Experimental Study on the Shear Strength and Durability of Microbial-Consolidated Silty Sand under Low pH Conditions

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Through orthogonal experiments, the optimal culture conditions were determined as follows: pH = 3, O D 600 = 4, and C S = 2 mol/L. Based on this optimal grouting scheme, the distribution of calcium carbonate in microbial-solidified soil samples, as well as the changes in sample strength and durability, were investigated. Scanning Electron Microscopy (SEM) tests were also conducted to observe the microstructure characteristics of the solidified samples. The results indicate that the low-pH single-phase grouting method contributes to promoting a more uniform distribution of calcium carbonate during the microbial reaction process. Compared to the two-phase grouting method, the internal friction angle of samples solidified using the low-pH single-phase grouting method increased by 17.9%, and the cohesive force increased by 46.3%. In immersion tests, the final mass loss rate of samples solidified with the low-pH single-phase grouting method decreased by 16.13%, and the strength loss decreased by 21.1%. In dry-wet cycling tests, the final mass loss rate of samples solidified with the low-pH single-phase grouting method decreased by 13.8%, and the strength loss decreased by 16.9%. Physical sciences/Engineering/Civil engineering Biological sciences/Biotechnology/Environmental biotechnology microbial-induced calcite precipitation grouting method low pH value geotechnical testing microstructure Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1. Introduction Microbially induced calcite precipitation (MICP) is currently one of the promising bio-mediated soil improvement technologies [ 1 ]. Compared to traditional soil improvement methods such as chemical grouting, electro-osmotic consolidation, and vacuum preloading, MICP offers advantages such as minimal soil disturbance, resource conservation, and environmental protection. Microbial mineralization, which widely exists in nature, refers to the phenomenon where certain microorganisms form mineral crystals through their metabolic activities. Calcium carbonate, a widely distributed carbonate with stable properties, excellent strength, and durability, has always been a research hotspot in microbial mineralization, particularly in the context of MICP [ 2 ]. In 2004, literature [ 3 ] was the first to apply MICP technology in the field of soil improvement, demonstrating that the technology could induce the precipitation of calcium carbonate in sandy soil, significantly enhancing the mechanical properties of the solidified soil. Literature [ 4 ] further confirmed through microscopic analysis that calcite-type calcium carbonate was the primary cementing component in the mineralized products. Subsequently, scholars investigated the effects of various factors, including different types of microorganisms [ 5 ], calcium sources [ 6 ], and cementing solutions [ 7 ], on the MICP reaction. Currently, there are still many challenges in the application of MICP technology for soil improvement, with one of the key issues being how to ensure uniform strength in the solidified soil [ 8 ]. Specifically, during the grouting process, calcium carbonate tends to precipitate preferentially near the grouting port, resulting in significant regional differences in soil improvement effectiveness [ 9 ]. Literature [ 10 ] points out that achieving uniform distribution of calcium carbonate within the target treatment area has been identified as one of the major challenges facing the upgrading of microbial grouting technology. In early studies, literature [ 11 ] employed a single-phase grouting method where a mixture of bacteria and cementing solution was directly injected into the soil. Due to bacterial aggregation and rapid calcium carbonate formation, the grouting orifice became clogged, making it difficult for the reaction to penetrate deeply into the soil. Literature [ 12 ] proposed a two-phase grouting method, which to some extent alleviated the issue of orifice clogging. However, since the bacteria first contacted and reacted with the cementing solution at the injection site, there were still significant differences in strength at different locations within the sample. Literature [ 13 ] introduced an improved two-phase grouting method based on the original two-phase method, which led to some improvement in strength uniformity across different locations of the sample. Yet, during the injection of the cementing solution, bacteria were carried away, making it difficult to determine the bacterial quantity at different locations, which affected the uniform distribution of calcium carbonate. Some scholars attempted to use other methods to improve the uniformity of calcium carbonate distribution. Literature [ 14 ] resuspended the bacterial cells in distilled water and studied the effect of different urease activities on the strength of sand columns. It was found that the compressive strength at the top of the sand column was approximately one-fifth of that achieved through traditional grouting methods, but the distribution of calcium carbonate was significantly improved. Literature [ 15 ] compared the effects of different concentrations of bacterial solution on the consolidation of quartz sand and found that higher concentrations of bacterial solution led to increased calcium carbonate production and improved mechanical properties. Literature [ 16 ] employed a temperature-controlled method to improve the uniformity of calcium carbonate distribution by mixing the bacterial solution with the cementing solution at 6℃. Due to the inhibition of microbial activity at low temperatures, the distribution of calcium carbonate precipitation in the soil was significantly improved. Literature [ 17 ] conducted experiments on small-sized sand columns to investigate the impact of two calcium sources, calcium chloride and calcium acetate, on the uniformity of cemented samples. It was found that calcium acetate as a calcium source could improve the uniformity of calcium carbonate distribution within the samples. Current research on improving the uniformity of soil solidification using Microbially Induced Carbonate Precipitation (MICP) technology mainly focuses on grouting procedures, bacterial solution concentration, nutrient solution formulation, and other aspects. Literature [ 18 ] proposes a low-pH one-phase grouting method (hereinafter referred to as DYF), which involves lowering the pH of the one-phase slurry (a mixture of bacterial solution and cementing solution) before grouting to inhibit initial reactions. Controlling the grouting process under low-pH conditions has proven effective in enhancing the uniform distribution of calcium carbonate in the solidified soil, providing a new direction for solving the problem of grouting orifice clogging. However, there is a lack of research in this area, and no studies have yet reported on the influence of multiple factors under these conditions on MICP-solidified soil or the underlying mechanisms of strength enhancement. This study aims to determine the optimal grouting scheme through orthogonal aqueous solution experiments and conduct experimental research on the uniformity of calcium carbonate distribution, shear performance, and durability of grouted and solidified samples. It explores the effects of different influencing factors (bacterial solution concentration, pH, cementing solution) on calcium carbonate production, shear performance, and durability of sand columns, providing theoretical support and references for the application of MICP technology in practical engineering. 2 Experimental Materials and Equipment 2.1 Test Materials Before the experiment, impurities in the undisturbed soil were removed using deionized water, and the soil samples were adjusted to a neutral pH and then completely dried in a constant temperature oven at 100 ℃. Particle size analysis was conducted on the experimental soil samples according to the "Chinese code" (GB/T50123-2019) [ 19 ]. The particle size distribution curve is shown in Fig. 1. The soil samples exhibited d 60 = 0.77 mm, d 30 = 0.13 mm, d 10 = 0.020 mm, C u = 38.5, and C c = 1.1, indicating a well-graded soil. 2.2 Microbial strains and cultivation process The bacterial strain used in the experiment is Bacillus pasteurii, a Gram-positive aerobic bacterium that secretes a large amount of urease through metabolism. The activated bacteria were inoculated into a liquid medium at a volume ratio of 1:100 and cultivated in a constant temperature shaking incubator at 28 ℃ and 180 r/min for 36 to 48 hours. The medium was formulated with 10 g/L of peptone, 5 g/L of sodium chloride, and 3 g/L of yeast extract powder. The bacterial cultivation process is illustrated in Fig. 2. Before the experiment, the absorbance of the bacterial suspension was measured using a V-1100D visible spectrophotometer, and the bacterial concentration was characterized by the O D 600 value. The urease activity of the bacterial suspension was measured using the conductivity method proposed in literature [ 20 ]. The microbial growth curve and urease activity curve are shown in Fig. 3. Based on the test results, Bacillus pasteurii cultivated for 48 hours was selected, as both the microbial count and urease activity reached their peaks at this time. The prepared bacterial suspension was stored at a low temperature of around 4 ℃ to prevent environmental temperature from affecting bacterial activity [ 21 ]. During the experiment, bacteria cultivated at a constant temperature for 48 hours were used to prepare four groups of bacterial suspensions with different concentrations, with OD600 values of 4.0, 2.0, 1.0, and 0.5 from highest to lowest. The cementation solution (CS) provides nutrients for microbial reactions and is a mixture of equimolar calcium chloride (CaCl 2 ) and urea. Four concentrations of 0.75, 1.0, 1.50, and 2 mol/L were set for the experiment. The preparation method for the low-pH one-phase slurry follows the configuration described in reference [ 18 ], with specific steps as follows: (1) Mix equal volumes of bacterial suspension and cementation solution in an Erlenmeyer flask; (2) Adjust the pH of the mixture to 6.0, 5.0, 4.0, and 3.0, respectively, using hydrochloric acid. 2.3 Preparation of Sand Column Samples The mold used for preparing the sand column samples is a transparent PC cylinder with an inner diameter of 61.8 mm and a length of 182 mm. During the experiment, permeable stones and filter paper are placed at both ends of the mold to prevent reverse osmosis, as shown in Fig. 4. To ensure uniform packing of the sand column samples, the packing method described in reference [ 22 ] is followed, with the sand being loaded in three layers. The dry density of the sand column samples is controlled at (1.8 ± 0.5) g/cm 3 . After packing, deionized water is introduced into the samples to remove excess air bubbles. 3 Experimental Methodology 3.1 Aqueous Solution Test An orthogonal experiment with three factors and four levels was conducted to investigate the ability of microbially induced calcium carbonate precipitation (MICP) under different influencing factors. The orthogonal experiment included 16 parallel tests, with the effective precipitation rate of calcium carbonate as the evaluation index. Regression analysis was performed to determine the sensitivity of the influencing factors and the optimal cultivation scheme. (The effective precipitation rate of calcium carbonate is defined as the ratio of the actual mass of calcium carbonate produced ( m 2 ) to the theoretical mass of calcium carbonate that could be produced ( m 1 )). The levels and factors of the orthogonal experiment are shown in Table 1 , and the design of the orthogonal experiment is presented in Table 2 . Table 1 Orthogonal test levels and factors table horizontal O D 600 C S /(mol‧L − 1 ) pH 1 0.5 0.75 3 2 1.0 1.00 4 3 2.0 1.50 5 4 4.0 2.00 6 Table 2 Orthogonal experimental design table O D 600 C S / (mol‧L − 1 ) pH A 1 0.5 0.75 3 A 2 0.5 1.00 4 A 3 0.5 1.50 5 A 4 0.5 2.00 6 A 5 1.0 0.75 4 A 6 1.0 1.00 3 A 7 1.0 1.50 6 A 8 1.0 2.00 5 A 9 2.0 0.75 5 A 10 2.0 1.00 6 A 11 2.0 1.50 3 A 12 2.0 2.00 4 A 13 4.0 0.75 6 A 14 4.0 1.00 5 A 15 4.0 1.50 4 A 16 4.0 2.00 3 3.2 Experiment on Sand Column Solidification Using Low-pH One-Phase Grouting Method In this study, a comparative analysis was conducted between the experiment on sand column solidification using the low-pH one-phase grouting method and the experiment on sand column solidification using the two-phase grouting method (hereinafter referred to as LXF). 