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Article

Strength and Mechanism of Granite Residual Soil Strengthened by Microbial-Induced Calcite Precipitation Technology

by
Rong Wang
1,
Huawei Li
1,
Zichuang Chen
2,
Fang Liu
3,
Muwang Wei
1,
Feiyu Liu
1,
Qian Wang
1 and
Changbin Hu
2,*
1
School of Civil Engineering and Architecture, Wuyi University, Wuyishan 354300, China
2
College of Civil Engineering, Fuzhou University, Fuzhou 350116, China
3
College of Life Sciences, Fujian Agriculture and Forestry University, Fuzhou 350002, China
*
Author to whom correspondence should be addressed.
Appl. Sci. 2023, 13(15), 8863; https://doi.org/10.3390/app13158863
Submission received: 7 July 2023 / Revised: 29 July 2023 / Accepted: 30 July 2023 / Published: 1 August 2023
Browse Figures
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Abstract

:
High rainfall environmental conditions can easily cause erosion or collapse of the granite residual soil slope. However, traditional slope reinforcement methods have drawbacks such as poor landscape effect, high energy consumption of raw materials, and environmental pollution. This study studied the application of microbial-induced calcite precipitation (MICP) in the reinforcement of granite residual soil. The consolidation effect of various methods was investigated, and the influence of cementing liquid concentration and pH value on consolidation under optimal curing conditions was explored. The results showed that the bacteria concentration reached OD600 = 3.0 and urease activity was 31.64 mM/min, which positively impact the production of calcium carbonate and the stability of crystal morphology. In addition, the soaking method was found to have the most effective consolidation effect on the surface soil samples, with the lowest disintegration rate. On the other hand, the peristaltic pump grouting method is the most effective in strengthening depth. This method resulted in a 513.65% increase in unconfined compressive strength (UCS), a 297.98% increase in cohesion, and a 101.75% increase in internal friction angle. This study also found that after seven rounds of grouting, the highest UCS was achieved in consolidated soil samples with a 0.5 mol/L cementing solution concentration, reaching 1.602 MPa. The UCS of soil samples increases as the pH value of the cementing fluid increases within the range of 6–8. As the pH value reaches 8–9, the strength increases and stabilizes gradually. These research findings can serve as an experimental basis for strengthening granite residual soil slopes and a guide for improving microbial geotechnical strengthening methods.

1. Introduction

To ensure high-quality economic development, it is crucial for highway construction to prioritize safety and green development. This includes paying close attention to the fully weathered rock-cutting slope of mountainous highways exposed to strong physical weathering [1,2]. Meanwhile, heavy rainfall may induce landslides, making it imperative to take preventive measures. In Southeast China, there are thick residual layers of granite that have weathered over time [3]. The original rock was composed of feldspar, mica, quartz, and amphibole, with a hard texture, uniform nature, and high strength [4,5]. However, due to weathering, a significant amount of feldspar has undergone hydrolysis and carbonation, forming kaolinite. Kaolinite possesses a compact structure yet exhibits a high water absorption capacity. Upon exposure to water, it tends to swell and soften [3,4,6,7]. As a result, in regions of southeastern China where rainfall is consistently high, slopes composed of granite residual soil are susceptible to erosion and potential collapse. Traditional methods of slope protection, such as mortar rubble slope protection and sprayed cement mortar, have been found to have certain drawbacks. These include poor landscape aesthetics and high energy consumption leading to environmental pollution [8,9]. However, the combination of concrete lattice beam and vegetation protection partially fulfills the requirements of ecological protection, but it has complex construction technology and management workload issues [10,11]. Moreover, granite residual soil is unsuitable for plant growth [12], resulting in high input costs and little protection effect. Therefore, it is crucial to research soil reinforcement techniques that are both environmentally sustainable, cost-effective, and high-performing.
In recent years, researchers have explored microbial-induced calcite precipitation (MICP) technology for soil reinforcement. This technology utilizes high-yield urease bacteria to decompose urea and produce carbonate particles. In an alkaline environment, these particles combine with calcium ions to form calcium carbonate crystals, which cement loose soil particles together and significantly enhance soil strength [13,14]. Dr. Whiffin, from Murdoch University in Australia, was the first to utilize MICP technology to solidify loose sand. As a result, the physical and mechanical indexes, including stiffness and unconfined compression strength (UCS), were significantly improved after solidification [15,16]. Additionally, the study revealed that the degree of cementation, or strength distribution, varied significantly across different sections of the sand column [17]. Subsequently, other researchers investigated the uniform distribution of calcium carbonate in the sand. They found that the solidification effect of the soil was influenced by various factors, including colony distribution, initial concentration of the bacterial solution, and standing time [18,19,20,21]. Moreover, they expanded the application of MICP technology to silty sand [22], expansive soil [23], dredger fill [24], and other types of soil solidification. Further research indicates that soil properties are closely linked to the crystal type and calcium carbonate content, which directly impacts the soil’s reinforcement effect.
In the application of granite residual soil reinforcement, Wang et al. discovered that bio-cementation forms a surface coating on granite residual soils, which leads to the hydraulic conductivity by 90.9% from the initial value, and the erosion rate can be reduced by 95.2% [25]. Liang et al.’s research found that the internal friction angle of MICP-treated granite residual soil increased by 10% under a moisture content of 30%, while its cohesion increased by 218% [26]. Moreover, Zhu et al. conducted a study on the effectiveness of adding calcium lignosulfonate to improve the microbial growth environment and pore structure of granite residual soil. The results showed a 41.2% increase in compressive strength [27]. Their research indicates that MICP technology can potentially solidify granite residual soil. However, further research is needed to systematically investigate the factors that affect the solidification effect of soil, as the research on this topic is still in its early stages.
Hence, this study investigates the regional characteristics and physical properties of granite residual soil in Southeast China. Various factors, including reinforcement methods, environment, grouting times, and cementing liquid concentration, were examined to explore the application scope of different consolidation methods. Besides that, the disintegration rate, shear strength, UCS, and uniformity of calcium carbonate distribution of consolidated soil were measured to determine the effectiveness of each method. Meanwhile, microscopic test was also conducted to summarize the solidification control mechanism. These findings provide a reliable basis for relevant engineering design and practice.

