Model test and DEM investigations into effects of cavities on a single pile in weak rock

The purpose of this study is to examine the effects of different cavity locations on the bearing capacity of pile foundations. To accomplish the purpose, a series of model tests was carried out on a small-scale single pile embedded in gypsum rock with predetermined cavities, thereafter, the numerical analysis was conducted. The studied model was simulated by the discrete-element method (DEM) using the two-dimensional discontinuous program PFC2D. The reduction factor was calculated to quantify the impact of cavities on the bearing capacity of pile foundations. The experimental and analytical results clearly show that the reduction factor decreased with an increase in the depth from the pile tip to the cavity, and the pile capacity is significantly reduced when cavities are located close to the pile tip. The two-dimensional DEM results visualised the cracks appeared inside the rock mass and the collapse of the cavity roof area, which cannot be seen in the experiment. The study also indicated a critical distance from the pile tip to the cavity that the influence of cavities to the pile is negligible.