Evaluation of tunnels under squeezing rock condition

Abstract

Purpose

The purpose of this study is to evaluate the methods employed for classifying and quantifying the potential of squeezing in tunnels. Along with the empirical and semi‐empirical approaches presently available in order to anticipate the potential of squeezing tunnel problems, the squeezing potential of Karaj water transfer tunnel and North West Tunnel Convey (NWTC) tunnels (Lot 2), located in Iran, are evaluated and presented. Those two case studies have an interesting geology profile and parameters to identify and then evaluate the squeezing potential.

Design/methodology/approach

In recent years, there has been an increasing interest in the tunnel construction. This paper describes the squeezing behavior of poor rock mass associated with deformability and strength properties. In Karaj water transfer tunnel, there are eight lithological rock types; and NWTC tunnel (Lot2) has 21 Lithological rock types. The parameters for rock classification, such as rock quality designation (RQD), rock mass rating (RMR), modified RMR, Q‐system, geological strength index (GSI), rock mass index (RMi), and rock structure rating (RSR) are evaluated and presented here. The parameters mentioned above are the input parameters for squeezing study in Karaj and NWTC tunnels. According to different methods of squeezing evaluation of tunnel presented in tables, the results of two case studies are presented in this paper.

Findings

One of the more significant findings to emerge from this study showed that about 3 km of the second part of NWTC tunnel, and 2 km of the Karaj tunnel have high squeezing potential. This research deals with not only an overview of the methods used for the identifying and quantifying of squeezing along with the empirical and semi‐empirical approaches presently available in order to anticipate the potential of squeezing tunnel problem, but also the case studies of NWTC and Karaj tunnels to evaluate and compare the potential of squeezing by different methods. These two tunnel case studies have high potential of squeezing therefore the lining of those two tunnels must be strong enough to overcome this issue.

Originality/value

This study is a precise and concise comparison of the evaluation of tunnels under squeezing rock condition. The present study confirms the previous findings and contributes additional evidence that suggests that there are many studies conducted using empirical and analytical methods to determine the squeezing phenomenon in tunnels. This paper responds to the various questions like, what is the squeezing phenomenon. How can we quantify the potential of squeezing in weak rock? What are the different approaches to the understanding of squeezing phenomenon?

Citation

Ghiasi, V., Ghiasi, S. and Prasad, A. (2012), "Evaluation of tunnels under squeezing rock condition", Journal of Engineering, Design and Technology, Vol. 10 No. 2, pp. 168-179. https://doi.org/10.1108/17260531211241167