| Portal of mountain tunnel located at high intensive earthquake zone is prone to seismic damage,especially when crossing areas with adverse geological or geological conditions that have changed significantly,and tunnel structures are more likely to suffer damage during earthquakes.At present,rare studies have been focused on mountain tunnels with ground shaking more than 0.4g at home and abroad,and there are few provisions in the existing code system for the design of strong earthquake areas.The code is only applicable to areas with ground motion less than 0.4g.As a national strategic project,a line of oil pipeline tunnel projects in Central Asia is located in one of the most active regions of geological structure in the world.The intensity of regional earthquake and the complexity of geology and terrain are far more than any project encountered at home and abroad in the past.Therefore,based on a line of oil pipeline tunnel projects in Central Asia,by using data investigation,theoretical analysis and numerical simulations to study the dynamic characteristics and anti-seismic measures of the tunnel portal crossing anti-dip fault,under the action of PGA=0.6g ground shaking.The details of the study are as follows:(1)A study of the dynamic characteristics of two types of fault effect,namely anti-dip fault and inclined fault,considering the tendency effect of the fault.The analysis not only considers the acceleration and velocity amplification effects of the elevation slopes of the two fault dips under the action of different seismic waves,but also investigates the displacement and stress response characteristics of the elevation slopes under the action of different seismic waves,and concludes that the anti-dip fault is the more unfavourable fault effect.(2)The dynamic response characteristics of the tunnel opening structure under different elevation slope angles and interface inclination angles were studied by means of numerical simulations,and it was concluded that: with the increase of elevation slope angles,the stress response and displacement response of the tunnel structure increase,and the plastic zone of the surrounding rock increases;with the increase of interface inclination angles,the stress response and displacement response of the tunnel structure decrease,and the plastic zone of the surrounding rock decreases.The minimum principal stress amplification factor was used to determine the reasonable influence zone of typical tunnel structure,that is the location from the tunnel entrance to the intersection and the 4D(D is the tunnel span)range of the intersection along the longitudinal direction of the tunnel are the main influence zones.(3)Research on different anti-seismic measures for the tunnel entrance section passing through the anti-dipping fault tunnel structure has been carried out.The research analyzes the anti-seismic effect of different seismic joints,different thickness of damping layer and different thickness of grouting reinforcement.The results show that the installation of seismic joints significantly reduces the stress response of the tunnel structure,but the displacement response increases.The seismic effect of the circular seismic joints parallel to the inclination of the rock interface is better than that of the conventional vertical circular seismic joints;Setting the damping layer reduces the stress response and displacement response of the tunnel structure,but the reduction in the displacement response is relatively small.The thickness of the damping layer is more suitable to be 10?15 cm;Grouting reinforcement of the surrounding rock can effectively reduce the stress and displacement response of the tunnel structure.When the thickness of the grouting circle reaches a certain value,the reduction effect tends to stabilize and no longer increases. |
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