Predicting three-dimensional displacement around the tunnel and its impact on the value of Q-system

Having knowledge of stability of an underground space depends on stresses and strains around it. Creating underground tunnels leads to significant changes in the rock mass stress. Therefore, to achieve the necessary stability, stresses and deformations around the tunnel must be examined carefully. Usually, stress-strain behavior analysis is conducted in two-dimensional mode. This paper was conducted to compare two-dimensional and three-dimensional analysis of deformation around the tunnel proposed as new work in relationship between the two-dimensional and three-dimensional deformation. Then, its impact on the value of Q-system in seismic mode is studied. Two-dimensional analyses are usually conservative. Therefore, the proposal relationship between two-dimensional and three-dimensional mode will lead to reduced costs and save in support materials. The results of different analyses in the intact and sparsely jointed rock masses show that displacement around the tunnel is greater in two-dimensional analysis compared with three-dimensional analysis. However, in the heavily jointed rock masses, displacement around the tunnel is lower in two-dimensional analysis than three-dimensional one. As three-dimensional analyses are closer to reality, results of equations proposed in this paper can be used to calculate three-dimensional displacement. Different analyses for intact or sparsely jointed rock masses carried out in 2D and 3D states. According to conclusions made, the new equation proposed between 2D (U_2D) and 3D (U_3D) displacement. Data obtained by local measurements (3D) and the results of the 2D analyses for heavily jointed rock masses were compared. Then relationship between 2D and 3D displacements in the heavily jointed rock masses proposed. The results of this research have been applied for tunnel of Gavoshan Dam in West of Iran. There is good consistency between equations proposed in this paper and three-dimensional analyses.

Keywords:

3D displacement , Q-Value , 2D displacement , Heavily jointed rock mass