2. Materials and methods

2.1. Materials

2.1.1. Soil

The soil used in this study was obtained from the slope of 237 National Highway K1347+400 in Wuyishan, Fujian Province, China. The particle size distribution was characterized by the sieve analysis method and the laser particle size analyzer and is presented in Table 1 and Figure 1.
It can be seen from the table that the soil samples contain 75.5% sand particles, 17.64% silt particles, and only 6.86% clay particles. According to the Chinese National Standard for Engineering Classification of Soils (GB/T50123-2019) and the grain grading curve [28], the soil sample has a nonuniformity coefficient Cu of 0.86 and a curvature coefficient CC of 29 (determined by Equations (1) and (2)), indicating that it belongs to poorly graded fine-grained soil.
C u = d 60 / d 10
C c = d 30 2 / d 60 d 10
where d10, d30, and d60 represent the corresponding particle size values when the percentage of particle size distribution reaches 10%, 30%, and 60%, respectively.
The physical parameters of soil samples were further determined by indoor tests, and the results are shown in Table 2. The test results indicate that the soil sample is categorized as low-liquid limit soil, with a saturation percentage of 23.39% and a void ratio of 1.27. Compared with relevant research [29], granite residual soil in Wuyishan has typical regional characteristics.

2.1.2. Preparation of the Bacterial Solution

Sporosarcina pasteurii used in this study was purchased from the China General Microbiological Culture Collection Center. The AB double culture medium was used to obtain the bacterial solution with OD600 of 2.8 and urease activity of 31.64 mM/min through twice inoculation. The A culture medium contained Yeast extract 20 g/L, ammonium chloride 10 g/L, nickel chloride 0.05 g/L, and peptone 10 g/L. The B culture medium contained beef extract 10 g/L, sodium chloride 5 g/L, urea 20 g/L, and nickel chloride 0.05 g/L. The Sporosarcina pasteurii was grown at 30 °C with a culture medium pH value of 8. The morphology characteristic of Sporosarcina pasteurii is shown in Figure 2.

2.2. Test Plan and Device

2.2.1. Test Plan

The test was divided into two stages, namely stage I and II respectively. Due to the soil being mainly composed of fine particles, the grouting mold was improved for granite residual soil in stage I. Then, three different grouting methods—air compressor grouting, immersion method, and peristaltic pump grouting—were adopted. Lastly, based on the UCS test, shear test, calcium carbonate content determination, and disintegration test, the optimal grouting method was selected for stage II. In stage II, the optimum curing scheme was determined by changing the concentration and pH value of the cementing solution. The curing test was conducted in an indoor environment with a temperature range of 25–30 °C, and the specific test scheme is presented in Table 3 and Table 4. All solidified soil samples were cured in the natural environment for seven days after demolding.

2.2.2. Test Mold and Device

After drying, the soil sample is compacted into three layers and loaded into a mold. The peristaltic pump and air compressor are grouted with a cylindrical model made of acrylic material. The two ends of the mold are equipped with threaded covers, on which liquid inlet and outlet holes are reserved (Figure 3a). The soaking group adopts a complete contact flexible mold with white geotextile material for the outer layer and high-density gauze for the inner layer. Once the soil sample is filled, the top cover is sewn shut with a needle and thread (Figure 3b).
The peristaltic pump is equipped with a 4-channel DG pump head designed for grouting. To control the air compressor grouting, a pressure-regulating valve and switch are added to regulate gas transmission. Additionally, for oxygen supply during the immersion method, an electromagnetic ACO series oxygen pump is utilized (Figure 4).

2.3. Test Method

2.3.1. Disintegration Test

In consideration of the susceptibility of Wuyishan granite residual soil slope to landslide disasters in the event of heavy rainfall after prolonged sun exposure, two soil samples (before and after strengthening) were dried at 60 °C until reaching a constant weight. Subsequently, the samples were soaked in water until disintegration ceased, followed by another round of drying and weighing of the residual mass. This process was repeated four times to complete the disintegration test.
D r = ( W 1 − W 2 ) / W 1
where Dr represent the disintegration rate of granite residual soil, and W1 and W2 represent the quality before and after disintegration, respectively.

2.3.2. Unconfined Compressive Strength

The soil samples are dried for 7 days at room temperature after strengthening, and the shear stress and UCS are measured according to the Chinese National Standard for Soil Test Methods (GB/T50123-2019) [28]. The shear stress is measured under 100–400 kPa vertical pressure with a shear rate of 0.8 mm/min.

2.3.3. Determination of Calcium Carbonate Precipitation

The soil samples injected by the peristaltic pump and air compressor were divided into four equal parts according to their height for calcium carbonate content determination; then, the content of calcium carbonate in the solidified soil samples (from the surface 2 cm and inside) was measured with the soaking method, as shown in Figure 5. To prepare the samples, they were ground into powder and dried. Three 10 g soil samples from each part were taken and titrated with 1 mol/L hydrochloric acid until no bubbles formed for half an hour. The remaining soil mass was then weighed.

2.3.4. Micro-Analysis

The composition and crystal form of mineralized products were analyzed by X-ray diffraction phase (XRD) analysis, and the micro morphology of the solidified soil was analyzed with a scanning electron microscope (SEM).

