Water retention properties of unsaturated coarse-grained soils: The experimental study of the effect of microbialy induced calcite precipitation

The soil water retention curve is one of most fundamental characteristics of unsaturated soils.The soil water retention curve indicates the amount of moisture content of the soil with respect to different values of soil suction. Shear strength, permeability coefficient, and volume change of unsaturated soils are closely related to the soil water retention curve.Therefore, determination of this curve is essential for understanding of the hydraulic and mechanical characteristics of unsaturated soils. Soil improvement is one of the key subjects of geotechnical engineering. In fact, the very first step in understanding the efficiency of various soil-improvement methods for unsaturated soils, is by no doubt, investigating their influences on the soil water retention properties. In recent years, in order to improve the soil mechanical characteristics, a new soil improvement technique (i.e., biological soil stabilization) has been developed which is more compatible with the environment. This technique is based on the so-called Microbially Induced Calcite Precipitation (MICP). In this study, the influence of MICP on the retention properties of an unsaturated coarse-grained soil sample has been explored using pressure plate apparatus experiment. The results of this study revealed that by increasing the amount of bacterial solution, the retention properties of soil samples are considerably affected. The soil water retention alterations are mainly manifested in the change in air entry value of the retention curve as a result of the change in bacterial concentration.