• An axisymmetric numerical model with 945 parameters was constructed for circular pits. • Two typical failure modes were identified: spoon-shaped and U-shaped collapses. • A machine learning-based slip surface characterization method was proposed. • Results provide a theoretical basis for circular excavation stability control. To address the unclear instability failure mode and the insufficient characterization of slip surfaces in circular foundation pits, an axisymmetric numerical model for circular foundation pits was developed. Based on the strength reduction method, the influence of excavation radius, pit depth, embedment depth of the supporting structure, and soil parameters on the stability of the circular foundation pit was analyzed. An instability failure mode for the circular foundation pit was established, and a function-based slip surface method was proposed. The proposed method was validated with existing findings. It is demonstrated by the results that spoon-shaped and U-shaped patterns represent the major instability failure modes of circular foundation pits. The excavation radius, pit depth, and embedment depth of the supporting structure significantly influence the shape of the slip surface, while the effect of soil parameters is relatively minor. Increasing the excavation radius and decreasing the embedment depth can cause the slip surface to transition from spoon-shaped to U-shaped. The accuracy of the slip surface method exceeds 95%. This research clarifies the slip surface shape of circular foundation pits, providing a theoretical basis for their stability, design and control measure selection.
Zhang et al. (Wed,) studied this question.