Monitoring analysis of super large and deep foundation pit in alluvial plain of Yellow River

A foundation pit with excavation zone of 271 m×192 m and excavation depth of 18.7 m~19.5 m is monitored during excavation. The foundation pit is located in the alluvial plain of the Yellow River and supported by soil nailings, bored piles and prestressed anchor cables. Based on the monitoring results, the variation of deformation of retaining structures, ground settlement and anchor cable force are analyzed. It can be concluded that the horizontal displacement and the location of the maximum horizontal displacement of retaining piles increase with the increasing excavation depth. The longitudinal ground settlement has a saddle-shaped distribution. The maximum ground settlement appears in the middle zone of excavation, and the value of pit corner settlement is about 33.9% times that of the middle zone settlement in the longitudinal direction of pit. The longitudinal surface settlement trench is wider than the pit. Moreover, the value of the anchor cable force dynamically varies with the excavation depth. The value of the upper anchor first decreases, then slowly increases, and tends to be stable after the lower anchor is completed. The influences of the anchoring effect caused by drilling bore hole of anchor and high pressure grouting can not be ignored.