Research On The Simulation Of The Excavation Deformation And The Internal Force Of Support Structure In Loess Tunnel

Loess is a special kind of soil widely distributed in western China.With the development of One Belt One Road policy in recent years,the construction of highway and railway in loess region has been rapidly developed,and the use of loess tunnel is becoming more and more common.Research on rock tunnels in China was conducted earlier,the relevant theories and practices are relatively abundant and mature.The design and construction of loess tunnels is currently dominated by engineering analogies,though the development is relatively fast in recent years,the theoretical system is not yet perfect and needs to be further improved.Therefore,it is necessary and urgent to carry out relevant research.This paper used finite element simulation as the main method,selected a reasonable constitutive model,and studied the influence of construction method,support parameters,flat ratios,and buried depth on the excavation deformation of loess tunnel and the internal force of supporting structure,and practical engineering data were combined to carry out the comparative analysis.The conclusion of the study provides theoretical guidance and reference for the engineering practice of loess tunnel,which has good academic value and practical significance.(1)UH model is selected as the constitutive relation of numerical simulation.The tunnel dynamic excavation model was established by ABAQUS software to study the influence law of the length of foot anchors,the angle of the foot anchors,and the space between the steel frames on the loess tunnel deformation and the internal force of the supporting force under three construction methods of three-bench seven-step excavation,double side draft method and single side draft method.Through comparative analysis,it was found that in three-bench seven-step excavation method,the length of the foot anchors had little effect on the loess tunnel deformation and the internal force of support structure,but the effect of the foot anchors angle was obvious,and the steel frame spacing has little influence on the loess tunnel deformation,but had greater impact on the internal force of the support structure.In the double side draft method and the single side draft method,the length of the foot anchors had little effect on the deformation of the loess tunnel,but had a significant effect on the internal force of the support structure.The angle of foot anchors and spacing of the steel frame had significant effect on the deformation of the loess tunnel and the internal forces of the supportstructure;In terms of the stability and safety of the loess tunnel excavation,the double-sidewalk method is more effective than the other two methods in controlling the deformation of the tunnel.Therefore,the double side draft method can be used priorly in the construction of the tunnel when the tunnel deformation is strictly requested.(2)this paper also simulated the effect of flat ratios on the stress-strain relationship of loess tunnels under the same construction method and support parameters.It is found that oversize or undersize flat ratios are not beneficial to the stability of loess tunnels.According to the research results and formerly practical experience of the tunnel,the stability of the tunnel is better when the flat ratio is between 0.56 and 0.69.(3)this paper summarized the existing demarcating methods for the deep and shallow burial of the tunnel,and selected several typical calculation methods in combination with the actual project for calculation and analysis.At the same time,the effect of buried depth on the deformation of loess tunnel and internal force of the support structure was studied under the same construction method,support parameters,and flat ratio.The results show that the theoretical calculating value of Bill Bowman was the largest,and there was little difference between the theoretical calculation value of Xie Jiaji and the calculated value of the tunnel design specification;With the increase of the buried depth,the loess tunnel deformation and the internal forces of support structure showed increase with different degrees.