Behaviour of embankment on composite foundation with geosynthetic-encased stone columns under freeze-thaw condition

A set of freezing test system for composite foundation with geosynthetic-encased stone columns (GESCs) is developed. The centrifugal model tests are conducted on an embankment on composite foundation with GESCs under freeze-thaw condition, and the comparative tests under non-freezing condition are also conducted. The behavior of embankment built on composite foundation with GESCs subjected to seasonal freezing is studied under freeze-thaw condition. The results show that under freeze-thaw condition, the consistent settlement is found on the top of the columns and on the soil when the soil and the columns are in the frozen state, while that on the soil increases significantly after complete melting. The embankment slope remains the original slope angle and has relatively uniform settlement under freeze-thaw condition, while the significant decrease in slope angle and differential settlement are observed under non-freezing condition. When the soil and the columns are in the frozen state, the stresses on the top of the columns and on the soil between the columns are consistent. However, columns melt before the soil, the stress on the top of the columns decreases while that on the soil increases. After the soil melts completely, the stress on the soil decreases rapidly while that on the top of the columns increases rapidly. Under the freeze-thaw condition, the stress concentration ratio is relatively small, which is about 2/3 of that under non-freezing condition. Because the soil around the top of the columns is in a frozen state during the embankment loading, the lateral displacement of the top of the columns is restricted. However, the soil below the frozen soil layer pushes the lower part of the columns outward that makes the columns under the embankment slope bend inward, but small bending deformation is observed. Inversely, the columns bend outward under non-freezing condition, and the bending deformation is obvious. The GESCs are suitable for the soft soil foundation treatment of wetlands in the seasonal frozen soil areas, and the overall performance of embankment built on the composite foundation with GESCs subjected to seasonal freezing is satisfactory.