Microbially induced carbonate precipitation (MICP) using ureolytic bacteria has emerged as a promising technique for geotechnical applications, including soil stabilization, land remediation, and groundwater control. This bio-mediated process relies on urease activity to hydrolyze urea, leading to calcium carbonate precipitation, which enhances soil strength and stiffness. In this study, the mechanical behavior of silica sand treated with MICP was investigated under varying cementation concentrations (µ) (0.25–1 mol/L), cementation ratios (β) (10–90%), and injection cycles (3, 14, and 21). Key parameters evaluated included unconfined compressive strength (UCS), secant modulus (E50), and calcium carbonate content. The results demonstrated a significant correlation between calcite content and mechanical properties, with optimal performance observed at 14.98% calcite content. This configuration yielded a UCS of 1030 kPa and an E50 of 389 MPa, achieved using Sporosarcina pasteurii, a β = 50%, and a µ = 0.75 mol/L over 21 days. Findings highlight the critical role of injection cycles and cementation concentration in achieving uniform calcium carbonate distribution and enhancing soil behavior. This study underscores the potential of MICP for tailored geotechnical solutions, providing valuable insights into optimizing bio-cementation processes.

In addition to being a major environmental hazard, hydrocarbon Contamination, in contaminated sandy soils, reduce its resistance parameters and are released as an environmental and engineering hazard to nature. There are many ways to refine and improve such soils. In the present study, improvement of soils contaminated by two types of hydrocarbons (motor oil and gasoline) was performed using the Sporsarcina pasteuri strain bio-based injection method and then calcium carbonate sequestration in a tank based on the gravity penetration of microbial improvers. Effects of Hydrocarbon, Density and Inhibitory Effects on Exposure to Microorganisms (Using Disk Inhibitory Test Results) are among the factors that influence the rate and mode of recovery and improvement with any degree of success in hydrocarbon contaminated soils. Thus, the results of the improvement process were investigated after injection and, obviously, due to the high inhibitory of the motor oil to the gasoline, the improvement process in this pollutant was less than that of the gasoline. Most bio-improvement also occurred in non-polluted soil.

The use of biotechnology-based methods in the field of geotechnical engineering has led to the birth of new knowledge of biogeotechnology and several studies have been conducted using this new knowledge in various geotechnical issues including reducing permeability and increasing shear strength, especially in sandy soils and the desired results have been obtained. Nevertheless, little research has been done using biogeotechnology in the field of improving the mechanical properties of clay soils, especially in reducing the swelling of expansive soils, which is considered one of the types of problematic soils. The main cause of swelling of expansive soils is the presence of montmorillonite clays in these types of soils. Using chemical additives to stabilize expansive soils such as lime and cement is a common practice. However, environmental concerns related to greenhouse gas production caused by the production of chemical substances and the destructive effects of these substances on the environment and soils have encouraged researchers to use other sustainable stabilization alternatives. Microbial Induced Carbonate Precipitation (MICP) is a technique that can be a promising solution to solve this problem. The objective of the present study was to investigate the effect of the MICP method on the swelling of expansive clay soils and its effect on the mechanical strength of this type of soil. One-dimensional swelling tests, uniaxial compressive strength tests, and Atterberg limits tests were performed on clay soil with a liquid limit of 53 using Sporosarcina pasteurii bacteria, calcium chloride, and urea as nutrients. Taguchi's method was used for the design of the experiments and the statistical analysis of the results. This method designs experiments through partial factorial and reduces their number without a significant effect on the results. Bacterial concentration, nutrient molarity ratio, treatment time, and soil moisture were selected as four factors with Four levels of variation. The results showed that the (MICP) method was effective in reducing the swelling potential of expansive soils and also caused a significant increase in the unconfined compressive strength of the soil and its undrained shear strength.

