Abstract
In recent years, biogeotechnology has been introduced as a novel and environmentally friendly technique for soil improvement. The need to address global warming and the adverse environmental effects of the chemical additives have led to the emergence and development of the techniques which use calcite producing microorganisms in order to improve soil mechanical properties. While the effects of microbial induced calcite precipitation (MICP) on the hydraulics and mechanics of saturated coarse-grained soils have been well examined and studied, there is not yet much information on the effects these microorganisms would have on the unsaturated soil mechanical behaviour. The first step, in this regard, is to understand the effect of the processes involved in the MICP on the soil retention properties. Soil water suction is a key factor controlling soil hydraulic and mechanical behaviour. In this study, the influence of MICP on the soil total suction in an unsaturated fine-grained soil sample has been explored using filter paper experiment. The results of this study revealed that by increasing the amount of bacterial solution, the soil saturation-total suction curves are significantly affected. The soil water retention changes are attributed to the change in double layer thickness as well as the precipitation of calcite crystals.
Highlights
In recent years, the urgent need to address the global warming has led to the emergence of new scientific solutions and approaches to the conventional engineering problems
The observed patterns can be attributed to the effects of different mechanisms and the biogeochemical reactions involved in the microbial induced calcite precipitation (MICP) on the soil fabric and on the soil retention properties
The results of Stocks-Fischer et al (1999) describe the metabolism of Bacillus pasteurii, and not the Bacillus Sphaericus used in this study, it can at least give primary clues on the possible mechanisms responsible for the patterns observed in the change of the retention curves by increasing the bacterial cell concentration [12]
Summary
The urgent need to address the global warming has led to the emergence of new scientific solutions and approaches to the conventional engineering problems One such approach has been searching for alternative soil improvement techniques. The biological soil improvement has been employed for various engineering purposes such as increasing shear strength [4,5], mitigating the liquefaction potential [6,7,8], and reducing the swelling and collapse potential in fine-grained problematic soils [9,10]. As two third of the earth surface is covered by arid and semiarid regions, one would expect the climatic changes would bring about short intense rainfall periods in such regions in which the soil layers will experience saturated state and unsaturated conditions. In such regions knowledge of unsaturated soil behavior would be essential to understand the changes that in the soil hydromechanical behavior would occur as a result of the change in the soil degree of saturation
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