Damage Mechanism In Portal Section Of Shallow Buried Bias Tunnel Lining Under Seismic Action

Slope instability and damage to the lining structure are the most common instability problems in tunnel entrances.The triggering of instability problems may be dynamic effects such as earthquakes and blasting.In this paper,based on the shallow buried side hole section of tunnel in previous earthquake damage data,by shaking table test and numerical simulation method of bias Angle of 30 ° of shallow buried side hole section of tunnel,the dynamic response characteristics and the damage characteristics of lining were studied,to reveal the stress characteristics of tunnel lining under the earthquake excitation and the damage characteristics of tunnel lining structure.The main research conclusions of this paper are as follows:(1)Based on the analysis and statistics of the damage and seismic characteristics of the tunnel entrance section,it is concluded that the damage of the tunnel entrance section is mainly: the damage of the entrance and the slope,the damage of the tunnel door structure and the lining structure of the entrance section;The factors affecting the degree of earthquake damage were analyzed.(2)In order to study the damage characteristics of shallow buried bias tunnel under the action of earthquake,the shaking table model test of shallow buried bias tunnel was designed and completed.When the amplitude of seismic wave acceleration is 0.05 g ～ 0.3g,the peak acceleration of each monitoring point has a significant amplification effect;when the input acceleration reaches 0.3g,the tunnel lining may appear plastic damage,reaching the "saturation" state.The bending moment value at the arch foot of the portal section is larger than that at the shoulder.Under the action of the earthquake,the response at the arch base of the portal section is more likely to reach plastic damage,and the possibility of damage and damage is greater.In the model test,the tunnel lining has cracks of varying degrees at the arch foot and arch waist of the portal section.(3)In order to verify with the shaking table test results,a three-dimensional finite element model of the shallow buried bias tunnel was established.The analysis results show that: When the tunnel is under the condition of shallow buried bias,there is a serious stressconcentration at the shoulder and foot of the tunnel lining,which leads to the damaged area at the shoulder and foot of the tunnel lining of the tunnel entrance.The damage area of the right arch foot was the first and the damage degree of the right arch foot foot was the greatest.The damage cracks at the maximum principal stress position are damaged because the tensile strength of concrete reaches the limit value.When the earthquake ends,the damage area of the tunnel lining arch shoulder and arch foot tends to be stable,the maximum principal stress of the tunnel lining structure is completely released,the maximum value decreases and the corresponding position shift occurs.