3. Test Results and Analysis

3.1. Disintegration Rate

The disintegration of granite residual soil is caused by water infiltration through soil fissures, which dissolve free oxides crucial for cementation between soil particles [30]. The test soil samples were dried to a constant weight at 60 °C and then soaked in water. The reference group used the uncured soil samples, which generated bubbles and rapidly disintegrated after encountering water for 30 s and disintegrated entirely after 3 min. The soil samples strengthened with five different methods illustrate different anti-disintegration properties. After four cycles of disintegration tests, the residual soil solidified with the soaking method had the lowest amount of disintegration at only 3.21%. This is mainly due to the homogeneity and thickness of the surface consolidated layer that was formed. In addition, the disintegration rates for multiple and single grouting using a peristaltic pump were 9.7% and 13.77%, respectively. In comparison, the disintegration rates for primary grouting using an air compressor and multiple grouting machine were 9.26% and 16.28%, respectively. The results showed that the strengthening effect of multiple grouting is significantly better than that of primary grouting, and the grouting effect of the peristaltic pump is slightly better than that of air compressor grouting. Additionally, the highest disintegration rate for all five grouting modes occurred during the second soaking, as shown €n Figure 6 and Figure 7. The surrounding consolidated soil protects the unconsolidated soil in the first disintegration test. However, in the second test, the uncured soil’s cohesion and internal friction angle decrease, leading to rapid soil disintegration. The third and fourth disintegration tests showed that the disintegration rate was almost zero and tended to be stable. This indicated that a stabilized soil structure was gradually formed due to the deposition of calcium carbonate.

3.2. Shearing Strength

After 7 days of natural air drying, the soil samples were consolidated into a whole by using five methods, as shown in Figure 8. The results show that the soil particles, after strengthening, are evenly distributed using a peristaltic pump for grouting. However, the soil sample grouted with an air compressor was subject to air pressure, and a large number of fine particles sank to the bottom of the sample. It had a significant impact on the uniformity of the soil particles. On the other hand, the soil surface solidified with the immersion method was dense and thick.
According to the stress-strain curve obtained from the shear test (Figure 9), the shear strength (Table 5), the internal friction angle, and cohesion (Table 6) of granite residual soil are obtained. It can be seen from the table that a significant improvement in the shear strength of soil solidified with five methods was achieved. The group JR under the same vertical stress shows a maximum cohesion of shear strength of 167.59 kPa and an internal friction angle of 54.15°. These values are 101.75% and 297.98% higher than the uncured group (cohesion: 42.11 kPa, internal friction angle: 26.84°). The lowest degree of improvement in the strengthening effect is group JPY, with the cohesion and internal friction angle increased by 14.42% and 122.51%, compared with the uncured soil. It can be seen that microbially induced CaCO3 precipitation can effectively bond soil particles, fill the space between soil particles, increase the surface’s roughness, improve the sample’s integrity and enhance the friction resistance. Further comparison between the test group of one-time grouting and multiple grouting revealed that multiple grouting with peristaltic pump increased the cohesion by 55.03% and the internal friction angle by 44.86% compared with one grouting. The cohesion increased by 34.79%, and the internal friction angle increased by 53.74% when the air compressor was used for multiple grouting compared to a single grouting. The effectiveness of multiple grouting’s strengthening is significant due to the increase in the number of bacteria on the surface or between soil particles with each injection of bacterial liquid. This promotes the precipitation of calcium carbonate between soil particles, resulting in a more apparent bridging effect between soil particles [31]. The cohesion increase of air compressor grouting is lower than that of peristaltic pump grouting, but the friction angle increase is greater. This is due to the fine-grained soil sinking to fill the bottom gap under the air pressure, which affects bacterial adhesion and cementing fluid injection, resulting in a lower adhesive force after soil sample solidification. However, the consolidated soil with coarser particles is formed in areas except for the bottom. The interlocking effect between soil particles and the surface friction and the connection bite force between them are improved. Figure 10 presents the relationship curve between the shear strength and normal pressure of granite residual soil under different normal pressures. The figure demonstrates that the curing effect of groups JPY, JKY, and JRY mainly enhances cohesion. The soaking method used in the group JPY resulted in a one-dimensional surface consolidation, which prevented the bacteria and cementation liquids from entering the soil and forming a complete consolidation body. Groups JKY and JRY had limited bacterial adsorption due to a one-time injection, which affected the amount of calcium carbonate between the soil particles and failed to form a complete consolidated body. The cohesion and friction angle of groups JR and JK are significantly improved, especially in group JR; the peristaltic pump grouting has little disturbance on soil samples and is most effective for transporting colony and cementing fluid into the lower soil mass, with the best consolidation effect.
The research on the reinforcement of granite residual soil shows that the cohesion of the soil after reinforcement increases by 115.43%, and the internal friction angle decreases slightly [26]. The effect of reinforcement is lower than that of this test. This was mainly due to the low urease activity of the bacteria used, which was only 41.75% of the test. Therefore, the impact of urease activity on calcium carbonate deposition is significant. The use of a double medium culture promotes the production of high urease bacterial fluid, which is crucial for soil sample consolidation.

3.3. Unconfined Compressive Strength

The UCS test revealed significant variations in failure forms of soil samples with different strengthening methods, as depicted in Figure 11. The group JR exhibited a typical tensile failure, with cracks running through the whole sample column from top to bottom, similar to the uniaxial compression failure mode of brittle materials [32]. In group JK, the soil bottom was partially broken, and an obvious weak strengthening area was observed. Groups JRY and JKY showed multiple fracture surfaces, indicating the presence of several weak points in the test piece. Group JPY resulted in an overall fracture, with the internal soil not consolidated together, except for the massive exfoliated soil on the surface of the test piece.
The results presented in Figure 12 indicate that the UCS of group JR reached a maximum of 1.663 MPa, which is 513.65% higher than the uncured group (0.271 MPa). On the other hand, group JRY only achieved a strength of 0.484 MPa, which is significantly lower than group JR, which underwent multiple injections of bacteria, confirming the shear test phenomenon. The air compressor grouting mode showed the second-best strengthening effect, while the JK group with multiple grouting also demonstrated a better effect, with a strength increase of 331.37%. Despite multiple attempts at grouting, the strengthening effect of the bottom soil has been poor due to the sinking of fine particles caused by air pressure. This destroyed the bottom soil sample before the upper soil reached the ultimate bearing capacity. The strengthening of group JPY only affected the surface soil, resulting in a weak UCS of only 0.351 MPa, with the lowest increase.

