Bearing capacity mechanism of vibro-replacement stone columns in coral sand with particle breakage

Coral sand presents significant challenges to ground improvement design due to its high void ratio, high compressibility, and particle breakage. Traditional bearing capacity theories for vibro-replacement stone columns are typically based on the assumption of soil shear dilation or constant volume. However, these assumptions fail to account for the particle breakage-induced energy dissipation and volume contraction characteristic of coral sand under high stress, leading to significant discrepancies in calculation results. Based on an analysis of the physical and mechanical properties and the breakage mechanism of coral sand, this paper proposes a novel three-step method for in-situ porosity measurement. Furthermore, a dual-mechanism coupling model, incorporating both energy-equivalent additional confining pressure and breakage-friction coupling, is proposed. By introducing the particle breakage energy dissipation coefficient [Formula: see text] and the energy-confining pressure conversion efficiency [Formula: see text], a modified limit equilibrium model for bulging failure is established to dynamically couple the void ratio evolution and the mobilized internal friction angle. Validation through an airport runway project in coral sand geological conditions demonstrates that the proposed method accurately captures the lateral restraint enhancement of coral sand particle breakage. The calculated lateral ultimate stress (166.3 kPa) is consistent with the field measured range of 158.0-175.0 kPa from nine parallel plate load tests. Considering the full range of measured data, the relative error of the prediction ranges from - 5.3% to + 5.0%. This approach yields significantly higher accuracy compared to traditional standard methods, providing a reliable theoretical basis for engineering design under the conditions of coral sand geology.