| Since the new century,Chinese earthquake disaster has occurred,in view of the special physical and mechanical properties of loess in the northwest region and the complex geological conditions and geographical environment where is an area with frequent earthquakes and landslides,however,with the development of the western development strategy in full swing,there will be a large number of transport infrastructure construction in the loess region,such as the new railway Baoji-Lanzhou Passenger Dedicated Line,located in two provinces of Shanxi and Gansu,Line length of 401.71 km,which has 78 loess tunnel,the total mileage reached 273 km,accounting for nearly 70% of the length of railway line.Because the tunnels are mostly distributed in the valley,so there is the phenomenon that many high bridges connected with high tunnel.Many bridge reach tens of meters high or even hundreds of meters,therefore,there is tunnel in the different portal elevation,it is closely related to the safe operation,the seismic performance and the rapid repair after the earthquake.There are some differences in the dynamic response of the tunnel in the loess slope under different portal elevation,so it is very important to study the dynamic response of the tunnel entrance in different portal elevation.In this paper,the numerical simulation and large scale shaking table model test are used to the research.In the numerical simulation,the dynamic response laws of portal section in different portal elevation and different slope angle were studied;In the shaking table model test,the main consideration was focused on(we mainly take consideration on)different portal elevation under the 60 degrees of slope,to study the stability of loess slope failure and the tunnel portal section of the force characteristics.The following aspects are mainly discussed:(1)Referring to the domestic and foreign related literature about the classification of tunnel portal damage,through preliminary statistical summary,summarizes the types of earthquake damage and damage mechanism of tunnel lining and portal slope,to provide reference theory basis for the subsequent numerical calculation and model test results.(2)There are four different models which slope angle are 30°,45°,60°and 75° to study the dynamic response laws of portal section.Analyzing the acceleration and displacement of slope,variation of magnifying coefficient under the different slope angle,and discussed the tunnel lining structure stress and deformation characteristics in each slope,including the variation trend of acceleration,displacement and stress along the tunnel axis.From the result,we can get the conclusion that the greater the slope angle,the lager the slope displacement and the displacement of monitoring points in portal section and the maximum slope displacement and the maximum displacement monitoring points in portal section appear in75degrees;the acceleration and the displacement monitoring points with the whole slope increases.The acceleration of the slope and the acceleration of the monitoring points at the portal section are decreased with the increase of the slope angle.(3)There are three different portal elevation which are foot,0.3Hand 0.6H,to study the dynamic response laws of portal section in large section loess tunnel.The variation law of the acceleration,displacement and amplification coefficient of the slope and the portal section at different working conditions are discussed.The results show that the influence of the portal elevation on the displacement and acceleration of the slope is small,but the displacement and acceleration of the lining have a greater influence;With the increase of the portal elevation,the maximum stress peak decreases gradually,and the maximum stress appears at the foot of the peak.(4)In order to prepare for the shaking table model test,according to the relevant requirements of ?Code for soil test of railway engineering?,the physical parameters of the test model are determined,include water content,density,optimum moisture content,maximum dry density,cohesion,internal friction angle,liquid limit and plastic limit,etc..Based on the shaking table test in the relevant literatures,this paper designs the experimental model of the study and makes the test plan.etc..(5)Carrying on shaking table model test.The model test was carried out by using the4m*6m electric servo shaking table of Lanzhou Institute of seismology,China Earthquake Administration.We study the stress characteristics and failure process of the slope and the lining structure of loess tunnel portal section at portal elevation of foot and 0.5H when slope is 60 degrees. |
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