A rapid method to identify clay type in soils By the free-swell technique

Abstract

This paper reports a rapid method to identify the presence of nonswelling clay, swelling clay, or a mixture of the two types of clays in a soil from the sediment volumes occupied by 10 g of dry soil in 100 mL of water and carbon tetrachloride, respectively, under no external constraint. Soils that occupy a sediment volume of < 1.50 m³/Mg in water and 1.10 to 3.00 m³/Mg in carbon tetrachloride contain nonswelling clay. Soils that occupy sediment volume of ≤ 1.10 m3/Mg in carbon tetrachloride and a volume ≥1.50 m³/Mg in water contain swelling clay. Soils that occupy sediment volumes > 1.10 m³/Mg in carbon tetrachloride and volumes ≥ 1.50 m³/Mg in water contain both nonswelling and swelling clays. The results agree well with X-ray diffraction and infrared analysis.In the latter part of the work, the limitations in the existing definition of the free-swell index of soils is brought out. The present definition gives a negative free-swell value for soils containing nonswelling clay and a reduced value for soils containing a mixture of nonswelling and swelling clays. The free-swell index of soils is defined as the sediment volume occupied by 10 g of dry soil in 100 mL of water under no external constraint and expressed in units of m³/Mg. Further, the sediment volume of a soil (10 g) in a nonpolar solvent, is utilized to give information on the clay type present in the soil, namely, nonswelling, swelling, or a combination of both. A classification for identifying a soil's expansivity based on the new definition of the free-swell index and the clay mineralogical composition of the soils is given.