A Geotechnical Centrifuge Study on the Bearing Capacity of Ring Foundations Reinforced by Stone Columns

Ring foundations are a distinct category of shallow foundations designed for the bearing loads of symmetrical structures with circular planes, such as bridge piers, liquid storage tanks, and wind turbines. In this study, six geotechnical centrifuge models were tested to simulate the performance of ring foundations supported by stone columns over loose sandy silt. The effects of column length (L) and diameter (D) on bearing capacity were evaluated by testing values of L/D at 6, 8, and 10. Furthermore, three different arrangements of columns including triangular, square, and annular were considered, and also the load–settlement behavior of the ring foundation was examined. The optimal L/D ratio and the most effective type of column arrangement were determined. The ultimate bearing capacity (qult), the coefficient of subgrade reaction (ks), and Young’s modulus (Es) of the soil layer were also analyzed. The experimental qult of the ring foundation with a rough base, situated on an unreinforced soil layer, and aligned with the analytical formulations for qult was found in previous studies. The results indicated that the use of the annular arrangement of stone columns with L/D = 8 increased the bearing capacity by 2.8 times and the values of ks and E by approximately 3.4 times as compared with the unreinforced case. According to observations, the bulging failure mode governed stone column groups at a depth of 2D to 2.5D from their heads, while the soil layer failed because of the general shear mechanism.