Calculation Method of Vertical Bearing Capacity of Super-Long, Large-Diameter and Step Tapered Composite Steel Pile

Step tapered steel composite piles have excellent mechanical performance and they are widely used in engineering, but the related theoretical research is lagging behind. The calculation method of the vertical bearing capacity of the pile type was studied, and the load transfer rules were analyzed. The limit state of the pile foundation was analyzed. Considering the action of the steel tube and the bearing capacity at the stepped cross section, the vertical ultimate bearing capacity calculation formula of the super-long and large-diameter steel tube composite pile with stepped cross-section was derived by using the coordination relationship between the pile and soil displacement. The vertical bearing capacity of No. 37 pile foundation of Yushan Bridge was calculated by using this method and the calculation method in the current standard, which were compared with the measured value in the self-balancing test of the test pile. The results show that the self-balancing test curve of the test pile is smooth and without mutation. Besides, the bearing capacity of single pile is 120056 kN. Moreover, the deviation between the calculated value of the current standard formula and the measured value is too large, while the calculated value by using the method in this paper is close to the measured value, which verifies the reliability of the method in this paper.