Uplift capacity and failure mechanism for belled pile embedded in soft-rock ground

This study aims to investigate the failure mechanism and uplift capacity of a belled pile embedded in soft rock. The laboratory model test for evaluating the uplift capacity of a belled pile at the circular chamber was conducted for two belled angles (0 degrees and 12 degrees) and penetration depths (160 mm and 80 mm) under the same strength condition on soft-rock ground. In addition, to investigate the failure mechanism of the belled pile, the failure behavior of the belled pile embedded in soft-rock ground was analyzed under different conditions of the belled angle (12 degrees and 30 degrees) and strength at the soft-rock ground (0.3 MPa and 1 MPa) via image analysis in a half-circular chamber. A higher belled angle and ground strength resulted in a higher uplift capacity under the same penetration depth. In addition, the uplift capacity under the same belled angle and ground strength increased with penetration depth. For the image analysis, the shape of the failure surface was an inverted cone regardless of the test conditions. In addition, the failure mechanism was observed in three stages: (a) static, (b) compression, and (c) formation of the failure surface. A new predictive model for the uplift capacity of the belled pile applicable to the soft-rock ground was proposed based on the result. In addition, the predicted value was in good agreement with the measured value. Therefore, this model can be very useful for estimating the uplift capacity of a belled pile embedded in soft-rock ground.