| Tunnel collapse and leakage are easy to occur in the process of construction.At present,the research data on the construction technology and surrounding rock stability of the gneiss fault fracture zone tunnel in qinling mountains are relatively insufficient.How to construct this kind of tunnel reasonably and provide scientific basis and design parameters for the tunnel being built in this area is very important.This article depends on scientific research project of Transport Department of Shaanxi province,that is "Study on key technology of highway tunnel construction in fracture section in the Qinba Mountain area".Aiming at the problems of deformation and stress during the highway tunnel construction of gneiss along fault fracture zone of Taifeng highway,many research methods such as indoor experiment,field test and numerical modeling are adopted to carry out a systematic study on the key technology of highway tunnel construction in fault fracture zone of soft rock.The main research contents and results are as follows:(1)It is found that the fracture zone has dense joints with small spacing and poor rock integrity;According to the field investigation,laboratory test results and field test results,it is concluded that wall rock in the fracture zone of gneiss has the characteristics of large deformation rate,long deformation duration and large surrounding rock pressure,indicating that the surrounding rock deformation has a certain rheological property.(2)Determine the experiment plan according to the rock experiment procedure,and make the specimen according to different mechanical test.Then a series of rock mechanical properties tests,including point load experiment,uniaxial compressive strength experiment.Based on the data of point load strength and uniaxial compressive strength,the mechanical properties of surrounding rocks in the fracture zone of gneiss are evaluated.It shows that the rock mass of the broken zone has low strength and poor bearing capacity,which has a great influence on the stress and deformation of the tunnel structure.(3)Typical test sections are selected to test the deformation of surrounding rockand the stress of tunnel structure,and the time-history curves of displacement,surrounding rock pressure and steel arch stress were obtained.Then the structural stress and deformation characteristics of gneiss tunnel in the fault fracture zone are analyzed.Based on the above time history curves,it is preliminarily concluded that the deformation and structural stress increase rapidly in the early stage,the surrounding rock deformation tends to converge in the middle and late stage of construction,and the tunnel structure is in a stable state.The settlement of arch roof,right and left arch waist is about 10 cm.(4)Finite element analysis software Midas-GTS is used to simulate the tunnel construction process.By controlling the excavation cycle footage and the length of steps,the optimization and comparative analysis of tunnel construction are carried out from the aspects of deformation of surrounding rock,stress of steel arch and stress of shotcrete.The results show that the deformation and structural stress characteristics of the surrounding rock in the gneiss tunnel in the fault fracture zone are similar to the development trend of the deformation and stress in the field test,but the numerical values are smaller than the measured values.The smaller the excavation cycle footage and step length is,the more stable the tunnel structure is and the more favorable it is to restrain the deformation of surrounding rock.The vertical displacement of surrounding rock is obviously larger than the horizontal displacement,indicating that the deformation of surrounding rock is mainly in the vertical direction. |
