Damage Mechanism Of Underwater Tunnel Under Earthquake Condition

With the development of China's economy,the construction of underwater tunnels has had a huge socio-economic effect.However,due to the complex geological environment of underwater tunnels,the failure mechanism of underwater tunnels under earthquake condition has plagued geotechnical engineers for a long time.Therefore,this paper focuses on the failure mechanism of underwater tunnels in liquefaction and non-liquefaction zones under earthquake condition.?1?Considering the accumulative damage of concrete under cyclic loading,based on the Mazars damage theory and the D-P constitutive model,a treatment method considering concrete damage is proposed.The secondary development of the nonlinear concrete damage constitutive model is realized on the FLAC^3Dplatform and verified by theoretical formulas and experimental data.The results show that the convergence of the model is good,the calculation results agree well with the experimental values,and the damage form is highly consistent with the experiment.The developed nonlinear concrete damage model can provide support for seismic hazard assessment in actual projects.?2?Using the damage model,the underwater tunnel failure mechanism in non-liquefied areas was researched.Compression and shear waves are input at the same time from the base of the bedrock,and efforts are made to study the weak points where the tunnel lining begins to damage under seismic response and the process of damage propagation.The results show that under earthquakes condition,the damage of the tunnel first started at the arch foot and the arch bottom of the section,and then the damage area gradually developed upwards and penetrated,resulting in the destruction of the tunnel.?3?To research the damage mechanism of the underwater tunnel in the liquefaction area,the finite-difference software FLAC³DD is used to perform longitudinal 3D numerical analysis of the shield tunnel in the liquefied soil layer.The simultaneous compression and shear waves are input from the bottom of the bedrock to study the bidirectional seismic waves..The results show that the liquefaction of the local soil floats to make the tunnel lining structure produce a relatively large displacement,while the displacement of the tunnel lining structure in the non-liquefied site is smaller,so that the tunnel has a larger bending moment in the longitudinal direction.The head of the tunnel lining is under tension and the bottom is under pressure.The tensile stress at the head far exceeds the design tensile strength of the lining.It shows that the tensile damage is the leading factor to the liquefaction-induced tunnel failure.