Sand columns have been widely used to accelerate drainage and then improving the mechanical properties of soft soil foundations. The sand column has also been introduced into the triaxial test by researchers, in the center of the cylindrical specimen, to greatly accelerate drainage and consolidation process. The objective of this paper is to evaluate the consolidation properties of the triaxial cylindrical specimen considering the presence of a sand column, and then to propose a consolidation model that simulates the consolidation process of the triaxial test. The consolidation equations were derived considering the drainage of the specimen with a sand column composed of both vertical and double-radial flows. Then the analytical solution of the model was obtained based on specific initial and boundary conditions. The comparison between the consolidation model and the laboratory tests yielded highly consistent. The case study demonstrated that the proposed consolidation model accurately simulates the evolution of average pore pressure and degree of consolidation in triaxial specimens containing a sand column. The studies on the consolidation parameters showed that there were different effects on the drainage rate for the diameter of specimen, the permeability coefficients of specimen and sand column, as well as the radius of the sand column.

Soil erosion is a common phenomenon which causes lots of geological and engineering disasters. Clayey soil erosion control is a hot research topic and a challenging issue for its low permeability and lack of effective infiltration of treatment solutions. In this study, a coupling microbially induced calcium carbonate precipitation (MICP)-sand column method was proposed as a promising and sustainable technique to mitigate surface clayey soil erosion with adjustable treatment depth. Seven groups of soil samples were prepared, including pure soil, MICP-treated soil, and MICP-sand column method-treated soil. A series of disintegration tests and penetration tests were conducted to investigate the method feasibility and adjusting mechanism of erosion mitigation with varying sand column heights and diameters. Compared to pure soil sample, sample treated by MICP-sand column (6 cm-height and 3 cm-diameter) method could reach a maximum reduction of 50 % in ultimate disintegration rate and a 30 % increase in the highest penetration resistance. The sample has a 7.9 cm effective treatment depth, which is 5.3 times of the MICP-treated sample. The mechanism of erosion mitigation can be attributed to that the sand column serves as a favorable path for the bacteria suspension and cementation solution in low-permeabilityclayey soil and improves the effective depth of MICP treatment. Adjusting the height and diameter of sand column can change the calcium carbonate distribution, especially at the locations near the surface and around the sand column. In this study, the optimal height and diameter are 6 cm and 3 cm, respectively, and finally form a U-shape three-layer structure. The structure significantly increases the proportion of the hard crust layer and weak-cemented layer with high hydro-mechanical properties. In conclusion, the coupling MICP-sand column method with reasonable height and diameter of sand column shows the ability to control surface erosion of soil and has better long-term mitigation performance.