Microbially Induced Calcite Precipitation Research Articles

Novel Strategies for Concrete Restoration: a Deep Dive into Microbially Induced Calcite Precipitation Technology

Novel Strategies for Concrete Restoration: a Deep Dive into Microbially Induced Calcite Precipitation Technology

Numerical analysis of microbially induced calcite precipitation and enzyme induced calcite precipitation in calcareous sand: Multi-process and biochemical reactions

Microbially induced calcite precipitation (MICP) and Enzyme induced calcite precipitation (EICP) techniques were implemented to reinforce the large-scale calcareous sand in this study. Then a coupled numerical model to predict the biochemical reactions and hydraulic characteristics of MICP and EICP reaction was proposed and verified by physical experiments. Results showed that: This model could describe the variations of bacteria, calcium, calcite, permeability over time reasonably. It is necessary to consider the influence of the calculation domain scale when simulating the convection-diffusion-reaction in the multi-process of MICP and EICP reactions. The numerical and experimental values of calcite content are 0.841 g/cm3 and 0.861 g/cm3 for MICP-reinforced sand, 0.263 g/cm3 and 0.227 g/cm3 for EICP-reinforced sand after 192 h of reaction. The reaction rate krea is an important parameter to control the calcite content. Accordingly, the permeability coefficient of MICP and EICP reinforced calcareous sand decreases by 32% and 18%. Due to the influence of substance transportation and calcite precipitation, the calcite shows a trend of decreasing firstly and then increasing with the enhancing of the initial permeability coefficient in biochemical reactions. The optimal injecting ratio q11: q12 in this study is 100:300 mL/min. The process for the application of MICP and EICP coupled numerical model is also recommended, which provides reference for engineering projects in ground improvement.

Effects of bacterial strains on undrained cyclic behavior of bio-cemented sand considering wetting and drying cycles

The microbial-induced calcite precipitation (MICP) technique has been developed as a sustainable methodology for the improvement of the engineering characteristics of sandy soils. However, the efficiency of MICP-treated sand has not been well established in the literature considering cyclic loading under undrained conditions. Furthermore, the efficacy of different bacterial strains in enhancing the cyclic properties of MICP-treated sand has not been sufficiently documented. Moreover, the effect of wetting-drying (WD) cycles on the cyclic characteristics of MICP-treated sand is not readily available, which may contribute to the limited adoption of MICP treatment in field applications. In this study, strain-controlled consolidated undrained (CU) cyclic triaxial testing was conducted to evaluate the effects of MICP treatment on standard Ennore sand from India with two bacterial strains: Sporosarcina pasteurii and Bacillus subtilis. The treatment durations of 7 d and 14 d were considered, with an interval of 12 h between treatments. The cyclic characteristics, such as the shear modulus and damping ratio, of the MICP-treated sand with the different bacterial strains have been estimated and compared. Furthermore, the effect of WD cycles on the cyclic characteristics of MICP-treated sand has been evaluated considering 5–15 cycles and aging of samples up to three months. The findings of this study may be helpful in assessing the cyclic characteristics of MICP-treated sand, considering the influence of different bacterial strains, treatment duration, and WD cycles.

Potentiometric ion-selective membrane sensing of microbially induced calcite precipitation

Microbially induced calcite precipitation (MICP) is an emerging biogeotechnical technique that facilitates a bio-cementation process through biomineralisation and which can bond otherwise loose soil particles, thereby increasing the shear strength and stiffness of the soil while decreasing its permeability and compressibility. However, the uniformity of calcite (calcium carbonate) precipitation may have a relatively low ‘certainty of execution’ in situ due to strict environmental conditions required for the reaction, highlighting a strong need for in situ monitoring of the subsurface during and following the treatment. This research explored an electrochemical approach to monitoring MICP treatment through the development and use of potentiometric ion-selective sensors to measure ammonium and calcium ions continuously in both aqueous batch reactors and small laboratory-scale soil test cells. Sensor calibrations indicate a strong and reliable correlation between the electrochemical potential and target ion concentration, which shows promise in sensor technology for monitoring MICP and other similar processes. Improvements to the current design are, however, needed, as fouling due to calcite precipitation, and to some extent biofouling of the sensor, was observed in the highly dynamic, biomineralisation environment, which caused data drift/interference. These effects should be considered in data analysis and eliminated/minimised for eventual adoption towards monitoring the efficacy of MICP treatment in situ.

