Physical and numerical modelling of axially loaded bored piles with debris at the pile tip

Abstract

For bored piles, a careful cleaning work must be implemented to minimize the trapped debris in the drilled hole; otherwise, the presence of debris can result in the soft toe effect, influencing the axial resistance. There is a lack of systematic studies on bored piles with debris. This investigation fills the gap by conducting a series of model scale laboratory tests, in which the debris is simulated using foam rubber, to assess the behaviour of single pile, pile composite foundation, and pile group. The measured pile responses are then employed to calibrate a numerical model. Numerical simulation is also compared against a destructive field test to explain the impact of debris on bored piles. It is found that the existence of debris causes the load settlement curve to follow a stepped profile. Skin friction dominates the pile resistance initially, and load transfer occurs to mobilize the pile tip resistance with the compression of debris. A bored pile with debris should not be discarded directly; instead preloading the pile to compress the debris can help to regain the axial resistance compared to a pile without debris.