Abstract: Cushion is a key component of composite foundation, which ensures the deformation coordination and rationality of load distribution between soils and piles. However, the mesoscopic working mechanism of the cushion is not well investigated and the design parameters of cushion are mainly determined according to the experience. In order to reveal the coordination mechanism of the cushion, a test apparatus was designed to simulate the working of cushion in the composite foundation. Three visualized plane strain tests were carried out with different heights of the cushion. A series of 2D DEM simulations was conducted with an orthogonal array. Both the model tests and simulation results showed the three similar patterns of deformation which related to the ratio of the cushion height and the net spacing of the piles. Mesoscopic force chain distribution was also analyzed. In addition, a design suggestion of the cushion height was proposed by analyzing. Meanwhile, an index applied to assess the deformation coordination capability was presented. According to the variance analysis and range analysis, it was found that the height of the cushion and the net spacing of the piles were the significant factors which affected the deformation coordination capability. The upper limit value of the index was also explored and proposed to guide the design of cushion.

Key words: cushion, composite foundation, rigid slab, working mechanism, model test