Numerical Evaluation of Bearing Capacity of Step-Tapered Piles Using P-Y Curves Analysis

Step-tapered piles are those with a larger top diameter, and a smaller diameter at lower sections as the body gets slender stepwise from top to toe in one or some steps. This study aims to investigate the behaviour of step-tapered piles having only one step under axial loading condition. Three series of piles embedded in sand are examined numerically using the three-dimensional finite element method. Each set consists of five piles, including one reference straight sided wall pile and four step-tapered piles having the same volume. Different internal friction angles of 33°, 37°, 41° (to represent loose, medium and dense sands, respectively) and corresponding elastic modulus and lateral earth pressure coefficients are considered to observe their effect on the bearing capacity and settlement of piles. The load-displacement diagram of each pile is obtained, and accordingly, the frictional and end bearing resistances are calculated using conventional methods. A MATLAB code is developed to get the numerical data and carry out the calculations. Moreover, the normal and shear stress states, plastic points, and deformations around the step and toe of piles are computed and compared. According to the results, the advantages of step-tapered piles over their counterpart cylindrical ones in terms of bearing capacity and settlement are discussed. Finally, the optimum stepped length of the pile is determined.