Hydraulic barrier properties of soil beneath Egbedi active municipal solid waste dumpsite

This study researches the potential of soil underlying an active municipal solid waste dumpsite as compacted clay liner in municipal solid waste repository structure. Identification of soil samples and their chemical constituents was conducted. Ex-situ tests were conducted in the laboratory to obtain three important hydraulic barrier parameters: coefficient of hydraulic permeability (k), volumetric shrinkage strain (VSS) and shear strength (UCS) of the natural soil samples employing three compaction techniques namely; British Standard Light (BSL), West African Standard (WAS) and British Standard Heavy (BSH). Soil specimens were also prepared with varying moulding moisture contents −2%, +2 and + 4 % of optimum moisture content (OMC). The microstructure of the natural specimen was investigated via scanning electron microscopy. The natural samples were identified as; A-2-7(0), A-2-7(2) and A-7-5(5) for sample A, B and C respectively according to AASHTO classification while all samples are classified as SC (Clayey Sand) according to USCS classification. The moulding moisture content that satisfy the k and VSS conditions of k ≤ 1.0 × 10−7 cm/s and VSS ≤ 4 % falls between 9.63 – 17.68 % and 9.63–12.75 % respectively, but the tested specimens fall short of strength condition. This study revealed that the natural soil samples fail to fulfil the design parameter requirements for strength in its application as liner/cover in the active waste dumpsite, therefore further investigation to ameliorate the strength property of the soil samples using additives or microbial induced calcite precipitation (MICP) technique is recommended.

Experimental study on shield tunnel seepage control via microbially induced calcite precipitation

This study investigated the potential use of microbially induced calcite precipitation (MICP) to prevent seepage in shield tunnels with the aim of decarbonizing tunnel engineering. An apparatus was developed to conduct scale model tests to evaluate the effectiveness of using MICP for shield tunnel seepage control. To understand the MICP process and its induced change in seepage flow rate, a series of 1-g physical model tests were conducted using the designed apparatus to investigate the effect of injection methods, grouting pressure, and calcium carbonate (CaCO3) content produced as well as its distribution on the reduction of seepage flow rate for thephysical tunnel model with different backfills behind its linings. The variation law of the pore pressure near grouting hole of the tunnel segment was also revealed. Results indicated that when the amount of CaCO3 precipitation in sand-grout mixtures was 10.53% and 10.12%, water seepage flow rate for thephysical tunnel modelwith Fujian- and coarse-sand-grout backfill respectively reduced by 94.3% and 73.8% of their respective initial values, and S-wave velocity increased by 89.6% and 84.9% for Fujian- and coarse-sand-grout mixture, respectively. The grouting pressure needed to be controlled within a certain range to prevent the unstable CaCO3 precipitates from being washed away. The testing results also showed that the one-phase injection method was more effective in controlling seepage water into a shield tunnel. Based on the findings of the scale model tests, some vital considerations and suggestions were presented on the use of MICP approaches for shield tunnel seepage control.

Strengthening of Soil Through Microbial Induced Calcite Precipitation Using Acetobacter xylinum

Strengthening of Soil Through Microbial Induced Calcite Precipitation Using Acetobacter xylinum

Influence of biocementation treatment extent on dynamic system performance: A centrifuge liquefaction study

Previous centrifuge experiments have shown Microbially Induced Calcite Precipitation (MICP) is a viable ground improvement technique to mitigate liquefaction. However, in these past experiments the entire sample in the model container was MICP treated. This study is an investigation of the effect of treatment extent on the system seismic performance by varying the depth of improvement, while maintaining the same cross-sectional area. Specifically, MICP treated zones (10 cm × 10 cm in model scale in plan view) were varied in depth to 100%, 75%, and 37% of the liquefiable sand layer depth. As a comparison, two additional models were constructed, an untreated and fully treated model. The treated models were initially prepared to a relative density of less than 40% and MICP treatment applied until a change of shear wave velocity (Vs) of 300 m/s was measured. All models were instrumented with accelerometers and pore pressure transducers to capture the dynamic responses during the same sequence of eight shaking events. Cone penetration resistance was measured to verify the uniformity of the untreated zones in the models and track the evolution of penetration resistances at three different times during the shaking sequence. Vs was measured after each shaking event to assess the cementation integrity of the MICP treated zones. Linear potentiometer and pre- and post-surface measurements were obtained to track seismic-induced settlements. Pore pressure generation and settlements were reduced in the MICP treated zones compared to untreated zones, showing the increased liquefaction resistance and system performance of MICP. Amplification of the strong ground motions in the models with treatment through the full liquefiable layer lead to significant degradation of the MICP. While a base isolation effect was observed in the models not treated to the full depth of the liquefiable layer, reducing seismic demands to the MICP treated zoned, and leading to minimal changes in cementation integrity. These findings suggest that there may be a benefit to not improving the entire liquefiable depth for maintaining cementation integrity of MICPtreated soils.

