Effect of Glutinous Rice Slurry on the Reinforcement of Silt in the Yellow River Basin by Microbially Induced Carbonate Precipitation (MICP): Mechanical Property and Microcosmic Structure

-e silty clay in the lower reaches of the Yellow River is characterized by loose structure, low strength, and strong capillary effect. Based on the technology of ancient glutinous rice mortar and microbial-induced calcium carbonate precipitation (MICP), experiments on optimal mass ratio of cementitious liquid to bacterial liquid and optimal concentration of cementitious liquid for MICP and improved MICP technology were carried out by measuring the production of CaCO3, and direct shear test and unconfined compressive strength test of plain silt, glutinous mixing silt, and improved silt with MICP and modified MICP were conducted. -e microstructure of the reaction products of MICP and improved MICP technology were also evaluated based on scanning electron microscopy (SEM). Research results showed that the mechanical properties of silt with glutinous rice slurry were effectively improved. With the increase in the concentration of glutinous rice slurry, the strength and internal friction angle of soil samples first increased and then decreased, and the cohesion presented a linear increasing trend.When the concentration of cementitious liquid was 0.5M and the mass ratio of cementitious liquid to bacterial liquid was 2 :1, the amount of CaCO3 formed was the most, and the conversion rate of Ca was more than 80%.-e improvedMICP could increase the conversion rate of Ca (93.44%). An improvedMICP showed that glutinous rice slurry could improve bacterial activity, increase the urease content in the bacterial solution, and promote the production of CaCO3. Silt cohesion and internal friction angle of the silt were improved by the improvedMICP technology, and the strengthening effect of mechanical properties of modifiedMICP-reinforced soil is better than that of theMICP-reinforced soil; conventionalMICP technology could also improve the soil cohesion, but the improvement in the internal friction angle was not obvious. -e SEM results indicated that compared with the reaction product of MICP technology, the structure of the product of improved MICP technology is more compact, resulting in a marked reinforcement of MICP performance with glutinous rice slurry. -is study provides new insights into enhancing the mechanical behaviour of MICPtreated silt in the Yellow River Basin with glutinous rice slurry.


Introduction
Soil stabilization or soil strengthening is the process whereby soils are made stronger and more durable. Physical, biological, or chemical methods can be used. Cement has been widely used in foundation treatment for a long time [1]. environmentally friendly materials. Several innovative and sustainable green soil improvement techniques were introduced for geotechnical applications [4].
ere are humongous amounts of bacteria in soil, which generate various biochemical products such as biofilms, various gases (e.g., N 2 , CO 2 , NO, H 2 , and H 2 S), biopolymers, or biominerals. erefore, the direct use of in situ microbial activities or exsitu microbial products has been proposed as a potential soil improvement method with a low environmental impact [5]. Microbial-induced calcium carbonate precipitation (MICP) is a technology, which has been emerging in recent years, which uses bacteria to induce calcium carbonate precipitation and thus has very good cementation and reinforcement effect on sandy soil and silty soil [6][7][8].
e MICP method has been investigated for improving various soil properties, including strength and stiffness [9,10], liquefaction resistance [11,12], wind/water erosion control [13], and permeability [14,15]. e concentration of cementitious liquid affects the unconfined compressive strength of the treated soil. A high concentration of CaCl 2 is not conducive to urea hydrolysis and calcium carbonate deposition, while a low concentration of CaCl 2 is conducive to the reaction [16]. e calcium ion conversion rate is the highest when the cementitious liquid is 0.5 M. Calcium source and Ca 2+ concentration have a direct effect on MICP. 0.25 M CaCl 2 can induce the highest calcium carbonate deposition efficiency [17]. e same concentrations of CaCl 2 and urea have a good mineralization effect, and a high concentration of cementing fluid will inhibit the mineralization reaction [18]. In current research and applications, multiple injections of bacteria and reaction solutions are still necessary to achieve the appropriate effect, which leads to long mineralization time, harmful intermediate products, etc., thereby, resulting in environmental pollution and disadvantages in the mineralization process [10,19].
In ancient China, the composite material of the glutinous rice mortar was often used in the construction of city walls [20][21][22][23]. e components of glutinous rice have a similar function to that of organic matter in the process of biomineralization, the modified glutinous rice mortar has good initial fluidity, controllable setting time, and high early strength, and travertine particles form the calcium carbonate "crystal nucleus", which can provide a stable adhesion environment [24]. It is proved that the surface hardness, compressive strength, and splitting tensile strength of the treated soil could be affected by mixing a concentrated glutinous rice paste [25]. Liu et al. have obtained calcium carbonate crystals with various morphologies by using glutinous rice slurry as an organic control material and carbon source of carbon dioxide. e influence of the concentration of Ca 2+ and reaction time on the morphology and polymorph of CaCO 3 crystals was researched to reveal the mechanism of MICP [26]. e combination of glutinous rice slurry and calcium carbonate can further strengthen the mechanical properties of soil [27][28][29][30].
In history, the Yellow River always burst its banks and caused severe floods, which makes the silt rich in organic matter and soluble salts, which makes it easy for bacteria to survive. In this paper, an improved MICP technology was proposed by introducing glutinous rice slurry into the MICP technology. e mechanical properties of the modern glutinous rice mortar, which consists of glutinous rice slurry, bacterial liquid, cementitious liquid, and calcium carbonate precipitation, were studied. Glutinous rice slurry can provide nutrients for microorganisms, and then improve the activity of microorganisms. e primary objectives of this work are to investigate the effects of the glutinous rice slurry on the MICP technology. On one hand, glutinous rice pulp can provide a nutrient source for microorganisms and improve microbial activity; on the other hand, the combination of glutinous rice slurry and calcium carbonate forms a glutinous rice mortar, which further strengthens the mechanical properties of soil. e mechanical properties of the MICP-treated silt, the microstructure of the specimen, and the interactions between the glutinous rice slurry and microorganisms were investigated and analysed using the direct shear test, unconfined compressive strength, and scanning electron microscopy (SEM). It is a potentially environmentally friendly technique, while improving the foundation bearing capacity of soil.

