Distribution Of Calcium Carbonate Research Articles

Temperature- and alkali-resistant induced domestication of Bacillus pasteurii in drilling fluid and its borehole wall enhancement properties

The microbial induced calcium carbonate precipitation (MICP) technology provides a new approach to solve borehole destabilization in broken formations; however, the high-temperature and alkaline environments inhibit the growth of microorganisms, which in turn affects the performance of their wall enhancement performance. In this study, a pH and temperature-coupled induced domestication method was applied to Bacillus pasteurii, and its wall enhancement performance was evaluated. Post domestication, Bacillus pasteurii exhibited high growth activity at pH 10.3 and temperature 45 °C. In a sodium carboxymethyl cellulose (CMC) drilling fluid environment, bacterial concentration reached 1.373 with urease activity at 1.98 after 24 h, and in a xanthan gum (XG) environment, the figures were 0.931 and 1.76, respectively—significantly higher than those before domestication. The Bacillus pasteurii-CMC system exhibited enhanced performance with the unconfined compressive strength of the specimen up to 1.232 MPa, permeability coefficient as low as 0.024, and calcium carbonate production up to 24.685 g. The crushed specimen portions remained lumpy with even calcium carbonate distribution. In contrast, the Bacillus pasteurii-XG system exhibited the highest unconfined compressive strength of 0.561 MPa, lowest permeability coefficient of 0.081, and the greatest calcium carbonate production of 16.03 g, with an externally cemented shell but internally loose structure and uneven calcium carbonate distribution, resulting in weaker mechanical properties. The Bacillus pasteurii induced predominantly vaterite calcium carbonate crystals in the CMC drilling fluid. In the XG drilling fluid, the crystals were mainly calcite. Both types effectively cemented the broken particles, improving formation strength and reducing permeability. However, under the same conditions, the Bacillus pasteurii-CMC system demonstrated a more pronounced enhancement effect.

Enhancing biocementation performance in low permeability clayey soil through sand column strategy

Soil erosion is a common phenomenon which causes lots of geological and engineering disasters. Clayey soil erosion control is a hot research topic and a challenging issue for its low permeability and lack of effective infiltration of treatment solutions. In this study, a coupling microbially induced calcium carbonate precipitation (MICP)-sand column method was proposed as a promising and sustainable technique to mitigate surface clayey soil erosion with adjustable treatment depth. Seven groups of soil samples were prepared, including pure soil, MICP-treated soil, and MICP-sand column method-treated soil. A series of disintegration tests and penetration tests were conducted to investigate the method feasibility and adjusting mechanism of erosion mitigation with varying sand column heights and diameters. Compared to pure soil sample, sample treated by MICP-sand column (6 cm-height and 3 cm-diameter) method could reach a maximum reduction of 50 % in ultimate disintegration rate and a 30 % increase in the highest penetration resistance. The sample has a 7.9 cm effective treatment depth, which is 5.3 times of the MICP-treated sample. The mechanism of erosion mitigation can be attributed to that the sand column serves as a favorable path for the bacteria suspension and cementation solution in low-permeability-clayey soil and improves the effective depth of MICP treatment. Adjusting the height and diameter of sand column can change the calcium carbonate distribution, especially at the locations near the surface and around the sand column. In this study, the optimal height and diameter are 6 cm and 3 cm, respectively, and finally form a U-shape three-layer structure. The structure significantly increases the proportion of the hard crust layer and weak-cemented layer with high hydro-mechanical properties. In conclusion, the coupling MICP-sand column method with reasonable height and diameter of sand column shows the ability to control surface erosion of soil and has better long-term mitigation performance.

CT image-based simulation of microbially induced carbonate precipitation

Soil improvement efforts occasionally negatively impact the delicate balance of the natural environment and disrupt ecosystems. Thus, adopting ecologically sensitive techniques that can harmoniously safeguard the Earth is imperative. Recently, researchers have focused on microbially induced carbonate precipitation (MICP), an eco-friendly soil enhancement method that fosters increased interparticle cohesion and augments the mechanical strength of soil. The spatial distribution of calcium carbonate precipitation in MICP-treated soil can be observed using scanning electron microscopy and X-ray computed tomography (CT). However, since this precipitation occurs in the microscopic region, it cannot be directly observed over time. Therefore, in this study, we propose a simulation technique to replicate the MICP process using a voxel dataset obtained via X-ray CT analysis. The calculated patterns of calcium carbonate were distributed on the soil particles in the same manner as the spatial precipitation observed in the experiments. Notably, some precipitates bridged the soil particles, indicating that the proposed technique could morphologically estimate the calcium carbonate distribution through MICP. Evidently, the proposed technique could accurately simulate MICP phenomena. Furthermore, the results showed that the proposed technique can effectively express a multidiscliplinary phenomenon. Therefore, the study can inspire further studies that employ such techniques to investigate MICP.

