Geological Journal of China Universities

Bio-geoengineering Technology and the Applications

TANG Chaosheng, PAN Xiaohua, LYU Chao, DONG Zhihao, LIU Bo, WANG Dianlong, LI Hao, CHENG Yaojia, SHI Bin

2021, 27(6): 625-654. DOI: 10.16108/j.issn1006-7493.2021011

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Bio-geoengineering technology is defined as a technology that using various types of microbial biochemical process to improve the hydro-mechanical behavior of soil and rock, aiming for the prevention and mitigation of engineering geology problems. Previous studies indicate that bio-geoengineering technology is a hot research topic in recent years and has the advantages of low cost, environmental friendliness, low energy consumption and process controllable. It has been recognized as an important development direction of modern engineering geology. Based on research progress on this topic, this paper systematically summarizes the principles and application fields of three representative bio-geoengineering technologies that can be well controlled and efficiently used, including bio-mineralization, bio-film growth and bio-gas production. It focuses on the engineering properties (i.e. mechanical behavior, permeability, and erosion resistance) and the corresponding involved mechanisms of the rock and soil improved by bio-mineralization that have been studied the most and with the broadest application prospects. Moreover, the key factors (i.e. bacteria species, bacterial solution concentration, environmental temperature, pH value, cementation solution composition, soil nature and grouting technology) that affect the improvement effect of bio-mineralization are discussed in depth. In addition, the application status of bio-mineralization in foundation treatment, island and reef construction, wind and sand fixation, soil and water conservation, crack resistance and seepage prevention, cultural relics protection, geological disaster prevention and other fields are introduced in detail. The main challenges of the application of bio-mineralization are listed, and the future research directions on this topic are proposed.

Study on the Effect of MICP on the Crushing Behavior of Calcareous Sand Particles

SHEN Jiawei, ZHOU Bo, ZHANG Xing, LI Yao, WANG Huabin

2021, 27(6): 655-661. DOI: 10.16108/j.issn1006-7493.2020056

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As a special geotechnical material, calcareous sand is easy to break under low pressure. In recent years, microbially induced calcite precipitation (MICP) technology has gained wide attention and recognition, which can be used to improve the crushing characteristics of calcareous sand. In this paper, the single particle crushing test of calcareous sand particles before and after MICP was carried out through two aspects of laboratory test and discrete element model simulation, respectively. The effects of MICP on the crushing behavior of calcareous sand particles was investigated through Weibull distribution and SEM scanning. The results show that the survival probability curve and the value of Weibull modulus m obtained by discrete element model simulation are in good agreement with the experimental results, which verifies the validity of the numerical model. Compared with the laboratory test, numerical simulation can accurately reflect the crack distribution and crushing process of the particle as well as studying the situation before and after MICP for the same particle, which makes up the deficiency of the laboratory test. However, it depends on the selection of model parameters. After MICP, calcareous sand particles have obvious calcite crystal formation on its surface, and the surface and internal pores of the particles are wrapped and filled to a certain extent, respectively, resulting in significantly enhanced particle crushing strength and greatly reduced discreteness, and the crushing mode changes from “multi-peaks type” to “single-peak type”, as well as local crack reduction mainly surface abrasion and direct generation of through-wall crack.

Direct Shear and Compressibility Behavior of Bio-stimulated MICP Treated Calcareous Sand

WANG Yijie, JIANG Ningjun

2021, 27(6): 662-669. DOI: 10.16108/j.issn1006-7493.2020094

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Calcareous sands are widely distributed in coastal areas around the world. They are considered as a material with low shear strength and high compressibility. Stabilizing calcareous sand has become a hot research topic in coastal geotechnics recently. Microbial induced calcite precipitation (MICP) is a new soil improvement technique. Currently, MICP is primarily implemented through the bio-augmentation approach, which is expensive and has a bad compatibility with the natural soil environment. This study focuses on the bio-stimulated MICP approach by enriching indigenous ureolytic bacteria to stabilize calcareous sand. Direct shear and one-dimensional compression tests are conducted on the bio-cemented samples. The results show that the bio-stimulated MICP approach could create up to 6.26% cementation level within the sand matrix. Increasing the concentration of cementation solution or treating multiple times could yield higher cementation level. during the direct shear test, the peak stress ratio, peak dilation angle, and near critical state friction angle increase significantly with elevated cementation level. However, these mechanical parameters could be suppressed at higher normal stress levels. Meanwhile, the compressibility of bio-cemented sand is significantly reduced with the increase in the cementation level. Upon the completion of the compression test, the proportions of both very fine and vary coarse particles increase with elevated cementation level.

