Assessment of Discontinuity Properties Effect on the Steady State Flow of Water into the Tunnel- Case Study: Koohrang 3 Tunnel

Water flow in tunnel projects is one of the main issues that can affect the plan and tunneling activity. Therefore، it is necessary to predict the location and the amount of water flowing into the tunnel. The experience has shown that the accurate prediction of water flow in excavated tunnels due to the lack of consideration all influencing factors، especially the properties and condition of discontinuity is not possible. In this paper، In order to investigate the effect of discontinuities properties on the rate of water flow، the cross section of Koohrang 3 (1+897 - 1+950) with the UDEC software has been modeled. By variation of the properties of discontinuity، the flow rate into the tunnel has been assessed. Results of this study have shown that the variation of the properties of discontinuity has significant influence on the steady state flow of water. Among these properties، the aperture of joint has the most significant effect on flow rate in the tunnel. Analysis of water flow is necessary for construction of underground structures. In this analysis، the possibility of any kind of change in the ground water behavior and flow rate should be considered. In this paper by using numerical model، the effect of discontinuity properties on the water flow rate were studied. Methodology and Approaches: The discontinuity properties have great influence on the water flow rate into tunnels. In order to investigate the effect of discontinuities characteristics on the flow rate of water، the cross section of Koohrang 3 with the UDEC software has been modeled. By variation of the properties of discontinuity، the rate of flow to the tunnel has been assessed. Finally، The water flow rate calculated by numerical modeling were compared with the values obtained from the analytical methods. Results and Results of this study have shown that the increase of the joint spacing reduced the rate of water flow into the tunnel due to the increase of formed blocks’ size. In addition، increase of the joint aperture has substantially increased the amount of water flow to the tunnel. Moreover، by increasing the joint orientation from 30 to 120 degree، the maximum water flow occurred at an angle between 50 and 70 degree. According to results of the investigation among the discontinuities properties، the joint aperture had the greatest effect on the flow rate of water to the tunnel.