3.2.1 Experiment on Sand Column Solidification Using Low-pH One-Phase Grouting Technique (1) A peristaltic pump is used to introduce deionized water into the sample until saturation to expel internal gases. (2) Each time, prepare 40 mL of low-pH one-phase grout, ensuring it is used within a short period. (3) Use a peristaltic pump to pump 1.2 times the volume of the sand column with grout at a rate of 60 mL/h. (4) After grouting, allow the sand column sample to stand in a constant temperature incubator at 26 ℃ for 12 hours to complete the first grouting cycle. (5) Repeat the above steps for a total of three grouting cycles to enhance the reinforcement effect. After completion, incubate the sample in the incubator for 24 hours and then demold it. 3.2.2 Experiment on Sand Column Solidification Using Two-Phase Grouting Method (1) A peristaltic pump is used to introduce deionized water into the sample until saturation to expel internal gases. (2) A 0.5 mol/L CaCl 2 solution is used as the fixing solution and mixed with the bacterial suspension for injection into the sand column to immobilize the bacteria. (3) A peristaltic pump is used to pump in 1.2 times the volume of the sand column with cementation solution (using the commonly set pH in current MICP research, i.e., pH = 8.5) at a rate of 60 mL/h. (4) After grouting, the sand column sample is allowed to stand in a constant temperature incubator at 26 ℃ for 12 hours to complete the first grouting cycle. (5) The above steps are repeated for a total of three grouting cycles to enhance the reinforcement effect. After completion, the sample is incubated in the incubator for 24 hours and then demolded. 3.3 Experiment on Uniformity of Sand Column After demolding and drying, the specimens are polished with sandpaper to prevent interference from precipitated calcium carbonate crystals in the test results. The sand column samples are divided into three equal-mass sections: top, middle, and bottom. From each section, both the outer ring and inner core are taken. The calcium carbonate content of each sampled sand soil section is measured, and a comparative analysis is conducted to evaluate the uniformity of calcium carbonate in the solidified sand column by assessing the calcium carbonate content in different parts after cementation. The sampling of the solidified sand column is illustrated in Fig. 5. The acid washing method [ 23 ] is employed to determine the calcium carbonate content in the sample. The microbially treated sample is dried to a constant weight (denoted as M 1 ). It is then stirred and soaked in 4 mol/L hydrochloric acid, filtered using a vacuum filtration device, and the process of adding hydrochloric acid, stirring, and filtering is repeated until no calcium carbonate residue remains in the soil sample (denoted as M 2 ). The mass loss of the soil sample after drying represents the mass of the calcium carbonate formed. The mass loss of the soil sample after drying represents the mass of the calcium carbonate formed, denoted as CCaCO3, i.e., C CaCO3 = \({M_1} - {M_2}\) ( 1 ) 3.4 Shear Performance Test The main geotechnical tests include direct shear tests and consolidation tests, both conducted according to the "Chinese code" (GB/T50123-2019) [ 19 ]. The shear rate for the direct shear test is 0.01 mm/min, with vertical pressures of 50, 100, 150, and 200 kPa. 3.5 Durability Test 3.5.1 Soaking Test The specimens solidified by the two grouting methods are dried and allowed to reach room temperature before being subjected to a soaking test in deionized water. During the soaking test, the liquid level is maintained 15 mm above the specimens, and the deionized water is replaced every 3 days to avoid contamination of the solution. With each cycle lasting for 12 hours, the soaking cycles are set at 1, 5, 10, 15, 20, 25, and 30 cycles for the test. 3.5.2 Drying-Wetting Cycle Test (1) Place the specimens solidified by the two grouting methods into a solution with the liquid level 15 mm above the top surface of the specimens. Maintain the solution temperature at (25 ± 2) ℃ and soak for a total of 12 hours. (2) After soaking, allow the specimens to air-dry naturally at room temperature for 3 hours. (3) After air-drying, place the specimens in an oven set to 60 ℃ for drying for 3 hours. (4) After the drying process, allow the specimens to cool at room temperature for 1 hour. The above steps constitute one drying-wetting cycle with a total duration of 24 hours. Place the cooled specimens back into the solution and repeat steps (1) to (4) to enter the next drying-wetting cycle. The drying-wetting cycle also has a duration of 24 hours per cycle, and the test is set to run for 1, 5, 10, 15, 20, 25, and 30 cycles. 3.5.3 Mass Loss Rate Before conducting the durability test, record the initial mass of the specimen as m 0 . After soaking or completing the drying-wetting cycles, clean and dry the specimen, then measure its mass as m1. The mass loss rate of the specimen is calculated as the ratio of ( m 0 - m 1 ) to m 0 . 3.5.4 Unconfined Compressive Strength Test The unconfined compressive strength is used to reflect the strength loss of the specimen. After cleaning, drying, and cooling the treated specimen to room temperature, the upper and lower surfaces are leveled. The test is conducted using a strain-controlled unconfined compression apparatus. 4 Test Results and Analysis 4.1 Analysis of Aqueous Solution Tests The aqueous solution tests analyze the production of calcium carbonate as an indicator, and determine the optimal cultivation scheme using the K-value method. The larger the range indicator R, the better the evaluation of the results, as shown in Tables 3 and 4 . According to Tables 3 and 4 , the three factors in the orthogonal test have different degrees of influence on the utilization rate of calcium ions. The order of influence on the test results is: C S > O D 600 > pH. The mean effect of calcium carbonate production under different influencing factors is shown in Fig. 6. Figure 6(A) indicates that the production of calcium carbonate is positively correlated with the O D 600 value, consistent with the conclusions of references [ 24 ] and [ 25 ]. As the O D 600 value increases from 0.5 to 4, the production of calcium carbonate increases by 71.43%. Figure 6(B) shows that the production of calcium carbonate is positively correlated with C S , and a high concentration of cementing solution promotes the production of calcium carbonate. As the cementing solution increases from 0.75 mol/L to 2 mol/L, the production of calcium carbonate increases by 281.36%. Figure 6(C) reveals that as the pH of the single-phase slurry increases, the production of calcium carbonate first decreases and then increases, with an overall decrease of 32.90%. At low pH levels, bacterial activity is inhibited, delaying the flocculation phenomenon of bacteria and allowing them to be evenly distributed in the solution, which increases the contact area between bacteria and the solution, resulting in increased calcium carbonate production. When the pH reaches around 5, although the acidic environment inhibits the activity of most bacteria, bacterial flocculation gradually increases [ 18 ], delaying the production of calcium carbonate. As the pH continues to rise to around 6, the solution environment becomes alkaline, bacterial activity rapidly increases, and the production of calcium carbonate increases and shows an upward trend. Figure 5 intuitively suggests that the optimal combination of factors is: pH = 3, O D 600 = 4, and C S = 2 mol/L. Table 3 Results of orthogonal test Test Number M 3 /g A 1 0.053 A 2 0.069 A 3 0.099 A 4 0.171 A 5 0.055 A 6 0.065 A 7 0.108 A 8 0.169 A 9 0.054 A 10 0.091 A 11 0.133 A 12 0.204 A 13 0.075 A 14 0.085 A 15 0.157 A 16 0.356 Table 4 Range analysis of orthogonal experiment Factor O D 600 C S pH k 1 0.098 0.059 0.152 k 2 0.099 0.078 0.121 k 3 0.121 0.124 0.102 k 4 0.168 0.225 0.111 R 0.070 0.166 0.050 4.2 Analysis of Uniformity Test for Sand Column Specimens To evaluate the uniformity of sand specimens reinforced with DYF, acid washing tests were conducted on equal masses of sand collected from different parts of the solidified specimens, and the calcium carbonate content of each part was measured, as shown in Table 5 . The table indicates that the calcium carbonate content in both LXF and DYF solidified specimens decreases from the top to the bottom of the specimens. The maximum differences in calcium carbonate content between the inner and outer rings of the DYF solidified specimens are 0.51 g and 0.44 g, respectively, while those for the LXF solidified specimens are 1.13 g and 1.21 g, respectively. A smaller difference indicates a more uniform distribution of calcium carbonate. Comparison shows that the calcium carbonate content varies less among different parts of the DYF solidified specimens, with the maximum differences in calcium carbonate content between the inner and outer rings reduced by 54.9% and 63.6%, respectively, compared to the LXF solidified specimens. Therefore, the calcium carbonate distribution is more uniform in DYF solidified specimens. Due to the inhibition of microbial activity at low pH levels, bacterial flocculation decreases, delaying the initial reaction of calcium carbonate. This allows the grout to penetrate downward with sufficient pathways. Subsequently, urea hydrolysis gradually joins the reaction, increasing the environmental pH and resuscitating microbial activity. The in-situ flocculation reaction and calcium carbonate production reaction around soil particles in various parts of the sand column begin to proceed synchronously, resulting in a uniform distribution of calcium carbonate in all parts of the specimen. Table 5 Calcium carbonate content in different parts of the test specimen Location Upper part of the specimen/g Middle section of the specimen/g Lower part of the specimen/g Outer layer of DYF sample 7.41 6.97 7.00 Inner layer of DYF sample 6.75 6.5 6.24 Outer layer of LXF sample 7.72 7.2 6.51 Inner layer of LXF sample 7.76 7.1 6.63 4.3 Analysis of Shear Test Results The relationship curve between shear stress and shear displacement for the direct shear test of the specimens is shown in Fig. 7. During the shearing process, as the shear displacement increases, the shear stress of the specimens gradually rises, and the rate of increase gradually flattens out. At the same shear displacement, the peak strength of specimens solidified with DYF is 20–35% higher than that of specimens solidified with LXF. This is because DYF improves the uniformity of calcium carbonate distribution in the specimens, and the uniformly distributed calcium carbonate crystals form a three-dimensional calcium carbonate network structure within the specimens, causing the surrounding soil particles to share the load together. This results in a more widespread distribution of the load and subsequently enhances the strength of the specimens. The Coulomb strength fitting envelope is illustrated in Fig. 8. According to the fitting results, the cohesion of the undisturbed soil is 9.63 kPa, with an internal friction angle of 29.8°. After solidification with LXF, the cohesion of the specimens increases to 13.27 kPa, an increase of 37.8%, and the internal friction angle rises to 31.7°, an increase of 6.4%. After solidification with DYF, the cohesion of the specimens further increases to 19.42 kPa, an increase of 101.6%, and the internal friction angle rises to 37.4°, an increase of 25.5%. Both grouting methods improve the internal friction angle and cohesion of the specimens. Compared to LXF, the cohesion of DYF-solidified specimens is enhanced by 46.3%, and the internal friction angle is increased by 17.9%. In DYF-solidified specimens, calcium carbonate uniformly fills the pores of the soil, strengthening the biting force between soil particles and increasing the cohesion among them. The three-dimensional network framework formed by calcium carbonate shares the shear stress, reinforcing the structurally weak planes of the soil. 4.4 Analysis of Durability Test Results The experimental design included 10 groups of samples reinforced with DYF and 10 groups of samples reinforced with LXF, with three parallel samples in each group and all samples undergoing 12 rounds of reinforcement. These samples were subjected to durability tests in deionized water, with treatment cycles of 1, 5, 10, 15, 20, 25, and 30 rounds, respectively. After the durability tests, each group of samples was cleaned, demolded, and dried. Firstly, their mass loss rates were measured. Subsequently, unconfined compressive strength tests were conducted. The data from these tests were then compiled and analyzed along with data from samples that had not undergone durability testing. 