| With the development of urbanization,the available space on the ground is decreasing day by day.Developing underground rail transit has become the main measure to solve this problem.This kind of long-span underground engineering is required to control the deformation of strata,adjacent buildings and underground pipelines.Currently,the main construction methods of our subway station construction include open excavation,cover excavation,and so on.Based on the complex construction conditions of urban metro stations,the hole pile method(PBA construction method)is widely used in the construction of urban metro,relying on the advantages of less space occupied by the road surface,flexible construction,fast speed,high precision and effective control of formation deformation.This method was first applied in the construction of Beijing subway,and has achieved great success in the construction of Beijing subway,which provides an important reference for the construction of subway.However,at present,the theoretical research of cave-pile method is higher than the practical application,and the construction under different geological conditions causes a large difference in surface settlement,and the load-bearing structure in the construction process is a lot of stress transformation.In order to further analyze the influence law of the main construction stages of cave-pile method on the surface settlement and the structural stress and deformation characteristics,this paper takes the practical project of Sanhao Street Station of Shenyang Metro Line 3 as the background,through laboratory test,numerical simulation,field monitoring,theoretical derivation and other methods,The deformation law,structural stress and differential settlement,settlement prediction of Peck formula and optimization of pilot tunnel excavation plan were further studied.The main research contents of this paper include:(1)Based on the sand geology of Sanhao Street subway Station in Shenyang,triaxial compression tests under different confining pressures and water content were carried out,and the evolution characteristics of sand deformation and strength parameters under different confining pressures and water content were obtained.(2)Midas-GTS finite element analysis software was used to establish a three-dimensional numerical model to analyze the variation rules of surface settlement,horizontal displacement and building settlement during the whole construction process,and the model was verified by comparing with measured data.The results show that the horizontal displacement of the station reaches its peak value at 20 m distance from the central axis.Attention should be paid to the variation of horizontal displacement of the inner floor within this range during excavation.The settlement value of building B(Jinke Building)and Building A(Shengjing Hospital)is inversely proportional to the distance from the station.The ratio of ground settlement to total settlement is as high as 85.4% in the phase of guide tunnel excavation and buckle arch construction.(3)According to the construction simulation results of station with cave-pile method,the stress and settlement variation law of side pile,beam,arch and column structures in the construction process is analyzed,and the mechanical transformation,stress concentration location,stress mutation,stress peak value,structural displacement peak value and settlement difference variation of vertical support system in the construction process of structural members are summarized.The tensile stress of the upper bearing structure and side pile increases first and then decreases with the progress of construction,and the peak stress appears at the buckle arch stage.The settlement value of all stressed components increases first and then decreases with the construction,and the maximum settlement value appears in the construction stage of buckle arch.(4)The feasibility of Peck formula regression method was confirmed by linear regression analysis fitting the measured data.According to the special geological conditions of Shenyang,the measured data and Peck formula settlement prediction results were compared and analyzed,and the conventional Peck formula was modified by introducing a correction factor.The results show that: The maximum correction coefficient of land subsidence ranges from 0.23 to 0.35,and the correction coefficient of land subsidence trough width ranges from 1.02 to 1.78.The predicted result of Peck formula is more consistent with the actual settlement deformation law.(5)By using Midas-GTS simulation software,the surface settlement and existing building deformation were taken as control indexes,and the orthogonal test method was adopted to establish a four-factor and four-level test scheme to optimize the overall scheme of guide tunnel excavation.By comparing and analyzing the test results,the factors of construction error distance,construction sequence,construction step distance,excavation method and surface deformation law under different levels are obtained.Range analysis results show that the excavation method of guide tunnel is the biggest factor affecting the surface settlement and existing buildings,while the excavation step has the least effect.The optimal excavation scheme suitable for the construction of tunnel with cave-pile method in Shenyang area is obtained. |
