Study On Water And Soil Pressure Response Of Subaqueous Tunnels Under Static And Dynamic Water Level

Tunnel projects play a significant role in perfecting transportation infrastructure.However some tunnels are designed drained,some have seepage passages due to the construction technologies,and some will generate numerous deformation cracks during the long-term service period.All of these will alter the distribution of the water and soil pressure around tunnels.Meanwhile,as the rapid development of the eastern coastal cities,many cross-river and submarine tunnels have been constructed.These tunnels will suffer from the high water pressure and the water level variation.Especially for the submarine tunnels,they will experience the cyclic wave and strong storm surges as well.Thus,the effect induced by the water level fluctuation is the other indispensible issue when it comes to tunnels.This study obtained the analytical answers to the seepage field response under the static or dynamimc water level,by deriving the governing equations of the seepage.Numerical simulations were conducted to investigate the regularities of the water and soil pressure under constant or changing water level,considering the interaction between seabed and tunnel.An underwater tunnel model device was designed to explore the characteristics of the pore pressure response and water inflow into a tunnel immersed in a sandy seabed.The major research work and novel achievement are listed as below.(1)Analytical solutions of the seepage field for underwater tunnel with arbitrary burial depth were acquired using the technique called conformal mapping,based on the governing equation of the steady seepage and abandoning the assumptions of equal water pressure or equal hydraulic head outside the lining,which is normally adopted in the previous literature.With a further step,analytical solutions that take into account the effect of the finite soil thickness or twin tunnels were derived based on the principle of superposition.It was found that ignoring the effect of the finite soil thickness and twin tunnels would overestimate the water pressure acting on the lining and the water inflow.(2)Based on the principle of superposition,the seepage response induced by the dynamic water level was divided into pure ground or seabed response and the disturbance from the tunnel.Afterward,analytical solutions were rigorously derived in cases of water table variation and tide effect.It was revealed that the existence of tunnel,on one hand,would block the excess pore pressure diffusion;on the other hand,it would reduce the pore pressure aside.Besides,when it comes to tide,there exists a critical depth in the seabed,above and below which there is a distinct difference in terms of pore pressure response.(3)The analytical solution of the seepage field response was strictly deducing,which could consider the complex boundary condition induced by the complex wave load.A parametric discussion was given about the influence on the seepage field of submarine tunnel with different wave,soil and tunnel properties.Larger pore pressure on the incident flow side of the tunnel was found than the same horizontal position on the other side.(4)The performance of the "Terzaghi-Rendulic Theory" and "Biot Consolidation Theory"on the seepage problem was compared using the multi-physics field software COMSOL.A detailed discussion is given about the water and soil pressure response under four different working conditions,i.e.steady water level,water table fluctuation,tide load and wave load.It was found that tunnel leakage would increase the normal total stress around the lining.The esisting norms on changing water level overestimate the effect caused by the water table variation,but underesitimate the influence from tide and wave load.(5)The underwater tunnel model experiment device considering the tunnel leakage was designed and manufactured.The linear relationship between water inflow and water level was found based on the experiment results from the submarine tunnel buried in a sandy seabed in cases of constant water level and wave load.Moreover,the critical depth was observed and the water level periodic fluctuation would not influence the water inflow within a period.These discuveries verify the theoretical research achievement.