4.4.1 Analysis of Mass Loss Rate As the experiments progressed, there was varying degrees of surface spalling on the samples and some loss of internal particles. The change patterns in mass loss rate for the samples in each experimental group are recorded and shown in Fig. 9. For both grouting methods, the mass loss rate of the solidified samples increased rapidly in the first 10 cycles and basically stabilized by the 20th cycle. In the drying-wetting cycle test, after 30 cycles, the highest mass loss rate was observed in the LXF-solidified samples, which was 2.6%, while the final mass loss rate of the DYF-solidified samples was 2.25%. Compared to the LXF-solidified samples, the final mass loss rate of the DYF-solidified samples was reduced by 13.8%. In the deionized water immersion test, after 30 cycles, the highest mass loss rate was again observed in the LXF-solidified samples, which was 1.55%, while the final mass loss rate of the DYF-solidified samples was 1.3%. Compared to the LXF-solidified samples, the final mass loss rate of the DYF-solidified samples was reduced by 16.13%. Due to the inhibition of microbial activity in a low pH environment, bacterial flocculation decreased, delaying the initial reaction of CaCO 3 . This allowed the grout to penetrate downward through sufficient pathways. Subsequently, urea hydrolysis gradually joined the reaction, increasing the environmental pH and resuscitating microbial activity. The in-situ flocculation reaction and calcium carbonate formation reaction around soil particles began to occur synchronously in various parts of the sand column, resulting in a uniform distribution of CaCO 3 throughout the samples. The uniformly distributed calcium carbonate crystals evenly encapsulated the soil particles, enhancing the compactness of the samples. In both the drying-wetting cycle test and immersion test, the mass loss rate of the LXF-solidified samples was higher than the final mass loss rate of the DYF-solidified samples. This is because the erosion of microbial-solidified calcareous sand is predominantly physical. During immersion, the solution slowly infiltrates and soaks the samples, weakening the bonds between sand grains and calcium carbonate crystals, causing weaker sections to spall off under erosion. Additionally, internal air venting in the samples generates tensile stress at the bonds, resulting in cracking at particle connections. However, in DYF-solidified samples, CaCO 3 uniformly fills the soil pores, strengthening the biting force between soil particles and increasing the cohesion among them. The three-dimensional network framework formed by CaCO 3 distributes stress, reinforcing the structurally weak planes of the soil. Under the action of drying-wetting cycles, the samples undergo cycles of water absorption and drying: during drying, soil particles expand slightly, causing compressive stress between particles; during water absorption, the hygroscopicity of dry calcareous sand enhances the invasion speed and depth of the solution, and particles contract upon cooling. Compared to LXF-solidified samples, the calcium carbonate in DYF-solidified samples is uniformly distributed throughout the sample, tightly encapsulating the soil particles. Under repeated drying-wetting cycles, due to the uniform filling and encapsulation of the calcium carbonate skeleton around the soil particles, the energy difference between various parts of the sample is smaller, enabling it to better resist the damage caused by drying-wetting cycles. 4.4.2 Analysis of Strength Loss As shown in Fig. 10, the unconfined compressive strength (UCS) of both LXF-solidified and DYF-solidified samples decreases continuously with increasing treatment cycles. The strength of the samples drops more rapidly in the first 10 cycles and then tends to stabilize after reaching 20 cycles. According to Fig. 10, the most severe degradation was observed in the LXF-solidified samples subjected to drying-wetting cycles, with a strength reduction of 507 kPa (49.7%) after 30 cycles. In contrast, the DYF-solidified samples experienced a strength decrease of 421.3 kPa (about 32.8%) after 30 drying-wetting cycles. Compared to LXF-solidified samples, the strength loss of DYF-solidified samples was reduced by 16.9%. In the deionized water immersion test, after 30 cycles, the LXF-solidified samples had the highest remaining strength of 28.3%, while the strength loss rate of DYF-solidified samples was 17.1%. Compared to LXF-solidified samples, the strength loss of DYF-solidified samples was reduced by 21.1%. After 30 treatment cycles, the strength loss of LXF-solidified samples was greater than that of DYF-solidified samples in both the drying-wetting cycle test and immersion test. Additionally, under the same number of treatments, the strength loss of samples in the drying-wetting cycle group was greater than that in the immersion group, which corresponds to the pattern of mass loss rates. This is because when the samples are immersed, water infiltrates through pores and cracks, filling the interior. The intrusion of the solution disrupts the weak bonds between soil particles. Compared to DYF-solidified samples, the uneven distribution of calcium carbonate in LXF-solidified samples results in unstable cementation that is more susceptible to damage in aqueous environments. Under the action of drying-wetting cycles, the samples undergo drying treatment. Due to the different calcium carbonate contents in various parts of the samples, there is an energy difference. As the number of drying-wetting cycles increases, the uneven calcium carbonate crystals exert pressure on the inner walls of soil particle pores. This force causes pores and cracks to expand continuously, ultimately leading to a significant reduction in the strength of the samples in seawater environments. In DYF-solidified samples, the distribution of CaCO 3 is more uniform, with a large amount of CaCO 3 crystals filling and encapsulating the soil particles, reducing soil porosity and increasing soil compactness. Additionally, the uniform distribution of calcium carbonate within the samples results in a smaller energy difference between different parts, enhancing the deformation resistance of the soil. 4.5 Analysis of Microstructural Mechanisms The above analysis indicates that DYF can effectively improve the uniformity of microbially solidified soil and enhance its mechanical properties. To explore the mechanism of action of DYF in solidifying soil, scanning electron microscopy (SEM) was used to analyze the microstructure of the solidified samples, as shown in Fig. 11. As shown in Figs. 11(A) and (B), the calcium carbonate crystals formed in the LXF-solidified samples have a certain filling effect on the soil pores, but the filling effect is limited. There are significant differences in the distribution of calcium carbonate crystals around the soil particles, resulting in numerous pores between them. Calcium carbonate uses bacteria as nucleation sites [ 26 ], indicating that the amount of bacteria attached between soil particles is different and unevenly distributed, leading to unsatisfactory pore filling and interparticle bonding effects of calcium carbonate crystals. As illustrated in Figs. 11(C) and (D), the internal pores in the DYF-solidified samples are significantly reduced. The calcium carbonate crystals encapsulate the soil particle surfaces and fill the pores between them, forming a large number of aggregates of soil particles and calcium carbonate crystals. DYF enables a more uniform distribution of bacteria in the soil, providing numerous nucleation sites for calcium carbonate crystals. This reduces the number and size of pores between soil particles, making the soil structure more compact and effectively improving the soil's micro-pore structure [ 27 ]. 5 Conclusions Addressing the issue of uneven calcium carbonate formation during soil solidification using microbial grouting technology, a series of experiments were conducted based on DYF, including MICP (microbially induced calcium carbonate precipitation) aqueous solution tests, sand column grouting solidification tests, direct shear tests, and consolidation tests. These experiments aimed to explore the influence of multiple factors on the mechanical properties of DYF-solidified soil samples and the underlying mechanism of strength enhancement. The following conclusions were drawn: (1) Through aqueous solution experiments, calcium carbonate precipitation curves under different influencing factors were obtained. Based on orthogonal experiments, the optimal cultivation scheme was determined as follows: pH = 3, O D 600 = 4, and C S = 2 mol/L. The order of influence on the experimental results, from greatest to least, is: C S concentration > O D 600 value > pH. (2) In the sand column uniformity test, compared to the two-phase grouting method, the distribution of calcium carbonate in the DYF-solidified sand column was more uniform. This is attributed to the low pH condition which inhibited bacterial activity and delayed the formation of calcium carbonate, allowing the grout to have sufficient infiltration time and penetration pathways to flow towards the bottom of the sample. (3) According to the direct shear test and durability test, compared to LXF, the DYF-solidified samples exhibited an increase in the internal friction angle by 17.9% and an increase in cohesion by 46.3% in the direct shear test. In the soaking test, the final mass loss rate and strength loss of DYF-solidified samples were reduced by 16.13% and 21.1%, respectively. In the dry-wet cycling test, the final mass loss rate and strength loss of DYF-solidified samples were reduced by 13.8% and 16.9%, respectively. The uniform distribution of calcium carbonate within the samples is the fundamental reason for the enhanced strength of the sand columns. (4) SEM microstructural analysis reveals that the distribution of calcium carbonate in samples treated with DYF is more uniform, with a significant amount of calcium carbonate encapsulating the surface of soil particles. This optimizes the pore structure of the soil and enhances the overall effectiveness of the solidified samples. Declarations Competing interests The authors declare no competing interests. Author Contribution Conceptualization, G.Q. and H.Z.; methodology, G.Q. , H.Z. , C.M. and X.Z. ; formal analysis, G.Q. , H.Z. , C.M. ; investigation, G.Q. , H.Z. ,X.Z. , H.S. ; data cu-ration, H.S. ; writing—original draft preparation, H.Z. ; writing—review and editing, G.Q. and H.Z. ; supervision, G.Q., C.M. ; project administration, G.Q. ; funding acquisition, G.Q.. All authors have read and agreed to the published version of the manuscript. Acknowledgments This research was funded by the Inner Mongolia Autonomous Region's Universities Basic Scientific Research Operating Expenses Project: Application of Green Microbial Mineraliza-tion Technology in Restoration and Control of Abandoned Open-pit Mines in Inner Mongolia (2024QNJS063). Data Availability The original contributions presented in the study are included in thearticle. Further inquiries can be directed to the corresponding author. References Ji, X. et al. Long-Term Performance on Drought Mitigation of Soil Slope Through Bio‐Approach of MICP: Evidence and Insight from Both Field and Laboratory Tests[J]. Water Resour. Res. 2024 , 60 (7): e2024WR037486-e2024WR037486. Wang, J. Y. et al. Soil improvement using biostimulated MICP: Mechanical and biochemical experiments, reactive transport modelling, and parametric analysis[J].Computers and Geotechnics,2024, 172106446-. WHIFFIN V S.Microbial. CaCO 3 precipitation for the production of biocemen[D] (Western Australia:Murdoch University, 2004). QIAN C X & YU X N,WANG X.A study on the cementation interface of bio-cement[J]. Mater. Charact. 