Study On The Interaction Between Foundation Pit Support Structure And Adjacent Subway Tunnel

Nowadays,the urban subway system extending in all directions provides a lot of convenience for people’s travel.However,with the increasing shortage of urban land,it is inevitable to construct close to the subway tunnel,such as foundation pit engineering.How to excavate the foundation pit under the condition of ensuring the normal operation and construction safety of the subway tunnel has become a problem that needs to be deeply studied.At present,the research on the interaction between the foundation pit support structure and the adjacent subway tunnel often does not consider the influence of subway train vibration,and it is found that this influence should not be ignored in the project.Therefore,starting from this problem,this paper focuses on the influence of retaining wall movement and subway train vibration on the support structure and the earth pressure around the tunnel,and studies the distance between the tunnel and retaining wall through numerical simulation When the three parameters of vibration frequency and vibration times change,the change law of the influence of vibration on earth pressure provides a certain reference for similar projects in the future.The main conclusions of this paper are as follows:(1)In the mode of translation and rotation of the retaining wall,with the increase of retaining wall movement,the amplitude of vertical acceleration and horizontal acceleration perpendicular to the tunnel direction on the top of retaining wall caused by subway train vibration increase continuously,while the amplitude of horizontal acceleration perpendicular to the tunnel direction on the top of soil body increases,and the amplitude of vertical acceleration fluctuates within a certain range.(2)The influence of vibration on the horizontal earth pressure on the side wall of retaining wall is closely related to the state of soil behind the wall.When the retaining wall does not move,the subway train vibration has little effect on the earth pressure behind the wall;The train vibration load applied after the movement of the retaining wall will increase the earth pressure on the back of the wall,and the greater the movement of the retaining wall,the greater the change of the earth pressure;When the soil behind the wall reaches the active limit state,the influence of vibration on earth pressure reaches the maximum;There are three extreme points of the change of earth pressure on the back of the wall caused by vibration,which are located in the shallow soil layer,the depth of the tunnel and the 45° diffusion angle under the tunnel.(3)When the tunnel is located in the sliding surface,with the movement of the retaining wall,the earth pressure at the four control points(i.e.0°,45°,180°,225°)around the tunnel parallel to the sliding surface increases gradually under the influence of sliding force,while the earth pressure at the four control points(i.e.90°,135°,270°,315°)perpendicular to the sliding surface decreases gradually.Vibration will increase the earth pressure around the tunnel,and the influence of vibration becomes more and more obvious with the increase of retaining wall movement;The earth pressure around the tunnel is greatly affected by vibration at the position perpendicular to the sliding surface,while the earth pressure at the position parallel to the sliding surface is less affected by vibration.(4)When the distance between the tunnel and the retaining wall increases,the influence of vibration on the earth pressure of the retaining wall decreases obviously,while the influence of vibration on the earth pressure around the tunnel changes little.When all or part of the tunnel is located in the slip surface,the influence of vibration on the earth pressure of the retaining wall is more sensitive to the spacing.At this time,the influence of vibration will be greatly reduced if the spacing is slightly increased;When the tunnel is outside the sliding surface,the influence of spacing is greatly weakened.(5)The variation of vibration frequency and vibration times will affect the accumulation of earth pressure on the retaining wall.When the peak load and the number of vibration are the same,the lower the frequency,the more the earth pressure on the retaining wall increases.When the frequency is higher,the influence of vibration on earth pressure is relatively small;With the increase of vibration times,the horizontal earth pressure on the side wall of the retaining wall presents a three-stage growth mode,which is rapid growth stage,slow growth stage and stable stage respectively.