Study On The Influence Of Dewatering And Excavation Of Bridge Pier Foundation Pit On Adjacent Operation Lines

High-speed rail lines have strict requirements for foundation settlement,and any construction within the area of influence needs to be assessed for safety.With the rapid development of national transport networks and three-dimensional transport hubs,there are a large number of new railways spanning,crossing or adjacent to the business lines of high-speed railways.At present,there is less research on the impact of new bridge pier foundation excavation on the foundation of the adjacent high-speed railway business line,and the foundation of the new foundation may lead to uneven settlement of the foundation of the adjacent high-speed railway business line or bridge deflection,which will have a negative impact on the safety operation of the adjacent high-speed railway business line structure and trains.This paper relies on the Changjing Huang High Speed Railway Nanchang Junction Project,and investigates the impact of foundation excavation on the lateral displacement of the surrounding soil and the deformation of the adjacent high-speed railway business line through on-site monitoring of the typical binary geological conditions in Nanchang.The main research contents and results are as follows.(1)Through on-site in-situ monitoring of the soil displacement around the foundation pit caused by the dewatering and excavation of the foundation pit of the bridge pier and the deformation of the bridge pier platform adjacent to the high-speed railway business line,the influence of free field and non-free field dewatering and excavation on the surrounding soil displacement and the adjacent high-speed rail business line was analyzed.The measured data show that the influence trend of foundation pit dewatering and excavation on the horizontal displacement of surrounding soil under free field and non-free field conditions is the same,and the horizontal displacement of soil caused by foundation pit dewatering and excavation to the end is the largest,and the maximum settlement value affecting the adjacent high-speed railway business line is 0.4mm,which is less than 1.2.mm the standard warning value,and it is within the safe range.(2)Two-stage analysis method is used to study the vertical and horizontal displacement of the group piles of the adjacent high-speed railway business line caused by the foundation pit dewatering and excavation,the first stage through the inverse analysis of the measured data of soil displacement caused by the foundation pit dewatering and excavation of the bridge pier at the engineering site,more accurate to obtain the three-dimensional soil displacement field formula of soil displacement outside the pit caused by the foundation pit dewatering and excavation of Nanchang binary geology,the second stage based on Winkler and Kerr foundation beam model,the obtained soil displacement will be equivalent to the load acting on the adjacent pile foundation,calculate the adjacent single pile displacement,followed by considering the soil sheltering effect in the group pile,calculate the adjacent high speed railway business line group pile displacement.The comparison with the field measurement and PLAXIS 3D numerical simulation results is in good agreement,which verifies the accuracy of the two-stage analysis method.(3)PLAXIS 3D was used to establish a model of the impact of foundation pit precipitation excavation on monopiles and adjacent high-speed rail business lines,and the effects of foundation pit precipitation excavation on soil displacement around foundation pits and adjacent high-speed rail business lines under different distances,different foundation pit depths and different water levels were analyzed.The calculation results show that Nanchang binary geology is adjacent to the high-speed railway foundation pit construction impact zone,and the main impact area,general impact area and light impact area are divided by 0.8H,(1.5～2.0)H and(2.0～4.0)H.Finally,the main protective measures of adjacent high-speed railway business lines are proposed when the construction of foundation pits affects the operation safety of adjacent high-speed railway business lines.