AN EXPERIMENTAL STUDY ON STABILIZING COHESIVE SOIL USING MICROBIALLY INDUCED CALCIUM CARBONATE PRECIPITATION

Bio-cementation is an environmentally friendly procedure grounded on microbial induced carbonate precipitation mechanism, occurring in environments abundant in calcium. In the effort to bolster soil stability, traditional urea is combined with bacteria to enhance the mechanical properties of soil. The research delves into the microbial mechanisms involved in microbially induced calcite precipitation, highlighting the role of urease-producing bacteria in facilitating calcium carbonate precipitation within the soil structure. This also entails pivotal laboratory and field experiments, evaluating the efficacy of microbially induced calcium carbonate in improving soil engineering characteristics, such as strength, permeability, and durability. Furthermore, this process can be employed across various soil types, offering adaptability in geotechnical applications. Additionally, we investigate the environmental consequences and sustainability aspects by underscoring its potential as an eco-friendly substitute for soil enhancement. Nonetheless, challenges such as optimizing bacterial activity, regulating the precipitation process, and ensuring even distribution of calcium carbonate within the soil necessitate further exploration. Based on the envisioned review, it contributes to the comprehension of MICP as a promising method for soil stabilization, providing insights for researchers, practitioners, and policymakers keen on sustainable and inventive approaches to geotechnical engineering. Key Words: Bio-geotechnical engineering, soil stabilization, Microbially induced calcium carbonate Precipitation, Soil improvement.

Study on Carbonation of Porcine Blood Hydrogel in the Composite Mortar of Ancient Chinese Architectural Painting.

In the ancient Chinese recipe for composite mortar used in the construction of ground layers for architectural painting, the mixture of porcine blood and lime water is one of the constituent materials. Herein, according to the traditional recipe, the interaction between porcine blood and lime water was systematically and deeply investigated. The experimental investigation demonstrated that porcine blood mixed with lime water at the ratio found in the recipe can form a hydrogel with a hydrophobic surface. During air-drying, the lime water in porcine blood hydrogel can react with CO2 to form calcium carbonate. The crystal morphology of the formed calcium carbonate depends on the surrounding micro-environment of calcium ions in the porcine blood hydrogel. The formed morphology of calcium carbonate includes small calcite crystallites, small graininess calcite crystals with round features, calcite aggregates with layered ladder-like structures, and amorphous calcium carbonate (ACC). Interestingly, the calcium carbonate formed in the inner part of the porcine blood hydrogel exhibits lamellar distribution due to a Liesegang pattern formation. Based on the findings that the porcine blood hydrogel has surface hydrophobicity and brittleness, it can be predicted that in the preparation process of composite mortar for ancient building color painting base course, porcine blood used in the form of a hydrogel is not only easier to be dispersed in hydrophobic tung oil than in liquid porcine blood but also the affinity between porcine blood gel and tung oil is enhanced. As constituent material dispersed in the composite mortar, the layered distribution of calcium carbonate in the porcine blood hydrogel may presumably be beneficial to reduce the internal stress of the composite mortar material.

The role of electrical current mode in calcium carbonate deposition on conductive carbon nanofiber–epoxy coating

AbstractCalcium carbonate is one of the most common scaling minerals. In this paper we have used different electrical current modes (direct current [DC], pulsed DC, and alternating current [AC]) to control the amount, morphology, and distribution of calcium carbonate deposit on electroconductive epoxy/carbon nanofiber (CNF) coating. The effect of different current modes on surface scaling was visualized using scanning electron microscopy. It has been shown that both AC and DC anodic polarization limited scale deposition on epoxy/CNF coated surfaces, although the mechanisms of scale inhibition during AC and DC polarization were different. DC polarization of the coating at +2 V resulted in the smallest scale buildup without leading to coating degradation, while DC polarization at potentials as high as +5 V caused the coating to degrade. Interestingly, application of pulsed DC with high pulse frequency (50 Hz) inhibited the degradation. The type of current applied affected also the morphology of the precipitate at the cathode. The results presented in this work show, for the first time, how different modes of electrical current applied to electroconductive composite coatings can be used to control the morphology and distribution of calcium carbonate scale, and how the organic coating degradation at high polarization potentials can be avoided.

