NUMERICAL ANALYSIS OF THE NEW PROPOSED TUNNEL USING THE FINITE ELEMENT METHOD: THE CASE OF ARBA MINCH – WOLAITA SODO ROAD SEGMENT NEAR TO LANTE VILLAGE

Abstract

Tunnels are practicable options to get over physical obstacles like mountains, existing roads, trains, or infrastructure, to meet environmental or ecological requirements, or to traverse a body of water. The road connecting Wolaita Sodo - Arba Minch near Lante village passes between mountain and Lake barriers which needs to propose a tunnel. Stability is a big problem if these tunnels are excavated in the jointed rock mass. For an in-depth comprehension of the stability of these tunnels, the numerical modeling method can display many responses, including stresses, strains, and displacements. The main aim of the study is to predict the stress, deformation, and overall stability of the surrounding rock mass of the proposed tunnel excavation. A 3D finite element analysis has been carried out by using MIDAS GTS NX software. In doing this a Hoek-Brown failure criterion has been implemented for the surrounding rock mass. A parametric study has been carried out varying the tunnel diameters to show its effect on the stress and deformation of the proposed tunnel. From the analysis, it is found that the principal stress for each tunnel size was, the maximum compressive (-) stress for D=8m, D = 8.5m, D = 9m, D = 9.5m and D = 10m is 570.55 kN/m2 , 570.16 kN/m2 , 569.76 kN/m2 , 569.35 kN/m2 ,568.90 kN/m2 , and the maximum tensile (+) stress for D=8m, D = 8.5m, D = 9m, D = 9.5m and D = 10m is 168.74 kN/m2 , 148.03 kN/m2 , 147.66 kN/m2 , 147.0 kN/m2, and 143.78 kN/m2 . The magnitude of principal stress decreases with increasing the size of the tunnel. The deformation for different tunnel sizes was 0.39 mm, 0.41mm, 0.44 mm. 0.46 mm, and 0.49 mm for tunnel width (D=8m, D = 8.5m, D = 9m, D = 9.5m and D = 10m) respectively. The deformation of the tunnel increases with increasing the tunnel diameter. The stability indicators, the floor heave ratio of all tunnel sizes is less than 0.05% and the roof sag ratio is also less than 1.0%, The value of the wall convergence ratio is less than the maximum value (<2%). Overall this study found that the surrounding rock mass in the study area has satisfactory performance to provide the proposed road tunnel on a studied tunnel size range.