3.4. Homogeneity of Calcium Carbonate

Figure 13 shows the calcium carbonate content of soil samples in different parts following the UCS test. The soil mass, strengthened by the soaking method, in one-dimensional form is the most severe. The calcium carbonate content in the surface layer is remarkably high at 10.03%. However, it is only 1.97% in the inner layer. It can be concluded that the solidification effect is only effective for the soil mass with a thickness of 2 mm in the surface layer. Consequently, the shear strength and UCS of the soil sample are the lowest in the strengthened soil.
The study found that the calcium carbonate content of soil samples decreased from top to bottom in both the group JRY and JKY. However, there was a difference in the distribution pattern. In group JRY, the calcium carbonate content slowed down the most in the upper to middle upper regions, resulting in a more significant decline compared to group JKY. On the other hand, in group JKY, the calcium carbonate content dropped sharply in the lower part of the soil, while the rest of the soil mass showed an even distribution of calcium carbonate. The peristaltic pump and the air compressor have significant differences in the transmission and distribution of bacterial fluid. The bacterial fluid is more evenly distributed under the action of the air compressor, which promotes the uniform distribution of calcium carbonate in the soil. However, the fine particles of the soil sample sink to the bottom due to the action of the air compressor, resulting in dense soil at the bottom that hinders the entry and attachment of bacterial fluid [33]. When comparing the one-time and multiple grouting methods of the peristaltic pump, it has been found that multiple bacterial injections can significantly increase the calcium carbonate content in the soil, which in turn promotes conditions conducive to soil consolidation and repair. However, it is essential to note that with an increase in the number of bacteria injections, the degree of decreasing calcium carbonate content from top to bottom in the soil is also increased. Therefore, to achieve optimal strengthening, it is necessary to coordinate the effective strengthening depth of the soil with the progressive compaction of the upper soil in order to reduce the one-dimensional effect.
In summary, the research works of stage I show that MICP technology can be applied to the strengthening of granite residual soil. This is mainly due to the soil environment of granite residual soil being suitable for bacterial growth and a rich calcium source. Besides that, different strengthening methods have significant effects on bacterial adhesion and calcium carbonate production. The effects of cementing solution concentration and pH value on the curing effect are further explored below.

3.5. The Effect of Cementing Solution Concentration on Strengthening

During the process of grouting solidification, it was observed that an increase in cement concentration resulted in earlier one-dimensional calcium carbonate deposition in some groups, leading to the early termination of the test. Specifically, group JRN6 terminated at the third round of bacterial fluid injection failure, group JRN5 terminated at the third round of cementing fluid injection failure, and group JRN4 terminated at the fourth round of bacterial fluid injection. Only groups 1–3 were successful in completing the grouting process. In the UCS test, groups 1–3 exhibited typical tensile failure, while groups 4–6 showed a more serious one-dimensional phenomenon, with sample failure resulting from weak yield at the bottom. When comparing groups 1, 3, and 5, which had the same concentration of urea and calcium chloride, it can be seen from Figure 14 that group 3 had the highest strength of 1.602 MPa, followed by group 1 with 1.401 MPa, and group 5 had the lowest strength of 1.032 MPa due to incomplete grouting. According to the calcium carbonate content determination results in Figure 15, it can be observed that group 3 has the highest calcium carbonate content, with an even distribution from top to bottom, namely 13.0, 11.72, 12.06, and 10.42%. On the other hand, group 1 shows the most uniform distribution of calcium carbonate, with values of 10.7, 10.43, 10.42, and 10.93%, respectively, although the total amount is slightly lower. Meanwhile, group 5 has a relatively high total content, but the calcium carbonate content in the upper and lower parts exceeds 10%, which results in an apparent one-dimensional grouting problem. The results indicate that a lower concentration of cementing fluid leads to a slower consolidation rate of the upper sample. This is beneficial for the complete consolidation of deep soil samples. As the concentration of the cementitious solution increases, the distribution of calcium carbonate in the sample gradually appears as high in the upper part and low in the lower part until severe one-dimensional transformation occurs [34]. The grouting scheme of the first group has the potential for further strength improvement with a continuous increase in grouting times, making it suitable for sites requiring deep slope reinforcement. However, this also means higher reinforcement costs. The third group of grouting schemes is recommended for consolidating surface soil up to a depth of 20 cm. Only groups 1 and 2 showed better reinforcement effects when the urea concentration was twice that of the bacterial solution. It can be seen that when the concentration is low, better strengthening effects can be achieved by increasing the concentration of cemented urea. However, there will be a problem of one-dimensional solidification with high concentration, such as in groups 4 and 6.

3.6. Effect of pH Value of Cementing Solution on Strengthening

The grouting effects vary depending on the concentration of cementing fluid and the pH value. Group 1, with a pH value of 6, was blocked during the third round of grouting, while group 2 failed during the fourth round. Groups 3 and 4 were successful in completing five rounds of grouting. The strengthening soil samples of groups 1 and 2 yielded at the bottom first. The third and fourth groups exhibited typical tensile failure as cracks appeared from top to bottom. As shown in Figure 16 and Figure 17, group 3 has the highest strength and average calcium carbonate content, followed by group 4. The strength of group 3 is 1.549 MPa, which is 0.18% higher than that of group 4 (1.522 MPa), while the average calcium carbonate content of group 3 is 54.39%, which is 0.08% higher than that of group 4 (54.04%). It can be concluded that the calcium carbonate content significantly affects the strength growth. The lowest UCS is group 1, which is only 1.009 MPa. The rapid blockage of the grouting mouth in this group indicates fast mineralization sedimentation. Nevertheless, previous studies suggest that the influence of pH values of 6–8.5 on urease activity can be almost ignored [35]. Therefore, if the concentrations of bacterial solution and cementation solution are equal, calcium ions are easily adsorbed onto bacterial surfaces in acidic and neutral environments. This will promote the deposition of calcium carbonate rapidly. However, in an alkaline environment with a pH of 8–9, the calcium source exists in the form of an emulsion, which slows down the rate of mineralization deposition. Additionally, when the pH is greater than 8.5, the activity of urease is inhibited to some extent. As a result, for group 3 with a pH of 8, grouting has the most favorable effect.