Experiment on MICP-solidified calcareous sand with different rubber particle contents and sizes

Microbially induced calcite precipitation (MICP) is a new environmentally friendly technology, with the ability to improve the mechanical properties of calcareous sand. Rubber is a high-compressibility material with a higher damping ratio than that of calcareous sand. In this study, calcareous sand was replaced by equal volume contents (0%, 1%, 3%, 5%, 7%, and 9%) and different sizes (0–1, 1–2, and 2–3 mm) of rubber, and a series of water absorption and unconfined compressive strength (UCS) tests were conducted on MICP-solidified rubber–calcareous sand (MRS). The results showed that the water absorption is reduced when the rubber content is larger. The UCS of 0–1-mm MRS decreased with the increase in rubber content. For 1–2-mm and 2–3-mm MRS, the UCS was improved by 11.30% and 15.69%, respectively, compared with the clean sand. Adding rubber promoted the formation of calcium carbonate, but the strength and stiffness of rubber particles were lower than those of the calcareous sand. Therefore, higher rubber content weakened the sand frame bearing system, and the UCS decreased when the rubber content was more than 5%. Moreover, a large amount of 0–1-mm rubber led to the increase in transverse deformation of the samples, which caused the acceleration of the destruction of the sand structure. The water absorption of 0–1-mm MRS was higher than that of 1–2-mm and 2–3-mm MRS, but the UCS of 0–1-mm MRS was lower. The best rubber size is 1–2 mm and 2–3 mm, and the best rubber content is 3%–5%. The outcome of this study may, in the authors’ view, prove beneficial in improving the strength of calcareous sand when it is reinforced by MICP-combined rubber.

Reduction of the Wetting Collapse of Sandy Gypseous Soil by Using Microbial-Induced Calcite Precipitation

Microbial-induced carbonate precipitation (MICP) is a promising technology for cementing sandy soils, improving ground, repairing concrete cracks, and remediating contaminated land. The aim of this research is to implement this technology in mitigating wetting collapse of Ramadi sandy gypseous soil which has a gypsum content of about 35%. To achieve this aim, the urease-producing bacterial strain Bacillus Megaterium SI was used and treated soil specimens were prepared. The preliminary results showed a well-defined bacterium activity with a precipitated calcite of 13-16.5% by the end of the first week. The results of the collapsibility test showed that increasing cementation solution molarity from 0.25M to 1M lowered the wetting strain and total strain caused by both loading to 100 kPa and wetting by about 75%. Therefore, the MICP demonstrates the potential to mitigate the wetting collapse of the sandy gypseous soil despite its high gypsum content.

Time-Varying Modeling of Microbial-Induced Calcite Precipitation in Cracked Concrete and Its Inhibitory Effect on Chloride Diffusion

Time-Varying Modeling of Microbial-Induced Calcite Precipitation in Cracked Concrete and Its Inhibitory Effect on Chloride Diffusion

A biotechnological approach for suspended solids removal in biogas slurry via microbially induced calcite precipitation (MICP)

This study investigated the application of the microbially induced calcite precipitation (MICP) technique for removing suspended solids from biogas slurry. A series of laboratory tests on suspended solids content and colority determination was conducted to evaluate the feasibility of this technique and the removal performance of suspended solids. Combined with tests on residual calcium ions concentration and micro scale, the effects of crucial factors (including urease activity and CaCl2-Urea content) and the mechanisms of suspended solids removal were explored. The results unequivocally demonstrated the effectiveness of the MICP technique in removing suspended solids, achieving optimum removal efficiencies of 91.67 ± 1.68% for suspended solids and 96.50% for colority. The introduction of additional urease-producing bacteria via centrifugation-extraction increased the urease activity of bacterial solution and further enhanced the degree of MICP reaction, but undesirably led to a slight reduction in the removal efficiencies of suspended solids and colority due to the presence of bacteria themselves as suspended solids. Appropriately increasing the CaCl2-Urea content could offer a more adequate material supply to prolong the duration of the MICP process, significantly enhancing the removal efficiency. Nevertheless, the high salinity environment associated with excessive CaCl2-Urea addition (2.0 mol/L) would impair bacteria survival and impede the MICP process, negatively affecting suspended solids removal. The SEM-EDS analysis indicated that in the MICP process, suspended solids were tightly encapsulated by calcium carbonate (mainly calcite) to form strong immobilization aiding their gravity-driven removal. Due to the richness of organic components, they could be considered for reuse as soil amendments and fertilizers. This research provides an innovative insight into the removal of suspended solids from biogas slurry using a biotechnological approach. The MICP technique holds promise for practical applications due to its effectiveness and workability.

