Desiccated state free swell index – a simple method for classification of soil expansivity.

Index properties such as liquid limit, plasticity index, shrinkage index, colloidal content, and free swell index (FSI) are used to identify and classify the nature of soil expansivity. However, for these tests either powdered or remoulded soils are used for testing and do not reflect the field placement conditions and soil structure. Hence, the present article proposes a new Desiccated State Free Swell (DSFS) index to encompass the field placement conditions and soil structure. In this method, the small compacted soil specimens are subjected to two-stage process – desiccation followed by swell measurement. The compacted or undisturbed soil specimens are placed in 100 ml glass measuring jars and allowed to swell in distilled water, similar to the FSI test. The percentage increase in the volume of the desiccated soil specimens is measured, and the same is used for the classification of degree of soil expansion. A total of 21 soils covering a wide range of plasticity characteristics and swell potentials were used for the present study. Based on the DSFS test results, a new classification chart is proposed for the prediction of the degree of soil expansion. The experimental findings revealed that the soil expansion predicted using the DSFS method is superior to the conventional indirect methods and matches well with the oedometer swell potentials. [ABSTRACT FROM AUTHOR]