Abstract: The spread footing is one of the simplest foundation types, whose failure mode is related to both self-construction and the mechanical properties of the subgrade material. The failure mode of spread footings on high stiffness ground such as bedrock may be different from those on soil. The failure process of vertically loaded concrete foundations was numerically simulated by the two-dimensional hybrid finite discrete element method (2D-FDEM). The influence of the foundation thickness and subgrade stiffness on the bearing capacity and the failure mode of the spread footing has been studied in this paper. The results show that: (1) the vertically loaded concrete spread footing mainly experiences the punching shear failure. With the increase of foundation thickness, the angle between the failure surface and the vertical direction decreases slightly and tends to be constant, which means that the failure mode changes from the punching to the shear failure. (2) The base pressure of the spread footing on the high stiffness subgrade is parabolic distribution or in a inverted bell distribution. Meanwhile, as the stiffness of the foundation subgrade increases, the non-uniformity of the base reaction also increases. (3) The FDEM model can simulate the formation process of failure surfaces, which is hard to achieve by finite element method (FEM). Compared with the structured mesh, the simulated shape of the punching cone and the location of the failure surface are more accurate in the model using unstructured mesh, such as Delaunay triangle mesh.

Key words: Rock Subgrade, Spread Footings, Hybrid Finite Discrete Element Method (FDEM), Punching Failure, Shear Failure