Monitoring and Analysis of Subway Shaft Construction Displacement

Abstract

According to the construction site monitoring of a subway tunnel shaft in Beijing, the deformation laws of surface settlement, horizontal displacement and vertical displacement of retaining structure during shaft construction were analyzed. The results show that: firstly, the ground settlement around the shaft can be divided into two stages, the rapid settlement stage before the floor construction and the stable settlement stage after the floor construction. The settlement rate and value of the middle point of the long side of the shaft is faster and bigger than the corner point and the middle point of the short side. The settlement value first increases and then decreases with the increase of the distance to the pit side. The maximum settlement is located at (0.61 ∼ 1) times the excavation depth behind the diaphragm wall. Secondly, the horizontal deformation of the long side of diaphragm wall is obviously different from the short side. The horizontal deformation of the long side is larger than the short side, and the position of the maximum horizontal deformation is deeper than the short side. The horizontal deformation curve of the middle point of the long side has obvious inflection point, and the middle point of the short side presents reciprocating type. The variation range of horizontal displacement of diaphragm wall top is between 10 mm, and the maximum horizontal displacement is 0.037% of shaft depth. Finally, the vertical displacement of the top of the diaphragm wall settles rapidly before the excavation of the bottom plate, and the settlement value decreases gradually after the excavation, and the increase rate of the diaphragm wall settlement is the largest when it is excavated to the bottom of the shaft. This deformation law can provide reference for the optimization of support design of similar projects.