Multi-scale study of load-bearing mechanism of uplift piles based on model tests and numerical simulations.

The uplift pile is an anti-uplift measure in engineering widely used in practice. In order to study the mechanical parameters of the pile and the surrounding soil under the uplift load, a pile uplift model test and relevant numerical test were conducted. Image analysis technique was applied to the model test to investigate the soil displacements caused by pulling the pile. The load-displacement and pile axial force-lateral friction resistance relationships were investigated at three burial depths. Comparing the model test and numerical test results, it reveals that the pile primarily underwent four stages under the influence of uplift load: initial stage of loading, strain-hardening stage, peak of loading stage, and the strain-softening stage; the soil displacements around the pile exhibited inverted conical shape as the uplift load increases; and obvious soil arching effects could be observed near the ground surface. In addition, the development of force chains and major principal stresses indicated that the pile lateral frictional resistance first increased to its maximum value and then decreased sharply along the depth direction.