Stability Of Surrounding Rock Of Dolomite Tunnel With Different Inclinations And Optimization Of Bolt Support In Suspension Area

As a kind of sedimentary rock widely occurring in Guiyang area,bedded dolomite contains complex mineral composition,natural cracks and muddy development,and obvious bedding structure.As a result,the rock mass has heterogeneity and anisotropy,which greatly affects the stability of the muddy dolomite tunnel.Therefore,it is necessary to study the mechanical properties of argillaceous dolomite through experiments to obtain the strength characteristics and fracture morphology of argillaceous dolomite under the influence of bedding.With the construction of Guiyang Rail Transit,it is of great theoretical significance and engineering value to study the stress distribution,stability and failure mode of surrounding rock at different intersection angles between dolomite tunnel and bedding,and to explore reliable and reasonable support measures under different failure modes.The research content of this paper comes from the National Natural Science Foundation of China(NSFC)"Stability Analysis of Surrounding Rock and Supporting Measures for bedding controlled Dolomite Tunnel"(51608141).Based on the railway station-Shachong Road Station Interval Tunnel(hereinafter referred to as Huo-Sha Tunnel)project of Guiyang Rail Transit Line 1,the mechanical properties of stratified dolomite and stratified dolomite are studied by means of laboratory test and numerical simulation.The stability of surrounding rock of rock tunnel is studied.The main contents are as follows:(1)Based on Huo-sha Tunnel Project,the Brazilian fracturing and uniaxial compression tests were carried out on the bedded argillaceous dolomite.The test results show that the tensile strength,compressive strength,splitting modulus and elastic modulus of the argillaceous dolomite with different bedding dips are discrete.The inclination angle of fragile bedding is 22.5 45 and the average compressive strength is about 18.97 times of the average tensile strength.With the characteristics of elastic brittle failure and hard rock,the specimens are split into two halves along the loading direction under Brazilian splitting test,but the failure modes of uniaxial compression test include splitting failure,compression-shear slip failure and crushing failure.(2)The stability of surrounding rock of bedded dolomite tunnel is studied by using finite element software.The influence of six factors on the stability of surrounding rock of tunnel is analyzed,such as the dip angle of different strata,the thickness of dolomite strata,the thickness of contact interlayer,the elastic modulus of contact interlayer,the internal friction angle of contact interlayer and the cohesion of contact interlayer.It is found that the displacement of surrounding rock is the largest at the dip angle of 22.5 degrees,and the interlayer peeling is obvious.The plastic zone of surrounding rock concentrates in the suspended zone of tunnel,and the contact interlayer has a weakening effect on the displacement of surrounding rock and the expansion of plastic zone.The influence of the thickness of dolomite and contact interlayer on the displacement of surrounding rock varies with the apparent dip angle.Increasing the elastic modulus of contact interlayer can reduce the displacement of surrounding rock,increasing the friction angle of contact interlayer has little effect on the displacement of surrounding rock,and increasing the cohesion of contact interlayer can.Reduce the displacement of surrounding rock.(3)The numerical model is constructed with the main parameters of bedding dip angle 22.5 degree,dolomite layer thickness 0.5m and contact interlayer thickness0.05 m.Two optimization schemes are proposed,i.e.bolt lengthening without densification and bolt encrypting without lengthening,aiming at the concentrated area(suspended area)of displacement and plastic zone of tunnel surrounding rock.The calculation shows that the bolt lengthening and non-dense scheme can effectively reduce the displacement and plastic zone of the surrounding rock in the suspended zone,and the stress distribution of the surrounding rock is more uniform.