Study on the rupture surface morphology and ultimate bearing capacity of a self-anchored test pile

The expression of the ultimate bearing capacity of the upper uplift pile and the lower compressive pile of a self-anchored test pile was obtained by studying their rupture surface morphology. The upper uplift pile had a composite shear rupture surface shape, and the lower compressive pile had the Meyerhof rupture surface shape. Since the interaction between the upper pile and lower pile of a self-anchored test pile is negligible, the expression form of the ultimate bearing capacity of a self-anchored test pile was obtained based on the transformation formula of its bearing capacity. Under the test conditions, the rupture surface morphology of a self-anchored test pile belongs to the situation when the equilibrium point is inside the rupture surface of the lower compressive pile. The theoretical rupture surface is approximately 0.09 m away from the pile side at ground level (1.8 d, where d is the pile diameter). Compared with the distance of the measured rupture surface of the upper uplift pile to the pile side, the difference value is -2.17%. The calculated ultimate bearing capacities of the upper uplift and lower compressive piles are 1287.34 N and 1201.65 N, respectively. The ultimate bearing capacity of the self-anchored test pile is approximately 2726.16 N. Compared with the experimental values of the upper pile and lower pile of the self-anchored test pile, the difference values are + 0.97% and − 7.57%, respectively. Compared with the experimental values of the traditional test piles, the difference value is − 2.64%. The rupture surface morphology and the expression of the ultimate bearing capacity of the self-anchored test pile in this paper can provide a research basis reference for calculating the ultimate bearing capacity of the self-anchored test piles with different pile sizes and soil properties.