Soybean urease-induced calcium carbonate precipitation (SICP) is an innovative and eco-friendly approach with demonstrated potential for mitigating soil liquefaction. However, the specific impacts of the concentrations of soybean urease and salt solutions require further elucidation. The research examines how the two compositions influence calcium carbonate formation. Dynamic characteristics of one-cycle SICP-treated clean and silty sand were analyzed based on cyclic triaxial tests. It was revealed that SICP-treated specimens of both liquefied sand and silty sand exhibit reduced accumulation of excess pore pressure and diminished strain growth under cyclic loading, thereby delaying liquefaction failure. Although higher concentrations of both soybean urease and salt solution can enhance liquefaction resistance, salt solution concentration has a more pronounced effect on improving liquefaction resistance due to the more production of calcium carbonate. Scanning electron microscopy observations confirmed the presence of calcium carbonate crystals at the interfaces between sand particles and between sand and fine particles. These crystals effectively bond the loose sand and fine particles into a cohesive matrix, reinforcing soil structure. A direct linear correlation was established between the liquefaction resistance improvement and precipitated calcium carbonate content. Notably, the one-cycle SICP treatment method adopted in this study demonstrates a better biocementation effect compared to cement mortar or multi-cycle MICP-treated sand under the same content of cementitious materials. These findings provide valuable insights for optimizing SICP treatments, aiming to reduce the risk of soil liquefaction in potential field applications.

To address the material requirements for grouting reinforcement in fine sand strata, a novel silicate-modified polymer two-component grouting material was designed. In this material, the traditional organic polyol component of the two-component polymer was replaced with an inorganic silicate (water glass) component, along with the addition of tertiary amine catalysts, organotin catalysts, water. The response surface methodology (RSM) was used to statistically predict the performance of the modified polymer grouting material. The effects of four parameters (two-component mass ratio, tertiary amine catalyst content, organotin catalyst content, and water content) and their interactions on response variables (gelation time, polymer solids strength, cemented body strength) were investigated. Based on a comprehensive consideration of various performance requirements for grouting materials in loose fine sand strata, multi-objective optimization was employed to determine the optimal formulation of the modified polymer grouting material (A/B ratio of 0.85, tertiary amine catalyst at 2.48 %, organotin catalyst at 0.63 %, and water at 1.87 %). A series of experimental tests were conducted to evaluate the material properties of the optimal formulation, and its mechanical performance and microstructural characteristics were compared with those of traditional polymer grouting materials to verify the proposed formation mechanism of the modified polymer. The results demonstrated that the proposed design method effectively determines the optimal grouting material formulation. The optimized modified polymer grouting material exhibited excellent comprehensive performance. Finally, the optimized modified polymer grouting material was applied in a pavement repair project on a of a highway. After grouting, the structural layer's uniform integrity was significantly restored, the damaged areas were effectively repaired, the modified polymer slurry showed good diffusion, and the repair effect was satisfactory, meeting the engineering requirements for grouting in loose fine sand strata.

In this study, carbide slag, fly ash, cement, and sodium sulfate were used to stabilize silt from the Yellow River Alluvial Plain. An orthogonal test was conducted to evaluate the optimal mix design for soil stabilization. The mechanical properties, hydration products, and microstructure of the stabilized silt were examined. The effects of stabilizer concentration, compaction, and moisture content on the mechanical properties were investigated. Based on mechanical performance, the optimal stabilizer mix was found to consist of 30% cement, 13.6% carbide slag, 54.4% fly ash, and 2% sodium sulfate. The results indicated that the California Bearing Ratio (CBR), unconfined compressive strength, and splitting tensile strength of the stabilized silt increased with higher stabilizer dosage and compaction degree. In the early stages, the hydration products of the stabilized silt were primarily calcium hydroxide, ettringite, and C-S-H, which exhibited a loose structure. Over time, the microstructure densified, and more crystalline C-S-H was formed. This study provides valuable insights into the use of industrial by-products for soil stabilization, offering a sustainable and cost-effective solution to improve the strength and stability of silt in construction projects.

Silt is widely utilized as a filling material in transportation construction, However, it frequently suffers from problems, such as excess pore water pressure buildup, settlement, and mud pumping. Wicking geotextiles have emerged as a sustainable solution by improving both drainage and reinforcement capacities, yet their optimal design parameters remain unclear. To address this gap, a series of tests were performed to investigate the effects of compaction degree, reinforcement configuration (number, spacing, position), and specimen geometry on the mechanical and consolidation of silt reinforced with wicking geotextiles. The results reveal that the failure mechanism of reinforced silt progresses through four distinct stages, which the wicking geotextile improved interparticle contact, delays crack initiation, and improves post-peak stability. Wicking geotextiles significantly improve strength, particularly at lower compaction degrees, by restraining crack propagation and promoting uniform stress distribution. Optimal mechanical performance was achieved with three reinforcement layers and compaction degrees of 93-95 %. Mid-depth placement of a single layer or uniform spacing of multiple layers produced the best outcomes. Although non-uniform spacing provided advantages at early deformation stages, it ultimately induced premature failure, whereas uniform spacing (= 1.27 exhibited improved ductility, while larger specimens with multiple layers demonstrated improved post-peak stability. Wicking geotextiles accelerated drainage and void ratio reduction but concurrently decreased the compression modulus. These findings contribute to a more comprehensive understanding of the mechanical and hydraulic responses of wicking geotextile-reinforced silt and provide practical insights for the design and optimization of reinforced subgrades.