Tensile Strength of Fiber-reinforced Micp-treated Calcareous Sand

WANG Dianlong, TANG Chaosheng, PAN Xiaohua, LIU Bo, LI Hao, LYU Chao, CHENG Yaojia

2021, 27(6): 670-678. DOI: 10.16108/j.issn1006-7493.2020211

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The microbially induced carbonate precipitation (MICP) treated calcareous sand tends to be brittle and has low tensile strength. To solve this problem, a special “8” shaped mold was designed and a series of direct tensile tests were conducted to investigate the improvement of fiber reinforcement, the mechanism of fiber-reinforced MICP-treated, and influencing factors such as fiber content and fiber length. The results showed that fiber can improve tensile strength, peak displacement, and residual strength and reduce brittle failure. Overall, the tensile strength of fiber-reinforced MICP-treated calcareous sand samples was influenced by the fiber content and fiber length, the tensile strength tended to increase and then decrease with increasing fiber content and fiber length. Compared to the unreinforced sample, the tensile strength of the sample with 0.60% fiber content (the optimum fiber content) increased by172.40%，the peak displacement increased by 158.1%. The mechanism of fiber reinforcement can be explained by the fact that the fiber increased the amount of adsorption of Sporosarcina pasteurii, promoted the precipitation of calcium carbonate between the fibers and calcareous sand and the surface on the fibers, increased the interfacial forces between the fiber and the calcareous sand, improved the tensile strength of MICP-treated calcareous sand. Fiber can significantly alter the failure characteristics of samples, the tensile stress-displacement curve of the unreinforced sample had only two phases, and an initial phase, and an elastics phase, the curves of fiber-reinforced samples could be characterized by four phases including an initial phase, an elastic phase, a damage phase, and a residual phase. The effect of fiber content was mainly related to the interfacial forces between the fibers and calcareous sand, and the spatial disturbution of fibers. The effect of fiber length was mainly related to the number of fibers near the failure surface and the tensile stress per unit length of fiber could bear. Furthermore, the results of this study have certain guiding significance for the stability and safety of oceanic projects.

Experimental Study on Mechanical Behavior of Micp-fiber Reinforce Treated Calcareous Sand

YIN Liyang, TANG Chaosheng, ZHANG Long

2021, 27(6): 679-686. DOI: 10.16108/j.issn1006-7493.2021075

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Calcareous sand have the characteristics of high compressibility, high void ratio and tend to be fragile, which lead to poor mechanical properties and often have adverse effects in the construction of reefs island. In order to improve the mechanical properties of calcareous sand, a new method of strengthening calcareous sand based on microbial induced calcium carbonate precipitation (MICP) combined with Fiber Reinforced （FR）technology is proposed in this paper. The mechanical response and failure mechanism in microcosmic of MICP treated Calcareous sand with different fiber content were analyzed by unconfined compression test and SEM. The main research conclusion is as follows: (1) MICP can effectively solidify the calcareous sand and improve its strength (2) PP Fiber can expand the colonization area of urealysis bacteria, and accelerate the deposition of calcium carbonate, thus enhancing the ductility and toughness of the MICP treated sample. (3) It shows a multi peak characteristic in unconfined compress stress-strain curve that in stress-rising stage, the sand particles and calcium carbonate will be broken locally, but does not affect on the peak strength of the sample; In the stress-decreasing stage, the cementation effect coupling with calcium carbonate, sand particles and fibers could enhances the resistance of the fibers and limits the development of the failure surface. （4）The cementation effect coupling with calcium carbonate, sand particles and fibers contribute majorly to the improvement of the toughness and ductility of the samples.

