Dynamic Response Analysis Of Rock Tunnel Slope In High Intensity Area

China’s mountainous area is the majority,and the highlands,mountains and hills account for about 69% of the country’s total land area.In recent years,a large-scale of foundation projects are bound to be built around mountain faults and earthquake-prone high-intensity areas.On May 12 th 2008,a sudden earthquake occurred in Wenchuan,with a magnitude of8.0.The earthquake caused the collapse of many slopes of the tunnels,and buried the tunnel holes,which added difficulties to the rescue after the disaster.The entrance of the tunnel is the "Throat" of the whole tunnel,which is particularly important.Once blocked or buried,it will seriously affect the implementation of post-earthquake rescue.Therefore,it is more and more important to study at the dynamic response of slopes of the tunnel entrance under the earthquake.By consulting a lot of documents,the general situation of ten earthquake landslides in China in the last 20 century and the geological disasters induced by earthquakes in recent years are summarized in the article,and the paper analyzes and generalizes the failure mode and mechanism of rock slope in high intensity area under earthquake action.The factors affecting slope instability are also summarized.Then,a 3D finite element numerical model is established by using Midas GTS NX based on the construction of the entrance of the Erla Tunnel of the Lalin Line,and they are investigated about the effects of different seismic waves and different ground motion parameters(amplitude,frequency spectrum and duration)on the dynamic response characteristics of rock tunnel entrances with joints.Finally,find out the weak positions by comparing the static stability analysis of rock slope before and after excavation,and strengthen the slope of the tunnel entrance,and also analyze the dynamic response characteristics and variation law of the slope of the tunnel under the variation of ground motion parameters.And these would provide a reference for seismic design of rock tunnels with different seismic parameters in high intensity region.The main conclusions are as follows:(1)By inputting three kinds of typical seismic wave records,it can be seen that the distribution of displacement and acceleration of tunnel vertical slope and lining structure are obviously different because of the difference of ground motion parameters(amplitude,frequency spectrum and duration)under the action of different seismic waves.(2)The amplitude of the original seismic wave is reduced to 0.8,0.6 and 0.4 times by adjusting the amplitude coefficient of the seismic wave generator in Midas GTS software.The results show that the amplitude can amplify the displacement and acceleration of the slope.With the increase of amplitude,the displacement and acceleration of the corresponding monitoring points are magnified,which indicates that the stronger the seismic wave intensityis,the more destructive it is to the slope body.(3)By changing the time coefficient of the seismic wave generator,the spectrum characteristics of the seismic wave can be changed.It is found that the low frequency band of seismic wave can amplify the displacement response of rock tunnel’s upside-slope,and the lower the excellent frequency of seismic wave is,the greater displacement response.The high frequency band of seismic wave can amplify the acceleration response of rock tunnel’s vertical slope,and the higher the excellent frequency of seismic wave is,the greater acceleration response.(4)The duration of seismic wave duration has a great influence on rock slope.In this paper,the duration of the original seismic wave is processed into 41.44 s and 28.70 s,which are loaded respectively.It is found by calculation that the durative time has a magnified response to the displacement of the monitoring points of the tunnel’s upside-slope,but has little response on the acceleration response of the top and surface of the upside-slope.That is,hat is,the longer the seismic wave duration is,the more serious the accumulation of displacement in the slope caused by earthquake is,increasing the probability of slope instability during earthquake.(5)After the excavated tunnel’s upside-slope is protected and strengthened,by changing the ground motion parameters,it is found that both the upside-slope’s displacement and acceleration have been greatly improved,indicating that bolting and shotcrete,reinforcement measures on the slope,can effectively restrain the development of the dynamic response of the slope and increase its stability.