Study On Seismic Dynamic Response Characteristics Of Tunnel Around Cavities In Strongly Seismic Regions

With the continuous development of road network in our country, more tunnels will be built in high seismic regions. Karst geology are widely distributed in China and resources are overexploited, which result in many cavities in layers. Due to the restrictions of road line, many tunnels will pass through bad poor geological region. Under seismic loads, these tunnels are likely to damage and block traffic. It’s very important to study the characteristics of seismic dynamic response about tunnels around cavities.Based on numerical simulation method, this paper studied the characteristics of seismic dynamic response about tunnels around cavities. First of all, the basic theories of Earthquake Dynamic were carried out in order to find an effective input method for outer fluctuations about infinite element boundary in ABAQUS. Secondly, orthogonal experimental scientific methods was adopted to study the sensitivity of seismic response about tunnels around cavities. Once again, taking into account the characteristics of the lining material damage, nonlinear analysis of damage evolution for tunnels around cavities were carried out. Finally, the measures of grouting were studied when the cavity is on the right side of the tunnel. The main conclusions are as follows:(1) For the infinite element boundary in ABAQUS software, the equivalent nodal loads are applied on the bottom and sides with PYTHON script after the technique of wave field separation, which can effectively deal with the problem of the outer fluctuation input.(2) The sensitivity of moment extreme and dynamic stress concentration for tunnel lining among the depth of tunnel’H’, the span of the cavity ’D’, the span ratio of the cavity ’R’is:when the cavity is located at the side of the tunnel, the span ratio of the cavity’R’> the span of the cavity’D’> the depth of tunnel ’H’; when the cavity is located in the upper of the tunnel, the depth of tunnel ’H’> the span of the cavity’D’> the span ratio of the cavity’R’; when the cavity is located in the lower of the tunnel, the span of the cavity ’D’> the span ratio of the cavity’R’> the depth of tunnel’H’.(3) Under the effect of shear wave, the Shear deformation of the tunnel lining results in the reversals stiffness degradation at the direction of conjugated 45°. The cracks of lining repeated opening and closing in appearance. Due to the presence of the cavity around the tunnel, the deformation of the tunnel to the cavity has occurred. The stiffness degradation and damage of the lining for this part is very serious. Comprehensive comparison via the tension damage index, the compression damage index and stiffness degradation index, a conclusion can be drawn. The influence of the cavity’s location on the safety of the tunnel is the cavity on the right of the tunnel, the cavity in the lower of the tunnel, the cavity in the upper of the tunnel.(4) When the thickness of grouting circle was set as 2m and the elastic modulus of the grouting material was set as 6GPa, the peak value of maximum principal stress (SMAX) at right hance and the right skewback had been reduced for tunnels around cavities which designed in this paper. The tensile stress of the lining concrete met the requirements of bearing capacity. This way of grouting shows superior anti-seismic effects in the earthquake.