Study of Pipe Pile Bearing Characteristic in Foundation Pit for Excavation and Unloading

To pipe pile installed before excavation under foundation pit, the soil squeezing effect for installation of pipe pile is weakened under foundation pit. For excavation and unloading of foundation pit, the vertical bearing capacity of pipe pile will been affected which has rarely been studied. Based on cavity expansion theory of Vesic and considering the influence of soil squeezing effect of pipe pile for excavation and unloading, the computing method of reduction coefficient k of bearing capacity is proposed for excavation of foundation pit in this paper. By indoor model test, the load-displacement relationship of jacked pile is compared with bored pile. It is indicated that the displacement increment of unlimate bearing capacity of jacked pile is three times that of bored pile for excavation of foundation pit. The reduction coefficient k of bearing capacity measured is 0.856 which has 2.72% difference with 0.923 calculated by method in this paper. Moreover, the calculation result indicates that the curve of k and H/L₀ shows a significant nonlinearity and the change of δ has more significant effect on k than k₀ and c. The study can provide useful references for bearing capacity design of pipe pile in foundation pit.