Seismic Response Analyses Of Metro Tunnel Across Active Fault

Metro tunnel is an important part of lifeline engineering, and its aseismic prob-lems demand more attentions. In the early days, it is widely accepted that undergroundstructures, being confined by the surrounding soil, have good antiseismic ability. In1995Hyogoken Nambu earthquake of Japan, subway station and metro tunnel hadbeen partially damaged severely to need complicated repair and reinforcement, whichbrings huge economic loss. Then people realized that the antiseismic research of under-ground structures can not be ignored. Our country is one of the regions with manyearthquakes, and active fault is widely distributed. Metro tunnel should adopt measuresto avoid the fault firstly in the construction and route selection. But it is inevitable toacross active fault by reason of subway engineering alignments depending on thetraffic function requirements in many cases, subway tunnel and other undergroundengineering will suffer serious threats due to seismic fault rupture. At present, thecorrelational studies about the aseismic design of across active fault tunnel are limited,and our country does not develop a set of reasonable and complete aseismatic designcode on underground structures across fault until now. In order to study the charactersof earthquake response and damage mechanism of metro tunnel across fault, and tofind the weak parts of anti-seism, so as to provide some suggestions on seismic designand safety evaluation, the main content of the paper are as follows:1. The historical earthquake damage data of surface dislocation is gatheredariseing from fault activity. The method of statistical regression analysis is adopted tofit the relationship between bedrock dislocation and magnitude under different faulttypes according to earthquake damage data. The software of soil seismic rupture whichis programmed on the finite element method of pseudo-static elastoplasticity is used tostudy surface rupture dislocation of different soil properties. The relationship is set upbetween surface dislocation and magnitude, soil thickness under strike-slip fault. Therelationship is set up between surface dislocation and magnitude, soil thickness, faultdip angle under reverse fault. The statistical formulas estimate surface rupturedislocation not just depending on magnitude, so we can accurately evaluate surfacedislocation according to magnitude. The results show that surface earthquake disastercan decrease gradually with the increasing of soil thickness, and earthquake damage ofsilty clay is more serious than that of clay.2. Taking the range of Beijing metro line7as an study object, based on the finiteelement method of pseudo-static, damage index is adopted to research the failure mode of lining structure under different types of fault dislocation, especially the first position,process and final degree of damage. The results show that: the destruction is the firststart and the most serious at the vault under the effect of normal and reverse fault. Thedestruction is the first start and the most serious at the hance under the effect ofstrike-slip fault. The damage range of lining structure is located in active fault.According to calculation results, the relationship between the critical value of soilthickness and fault dislocation is set up, and the statistic formulas estimating structuraldamage region and the most severely location are developed. The obtained results areuseful for quake-proof design of metro tunnel across active fault. According tocalculation results, the value of soil thickness applying to Beijing is estimated underdifferent magnitudes, which does not need to worry about the effect of active faultrupture on the shallow tunnel. Moreover, the factors of weaken earthquake disastersare suggested from the aspects of lining thickness, lining outer diameter, soil property,buried depth and the angle of tunnel passing through fault.3. The dynamic strength and deformation properties of concrete and steel wereexperimentally investigated considering strain rate effect under earthquake. Modifyingthe static constitutive model for concrete in Code for Concrete Structure Design(GB50010-2010) through test results, the dynamic damage constitutive model ofconcrete was established. The results showed that the damage is relate to strain rate,and the explanation about delay of concrete damage is given.4. Numerical simulation was conducted to study the resistance to faultdislocation,deformation characteristics,and failure mode of tunnel structure underdifferent fault rupture rate by using reasonable dynamic damage constitutive model ofconcrete,and considering the relationship between damage and strain rate.Thecalculating results show that resistance to fault dislocation of tunnel structure isincreased in elastic stage as fault rupture rate improving. But structural deformabilitydecreasing leads to its sudden damage, and the destruction is serious.5. The infinite boundary method is proposed for simulating semi-infinite space soilreasonably, and realizing the infinite calculation region. The infinite boundary methodcan simulate wave to go through the boundaries well by example.The results generallyaccord with the law of actual wave propagation in soil.A coupling model of finite andinfinite elements on soil-tunnel structure is established to analyze time history by usingthree classical seismic waves as the ground motion input, and to summarize damagecharacteristic and failure mechanism under seismic action.The results show that tunnelvault is the relative weak parts in the seismic response of structure.