Research Progress of Bio-cementation for Sand Stabilization and Wind Erosion Control

HE Jia, WU Min, MENG Hao, QI Yongshuai, GAO Yufeng

2021, 27(6): 687-696. DOI: 10.16108/j.issn1006-7493.2020072

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This paper reviews recent research studies on biological soil cementation methods, or bio-cementation, for sand stabilization and wind erosion control. The biological processes adopted for bio-cementation involve microbially- or enzymeinduce carbonate precipitation (MICP or EICP), and the auxiliary use of biopolymers such as xanthan gum can achieve better soil stabilization effects. In the process of soil wind erosion, in addition to the wind itself, the bombardment of the saltating particles carried by the wind is also a key factor of erosion damage. This has been evidenced in the wind erosion tests of bio-cemented soils. The treatment process of soil bio-cementation for wind erosion control is simple and easy. Using urea and calcium salt as treatment materials, and bacteria or urease as catalytic agents, a single-pass spraying treatment on the soil can obtain a good wind resistance effect. In the laboratory wind resistance tests, the combination of wind erosion rate and threshold detachment velocity is a more reasonable evaluation method for wind erosion. In laboratory and field conditions, the surface penetration test can be a simple and quick method to determine the treatment effect and wind erosion resistance. Current field studies indicate that plants can grow in soil with bio-cemented crust, but their growth is restricted under some adverse conditions. Further studies may concentrate on erosion resistance capability under multiple erosion factors, ecological restoration ability in bio-cemented soil, and construction technologies related to the use of bio-cementation, etc.

Review on Application of Microbially Induced Carbonate Precipitation (MICP) for Soil Stabilization

ZHOU Yingzheng, GUAN Dawei, CHENG Liang

2021, 27(6): 697-706. DOI: 10.16108/j.issn1006-7493.2020116

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Microbial mineralization is a recently developing new branch in engineering of soil improvement that deals with the application of microbiological activity to improve characteristics of soils. One of the most commonly adopted processes to achieve soil bio-cementation is through microbially induced carbonate precipitation (MICP). This technique utilizes the metabolic behavior of urease bacteria to induce calcite that binds the loose soil particles integrally, leading to increased mechanical properties of soils. This paper systematically introduces the study of MICP about mineralization mechanism of urease bacteria, relative treatment methods, influencing factors, derived new technique (EICP) and relative field trials in geotechnical engineering. The practicability of the MICP is summarized. Finally, the challenges and potential solutions of MICP engineering applications in the current research stage are briefly discussed.

Properties of Runoff and Erosion on Silt Slope Surface Reinforced by Microbial Induced Mineralization

SHAO Guanghui, YANG Zhi, TANG Biao, LIU Peng, HUANG Rongpin, ZHAO Zhifeng

2021, 27(6): 707-715. DOI: 10.16108/j.issn1006-7493.2020111

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Microbial induced carbonate precipitation (MICP) is a microbial mineralization process which can be adopted to cement loose soil. It has a potential development prospect to improve the anti-rainfall erosion ability of soil slope. Through the simulated rainfall erosion test, the hydrodynamic and erosion characteristics of the silt slope surface before and after the microbialinduced mineralization reinforcement were investigated. The correlation between the hydrodynamic parameters and the influence on the soil erosion rate were analyzed and discussed. The results showed that the Froude number of silt slope runoff decreased by 50% on average after reinforcement compared with before reinforcement. Moreover, the resistance coefficient decreased by 66% on average in the early stage of rainfall, and was close to that after runoff was stabilized. The runoff shear stress was increased by 52% on average. There was a linear negative correlation between runoff coefficient and slope surface infiltration velocity (R²=0.857), and an exponential negative correlation between runoff coefficient and penetration strength of the crust on slope (R²=0.824). There was a quadratic negative correlation between infiltration rate and penetration strength of the crust on slope (R²=0.930). The runoff shear stress was positively correlated with the slope gradient (R²=0.964). The detachment rate of the reinforced silt

slope was negatively correlated with penetration strength of the reinforced crust on slope (R²=0.822), linearly correlated with
runoff shear stress (R²=0.912). The critical runoff shear stress of reinforced silt slope was 0.5Pa. For silt slopes with a gradient of
10-25°, the detachment rate could be reduced from 58.2-118.4 g/(m2s) to 2.4-21.2 g/(m2s) by microbial reinforcement, and the
maximum detachment rate could be reduced by 95.0%. The hydrodynamic parameters of silt slope were significantly changed due
to the microbial-induced mineralization reinforcement. Furthermore, the runoff characteristics were related to the hydrodynamic
parameters, the reinforced crust properties and slope gradient. The microbial-induced mineralization reinforcement effectively
improved the anti-erosion performance of the silt slope.

