Dynamic analysis of tunnels

In dynamic analysis, it is very important to represent all the dynamicproperties of the system. Also, The infmite media of the supporting soil andits nonlinear performance must be represented. One of the main dynamicforces, is the damping force. The true damping characteristics of typicalstructural systems are complicated and difficult to be defined. However, it iscommon practice to express the damping of such systems in terms ofequivalent viscous damping ratio S , but it is necessary to make someassumptions about these forces on the basis of experience. For this reason,the damping in most structural systems must be evaluated directly byexperimental methods.In this study, The underground tunnel is investigated under seismicloads. The damping in the system is modeled using Rayleigh equation andthe damping matrix is evaluated explicitly rather than by modal dampingratios.The infmite media of the surrounding soil is modeled using theinfinite element technique and the analysis is performed in time domain. Awide parametric study of tunnels under earthquake excitation is performedconsidering different damping levels, boundary conditions, soil typeembedment depth and surcharge load.The results show that these parameters have considerable effect onthe dynamic behavior of tunnels.