Simulation of longitudinal dowels performance in stability of tunnels face

For safe underground excavation, different supporting system can be used in weak ground conditions. However, rock mass instability does not give opportunity to install an appropriate supporting system. Pre-reinforcement of tunnel face can be an effective solution for this condition. Fiber glass dowels are one of the most efficient and economic methods of ground reinforcement. Fast installation, flexibility in using with other supporting systems … are the other advantages of this pre-reinforcement. This paper studied numerically the behavior of the longitudinal fiber glass dowels which may accompanied with the different supporting system i.e. with shotcrete layer as the main supporting system or with pre-cutting system as another pre-support method. The analyses was carried out by FLAC 3D in different weak ground condition subjected to different in-situ stresses implying tunnel depths. The fiberglass forces as well as tunnel center displacements are the output of this simulation. The results showed the location of critical zones developed in tunnel face in non-hydrostatic stress field. It leads to employ more concentration of dowels on those zones. As well, the best result for the dowels could be seen when they were accompanied with pre-cutting system. Finally, from the results of numerous analyses, mathematical formulations were presented to fast calculate the maximum stress of dowels and strain of the tunnel center in any different condition of weak ground condition.