Research on the Uplift Bearing Capacity of the Rock-socketed Pile and Failure Mechanism

The ultimate uplift bearing capacity calculation of rock-socketed piles in the current standard only applies to the shear failure, which takes place at the pile-rock interface. However, the inverted cone tensile failure at the top of the rock mass exists might occur under uplift load when the rock socketed depth is shallow. A calculation method for the uplift bearing capacity of rock socketed piles considering different failure modes has been proposed based on theoretical analysis. The proposed method considers both shear and tensile failure modes and is validated through model experiments. The inverted cone failure mode of rock socketed piles under uplift load is identified in the experiment. When the depth of the embedded rock pile is less than 2 times the pile diameter, the height of the inverted cone is basically the same as the embedded rock depth, implying that the rock mass begins to crack from the bottom of the pile. The overburden stress has an impact on the angle between the failure surface of the inverted cone and the horizontal plane. The angle between the failure plane and the horizontal plane for pile with covering soil layer is greater than that for pile without covering soil layer. The calculation method for the uplift bearing capacity of rock-socketed piles considering the tensile failure of the inverted cone provide analysis results close to those of the model test, and it can be used to calculate rock-socketed piles with small depth.