A numerical model of the MICP multi-process considering the scale size.

As an environmentally friendly and controllable technology, Microbially induced carbonate precipitation (MICP) has broad applications in geotechnical and environmental fields. However, the longitudinal dispersivity in MICP multi-process varies with the scale size. Ignoring the effect of the scale size of the research object on the dispersivity leads to the inaccuracy between the numerical model and the experiment data. Thus, this paper has established the relationship between the scale size and the dispersivity initially, and optimized the theoretical system of MICP multi-process reaction. When scale size increases logarithmically from 10-2 m to 105 m, longitudinal dispersivity shows a trend of increasing from 10-3 m to 104 m. The distribution of calcium carbonate is closer to the experimentally measured value when the size effect is considered. After considering the scale size, the suspended bacteria and attached bacteria are higher than the cased without considering the size effect, which leads to a higher calcium carbonate content. Scale has little effect on the penetration law of the suspended bacteria. The maximum carbonate content increases with the increase of the initial porosity, and the average carbonate shows a significant increasing trend with the increase of the bacterial injecting rate. In the simulation of the microbial mineralization kinetic model, it is recommended to consider the influence of the scale size on the MICP multi-process.

Development of bio-grout injection strategy and design guide using reactive transport model for field-scale soil improvement based on microbially induced calcium carbonate precipitation (MICP)

Microbially induced calcium carbonate precipitation (MICP) has garnered huge interest for its potential as an alternative and sustainable ground improvement method as it exploits natural microbiological processes. To this date, there is little or no guidance on the injection strategy to achieve a uniform calcium carbonate distribution at a field scale and most of the MICP method is still limited to lab-scale or meter-scale experimentation. Therefore, this study investigates effect of biochemical factors on spatial distribution of calcium carbonate precipitation at a field scale by using a reactive transport model, and suggests a guide to field-scale MICP treatment strategies for ground improvement. The reactive transport model couples microbial, chemical, hydrological processes associated with MICP, in which the key model parameters are validated with half-meter column experiments. The parametric case study primarily examines the effects of bacterial density in biological solutions, chemical concentration in cementation solutions, and bacterial attachment rate on spatial distribution of precipitated carbonate. The results reveal that the density of attached bacteria has a profound effect on the uniformity in calcium carbonate content around the injection point. Bio-augmentation with low bacterial density facilitates in achieving a homogeneous precipitation due to the slow reactions of urea hydrolysis. The findings in the parametric study leads to the development of preliminary design guide to achieve the uniform distribution of calcium carbonate with the minimal heterogeneity and the minimal over-precipitation and to account for the calcium loss due to the diffusion and solution mixing.

Effect of fiber type and content on mechanical properties of microbial solidified sand

Fibers are applied to construction works to improve the strength and brittle failure of the soil. In this paper, fibers with a length of 6 mm are added to the microbial cemented sand, and fiber types and content are research variable. Unconfined compressive strength (UCS), permeability coefficient, water absorption rate, dry density, and calcium carbonate precipitation of the solidified sand were tested. The physical and mechanical properties of fiber types and content on the immobilization of microorganisms were also analyzed from the micro–macro perspective. Results are presented as follows. The UCS of the Microbial induced calcium carbonate precipitation (MICP) treated sand increases first and then decreases with the increasing fiber content. This phenomenon is due to the promotion of calcium carbonate precipitation by short fiber reinforcement, the limited movement of the sand particles caused by the formed network between the fibers, and the enhanced strength of the microbial solidified sand. However, the agglomeration caused by additional fibers leads to the uneven distribution of calcium carbonate and the reduction in strength. The optimum fiber contents of polypropylene, glass, polyvinyl alcohol, and basalt fibers are 0.4%, 0.2%, 0.2%, and 0.1%, respectively.

