Research On New Support Form And Excavation Method For Large-section Small Spacing Tunnel In Loess

It is always a difficult problem to engineering in the construction of large-section and small spacing tunnel in loess.So that the depth research has been carried out on adaptability of double-arched tunnel in loess and small spacing tunnel in loess.In the meantime,the research was also performed on reasonable spacing,the effect on the construction of later tunnel to that of the former tunnel,the support system and the construction method of large-section small spacing tunnel in loess.We have associated with Tao Huayu tunnel of Wu Xi highway in Henan and made thorough studies,through research results,engineering analogy,theoretical analysis,numerical model and methods of field test and in-situ test.Mainly working content and research results are as follows:(1)Through engineering analogy to the previous works,we have compared double-arched tunnel with small spacing tunnel,combining with the suitability of Loess Tunnel.Associating with Tao Huayu tunnel engineering,we have established an analysis model of a three-dimensional finite element,analyzed the regularity on the force and deformation of the surrounding rock in the tunnel during the excavation of double-arched tunnel and small spacing tunnel.And then,the small spacing form has been taken as reasonable structure in the Tao Huayu loess tunnel.(2)In order to Tao Huayu loess tunnel as engineering background,through theoretical analysis and in-situ test,the laws are studied on the deformation and stress of large-section and small spacing tunnel in loess by the CD excavation method.The stability is analyzed on surrounding rock under different small spacing tunnels.It is concluded that the minimum distance should be set to 4.38m(Single tunnel excavation span is 17.5m).(3)In the course of construction adopting CD excavation method,the test sections are analyzed by test,where the spacing distance between two tunnels is 5m,where the distance between two tunnel faces is about 1.5D.The research shows that the construction of the later tunnel has a little influence on that of the former tunnel.(4)We set two compared test sections:one is that the steel arch support system compares with grid steel support system test section,the other is with/without systematic bolts test section.In the test sections,tunnel vault settlement,horizontal convergence,surrounding rock pressure,supporting structure internal force are tested.And then comprehensive comparative analysis of test data has been done.When early strength of sprayed concrete is greater than the required strength,the controlling deformation capacities of the two kinds of supporting systems are similar,therefore,which all could be applied to large-section small spacing tunnel in loess.Through comprehensive comparison of the testing result with/without systematic bolts,it is found that there was little improvement of supporting effect on the systematic bolts in large-section and small spacing tunnel in loess,thus systematic bolts can be cancelled to quicken the enclosed time of the initial supporting section of the tunnel.And it also will be helpful for controlling the supporting settlement and deformation.(5)Through the study on bilateral wall excavation method,CD excavation method and bench excavation method,the method of finite element numerical simulation and in-situ test,we innovatively put forward the construction method of CD excavation method of the vertical partition wall.It is found that method would be helpful for controlling crown settlement of the large span flat tunnel.The construction efficiency has been improved.