Soil Preparation and Analysis.
e research soil is selected from the Puyang City in the Yellow River area. Puyang City soil is mostly silt soil formed by the Yellow River flood and alluvial with poor water stability, strong water capillary effect, high strength when dry, but significantly reduced when wet [31]. e bearing capacity characteristic value of foundation soil before and after improvement is calculated with regard to the code for design of building foundation [32]. e basic physical properties of the soil used in this study are shown in Table 1.
e basic physical property indexes of the research soil were measured according to the standard for the geotechnical testing method (GB/T 50123-2019) [33]. e grain size distribution of the site soil is presented in Figure 1, which are analysed through the particle grading test. e silt was taken from 2 m underground. e soil samples are made according to the optimal moisture content and 96% compactness. e design dry density is 1.6 g/cm 3 , and the moisture content is 17%.
Direct shear test: the diameter of the ring cutter sample is 61.8 mm, height is 20 mm, and volume is 60 cm 3 . e theoretical weight of the ring cutter sample is 112.32 g, and the water content is 16.32 g. e sample is made and put it into the box for sealing and curing for 7 days.
Unconfined compressive strength test: a strain-controlled unconfined compression instrument was used. e soil sample is prepared by the mold of the triaxial test, and the sample size is Φ38 × 76 (mm), volume is 86.193 cm 3 , theoretical mass of one sample is 161.35 g, and theoretical water addition is 27.43 g. e prepared samples are added with a layer of fresh-keeping film and then put into the box for curing. ree samples are required for a group of unconfined tests. e compression test is carried out after 7 days of sealing and curing. 2 Advances in Materials Science and Engineering 2.2. Glutinous Rice Slurry. Glutinous rice slurry: commercial pulverized sticky rice was used in this study. e pulverized sticky rice was purchased from the local market in Kaifeng city of Henan province, which are food grade materials. e amylose content in the rice starch ranges from 0.9 wt. % to 1.1 wt. % with a protein content of around 7.6 wt. %. e glutinous rice powder is mixed with distilled water to prepare slurry with a concentration of 1%, 3%, 5%, 7%, and 9%. Glutinous rice flour of different qualities is cooked with water and high pressure to prepare glutinous rice pulp with a concentration of 1%, 3%, 5%, 7%, and 9%. e preparation method of the glutinous rice pulp with 1% concentration is as follows: wash and dry the conical flask, add 1 g glutinous rice flour into the bottle, add tap water to the bottle to 100 g, and seal the bottle mouth with air permeable materials such as newspaper, and then put it into an electric rice cooker to heat and boil for at least 4 h [34] (refer to this for other concentrated glutinous rice paste). During the process, write down the scale of the electric rice cooker and add an appropriate amount of water to keep the consistency of glutinous rice slurry unchanged [35][36][37].

Preparation and Treatment of Bacteria.
is study utilized Sporosarcina pasteurii ATCC 11859 purchased from Shanghai Bioresource Collection Center.

