Study On Structural Stability Of Concealedkarst Shield Tunnel During Operation

Itcan provide an important guarantee for the safe operation of shield tunnel in karst areawithstudying on the deformation and stress of segment structure and stratum state under theaction of threefactors of karst geologicalvariation,metro train vibration and accidental earthquake.In view ofthe lack,based on the karst geology of Guangzhou Metro Line 9,thisarticleanalysis the dynamic response of segment and stratum when the size and distance of the hidden cave change under the action of metro train vibration and accidental earthquake.It is also studyed the fatigue life of the segment structure and the cumulative settlement of cave fillingsbelow the tunnel basementcombined with empirical formula,the results are as follows:(1)Based on the deformation and strength criterion of tunnel segment structure during the operation period,the dynamic responses of the segment under train vibration and accidental earthquake are analyzed.The results show that the deformation and stress of the segment structuremeet the limit requirementsthroughthe whole numerical solution of the cave exists around the tunnelunder train vibration,the stress intensity of the segment does not meet the limit requirement in partial numerical test scheme under earthquake dynamic loading.Based on it,the safety distance and the critical height of the cave are obtained,which meet the stability requirement of the segment strength of the shield tunnel during accidental earthquake.(2)Through the analysis of the maximum shear strain distribution of the strata under the action of train vibration and accidental earthquake,clearing the safety distance and the critical height of the cave by the breakthrough trend of thethe maximum shear zone where is the finite rock columnbetween the cave and the tunnel.(3)Under the repeated train vibration,the fatigue life of segmentis predicted by the fatigue experience formula for concrete standard specimens with the influence of the influence ofthe bottom caveundershield tunnel.and the safety distance and critical height of the cave at the bottom of the shield tunnel are givenaccording to the fatigue life of the segment.(4)Under the repeated train vibration,the accumulative settlement of the filling material at the bottom of the shield tunnel is predicted by the empirical formula of cumulative settlement of the soft soil in the tunnel basement.During the operation period,the safe distance and critical Height of bottom fully filled caverns which meet the stability requirements of tunnel basement are cleared by the standard of the filler's cumulative deformation.