Seismic Response Analysis And Reliability Of Utility Tunnel

A utility tunnel is a public underground structure that holds wires, conduits, and pipes of power, gas, water supply and communication utility system and provides also enough space for maintance opertation. Contruction of utility tunnel represents the future orientation of development for underground infrastructure system in both megalopolis and small towns due to its many advantages as improving the reliability, reducing deferred maintenance and improving the environment. However, few researches have been carried out so far about the dynamic responses and reliability of utility tunnel under earthquake attack. This fact invokes the research of this paper.This paper first investigates some key factors that are crucial for proper earthquake response analysis of utility tunnel, such as artificial boundary conditions and the effective stress method. And some examples are investigated. This has laid a solid foundation for modeling of utility tunnel. Taking ABAQUS as a platform, a three dimentional finite-element-model (FEM) of soil-structure system is estabilished, in which the artificial boundary conditions, contact between soil and structure, the plasticity of soil and the effective soil stress method are considered. The type of input for underground structure analysis is then studied and it is found more accurate responses can be obtained when displacement time history of earthquake wave is adopted. Based on all the above results, the dynamic seismic response of utility tunnel has been calculated using the proposed model. The influences of factors as artificial boundary conditions, contact feature, effective stress method, wave passage effect and inconsistent seismic excition on the dynamic responses of unitily tunnel has been investigated. The results reveal that the utility tunnel show global bending deformation pattern under shear wave excitation and the amplitude of deformation is the same as soil. The artificial boundary conditions and the inconsistent excitation have much more significant influence on the structural responses than other factors. Therefore, special attention should be paid on these two factors for seismic responses analysis. Since the utility tunnel is a typical shallow-buried structure, the earthquake surface wave especially Rayleigh wave will have considerable effect on the structural response. To learn the effect of Rayleigh wave, the propagation characteristics of Rayleigh wave in soil is reviewed and approximate Rayleigh earthquake wave is simulated using Fourier transform technique. Taking the simulated Rayleigh wave as input, the seismic response of utility tunnel is calculated. The results demonstrate that the effect of Rayleigh wave on the seismic response of shallow-buried underground structures can not be ignored. And it shows that the deformation is mainly the bending and the amplitude of the strain at the top of the structure is about 2 times bigger than the corresponding bottom point.The numerical model suggested is then applied to an experimental model and the computational results are compared with shaking table test results. The numerical results and the test results match quite well. The feasibility and efficiency of the proposed FEM model is validated by the comparison, and it can be adopted for further investigations.Reliability-based design is the final goal of structural design. This paper extends the physical stochastic earthquake model, using the sprectral representation method, to get the stochastic inconsistent excitation. Then based on the probability density evolution method (PDEM), the probability desity surface is calculated. Furthermore, the failure criterion of utility tunnel is analyzed and the equivalent extreme value event is introduced and applied to calculate the seismic reliability.