Experiment on Improved Silt with Glutinous Rice Slurry
3.1.1. Mechanical Properties of Improved Silt. To verify the effectiveness of glutinous rice slurry in improving the soil properties, 1%, 3%, 5%, 7%, and 9% glutinous rice slurry was mixed to the soil evenly. en, the sample was cured for 7 days in the sealing box.
(1) Direct Shear Test Under Low Stress. e number of floors of rural buildings in the Yellow River region is low, and the actual vertical pressure is often lower than that of high-rise buildings [38]. In this paper, the vertical stress is 50 kPa, 100 kPa, 150 kPa, and 200 kPa, respectively. According to the standard of geotechnical test methods [33], direct shear tests were carried out. e shear stress and shear displacement of the improved soil samples are shown in Figure 2.
It can be seen from Figure 2 that with the increase in the vertical stress, the shear stress increases. With the increase in the concentration of glutinous rice slurry, the shear strength of the samples first increases and then decreases. It can be seen that different concentrations of glutinous rice slurry have different effects on the improvement of the sample. e 3% glutinous rice slurry samples show a good shear strength performance. e sample without glutinous rice slurry has lower peak strength and later strength.
e sample with glutinous rice slurry shows a better performance under lower stress, which indicates that glutinous rice slurry is more suitable for engineering under low-stress conditions. According to the shear strength of the samples under different glutinous rice slurry content, the relationship curve between the shear strength and vertical stress is fitted, as shown in Figure 3. Figure 3 shows that with the increase in the glutinous rice slurry content, the shear strength of samples first increases and then decreases. When the glutinous rice slurry content is 3%, the internal friction angle is the largest. In addition, when the glutinous rice slurry content is 9%, the cohesion is the largest. e cohesion and internal friction angle of the samples under different glutinous rice slurry  Advances in Materials Science and Engineering contents are shown in Figure 4. With the increase in the content of glutinous rice slurry, the internal friction angle first increases and then decreases, and the cohesion increases linearly. e reason for this phenomenon is that the pores between the soil particles are gradually filled with glutinous rice slurry, which improves the cohesion between particles [39,40].
However, with the continuous increase in the glutinous rice slurry content, excessive glutinous rice slurry adheres to the surface of soil particles, resulting in the decrease of frictional force between particles and the decrease of the internal friction angle.
(2) Unconfined Compressive Strength Test. e unconfined compressive strength can reflect the relationship between the mechanical properties of the specimen and the improved materials. According to the standard of geotechnical test methods [41], the unconfined compressive strength test of the specimens was carried out by using the strain-controlled unconfined compression instrument at the axial strain rate of 1 mm/min. e relationship between axial stress and strain of specimens at different concentrations of glutinous rice slurry is shown in Figure 5.
It can be seen from Figure 5 that with the increase in the glutinous rice slurry content, the maximum axial stress of the samples first increases and then decreases. When the concentration of glutinous rice slurry is 3%, the axial stress reaches the maximum value, that is, the unconfined compressive strength reaches the maximum value. e unconfined compressive strength (i.e., antideformation ability) of the samples with glutinous rice slurry solution is significantly improved. e unconfined compressive strength of the samples increased by 19.3%, 60.5%, 43.7%, 35.8%, and 32.1%, respectively, with 1%, 3%, 5%, 7%, and 9% glutinous rice slurry, respectively, and the deformation resistance of the samples increased by 11

Microbial Cultivation and
Improvement. e 1 L microbial liquid culture medium formula is shown in Table 2 [42].

Microbial Activity.
e OD 600 value of bacteria reflects the bacterial activity [42,43]. e higher the activity of the bacterial liquid, the lower the transmittance is, which indicates that the OD 600 value of the bacterial liquid is higher.
e formula of the three groups of the bacterial liquid is shown in Table 2, of which group I is a common bacterial liquid, group II is a modified bacterial liquid, and group III is a bacterial liquid containing 3% glutinous rice slurry. e OD 600 value of group I is 1.542, that of group II is 1.836, and group III is 0.405. e activity of group II was increased by 19% compared to that of group I, which indicated that the amount of urease in improved microbial metabolism was higher than that of the common bacterial solution; the activity of group III was lower than that of group I and II, but it also showed that glutinous rice slurry could provide nutrition for bacteria and increase the activity and concentration of bacteria.

Optimal Ratio of Calcium to Bacteria for MICP.
e mass ratio of cementitious liquid to bacterial liquid is shown in Table 3. e optimal mass ratio of cementitious liquid to bacterial liquid was studied by measuring the production of CaCO 3 . e test was divided into two groups A-F and a-f, as shown in Figure 6. Group A-F was dried and weighed after filtration, and group a-f was dried and weighed directly. e residual solid after drying is shown in Figure 7. It can be seen from Figure 7 that there are more brown solids in group A, B, and C after drying, and more white solids appear in group C to group F, but many white CaCl 2 crystal substances appear on the surface of group F. erefore, the remaining solids after drying include bacteria, CaCO 3 precipitation, and CaCl 2 crystals, which were not completely reacted.
MICP is to convert Ca 2+ into CaCO 3 precipitation. After filtration and drying of group A∼F, the concentration of the calcium ion was measured by the EDTA standard solution titration method [44], and the actual amount of CaCO 3 precipitation can be measured.

