Study On Stability And Deformation Control Of Softrock Goaf Under High-speed Railway

There are many problems in the high-speed railway crossing the goaf,and there are relatively few research cases on the high-speed railway crossing the soft rock and coal mining subsidence area at the same time,and systematic research method including survey detection,stability evaluation,hidden area management and roadbed reinforcement have not been formed.Therefore,systematic and in-depth research on this aspect has important theoretical significance and practical engineering value.This paper relies on the Nanning section of the Guinan High-speed Railway to cross the soft rock mining subsidence area project,systematic research has been carried out on the stability of the goaf,detection of hidden danger areas,stratum activation deformation,control of hidden danger areas and roadbed reinforcement through the methods of investigation and survey,theoretical calculation,numerical simulation and laboratory test.The main research contents and conclusions are as follows:（1）Through historical data analysis and site survey,preliminary analysis shows that the collapse and bending deformation of the original goaf have basically completed,and most areas of original goaf have been filled with water-bearing silt or collapsed mudstone.Based on the factors of comprehensive line selection,project overview,social impact,and cost of demolition,the line plan 3 is selected from the original three planned routes as the high-speed railway planning route.（2）The stratum deformation and surface settlement caused by the mining of Shangjiu Nine Coal Mine in Dapanjing were analyzed through the combination methods of theoretical calculation and FLAC^3D numerical simulation.Comparing the results of calculation and simulation,we can know that the maximum ground settlement in the goaf of Dapanjing can reach 1319.10mm,and the maximum horizontal deformation is 457.19mm.In addition,the existence of the Wangshengling normal fault in research area will lead to different degrees of stratum deformation.The stratum below the high-speed railway planning line is affected by mining deformation.（3）The stability of the original Dapanjing goaf was analyzed and evaluated by the analysis of the mining time,the concentrated movement deformation and the residual deformation calculation.The surface movement of Dapanjing goaf is about 500 days,and it is known that the goaf has reached initial stability compared with the 37-year final mining time.It is further estimated from the original Knothe time function that the surface subsidence of the Dapanjing goaf has been completed within 5 years after the mine closed,reaching the stable period of concentrated moving deformation and entering the residual deformation period.According to the formula derived from the limit sinking curve,the deformation parameters of the residual deformation period are calculated,and combined with the calculation results of the centralized movement period,it is concluded that the various indicators of Dapanjing goaf meet the site stability requirements at the same time,and the goaf has reached a stable state without being disturbed by external loads.（4）The geophysical method combined with seismic mapping method and high-density resistivity method is used to detect the distribution of residual hidden danger zone,and the reliability of geophysical results is verified by drilling.The residual hidden danger zone has been filled with collapsed mudstone or water-bearing silt,the existence of the residual hidden danger zone may aggravate the stratum deformation under the upper load.（5）The influence of the existence of residual hidden danger zone under load on the stratum deformation is simulated by FLAC^3D software with different working conditions.The existence of residual hidden danger zone will adversely affect the stratum deformation,the worse the filling property is,the larger the subgrade post-construction settlement is,and the maximum additional settlement deformation value in the simulated working condition is 61mm.The settlement deformation under all working conditions is basically the same（22²3mm）after applying high-speed railway load,and there is no further settlement under the influence of the residual danger zone,it is analyzed that the stress generated by the high-speed railway load is hardly transmitted to the residual hidden danger zone.Due to the water filling condition in the residual hidden danger zone,new cracks may be formed in the surrounding stratum of the residual hidden danger zone under the external load,causing water body seepage and aggravating the stratum deformation.（6）The residual hidden danger zone is treated by the full cementing grouting method,and the high-speed railway foundation is strengthened by the pile-slab composite structure on the basis of the completion of the residual hidden danger zone.FLAC^3D software was used to simulate the roadbed reinforcement effect,it was found that the pile deformation and side friction resistance played a normal role under load,and the maximum settlement value of the subgrade surface is 8.6mm,in which the subgrade settlement is 5.2mm,and the settlement under the high-speed railway load is increased by 3.4mm,which can meet the requirement of“post-construction settlement should not exceed 15mm”in the high-speed railway design specification.The composite structure of pile-slab is effective in the reinforcement of soft rock roadbed.