Analytical study on seepage field of tunnels with external drainage considering effect of grouting rings

The external drainage method has been gradually applied in the tunnel engineering, but the analytical theory of the seepage field of the external drainage tunnel considering the grouting effect has not been reported, which leads to that the theory lags behind engineering practice. Based on the mirror image method and the theory of seepage mechanics, the theoretical model of seepage field of the external drainage tunnel considering grouting rings is proposed. The correctness of the formula is verified through the analytical degradation and numerical simulation. The influences of the permeability coefficient and thickness of the grouting rings on the water inflow and the water pressure outside the tunnel are discussed. The analysis results show that the permeability coefficient of grouting rings has a significant influence on the seepage field of external drainage tunnel, and with the increase of the ratio, the water inflow can be controlled obviously, but it will cause the increase of external water pressure. The influences of grouting ring thickness are relatively small, which mainly lies in that the greater the grouting ring thickness, the stronger the control of the bottom external water pressure. The reasonable parameters of grouting rings are put forward considering the requirements of groundwater environmental protection and the control effect of water pressure. The research results may provide reference for the design of grouting parameters and the construction practice of external drainage tunnels.