Abstract：The failure modes of the gravel cushion in the composite foundation are studied from the viewpoint of meso-scale. Combined with the theoretical analysis, laboratory experimental tests and numerical simulations are employed to track the particle movement of the cushion during the upward penetration of the pile. The CCD tracking shot and digital speckle correlation technique are used for the laboratory experiments. And the discrete element method is used for the numerical simulations. The results show the development of the failure from the Terzaghi mode to the Mandel-Salencon one. Macroscale characteristics of the gravel cushion are investigated and explained from the meso-scale viewpoint.
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