3.7. Soil Strengthening Mechanism

3.7.1. XRD

Calcium carbonate occurs in various crystal forms, including calcite, aragonite, and vaterite [36]. Among these, calcite is the most stable of the three crystal forms, and the crystal shapes are mainly plate and cube. The samples before and after the curing of MICP were analyzed by XRD. It can be seen from Figure 18 that the soil samples before solidification are mainly composed of kaolinite and silica. After solidification, it was found that only the internal soil samples consolidated with the soaking method did not exhibit a characteristic peak for calcium carbonate. This is because these samples were not effectively consolidated. On the other hand, the remaining groups of samples showed calcite characteristic diffraction peaks in the range of 29.4–29.6°. The samples that were strengthened with multiple injections of bacteria into a peristaltic pump and air compressor show a significantly higher characteristic diffraction peak for calcite compared to those that were strengthened with a single injection of bacteria. This indicates a notable significant difference in the amount of calcium carbonate precipitation produced by the two consolidation methods.

3.7.2. SEM

The microstructure of strengthened soil further reflects that the solidification effect is closely related to the compactness and uniformity of calcium carbonate cemented soil particles. The surface sampling of the test group JPY (Figure 19a,b) shows that the calcium carbonate is dense and uniform, completely covering the soil. Therefore, the disintegration rate of the immersion sample is the lowest due to the dense consolidation layer on the surface. It can be seen from the JR samples of the test group (Figure 19c,d) that after multiple grouting, the calcium carbonate crystals were evenly distributed and formed solid cubes. This is similar to relevant research results [37]. This is the reason why the effect of the peristaltic pump is the best. It can be seen from the JK sampling (Figure 19e,f) that the soil particles are also tightly wrapped by calcium carbonate. However, the consolidation is uneven, there are many plate-like crystals, and there are many voids between the soil samples. This may lead to a poor grouting effect of the air compressor.

4. Conclusions

In this study, MICP technology was utilized to investigate the effect of different reinforcement methods and conditions on the strengthening effect of granite residual soil. The following conclusions can be drawn:
(1) After culturing the bacteria in a double culture medium, the concentration of the bacteria solution reaches OD600 = 3.0, and the urease activity is measured to be 31.64 mM/min. The concentration of the bacterial solution and urease activity directly impact the output of calcium carbonate, as well as the stability of crystal shape and appearance. These factors are crucial to strengthening poorly graded soil such as granite residual soil.
(2) MICP technology can effectively improve the anti-disintegration performance of granite residual soil. The sample disintegration rate of the soaking method is the lowest, reflecting a close correlation between the disintegration rate and the calcium carbonate content generated on the soil surface. Therefore, the granite residual soil slope may achieve shallow consolidation by strengthening through spraying, preventing the surface from peeling and collapsing year by year.
(3) The peristaltic pump grouting method strengthens the more effectively than the air compressor and immersion method. Compared with the uncured soil, the UCS increased by 513.65%, while the cohesion and internal friction angle increased by 297.98% and 101.75%, respectively.
(4) A high concentration of cement can lead to one-dimensional consolidation, which is not ideal for deep consolidation of soil samples. To a certain extent, reducing the concentration of cement and increasing the number of grouting rounds can enhance the UCS of the soil sample. After seven grouting rounds, the consolidated soil sample with a cement concentration of 0.5 mol/L showed the highest UCS of 1.602 MPa.
(5) The pH value of the cementing fluid plays a crucial role in the acceleration of calcium carbonate formation, and the optimal pH range for this process is 6–8. As the pH value increases, the UCS of the soil samples also increases. However, when the pH value is 8–9, the increase in UCS tends to be gentle.
(6) According to the results of XRD, the diffraction peaks of kaolin and silica in the consolidated soil samples decreased significantly. In contrast, the characteristic diffraction peaks of the calcite crystal type appeared in the range of 29.4–29.6°. The soil sample consolidated with multiple grouting with the peristaltic pump showed the highest peak value of calcite diffraction. Combined with the soil consolidation state observed under SEM, it can be concluded that the peristaltic pump grouting solidification mode produced a large amount of evenly distributed calcium carbonate content, resulting in an optimal consolidation effect.
(7) In order to achieve the application of MICP in engineering, the grouting test of undisturbed soil samples should be carried out in the next stage. Meanwhile, long-term performance of soil samples, including freezing and thawing, acid rain resistance, long-term creep, and settlement deformation also need systematic study. Importantly, if local bacteria can be extracted and applied in MICP, this may strengthen the environmental adaptability of bacteria and improve the long-term performance of the soil.

Author Contributions

Conceptualization, R.W. and C.H.; Methodology, F.L. (Fang Liu); Investigation, F.L. (Feiyu Liu); Resources, M.W. and C.H.; Data curation, Z.C.; Writing—review & editing, R.W. and H.L.; Project administration, Q.W. All authors have read and agreed to the published version of the manuscript.

Funding

Natural Science Foundation of Fujian Province of China: 2020J01403; Natural Science Foundation of Fujian Province of China: 2023J011044; Resource Chemical Industry and Technology Foundation of Nanping of China: N2021Z002; Natural Science Foundation of Fujian Province of China: 2020Y0092; Teachers and Students Co-construction Team of Wuyi University: 2021-SSTD-04.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Date will be available on request.

Conflicts of Interest

The authors declare that there is no conflict of interest.

