Study On Seismic Dynamic Response Of The Forked Tunnel With The Transition Section Of Single-track And Double-track

The branched tunnel which is the key project in design and construction is usually composed of long span section,multi-arch section and small spacing section.The structure and the stress distribution of surrounding rock are complex and the serious damage is more likely to occur during an earthquake around the branched tunnel.It is of great value to study the seismic dynamic response and anti-seismic measures of the branched tunnel in the strong earthquake district.Based on the Yangjiaping Tunnel of the Chenglan Railway,the dynamic response of seismic action and the ant-seismic measures are being studied and put forward through the method of numerical simulation.The main work and research results of this paper are as follows:(1)The difference of seismic dynamic response of tunnel between the mid-partition wall and middle rock pillar is studied by comparative analysis with numerical calculation,and the research indicates that:The peak value of tensile stress and compressive stress in the middle wall of double arch tunnel are larger than that of the small spacing tunnel,and the shear stress of the middle wall is larger than that of the middle rock pillar.With the increase of the width of the middle rock pillar,the maximum value of compressive stress is transferred to the center position from the angle position of the middle rock pillar.(2)A three dimensional numerical model for Yangjiaping Tunnel with the the transition section of branched tunnel in single and double track lines is established,and the research of seismic dynamic response of tunnel shows that:The relative displacement of vault and invert is large.The diagonal relative deformation of the tunnel in the transition of the port of bifurcation,multi-arch section and small spacing section has a significant change.The longitudinal relative displacement deformation of the large arch section and double hole with single line segment of the tunnel is small.The head wall deformation is large and prone to damage.The peak value of the internal force of the arched shoulders and skewback near the side of the middle rock pillar at the transition section between the middle wall and the middle rock pillar has a big change.The stress of the lining on the left and the right skewback and the arch waist of the small clearance section and multi arch section is large.The internal force of the head wall on the skewback and arch waist position which are the weak parts of the tunnel in earthquake is relatively large.(3)The effect of shock absorption of the different parameters of grouting range,head wall and absorbing joint is studied,and the results shows that:The greater the range of grouting,the smaller the internal force and displacement of the structure is,and the position of the best effect of grouting zone locate before and after 4m from the head wall.The smaller the head wall material stiffness,the smaller the internal force of the structure is.The structure of internal force can be reduced significantly by setting the damping joint which has little effect on the internal force of lining structure in the distance.(4)The position of the skewback especially near the middle wall and the middle rock pillar is the weak part of the tunnel in earthquake.