Assessment of Unconfined Compressive Strength of MICP-Treated Sand Using Computational Approaches

The current study applies a soft-computing approach based on the gradient boosting method to predict the unconfined compressive strength (UCS) of sands treated with microbially-induced calcite precipitation (MICP). A 10-fold cross-validation method and hyperparameter tuning are performed to find the optimal architecture of the gradient boosting algorithm. A total of 402 data of unconfined compression tests performed on biocemented sands are utilized in this study. The dataset includes eight input parameters: median sand particle size, uniformity coefficient of sand, initial void ratio, calcium chloride concentration, urea concentration, urease activity, optical density of bacteria, and calcite content. The finding demonstrates that the gradient boosting method outperformed five commonly used machine learning algorithms (artificial neural networks, random forests, k-nearest neighbors, support vector regression, and decision trees) in predicting the UCS of biocemented sands. Using the gradient boosting, the predicted UCS has a strong correlation with the actual values (R2 = 0.95). Moreover, a series of correlation and feature importance analyses are carried out over the dataset. The relationships between unconfined compressive strength, calcite content, and initial void ratio are discussed within the article. Furthermore, some guidelines are provided for assessing the effect of environmental factors on the UCS of biocemented sands. For further study, the limitations of this study regarding the insufficiency of data for correlation and environmental modification are addressed.

Unconfined compressive strength of bio-cemented sand: state-of-the-art review and MEP-MC-based model development

The Microbially Induced Calcite Precipitation (MICP) grouting technique was conducted to cement strongly weathered granular granite, and the influence on physical and mechanical properties and disintegration characteristics of specimens after being cemented with different cementing solvents, cementitious concentrations, and rounds of grouting cycles in the seawater environment was analyzed. The results showed the physical and mechanical properties and disintegration resistance of the strongly weathered granular granite were distinctly improved after being cured by MICP; meanwhile, when seawater was used as cementing solvents, the cementitious effect for specimens was better than that in freshwater, and its unconfined compressive strength, calcium carbonate content, dry density and disintegration resistance were higher than those in freshwater. In addition, with the increase in the cementitions concentration, unconfined compressive strength, calcium carbonate content and dry density of specimens tended to first increasing and then decreasing, simultaneously, the final disintegration ratios of specimens tended to first decreasing and then increasing. The optimum cementitious concentration was 0.75 mol/L. The calcium carbonate content and unconfined compressive strength of cured specimens increased with the increase in rounds of grouting cycles and the final disintegration ratios were gradually decreased in the optimum cementitious concentration solution; the maximum value of unconfined compressive strength of specimens after 4 rounds of grouting cycles was up to 9.38 MPa, and the disintegration ratio was only 1.5%.

As an eco-friendly treatment method, the microbially induced calcite precipitation (MICP) approach has been widely adopted in sand, but its use on compacted fine-grained soils remains scarce. In this study, compacted completely decomposed granite (CDG) soils at both the dry and wet side of the optimum water content (dry- and wet-of-optimum) were treated by the MICP approach, using a bacterial suspension and chemical reagents at fixed concentrations. After various curing periods, the microstructure (by scanning electron microscopy testing), the produced calcium carbonate content, the unconfined compressive strength (UCS), and the thermal conductivity were analyzed through a series of laboratory tests. The testing results indicate that the sample at dry-of-optimum exhibits a flocculated microstructure, while a dispersed microstructure is shown for the sample at wet-of-optimum. The calcium carbonate content increases with the curing period until reaching a stable value at around 6 days’ curing. After 6 days’ curing, the MICP process is relatively static, without significant amounts of calcium carbonate produced. With this treatment, the UCS of the sample is improved, where higher efficiency was observed for the sample at wet-of-optimum conditions. The variation of UCS for the MICP-treated samples with respect to the curing period follows the same trend as that of calcium carbonate content. At dry-of-optimum, the air-solid phases control the heat transfer in the MICP-treated samples with a discontinuous water phase, leading to insignificant effects of the MICP treatment on the thermal conductivity. In contrast, the water-solid phases dominate the heat transfer in the MICP-treated samples at wet-of-optimum, resulting in variation of the thermal conductivity with the curing period similar to that for the calcium carbonate content.

