Responses of karst-penetrating piles under active and passive loading: experimental and numerical investigation

Abstract

This study, part of a preliminary safety evaluation for a real project, investigates the responses of karst-penetrating piles under active and passive loading, compared to non-cave cases. A series of reduced-scale model experiments and numerical simulations were conducted with a 1:35 similarity ratio, considering the effects of cave number and height on dimensionless pile responses. The results revealed that the decrease in axial force within and near the caves is due to the vertical resistance generated by the bulged pile segment, the pile-rock interface, and the cave bottom against the bulged pile segment. The deflection and bending moment profiles of karst-penetrating piles, which are significantly affected by pile head constraints, resemble those in non-cave cases, but with increased magnitudes as cave number and height rise. Additionally, reduced pile-rock contact shortens the effective pile length, preventing the shallow soil layer from providing sufficient lateral resistance. Consequently, deeper soil layers must mobilize their resistance to maintain lateral equilibrium. The effects of caves on pile responses depend on their position relative to the critical pile length of 4/α. Finally, pile head settlement and deflection exhibit a nearly linear positive relationship with both cave number and height. To simplify future predictions, several fitting formulas are proposed to link pile responses with and without karst caves. These formulas enable convenient prediction of the responses of karst-penetrating piles by scaling non-cave responses, reducing the need for extensive testing across various undetected cave scenarios.