Stone columns are frequently employed to improve the bearing capacity of soft soils, to reduce settlements, and to increase the speed of consolidation. Their behaviour depends on several factors, such as the density of the aggregate that forms the column and the area replacement ratio. This paper presents a study of the influence of the density of the gravel forming the columns on the deformation and stresses around end-bearing stone columns installed in soft soils. For this purpose, the behaviour of a horizontal slice of a unit cell has been analyzed by small-scale laboratory tests performed in a Rowe–Barden cell. Tests have been performed with a gravel relative density of D_r = 30% and with two area replacement ratios. Their results have been analyzed along with those from similar tests performed with a gravel density of D_r = 100%. The study is focused on the soil–column stress concentration ratio and the reduction of settlements. Finally, the experimental results are compared with numerical simulations. The results show that a reduction of settlements around 10% occurs when the relative density of the gravel increases from D_r = 30% to 100%. Numerical analyses reproduce well the behaviour of stone columns and are in good agreement with the experimental results.

Sand−rubber mixture (SRm) behaviour is affected by rubber content (RC) while dissipation in sands is caused by inter-particle sliding. Dissipation in SRm is as, or more significant than in sands. However, the mechanisms of dissipation in SRm are not well understood. In this study, one-dimensional compression tests on sand samples with RC of 0, 15, 30, 45 and 100% by mass were performed on a standard oedometer. In addition, a SRm with RC of 30% was tested on a mini-oedometer placed inside an X-ray scanner and three-dimensional images of the internal structure of the material were acquired at three stages during loading and unloading. Image analysis was used to infer particle-scale measurements and provide experimental evidence to help explaining the energy dissipation mechanisms for SRm. It is postulated here that energy dissipation in these mixtures is dominated by inter-particle sliding at initial stages of loading, but once rubber particles fill the void spaces between the sand, deformation and dissipation mechanisms are dominated by the deformation of the rubber particles.