Study On Anti-seismic Technology For Tunnel Entrance By Considering The Portal Elevation Of Slope

During the course of traffic engineering construction, Tunnels structures represent a growing proportion of the whole line. For example, the Bridges and tunnels accounted for seventy percent in the Lanzhou-Chongqing railway, but more and more bridges with high piers appears. After crossing the river valle, Bridges will directly connect with the tunnel on the slope, As a result, these tunnels will surely cannot be located in the slope toe. Tunnel entrance always locates on the slopes that eroded by surface water.Once seismic destruction occurred, these areas would be the most easily damaged parts. Therefore, the portal elevation should be the very key parameters in the seismic design of tunnel. The tunnel with different portal elevations should have different presentation formats under the dynamical actions.and it’s same to The slop that with tunnel or not.This paper focus on the dynamic response of the tunnel portal. For the seismic responses of the mountain tunnel portal are investigated with different input wave directions, different portal elevation, different slope height and slope ratio.So different dynamic numerical simulation models was established with Midas-GTS program.the interaction of tunnel and slope will be mentioned in this article. The main research contents are as followed:(1) The models show different dynamic responses laws under three different direction seismic waves,and the wave direction includes x, y and z. The results shows that it is serious destroy on the tunnels and slop when input the x-horizontal ground motion.(2) There are Four different models which size of portal slopes are30°,45°,60°and 75°. The results showed when the portal elevation has been confirmed,the △max-y will increase with increasing toe of slope.(3) There are three different portal elevation models which the tunnels located in the slope toe or 0.3 times slope elevation and 0.6 times.the results shows that the size of portal slopes and portal elevation has certain influence on the vibration response of the tunnel.When the toe of slope has been confirmed, there is a trend that the △max-y will decrease with increasing portal elevation. The stress peak, axial force peak and displacement peak are not located at the tunnel entrance, but from the tunnel entrance away 0.4 times to 0.7 times. There are certain difference between the vault and invert.The stress peak, Axial force peak and Displacement peak of invert is farther away from tunnel entrance than the the vault. What’s more, displacement peak andacceleration peak are decreased rapidly after cross section y=40, therefore, the author puts forward that seismic amplification effect tend to stable away from 40 m to 70 m of tunnel portal.(4) Setting the pure slope that without tunnel, and make a contrast with the slope that with tunnel. The results shows that the peak displacement of the slope with a tunnel is less than that no tunnel. With the increase of the portal elevation, the dynamic response of the peak displacement is more and more evident. The acceleration curve has an inflection point at the portal elevation of the tunnel, the acceleration trend is connected with front slope angle size after the inflection point.(5) Setting different high slope mode, and studied the dynamic response of the slope and tunnel, the results shows that the dynamic response of different height slope s have the same change trend in the displacement,acceleration and stress.