Analysis Of Dynamic Response Of Special Tunnel Section Under Near-fault Ground Motion

Tunnel engineering is the lifeline of traffic engineering.Near-fault ground motions have long-period,large-peak speed and displacement pulses,which have a greater impact on tunnels.The entrance section and fault zone are the main areas of tunnel structural damage.Research on its effects under near-fault ground motions The seismic response characteristics are extremely necessary.Based on the previous earthquake damage data of the near-fault tunnel,this paper carries out shaking table tests and establishes a finite element numerical model to study the dynamic response of special tunnel sections under the action of near-fault ground motions.The main research results are as follows:(1)Based on the seismic damage data,analyze and summarize the structural failure characteristics of the tunnel under the action of the earthquake,including: the slope failure at the entrance of the tunnel,the crack of the portal and the structural damage at the entrance;the lining and surrounding rock collapse of the tunnel in the fault zone,and the collapse of the lining Cracking,dislocation,etc.(2)The acceleration response of the tunnel entrance section is similar to the input seismic wave waveform trend,and the acceleration response of the arched shoulder,arched waist,and arched feet are more prominent;The internal force of the lining is greater at the structural spandrel and arch foot than at the dome,and the peak value of the internal force appears at the arch foot;The internal force of the lining and the maximum and minimum principal stresses under impulsive ground motions are larger than those without impulse ground motions.The test analysis also shows that the surrounding rock has a filtering effect on the high frequency band of the seismic wave,and the low frequency band(<30Hz)seismic wave has a significant impact on the tunnel structure;The acceleration response of the monitoring point decreases with the increase of the structural damping ratio.After the damping ratio exceeds 20%,the trend of the response spectrum curve tends to be stable and consistent.(3)The fault zone has poor geological characteristics.Under the action of an earthquake,tensile damage first appears at the arch foot,and compression damage appears at the junction of the surrounding rock and the fault zone.Input the same acceleration peak value,the maximum value of each monitoring point under the action of forward directional ground motion is larger than the maximum value of bending moment and axial force at each monitoring point under the action of non-pulse ground motion,and the internal force value and compression damage degree performance of the arch waist prominent.The numerical analysis calculation process also shows that the damage area of the tunnel lining under the action of ground motion gradually expands from the vicinity of the fault zone,and the stress peak appears after the input ground motion reaches the peak value;At the end of the calculation,the damaged crack area of the tunnel lining tends to be stable,the principal stress is completely released,the maximum value is reduced,and the location of the area shifts.