References

  1. Basahel, H.; Mitri, H. Application of rock mass classification systems to rock slope stability assessment: A case study. J. Rock Mech. Geotech. Eng. 2017, 9, 993–1009. [Google Scholar] [CrossRef]
  2. Yokota, S.; Iwamatsu, A. Weathering distribution in a steep slope of soft pyroclastic rocks as an indicator of slope instability. Eng. Geol. 2000, 55, 57–68. [Google Scholar] [CrossRef]
  3. Liu, X.Y.; Zhang, X.W.; Kong, L.W.; Wang, G.; Liu, H.H. Formation mechanism of collapsing gully in southern China and the relationship with granite residual soil: A geotechnical perspective. Catena 2022, 210, 105890. [Google Scholar] [CrossRef]
  4. Liu, W.P.; Song, X.Q.; Luo, J.; Hu, L.N. The processes and mechanisms of collapsing erosion for granite residual soil in southern China. J. Soils Sediments 2020, 20, 992–1002. [Google Scholar] [CrossRef]
  5. Li, C.S.; Kong, L.W.; Shu, R.J.; An, R.; Zhang, X.W. Disintegration characteristics in granite residual soil and their relationship with the collapsing gully in South China. Open Geosci. 2020, 12, 1116–1126. [Google Scholar] [CrossRef]
  6. Yuan, B.; Chen, W.; Zhao, J.; Li, L.; Liu, F.; Guo, Y.; Zhang, B. Addition of alkaline solutions and fibers for the reinforcement of kaolinite-containing granite residual soil. Appl. Clay Sci. 2022, 228, 106644. [Google Scholar] [CrossRef]
  7. Liu, X.Y.; Zhang, X.W.; Kong, L.W.; Wang, G.; Lu, J.F. Disintegration of granite residual soils with varying degrees of weathering. Eng. Geol. 2022, 305, 106723. [Google Scholar] [CrossRef]
  8. Yuan, B.X.; Chen, W.J.; Zhao, J.; Yang, F.; Luo, Q.Z.; Chen, T.Y. The Effect of organic and inorganic modifiers on the physical properties of granite residual soil. Adv. Mater. Sci. Eng. 2022, 2022, 9542258. [Google Scholar] [CrossRef]
  9. Chehlafi, A.; Kchikach, A.; Derradji, A.; Mequedade, N. Highway cutting slopes with high rainfall erosion in Morocco: Evaluation of soil losses and erosion control using concrete arches. Eng. Geol. 2019, 260, 105200. [Google Scholar] [CrossRef]
  10. Lian, J.F.; Wu, J.J.; Luo, Q. Theoretical analysis and optimization of frame protection to control shallow slope stability and soil erosion. Transp. Geotech. 2022, 33, 100724. [Google Scholar] [CrossRef]
  11. Fan, J.W.; Yang, S.J.; Deng, B.; Sun, B.; Liu, T.Y. A New Technique of Lattice Beam Construction with Pre-Anchoring for Strengthening Cut Slope: A Numerical Analysis of Temporary Stability during Excavation. Buildings 2022, 12, 1930. [Google Scholar] [CrossRef]
  12. Chen, J.; Lei, X.W.; Zhang, H.L.; Lin, Z.; Wang, H.; Hu, W. Laboratory model test study of the hydrological effect on granite residual soil slopes considering different vegetation types. Sci. Rep. 2021, 11, 14668. [Google Scholar] [CrossRef]
  13. DeJong, J.T.; Mortensen, B.M.; Martinez, B.C.; Nelson, D.C. Bio-mediated soil improvement. Ecol. Eng. 2010, 36, 197–210. [Google Scholar] [CrossRef]
  14. Yu, T.; Souli, H.; Pechaud, Y.; Fleureau, J.M. Review on engineering properties of MICP-treated soils. Geomech. Eng. 2021, 27, 13–30. [Google Scholar]
  15. Harkes, M.P.; van Paassen, L.A.; Booster, J.L.; Whiffin, V.S.; van Loosdrecht, M.C.M. Fixation and distribution of bacterial activity in sand to induce carbonate precipitation for ground reinforcement. Ecol. Eng. 2010, 36, 112–117. [Google Scholar] [CrossRef]
  16. VWhiffin, S.; van Paassen, L.A.; Harkes, M.P. Microbial carbonate precipitation as a soil improvement technique. Geomicrobiol. J. 2007, 24, 417–423. [Google Scholar] [CrossRef]
  17. Wang, Y.Z.; Konstantinou, C.; Soga, K.; Biscontin, G.; Kabla, A.J. Use of microfluidic experiments to optimize MICP treatment protocols for effective strength enhancement of MICP-treated sandy soils. Acta Geotech. 2022, 17, 3817–3838. [Google Scholar] [CrossRef]
  18. Chek, A.; Crowley, R.; Ellis, T.N.; Durnin, M.; Wingender, B. Evaluation of Factors Affecting Erodibility Improvement for MICP-Treated Beach Sand. J. Geotech. Geoenviron. Eng. 2021, 147, 4021001. [Google Scholar] [CrossRef]
  19. Tang, C.S.; Yin, L.Y.; Jiang, N.J.; Zhu, C.; Zeng, H.; Li, H.; Shi, B. Factors affecting the performance of microbial-induced carbonate precipitation (MICP) treated soil: A review. Environ. Earth Sci. 2020, 79, 94. [Google Scholar] [CrossRef]
  20. Murugan, R.; Suraishkumar, G.K.; Mukherjee, A.; Dhami, N.K. Insights into the influence of cell concentration in design and development of microbially induced calcium carbonate precipitation (MICP) process. PLoS ONE 2021, 16, e0254536. [Google Scholar] [CrossRef] [PubMed]
  21. Hang, L.; Yang, F.; Xu, J.; Zhao, Z.H.; Xiao, W.; He, J. Experimental Study on the Effective Production of Biocement for Soil Solidification and Wind Erosion Control. Sustainability 2023, 15, 5402. [Google Scholar] [CrossRef]
  22. Karimian, A.; Hassanlourad, M. Mechanical behaviour of MICP-treated silty sand. Bull. Eng. Geol. Environ. 2022, 81, 285. [Google Scholar] [CrossRef]
  23. Yu, X.P.; Xiao, H.B.; Li, Z.Y.; Qian, J.F.; Luo, S.P.; Su, H.Y. Experimental study on microstructure of unsaturated expansive soil improved by MICP method. Appl. Sci. 2022, 12, 342. [Google Scholar] [CrossRef]
