Deformation and failure modes of composite foundation with sub-embankment plain concrete piles

With the development of high-speed railway in China, composite foundation with rigid piles has become a standard solution of meeting the high requirements of stability and post-construction settlement of embankment on soft subgrade. Among several improvement patterns, plain concrete piles have been extensively used to treat soft ground supported embankment. To investigate the deformation and failure modes of unimproved soft ground and soft ground reinforced by sub-embankment plain concrete piles, and to learn the influences of track and vehicle load, the effect of pile spacing, as well as the compression moduli of soil layers and upper load condition on the failure modes, a series of centrifuge model tests were performed. Test results indicate that the displacement of unimproved soft ground under the embankment increases continuously as embankment, track and train loading, and slip circle failure takes place. The deformation law of soft ground reinforced by sub-embankment plain concrete piles depends on pile spacing, compression modulus of the soft ground, and loading conditions. It was also found that plain concrete piles show displacement and failure patterns depending on its location, compression modulus of soft soil around the pile, and loading conditions. Furthermore, the evaluation of improved ground stability as well as the model test procedure is also presented.