Group
Yeast powder (g/L) Peptone (g/L) Sodium chloride (g/L) Urea (g/L) Glutinous rice slurry Agar  I  5  10  10  10  0  30  II  5  10  10  10  30  30  III 30 0  e concentration of calcium ion and the mass of calcium carbonate precipitation were calculated as follows: where c (Ca 2+ ) is the concentration of the calcium ion (mol/ L), V (EDTA) is the amount of the EDTA standard solution (ML), c (EDTA) is the concentration of the EDTA standard solution (mol/L), taking 0.1 mol/L, V (HCl + NaOH) is the total volume of hydrochloric acid and sodium hydroxide dropping (ml), M (CaCO 3 ) is the amount of calcium carbonate, taking 100, and m (CaCO 3 ) is the mass of calcium carbonate (g).
By measuring the amount of CaCO 3 precipitation in group A∼F, it was found that the conversion rate of Ca 2+ in group A∼D was 83.22%, 76.69%, 74.16%, and 80.69%, respectively. e amount of CaCO 3 precipitation increased gradually, which were 0.0799 g, 0.1227 g, 0.178 g, and 0.258 g, respectively. e conversion rate of Ca 2+ in Group E and F was 43.30% and 26.95%, respectively, and the precipitation amount of CaCO 3 was 0.1559 g and 0.1035 g, respectively.
e actual mass of CaCO 3 , the solid content after filtration and drying, the amount of residual solid after drying, and the conversion rate of Ca 2+ are shown in Figure 8. It can be seen that group D produces the most CaCO 3 , and the conversion rate of Ca 2+ is more than 80%, which is the best mass ratio of cementitious liquid to bacterial liquid.

Optimal Concentration of Cementitious Liquid for MICP.
e optimal concentration of cementitious liquid for MICP technology was studied with the best mass ratio of cementitious liquid to bacterial liquid (2 : 1). e experimental cementitious liquid concentrations were 0. 25 Table 4. e experiment was conducted in G-L and g-l groups, as shown in Figure 9. After filtration and drying, the G∼L group was titrated with EDTA standard solution [45], and the g-l group was dried for observation. e residual solids after drying are shown in Figure 10.
e actual mass of CaCO 3 , the amount of residual solid after drying, and the conversion rate of Ca 2+ are shown in Figure 11. In Figure 9, white precipitates can be observed in G/g and H/h, but no obvious precipitation was found in the other four groups, which is mainly due to the inhibition of urease induced ions by a high concentration of cementitious liquid, thus affecting the formation of CaCO 3 .
It can be seen from Figure 10 that there are more white solid precipitates after drying in groups g and h; the solid colour in groups i and j are yellowish after drying, and many white CaCl 2 crystal substances appear on the solid surface after drying in groups K and l, which are mainly caused by the high concentration of the cementitious liquid. e remaining substances in group i − 1 after drying are bacteria, calcium chloride, and a small amount of calcium carbonate. e results showed that the conversion rate of Ca 2+ in group G and group H was 83.94% and 82.19%, respectively. e precipitation of CaCO 3 was 0.1343 g and 0.263 g. e conversion rate of Ca 2+ in group i − l decreased from 73.44% to 34.79%, but the amount of CaCO 3 increased slowly. e best calcium concentration (0.5 M) was obtained by the experiment of the best mass ratio of cementitious liquid and bacteria liquid. When the concentration of cementitious liquid was 0.5 M and the mass ratio of gum fungus was 2 : 1, the conversion rate of Ca 2+ and the production of calcium carbonate were the highest. Based on this ratio, glutinous rice slurry was introduced to improve the MICP technology.

Research on Improved MICP Technology.
Based on the optimal calcium concentration (0.5 M), the optimal mass ratio of cementitious liquid to bacterial liquid (2 : 1) and improved bacterial liquid, the CaCO 3 production under the improved MICP technology was studied. e mass of improved bacterial solution and cementitious liquid is shown in Table 5.
e test was divided into two groups M and m as shown in Figure 12. After filtration and drying, group M was titrated with EDTA standard solution. e actual amount of CaCO 3 precipitated was 0.299 g, and the conversion rate of Ca 2+ was 93.44%. e remaining solids in group M after drying are shown in Figure 13. e white solid material was white with a few transparent flakes, which were preliminarily judged as the state of glutinous rice slurry after drying.
After improvement, the Ca 2+ conversion rate of group M was 12.75% higher than that of group D and 11.25% higher than that of group h. ese results indicated that the modified MICP can help to increase the concentration of bacteria, thus increasing the urease content in the bacterial solution and promoting the production of CaCO 3 . Comparing group M, group D, and group H, it was found that group M had one more layer of slurry film than the other two groups after drying. e film and CaCO 3 were beneficial to improve the adhesion between particles, which indicated that glutinous rice slurry played a favourable role in traditional earthen sites.

