A new multi-graph approach for selecting the sequential excavation method of civil tunnels

Abstract

Growth of urban population, traffic congestion and global warming emissions, have caused the experts to design and construct large span tunnels even in the complex geotechnical conditions where the selection of tunnel excavation method in view of its effect on the stability on the one hand and the cost, allocation of the resources, and project scheduling on the other hand are of vital significance. Two methods of Hoek (2001) and Yu and Chern (2007) have been proposed to predict the sequential excavation method so far. Nevertheless, the comparison made among the results pertaining to the application of these methods with actual cases, indicates that there is no more accurate method for predicting the excavation method. This study includes a practical multi-graph, based on some parameters such as failure strain, modified secant modulus, strength factor and the tunnel span to determine the sequential excavation method of the tunnels. The comparison made on the predicted results using the proposed multi-graph in 21 constructed and/or under construction tunnels suggests that the accuracy of the proposed method is 15% and 47% more than that of the previous methods. In addition, the tunnel stability status, type of probable failure and the supporting system can be foreseen making use of the proposed multi-graph. The proposed method is an efficient tool for selecting the sequential excavation method (SEM) and predicting the ground behavior in the primary phase of design of tunnels and also during the excavation.