DEFORMATION BEHAVIORS OF MOUNTAINOUS TYPE SOFT SUBGRADE REINFORCED BY DYNAMIC COMPACTION OF GRAVEL COLUMNS

This paper aims to clarify the intrinsic relationship between the deformation behaviors of dynamic compaction gravel columns and the stability of the embankment under the load of the embankment. It examines an example of embankment failure of a high-speed railway station located in mountainous type soft soil. It is based on the field measured data and the three-dimensional numerical analysis model. It studies the bulging deformation and lateral deformation of the gravel columns. It further defines the bulging ratio and maximum lateral deformation of the gravel columns to describe their deformation characteristics. The results show that the gravel columns at different positions under the embankment have different degrees of bulging deformation and lateral bending deformation. The bulging deformation is mainly composed of the compression bulging caused by embankment load and the shear bulging caused by lateral sliding of embankment. The maximum bulging deformation area is concentrated in the range of 1~2 times of the pile diameter from the tip of pile. Especially, the bulging ratio of the gravel column near the entrance of the potential slip surface of the composite foundation is the largest(0.75%), which is about 1.5 times the bulging ratio of the gravel columns at the center of the embankment. The bulging deformation is mainly due to sliding shear. The growing trend of the maximum lateral deformation for dynamic compaction of gravel columns at different locations along the centerline of the embankment is approximately the three segment line mode. The lateral deformation of gravel columns begins to increase sharply from the 17th gravel column, which indicates that the 17th and its adjacent gravel columns are the key components for controlling the lateral deformation and stability of the embankment. The reason for the occurrence of several cracks in the embankment filling process may be caused by the shear failure of the dynamic compaction of gravel columns. Additional reinforcement measures should be adopted to ensure the stability of the filling embankment when granular columns are used to treat the mountainous type soft soil.