This study explored the effect of indigenous bacteria present in the soil to stabilized swelling behavior and improving the mechanical property of expansive soil. The objective of the research is to investigate the effectiveness of the biostimulation microbial induced calcite precipitation (MICP) for controlling the swelling-shrinkage behavior and improving shear strength of expansive soil. An attempt was made to develop an effective procedure to culture the indigenous bacteria for treating clays with varying plasticity and improve their engineering behavior. The detailed procedure has been investigated to effectively apply the MICP technique in clay soil, considering its low permeable nature. The applicability of biostimulation to clayey soils in minimizing their swelling potential and improving the strength is assessed. Both macroscale and microscale studies were conducted on untreated and biostimulated soils to observe changes in plasticity, strength, swelling, mineralogical, chemical characteristics. The present method has shown an effective alternative to improve the road pavement subgrade without affecting the eco-system of natural soil. The method investigated the effective way of providing the enrichment and cementation solution in clayey soil, which is the major concern in current literature. The study confirms that the calcite content has been increased with biostimulated MICP treatment up to 205% in the treated specimens and which future increased the unconfined compressive strength and split tensile strength. A reduction in the swelling pressure and swell strain is also observed. The results show that a cost-effect and eco-friendly method can be deployed for stabilizing the road pavement subgrades. The statistical assessment using multivariate analysis and hierarchical clustering dendrogram has been carried out to investigate the effect of the MICP treatment protocol on different soil and engineering parameters.

In lieu of the conventional carbon-intensive and expensive cement-based ground improvement methods, microbially induced calcite precipitation (MICP) method has gained prominence recently as a sustainable approach to improve the engineering properties of soil. MICP involves calcification by microbial processes, inducing cementation effect in granular soil particles. Several studies have demonstrated the use of Sporosarcina pasteurii bacteria to improve density, stiffness, shear strength, and liquefaction resistance of sand. However, the effects of different bacteria on calcite formation have not been systematically examined in the Indian context. This study investigates MICP in poorly graded, liquefiable Narmada sand, using gram-positive bacteria (i.e. Sporosarcina pasteurii, Bacillus subtilis, and Bacillussphaericus). Several controlled microbial and cementation media concentrations were tested in sand-filled tubes. Calcite precipitation was analyzed using SEM, FTIR, XRD, and calcimeter. Bacillus subtilis and Bacillus sphaericus resulted in calcite precipitation comparable to that of Sporosarcina pasteurii and can be utilized for sand stabilization.

Earthquake-induced liquefaction causes soil to exhibit fluidlike behavior due to a sudden increase in pore water pressure and a concurrent decrease in effective stress. The liquefaction can destroy or damage existing substructures and superstructures that results in considerable economic and human losses. Hence, there is a need for ground improvement in liquefiable soils for liquefaction hazard mitigation. Various conventional methods, such as soil replacement, densification, and grouting have been used for liquefaction mitigation historically. However, these methods are carbon-intensive, uneconomic, and environmentally unfriendly. Recently, some researchers have demonstrated new techniques that can significantly mitigate liquefaction and achieve cost-effectiveness, are ecologically friendly, and have less associated disturbances. The objective of this review is to provide an overview and the associated challenges of emerging techniques that increase the liquefaction resistance of sandy soils. Initially, the advantages and disadvantages of conventional methods are discussed to justify the requirement for advanced methods. The rapid evolution of novel materials and techniques, as well as multidisciplinary collaborations, has led to new and innovative advanced methods for effective mitigation of liquefaction. Among these methods, the biogeotechnological methods that have received great attention recently are discussed in detail. Many studies have reported the effects of biotreatment on soil properties and liquefaction resistance, factors affecting the biocementation process, and various challenges associated with the biocementation methods. Finally, additional research directions needed for biogeotechnical methods to be effective, sustainable, and resilient for liquefaction mitigation in actual field applications are presented.

Metabolites generated from microorganisms have a high potential for the strength improvement and contaminant remediation of soils. The consortium of naturally available bacteria and microalgae in soils provides a sustainable, carbon-neutral, economical, and environmentally friendly approach for both biocementation and contaminant remediation. This combined approach has not been explored earlier. The study aims to improve the strength and reduce leachable lead in cohesionless soil by providing optimal nutrients and chemicals to expedite the metabolic activity for the formation of calcite crystals in between the sand grains. Laboratory experiments were conducted using a poorly graded sand that was artificially contaminated with lead (toxic heavy metal). Algae Nostoc commune (blue-green algae) was used individually and in consortium with Bacillus (B.) sphaericus and Sporosarcina (S.) pasteurii in sand. The uncontaminated and artificially contaminated soil specimens were inoculated with different consortia combinations and treated with two different cementation media concentrations up to 16 days. After biocementation, unconfined compressive strength, direct shear, permeability, and leachability tests were conducted to analyze the engineering properties of the sand and the contaminant (lead) immobilization. The amount of calcite content was analyzed based on a calcimeter test. The leachability of lead from biocemented sand was analyzed using toxicity characteristics leaching procedure (TCLP), which showed 94%–99.2% immobilization of lead. The formation of CaCO₃ and PbCO₃ was identified by microcharacterization, which showed immobilization of leachable lead. The results revealed that biotreatment with the consortium of B. sphaericus and Nostoc commune increase strength, decrease permeability, and increase contaminant immobilization of sands.