136 , 122–127 (2018). YU et al. Microbial self-healing of cracks in cement-based materials and its influencing factors[J]. Front. Struct. Civil Eng. 2023 , 17 (11):1630–1642 . CUI M J,LAI H J,HOANG et al. Modified one-phase-low-pH method for bacteria or enzyme-induced carbonate precipitation for soil improvement[J]. Acta Geotech. 17 (7), 2931–2941 (2022). MUJAH D,LIANG C,MOHAMED A, S. Microstructural and geomechanical study on biocemented sand for optimization of MICP process [J]. J. Mater. Civil Eng. 2019 , 31 (4):19–25 . MARTINEZ B C,DEJONG J T,GINN T R.Bio-geochemical reactive transport modeling of microbial induced calcite precipitation to predict the treatment of sand in one-dimensional flow[J]. Computers Geotechnics 2014 , 58 (20):1–13 . GOMEZ M G,GRADDY C,DEJONG J et al. Biogeochemical changes during bio-cementation mediated by stimulated and augmented ureolytic microorganisms [J].Scientific Reports,2019, 7 (9):115–163 . DAWOUD O,CHEN C Y & SOGA K.. Microbial-induced calcite precipitation (MICP) using surfactants[C]. Geocongress,2014,London,2014.31 (5). 1635–1643. STOCKS-FISCHER S,GALINAT J K,BANG S S.Microbiological precipitation of CaCO 3 [J].Soil Biology and Biochemistry,1999, 31 (11):1563–1571 . WHIFFIN V S,VAN PAASSEN L A,HARKES M P.Microbial carbonate precipitation as a soil improvement technique[J]. Geomicrobiol. J. 2007 , 24 (5):417–423 . HARKES M P,VAN PAASSEN L A,BOOSTE R J et al. Fixation and distribution of bacterial activity in sand to induce carbonate precipitation for ground reinforcement[J]. Ecol. Eng. 36 (2), 112–117 (2010). NAYANTHARA et al. Biocementation of Sri Lankan beach sand using locally isolated bacteria: a baseline study on the effect of segregated culture media[J]. Int. J. Geomate 2019 , 17 (63):55–62 . Qian, Z. H. A. O. et al. Factors affecting improvement of engineering properties of MICP-treated soil catalyzed by bacteria and urease[J]. J. Mater. Civil Eng. 2014 , 26 (12):401–409 . XIAO et al. Strength and deformation responses of biocemented sands using a temperature-controlled method[J]. Int. J. Geomech. 2019 , 19 (11):191–201 . ,GUO Hongxian,CHENG Xiaohui,et al. The Influence of Calcium Sources on the Uniformity of Microbially Induced Carbonate Precipitation (MICP) in Cemented Sand Materials[J]. Journal of Civil &Environmental Engineering (Chinese and English),2023,12 (5):1–8.(in Chinese). CHENG, L. & SHAHIN M A, C. H. U. J. Soil bio-cementation using a new one-phase low-pH injection method[J]. Acta Geotech. 14 (3), 615–626 (2019). Standard for Soil Test Methods. GB/T50123-2019 (China Planning, 2019). WHIFFIN V S.Microbial. CaCO 3 precipitation for the production of biocement[D] (Perth:Murdoch University, 2004). Guanghui, S. H. A. O. & Min, H. O. U. LIU Peng.Distribution and immobilization of bacteria in solidified silty soil[J]. J. Forestry Eng. 2019 , 4 (01):128–134 .(in Chinese). XIAO et al. Gradation-dependent thermal conductivity of sands[J]. J. Geotech. Geoenvironmental Eng. 2018 , 144 (9):60–68 . MO et al. Effects of environmental factors on microbial induced calcium carbonate precipitation[J]. J. Appl. Microbiol. 2011 , 111 (2):338–349 . ZHAO Qian. An experimental study on soil solidification by microbial-induced calcium carbonate precipitation (MICP)[D] (Beijing:China University of Geosciences, 2014). (in Chinese). OKWADHA G D O,LI J.Optimum conditions for microbial carbonate precipitation[J].Chemosphere,2010, 81 (9): 1143–1148 . Xiaohao, S. U. N. et al. Experimental study on microbial deposition of calciumcarb onate solidified sand[J].Geotechnical mechanics,2017,38 (11):3225–3230 .(in Chinese). LIN H,SULEIMAN M T,BROWN D G.Investigation of pore-scale CaCO 3 distributions and their effects on stiffness and permeability of sands treated by microbially induced carbonate precipitation (MICP)[J].Soils and Foundations,2020, 60 (4):944–961 . Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5335157","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":381168358,"identity":"4a446c1a-55b4-4331-b81a-a3f1b1071c4a","order_by":0,"name":"Guangqin Cui","email":"","orcid":"","institution":"The Inner Mongolia University of Science and Technology School of Civil Engineering","correspondingAuthor":false,"prefix":"","firstName":"Guangqin","middleName":"","lastName":"Cui","suffix":""},{"id":381168359,"identity":"bd8e38ef-3085-4679-8fd0-897952357a04","order_by":1,"name":"Hang Zhang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAv0lEQVRIiWNgGAWjYFACHgYGxgYGOTb29gOkaTHm4zmTQJqWxHkSDgbEaZDvX3vswc8dteltEgwJDD8qthHWwjjjXbph75njuW3SjQcYe87cJqyFWeKMmQRv27HcNpkDCcyMbURoYQNqkfzbdiydTSLBgDgtPPw9ZtK8bTUJxGuRkOAxk5ZtO2DYBgzkg0T5Rb4f6LC3bXXy8u3tBx/8qCBCC4NEAog8DGYfIEI9EPCD1dURp3gUjIJRMApGJgAAj887O/3h6XMAAAAASUVORK5CYII=","orcid":"","institution":"The Inner Mongolia University of Science and Technology School of Civil Engineering","correspondingAuthor":true,"prefix":"","firstName":"Hang","middleName":"","lastName":"Zhang","suffix":""},{"id":381168360,"identity":"2ad84b7a-3934-4e80-ad7c-730e57de24c4","order_by":2,"name":"Chenguang Ma","email":"","orcid":"","institution":"Zhongdi Yingang Construction Group 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02:38:07","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5335157/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5335157/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":70027606,"identity":"b87300f5-0252-4b5e-89d7-b1106f295812","added_by":"auto","created_at":"2024-11-27 15:47:22","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":185800,"visible":true,"origin":"","legend":"\u003cp\u003eCumulative particle \u0026nbsp;\u0026nbsp;size curve\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5335157/v1/f04d1d089f1985b1c2c705a9.png"},{"id":70026871,"identity":"f5038853-3fbf-4f50-a2ce-e5eda30538dc","added_by":"auto","created_at":"2024-11-27 15:39:22","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":164018,"visible":true,"origin":"","legend":"\u003cp\u003eFlowchart of bacterial culturing\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5335157/v1/db74f97815e0221fe272c66e.png"},{"id":70026879,"identity":"fde79934-7e5d-4208-a967-d68c2c86c75a","added_by":"auto","created_at":"2024-11-27 15:39:23","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":173891,"visible":true,"origin":"","legend":"\u003cp\u003eMicrobial growth curve and urease activity curve\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5335157/v1/db20e8f17e0929830191c7a6.png"},{"id":70028523,"identity":"86439b06-32a8-424b-b5d9-779aa603ba4b","added_by":"auto","created_at":"2024-11-27 15:55:22","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":460641,"visible":true,"origin":"","legend":"\u003cp\u003e\u0026nbsp;Schematic diagram of \u0026nbsp;\u0026nbsp;grouting solidified sample\u003c/p\u003e\n\u003cp\u003e(A) Schematic \u0026nbsp;\u0026nbsp;diagram of the setup,(B) Physical image of the setup\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5335157/v1/60b09d0d2cc66582c85476cb.png"},{"id":70027605,"identity":"4d309fce-b767-4ed7-8229-512acf331547","added_by":"auto","created_at":"2024-11-27 15:47:22","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":452280,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of sampling of solidified sand column\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5335157/v1/005e4bd3225c9d8d2c2bd468.png"},{"id":70026873,"identity":"c674974d-4a7e-44a1-8afc-58a3c7642498","added_by":"auto","created_at":"2024-11-27 15:39:22","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":78882,"visible":true,"origin":"","legend":"\u003cp\u003e\u0026nbsp;Mean effect diagram of different factors on calcium carbonate production\u003c/p\u003e\n\u003cp\u003e(A) Mean effect plot of O\u003cem\u003eD\u003c/em\u003e\u003csub\u003e600 \u003c/sub\u003evalue and \u003cem\u003eM\u003c/em\u003e\u003csub\u003e3,\u003c/sub\u003e(B) Mean effect plot of C\u003cem\u003eS\u003c/em\u003e concentration and \u003cem\u003eM\u003c/em\u003e\u003csub\u003e3,\u003c/sub\u003e(C) Mean effect plot of pH and \u003cem\u003eM\u003c/em\u003e\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5335157/v1/425852517de4f632b4640b83.png"},{"id":70027609,"identity":"e889228e-f469-40ea-9f76-f20cc4ac5d20","added_by":"auto","created_at":"2024-11-27 15:47:23","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":200349,"visible":true,"origin":"","legend":"\u003cp\u003eThe corresponding \u0026nbsp;\u0026nbsp;curve of shear displacement and shear stress\u003c/p\u003e\n\u003cp\u003e(A) LXF solidified sample,(B) DYF \u0026nbsp;\u0026nbsp;solidified sample,(C) \u0026nbsp;\u0026nbsp;plain soil\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-5335157/v1/d92bdb0de6f2a8548693f51d.png"},{"id":70026876,"identity":"99a46eeb-499d-4852-a65a-d4fe66b63eec","added_by":"auto","created_at":"2024-11-27 15:39:22","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":96577,"visible":true,"origin":"","legend":"\u003cp\u003eContour plot for Coulomb strength fitting\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-5335157/v1/41531bef8179f361e289d8cb.png"},{"id":70027608,"identity":"aabfb7d0-b722-4b69-a387-743680920d8e","added_by":"auto","created_at":"2024-11-27 15:47:22","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":87408,"visible":true,"origin":"","legend":"\u003cp\u003eMass loss under different treatment cycles\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-5335157/v1/62c57a20f01a230c36c3522f.png"},{"id":70026877,"identity":"183f38b5-75db-4f5f-9d67-b7bfb32c4dc8","added_by":"auto","created_at":"2024-11-27 15:39:22","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":93948,"visible":true,"origin":"","legend":"\u003cp\u003eUnconfined compressive strength under different treatment cycles\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-5335157/v1/1834b550d17c16db80ebd7d5.png"},{"id":70026882,"identity":"2132063c-19fd-4dd4-b730-4d9637de0855","added_by":"auto","created_at":"2024-11-27 15:39:23","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":561250,"visible":true,"origin":"","legend":"\u003cp\u003e\u0026nbsp;SEM of different \u0026nbsp;\u0026nbsp;grouting methods\u003c/p\u003e\n\u003cp\u003e(A) Effect \u0026nbsp;\u0026nbsp;diagram of LXF solidified sample,(B) \u0026nbsp;\u0026nbsp;Partial pore diagram of LXF solidified sample,(C) Effect diagram of DYF solidified sample,(D) Partial pore diagram of DYF solidified sample\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-5335157/v1/8cf4389dfd6e3562bfaaae42.png"},{"id":76748529,"identity":"ba77fae9-8804-4e78-9e23-3c130f968cb9","added_by":"auto","created_at":"2025-02-20 09:32:08","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3705787,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5335157/v1/128d6797-a590-4503-a6cf-ed35f9e0cbcf.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Experimental Study on the Shear Strength and Durability of Microbial-Consolidated Silty Sand under Low pH Conditions","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eMicrobially induced calcite precipitation (MICP) is currently one of the promising bio-mediated soil improvement technologies [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Compared to traditional soil improvement methods such as chemical grouting, electro-osmotic consolidation, and vacuum preloading, MICP offers advantages such as minimal soil disturbance, resource conservation, and environmental protection. Microbial mineralization, which widely exists in nature, refers to the phenomenon where certain microorganisms form mineral crystals through their metabolic activities. Calcium carbonate, a widely distributed carbonate with stable properties, excellent strength, and durability, has always been a research hotspot in microbial mineralization, particularly in the context of MICP [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. In 2004, literature [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e] was the first to apply MICP technology in the field of soil improvement, demonstrating that the technology could induce the precipitation of calcium carbonate in sandy soil, significantly enhancing the mechanical properties of the solidified soil. Literature [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e] further confirmed through microscopic analysis that calcite-type calcium carbonate was the primary cementing component in the mineralized products. Subsequently, scholars investigated the effects of various factors, including different types of microorganisms [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], calcium sources [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], and cementing solutions [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], on the MICP reaction. Currently, there are still many challenges in the application of MICP technology for soil improvement, with one of the key issues being how to ensure uniform strength in the solidified soil [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Specifically, during the grouting process, calcium carbonate tends to precipitate preferentially near the grouting port, resulting in significant regional differences in soil improvement effectiveness [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Literature [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] points out that achieving uniform distribution of calcium carbonate within the target treatment area has been identified as one of the major challenges facing the upgrading of microbial grouting technology.