Experimental Study on Load-Transfer Mechanism and Failure Mode of Batter Pile under Oblique Uplift Loading

Abstract

Batter piles are often designed as foundation of high-rise structures to resist large lateral loads. The sizeable overturning moment of the superstructure will be transferred to the foundation so that batter piles are subject to the oblique uplift loading with changing directions. Due to the lack of understanding of the working behavior, the design and application of the oblique uplift batter pile are limited. In this study, 11 groups of laboratory tests are carried out in a testing box. The instrumental batter piles are made of polyvinylchloride pipes and loaded via pulley and counterweight. The variation of internal force, pile deformation, and load–displacement curve of the pile head is acquired. The load transfer mechanism and failure mode are summarized. A new type of tactile pressure sensor (TPS) is attached to the pile surface, and the actual pile–soil interaction forces in the normal direction are measured. The results show that the loading angle α controls the overall stability of the pile, the critical angle is 15° (in this study, qualitatively). When the α is within ±15°, the axial component of the oblique uplift load controls the overall stability of the pile; otherwise, the lateral component controls the stability. The increase of the loading angle α will increase both the bending moment of the negative and positive batter pile, but with different increments. The increase of pile inclination β will weaken the bending moment concentration effect. The soil pressure on the batter pile is in the offset state, which can be fitted by elliptic function. The pile–soil interaction below a certain depth is not affected by the pile inclination β and loading angle α. The middle to lower sections of the batter pile can be designed as the axial uplift pile, considering its resistance of axial skin friction only. This study shows the working mechanism of the oblique uplift batter pile in a manner way, which has practical significance for design and engineering application of batter pile.