SEM Scanning Electron Microscopy.
e solid materials (bacteria, CaCO 3 precipitation, CaCl 2 crystal, and glutinous rice slurry) in group a-m and CaCO 3 particles produced by CaCl 2 and Na 2 CO 3 reaction products were scanned by SEM to observe the shape, structure, and other properties of the CaCO 3 solid substances induced by Bacillus Pasteurella, as shown in Figures 14-16.
e left side of Figures 14-16 shows the microscopic diagram of solid matter under 1000 times magnification, and the right side of Figures 14-16 shows the microscopic diagram of solid matter with a magnification of 5000 times. e results of scanning electron microscopy showed that in the group a-f, CaCO 3 precipitated less in groups a and b, and more bacteria were wrapped in CaCO 3 particles; in group c, CaCO3 precipitation began to increase, but many bacteria could still be observed; group d had the most CaCO 3 precipitation and fewer bacteria; groups e and f had less CaCO 3 Advances in Materials Science and Engineering precipitation, and more CaCl 2 crystals were wrapped on CaCO 3 particles. In groups g-l, the conversion rate of Ca 2+ in group g and group h was higher, and more CaCO 3 was visible; in group i-l, the conversion rate of Ca 2+ decreased gradually, and a small amount of CaCO 3 and a large number of CaCl 2 crystals were attached to CaCO 3 . Group M was added glutinous rice slurry based on group D and group h. Compared with group D and group H, more and more CaCO 3 particles can be seen in group M. On the one hand, the conversion rate of Ca 2+ in group M was increased by 10% compared with that in group D and H; on the other hand, glutinous rice slurry envelops CaCO 3 particles and formed a layer of invisible film on its surface. Comparing the three groups of samples D, H, and M in Figure 14 with those in Figures 15 and 16, their similarity was very high, which proved that they were CaCO 3 particles. Because CaCl 2 crystals were attached to the surface of group D and h, and glutinous rice slurry was attached to the surface of group M, the SEM images of the three groups of samples were slightly different from those of CaCO 3 particles. Previous studies have shown that the reduction in the void space due to the CaCO 3 precipitation is considered to be a primary strengthening factor in the reduced brittleness behavior of the MICP-treated sand [44].    ree groups of samples were set, namely, pure water group, common bacterial liquid group, and 3% glutinous rice slurry improved bacterial liquid group. Direct shear test specimens were 61.8 mm in diameter, 20 mm in height, and 60 cm 3 in volume. Unconfined compressive strength test specimens were Φ 38 × 76 (mm) and 86.193 cm 3 volume. Based on 96% compaction (dry density of 1.6 g/cm 3 ), dry soil quality needed for a direct shear test piece was 112.32 g, and an unconfined specimen required dry soil quality of 161.35 g. With 17% moisture content, a direct shear needed pure water of 16.32 g and an unconfined specimen needed pure water of 27.43 g. In the common bacterial solution group, the bacterial solution was added by 1% solute removal method, and in the improved bacterial solution group with 3% glutinous rice slurry, the bacterial solution was added by 3% solute removal method, as shown in Figure 17. e amount of slurry added to a direct shear sample and an unconfined compressive sample is shown in Table 6.
It can be seen from Figure 17 that water permeability was faster in the pure water group (Figure 17(a)). e permeation rate of the common bacterial solution group (Figure 17(b)) was the second, and the water permeation rate was slow due to the reaction of the bacterial solution and cementing solution to form calcium carbonate precipitate. e infiltration rate of the modified bacteria liquid group with a concentration of 3% was the slowest (Figure 17(c)).
e main reason was that the blocking effect of the glutinous rice paste and the reaction of the bacteria liquid with the cement liquid resulted in the formation of calcium carbonate precipitate, which made it difficult for water to enter the soil. According to the sample preparation method of the direct shear test and unconfined compressive strength test at different glutinous rice slurry concentrations, the prepared samples were put into a sealed box and cured for 7, 14, and 28 d. Some samples are shown in Figure 18.