Various Bacterial Attachment Functions and Modeling of Biomass Distribution in MICP Implementations

Microbial induced calcium carbonate precipitation (MICP) offers a robust technique to improve strength and stiffness properties of subsurface soils supporting infrastructures. Several unknown factors, including the MICP reactive transport parameters, however, limit the ability to predict spatial distribution of calcium carbonate (CaCO3) precipitation within a subsurface area and with depth. As it was shown that calcium carbonate distribution is highly affected by biomass profiles in subdomains, five bacteria attachment models (constant-rate, power-law, exponential, gamma distribution, and “cstr based on colloid attachment theory”) were calibrated here using data from both small- and large-scale testing programs. Out of the five models, colloid attachment theory with modified velocity and straining terms was shown to be the most promising approach in yielding the most fitted CaCO3 distribution compared with the experimental data. A new parameter, cstr, was incorporated to modify straining and the constraint peak value of biomass attachment due to straining at distances larger than a 0.14×sample size. Using the results from the numerical simulations, relationships were developed for velocity and straining coefficients of “the cstr based on colloid attachment theory” (hereafter “colloid attachment cstr”) as a function of bacteria size, soil particle size, sample size, volume of injected bacteria, and soil pore volume.

Experimental Study on the Effect of an Organic Matrix on Improving the Strength of Tailings Strengthened by MICP.

In order to improve the effect of microbial-induced calcium carbonate precipitation (MICP) in tailings reinforcement, sodium citrate, an organic matrix with good water solubility, was selected as the crystal form adjustment template for inducing calcium carbonate crystallization, and the reinforcements of tailings by MICP were conducted in several experiments. The effects of sodium citrate on the yield, crystal form, crystal appearance, and distribution of calcium carbonate were analyzed by MICP solution test; thus, the related results were obtained. These showed that the addition of a proper amount of organic matrix sodium citrate could result in an increment in the yield of calcium carbonate. The growth rate of calcium carbonate reached 22.6% under the optimum amount of sodium citrate, and the crystals of calcium carbonate were diverse and closely arranged. Based on this, the MICP reinforcement test of tailings was carried out under the action of the optimum amount of sodium citrate. The microscopic analysis using CT and other means showed that the calcium carbonate is distributed more uniformly in tailings, and the porosity of samples is significantly reduced by layered scanning analysis. The results of triaxial shear tests showed that adding organic matrix sodium citrate effectively increased the cohesion, internal friction angle, and peak stress of the reinforced tailings. It aims to provide a novel idea, a creative approach, and a method to enhance the reinforcement effect of tailings and green solidification technology in the mining environment.

Application of electric fields to improve cementation homogeneity of biogrouted sands

AbstractThe inhomogeneity of cementation is a common problem in soil improvement with microbially induced carbonate precipitation process (MICP), which is caused by uneven spatial distribution of bio‐induced calcium carbonate precipitation. Electric field adjustment method was developed and adopted for improving cementation homogeneity of bio‐grouted sands in this research. Horizontal one‐dimensional biogrouting experiments were conducted in sand columns under 0.1 V/cm of direct current (DC) electric field. The column treated with DC electric field showed a significant improvement in homogeneity of calcium carbonate precipitation as compared to the control (without DC electric field). Spatial distribution of calcium carbonate in columns were affected by the properties of bacteria, whether suspended or attached. In general, the attached bacteria with uneven spatial distribution played an important role in the calcium carbonate precipitation when flow rate was regulated at 0.54 cm/min, while the suspended bacteria could also be attached upon times with consumption of cations during biogrouting. With the influence of electric field, suspended bacterial transport in porous media occurred in one direction to the target locations because of the electrophoresis at an average speed of 0.14 cm/h, while sodium ion was found to be moved from anode to cathode by electromigration approach. Electrolysis of water, on the other hand, resulted a slight fluctuation in pH, even though this variation did not show any significant effect on the metabolic activity of bacteria and microbial‐induced carbonate precipitation process. The redistribution of suspended bacteria and sodium ion in porous media provided a possible for attached bacteria to distribute uniformly, which could be considered as the key factor to influence spatial distribution of the bio‐induced calcium carbonate in application of electric field adjustment method.

Impact of New Combined Treatment Method on the Mechanical Properties and Microstructure of MICP-Improved Sand

Microbially induced calcite precipitation (MICP) is a green bio-inspired soil solidification technique that depends on the ability of urease-producing bacteria to form calcium carbonate that bonds soil grains and, consequently, improves soil mechanical properties. Meanwhile, different treatment methods have been adopted to tackle the key challenges in achieving effective MICP treatment. This paper proposes the combined method as a new MICP treatment approach, aiming to develop the efficiency of MICP treatment methods and simulate naturally cemented soil. This method combines the premixing, percolation, and submerging MICP methods. The strength outcomes of Portland-cemented and MICP-cemented sand using the percolation and combined methods were compared. For Portland-cemented sand, the UCS values varied from 0.6 MPa to 17.2 MPa, corresponding to cementation levels ranging from 5% to 30%. For MICP-cemented sand, the percolation method yielded UCS values ranging from 0.5 to 0.9 MPa, while the combined method achieved 3.7 MPa. The strength obtained by the combined method is around 3.7 times higher than that of the percolation method. The stiffness of bio-cemented samples varied between 20 and 470 MPa, while for Portland-cemented sand, it ranged from 130 to 1200 MPa. In terms of calcium carbonate distribution, the percolation method exhibited higher concentration at the top of the sample, while the combined method exhibited more precipitation at the top and perimeter, with less concentration in the central bottom region, equivalent to 10% of a half section’s area.

