Volume Change Behavior of Natural Expansive Soils Subjected to Acid and Alkali Contamination

Acid/alkali contamination of expansive soils, which has been probed in recent years, gives rise to unexpected structural failure when exposed. However, a systematic research aiming at evaluating volumetric behavior of natural illitic clays when subjected to acid/alkali solution as pore fluid and its microlevel analysis is not well established. A series of oedometer tests and microanalytical experiments (X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy) have been carried out to investigate the effects of acid and alkali contamination on swelling and compressibility of natural expansive clays from Heilongjiang province in China and to identify the underlying controlling mechanisms. Distilled water, sulfuric acid of pH 3, and caustic soda of pH 13 were selected as three different pore fluids. The results show that compared to samples inundated with water, specimens exhibit greater swelling and lower compressibility after being exposed to acid solution, and lower swelling and greater compressibility after being subjected to alkali solution. In three different soaking solutions, all samples present an increasing tendency for swelling deformation with dry density from 1.4 to 1.8 g/cm3, while the highest compressibility occurs at dry density around 1.5 g/cm3. The microanalysis revealed that soils undergo reactions, including desiliconization and cation exchange, due to the acid and alkali erosion, which correspondingly leads to changes in soil mineralogy and texture. Acid and alkali contamination results in disintegration and loose structure, and acid exerts more destructive impacts than alkali do. The sulfuric acid promoted the dissolution of tetrahedral cations, while the caustic soda improved the dissolution of octahedral cations.