Direct Shear Test. Direct shear test under different
vertical pressures is a kind of more convenient and quick determination of cohesion and friction angle of soil, which can directly reflect the soil mechanics performance. e theoretical expression of soil strength is as follows [46]: where τ is the shear stress, σ is the normal stress, c is cohesion, V is the angle of internal friction, and σ·tanV represents internal friction. e test process is in strict accordance with the standard of the soil test method [33]. e maintenance of specimens was done for 7 d, 14 d, and 28 d, respectively. Shear stress and displacement curve under different curing days are shown in Figure 19, and the shear rate is 0.8 mm/min. e results are shown in Table 7.

10
Advances in Materials Science and Engineering        14 Advances in Materials Science and Engineering e Y-axis intercept of soil consolidated with improved MICP was the largest and increases with the increase in curing days. e Y-axis intercept of soil consolidated with MICP was larger than that of soil consolidated with plain soil. e slope of the soil consolidated with improved MICP was the largest and tends to increase with the increase in the curing days. e slope of the soil consolidated with MICP was similar to that of the plain soil and almost unchanged with the increase in the curing days. e cohesion and internal friction angle of the three samples changed regularly with the increase in curing days, as shown in Figure 21.
e cohesion of plain soil specimens cured for 7 d, 14 d, and 28 d was 25.05 kPa, 25.95 kPa, and 26.55 kPa, and the internal friction angle was 30.28°, 30.84°, and 31.52°, respectively. With the increase in curing time, the cohesion and internal friction angle of 7-14 d specimens were almost constant, and the cohesion and internal friction angle of 28 d specimens increased slightly. e reason may be that the moisture content of specimens in the process of curing was lower. e cohesion of MICP-reinforced soil cured for 7 d, 14 d, and 28 d was 32.7 kPa, 38.9 kPa, and 40.3 kPa, and the internal friction angle was 31.42°, 31.78°, and 32.28°, respectively. e cohesion of specimens increased with curing time. e cohesion of specimens cured for 7 to 14 d grew faster than that of 14 to 28 d, and the internal friction angle with the increase in the curing days were almost the same. Compared with plain soil, its cohesion in curing for 7 days grew by about 30%, curing for 14 days and 28 days grew by about 50%, but the internal friction angle change is small, at around 3%. e cohesion of the improved MICP-reinforced soil specimens cured for 7 d, 14 d, and 28 d was 37.65 kPa, 44.1 kPa, and 46.9 kPa, the internal friction angle was 35.44°, 39.1°, and 40.2°, respectively, with the increase in the curing days. e cohesion of 7 to 14 days grew faster than that of 14 to 28 d, compared to plain soil, its cohesion in curing 7 days grew by about 50%, curing in 14 d grew by about 70%, and curing in 28 d grew by about 77%; the internal friction angle had risen about 17% in curing 7 days. Compared with the MICP-reinforced soil, its cohesion increased by about 15% at different curing days, its internal friction angle increased by about 13% at curing for 7 d, and increased by about 24% at curing for 14 d.

Unconfined Compressive Strength Test.
Unconfined compressive strength of specimens reinforced with MICP and improved MICP was tested in strict accordance with the standard of the soil test method [33]. e axial stress and strain relationship curve of the three kinds of specimens under different curing days is shown in Figure 22.
For the same curing days, the soil reinforced with improved MICP had the maximum axial stress and the maximum corresponding axial strain, the specimens had the best resistance to failure and deformation, followed by the MICP-reinforced soil, and the plain soil had the minimum axial stress and the minimum corresponding axial strain, the specimens had the worst resistance to failure and deformation. e test results of unconfined compressive strength are summarized in Table 8.
e unconfined compressive strength of the three specimens varies regularly for different curing days, as shown in Figure 23.
With the increase in curing days, the unconfined compressive strength of soil reinforced with improved MICP for 7 to 14 d grew the fastest, with an increase rate of 34.2%. MICP-reinforced soil was the second with a growth rate of 11.2%, and that of the plain soil was the slowest with a growth rate of 5.7%. e growth rate of unconfined compressive strength of plain soil increased slightly from 14 to 28 days with an increase rate of 7.9%. e growth rate of the unconfined compressive strength of soil strengthened with MICP and modified MICP decreased to 4.0% and 7.2%, respectively. Compared with the unconfined soil, the unconfined compressive strength of the soil consolidated with MICP increased by 23%, 29.4%, and 24.6% after curing for 7, 14, and 28 d, and the unconfined compressive strength of the soil reinforced with MICP increased by 73.8%, 120.7%, and 119.1%, respectively. Compared with the MICP-reinforced soil, the unconfined compressive strength of the soil reinforced with improved MICP increased by 41.3%, 70.6%, and 75.8%, respectively, when curing for 7 d, 14 d, and 28 d.
With the increase in curing days, the axial strain to failure of the plain soil during 7 to 14 days remained unchanged. e axial strain to failure of the MICP-reinforced soil and the improved MICP-reinforced soil increased slightly, with the growth rates of 9.85% and 8.97%, respectively. During 14 to 28 d, the axial strain of plain soil, MICP-reinforced soil, and modified MICP-reinforced soil increased with growth rates of 11.86%, 8.87%, and 8.23%, respectively. During the same curing period, the deformation resistance ability of the three samples ranged from large to small from improved MICP-reinforced soil, MICPreinforced soil, and plain soil, respectively. Compared with plain soil, the axial strain of the MICP-reinforced soil during failure increased by 11.9%, 22.9%, and 19.7% when cured for 7, 14, and 28 d, respectively. When the improved MICP was used to reinforce the soil damage, the axial strain increased by 22.9%, 33.9%, and 29.5%, respectively. Compared with the MICP-reinforced soil, the axial strain of the improved MICP-reinforced soil cured for 7 d, 14 d, and 28 d were increased by 9.85%, 8.97%, and 8.23%, respectively.