  24. Li, J.; Tian, L.; Xu, Y.; Tian, Z.; Zhang, Z. Study on the solidification effect of dredger fill by microbial-induced calcium precipitation (MICP). Materials 2022, 15, 7891. [Google Scholar] [CrossRef] [PubMed]
  25. Wang, Y.-N.; Li, S.-K.; Li, Z.-Y.; Garg, A. Exploring the application of the MICP technique for the suppression of erosion in granite residual soil in Shantou using a rainfall erosion simulator. Acta Geotech. 2023, 18, 3273–3285. [Google Scholar] [CrossRef]
  26. Liang, S.H.; Xiao, X.L.; Fang, C.X.; Feng, D.L.; Wang, Y.X. Experimental study on the mechanical properties and disintegration resistance of microbially solidified granite residual soil. Crystals 2022, 12, 132. [Google Scholar] [CrossRef]
  27. Zhu, W.X.; Deng, H.F.; Li, J.L.; Xiong, Y.X.Y.; Cheng, L. Effect of calcium lignosulfonate on mechanical properties of fully weathered granite solidified by microorganism. China Civ. Eng. J. 2023. [Google Scholar] [CrossRef]
  28. GB/T 50123-2019; Engineering Classification of Soils. National Quality Supervision Bureau: Beijing, China, 2019. (In Chinese)
  29. Cui, Z.J.; Yang, J.G.; Chen, Y.X. The type and evolution of the granite landforms in China. Acta Geogr. Sin. 2007, 62, 675–690. [Google Scholar]
  30. Sun, Y.; Liu, Q.; Xu, H.; Wang, Y.; Tang, L. Influences of different modifiers on the disintegration of improved granite residual soil under wet and dry cycles. Int. J. Min. Sci. Technol. 2022, 32, 831–845. [Google Scholar] [CrossRef]
  31. Su, F.; Yang, Y.; Qi, Y.; Zhang, H. Combining microbially induced calcite precipitation (MICP) with zeolite: A new technique to reduce ammonia emission and enhance soil treatment ability of MICP technology. J. Environ. Chem. Eng. 2022, 10, 107770. [Google Scholar] [CrossRef]
  32. Wang, Y.; Wang, G.; Wan, Y.; Yu, X.; Zhao, J.; Shao, J. Recycling of dredged river silt reinforced by an eco-friendly technology as microbial induced calcium carbonate precipitation (MICP). Soils Found. 2022, 62, 101216. [Google Scholar] [CrossRef]
  33. Fu, T.; Saracho, A.C.; Haigh, S.K. Microbially induced carbonate precipitation (MICP) for soil strengthening: A comprehensive review. Biogeotechnics 2023, 1, 100002. [Google Scholar] [CrossRef]
  34. Mohapatra, S.S.; Pradhan, S.P.; Pradhan, P.K.; Pattnaik, P.; Jena, B.; Malla, S.K. Experimental study on mechanical properties of coarse graded soil incorporation with MICP process. Mater. Today Proc. 2022, 65, 3887–3892. [Google Scholar] [CrossRef]
  35. Chen, L.; Song, Y.; Fang, H.; Feng, Q.; Lai, C.; Song, X. Systematic optimization of a novel, cost-effective fermentation medium of Sporosarcina pasteurii for microbially induced calcite precipitation (MICP). Constr. Build. Mater. 2022, 348, 128632. [Google Scholar] [CrossRef]
  36. Fouladi, A.S.; Arulrajah, A.; Chu, J.; Horpibulsuk, S. Application of Microbially Induced Calcite Precipitation (MICP) technology in construction materials: A comprehensive review of waste stream contributions. Constr. Build. Mater. 2023, 388, 131546. [Google Scholar] [CrossRef]
  37. Al Qabany, A.; Soga, K.; Santamarina, C. Factors Affecting Efficiency of Microbially Induced Calcite Precipitation. J. Geotech. Geoenviron. Eng. 2012, 138, 992–1001. [Google Scholar] [CrossRef]
Applsci 13 08863 g001 550
Figure 1. Grain gradation curve.
Figure 1. Grain gradation curve.
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Figure 2. Morphology of Sporosarcina pasteurii.
Figure 2. Morphology of Sporosarcina pasteurii.
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Figure 3. Mold schematic: (a) grouting; (b) soaking.
Figure 3. Mold schematic: (a) grouting; (b) soaking.
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Figure 4. Schematic diagram of curing device: (a) peristaltic pump; (b) soak; (c) air compressor.
Figure 4. Schematic diagram of curing device: (a) peristaltic pump; (b) soak; (c) air compressor.
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Figure 5. Sampling location for determination of calcium carbonate content: (a) Grouting; (b) Soaking.
Figure 5. Sampling location for determination of calcium carbonate content: (a) Grouting; (b) Soaking.
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Figure 6. Disintegration test: (a) Side view; (b) Top view; (c) First test (bottom); (d) Second test (bottom); (e) Third test (upper); (f) Fourth test (bottom).
Figure 6. Disintegration test: (a) Side view; (b) Top view; (c) First test (bottom); (d) Second test (bottom); (e) Third test (upper); (f) Fourth test (bottom).
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Figure 7. Relationship between disintegration frequency and disintegration rate.
Figure 7. Relationship between disintegration frequency and disintegration rate.
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Figure 8. Soil samples solidified with different grouting methods: (a) JR; (b) JRY; (c) JK; (d) JKY; (e) JPY.
Figure 8. Soil samples solidified with different grouting methods: (a) JR; (b) JRY; (c) JK; (d) JKY; (e) JPY.
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Figure 9. Shear stress and displacement: (a) Uncured; (b) JR; (c) JRY; (d) JK; (e) JKY; (f) JPY.
Figure 9. Shear stress and displacement: (a) Uncured; (b) JR; (c) JRY; (d) JK; (e) JKY; (f) JPY.