Red mud is a kind of solid waste, which can be used as engineering roadbed filler after proper treatment. Due to the special physical and chemical properties of red mud, such as high liquid limit and high plasticity index, it may affect the stability of soil. Therefore, red mud can be improved by adding traditional inorganic binders such as lime and fly ash to improve its road performance as roadbed filler. Red mud-based modified silty sand subgrade filler will be affected by dry-wet alternation caused by various factors in practical application, thus affecting the durability of the material. In order to study the strength degradation characteristics and microstructure changes of red mud, lime and fly ash modified silty sand subgrade filler after dry-wet cycle, the samples of different curing ages were subjected to 0 similar to 10 dry-wet cycles, and their compressive strength, microstructure and environmental control indexes were tested and analyzed. The results show that the sample cured for 90 days has the strongest toughness and the best ability to resist dry and wet deformation. With the increase of the number of dry-wet cycles, the mass loss rate of the sample is in the range of 6 similar to 7 %, and the unconfined compressive properties and tensile properties decrease first and then increase. There are continuous hydration reactions and pozzolanic reactions in the soil, but the degree of physical damage in the early stage of the dry-wet cycle is large, and the later cementitious products have a certain offsetting effect on the structural damage. The internal cracks of the sample without dry-wet cycle are less and the structure is dense. After the dry-wet cycle, the microstructure of the sample changed greatly, and the cracks increased and showed different forms. Through SEM image analysis, it was found that the pore structure of the sample changed during the dry-wet cycle, which corresponded to the change law of mechanical properties. After wetting-drying cycles, the leaching concentration of heavy metals in the modified soil increased slightly, but the overall concentration value was low, which was not a toxic substance and could be used as a roadbed material. The study reveals the influence of dry-wet cycle on the strength characteristics and microstructure of red mud, lime and fly ash synergistically improved silty sand, which provides a technical reference for the engineering application of red mud-based materials.

Foundation soil treatment is a common method used to enhance soil strength in civil engineering, particularly in cold regions where ambient temperatures significantly affect soil mechanical properties. This study investigates the utilization of cement and municipal solid waste incinerator bottom ash (MSWIBA) for stabilizing silty clay under low-temperature curing conditions. Some experiments were performed to investigate the mechanical properties of cement-stabilized silty clay, varying the dosage of bottom ash (BA) and different curing temperatures. The influences of BA dosage, curing temperature and age on the shear and compressive strengths of soils were tested and analyzed. Results demonstrated that the shear strength was influenced by the comprehensive interactions among BA particles, soil particles, and ice crystals. Regardless of curing temperature and age, the shear strength of soil specimen firstly increased and then declined with BA dosage raised, with an optimal BA content range from 20 % to 30 %. Specifically, the 28-d shear strength enhancements of 2.46 %, 15.52 %, 20.20 %, and 11.33 % were observed with each successive 10 % BA addition for soil samples at 10 degrees C curing condition. Curing temperature significantly influenced shear strength, with higher temperatures promoting greater strength due to increased hydration reaction rates. Besides, the cohesion and internal friction angle of samples increased with BA dosage. Furthermore, the axial stress-strain curves illustrated a three-stage process, i.e., initial pore compression, plastic deformation, and decay stages. The compressive strength raised with both the BA dosage and curing age, with positive curing temperatures yielding higher strengths compared to sub-zero temperatures. This study elucidates the complicated mechanical behavior of BA-cement stabilizing silty clay, providing valuable insights into their performance under different curing conditions, and offering an innovative approach for foundation engineering applications in cold regions.

