PREDICTION OF SUBSIDENCE DUE TO EXCAVATION OF 2-BAHN STATION TUNNEL IN MUNICH

Abstract

Tunnel construction in urban areas is usually a very critical task as it involves excavation in areas that might have important structures or existing tunnels. Hence engineers face the problem of predicting these settlements very often. There are a number of methods to estimate the settlement and volume of settlement troughs in tunnel excavation. Fillebeck (2010) has proposed an empirical method for calculating the maximum settlement and settlement trough distribution in tunnel excavation. A detailed 3D analysis has also been caried out using PLAXIS 3D Tunnel software package simulating the actual ground conditions in the best possible manner. The results of the two methods are compared and it is observed that the results of the empirical are in close agreement with those of 3D numerical analysis. However there remains a certain degree of error in the results of the two methods. This is because empirical method is developed for Greeenfield conditions while the 3D analysis takes into account the urban tunnel construction practical considerations. Transverse settlement troughs and longitudinal settlement troughs obtained by the two methods have been studied. Depending on the maximum settlements observed due to the excavation of the tunnel from the two methods, an attempt has been made to compensate a portion of these settlements by heaving the existing tunnel which crosses the tunnel to be excavated for nearly 7.0 in. A number of cases have been developed in order to optimize the increase in Bending Moment and Normal Force in the tunnel lining of the existing tunnel.