Enhancing Soil Resilience to Climatic Wetting‐Drying Cycles Through a Bio‐Mediated Approach

AbstractClimatic wetting‐drying cycles exacerbated by climate change can trigger several weakening mechanisms in surface soils, potentially leading to instability and failure of slopes and earthen structures. This study proposes a bio‐mediated approach based on microbially induced calcite precipitation (MICP) to increase soil resilience to wetting‐drying cycles. To explore its viability and the underlying mechanisms, we conducted a series of laboratory tests on clayey soil that underwent six wetting‐drying cycles. The tests were conducted with different treatment methods to investigate the effect of treatment sequence and cementation solution concentration. After MICP treatment, the initial evaporation rate, surface crack ratio during drying, and total soil weight loss during rainfall erosion were reduced by up to 32%, 85%, and 90%, respectively. Spraying the cementation solution first in the MICP treatment sequence proves more effective in improving soil water retention capacity. On the other hand, initiating the sequence with the bacterial solution demonstrates a more pronounced effect in reducing soil desiccation cracks and erosion. Microstructure analysis reveals that the content and distribution of CaCO3 precipitation are the major factors controlling the effectiveness of MICP for the cementation of clayey soil. Employing MICP can minimize the carbon footprint and contribute to developing environmentally friendly solutions for soil improvement in regions affected by climatic wetting‐drying cycles.

Coupled multiphysical model for investigation of influence factors in the application of microbially induced calcite precipitation

The study presents a comprehensive coupled thermo-bio-chemo-hydraulic (T-BCH) modeling framework for stabilizing soils using microbially induced calcite precipitation (MICP). The numerical model considers relevant multiphysics involved in MICP, such as bacterial ureolytic activities, biochemical reactions, multiphase and multicomponent transport, and alteration of the porosity and permeability. The model incorporates multiphysical coupling effects through well-established constitutive relations that connect parameters and variables from different physical fields. It was implemented in the open-source finite element code OpenGeoSys (OGS), and a semi-staggered solution strategy was designed to solve the couplings, allowing for flexible model settings. Therefore, the developed model can be easily adapted to simulate MICP applications in different scenarios. The numerical model was employed to analyze the effect of various factors, including temperature, injection strategies, and application scales. Besides, a T-BCH modeling study was conducted on the laboratory-scale domain to analyze the effects of temperature on urease activity and precipitated calcium carbonate. To understand the scale dependency of MICP treatment, a large-scale heterogeneous domain was subjected to variable biochemical injection strategies. The simulations conducted at the field-scale guided the selection of an injection strategy to achieve the desired type and amount of precipitation. Additionally, the study emphasized the potential of numerical models as reliable tools for optimizing future developments in field-scale MICP treatment. The present study demonstrates the potential of this numerical framework for designing and optimizing the MICP applications in laboratory-, prototype-, and field-scale scenarios.

Exploring Porosity’s Role in Stiffening Waste Concrete Conglomerates Synthesized with Microbial Calcite: A Micromechanical Analysis

Abstract Amidst environmental challenges, this study utilizes the innovative method of microbially-induced calcite precipitation (MICP) to explore its application in recycling waste concrete fines (WCF). Specifically, we scrutinize the role of porosity in the mechanical behavior of MICP-cemented WCF conglomerates. Through a series of indentation tests, the study provides force-displacement relationships from which the stiffness of the samples is calculated. The Young’s modulus of the samples is then estimated using Sneddon’s solution, which assumes a conical indenter and homogeneous elastic behavior. Subsequently, the Mori–Tanaka scheme with Eshelby’s solution is employed to predict the Young’s modulus of the samples with different porosity, allowing a comparison with the calculated stiffness. This work contributes to the understanding of the role of porosity in the mechanical behavior of MICP-cemented WCF specimens and offers a pathway for optimizing the production process of such materials. Graphical Abstract

Feeding strategies for Sporosarcina pasteurii cultivation unlock more efficient production of ureolytic biomass for MICP.