Analysis of Mechanical Test Results.
e characteristic value of the foundation bearing capacity is decided by soil cohesion and internal friction angle. e characteristic value of the foundation bearing capacity is calculated according to formula (3), in which, f a is the characteristic value of the  foundation bearing capacity (kPa), and b is the base width.
In this paper, b is taken as 6 m, c k is the standard value of cohesion, Μ b , Μ c , and Μ d are the bearing capacity coefficients, c is the soil weight under the substrate, which is 18 kN/m 3 , M is the weighted mean weight of soil above the base, which is 18 kN/m 3 , and d is the buried depth of foundation, which is 1.5 m. According to the cohesion and internal friction angle measured in the direct shear test, the characteristic values of the bearing capacity of three soil specimens for different curing days are shown in Table 9, Under ideal conditions, the characteristic value of the soil foundation bearing capacity can be calculated by formula (3). e highest characteristic value of soil foundation bearing capacity of soil improved with MICP after 28 d is its maximum compressive strength. With the increase in curing days, the characteristic value of the bearing capacity of soil foundation treated by the improved MICP method after 7 to 14 d increased the fastest, with an increase rate of 34.03%. Soil reinforced with MICP followed by an increase rate of 11.71% and plain soil was the slowest, with a growth rate of 6.03%. From 14 d to 28 d, the growth rate of the characteristic value of the bearing capacity increased slightly, with a growth rate of 6.15%. e growth rate of the characteristic value of the bearing capacity of soil reinforced by MICP and the improved MICP was reduced, with a growth rate of 5.36% and 8.21%, respectively. Compared with plain soil, the characteristic values of the bearing capacity of the ground strengthened by MICP for 7 d, 14 d, and 28 d increased by 22.87%, 29.46%, and 28.49%, respectively, which was 72.17%, 117.63%, and 121.87%, respectively, by the improved MICP. Compared with the MICP-reinforced soil cured for 7 d, 14 d, and 28 d, the characteristic values of the bearing capacity of the modified MICP-reinforced soil were 40.12%, 68.11%, and 72.67%, respectively.

Effect of Glutinous Rice Slurry on Microbial
Mineralization. Biomineralization refers to the process of forming inorganic minerals through the regulation of biological macromolecules. e most obvious difference from general mineralization is that the organic matrix, cells, and biological metabolites are required to participate in the process of biomineralization [47][48][49]. Microorganisms are widely distributed in the soil and can induce the deposition of carbonates, phosphates, sulfates, and other minerals [50][51][52]. In the process of mineralization, microorganisms affect the formation and regulation of the crystal form and size of carbonate particles through their metabolism and secreted metabolites [53,54]. ere are a large number of hydroxyls, carboxyls, and phosphate groups on the surface of microbial cells [55]. Under alkaline conditions, the bacteria have a negative charge, which has a strong electrostatic attraction to metal cations, which makes calcium ions free near the bacteria to form chemical bonds (as shown in formula (4)). Calcium ions combine with carbonate to form calcium carbonate. Bacteria provide mineralizing nuclear sites for calcium carbonate, which enables crystallization and mineralization of calcium carbonate near the surface of bacteria, as shown in the following formulas: e main components of glutinous rice slurry are starch and protein, with the protein content of 7%-10% [56,57]. Protein can provide nitrogen and carbon required by bacteria. It was found that the protein in glutinous rice slurry could improve the activity of bacillus pasteurella and urease production. Urease can decompose urea to produce carbonate ion, which makes calcium ions to precipitate to calcium carbonate. With the extension of time, glutinous rice slurry continued to play a role in promoting the formation of more calcium carbonate and prolonging the biomineralization time.
e reason is that the starch content in glutinous rice slurry reaches 75%-77%. Studies have shown that some bacteria and fungi can produce amylase, and the related bacteria include bacillus, aspergillus, streptomyces, trichoderma, penicillium, clostridium, thermomonas, etc. [58][59][60][61]. Relevant studies have shown that thermophilic Bacillus, Bacillus gelatinosa, Bacillus cereus, and Alternaria have a certain impact on the morphology and crystal diversity of calcium carbonate [62][63][64][65][66]. Protein and starch play an important role in the decomposition of soil organic matter and nutrient cycling and can be used as a nutrient source for many microorganisms.
e mineralized calcium carbonate crystals in glutinous rice slurry are shown in Figure 24. From the above analysis, glutinous rice slurry provides certain organic matter for the mineralization process of microorganisms, promotes the process of microbial mineralization and microbial diversity, and has an important impact on biological mineralization.

