Model Test Study on Vertical Bearing Capacity of Stepped Piles

[Purposes] The stepped pile with variable cross-section is a new pile type that is improved on the basis of the pile with equal cross-section, but its loading and deformation are relatively complex, and the processes of exerting lateral friction resistance, end resistance at variable section, and pile end are not understood. [Methods] In this paper, the vertical bearing capacities of ordinary pile and stepped pile were studied by indoor model tests with the graded load application method. [Findings] Under identical conditions, the settlement of the stepped pile is reduced by 33%, and its bearing capacity of unit volume is increased by 19% compared with those of the pile with equal cross-section, indicating that the stepped pile has the advantage of reducing the settlement and better bearing capacity of unit volume. The axial force of the stepped pile decreases sharply at the position of the variable cross-section. It is shown that the existence of a variable section affects the axial force transfer of the stepped pile. In the initial stage of loading, as the load on the pile top increases, the ratio of the lateral friction resistance to the load on the pile top gradually increases, and the ratio of end resistance at the variable cross-section and the end to the load on the pile top gradually decrease; When the lateral frictional resistance reaches its limit, the ratio of the lateral frictional resistance to the pile top load gradually decreases, and the ratio of the end resistance at the variable cross-section and the end gradually increases, but the ratio of the end resistance at the variable cross-section tends to be stable first, which indicates that the soil at the variable cross-section is destroyed first. According to the Terzaghi theory, the formula for calculating the end bearing capacity at the variable cross-section of stepped piles has been revised, and the reliability of this theoretical method has been verified by comparing it with experimental results.