Experimental study on sand and gravel columns in clay

Theoretical and experimental studies have shown that stone columns can be used for accelerating the consolidation rate of soft soils by providing a drainage path, reducing foundation settlements, improving the bearing capacity of the soil, and limiting the risk of liquefaction due to seismic activity. This paper studies the influence of the main controlling parameters in the design of stone columns through a series of laboratory experiments. The effects of (a) the drainage conditions, (b) the grain size of the stone column material, (c) the confining pressure of the soil, and (d) the rate of deformation are investigated. Triaxial compression tests are performed on composite soil specimens of soft kaolin clay, reconstituted from a slurry with a central compacted reinforcement column. Two cases of reinforcement material are studied: sand and gravel. The behaviour of the reinforced soil compared with that of the unreinforced soil under the same loading and drainage conditions is analysed. The experimental results show the beneficial effect of this ground improvement technique on the strength characteristics of the foundation soil, even with a relatively low replacement factor compared with that used in practice. As the confining pressure increases, the improvement in the specimen with the sand column is more pronounced.