Dynamic Response Of Railway Tunnels Mobilized By High Speed Trains

The damage accumulation problems of tunnel linings with initial flaws which are subjected to static-dynamic loads,are born with the fast development of high speed railways.Since tunnels are complicated,hard to repair and sometimes irreversibly damaged,it is meaningful to disaster reduction to estimate the effect of the dynamic load of high speed trains on the fatigue life of lining concrete with initial flaws.Numerical models are provided to reveal the static-dynamic response,fatigue life and concrete fatigue damage of tunnel linings of typical high speed railways with II level and V level rocks around them.More details are as follows:(1)Shotcrete and rock bolt support and time-lapse support are modeled based on the New Austrian Tunneling Method,with regard to simulate the carrying capacity of surrounding rocks.Stress and deformation of linings are acquired after the unloading deformation of the surroundings finished.It turned out that the deformations were small enough with a good support,and linings were in much better stress conditions by using this method.(2)Viscous-spring artificial boundary conditions are introduced.Train loads to the lining-rock system are respectively modeled by a moving suspension system and a series of moving loads to acquire the dynamic respond of linings.A parameter study is conducted to find the impact of the train speed,single or both side driving,rock conditions and track irregularity on dynamic response.Meanwhile,coupling effect of parameters is also concerned.(3)The distribution of lining stress subjected to cycle loads has been acquired based on the static-dynamic analysis.Reciprocating tensile damage can be regarded as the main fatigue failure mode.The controlling position of linings is the baseboard in ?surrounding rocks,the invert arch and arch wall in ?surrounding rocks.Fatigue life of linings is estimated according to the fib model code for concrete structure,and baseboard anti-fatigue life is shorter than the design period,which means it needs more inspection and maintenance.(4)Homogeneous degree is assumed to obey the Weibull distribution to characterize the random distribution of initial flaws in space in order to study the mesoscopic mechanism of concrete fatigue damage.Periodic boundary conditions are conducted on concrete Representative Volume Element.The damage development law of concrete specimen under reciprocating tensile and shear loading conditions.The research indicates that mesoscopic non-homogeneous characteristics play a significantly restraining role on concrete fatigue damage.