Study On The Influence Of Loess Flooding On The Mechanical And Deformation Characteristics Of The Utility Tunnel Structure

The construction of utility tunnel has been developed rapidly in foreign countries such as Japan,Germany and the United States.It can greatly alleviate the problem of repeated excavation of traditional municipal pipelines and make full use of the underground space resources.In recent years,with the development of urbanization in China,utility tunnel construction has been put on the agenda,but the researches on various aspects of the utility tunnel is in its infancy,especially in the special land area of our country is a major challenge.This paper mainly studies the influence of loess stratum on the stress and deformation of the utility tunnel under different soaking conditions.The research process and conclusions are as follows:(1)Through the scale shrinkage model test,the influence on the overall stress and the joint deformation law of the utility tunnel structure under different water immersion conditions is studied,which lays the foundation for the study of the follow-up foundation treatment and the control of the residual wetting quantity.Through the study,it is found that stress and internal force values under uneven water immersion condition are obviously larger than that of full width uniform immersion condition.Similarly,under the condition of uneven water immersion,the change of soil pressure is also greater than that of full width uniform immersion and the effect of uneven immersion on the stress and deformation of the utility tunnel is greater,Except for the longitudinal uneven immersion of the base,the surface settlement under other conditions exceeds the prescribed value.(2)Select the same utility tunnel as the research object,use the finite element software to establish the three-dimensional numerical model,to explore the influence of the loess layer immersion on the structure of the tunnel,and verify the reliability of the model test.Through the analysis,it is found that the numerical simulation results are basically the same as the experimental conclusions.Under different water immersion conditions,pipe segments will undergo varying degrees of deformation,especially under uneven water immersion conditions,and even under certain conditions,tensile failure will occur.The surface settlement under all conditions of water immersion exceeds 20 mm,and the pipe breaks under the in homogeneous immersion condition,and the loess foundation should be pretreated.(3)Through the comparison of the commonly used collapsible loess foundation treatment methods,combined with the construction method of the tunnel and the clear excavation method,the cement soil mixing pile is selected to carry out the foundation treatment.The control variable method is used to optimize the pile spacing(replacement ratio),treatment range and treatment depth ratio in the foundation treatment parameters.The optimal disposal parameters are as follows: the pile spacing 2m,the treatment range of 3m,and the treatment depth 6m.The optimized foundation treatment parameters are used to analyze the stress and deformation of the tube corridor structure,the surrounding soil pressure,the displacement of the gallery and the surface settlement,and the effective control of the stress and deformation of the tube corridor after the foundation treatment is obtained,which shows that the optimized foundation treatment parameters are reasonable and feasible.On this basis,through the analysis of the optimum treatment depth corresponding to different thickness of loess layer under different treatment depth,the control standard of residual collapsibility of the collapsible loess foundation of tunnel is preliminarily given by reference to the relevant regulations of subway tunnel,which provides some experience for the future related research.