Study On Settlement Of Underground Structure Constructed By Open-cut Method Under Cyclic Loading

High-speed rail can meet the needs of people’s fast travel because of its large capacity,fast speed,comfort,safety and environmental protection.According to its spatial form,it can be divided into overground high-speed railway and underground high-speed railway.In recent years,more and more attention has been paid to the development and construction of underground space in planning and construction.Complex large-scale underground comprehensive transportation hub projects and supporting underground high-speed railways have gradually emerged.In this paper,the underground transportation hub of Xiong’an New Area is taken as the engineering background,and the junction of piles and piles in the throat area of Xiong’an Intercity Station is taken as the research object.The numerical model is established by using the finite element modeling software ABAQUS,and the secondary development of DLOAD subroutine is carried out.The simulation of train dynamic load is realized,and the settlement law of surface and lower soil of tunnel under train load is analyzed.In addition,combined with the cumulative plastic deformation model of soil,the settlement value of the soil under the tunnel under the cyclic dynamic load of the train during the operation period is predicted.The results are as follows:（1）By consulting relevant literature,the causes of high-speed rail train load,the definition and classification of track irregularity are clarified.Through comparison and selection,the excitation force function method is selected to calculate the train load,and the time history curves of excitation force at three different speeds are fitted.（2）The three-dimensional finite element model was established by ABAQUS,and the train load was applied to explore the settlement law of the tunnel structure,the surface and the lower part of the tunnel.It was found that the settlement deformation of the lining floor was the largest and the settlement deformation of the roof was the smallest.The settlement deformation at the upper end of the pile foundation is large,and the settlement deformation at the lower end is small.The maximum slope of the longitudinal settlement curve of the ground surface in the throat area under the moving load of the train is 3.59×10^-6,and the maximum slope of the longitudinal settlement curve of the 0m soil under the tunnel is 3.61×10^-6.The smooth transition of the settlement curve does not mutate,and the maximum settlement occurs in the pileless area.（3）The relationship between the settlement of the ground surface and the soil under the tunnel in the non-pile area and the different lining thickness and different running speed is explored.It is found that in the cross-sectional direction,the settlement at the central axis of the tunnel is the largest,and the farther away from it,the smaller the settlement.The vertical deformation curve of the soil under the tunnel has great fluctuation.The fluctuation value of the settlement curve of the two nearest monitoring points from the tunnel is about 1.3-2 times of the stable settlement value.The settlement of the soil under the tunnel is close to 0 when the depth of the soil under the tunnel exceeds 20m.Comparing the settlement curves of the lower soil of the tunnel under three driving speeds and three lining thicknesses,it can be seen that the faster the speed,the greater the settlement of the lower soil of the tunnel;the thicker the lining thickness,the smaller the settlement.With the increase of lining thickness,the settlement growth rate gradually decreases.（4）In order to explore the long-term settlement of the tunnel under the action of train load during operation,combined with the cumulative plastic deformation model proposed by Chai,the cumulative settlement of the lower soil of the tunnel under different train speeds and different tunnel lining thicknesses was predicted by using the layered summation method.It is found that the cumulative settlement of soil increases year by year,the fastest growth rate in the first year,the operation time increases,the growth rate of soil settlement decreases year by year,and the final settlement tends to be stable.The greater the speed,the greater the settlement,and the thicker the lining thickness,the smaller the settlement.Increasing the lining thickness can reduce the cumulative settlement of the soil under the tunnel under the train load,but with the increase of thickness,the effect gradually decreases.The settlement of the pile area is the largest in the first year,and then decreases year by year.The faster the speed,the greater the cumulative settlement.After 20 years of train operation,the settlement difference between piled and non-piled areas is 8.13mm.