| Gansu is an important channel connecting east and west,and mudstone is widely distribu ted.Due to the special stratigraphic distribution and hydrogeological conditions,there are a lar ge number of geological conditions of loess-mudstone interface in the loess area of Gansu Pro vince,which makes the construction of tunnel engineering face various design and constructio n control technical problems when crossing the loess-mudstone interface.Due to the differenc e of lithology between loess and mudstone,the expansion characteristics of mudstone and the secondary or multiple redistribution of groundwater caused by various geological and hydrolo gical reasons,the mechanical and deformation characteristics of surrounding rock change grea tly,resulting in serious deformation and failure of arch support structure and inverted arch flo or heave,which brings great challenges to the design and construction of tunnel.It is urgent to carry out further research on this problem.Therefore,it is of great scientific significance and engineering practical value to study the mechanism of inverted arch floor heave in loess muds tone boundary stratum and put forward the countermeasures and disposal measures of deform ation.The purpose of this paper is to explore the disease and control technology of inverted arc h floor heave caused by the difference of loess mudstone lithology and the water expansion ch aracteristics of mudstone when the highway tunnel passes through the loess mudstone compos ite stratum.By means of literature research,numerical simulation,model test and field monito ring,the influence of the relative position of loess mudstone interface and tunnel on the defor mation of surrounding rock and structural stress is discussed.The model comparison test of in verted arch floor heave in pure mudstone stratum and loess mudstone boundary stratum was c arried out.A tunnel of Tianzhuang Expressway was monitored and measured,and the deform ation law and stress characteristics of surrounding rock and supporting structure of the tunnel were analyzed.Under the condition of the most unfavorable loess mudstone boundary stratum,combined with the expansion characteristics of mudstone in the tunnel basement,the bearing and deformation characteristics of the inverted arch and the control measures of deformation a re studied.The main work and research results are as follows :(1)Based on the numerical simulation software,the numerical model of different relativ e positions between the loess-mudstone interface and the tunnel is established.The influence o f the loess-mudstone interface position on the deformation of the tunnel surrounding rock and the stress of the lining is analyzed,and the most unfavorable loess-mudstone interface position of the inverted arch structure is determined.(2)According to the most unfavorable interface position of inverted arch stress,combine d with the expansion characteristics of mudstone,the expansion model test and comparative a nalysis of pure mudstone stratum and loess mudstone composite stratum are carried out to obt ain the variation law and distribution characteristics of lining strain,tunnel displacement and s urrounding rock pressure.Then,combined with the failure characteristics of tunnel lining stru cture,the deformation mechanism of tunnel floor heave in loess mudstone composite stratum i s revealed.(3)According to the tunnel monitoring measurement data,the deformation law and stress characteristics of the surrounding rock and supporting structure of a tunnel in Tianzhuang Ex pressway are analyzed.(4)According to the most unfavorable position of the loess-mudstone interface of the inv erted arch,considering the expansion characteristics of the mudstone,a numerical model of th e expansion and deterioration of the mudstone in the loess-mudstone composite stratum tunnel is established,and the locking feet and floor bolts with different longitudinal spacing are used as the floor heave control measures to evaluate its control effect. |
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