Determination of Rock Mass Behavior and Characteristics Under Tunnel Widening in Reinforced Rock Mass Based on Numerical Analysis

Abstract

The role of underground spaces including tunnels and caverns is continuously increasing due to the increase in population as well as the growing demand owing to the development in communication systems, hydropower sector and mining industry. Consequently, the demand for enlargement of existing underground structures will be definitely required in order to meet the necessary increase in the demand of infrastructure development. That is why, it is mandatory to reduce the knowledge gap in widening of the underground structures. To fill up the knowledge gap, a detailed research work has been carried out to examine the tunnel widening characteristics on the basis of rock mass behavior under different rock types, with different in-situ stress conditions and different design parametric conditions. The main characteristics highlighted in the study are; (a) determination of most appropriate empirical design approach that best suits the tunnel widening, (b) the effect of widening of tunnel on different tunnel shapes and (c) to establish the deformation modulus of reinforced rock mass and to determine the difference of modulus for normal/virgin rock mass and reinforced rock mass. After using the numerical simulation techniques by opting Finite Difference Method (FDM) it was found that; (a) The Rock Quality Index (Q-system) was found to be the most suitable method for application in the widening of tunnels keeping in view the deformation control of rock mass, (b) The tunnels with a round shape such as horseshoe and semi-circular with flatbed are more effective in asymmetric widening, whereas the provision of a rounded invert in these shapes can reverse the widening option to symmetric. Furthermore, there is an insignificant effect of difference in asymmetric and symmetric widening of regular tunnel shapes such as box, rectangular and semi-elliptical and (c) The deformation between tunnel Abstract xxii model with support and without support was observed to be 21.23% which was back calculated to estimate deformation modulus of reinforced rock and was subsequently found to be 16.67% more than the deformation modulus of primary rock mass. This study provides better understanding and guidelines in planning stage of tunnel and cavern widening scenario for different shapes in different in-situ stress and with different underground support conditions under variety of parametric conditions. Through this study, a comprehensive understanding has been developed in determining the underground tunnel widening characteristics that will be of great help to have an appropriate technique in widening of tunnel in high in-situ stress conditions. Furthermore, the size and width of any widened tunnel can be evaluated appropriately in future on the basis of this study which ultimately increase the tunnel/cavern stability and with applicable solutions.