The bacterium Sporosarcina pasteurii is the most commonly used microorganism for Microbial Induced Calcite Precipitation (MICP) due to its high urease activity. To date, no proper fed-batch cultivation protocol for S. pasteurii has been published, even though this cultivation method has a high potential for reducing costs of producing microbial ureolytic biomass. This study focusses on fed-batch cultivation of S. pasteurii DSM33. The study distinguishes between limited fed-batch cultivation and extended batch cultivation. Simply feeding glucose to a S. pasteurii culture does not seem beneficial. However, it was exploited that S. pasteurii is auxotrophic for two vitamins and amino acids. Limited fed-batch cultivation was accomplished by feeding the necessary vitamins or amino acids to a culture lacking them. Feeding nicotinic acid to a nicotinic acid deprived culture resulted in a 24% increase of the specific urease activity compared to a fed culture without nicotinic acid limitation. Also, extended batch cultivation was explored. Feeding a mixture of glucose and yeast extract results in OD600 of ≈70 at the end of cultivation, which is the highest value published in literature so far. These results have the potential to make MICP applications economically viable.

Effect of fibre‐reinforced microbial‐induced calcite precipitation on the mechanical properties of coastal soil

AbstractCoastal erosion is a global environmental concern, threatening infrastructure, human livelihoods and ecosystems. Recently, microbial‐induced calcite precipitation (MICP) has emerged as a promising ground improvement technique. The present study examined the effects of adding three different fibre reinforcements, namely carbon, basalt and polypropylene, on the physical and mechanical properties of coastal soil through MICP. The fibre content used was 0.20%, 0.40% and 0.60% of soil weight. A comprehensive biotreatment investigation was conducted using Sporosarcina pasteurii (S. pasteurii) in a 0.5 molar cementation solution. The samples prepared for this study had aspect ratios of 2:1 and 1:1. These samples were subjected to biotreatment, consisting of a 24‐h cycle for 9 and 18 days. Unconfined compressive strength (UCS), split tensile strength (STS) and ultrasonic pulse velocity (UPV) tests were conducted on the biotreated samples to evaluate the effect of fibre reinforcement on the mechanical properties of the biotreated samples. The amount of calcite precipitation, scanning electron microscope (SEM) and energy dispersive X‐ray spectroscopy (EDS) were used to interpret biocementation. Results suggest that adding fibres to the MICP process enhances the mechanical properties of coastal soil. The optimum fibre content for carbon and basalt fibre was 0.40%, whereas, for polypropylene, it stood at 0.20%. The maximum UCS, STS, UPV and average CaCO3 were observed in a basalt fibre‐reinforced biotreated sample with a fibre content of 0.40%, subjected to 18‐day biotreatment. Conversely, the sample without fibre‐reinforcement, biotreated for 9 days, exhibited the lowest values for these parameters. Samples subjected to 18 days of treatment have higher values of UCS, STS, UPV and CaCO3 content than 9‐day‐treated soil samples. SEM revealed the presence of CaCO3 precipitates on the surfaces of soil grains and their contact points, and the EDS spectrum corroborated this observation.

Effects of microbially induced calcite precipitation on static liquefaction behavior of a gold tailings sand

Loose tailings are susceptible to static liquefaction during which they lose a substantial amount of their strength. This study examines a sustainable technique known as Microbially-Induced Calcite Precipitation (MICP) to improve the static liquefaction resistance of gold mine silty sand tailings. These materials were enriched with Sporosarcina pasteurii, consolidated in a direct simple shearing apparatus, and subjected to several injections of a cementation solution. Calcified tailings were then sheared under constant-volume and constant vertical stress conditions to evaluate their undrained and drained shearing behaviors. Results showed that bio-mineralization can prevent the occurrence of static liquefaction in tailings by reducing their contraction tendency. This is demonstrated by the strong strain-hardening behaviors of the treated tailings specimens compared to the strain-softening and undrained strength loss in specimens of the untreated tailings. Substantial increases in the tailings undrained and drained shear strengths (by up to 30 - 50 kPa), improvements (by up to 5 MPa) in their tangent moduli, and more than 5° rise in their friction angles are observed in the direct simple shear tests following MICP-treatment. The critical state line of tailings is also found to be steeper and shifted to denser void ratios following MICP treatment. These changes reduce liquefaction susceptibility of tailings and enhance their resistance against static liquefaction. Post-treatment acid dissolution further indicates that CaCO3 contents of about 4% to 11% precipitated in the treated specimens. This amount decreases with increasing specimens void ratio. Changes in the microstructural fabric of the cemented tailings particles are also characterized using scanning electron microscopic (SEM) images and X-ray diffraction (XRD) analyses.

