Research On Dynamic Supporting Parameters Of Heigang Metro Tunnel Against Monitoring Measurement

With the China’s economic construction development rapidly,the continuous expansion of city and the urbanization level improved.a large number of underground rail transits have been constructed to solve the "bottleneck" problem that traffic congestion brings to urban development.Tunnels as the most important part of the underground rail traffic,There are many unforeseen factors in the construction.It is very necessary to discuss the tunnel support parameter to ensure the safety of the tunnel constructionThis paper takes the subway tunnel of the first phase of Chongqing Rail Transit Line No.4 for the engineering background,we have monitored the measurement of tunnels.According to the monitoring information,the parameters of support I-beam,shotcrete thickness,the length of the upper and lower step anchors were studied of the section YK23+815 and section YK23+845.The main results are as follows1.Using the software of SPSS and MATLAB processing and regression monitoring data,the data show that the accumulative value and deformation rate of surrounding rock deform exceed 85 of the control value,which has reached the orange alert.By regression fitting the effect chart,the prediction of surrounding rock deformation is still in the rising stage,the surrounding rock does not converge2.Introduced the design of tunnel site monitoring measurement scheme;Do use software SPSS and MATLAB to the convergence of the section of YK23+815 and section of YK23+845 surface data processing and regression analysis,the data show that surrounding rock deformation of the cumulative value and the deformation rate of more than 85%of control values,has reached the orange alert,through regression fitting effect picture,to predict the surrounding rock deformation is still in the rising stage,the state of surrounding rock is no convergence.3.Using MIDAS/GTS software to simulate the tunnel construction process of section YK23+815 and section YK23+845.The displacement,plastic zone,anchor axial force and initial branch stress of the surrounding rock during were extracted in each construction stage.the simulation results were close to the on-site monitoring results,numerical simulation results show that the design of tunnel monitoring measurement scheme and construction method are reasonable,but the initial support parameters design does not meet the needs of the support strength,it is necessary to change the initial support parameters.4.Seventeen working conditions are established for section YK23+815 to study and analyze the support parameters of I-beam steel,the thickness of shotcrete and the length of bolt,we got these change results that the initial supporting parameters of section YK23+815 are I-steel I22a,the thickness of shotcrete is 27cm,the length of bolt is 3.5m.The monitoring information was functionally treated,the dangerous point of surrounding rock deformation is obtained as t=4 which corresponding to the upper stage of construction.The research order of supporting parameters is I-steel,concrete thickness and bolt length.Through the initial supporting parameters changing,the integrity and stability of surrounding rock are improved,making the deformation of surrounding rock convergence,eliminates the orange alert.5.The thickness of shotcrete and the length of upper and lower step anchors are studied and analyzed under 12 working conditions of section YK23+845.The results show that the thickness of shotcrete is 27 cm,the length of length of the upper step bolt is 4.0 m,and the length of lower step anchor bolt is 2.5 m.According to the functional monitoring of on-site monitoring information,combining with the characteristics of"S-type" and "factory-type",the research methods of supporting parameters are determined to increase the support strength of the upper step and reduce the support strength of the lower step.The results show that the strength of the initial support structure and the stress of the support structure are improved by changing the parameters,which effectively restrained the surrounding rock deformation,made the deformation into a convergent state,and eliminated the potentially dangerous problem of tunnel.According to all of the result,Compared the changed support scheme to the initial design scheme.The changed version played well self-bearing capacity of surrounding rock,the displacement of the surrounding rock decreases,and the initial compressive stress of the support structure and the axial force of the anchor bolt become smaller,the initial tensile stress of the support structure is slightly larger,but both are less than the allowable value.which ensures the safety of the tunnel construction.The research results of this paper provide references for the design and construction of similar projects in the future.The results of this paper can provide reference for design and construction foe similar projects.