\u003c/p\u003e \u003cp\u003eIn early studies, literature [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] employed a single-phase grouting method where a mixture of bacteria and cementing solution was directly injected into the soil. Due to bacterial aggregation and rapid calcium carbonate formation, the grouting orifice became clogged, making it difficult for the reaction to penetrate deeply into the soil. Literature [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] proposed a two-phase grouting method, which to some extent alleviated the issue of orifice clogging. However, since the bacteria first contacted and reacted with the cementing solution at the injection site, there were still significant differences in strength at different locations within the sample. Literature [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] introduced an improved two-phase grouting method based on the original two-phase method, which led to some improvement in strength uniformity across different locations of the sample. Yet, during the injection of the cementing solution, bacteria were carried away, making it difficult to determine the bacterial quantity at different locations, which affected the uniform distribution of calcium carbonate. Some scholars attempted to use other methods to improve the uniformity of calcium carbonate distribution. Literature [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] resuspended the bacterial cells in distilled water and studied the effect of different urease activities on the strength of sand columns. It was found that the compressive strength at the top of the sand column was approximately one-fifth of that achieved through traditional grouting methods, but the distribution of calcium carbonate was significantly improved. Literature [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] compared the effects of different concentrations of bacterial solution on the consolidation of quartz sand and found that higher concentrations of bacterial solution led to increased calcium carbonate production and improved mechanical properties. Literature [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] employed a temperature-controlled method to improve the uniformity of calcium carbonate distribution by mixing the bacterial solution with the cementing solution at 6℃. Due to the inhibition of microbial activity at low temperatures, the distribution of calcium carbonate precipitation in the soil was significantly improved. Literature [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] conducted experiments on small-sized sand columns to investigate the impact of two calcium sources, calcium chloride and calcium acetate, on the uniformity of cemented samples. It was found that calcium acetate as a calcium source could improve the uniformity of calcium carbonate distribution within the samples.\u003c/p\u003e \u003cp\u003eCurrent research on improving the uniformity of soil solidification using Microbially Induced Carbonate Precipitation (MICP) technology mainly focuses on grouting procedures, bacterial solution concentration, nutrient solution formulation, and other aspects. Literature [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] proposes a low-pH one-phase grouting method (hereinafter referred to as DYF), which involves lowering the pH of the one-phase slurry (a mixture of bacterial solution and cementing solution) before grouting to inhibit initial reactions. Controlling the grouting process under low-pH conditions has proven effective in enhancing the uniform distribution of calcium carbonate in the solidified soil, providing a new direction for solving the problem of grouting orifice clogging. However, there is a lack of research in this area, and no studies have yet reported on the influence of multiple factors under these conditions on MICP-solidified soil or the underlying mechanisms of strength enhancement. This study aims to determine the optimal grouting scheme through orthogonal aqueous solution experiments and conduct experimental research on the uniformity of calcium carbonate distribution, shear performance, and durability of grouted and solidified samples. It explores the effects of different influencing factors (bacterial solution concentration, pH, cementing solution) on calcium carbonate production, shear performance, and durability of sand columns, providing theoretical support and references for the application of MICP technology in practical engineering.\u003c/p\u003e"},{"header":"2 Experimental Materials and Equipment","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003e2.1 Test Materials\u003c/h2\u003e\n \u003cp\u003eBefore the experiment, impurities in the undisturbed soil were removed using deionized water, and the soil samples were adjusted to a neutral pH and then completely dried in a constant temperature oven at 100 ℃. Particle size analysis was conducted on the experimental soil samples according to the \u0026quot;Chinese code\u0026quot; (GB/T50123-2019) [\u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e]. The particle size distribution curve is shown in Fig.\u0026nbsp;1. The soil samples exhibited d\u003csub\u003e60\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.77 mm, d\u003csub\u003e30\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.13 mm, d\u003csub\u003e10\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.020 mm, C\u003cem\u003eu\u003c/em\u003e\u0026thinsp;=\u0026thinsp;38.5, and C\u003cem\u003ec\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.1, indicating a well-graded soil.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003e2.2 Microbial strains and cultivation process\u003c/h2\u003e\n \u003cp\u003eThe bacterial strain used in the experiment is Bacillus pasteurii, a Gram-positive aerobic bacterium that secretes a large amount of urease through metabolism. The activated bacteria were inoculated into a liquid medium at a volume ratio of 1:100 and cultivated in a constant temperature shaking incubator at 28 ℃ and 180 r/min for 36 to 48 hours. The medium was formulated with 10 g/L of peptone, 5 g/L of sodium chloride, and 3 g/L of yeast extract powder. The bacterial cultivation process is illustrated in Fig.\u0026nbsp;2. Before the experiment, the absorbance of the bacterial suspension was measured using a V-1100D visible spectrophotometer, and the bacterial concentration was characterized by the O\u003cem\u003eD\u003c/em\u003e\u003csub\u003e600\u003c/sub\u003e value. The urease activity of the bacterial suspension was measured using the conductivity method proposed in literature [\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e]. The microbial growth curve and urease activity curve are shown in Fig.\u0026nbsp;3. Based on the test results, Bacillus pasteurii cultivated for 48 hours was selected, as both the microbial count and urease activity reached their peaks at this time. The prepared bacterial suspension was stored at a low temperature of around 4 ℃ to prevent environmental temperature from affecting bacterial activity [\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eDuring the experiment, bacteria cultivated at a constant temperature for 48 hours were used to prepare four groups of bacterial suspensions with different concentrations, with OD600 values of 4.0, 2.0, 1.0, and 0.5 from highest to lowest. The cementation solution (CS) provides nutrients for microbial reactions and is a mixture of equimolar calcium chloride (CaCl\u003csub\u003e2\u003c/sub\u003e) and urea. Four concentrations of 0.75, 1.0, 1.50, and 2 mol/L were set for the experiment. The preparation method for the low-pH one-phase slurry follows the configuration described in reference [\u003cspan class=\"CitationRef\"\u003e18\u003c/span\u003e], with specific steps as follows: (1) Mix equal volumes of bacterial suspension and cementation solution in an Erlenmeyer flask; (2) Adjust the pH of the mixture to 6.0, 5.0, 4.0, and 3.0, respectively, using hydrochloric acid.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n \u003ch2\u003e2.3 Preparation of Sand Column Samples\u003c/h2\u003e\n \u003cp\u003eThe mold used for preparing the sand column samples is a transparent PC cylinder with an inner diameter of 61.8 mm and a length of 182 mm. During the experiment, permeable stones and filter paper are placed at both ends of the mold to prevent reverse osmosis, as shown in Fig.\u0026nbsp;4. To ensure uniform packing of the sand column samples, the packing method described in reference [\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e] is followed, with the sand being loaded in three layers. The dry density of the sand column samples is controlled at (1.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5) g/cm\u003csup\u003e3\u003c/sup\u003e. After packing, deionized water is introduced into the samples to remove excess air bubbles.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"3 Experimental Methodology","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1 Aqueous Solution Test\u003c/h2\u003e\n \u003cp\u003eAn orthogonal experiment with three factors and four levels was conducted to investigate the ability of microbially induced calcium carbonate precipitation (MICP) under different influencing factors. The orthogonal experiment included 16 parallel tests, with the effective precipitation rate of calcium carbonate as the evaluation index. Regression analysis was performed to determine the sensitivity of the influencing factors and the optimal cultivation scheme. (The effective precipitation rate of calcium carbonate is defined as the ratio of the actual mass of calcium carbonate produced (\u003cem\u003em\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e) to the theoretical mass of calcium carbonate that could be produced (\u003cem\u003em\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e)). The levels and factors of the orthogonal experiment are shown in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, and the design of the orthogonal experiment is presented in Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e\n \u003cp\u003e\u003c/p\u003e\u0026nbsp;\u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eOrthogonal test levels and factors table\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ehorizontal\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eO\u003c/em\u003eD\u003csub\u003e600\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eC\u003c/em\u003eS /(mol‧L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003epH\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003e\u003c/p\u003e\u0026nbsp;\u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eOrthogonal experimental design table\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eO\u003c/em\u003eD\u003csub\u003e600\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eC\u003c/em\u003eS \u003cem\u003e/\u003c/em\u003e(mol‧L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003epH\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e5\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e6\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e7\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e8\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e9\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e10\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e11\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e12\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e13\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e14\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e15\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e16\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2 Experiment on Sand Column Solidification Using Low-pH One-Phase Grouting Method\u003c/h2\u003e\n \u003cp\u003eIn this study, a comparative analysis was conducted between the experiment on sand column solidification using the low-pH one-phase grouting method and the experiment on sand column solidification using the two-phase grouting method (hereinafter referred to as LXF).