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Figure 10. Relationship between shear strength and vertical stress.
Figure 10. Relationship between shear strength and vertical stress.
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Figure 11. UCS test failure mode of samples: (a) JR; (b) JK; (c) JRY; (d) JKY; (e) JPY.
Figure 11. UCS test failure mode of samples: (a) JR; (b) JK; (c) JRY; (d) JKY; (e) JPY.
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Figure 12. UCS test result.
Figure 12. UCS test result.
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Figure 13. Calcium carbonate content: (a) JRY, JKY and JP; (b) JR and JRY.
Figure 13. Calcium carbonate content: (a) JRY, JKY and JP; (b) JR and JRY.
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Figure 14. Effect of cementing fluid concentration on the UCS.
Figure 14. Effect of cementing fluid concentration on the UCS.
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Figure 15. Effect of cementing fluid concentration on the Calcium carbonate content.
Figure 15. Effect of cementing fluid concentration on the Calcium carbonate content.
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Figure 16. Effect of cement pH on UCS.
Figure 16. Effect of cement pH on UCS.
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Figure 17. Effect of cementing fluid concentration on calcium carbonate content.
Figure 17. Effect of cementing fluid concentration on calcium carbonate content.
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Figure 18. XRD pattern: (a) Uncured; (b) JR; (c) JK; (d) JRY; (e) JKY; (f) JPY.
Figure 18. XRD pattern: (a) Uncured; (b) JR; (c) JK; (d) JRY; (e) JKY; (f) JPY.
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Figure 19. Microstructure: (a,b) JPY; (c,d) JR; (e,f) JK.
Figure 19. Microstructure: (a,b) JPY; (c,d) JR; (e,f) JK.
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Table
Table 1. Particle size distribution of granite residual soil.
Table 1. Particle size distribution of granite residual soil.
Granularity DivisionCoarse Sand
(<2 mm)		Medium Sand
(<1 mm)		Fine Sand
(<0.5 mm)		Silt
(<0.075 mm)		Clay
(<0.005 mm)
Content (%)10080.7856.9224.56.86
Table
Table 2. Physical parameters of granite residual soil.
Table 2. Physical parameters of granite residual soil.
Wet Density (g/cm3)Dry Density (g/cm3)Rate of Water Content (%)Plastic Limit (%)Liquid Limit (%)Plasticity IndexSpecific Gravity (g/cm3)Optimum Water Content
(%)
1.4381.28911.624.0737.2113.142.6215.06
Table
Table 3. Grouting scheme for stage I.
Table 3. Grouting scheme for stage I.
GroupGrouting MethodNumber of GroutingCementitious Liquid Component Content
BacteriaCementation Solution
JRYPeristaltic pump115Urea: 30 g/L;
Calcium chloride: 55.5 g/L
JR515
JKYAir compressor115
JK515
JPYSoak115
Note: JRY and JR represent one and multiple grouting of peristaltic pump; JKY and JK represent one and multiple grouting of air compressor; JPY represents grouting of soaking.
Table
Table 4. Concentration and pH value optimization test of cementing solution.
Table 4. Concentration and pH value optimization test of cementing solution.
GroupCementitious Liquid Concentration
Urea
(mol/L)		Anhydrous Calcium Chloride
(mol/L)		Cementitious Liquid pH
JRN10.250.258.5
JRN20.50.25
JRN30.50.5
JRN41.0 0.5
JRN51.0 1.0
JRN62.0 1.0
JRP10.5 0.5 6
JRP27
JRP38
JRP49
Note: JRN represents the test group that changes the concentration of cementing fluid; JRP represents the test group that changes the pH value of the cementing fluid.
Table
Table 5. Shear strength.
Table 5. Shear strength.
MethodTest Group Shear Strength under Different Vertical Pressures (kPa)
100 kPa200 kPa300 kPa400 kPa
/Uncured95.11143.71190.11244.17
Peristaltic pump groutingJR302.74448.698583.848718.998
JRY180.2273.5325.17412.66
Air compressor groutingJK263.09382.02517.17634.3
JKY163.98220.46268.12364.18
Soaking methodJPY147.76218.04276.61326.16
Table
Table 6. Cohesion and internal friction angle.
Table 6. Cohesion and internal friction angle.
Curing MethodTest Group Cohesion (kPa)Internal Friction Angle (°)
/Uncured42.1126.84
Peristaltic pump groutingJR167.5954.15
JRY108.137.38
Air compressor groutingJK136.9551.32
JKY101.633.38
Soaking methodJPY93.730.71
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Wang, R.; Li, H.; Chen, Z.; Liu, F.; Wei, M.; Liu, F.; Wang, Q.; Hu, C. Strength and Mechanism of Granite Residual Soil Strengthened by Microbial-Induced Calcite Precipitation Technology. Appl. Sci. 2023, 13, 8863. https://doi.org/10.3390/app13158863

AMA Style

Wang R, Li H, Chen Z, Liu F, Wei M, Liu F, Wang Q, Hu C. Strength and Mechanism of Granite Residual Soil Strengthened by Microbial-Induced Calcite Precipitation Technology. Applied Sciences. 2023; 13(15):8863. https://doi.org/10.3390/app13158863

Chicago/Turabian Style

Wang, Rong, Huawei Li, Zichuang Chen, Fang Liu, Muwang Wei, Feiyu Liu, Qian Wang, and Changbin Hu. 2023. "Strength and Mechanism of Granite Residual Soil Strengthened by Microbial-Induced Calcite Precipitation Technology" Applied Sciences 13, no. 15: 8863. https://doi.org/10.3390/app13158863

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