The Effect of Bacillus Pumilus on the Free Swell and Atterberg Limits of Black Cotton Soil for use in Road Subgrades

The study evaluated the potential utilisation of Bacillus pumilus (B. pumilus) induced calcite precipitate for the improvement of the engineering properties of black cotton soil in road construction which is an eco-friendly technique and forms part of what is referred to as green engineering. The effect of B. pumilus on the free swell and Atterberg limits of black cotton soil for use in road subgrades was studied using microbial induced calcite precipitation (MICP) method. Five stepped B. pumilus suspension density of 0, 1.5 x 108, 6.0 x 108, 1.2 x 109, 1.8 x 109 and 2.4 x 109 cells/ml, respectively, were utilized for the treated specimens, while only cementitious reagent acted as the control specimen. Three (3) mix ratios of % Bacteria suspension (B) - %Cementitious reagent (C) (i.e., 25B - 75C, 50B - 50C and 75B - 25C) were adopted. It was observed that free swell treated with 25B - 75C decreased from 70 % and 50 % for the natural and control specimens, respectively, to minimum value of 46 %, with increasing B. pumilus suspension density at 2.4 × 109 cells/ml. Atterberg limits results showed liquid limit values decreased from 53 % and 62 % for the natural and control samples, respectively, to 43 % for samples treated with 25B - 75C at B. pumilus suspension density of 2.4 x 109 cells/ml, while the plastic limit increased from 28.2 % for the control soil sample to 30 % for the 75B - 25C mix ratio at B. pumilus suspension density of 2.4 x 109 cells/ml. Tests results indicated a considerable improvement with 25B - 75C mix ratio at B. pumilus suspension density of 2.4 × 109 cells/ml which significantly reduced the free swell, while the Atterberg limits fell below Nigerian General Specifications requirements of not greater than 35% Liquid limit, 12% Plasticity index and 35% passing No.200 sieve for utilization as road subgrades. However, it could be used as a subgrade material in low-volume roads.

Predicting the precipitated calcium carbonate and unconfined compressive strength of bio-mediated sands through robust hybrid optimization algorithms

Biological soil stabilization through Microbial-Induced Calcite Precipitation (MICP) demonstrates the potential to be an eco-friendly and sustainable approach to enhance the strength properties of cohesionless granular soils. In this study, based on a comprehensive set of experimental data compiled from literature, the amounts of Precipitated Calcium Carbonate (PCC) and Unconfined Compressive Strength (UCS) of MICP-treated sands are estimated through hybridizing Artificial Neural Network (ANN) and Adaptive Neuro-Fuzzy Inference System (ANFIS) models with metaheuristic algorithms. During the data extraction procedure, a total of 70 and 115 datasets are used to predict the PCC and UCS, respectively. Accordingly, five key features of urea concentration (Mu), calcium chloride (Mcc), optical density of bacterial suspension (OD600), pH and total volume of injection per volume of sample (Vt), are first selected as the inputs of the hybrid models to estimate the amount of calcium carbonate precipitation within the porous structure of MICP-treated granular medium. The experimental data on the PCC along with the basic characteristics of the host sand including mean grain size (D50), uniformity coefficient (Cu) and void ratio (e), are then adopted as the inputs of the numerical models in the second phase whilst the UCS of bio-mediated sands is set as the output. The performance and accuracy of implemented models are rigorously assessed through analyzing various statistical indices and performance criteria. According to the numerical analysis, the ANN-PSO and ANFIS-PSO hybrid models show the best performance in predicting PCC and UCS of bio-mediated sands, respectively. Using the well-established Gene Expression Programming (GEP) algorithm, practical correlations are developed to predict the PCC and UCS values of MICP-mediated soils based on the characteristics of biological binding agents as well as the host material. The Machine Learning (ML)-based models presented in this study provide engineers with a fruitful framework for the rough and preliminary estimation of the amount of calcite precipitation as well as the UCS of bio-mediated sands in the field prior to stabilization and performing complementary tests.