EFFECTS OF TUNNELLING IN URBAN AREAS

Abstract

The always increasing demand in new transportation routes in urban area, in the last years, led to the need in increasing the present road transports; by then, the need to use the underground environment for new transportation lines became always more important. New underground lines started to be excavated in many of the largest cities in the world, leading to a large number of shallow and deep excavations in the urban environment. Many tunnels, often located at relatively shallow depth from the ground surface, started to be excavated, inducing not negligible effects on the preexisting buildings. For such a reason, methods directed to the induced tunnelling effects prediction were developed on the basis of empirical data collected all over the years. Despite such empirical methods resulted very useful and reliable for the designing process of a tunnel line, as to predict the tunnel induced displacements on the ground surface, they base on very simplified hypothesis, neglecting important phenomena such as the soil-tunnel-buildings interaction and considering in a simplified way the excavation technique influence. Indeed data collected from literature, demonstrated how the improvements in technologies in the last years allowed an important reductions in induced displacements on the ground surface. For a such a reason numerical analysis of the excavation technique influence on tunnelling induced displacements, became always more significant. Thus, the purpose of this research is to define the importance of excavations technologies, in terms of tunnelling induced effects on the ground surface, inspired by the current construction process of the Line 6 tunnel in Naples. For this purpose, a number of numerical analyses, by means Finite Element codes, were performed as to simulate the tunnel excavation process, and to carry on a parametric study on the technology influence on the induced effects, finally compared to results of a similar parametric study concerning the geotechnical properties of the soils affected by the excavation. Results of such analyses were then used to back-analyze monitoring data collected during the Line 6 tunnelling process.