Engineering geology of basaltic residual soil in Leiqiong, southern China

The physical, mechanical, chemical, mineralogical, and microstructural properties of basaltic residual soil obtained from Leiqiong area in southern China were examined. Emphasis was placed on the influences of minerals, oxides, and the soil fabric on engineering geological characteristics, particularly on strength and deformation properties. Distinctive properties, such as high strength and low compressibility relative to high void ratios, high liquid limits, and low natural densities, were explained. The soil fabric with the cement bond formed by iron oxides was considered as the main factor that caused to peculiar mechanical behavior, whereas mineralogy and climate processes also played important roles. Under the influence of repeated cycle of alternate wetting and drying, the residual soil generated a large collapsible deformation upon soaking, and its strength significantly decreased because of the derogation of cement bond, the formation of microcracks, and the weakening of microstructure failure zones.