\u003c/p\u003e\n \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\n \u003ch2\u003e3.2.1 Experiment on Sand Column Solidification Using Low-pH One-Phase Grouting Technique\u003c/h2\u003e\n \u003cp\u003e(1) A peristaltic pump is used to introduce deionized water into the sample until saturation to expel internal gases. (2) Each time, prepare 40 mL of low-pH one-phase grout, ensuring it is used within a short period. (3) Use a peristaltic pump to pump 1.2 times the volume of the sand column with grout at a rate of 60 mL/h. (4) After grouting, allow the sand column sample to stand in a constant temperature incubator at 26 ℃ for 12 hours to complete the first grouting cycle. (5) Repeat the above steps for a total of three grouting cycles to enhance the reinforcement effect. After completion, incubate the sample in the incubator for 24 hours and then demold it.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\n \u003ch2\u003e3.2.2 Experiment on Sand Column Solidification Using Two-Phase Grouting Method\u003c/h2\u003e\n \u003cp\u003e(1) A peristaltic pump is used to introduce deionized water into the sample until saturation to expel internal gases. (2) A 0.5 mol/L CaCl\u003csub\u003e2\u003c/sub\u003e solution is used as the fixing solution and mixed with the bacterial suspension for injection into the sand column to immobilize the bacteria. (3) A peristaltic pump is used to pump in 1.2 times the volume of the sand column with cementation solution (using the commonly set pH in current MICP research, i.e., pH\u0026thinsp;=\u0026thinsp;8.5) at a rate of 60 mL/h. (4) After grouting, the sand column sample is allowed to stand in a constant temperature incubator at 26 ℃ for 12 hours to complete the first grouting cycle. (5) The above steps are repeated for a total of three grouting cycles to enhance the reinforcement effect. After completion, the sample is incubated in the incubator for 24 hours and then demolded.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3 Experiment on Uniformity of Sand Column\u003c/h2\u003e\n \u003cp\u003eAfter demolding and drying, the specimens are polished with sandpaper to prevent interference from precipitated calcium carbonate crystals in the test results. The sand column samples are divided into three equal-mass sections: top, middle, and bottom. From each section, both the outer ring and inner core are taken. The calcium carbonate content of each sampled sand soil section is measured, and a comparative analysis is conducted to evaluate the uniformity of calcium carbonate in the solidified sand column by assessing the calcium carbonate content in different parts after cementation. The sampling of the solidified sand column is illustrated in Fig. 5.\u003c/p\u003e\n \u003cp\u003eThe acid washing method [\u003cspan class=\"CitationRef\"\u003e23\u003c/span\u003e] is employed to determine the calcium carbonate content in the sample. The microbially treated sample is dried to a constant weight (denoted as M\u003csub\u003e1\u003c/sub\u003e). It is then stirred and soaked in 4 mol/L hydrochloric acid, filtered using a vacuum filtration device, and the process of adding hydrochloric acid, stirring, and filtering is repeated until no calcium carbonate residue remains in the soil sample (denoted as M\u003csub\u003e2\u003c/sub\u003e). The mass loss of the soil sample after drying represents the mass of the calcium carbonate formed. The mass loss of the soil sample after drying represents the mass of the calcium carbonate formed, denoted as CCaCO3, i.e.,\u003c/p\u003e\n \u003cp\u003e\u003cem\u003eC\u003c/em\u003e \u003csub\u003eCaCO3\u003c/sub\u003e=\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({M_1} - {M_2}\\)\u003c/span\u003e\u003c/span\u003e ( 1 )\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n \u003ch2\u003e3.4 Shear Performance Test\u003c/h2\u003e\n \u003cp\u003eThe main geotechnical tests include direct shear tests and consolidation tests, both conducted according to the \u0026quot;Chinese code\u0026quot; (GB/T50123-2019) [\u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e]. The shear rate for the direct shear test is 0.01 mm/min, with vertical pressures of 50, 100, 150, and 200 kPa.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n \u003ch2\u003e3.5 Durability Test\u003c/h2\u003e\n \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e\n \u003ch2\u003e3.5.1 Soaking Test\u003c/h2\u003e\n \u003cp\u003eThe specimens solidified by the two grouting methods are dried and allowed to reach room temperature before being subjected to a soaking test in deionized water. During the soaking test, the liquid level is maintained 15 mm above the specimens, and the deionized water is replaced every 3 days to avoid contamination of the solution. With each cycle lasting for 12 hours, the soaking cycles are set at 1, 5, 10, 15, 20, 25, and 30 cycles for the test.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e\n \u003ch2\u003e3.5.2 Drying-Wetting Cycle Test\u003c/h2\u003e\n \u003cp\u003e(1) Place the specimens solidified by the two grouting methods into a solution with the liquid level 15 mm above the top surface of the specimens. Maintain the solution temperature at (25\u0026thinsp;\u0026plusmn;\u0026thinsp;2) ℃ and soak for a total of 12 hours. (2) After soaking, allow the specimens to air-dry naturally at room temperature for 3 hours. (3) After air-drying, place the specimens in an oven set to 60 ℃ for drying for 3 hours. (4) After the drying process, allow the specimens to cool at room temperature for 1 hour. The above steps constitute one drying-wetting cycle with a total duration of 24 hours. Place the cooled specimens back into the solution and repeat steps (1) to (4) to enter the next drying-wetting cycle. The drying-wetting cycle also has a duration of 24 hours per cycle, and the test is set to run for 1, 5, 10, 15, 20, 25, and 30 cycles.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e\n \u003ch2\u003e3.5.3 Mass Loss Rate\u003c/h2\u003e\n \u003cp\u003eBefore conducting the durability test, record the initial mass of the specimen as \u003cem\u003em\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e. After soaking or completing the drying-wetting cycles, clean and dry the specimen, then measure its mass as m1. The mass loss rate of the specimen is calculated as the ratio of (\u003cem\u003em\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e - \u003cem\u003em\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e) to \u003cem\u003em\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec17\" class=\"Section3\"\u003e\n \u003ch2\u003e3.5.4 Unconfined Compressive Strength Test\u003c/h2\u003e\n \u003cp\u003eThe unconfined compressive strength is used to reflect the strength loss of the specimen. After cleaning, drying, and cooling the treated specimen to room temperature, the upper and lower surfaces are leveled. The test is conducted using a strain-controlled unconfined compression apparatus.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"4 Test Results and Analysis","content":"\u003cdiv id=\"Sec19\" class=\"Section2\"\u003e\n \u003ch2\u003e4.1 Analysis of Aqueous Solution Tests\u003c/h2\u003e\n \u003cp\u003eThe aqueous solution tests analyze the production of calcium carbonate as an indicator, and determine the optimal cultivation scheme using the K-value method. The larger the range indicator R, the better the evaluation of the results, as shown in Tables \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e. According to Tables \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e, the three factors in the orthogonal test have different degrees of influence on the utilization rate of calcium ions. The order of influence on the test results is: C\u003cem\u003eS\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;O\u003cem\u003eD\u003c/em\u003e\u003csub\u003e600\u003c/sub\u003e\u0026thinsp;\u0026gt;\u0026thinsp;pH.\u003c/p\u003e\n \u003cp\u003eThe mean effect of calcium carbonate production under different influencing factors is shown in Fig.\u0026nbsp;6. Figure\u0026nbsp;6(A) indicates that the production of calcium carbonate is positively correlated with the O\u003cem\u003eD\u003c/em\u003e\u003csub\u003e600\u003c/sub\u003e value, consistent with the conclusions of references [\u003cspan class=\"CitationRef\"\u003e24\u003c/span\u003e] and [\u003cspan class=\"CitationRef\"\u003e25\u003c/span\u003e]. As the O\u003cem\u003eD\u003c/em\u003e\u003csub\u003e600\u003c/sub\u003e value increases from 0.5 to 4, the production of calcium carbonate increases by 71.43%. Figure 6(B) shows that the production of calcium carbonate is positively correlated with C\u003cem\u003eS\u003c/em\u003e, and a high concentration of cementing solution promotes the production of calcium carbonate. As the cementing solution increases from 0.75 mol/L to 2 mol/L, the production of calcium carbonate increases by 281.36%. Figure\u0026nbsp;6(C) reveals that as the pH of the single-phase slurry increases, the production of calcium carbonate first decreases and then increases, with an overall decrease of 32.90%. At low pH levels, bacterial activity is inhibited, delaying the flocculation phenomenon of bacteria and allowing them to be evenly distributed in the solution, which increases the contact area between bacteria and the solution, resulting in increased calcium carbonate production. When the pH reaches around 5, although the acidic environment inhibits the activity of most bacteria, bacterial flocculation gradually increases [\u003cspan class=\"CitationRef\"\u003e18\u003c/span\u003e], delaying the production of calcium carbonate. As the pH continues to rise to around 6, the solution environment becomes alkaline, bacterial activity rapidly increases, and the production of calcium carbonate increases and shows an upward trend. Figure\u0026nbsp;5 intuitively suggests that the optimal combination of factors is: pH\u0026thinsp;=\u0026thinsp;3, O\u003cem\u003eD\u003c/em\u003e\u003csub\u003e600\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;4, and C\u003cem\u003eS\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2 mol/L.