Design of Tunnel Support System Based on Instrumented Data Using Direct Back Analysis Method (Case Study: Pooneh Tunnel, Khorramabad - Arak Freeway)

Stability analysis of tunnels and determination of behavioral characteristics of rock mass using numerical methods such as finite element, boundary element and discrete element are associated with limitations in terms of validation of input and output data. One of the practical methods to solve these problems is the use of monitoring and instrumentation system in tunnels, which is done with the aim of controlling displacements and assessing the stability of underground structures and rock mass characteristics. In mountainous tunnels, the main purpose is to measure the deformation during tunnel construction and to ensure that ground pressures are controlled on the temporary support system. One of the methods to determine the parameters in situ is to use the instrument and perform back analysis on the resulting data. In this research, the direct method of back analysis based on univariate search algorithm has been used to determine the geomechanical parameters of rock mass in Pooneh tunnel. Numerical analysis were performed using Phase2 software. Based on this research, four zones along the tunnel route were selected along with four convergence-measuring stations then by changing the parameters E, K, C and ϕ and performing back analysis the best relationship between tool displacement and modeling results was obtained and a suitable support system is provided accordingly. A ground reaction curve (GRC) is plotted for each zone to determine the appropriate time to install the support system.