Study on the Crystallization Phenomenon of Calcium Carbonate for Soil Treatment with a Urease-producing Bacteria Species Isolated from a Hot and Humid Region of South China

HUANG Ming, ZHANG Jinxuan, LIU Zijian, XU Kai

2021, 27(6): 716-722. DOI: 10.16108/j.issn1006-7493.2020073

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A new urease-producing bacteria was isolated from the natural environment in the southern humid and hot area of China, and its high-yielding mutant strain was applied to the sea sand indoor MICP grouting test. To study the crystallization phenomenon of calcium carbonate, the Scanning Electron Microscope (SEM), Energy Dispersive Spectrometer (EDS), and Raman were used to observe the microstructure of the treated samples. By analyzing the basic characteristics of calcium carbonate, such as the morphology, size, spatial distribution, and crystalline state, the regulatory effect on the growth of calcium carbonate crystals and the effect of solidifying soil of the urease-producing bacterial were initially explored. The results show that it is feasible to solidify the soil with urease-producing bacteria in the southern hot and humid area, but the morphology of calcium carbonate crystals is not uniform. The crystal crystallization process, biological regulation and soil structure will all affect the formation of calcium carbonate. In addition, the crytallization of calcium carbonate is from disorder to order, dispersion to aggregation, unstable to stable, and the calcium carbonate eventually develops into a complete and large aggregates in an environment with sufficient growth space. Conclusions in this paper can be used as reference for further study on the action process and regulation mechanism of calcium carbonate precipitation induced by different urease-producing bacteria.

Experimental Investigation of Microbial Induced Calcite Precipitation (MICP) Improvement on Freeze-Thaw Resistance of Sandstone with Various Types of Porosity

PAN Xiaohua, TANG Chaosheng, SHI Bin

2021, 27(6): 723-730. DOI: 10.16108/j.issn1006-7493.2020110

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Sandstone is the most common rock type for geological relic and historic stone. Lithologic deterioration induced by freeze-thaw is the dominant reason that cause sandstone geological disaster. Permeability reduction and physico-mechanical property improvement is an effective way to solve this problem. In this study, the feasibility using Microbial Induced Calcite Precipitation (MICP) to improve the freeze-thaw resistance of sandstone with various types of porosity was studied as well as its mechanism was analyzed. MICP treatment and freeze-thaw test were carried out based on two types of sandstone with mediumgrain size and fine-grain size. Experimental results indicate that (1) MICP treatment could improve the freeze-thaw resistance of the two types of sandstone, which is contribute to the production of the CaCO3 crystals during the MICP process. These CaCO₃crystals occupy the porosity and reduce the volume of pore water and damaging force as well as enhance the bonding of the stone particles. However, MICP improvement performance is affected the effect of porosity. (2) After 40 cycles of freeze-thaw test, apparent damages at angular position were only observed from the samples without MICP treatment compared to the samples with MICP treatment. (3) The reduction rate of porosity of sandstone with medium-grain size and fine-grain size were reduced to 4.4% and 6.3% from 17.0% and 14.8% due to the MICP improvement when subjected to 40 cycles of freeze-thaw test. The same phenomenon can also be observed from the mass loss rate, water absorption, the reduction rate of wave velocity, corresponding values are 0.04% and 0.02% from 0.22% and 0.14%, 0.75% and 1.5% from 6.8% and 4.4%, 7.3% and 3.8% from 18.5% and 12.4%. (4) The efficiency of MICP process, effective treatment depth, distance of pore near surface of sandstone with mediumgrain size were higher because that its pores are larger, inducing higher values of the reduction rate of porosity and water absorption, growth rate of mass and wave velocity.

Mitigating Erosion of Collapsing Gully by Microbial Technology under Rainfall Conditions

LU Huaming, ZHANG Zhichao, XIAO Yang, MA Guoliang, YE Longzhen

2021, 27(6): 731-737. DOI: 10.16108/j.issn1006-7493.2020095

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Collapsing gully is the most serious soil erosion phenomenon in granite region in China. Slope surface protection is an important measure to control the erosion of collapsing gully soil. Collapsing gully soil in Guanqiao town in Anxi county, one of the most developed areas in Fujian Province, was investigated in this study and a model experiment was carried out to investigate the feasibility of the application of microbially induced carbonate precipitation (MICP) technology on the slope surface erosion protection. The MICP spraying technology was used to treat the surface of the collapsing gully soil slope. Then, the slope was flushed by an artificial rainfall simulation system. The impacts of the MICP technology on the amount of substance in the effluent and erosion depth on the slope surface were analyzed. The results show that the amount of matter in the effluent of treated slope decreased from 7648.43 g to 266.61 g, which was 96.51% lower than that before treatment; the erosion depth decreased from 60 mm to no obvious erosion except for individual erosion hole compared with untreated slopes. The current work shows that the MICP technology can effectively reduce the erosion of residual soil slope in collapsing gully region.

