The Influence Of Some Factors To Seismic Response Of Tunnel

Underground structures are important to support social activities. Once they suffer anstrong earthquake, it may bring serious influences on urban development and nationalpolitical stability. China is located in the circum-pacific seismic belt and nearly half of citiesare located in this seismic belt of more than 7 degree basic intensity. Especially, manyimportant cities, such as Beijing, Tianjin and Xi'an etc, are even located in higher intensityseismic belt with 8 degree. Therefore, the research on seismic design of the undergroundstructures has an important theoretical meaning and engineering values.The movement of underground structure under earthquake is resulted from theinteraction between soil and the structure. Taking the soil-structure interaction as the coretheory and the dynamic FEM theory as the analysis method, a reasonable interaction modelfor tunnel structure under earthquakes is built based on the finite element software ANSYS inthis paper. By detaled calculations, some rules on the response of the underground structuresare summarized, which can provide reference to the seismic design of the undergroundstructure. The conclusions are as follows:(1) The seismic responses of a tunnel are analyzed using time history method. The focusis on the influence of horizontal width of artificial boundary to seismic responses of tunnel forseveral generally used artificial boundaries. The results show that the horizontal width shouldbe larger than five times of depth of computation zone for all the test artificial boundaries.Viscous-spring boundary is a better one than other type of artificial boundaries. The weak partof a circular tunnel liner is also discussed.(2) Based on the theorical method and the research results above, the influences of liningmaterial (concrete grade, lining thickness and density) and geologic conditions on seismicresponses of a tunnel are discussed. The results show that the seismic responses of a tunnelare controlled by its surrounding rock mainly and the influenced from the lining inertia andstiffness is not important. Therefore, it is unreasonable to improve the seismic performance byenhancing the strength of structure. In the seismic design of underground structure, it wouldbe better to absorb the deformation of structure through increasing the flexibility and ductilityof structure properly. The displacements and stress responses of the structures decrease withthe increasing of the grade of surrounding rock. The elastic modulus of lining materialinfluences the displacements of structure lightly but the stress of structure obviously. Theeffect of the lining thickness on the displacements can be neglected. With the increasing of lining thickness the internal forces of structure increase, but the stresses of structure decrease.The increasing of the lining density can increase the stresses of lining. Therefore, choosingsome light lining material can improve the seismic performance of tunnel.