Beheshtabad Water Transmission Tunnel is going to be driven in the Iranian central plate with an approximate length of 65 kilometers. There are several zones of weak rocks in its rout. Some of these zones are situated at great depths so that the squeezing phenomenon may occur during the tunnel exaction period. In this paper the mechanical behavior of weak rocks are studied and their effects on the stability of tunnel are investigated. Several empirical, theoretical and numerical methods are considered to model the time dependence behavior of the weak rocks. Some of these methods are used to study the time dependent behavior of the rocks surrounding this tunnel. The computed results are compared for different zones of weak rocks with potential of squeezing. These results are tabulated in tables and graphically shown in some related figures of the text. Based on these results, it is concluded that there may be a potential of squeezing causing instability in some part of the tunnel rout during its excavation.
Population growth, decreasing the level of underground water resources and concentration of vital industries in the central part of Iran demands a high amount of water to be transmitted to this region. Therefore, projects of water transmission to Zayande-rood (the Zayand River) are some practical and effective ways to convey the water from the West and North West of Iran to its central regions. The Beheshtabad tunnel project is planning to drive a tunnel of about 64.93 kilometer in length in order to bring water from Karoon's water resources to the Iran's central plate. This tunnel (with a SW-NE trend) will start from Darkesh-Varkesh Valley near the Ardal city and finishes at the Se-Cham Asman. This paper briefly discusses about the squeezing phenomenon associated with some part of the tunnel. Squeezing describes the reduction of the cross section of the tunnel during its excavation stages. It's due to the time dependent deformation of the surrounding rock mass resulted from the redistribution of the stresses in an elasto-visco-plastic medium. Three methods are usually used to evaluate the squeezing behavior of the surrounding rocks in a tunnel excavation sequence:
Semi-analytical method and
Theoretical- Analytical method. In this study, the following methods are used to estimate the squeezing of Beheshtabad tunnel and the corresponding results are compared with each other:
-Empirical methods (e.g. Geol (1994)'s approach based on N value).
-Semi-analytical methods (e.g. Hoek and Marinos (2000)'s approach).
-Analytical methods (e.g. Carranza-Torres & Fairhurst approach (2000) using Hoek-Brown criteria).
-Analytical methods (e.g. Duncan-Fama approach (1993) using Mohr-Coulomb criteria). In order to estimate the instability of each section of the tunnel, the first step is to determine that either the rock mass should be considered as continuum or dis-continuum material.