Study on Vertical Bearing Characteristics and Group Pile Effect of Expanded-base Piles
To investigate the vertical bearing characteristics of pile groups with expanded-base,static load model tests were conducted on single pile foundations with expanded diameter ratios of 1.5,2.0,2.5,and 3.0,as well as pile raft foundations with expanded diameter ratios of 2,using an expanded-base pile raft structure.Analyzed the load transfer law and established a finite element model for the expanded-base pile raft foundation with pile spacing of 3.75,4.00,4.50,and 5.00 times the pile diameter,and studied the influence of pile spacing on the group pile effect.The results show that the load settlement curves of single pile and raft structures with expanded-base are both of a slowly changing type.The ultimate bearing capacity of the expanded-base pile gradually increases with the increase of the expansion ratio.When the expansion ratio is 2.5～3.0,the increase in the ultimate bearing capacity slows down.It is recommended to take the expansion ratio of the expanded-base pile as 2.5～3.0.Due to the joint settlement of piles and soil,the soil between piles is compressed,and the pile-soil interaction is more sufficient.The load sharing ratio of the center pile side frictional resistance of the expanded-base pile raft foundation is increased by 17.71%compared to that of a single expanded-base pile.The coefficient of pile group effect gradually increases with the increase of pile spacing.When the pile spacing is 4.5～5.0 times the pile diameter,the increase in the coefficient of pile group effect is relatively small,and the effect of pile group is weak.It is recommended that the pile spacing of the expanded-base pile raft foundation be not less than 4.5 times the pile diameter.
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