Investigation on mechanical properties of biomimetic mineralized mortar incorporated with boric acid modifier

Microbially induced carbonate precipitation (MICP) has been intensively studied as a potential method to improve engineering properties of soil. However, MICP has limitations due to the introduction of microorganisms and the difficulty of controlling the calcium carbonate crystal precipitation model. This study proposed biomimetic mineralized mortar based on the biomimetic-chemically induced carbonate precipitation (BCICP) method with boric acid as a crystal modifier. Similar to the bacteria in MICP, boric acid can promote the nucleation of calcium carbonate and the adsorption of calcium carbonate on the surface of sand particles. Besides, the boric acid concentration can effectively change the precipitation mode of calcium carbonate. Unconfined compression strength (UCS) test and microscopic characterization were conducted to investigate the mechanism of boric acid modifying calcium carbonate crystal growth and precipitation morphology. The results show that with the increase of boric acid concentration, the reinforcement efficiency of calcium carbonate increased. With the increase of boric acid concentration, the crystalline calcium carbonate changed from a cube-shaped calcite with a smooth surface to a spherical calcite with a rough surface and the coating pattern of calcium carbonate distribution on the surface of sand particles was weakened, while the bonding-filling pattern was enhanced. Besides, the cementing fluid concentration can also affect the reinforcement efficiency of calcium carbonate and with the participation of boric acid, biomimetic mineralized mortar can use the high concentration cementing fluid to achieve effective strength enhancement. This study confirms that boric acid could effectively modify the form and distribution of calcium carbonate between sand particles, and enhance the cementation between calcium carbonate and sand particles.

Extraction of crude soybean urease using ethanol and its effect on soil cementation

One nature-based soil improvement method is the Enzyme Induced Carbonate Precipitation (EICP) approach using the crude soybean urease solution. This study aims to investigate the extraction of soybean urease using different contents of ethanol, and its effect on the cementation of EICP-treated sand. Crude urease enzyme was extracted from the soybean powder using the grinding-extraction method with distilled water containing ethanol. The activity of crude soybean urease extracted with various ethanol contents was studied. Sand columns treated using the crude soybean urease were tested to evaluate the calcium carbonate precipitation and unconfined compressive strength. The test results show that the proposed extraction method using ethanol can produce clearer crude urease solution from soybean powder. The urease activity and turbidity of the extracted urease enzyme solution are highly dependent on the content of ethanol, with the optimal ethanol content of 20%∼30% (v/v) for the preparation of 100 g/L crude soybean urease solution. The extracted relatively clear urease solution contributes to improve the uniformity of calcium carbonate distribution and thus the strength of the EICP-treated sand column.

Strength and uniformity of EICP-treated sand under multi-factor coupling effects

Enzyme-induced carbonate precipitation (EICP) is an environment-friendly method for improving soil mechanical properties. The extraction and application of plant crude urease reduces the treatment cost. However, in terms of the efficiency of calcium carbonate production and cementation, crude urease is considered inferior to pure urease or urease bacteria. In this paper, urease extracted from soybean was used to explore the effects of urease activity, treatment method, number of treatments (NTs), injection rate, and curing time on the unconfined compressive strength and calcium carbonate distribution characteristics of EICP-treated sand. The results showed that, compared with the pre-mixing method and the two-phase method, the one-phase method produced higher strength and a more uniform distribution of calcium carbonate. The cementation efficiency decreased with the increase of urease activity. The high-rate injection can improve the treatment effect of high-activity urease. Under the same cementation level, high strength and calcium carbonate cementation efficiency can be achieved by one-phase-low-activity EICP treatment. Data Availability StatementAll data, models, and code generated or used during the study appear in the submitted article.

