上海软土单层地下室大面积换撑基坑变形特性实测分析OACSTPCD

The underground basement of a hospital in Shanghai is a single-story large structure with a height of up to 8.5 meters.Due to the irregular foundation pit,two layers of concrete bracings are set.Before the removal of the first layer of concrete bracings and the construction of the basement ceiling,large-area bracing replacement operations are required to prevent the cantilevered deformation of the excavation pit retaining structure.For assessment,comprehensive monitoring is conducted during the excavation phase,including retaining structure deflection,lateral displacement of soil behind retaining structure,the vertical displacment of retaining structure top,uplifts of interior steel columns,axial forces of propping structs and water level of artesian water.Based on the analysis of field data,the deformation and internal force development trendency of retaining structure during the bracing replacement process is analyzed.The results reveal that the bracing replacement procedure inhibits the excessive deformation of the super-high single-story basement foundation pit after losing the first layer of bracings.However,the retaining structures still deform considerably during the process and needs to be closely monitored.Furthermore,placement of abandoned soil outside the pit may induce soil consolidation,causing the behavior of the retaining piles to transform from rebound to settlement.During the continuous rebound process of the column pillars,the uneven deformation of the concrete bracings will intensify and the secondary stress will be aggravated,thereby affecting the stability of the foundation pit.