| Based on the project of "Research on Key Technologies of Seismic Resistance and Reduction for Extra-large Section Highway Tunnels in High-Intensity Seismic Areas",with the aim to deal with the problem that stronger seismic response of the lining in the fault section of highway tunnels may make the lining structure more vulnerable to damage,this paper studied the seismic dynamic response in the fault fracture zone of such tunnels and the key technologies of seismic resistance and reduction in such areas by using the FLAC3D analysis software.The main contents and achievements of this paper are as follows:(1)In consideration of the seismic dynamic characteristics of the extra-large section highway tunnels,this paper studied the seismic response laws followed by the linings of the extra-large section and the general large section(two lanes)highway tunnels.The analysis results show that the dynamic response of the linings at the fault fracture zones of extra-large section and general section tunnels is obviously stronger than that at nonfault fracture zones.The dynamic response of the whole lining in the extra-large section tunnel is prominently bigger than that in the general large section tunnel;and the stress increment of the linings at the fault fracture zones are greater than that of the linings at the places of integral rocks.The longitudinal influence range of the fault fracture zone in the extra-large section tunnels is around 10m larger than that in the general large section tunnels.The increased aspect ratio of the extra-large section tunnel makes the section flatten.The numerical results show that the maximum principal stress peak on the cross section of the linings at the fault fracture zones of the extra large section appears at the position of the skewback,while the principal stresses on the arch crown and the inverted arch are very small.(2)In consideration of the different widths and angles of the fault fracture zones,this paper studied the seismic response laws followed by these zones in extra-large section highway tunnels in terms of acceleration response,displacement deformation,and changes of shear stress and principal stress.The results show that the law followed by the force on the cross section of the linings at the fault fracture zones stays the same.Generally,as the width of the fault becomes larger,the seismic dynamic response of the tunnel with larger cross-section is greater,especially when the fault width is greater than 30m,the parameters of the index are all significantly enhanced.As a result,the impact range of the fault zones with different widths on the linings of such tunnels is gained,which proposes measures of seismic resistance and fortification for the extra-large section highway tunnels:25～30m range before and after the interface.When the dip angle of the fault fracture zone changes,the stress on the cross section of the linings of the fault fracture zone is always concentrated at the skewback and the bottom of the wall.When the dip angle is relatively small,the forces on various points of the cross section of the tunnels are at a high level and they change slowly;when the dip angle is relatively big in the range of 60°～90°,the indices of the dynamic response on various points of the cross section don’t change much,which is to say,the extra-large section tunnels are not sensitive to the dynamic response of the fault fracture zones with large dip angles.but generally as the dip angle of the fault fracture zone decreases,the oscillation amplitude of the seismic response indices on the linings of the extra-large section tunnels become larger,which means the seismic dynamic response is more severe,and the longitudinal influence on the linings close to the fault fracture zones is also greater.(3)This dissertation also studied the seismic resistance and reduction effect of the measures of setting a shock absorption layer,changing the stiffness of the lining structure,and using grouting reinforcement at the fault section of the extra-large section tunnel.It pointed out the linings at such tunnels follow a different stress law from that at the general large section tunnels after the seismic resistance and reduction measures are set,and it briefly analyzed the mechanism of the seismic resistance and reduction measures.The paper also compared the dynamic response laws followed by the linings at the fault structure zones in respect of of the two layout modes of the shock absorption layer,the different thickness and different stiffness levels of the shock absorption layer,and optimized the parameters.The author further compared the dynamic response of four kinds of stiff lining materials;compared the seismic resistance effect of full-ring grouting and interval grouting and optimized and the interval thickness and grouting thickness.The results show that arranging the shock absorption layer between the primary lining and the secondary lining of the extra-large section tunnel has a better effect than setting the shock absorption layer outside of the primary lining;the radial range of the shock absorption layer of 20 cm in thickness considering the economic cost is the best instead of being the thicker the better;at the fault fracture zone of the extra-large section tunnels under high-intensity seismic conditions,when the elastic modulus of the shock absorption layer material is below 50 MPa,it has a good matching relationship with the lining,and can play a synergistic role under the action of earthquakes.This paper proposes rubber as the material of the shock absorption layer as it has a more obvious seismic reduction effect comparing with other materials with a higher elastic modulus.Considering the specification requirements of the lining materials under static conditions and the seismic reduction effect of changing the stiffness levels of the linings under high-intensity seismic conditions,and considering that reducing the stiffness of the linings improves the force but the displacement also increases,the author believes that the ductility of the structure should be increased to withstand the deformation of the surrounding soil,and to ensure that the tunnel does not fall even if it breaks after suffering an earthquake.As the full-ring interval grouting has a better seismic resistance effect than that of full-ring contact grouting,and the thickness of intervals in the form of interval grouting has no obvious influence on the seismic resistance effect,4m of grouting at the 1m interval has the best seismic resistance effect cconsidering the economic cost and the shock absorption effect. |
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