Study On Deformation Characteristics Of Weak Surrounding Rock And Supporting Opportunity In A Tunnel Of Chenglan Railway

Large deformation,distortion of steel arch,cracking of concrete and invasion of support system are easy to occur in deep buried soft rock tunnels with high geostress,which results in support replacement and cross-section expansion,which seriously affects the progress,quality and cost of tunnel construction.Based on the monitoring data of a tunnel construction in Chenglan Railway,combined with field investigation data and indoor experiments,this thesis develops a monitoring and measuring database system for tunnel,analyses the deformation characteristics of the tunnel,chooses typical sections for back-analysis of creep parameters,and discusses the reasonable time of tunnel support based on convergence-constraint method.Specific research contents and results are as follows:(1)This thesis completes the research and development of tunnel monitoring and measurement database system.MongoDB which is a kind of NoSQL database management system is used to establish tunnel monitoring measurement database,and using Python programming to realize database query graphical interface,including user login,cross-section data query,interval extremum query and target data download functions.Relevant interfaces for subsequent version development iterations are reserved.(2)The statistical bandwidth of histogram of vault settlement extremum is optimized by MISE.The statistical results show that the bandwidth difference of different construction methods at the same rock level is small.According to the statistical histogram,the surrounding rocks of grade IV,V and V are divided into one interval,four intervals and five intervals respectively.The surrounding rock of grade V(step method)and V(step method)are divided into five intervals.The extreme value of vault settlement development is not uniform;The time required for vault settlement deformation of some sections to reach stable state is inconsistent with that of convergent deformation of arch waist,while some sections almost reach stable state at the same time.(3)Using the built-in scientific calculation toolkit in Python,the time history data of vault settlement are fitted by the least square method.The results of different formulas are different in the degree of compliance with the time history curve of each section.Univariate Spline function is applied to extrapolate the time history curve of tunnel deformation.Compared with the fitting result of the formula,the fitting degree of this method is ideal.For most typical sections,the extrapolation result of this method is stable and has certain reference value.(4)The creep parameters of rock mass are inverted by GRNN generalized regression neural network.The inversion results are compared with the measured data.The results show that the time history curve of surrounding rock deformation calculated based on the inversion regression parameters has little difference with the measured data,which proves that the inversion parameters meet the current calculation requirements.(5)The elastic-plastic characteristic curves of surrounding rock at different positions of D5K222+235 section and the plastic zone distribution of corresponding stress release rate are calculated.When the stress release rate is about 60%,the surrounding rock begins to enter the plastic state from the elastic state;after the surrounding rock enters the plastic state,with the stress release of surrounding rock,the plastic zone gradually enlarges,and when the stress release rate reaches about 73%,the failure zone begins to appear.(6)The stability of support structure in different positions of tunnel section is analyzed: the restraint force of initial support structure of tunnel is mainly borne by shotcrete,the rigidity of initial support structure is high,the ultimate strength is low,and it can not reach the equilibrium state with the stress of stratum;when the second lining is set,the bearing capacity of support structure is larger than the stress of stratum,which can make the support system of tunnel reach equilibrium,and the stability of each point of section.The qualitative coefficients are all greater than 1.6.(7)Based on the convergence-restraint curve,the development of plastic zone in surrounding rock and the stiffness of supporting structure,the supporting opportunity is determined.For D5K222+235,the supporting system must reach equilibrium state before the stress release of surrounding rock is about 73%(i.e.the vertical settlement of surrounding rock vault reaches about 121.86 mm).According to the convergence constraint curve,the opportunity of the initial support facilities should be before the unlined tunnel displacement A point 76.10 mm,B point 65.02 mm,C point 72.95 mm,D point 39.51 mm,E point 64.10 mm,so as to ensure that the surrounding rock does not appear failure state.