Experimental Investigation in MICP Solidified Sands of Different Particle Sizes

XU Pengxu, WEN Zhili, YANG Simeng, LIU Zhiming, LENG Meng, PENG Jie

2021, 27(6): 738-745. DOI: 10.16108/j.issn1006-7493.2020075

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Three kinds of sand samples with different particle sizes are selected to carry out microbially induced calcium carbonate (MICP) grouting tests. The effects of particle sizes on sand strength are studied by grouting for 8，10, and 12 times，respectively，in combination with the data such as bacterial adsorption rate, effluent Ca2+ concentration, permeability coefficient, calcium carbonate content, pore structures, and final reinforcement effects. The results show that there is a certain relationship between bacterial adsorption rate and particle size，that is, the larger the particle size, the less bacterial adsorbance. In the meantime, particle size will affect the reinforcement process of samples and the development of pore structures. A sample with a smaller particle size can retain more nutrients. During the reinforcement process, sand samples with small particle sizes is easy to form blockage in the upper part of the sample due to small pores and low permeability coefficients, leading to uneven reinforcement effects. Samples of large particle sizes，large pores，weak water holding capacity，low calcium carbonate content，are mainly deposited in the lower part，leading to poor reinforcement effects.

Experimental Sthdy on Microbial Solidified Sand Based on Calcium Source Extracted from Limestone Powder

CHENG Yaojia, TANG Chaosheng, LIU Bo, PAN Xiaohua, WANG Dianlong, LYU Chao, LI Hao

2021, 27(6): 746-753. DOI: 10.16108/j.issn1006-7493.2020106

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Microbial induced calcite precipitation (MICP) is a new soil improvement technology. As an important reactant in MICP reaction, calcium source has an important effect on the effect of microbial induced calcite precipitation. At present, the most widely used calcium source— calcium chloride (CaCl2), has the disadvantages of high cost and high environmental pollution. Therefore, this paper proposes to extract calcium source from limestone powder by adding acetic acid solution to limestone powder for microbial solidification of soil. The unconfined compressive strength test, scanning electron microscope observation of microstructure and calcium carbonate content test were carried out to verify the feasibility of using calcareous powder to extract calcium source for microbial induced calcite precipitation. The results show that: (1) It is feasible to extract calcium source from limestone powder for microbial solidification of soil. The strength and calcium carbonate content of sand column after solidifying is high and the structural integrity is high. (2) The mechanical properties of solidified sand columns treated by different calcium sources are different. The sand columns solidified by three kinds of calcium show typical brittle failure mode. But the unconfined compressive strength of sand columns solidified by calcium acetate is slightly higher than that of sand columns solidified by calcium source from limestone, and the unconfined compressive strength of sand columns solidified by calcium chloride is much lower than that of the first two. Sand columns solidified by calcium chloride are rougher and have more pores on the surface than the other two. They also have lower integrity after destruction. (3) The content of calcium carbonate in solidified sand columns treated by different calcium sources is different. Sand columns solidified by calcium acetate and calcium source from limestone have almost no difference, but sand columns solidified by calcium chloride have less calcium carbonate content. There is a positive correlation between calcium carbonate content and unconfined compressive strength of sand columns solidified by different calcium sources. (4) A large amount of calcium carbonate is precipitated between the surface and contact point of sand particles in the sand column solidified by calcium acetate and calcium source from limestone. Calcium carbonate crystal is mainly thin stacked calcite. Sand columns solidified by calcium chloride have less calcium carbonate precipitation than the first two, and calcium carbonate crystal is mainly hexagonal calcite. (5) Different calcium sources change the soildifying effect mainly by affecting the crystal appearance, crystal content, crystal distribution and cementation characteristics of microbial mineralization.

Enzyme-induced Calcium Carbonate Precipitation (EICP) and Its Application in Geotechnical Engineering

CAO Guanghui, LIU Shiyu, YU Jin, CAI Yanyan, HU Zhou, MAO Kunhai

2021, 27(6): 754-768. DOI: 10.16108/j.issn1006-7493.2020200

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The technique of improving soil by enzyme-induced calcium carbonate precipitation is called EICP, which has attracted more and more attention over the past decade due to its wide application. The article describes the mechanism of EICP and summarizes the extraction methods of plant urease and bacterial urease. In addition, the influence of factors such as urease, calcium source, urea, skimmed milk powder, temperature and pH on the cementing effects of EICP is explored. Furthermore, methods for testing the strength, calcium carbonate content, microstructure and composition of EICP reinforced samples are summarized, and the application of EICP in geotechnical engineering is evaluated. The purpose of this article is to summarize the current status of EICP research and potential problems that need to be overcome in future research.