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

Experimental study on the effect of cementation curing time on MICP bio-cemented tailings

Systematic optimization of a novel, cost-effective fermentation medium of Sporosarcina pasteurii for microbially induced calcite precipitation (MICP)

Microbially induced carbonate precipitation (MICP) has proven to be an effective method for soil reinforcement. Sporosarcina pasteurii is widely used due to its high urease activity. However, being an alkaliphilic bacterium, its limitations in acidic soil environments tend to be overlooked. This study isolated a native urease-producing bacterial strain Bacillus aryabhattai with acid tolerance, and comparative analysis of the growth characteristics of B. aryabhattai and S. pasteurii. The grouting and spraying techniques were employed to reinforce granite residual soil by the B. aryabhattai and the S. pasteurii, and the reinforcement mechanisms were systematically investigated. Experimental results indicated that despite exhibiting slightly lower urease activity and growth, the indigenous urease-producing bacterium B. aryabhattai demonstrated superior environmental resilience in terms of both environmental temperature and pH range. The soil samples reinforced by grouting with B. aryabhattai and S. pasteurii exhibited increases in ultrasonic wave velocity, unconfined compressive strength, cohesion, and cumulative disintegration rate to varying degrees compared to the untreated soil samples. Meanwhile, the resistance value of the soil samples reinforced by spraying with B. aryabhattai and S. pasteurii decreased by 84.39% and 79.79%, respectively. Additionally, the calcium carbonate content in the upper section of soil reinforced with B. aryabhattai was comparable to that of S. pasteurii; however, while in the lower section, it exhibited a 36.22% higher precipitation rate than the S. pasteurii-treated soil. Overall, the indigenous strain B. aryabhattai demonstrated remarkable reinforcement effectiveness, attributed to its rapid adaptation to weakly acidic soil conditions and moderate urease activity, which promoted a homogeneous distribution of calcium carbonate. These findings provide significant insights for soil reinforcement applications through MICP.

Effect of freeze-thaw cycles on engineering properties of biocemented sand under different treatment conditions

Enhancing mechanical strength of Yili loess soil using microbial-induced calcite precipitation (MICP)

Granite residual soil is widely distributed in South China, which often brings landslide and other geological disasters because of its obvious characteristics of water disintegration. Microbial Induced Calcite Precipitation (MICP) technology could improve the engineering properties of granite residual cemented-soil in the process of calcite precipitation. This study presents a laboratory tests to verify the process and to explore the influence of MICP technology on the mechanical properties of cement-soil such as strength and stress-strain relationship. Various technological factors such as cement mixing ratio (CMR), calcium ion concentration (CC) and calcium source (CS) were studied for the mechanical property improving of reinforced soil. Unconfined compressive strength (UCS) test was conducted to analyze the mechanical strength of cemented-soil strengthened by MICP. Based on these works, we have the following conclusions: (1) MICP technology can significantly enhance and improve the engineering properties such as strength, stiffness and toughness of cemented-soil; (2) Compared with the control group, the maximum growth rate of strength in the test group is 87.5%, and the most economical cement mixing ratio is about 15% (3) Calcium chloride and calcium acetate can improve the toughness of the sample, but the effect of calcium acetate is better, compared with the control group, the maximum growth rate of the toughness of the test group is up to 69.67%, when the calcium ion concentration is 0.5 mol/L.KeywordsGeotechnical engineeringBacillus pasteuriiMicrobial Induced Calcite Precipitation (MICP)Cement-soilMechanical properties

The practice of soil treatment using cement and zeolite is an approach that can be widely used in soil stabilization particularly in road construction, as a support layer for shallow foundations, to strengthen slopes, and to prevent sand liquefaction. The present research intends to quantify the impact of both amounts of cement and zeolite, porosity index, porosity/cement and porosity/SiO2 and Al2O3 particles ratio on zeolite cemented sand mixtures by the assessment of unconfined compressive strength (UCS). A program of unconfined compression tests considering three distinct porosity ratio, four cement contents (2, 4, 6 and 8%) and six different percent of cement replacement by zeolite (0, 10, 30, 50, 70 and 90%) is performed in this study. Results indicate that cement replaced by zeolite at optimum proportion of 30%, the value of improved UCS of the cement sand specimens due to zeolite and cement chemical properties are exploited. Increasing cement content and porosity of the compacted mixture, the efficiency of using zeolite rises. In this paper, it has been shown that for the zeolite–cement–sand mixtures, UCS increases via cement content (C) raise and porosity (η) reduction and a power function is well-adapted to fit both UCS-C and UCS-η. Finally, key parameter SiO2 and Al2O3 particles as active particles (AP) introduced and six UCS-AP diagrams are drawn, any of which is traced to a specific amount of zeolite. Afterwards, UCS is plotted against 1/AP and η/AP which is regarded as a controlling parameter of UCS. As a consequence, for each of the zeolite–cement–sand mixtures studied, a target UCS value could be obtained using a specific correlation (1.5E8 η-1.713AP1.424, R2 = 0.982) by porosity reductions, cement content rises and zeolite variations. This experimental research and key parameter AP will introduce an acceptable description of the mechanical parameters which are extensively used in the subgrade and foundation designs.