Effect of Amylopectin on Glutinous Rice Slurry.
Glutinous rice slurry is rich in starch. Amylopectin is the main starch molecule, which can mineralize calcium carbonate. After the glutinous rice slurry is heated and gelatinized, the branched-chain molecules are open and form a spiral crystal structure. e adjacent branch chains form an adhesive ball structure, which can enhance the viscosity of glutinous rice slurry solution [67]. Amylopectin is a tree branch structure, which can regulate the position, size, and morphology of calcium carbonate crystals [66,68,69], as shown in Figure 25. e branched-chain structure can also provide coordination sites for Ca 2+ , which makes the distribution of Ca 2+ dendritic. Ca 2+ reacts with the silica and alumina in the soil to form hydrated silicon (calcium aluminate) gel CSH, which makes CSH arrange in a dendritic form. e CSH dendrite network structure can cement soil particles into aggregates, which makes soil particles to connect more closely and improve the integrity of soil particles. erefore, the mechanical properties of the silt can be improved by the amylopectin action of glutinous rice slurry.

Conclusion
Based on the technology of the glutinous rice mortar and the principle of biomineralization, experiments on improved silt with glutinous rice slurry, improved MICP with glutinous rice slurry, and improved silt with modified MICP were carried out, and the improvement of mechanical properties of silt by modified MICP was studied. e main conclusions are summarized as follows: (1) e mechanical properties and microstructure of Yellow River silt with glutinous rice slurry were studied. Adding glutinous rice slurry into the silt can effectively improve the mechanical properties of soil. With the increase in the concentration of glutinous rice slurry, the strength and internal friction angle of soil samples first increase and then decrease, and the cohesion presents a linear increasing trend. e shear strength, unconfined compressive strength, and internal friction angle of 3% glutinous rice slurry are the largest.
(2) When the concentration of glutinous rice slurry is too small, amylopectin has a weak ability to control calcium carbonate crystals, and its action time is short; when the concentration of glutinous rice slurry is too high, the excess glutinous rice slurry will adhere to the surface of calcium hydroxide, which will affect the crystallization process of calcium carbonate, and then affect the improvement effect of soil. (3) Glutinous rice slurry could improve bacterial activity and promote the formation of calcium carbonate; when the concentration of cement solution was 0.5 M and the mass ratio of cementitious liquid to bacterial liquid was 2 : 1, the optimal mass ratio of gelatinous bacteria was obtained, and the amount of CaCO 3 formed was the largest, and the conversion rate of Ca 2+ was more than 80%.
(4) Based on the optimal calcium concentration (0.5 M), the optimal mass ratio of cementitious liquid to bacterial liquid (2 : 1) and improved bacterial liquid, the CaCO 3 production under the improved MICP technology was studied. e actual amount of CaCO 3 precipitated was 0.299 g, the conversion rate of Ca 2+ was 93.44%, and the Ca 2+ conversion rate was 12.75% higher.
e results indicate that the modified MICP are able to increase the concentration of bacteria and increase the urease content in the bacterial solution and promote the production of CaCO 3 . (5) rough a direct shear test and unconfined compressive strength test, the mechanical properties of plain soil, MICP-reinforced soil, and modified MICP-reinforced soil are obtained. e results show that the strengthening effect of mechanical properties of the modified MICP-reinforced soil is better than the MICP-reinforced soil. MICP technology can improve the cohesion of soil, and the improvement of internal friction angle is not obvious; the improved MICP technology can not only improve the cohesion of soil, but also improve the internal friction angle, so that the mechanical properties of soil can be reinforced. With the increase in curing days, the strength of modified MICP soil increases continuously and the biomineralization time is prolonged.

Data Availability
Some or all data, models, or code that support the findings of this study are available from the corresponding author upon reasonable request.

Conflicts of Interest
ere are no conflicts to declare.