Determination of the Optimum Grouting Radius for Improving the Geomechanical Properties of KOUHIN Tunnel Using Multi Criteria Decision Making

Grouting operations as one of the main methods of ground improvement play a key role in tunneling quality. Grouting reduces the amount of surface subsidence, maximum loads on the support systems and on tunnel convergence by improving strength parameters of ground. On the other hand, grouting operation causes an increase in time and cost, and also reduces the continuity of tunneling operations. According to positive and negative effects of grouting operations in tunneling projects, selecting the optimum grouting radius is very important. Vertical displacement of the crown and the roof of the tunnel, the horizontal displacement of walls, subsidence at the surface, axial forces, shear forces and bending moment on support systems and also time and costs were selected as main parameters in determining an optimum grouting radius. It was primarily aimed to calculate parameters of the Qazvin-Rasht railway tunnels using Finite Difference Method FLAC2D. In the next step, the values of selected parameters in various radiuses of grouting were calculated; then, the degrees of importance of each parameter were determined using Analytical Hierarchy Process. Finally, optimum grouting radius was selected among different alternatives by using VIKOR technique. In this study, 100 cm was selected as an optimal grouting radius for improving geomechanical and design parameters in KOUHIN tunnel.