Study On The Uplift Deformation Analysis And Control Technology Of The Existing Tunnel With Overlying Soil Excavation

Urban Metros are now in the era of great developments,the constructions of the subway involve the excavations and unloading of the overlying soil in the next horizontal tunnels,which may affect and shorten the normal service life of the existing buildings or surrounding buildings in the construction process,meanwhile may produce the safety problems which are difficult to control.Based on the reconstruction project of the South Square of Hefei hgh speed railway station,this paper uses Midas-GTS simulation software to select suitable constitutive models to analyze the influences of different excavation methods and the existing tunnel deformations under the reinforcement methods.Comparing the simulation values with the monitoring data,the paper discusses the principles and control technologies of the excavation of overlying soil to the existing tunnel,and the main researching contents are as follows:1)This paper firstly summarizes the researched results of the influence of the excavations and unloading of overlying soil on the existing tunnels in recent years,and puts forward the law of deformation of the existing tunnels and the research methods;2)Without considering the space-time effect of large area excavations and reinforcements in sequence stratigraphic conditions of metro line 1 and line 5 of the stresses and deformations,the result shows that the deformation values are far higher than in the cases of limited values.In view of the safety factors,some reinforcement measures should be taken in the process of construction;3)This paper mainly discusses the impacts of three kinds of methods of excavations and reinforcements of existing tunnels,such as strengthening stratum,improving soil quality,setting uplift pile and compression beam,and unloading sequence of overlying soil excavation.From the simulation consequences,it is known that the existing tunnels in the overlying soil excavated presents the trend of vault uplift.In the meantime,three different types of excavations and reinforcements have effects on controlling and there is the best reinforcement effect in third condition;4)After the comparison between the Metro Line 1 and the Metro Line 5,it appears that dividing the soil layers into a small sections to dig over considering the space-time effect in the first place,then applying the piles in the tunnels and on both sides of the soil to strengthen the foundation pit,finally pouring the capping beams to make it into a portal pile structure.Compared to other methods,it can control the deformations of the existing tunnels more effectively and shows that the measured values are in line with the simulation values after the Metro Line 1,in the end the methods are practical in engineering by means of analysis.