Load Transfer Mechanisms of Granular Cushion between Column Foundation and Rigid Raft

Abstract

The granular cushion has been increasingly used as a load transfer platform between a column foundation and a raft to ensure appropriate contact and load transfer among the raft, the columns, and the soil. However, deformation compatibility and load transfer mechanisms of the cushion have not been well studied. A series of two-dimensional (2D) model tests with different cushion thicknesses and column widths were carried out to investigate the load transfer mechanisms of the cushion using a multitrapdoor apparatus. Deformation characteristics and slip surfaces were observed during the tests, and the observations indicate that the diffusion cone model is applicable, especially when the relative cushion thickness and the relative column net spacing are large. The measured load efficiency decreased with the increase in the relative cushion thickness and the relative column net spacing. This paper presents the calculated pressure diffusion angle on the columns, analyzes the distribution of the contact pressure between the raft and the cushion, and establishes the methods for evaluating the contact pressure distribution and the load efficiency of the column foundation.