Expansive soils are considered problematic for civil engineering applications due to their low strength, high compressibility, and poor bearing capacity, which limit their use as foundation or pavement subgrade materials. To overcome these limitations, this study investigates the stabilization of expansive soil using gypsum and Microbially Induced Calcite Precipitation (MICP) as strengthening agents. The experimental program was carried out in three stages. In the first stage, gypsum, an industrial by-product, was incorporated into the soil in varying proportions of 2%, 4%, 6%, 8%, and 10% by dry weight. The treated samples were tested for Unconfined Compressive Strength (UCS) and California Bearing Ratio (CBR). The results revealed a significant improvement in strength with increasing gypsum content up to 4%, beyond which a slight reduction was observed. Thus, 4% gypsum was identified as the optimum content for stabilization. In the second stage, MICP treatment was applied by introducing bacterial solutions in concentrations of 2 ml, 4 ml, 6 ml, 8 ml, and 10 ml under optimum moisture conditions. The treated samples were tested for Unconfined Compressive Strength (UCS) and California Bearing Ratio (CBR). The results revealed a significant improvement in strength with increasing MICP content up to 4ml-MICP, beyond which a slight reduction was observed. Thus, 4ml-MICP was identified as the optimum content for stabilization. In the final stage, 4% gypsum and MICP (4 ml MICP concentration) were combined and applied to new soil samples to evaluate the combined effect on strength enhancement. However, the results showed a decrease in strength in the UCS test. The comparative analysis indicated that the individual treatments performed better depending on the curing period. Overall, the study demonstrates that gypsum provides a more sustainable improvement when compared to MICP, whereas MICP offers a more cost-effective solution. Both gypsum and MICP are environmentally friendly stabilizers suitable for enhancing the performance of expansive soils in geotechnical and pavement applications

Stabilizing organic clay soils is pretty tough in geotechnical engineering because these soils are highly plastic, have low strength, and using common stabilizers like cement and lime often brings environmental concerns. This paper takes a close look at two new ways to stabilize soil using biological processes: Microbially Induced Calcite Precipitation (MICP) and Enzyme Induced Calcite Precipitation (EICP). This research looks closely at existing studies and experimental data to compare how well different sustainable options improve organic clay soil. The research uses supervised machine learning methods, like Random Forest, to build predictive models for soil stabilization. These models are based on key factors such as soil type, treatment concentration, curing time, and microstructural features. The results show that both MICP and EICP clearly improve the mechanical properties of soil. MICP can boost Unconfined Compressive Strength (UCS) by anywhere from 10% to 66% depending on the soil type, while EICP helps bring down the liquid limit from 79% to 58.It goes up by 8% and increases the plastic limit from 30% to 47.8%Putting biochar into MICP (MICP-BIN) really changed things, increasing shear strength by 389.It was 5% higher than soil that hadn’t been treated. Using SEM, EDX, and XRD to look at the microstructure, it was clear that calcium carbonate precipitation was the main way the soil got stabilized. The crystals form and clump the soil particles together, which reduces the spaces between them. The machine learning models were able to predict pretty accurately how effective the treatments would be. Looking at which features mattered most, it turned out that calcium carbonate content, curing time, and the soil’s initial plasticity were the key factors. This study offers a basic framework for choosing and improving bio-cementation methods based on data to stabilize cohesive soil. It focuses on a sustainable way to reduce carbon emissions while improving geotechnical performance in infrastructure projects.

The cementation of desert aeolian sand is a key method to control land desertification and dust storms, so an economical, green and durable process to reach the binding between sand grains needs to be searched. The method based on the microbially induced calcite precipitation (MICP) appeared in recent years as a promising process that proved its efficiency. The feasibility of the MICP technique to treat aeolian sand composed by low clay content, fine particles, low water content and characterized by weak permeability was demonstrated in the present paper. The effects of initial dry density, cementation number and curing time on the permeability and strength of MICP-treated aeolian sand were investigated using permeability tests and unconfined compressive strength (UCS) tests. The microstructure of aeolian sand was observed by scanning electron microscopy (SEM) tests and X-ray diffraction (XRD), aiming to reveal the solidification principle of MICP. The tests result indicated that when the initial dry density and the cementation number rose, the hydraulic conductivity of aeolian sand decreased while the mechanical strength given by UCS values improved. When the initial dry density was 1.65 g/cm3, the curing time was 3 h and the cementation number reached 20, the hydraulic conductivity and UCS reached 0.00151 cm/s and 1050.30 kPa, respectively. With increasing curing time, the hydraulic conductivity first decreased, followed by an increase, while the UCS exhibited an up and then a downtrend. Furthermore, the correlation between UCS values and the CaCO3 content reached a high R2 value equal to 0.912, which confirmed that the cementation occurred in sandy material and governed the soil strengthening. Indeed, the calcium carbonate crystals observed by SEM and XRD enhanced the friction between particles when they wrapped around the sand grains surface, while carbonates reduced the soil permeability when filling the pores and sticking the sand particles together. Finally, the theoretical and scientific knowledge brought by the present study should help in managing sand in desert areas.