advancement of the 'cut and cover method.' The 'cut and cover' method consists of several steps that must be strictly implemented and monitored in their sequence [5]. Figure 1 illustrates the excavation of trench cutter in one of the panels.…”

“…The DWs are almost impossible to be excavated in a single type of ground; however, it is generally feasible in the grounds of variable types and conditions [16]. It is well known that the ground type and conditions significantly affect the productivity rate (PR) of DWs (e.g., [5,[17][18][19]). The PR of DWs is an important performance parameter that necessarily requires to be assessed for the development of underground stations' time plans and cost estimate and control.…”

“…A better understanding of DWs productivity can therefore offer both programs and cost benefits [17]. Efforts have been made to investigate the factors influencing PR of DWs in underground stations (e.g., [5,[17][18][19]). However, the investigation into all the factors' effects on the PR of DWs has been a major challenge in the underground station in soft ground.…”