\u003c/p\u003e\n \u003cp\u003e\u003c/p\u003e\u0026nbsp;\u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eResults of orthogonal test\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTest Number\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eM\u003c/em\u003e\u003csub\u003e3\u003c/sub\u003e/g\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.053\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.069\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.099\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.171\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e5\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.055\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e6\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.065\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e7\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.108\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e8\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.169\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e9\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.054\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e10\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.091\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e11\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.133\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e12\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.204\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e13\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.075\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e14\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.085\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e15\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.157\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e16\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.356\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003e\u003c/p\u003e\u0026nbsp;\u003ctable id=\"Tab4\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eRange analysis of orthogonal experiment\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFactor\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eO\u003c/em\u003eD\u003csub\u003e600\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eC\u003c/em\u003eS\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003epH\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003ek\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.098\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.059\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.152\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003ek\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.099\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.078\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.121\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003ek\u003c/em\u003e\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.121\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.124\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.102\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003ek\u003c/em\u003e\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.168\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.225\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.111\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.070\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.166\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.050\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec20\" class=\"Section2\"\u003e\n \u003ch2\u003e4.2 Analysis of Uniformity Test for Sand Column Specimens\u003c/h2\u003e\n \u003cp\u003eTo evaluate the uniformity of sand specimens reinforced with DYF, acid washing tests were conducted on equal masses of sand collected from different parts of the solidified specimens, and the calcium carbonate content of each part was measured, as shown in Table \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e. The table indicates that the calcium carbonate content in both LXF and DYF solidified specimens decreases from the top to the bottom of the specimens. The maximum differences in calcium carbonate content between the inner and outer rings of the DYF solidified specimens are 0.51 g and 0.44 g, respectively, while those for the LXF solidified specimens are 1.13 g and 1.21 g, respectively. A smaller difference indicates a more uniform distribution of calcium carbonate. Comparison shows that the calcium carbonate content varies less among different parts of the DYF solidified specimens, with the maximum differences in calcium carbonate content between the inner and outer rings reduced by 54.9% and 63.6%, respectively, compared to the LXF solidified specimens. Therefore, the calcium carbonate distribution is more uniform in DYF solidified specimens. Due to the inhibition of microbial activity at low pH levels, bacterial flocculation decreases, delaying the initial reaction of calcium carbonate. This allows the grout to penetrate downward with sufficient pathways. Subsequently, urea hydrolysis gradually joins the reaction, increasing the environmental pH and resuscitating microbial activity. The in-situ flocculation reaction and calcium carbonate production reaction around soil particles in various parts of the sand column begin to proceed synchronously, resulting in a uniform distribution of calcium carbonate in all parts of the specimen.\u003c/p\u003e\n \u003cp\u003e\u003c/p\u003e\u0026nbsp;\u003ctable id=\"Tab5\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eCalcium carbonate content in different parts of the test specimen\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eLocation\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eUpper part of the specimen/g\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMiddle section of the specimen/g\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eLower part of the specimen/g\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eOuter layer of DYF sample\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.97\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.00\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eInner layer of DYF sample\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.24\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eOuter layer of LXF sample\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.72\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.51\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eInner layer of LXF sample\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.76\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.63\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec21\" class=\"Section2\"\u003e\n \u003ch2\u003e4.3 Analysis of Shear Test Results\u003c/h2\u003e\n \u003cp\u003eThe relationship curve between shear stress and shear displacement for the direct shear test of the specimens is shown in Fig. 7. During the shearing process, as the shear displacement increases, the shear stress of the specimens gradually rises, and the rate of increase gradually flattens out. At the same shear displacement, the peak strength of specimens solidified with DYF is 20\u0026ndash;35% higher than that of specimens solidified with LXF. This is because DYF improves the uniformity of calcium carbonate distribution in the specimens, and the uniformly distributed calcium carbonate crystals form a three-dimensional calcium carbonate network structure within the specimens, causing the surrounding soil particles to share the load together. This results in a more widespread distribution of the load and subsequently enhances the strength of the specimens.\u003c/p\u003e\n \u003cp\u003eThe Coulomb strength fitting envelope is illustrated in Fig. 8. According to the fitting results, the cohesion of the undisturbed soil is 9.63 kPa, with an internal friction angle of 29.8\u0026deg;. After solidification with LXF, the cohesion of the specimens increases to 13.27 kPa, an increase of 37.8%, and the internal friction angle rises to 31.7\u0026deg;, an increase of 6.4%. After solidification with DYF, the cohesion of the specimens further increases to 19.42 kPa, an increase of 101.6%, and the internal friction angle rises to 37.4\u0026deg;, an increase of 25.5%. Both grouting methods improve the internal friction angle and cohesion of the specimens. Compared to LXF, the cohesion of DYF-solidified specimens is enhanced by 46.3%, and the internal friction angle is increased by 17.9%. In DYF-solidified specimens, calcium carbonate uniformly fills the pores of the soil, strengthening the biting force between soil particles and increasing the cohesion among them. The three-dimensional network framework formed by calcium carbonate shares the shear stress, reinforcing the structurally weak planes of the soil.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec22\" class=\"Section2\"\u003e\n \u003ch2\u003e4.4 Analysis of Durability Test Results\u003c/h2\u003e\n \u003cp\u003eThe experimental design included 10 groups of samples reinforced with DYF and 10 groups of samples reinforced with LXF, with three parallel samples in each group and all samples undergoing 12 rounds of reinforcement. These samples were subjected to durability tests in deionized water, with treatment cycles of 1, 5, 10, 15, 20, 25, and 30 rounds, respectively. After the durability tests, each group of samples was cleaned, demolded, and dried. Firstly, their mass loss rates were measured. Subsequently, unconfined compressive strength tests were conducted. The data from these tests were then compiled and analyzed along with data from samples that had not undergone durability testing.\u003c/p\u003e\n \u003cdiv id=\"Sec23\" class=\"Section3\"\u003e\n \u003ch2\u003e4.4.1 Analysis of Mass Loss Rate\u003c/h2\u003e\n \u003cp\u003eAs the experiments progressed, there was varying degrees of surface spalling on the samples and some loss of internal particles. The change patterns in mass loss rate for the samples in each experimental group are recorded and shown in Fig.\u0026nbsp;9. For both grouting methods, the mass loss rate of the solidified samples increased rapidly in the first 10 cycles and basically stabilized by the 20th cycle. In the drying-wetting cycle test, after 30 cycles, the highest mass loss rate was observed in the LXF-solidified samples, which was 2.6%, while the final mass loss rate of the DYF-solidified samples was 2.25%. Compared to the LXF-solidified samples, the final mass loss rate of the DYF-solidified samples was reduced by 13.8%. In the deionized water immersion test, after 30 cycles, the highest mass loss rate was again observed in the LXF-solidified samples, which was 1.55%, while the final mass loss rate of the DYF-solidified samples was 1.3%. Compared to the LXF-solidified samples, the final mass loss rate of the DYF-solidified samples was reduced by 16.13%. Due to the inhibition of microbial activity in a low pH environment, bacterial flocculation decreased, delaying the initial reaction of CaCO\u003csub\u003e3\u003c/sub\u003e. This allowed the grout to penetrate downward through sufficient pathways. Subsequently, urea hydrolysis gradually joined the reaction, increasing the environmental pH and resuscitating microbial activity. The in-situ flocculation reaction and calcium carbonate formation reaction around soil particles began to occur synchronously in various parts of the sand column, resulting in a uniform distribution of CaCO\u003csub\u003e3\u003c/sub\u003e throughout the samples. The uniformly distributed calcium carbonate crystals evenly encapsulated the soil particles, enhancing the compactness of the samples.\u003c/p\u003e\n \u003cp\u003eIn both the drying-wetting cycle test and immersion test, the mass loss rate of the LXF-solidified samples was higher than the final mass loss rate of the DYF-solidified samples. This is because the erosion of microbial-solidified calcareous sand is predominantly physical. During immersion, the solution slowly infiltrates and soaks the samples, weakening the bonds between sand grains and calcium carbonate crystals, causing weaker sections to spall off under erosion. Additionally, internal air venting in the samples generates tensile stress at the bonds, resulting in cracking at particle connections. However, in DYF-solidified samples, CaCO\u003csub\u003e3\u003c/sub\u003e uniformly fills the soil pores, strengthening the biting force between soil particles and increasing the cohesion among them. The three-dimensional network framework formed by CaCO\u003csub\u003e3\u003c/sub\u003e distributes stress, reinforcing the structurally weak planes of the soil. Under the action of drying-wetting cycles, the samples undergo cycles of water absorption and drying: during drying, soil particles expand slightly, causing compressive stress between particles; during water absorption, the hygroscopicity of dry calcareous sand enhances the invasion speed and depth of the solution, and particles contract upon cooling. Compared to LXF-solidified samples, the calcium carbonate in DYF-solidified samples is uniformly distributed throughout the sample, tightly encapsulating the soil particles. Under repeated drying-wetting cycles, due to the uniform filling and encapsulation of the calcium carbonate skeleton around the soil particles, the energy difference between various parts of the sample is smaller, enabling it to better resist the damage caused by drying-wetting cycles.