Monitoring And Back Analysis On Displacement Of The Foundation Pit Of Zhandongguangchang Station In Line2of Chengdu Metro

Deep excavation is the key issue in the open cut of metro station. On account of the complicacy of foundation pit, construction monitoring is indispensable to ensure the safety of deep excavation and surrounding environment. The foundation pit of the Zhandongguangchang station in line2of chengdu metro have been researched in this paper, they have the following characteristics:the geological conditions is poor (contain expansive soil), the excavated depth is large(23m), the form of retaining is complicated(row piles and four steel tube brace), so the construction monitoring appear to be even more important.Construction monitoring on the excavation pit of Zhandongguangchang station in line2of chengdu metro and analysis of the monitoring results was done by the author, the construction process of excavation for row piles structure was simulated with finite element software ABAQUS, a method to back analysis the moment of pile using the measured data of horizontal displacements had been researched. The following conclusions have been achieved:(1) The main monitoring results do not exceed the permissible value, which showed that the retaining structure of the foundation pit is safe.(2)At the beginning of the excavation, usually the first brace isn’t fixed in time, which makes the pile in the state of the cantilever without support, as a result, the horizontal displacement at the top of pile is comparably big, while gradually decreases along the depth. With the going of excavation, the horizontal displacement curves of the pile assume in the shape of bow, that is, the maximum displacement appears at the middle of the pit and inflection point appears at the bottom of the pit in a general way. The maximum stress of steel bar is53%of the design value.(3) Basically the results of3-D Finite Element Simulation are in accordance with the actual measurement results, which proved that the finite element model and calculation method are reasonable and practicable.(4)With the increase of excavation depth, the moment of the pile increases, and the location of maximum moment moves down gradually, it is the most dangerous work condition to remove the forth brace during the excavation. Generally, the location where the brace is set have bending mutation, which indicates brace’s important function on reducing the moment.(5) The moment obtained from back analysis of the measured data of horizontal displacements basically agree with the s measured moment, which argues that the back analysis method is reasonable and practical.