Reserch On The Influence Of Long Distance Parallel Deep Station-Pit Excavation On The Adjacent Existing Metro

The long-distance parallel of the foundation pit and the existing operating metro is an unavoidable problem in urban construction,soil removal load during the foundation pit excavation,has a large impact on the structure of existing operating metro in the surrounding soil,improper treatment will cause hidden dangers such as deformation,cracking,and decreased structural strength on the structure.At present,domestic and foreign scholars are not perfect for the study of deformation characteristics for long-distance parallel metro,and the study of deformation characteristics for existing metro reinforcement needs to be deepened.Based on the new foundation pit of a station near the existing the metro in Fuzhou,this paper analyzes and studies influence of long distance parallel deep station-pit excavation on the adjacent existing metro by means of theoretical analysis and numerical simulation,in addition,research on the existing metro deformation rules under the reinforcement of door-type MJS construction method.The main research content is as follows:(1)The force transmission mechanism of the influence of foundation pit unloading on the long-distance parallel existing metro in the process of foundation pit excavation is deeply analyzed,This paper systematically puts forward the influencing factors and control measures for the three aspects of foundation pit,force transmission path and existing metro,introduces and deduces the method of two-stage theoretical calculation of existing metro deformation,and puts forward a semi analytical method based on two-stage method based on numerical simulation method and MATLAB software;(2)A simplified numerical analysis model is established by Midas GTS to analyze the deformation characteristics of the impact of foundation pit excavation on long-distance parallel existing metro.The numerical simulation results show that after the completion of foundation pit excavation,due to the existence of existing metro and the difference in the design stiffness of bite piles on the side near the existing metro,the horizontal displacement of bite piles on the side near the existing metro is greater,and the base uplift value is within a reasonable range,The horizontal displacement and vertical displacement of the existing line are 6.26 mm and 3.52 mm respectively,and the error between the calculated value of horizontal displacement and the semi analytical solution based on the two-stage method is 4.51%.(3)It is studied that after the existing line is strengthened with MJS construction method piles,the horizontal displacement,base uplift value and displacement of the existing line of the occluding piles on both sides are reduced to varying degrees compared with that before the reinforcement,in which the horizontal and vertical displacement of the existing line are reduced by 33.07% and 77.27%.After the existing line is strengthened and protected with MJS construction method piles,the existing line structure can be protected to a great extent to avoid excessive displacement of the existing line;(4)Through the analysis of the design parameters of MJS pile,this paper explores the influence of the elastic modulus of MJS pile,the distance between the pile and the existing metro and the thickness of the pile on the reinforcement effect.It is found that the greater the elastic modulus of MJS pile,the closer the distance between the pile and the existing metro,and the greater the thickness of the pile,the better the reinforcement effect of the existing metro.At the same time,the "door-type" reinforcement,"surrounding" reinforcement,"walltype " reinforcement,"C-shaped" reinforcement and "Γ-shaped" reinforcement,It is found that several reinforcement forms can limit the displacement of the existing metro,and the "surrounding" reinforcement effect is the best.