Review on the Enzyme-Induced Carbonate Precipitation Based on Soil Stabilization

LAI Hanjiang, CUI Mingjuan

2021, 27(6): 769-774. DOI: 10.16108/j.issn1006-7493.2020071

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Abstract：Carbonate precipitation based on soil improvement is an environmentally friendly ground treatment technology that emerges in geotechnical engineering in recent years. This technique utilizes the urease-producing bacteria (termed as Microbially
Induced Calcite Precipitation, MICP) or urease enzyme (named Enzyme Induced Carbonate Precipitation, EICP) to hydrolyse urea
and induce the precipitation of cementing calcium carbonate, which can bond loose soil particles together and thus enhance soil
strength. Compared with the MICP method, the EICP method is free from issues related to bio-safety and oxygen availability, and
can be used to treat soils with finer particles. Therefore, the EICP method is promising for applications in practical engineering.
This study presents a review on the enzyme-induced carbonate precipitation based on soil stabilization from the aspects of type
and sources of urease enzyme, soil treatment methods with the EICP approach, and the strength enhancement of EICP treated soil.

Research Progress of Methane Bio-mitigation Technology in Landfill Cover

SUN Wenjing, KONG Yi, CHEN Xueping, LIU Xiaoyang

2021, 27(6): 775-783. DOI: 10.16108/j.issn1006-7493.2020107

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During the service life of landfills, large amounts of methane will be released due to the degradation of organic matter by microorganisms. Even with the gas collection devices, methane still escapes into the atmosphere. Methane gas is one of the important gases that cause the greenhouse effect. Methane-oxidizing bacteria is a microorganism that takes methane as the only carbon source, and has an excellent methane oxidation efficiency. In small and medium-sized landfills, old landfills and large
landfills where it is no longer economical to turn on gas collecting devices, the landfill final cover soil can be mixed with methaneoxidizing bacteria to oxidize methane gas and reduce the release of methane from landfill, so as to reduce the greenhouse effect and achieve the purpose of environmental protection The relevant research on methane oxidation efficiency of methane oxidizing bacteria at home and abroad was reviewed. The classification of methane-oxidizing bacteria and its mechanism of methane oxidation, the factors that affect the oxidation efficiency of methane-oxidizing bacteria and the application of methane-oxidizing bacteria in landfill sites are summarized, and the future research and application area of methane-oxidizing bacteria is outlined.

Study on the Improving Effect of Soybean Urease Induced Calcium Carbonate Precipitation on the Bearing Capacity of Sand Ground：Based on Results from Static Cone Penetration Tests

LANG Chaopeng, MA Ming, QIU Lidong, YANG Yuanjiang, LI Mingdong

2021, 27(6): 784-788. DOI: 10.16108/j.issn1006-7493.2020212

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Soybean Urease Induced Calcium Carbonate Precipitation（SUICP） is a newly improveed technology of soil. The bearing capacity of ground is likely to be improved by filling effects and cementing function of precipitated calcium carbonate. In order to quantitatively investigate the improving effects of the SUICP on the bearing capacity of sand ground, we conducted a sand
column model test, which was 38.5 cm in diameter and 100 cm in height. The calcium carbonate deposition was 3% of the mass of sand. The improving effects on the bearing capacity of sand ground was studied by static cone penetration tests. The results show that the average value of cone tip resistance of the sand ground increased by 38.9%, from 0.564 MPa to 0.783 MPa. The average shaft friction increased by 49.83%, from 19.08 kPa to 26.92 kPa. The average bearing capacity of sand ground increased by 45.09%, from 79.02 kPa to 108.64 kPa. There are two mechanisms for the improvement of bearing characteristics of sand ground. On one hand, sands of coarser particles were connected to each other by calcium carbonate. On the other hand, sands with denser pores were filled by precipitated calcium carbonate. The results confirm the SUICP grouting effects on the bearing capacity of sand ground and the mechanisms were analyzed. It is found that the uniformity of improvement in the sand column was not ideal, suggesting the need to explore the mechanism and to develop better technology in the future.

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