The Investigation of the Mechanical Properties of EICP-Treated Sand Specimens Prepared by a Double-Reservoir Injection System for Uniform Precipitation of Carbonate via Triaxial Tests

Abstract The injection condition of enzymatic-induced carbonate precipitation (EICP) grouting for uniform precipitation and the mechanical properties of EICP-treated soil specimens were investigated in this study. Urease derived from yellow soybeans was used as the catalyst for the precipitation of the carbonate instead of the expensive purified urease commonly used. The uniformity of the calcium carbonate distribution was investigated by measuring the calcium carbonate content at various locations within the EICP-treated soil specimens through the soil column injection tests. The results showed that the uniformity of the calcium carbonate distribution depends on the reservoir system for the storage of the injection solutions and the injection volume that is associated with the colloidal transport of urease. Based on the proposed injection method, the EICP-treated soil specimens were prepared for two soil types and a series of consolidated undrained triaxial compression tests were conducted to investigate the mechanical properties. It was confirmed that the undrained shear behavior of the EICP-treated sand specimens shows more softening behavior. In addition, the use of a high molarity urea-CaCl2 solution resulted in pronounced reinforcing effects on the strength, which included both the peak and residual strength and the stiffness. The effects of the confining pressure and the soil types on the strength and stiffness were also investigated.

Microbially-Induced Calcium Carbonate Precipitation Test on Yellow Sandstone Based on LF-NMR Monitoring

The microbially-induced calcium carbonate precipitation (MICP) technique has shown great robustness in dealing with soil and groundwater contamination problems. A typical result of the implementation of MICP technique is a change in the pore structure. In this study, the effects of MICP on the pore structure of yellow sandstone from the Zigong area, Sichuan, China under different conditions, (e.g., temperature, pH, and calcium ion concentration) are investigated using LF-NMR resonance. The pore network of yellow sandstone is accurately measured using the peak area of the T2 spectral signal. The distribution of calcium carbonate in the pores of the yellow sandstone is characterized by the magnitude of the T2 signal variation. The results show that the precipitation of calcium carbonate caused by MICP tends to be deposited in relatively large pores. However, the calcium carbonate precipitates in the smaller pores at a higher temperature. A higher pH considerably enhances the precipitation, and the alkaline environment tends to cause the precipitation of the calcium carbonate in the large pores. Although the amount of produced calcium carbonate continuously increases as the MCIP process continues, which is expected, the production efficiency decreases steadily.

Electricity-reaction–diffusion system for microbially induced carbonate precipitation

Microbially induced carbonate precipitation (MICP) has attracted attention as a novel soil-improvement technique. The precipitation and growth of calcium carbonate on the surface of sand and in its pores can be simulated using the recently proposed numerical simulation techniques. However, these simulations have not incorporated certain parameters, such as electrical properties and adsorption. The current study proposes a novel coupling system that considers the adsorption of microorganisms and dissolved ions due to the weak electrostatic field generated on the surface of sand. Additionally, the Michaelis–Menten model was introduced into the system for the enzymatic reaction of ureolytic bacteria, the Monod model for bacterial growth, and a chemotaxis model. To validate the proposed simulation model, previously reported experimental and computational results were compared with the suggested simulation results. Consequently, the calcium carbonate precipitation obtained with the simulation model was 0.335 μmol/mm3 at 10.3 h, which is close to that obtained by the experiment of 0.315 μmol/mm3. Moreover, the spatial distribution of calcium carbonate was consistent with the precipitation pattern of the active bonding structure obtained by the traditional experiment.

Influence of Fiber Type and Length on Mechanical Properties of MICP-Treated Sand.

Fibers are applied in construction work to improve the strength and avoid brittle failure of soil. In this paper, we analyze the impact mechanism of fiber type and length on the immobilization of microorganisms from macroscopic and microscopic perspectives with fibers of 0.2% volume fraction added to microbial-induced calcite precipitation (MICP)-treated sand. Results show the following: (1) The unconfined compressive strength (UCS) of MICP-treated sand first increases and then decreases with increasing fiber length because short fiber reinforcement can promote the precipitation of calcium carbonate, and the network formed between the fibers limits the movement of sand particles and enhances the strength of the microbial solidified sand. However, the agglomeration caused by overlong fibers leads to uneven distribution of calcium carbonate and a reduction in strength. The optimal fiber length of polypropylene, glass, and polyvinyl alcohol fiber is 9 mm, and that of basalt fiber is 12 mm. (2) The UCS of the different fiber types, from small to large, is basalt fiber < polypropylene fiber < glass fiber < polyvinyl alcohol fiber because the quality of the fiber monofilament differs. More fibers result in more a evident effect of interlacing and bending on sand and higher strength in consolidated sand.