Displacement control in tunnels excavated by the NATM: 3-D numerical simulations

The high cost of urban space has significantly increased the demand for tunnels in big urban centres. In such areas, settlements induced by the tunnel excavation may cause serious damage to nearby structures. Therefore, it is necessary to investigate effective means of controlling tunnel-induced settlements. In many countries, tunnels in soils and rocks are constructed using the New Austrian Tunnelling Method (NATM). This is mainly due to its flexibility to adapted to different ground conditions and use of simple equipments. Tunnel designs by NATM are generally based on empirical methods taking into account local experiences. The method is said to be observational and the construction process may be changed according to the observed response of the earth mass, acquired by means of proper instrumentation. Induced displacements are empirically controlled by adjusting the speed of excavation, distance between tunnel face and support, partial-face excavation and closure of invert. The relative importance of these techniques in the final displacements is analysed in this paper using 3-D numerical analyses with the Finite Element Method. (C) 2003 Elsevier Ltd. All rights reserved.