Seismic Dynamic Response Analysis Of Large Diameter Seabed Shield Tunnel Under High Water Pressure

Compared with the cross-river tunnel,the subsea tunnel is faced with more significant problems of high water pressure and complex geological conditions,which has higher requirements on the seismic safety.At present,the study on the dynamic response of the tunnel is mainly concentrated on the land tunnel,many problems faced by undersea tunnel have not been solved yet.In this paper,based on the law of the change of elastic modulus with confining pressure in Duncan Chang E-B theory and FLAC3 D own development platform,Duncan Chang’s model is developed and used in the numerical simulation of the dynamic response of the Submarine Tunnel.The influence of different water pressure on the dynamic response of the subsea tunnel is analyzed.Under the condition of high water pressure,the tunnel crossing the earth rock boundary and the geological fault zone are simulated,the following results are obtained :(1)When the depth of buried is constant,the change of water pressure under the action of seismic wave has a great influence on the horizontal displacement of the tunnel structure.The peak value of the displacement and the first principal stress peak increase with the increase of the hydraulic pressure.However,the increase of the structural displacement is slowed down when the water pressure increases compared with the Mohr-Coulomb model.It is probably due to the use of the Duncan model in this paper.The increase of the confining pressure caused by the hydraulic pressure increases the elastic modulus of the soil,and the constraint of the tunnel is correspondingly increased,but the increase ratio is weakened.(2)When the tunnel passes through the earth rock interface,the change of water pressure has a great influence on the dynamic response of the structure.With the increase of water pressure,the displacement and stress of the structure are increased.The change of soil conditions has a great influence on the dynamic response of the structure.With the decrease of the elastic modulus of the soil,the difference of elastic modulus between the soil and the rock increases,the peak of stress and displacement of the structure increase The range of influence of the mutation of physical properties of the medium is also larger.(3)The fracture zone has a significant effect on the dynamic response of the structure.Especially in the fault zone,the dynamic response of the structure is more intense,which is greatly affected by the seismic wave fluctuation.With the increase of water pressure,the displacement and stress of the structure increase,especially the change of stress.The peak of the principal stress of the structure occurs at the junction of rock and soil along the axial variation of the tunnel.Due to the difference of the displacement and deformation between soft soil and rock,the shear deformation and large stress occurred in the structure.Especially in the shoulder and feet of the tunnel structure,it is easy to damage and should be protected.