Microbial induced carbonate precipitation (MCIP) is an environmentally and suitable method for soil remediation. In this method, urea is hydrolyzed by the urease enzyme, that is splashed from Sporosrcina Pasteurii bacteria. The calcium carbonate is formed in the presence of calcium ion. Calcium carbonate connects the soil particle like a bridge and improve its engineering characteristics. In the present research, the effect of MICP on the permeability of carbonated sand was investigated. The effect of factors such as concentration of the cementation solution, curing time and relative density on soil permeability have been studied. To consider the effect of different factors on the MICP performance, number of samples have been treated with MICP method and then constant head permeability test were conducted on the treated samples. the results show that as the concentration of cement solution was increased, the permeability of the samples was decreased. Loose Samples resulted in more decrease in permeability with respect to the dense samples. Also, bacterial activity was increased with time and after 14 days the variation in permeability was reduced. The highest rate of permeability reduction was around 60% for the sample prepared in loose state and cured with one molar concentration of cementation solution for 28 days

Background: Microbial induced carbonate precipitation (MICP) is a promising biological soil improvement method in geotechnical and geo-environmental engineering, which requires the recognition of the effects of various treatment methods on its applications. Methods: To improve the efficiency of MICP by urea hydrolysis bacteria, bio-grouting experiments were conducted at low urease activity using laboratory sand columns, and injection scenarios with different procedure steps were performed. The scenarios varied in the incubation time, fixation fluid, and number of the injection steps, and their efficiency was assessed using the unconfined compressive strength test. Results: The sand column experiments with multistep injection of bacteria and cementation solution showed that when the precipitated calcium carbonate content increased from 7. 7% to 18. 9%, the strength of the samples enhanced from 0. 25 to 1. 55 MPa, respectively. The precipitation conditions were influenced by the sand grain properties. The samples with diversified particle sizes had greater strength than those with uniform particle sizes. The multistep cementation solution injection at various concentrations had a significant clogging effect, thereby decreasing the sand column permeability. Conclusion: According to the laboratory results, this innovative technique could be potentially practical for engineering applications, such as liquefaction prevention, clogging, and sand in oil reservoir consolidation.

Fast growing of engineering infrastructure to meet human requirements is directly related to the need for a resistant soil to carry out construction load. On the other hand, the importance of environmental issues has led to an ever-increasing demand for new and environmentally friendly methods for soil remediation. The method of microbial induced calcium carbonate precipitation (MICP) is considered by the researchers as one of the most environmentally friendly methods. The purpose of this study was to investigate the effect of MICP on the uniaxial strength of carbonate sand. Therefore, samples of Bushehr carbonate sand were cured after the injection of bacteria and cement solution. Then a uniaxial compression tests were carried out to evaluate the compressive strength. Also, the effect of cement solution concentration and curing time on the results of MICP method was investigated. The results show that maximum uniaxial strength of sand stabilized with MICP is about 3. 5 kg/cm2, which indicates the proper performance of MICP method for stabilization of carbonate sand. The UCS of the samples depends on the concentration of cement solution. Stabilized samples with a higher cementation of concentration solution had more uniaxial resistance than samples with lower cement concentrations. The curing time more than 14 days did not significantly affect the uniaxial resistance.

The use of different soil improvement methods has always been accompanied by an assessment of the impact on strength parameters, costs and environmental impacts. Since new and eco-friendly methods are associated with a high initial cost, optimizing these methods in order to commercialize them is the priority of research projects. The use of biologic methods for soil improvement, despite its high environmental compatibility, has not been welcomed from the economic point of view in most parts of the world and is still being considered as an academic and not an executive method. Improvement of soil using calcium carbonate sedimentation is one of the most environmentally friendly biological methods. One of the most influential bacterial suspension parameters for calcium carbonate treatment is its culture medium, usually Nutrient Broth or Yeast Extract. An alternative culture medium is one of the ways to reduce the cost of biodiversity in the soil. In this research, the use of sugar beet molasses, which is a waste of sugar and sugar factories, has been investigated as a suitable culture medium for biological improvement along with other culture media. It can reduce the cost of producing a suitable culture medium by up to 500 times. The success of soil regeneration after bacterial cultivation has been evaluated in this study.