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec24\" class=\"Section3\"\u003e\n \u003ch2\u003e4.4.2 Analysis of Strength Loss\u003c/h2\u003e\n \u003cp\u003eAs shown in Fig.\u0026nbsp;10, the unconfined compressive strength (UCS) of both LXF-solidified and DYF-solidified samples decreases continuously with increasing treatment cycles. The strength of the samples drops more rapidly in the first 10 cycles and then tends to stabilize after reaching 20 cycles. According to Fig.\u0026nbsp;10, the most severe degradation was observed in the LXF-solidified samples subjected to drying-wetting cycles, with a strength reduction of 507 kPa (49.7%) after 30 cycles. In contrast, the DYF-solidified samples experienced a strength decrease of 421.3 kPa (about 32.8%) after 30 drying-wetting cycles. Compared to LXF-solidified samples, the strength loss of DYF-solidified samples was reduced by 16.9%. In the deionized water immersion test, after 30 cycles, the LXF-solidified samples had the highest remaining strength of 28.3%, while the strength loss rate of DYF-solidified samples was 17.1%. Compared to LXF-solidified samples, the strength loss of DYF-solidified samples was reduced by 21.1%. After 30 treatment cycles, the strength loss of LXF-solidified samples was greater than that of DYF-solidified samples in both the drying-wetting cycle test and immersion test. Additionally, under the same number of treatments, the strength loss of samples in the drying-wetting cycle group was greater than that in the immersion group, which corresponds to the pattern of mass loss rates. This is because when the samples are immersed, water infiltrates through pores and cracks, filling the interior. The intrusion of the solution disrupts the weak bonds between soil particles. Compared to DYF-solidified samples, the uneven distribution of calcium carbonate in LXF-solidified samples results in unstable cementation that is more susceptible to damage in aqueous environments. Under the action of drying-wetting cycles, the samples undergo drying treatment. Due to the different calcium carbonate contents in various parts of the samples, there is an energy difference. As the number of drying-wetting cycles increases, the uneven calcium carbonate crystals exert pressure on the inner walls of soil particle pores. This force causes pores and cracks to expand continuously, ultimately leading to a significant reduction in the strength of the samples in seawater environments. In DYF-solidified samples, the distribution of CaCO\u003csub\u003e3\u003c/sub\u003e is more uniform, with a large amount of CaCO\u003csub\u003e3\u003c/sub\u003e crystals filling and encapsulating the soil particles, reducing soil porosity and increasing soil compactness. Additionally, the uniform distribution of calcium carbonate within the samples results in a smaller energy difference between different parts, enhancing the deformation resistance of the soil.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec25\" class=\"Section2\"\u003e\n \u003ch2\u003e4.5 Analysis of Microstructural Mechanisms\u003c/h2\u003e\n \u003cp\u003eThe above analysis indicates that DYF can effectively improve the uniformity of microbially solidified soil and enhance its mechanical properties. To explore the mechanism of action of DYF in solidifying soil, scanning electron microscopy (SEM) was used to analyze the microstructure of the solidified samples, as shown in Fig. 11.\u003c/p\u003e\n \u003cp\u003eAs shown in Figs.\u0026nbsp;11(A) and (B), the calcium carbonate crystals formed in the LXF-solidified samples have a certain filling effect on the soil pores, but the filling effect is limited. There are significant differences in the distribution of calcium carbonate crystals around the soil particles, resulting in numerous pores between them. Calcium carbonate uses bacteria as nucleation sites [\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e], indicating that the amount of bacteria attached between soil particles is different and unevenly distributed, leading to unsatisfactory pore filling and interparticle bonding effects of calcium carbonate crystals. As illustrated in Figs.\u0026nbsp;11(C) and (D), the internal pores in the DYF-solidified samples are significantly reduced. The calcium carbonate crystals encapsulate the soil particle surfaces and fill the pores between them, forming a large number of aggregates of soil particles and calcium carbonate crystals. DYF enables a more uniform distribution of bacteria in the soil, providing numerous nucleation sites for calcium carbonate crystals. This reduces the number and size of pores between soil particles, making the soil structure more compact and effectively improving the soil\u0026apos;s micro-pore structure [\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e\n\u003c/div\u003e"},{"header":"5 Conclusions","content":"\u003cp\u003eAddressing the issue of uneven calcium carbonate formation during soil solidification using microbial grouting technology, a series of experiments were conducted based on DYF, including MICP (microbially induced calcium carbonate precipitation) aqueous solution tests, sand column grouting solidification tests, direct shear tests, and consolidation tests. These experiments aimed to explore the influence of multiple factors on the mechanical properties of DYF-solidified soil samples and the underlying mechanism of strength enhancement. The following conclusions were drawn:\u003c/p\u003e \u003cp\u003e(1) Through aqueous solution experiments, calcium carbonate precipitation curves under different influencing factors were obtained. Based on orthogonal experiments, the optimal cultivation scheme was determined as follows: pH\u0026thinsp;=\u0026thinsp;3, O\u003cem\u003eD\u003c/em\u003e\u003csub\u003e600\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;4, and C\u003cem\u003eS\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2 mol/L. The order of influence on the experimental results, from greatest to least, is: C\u003cem\u003eS\u003c/em\u003e concentration\u0026thinsp;\u0026gt;\u0026thinsp;O\u003cem\u003eD\u003c/em\u003e\u003csub\u003e600\u003c/sub\u003e value\u0026thinsp;\u0026gt;\u0026thinsp;pH.\u003c/p\u003e \u003cp\u003e(2) In the sand column uniformity test, compared to the two-phase grouting method, the distribution of calcium carbonate in the DYF-solidified sand column was more uniform. This is attributed to the low pH condition which inhibited bacterial activity and delayed the formation of calcium carbonate, allowing the grout to have sufficient infiltration time and penetration pathways to flow towards the bottom of the sample.\u003c/p\u003e \u003cp\u003e(3) According to the direct shear test and durability test, compared to LXF, the DYF-solidified samples exhibited an increase in the internal friction angle by 17.9% and an increase in cohesion by 46.3% in the direct shear test. In the soaking test, the final mass loss rate and strength loss of DYF-solidified samples were reduced by 16.13% and 21.1%, respectively. In the dry-wet cycling test, the final mass loss rate and strength loss of DYF-solidified samples were reduced by 13.8% and 16.9%, respectively. The uniform distribution of calcium carbonate within the samples is the fundamental reason for the enhanced strength of the sand columns.\u003c/p\u003e \u003cp\u003e(4) SEM microstructural analysis reveals that the distribution of calcium carbonate in samples treated with DYF is more uniform, with a significant amount of calcium carbonate encapsulating the surface of soil particles. This optimizes the pore structure of the soil and enhances the overall effectiveness of the solidified samples.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eConceptualization, G.Q. and H.Z.; methodology, G.Q. , H.Z. , C.M. and X.Z. ; formal analysis, G.Q. , H.Z. , C.M. ; investigation, G.Q. , H.Z. ,X.Z. , H.S. ; data cu-ration, H.S. ; writing\u0026mdash;original draft preparation, H.Z. ; writing\u0026mdash;review and editing, G.Q. and H.Z. ; supervision, G.Q., C.M. ; project administration, G.Q. ; funding acquisition, G.Q.. All authors have read and agreed to the published version of the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eThis research was funded by the Inner Mongolia Autonomous Region's Universities Basic Scientific Research Operating Expenses Project: Application of Green Microbial Mineraliza-tion Technology in Restoration and Control of Abandoned Open-pit Mines in Inner Mongolia (2024QNJS063).\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe original contributions presented in the study are included in thearticle. Further inquiries can be directed to the corresponding author.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eJi, X. et al. Long-Term Performance on Drought Mitigation of Soil Slope Through Bio‐Approach of MICP: Evidence and Insight from Both Field and Laboratory Tests[J]. \u003cem\u003eWater Resour. 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Experimental study on microbial deposition of calciumcarb onate solidified sand[J].Geotechnical mechanics,2017,38 (11):3225\u0026ndash;3230 .(in Chinese).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLIN H,SULEIMAN M T,BROWN D G.Investigation of pore-scale CaCO\u003csub\u003e3\u003c/sub\u003e distributions and their effects on stiffness and permeability of sands treated by microbially induced carbonate precipitation (MICP)[J].Soils and Foundations,2020,\u003cb\u003e60\u003c/b\u003e (4):944\u0026ndash;961 .\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"microbial-induced calcite precipitation, grouting method, low pH value, geotechnical testing, microstructure","lastPublishedDoi":"10.21203/rs.3.rs-5335157/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5335157/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAddressing the issue of uneven distribution of calcium carbonate during soil solidification using Microbial Induced Calcite Precipitation (MICP) technology, an experimental study was conducted on the distribution of calcium carbonate in microbial-solidified soil samples using a low-pH single-phase grouting method. Through orthogonal experiments, the optimal culture conditions were determined as follows: pH\u0026thinsp;=\u0026thinsp;3, O\u003cem\u003eD\u003c/em\u003e\u003csub\u003e600\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;4, and C\u003cem\u003eS\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2 mol/L. Based on this optimal grouting scheme, the distribution of calcium carbonate in microbial-solidified soil samples, as well as the changes in sample strength and durability, were investigated. Scanning Electron Microscopy (SEM) tests were also conducted to observe the microstructure characteristics of the solidified samples. The results indicate that the low-pH single-phase grouting method contributes to promoting a more uniform distribution of calcium carbonate during the microbial reaction process. Compared to the two-phase grouting method, the internal friction angle of samples solidified using the low-pH single-phase grouting method increased by 17.9%, and the cohesive force increased by 46.3%. In immersion tests, the final mass loss rate of samples solidified with the low-pH single-phase grouting method decreased by 16.13%, and the strength loss decreased by 21.1%. In dry-wet cycling tests, the final mass loss rate of samples solidified with the low-pH single-phase grouting method decreased by 13.8%, and the strength loss decreased by 16.9%.\u003c/p\u003e","manuscriptTitle":"Experimental Study on the Shear Strength and Durability of Microbial-Consolidated Silty Sand under Low pH Conditions","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-11-27 15:39:17","doi":"10.21203/rs.3.rs-5335157/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"6579691f-aef9-4131-acae-d94f9d921b1d","owner":[],"postedDate":"November 27th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":40597976,"name":"Physical sciences/Engineering/Civil engineering"},{"id":40597977,"name":"Biological sciences/Biotechnology/Environmental biotechnology"}],"tags":[],"updatedAt":"2025-02-20T09:23:49+00:00","versionOfRecord":[],"versionCreatedAt":"2024-11-27 15:39:17","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5335157","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5335157","identity":"rs-5335157","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}