Model Test of Rock-Socketed Pile under Axial and Oblique Tension Loading in Combined Composite Ground

With the rapid development of transmission-line engineering in western China and the frequent occurrence of extreme natural disasters, a great deal of attention has been paid to the bearing capacity of foundation systems. The uplift capacity is still the controlling factor in the design, but neglecting the horizontal load component will induce great potential risks to the stability of the foundation. This paper describes the model test of rock-socketed piles (with soil overlying rock) that were subjected to axial and oblique tension impacts. Furthermore, the load displacement response, failure mode, and load transfer mechanism of the model piles were compared and discussed. The research indicates that the uplift capacity of the model pile under the oblique load can be remarkably reduced by up to 27.3% in comparison with the vertical uplift. Moreover, the load–displacement curve of the model pile under axial and oblique loads present abrupt failure. Notably, the failure mode under the axial tension is an inverted cone-shaped axisymmetric failure, and the failure mode under the oblique tension shows the wedge failure on the compression side and the interface separation on the tension side. The compression side and tension side show the opposite load transfer mechanism, thus inducing the presence of a bending moment in oblique tension pile. The position of the maximum bending moment occurs at the depth of 2.3–2.8d below ground surface. In summary, the research results of this paper have important guiding significance for design of transmission tower foundation in similar geological settings.