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A failed embankment on a cement deep mixing (CDM)-formed column–improved soft clay deposit in Saga, Japan, has been reported and analyzed. Based on the results of the field investigation and numerical simulation, the postulated failure mechanism is that columns under the failed section failed by bending (tension), which caused the whole embankment system to collapse. However, bending failure of columns is not necessarily checked in the current design process in Japan. In addition, it has been found that the limited number of all-core boring checks as adopted in Japan cannot guarantee the quality of all constructed columns, and development of a more robust field quality-control technique is urgently needed. It has also been found that for an embankment system with a lower factor of safety, relatively large deformation of the system may cause cracks in the embankment; at the cracked locations, the shear strength (su) will practically reduce to zero. This phenomenon has to be considered in deformation and stability analyses. Finally, the numerical results indicate that in the design of a reinforced embankment slope on a soft clay deposit, both the stability of the reinforced slope itself and the interaction between the embankment and soft clay deposit should be considered.
Chai et al. (Fri,) studied this question.