The interface between geotextile and geomaterials plays a crucial role in the performance of various geotechnical structures. Soil-geotextile interfaces often suffer reduced performance under environmental stressors such as rainfall and cyclic loading, limiting the reliability of geotechnical structures. This study examines the influence of gravel content (Gc), compaction degree (Cd), and rainfall duration (Rd) on the mobilized shear strength at the silty clay-gravel mixture (SCGM)- geotextile interface through a comprehensive series of direct shear tests under both static and cyclic loadings. A novel approach using Polyurethane Foam Adhesive (PFA) injection is introduced to enhance the interface behavior. The results reveal that increasing Gc from 0 % to 70 % leads to a 35-70 % improvement in mobilized shear strength and friction angle, while cohesion decreases by 15 %-60 %, depending on Cd. A higher Cd further boosts shear strength by 6 %- 70 %, influenced by Gc and normal stress levels. Under cyclic loading, increasing displacement amplitude reduces shear stiffness (K), while having minimal impact on the damping ratio (D); K and D appear unaffected by the number of cycles in non-injected samples. Rainfall reduces mobilized shear strength by 8 %-25 %, depending on the normal stress, with a 47 % drop in friction angle and a 24 % increase in cohesion after 120 minutes of rainfall exposure. In contrast, PFA-injected samples exhibit a marked increase in mobilized shear strength under both dry and wet conditions, primarily attributed to enhanced cohesion. Notably, PFA treatment proves particularly effective in maintaining higher shear strength and stiffness in rainfall-affected interfaces, demonstrating its potential in improving geotextile-soil interaction under challenging environmental conditions.

The large amount of slag generated during the construction of earth pressure balance shield (EPBS) not only incurs significant disposal costs, but also exacerbates environmental pollution. To improve the utilization of the shield slag, silty clay with additive is proposed as a slag conditioner instead of bentonite. Firstly, various macroscopic properties of the bentonite and silty clay slurries are tested. Subsequently, the relationships between the macroscopic properties of the silty clay slurries containing additives and the modification mechanism are evaluated at microscopic, mesoscopic, and macroscopic scales by using infrared spectroscopy (IR), scanning electron microscope (SEM), and Zeta potential tests, respectively. Based on these tests, reasons for variations in modification effects of different slurries are identified. The results show that addition of 3 % sodium carbonate to the silty clay can effectively improve the rheological properties of the slurry. The modification mechanism of sodium carbonate involves the formation of hydrogen bonds between water molecules and inner surface hydroxyl groups within the lattice layer of kaolinite. This process significantly enhances the rheological properties of the silty clay slurry. Furthermore, sodium carbonate alters the contact relationships between the silty clay particles, which increases viscosity and reduces permeability of the slurry. Finally, sodium carbonate increases thickness of the electrical double layer of the silty clay particles. This allows the particles to bind more water molecules, therefore improving slurry-making capacity of the silty clay. This paper presents an innovative multiscale analysis of the modification process of silty clay. The substitution of recycled silty clay for bentonite as a slag conditioner not only substantially reduces the cost of purchasing materials, but also considerably decreases the expenses associated with transportation and disposal of the soil discharged by EPBS.

A novel approach to enhance wellbore stability was put forth, based on the wellbore rock properties and instability mechanism of the hydrate reservoir, given the issue of wellbore instability when using water-based drilling fluids (WBDFs) in drilling operations, in weakly cemented muddy fine silt reservoirs of natural gas hydrates in the South China Sea. Three main strategies were used to increase the stability of reservoirs: enhancing the underwater connection between sandstone particles and clay minerals, preventing clay hydration from spreading and expanding, and strengthening the stability of hydration skeleton structure. An appropriate drilling fluid system was built with soil phase containing wellbore stabilizer. Sulfonic acid groups and electrostatic interaction were introduced based on the characteristics of underwater adhesion of mussels. Through the process of free radical polymerization, a zwitterionic polymer containing catechol groups named DAAT was prepared for application in natural gas hydrate reservoir drilling. DAAT is composed of tannic acid (TA), dimethyl diallyl chloride ammonium chloride (DMDAAC), 2-acrylamide-2-methylpropanesulfonic acid (AMPS) and acrylamide (AM). Experimental results from mechanical property testing reveal an adhesion force of up to 4206 nN between SiO2 and 5 wt % DAAT, demonstrating its ability to bind quartz sand particles effectively. The compressive strength and cohesion of the cores treated with DAAT increased by 58.33 wt % and 53.26 wt %, respectively, at -10 degrees C, compared with pure ice particle cores. This demonstrates DAAT can significantly enhance the compressive strength and cohesion of the core. Furthermore, the adhesion force between DAAT and hydrate particles reaches up to 344.4 mN/m, significantly improving the structural stability between hydrate particles. It demonstrates excellent adhesive properties to hydrate particles. In addition to adsorbing clay minerals, rocks, and hydrate particles, DAAT also forms hydrogen bonds with argillaceous fine silt particles with its low temperature cohesiveness characteristic. As a result, it improves the cohesion between core particles, and enhances the adhesion between hydrates and rocks, thereby enhancing the stability of hydrate reservoirs. In summary, DAAT is characterized by a simple preparation process, cost-effectiveness, and environmental friendliness. It is an innovative and practical material for enhancing wellbore stability in WBDFs for natural gas hydrate exploration in the South China Sea.

This study investigates the mechanical performance and deformation characteristics of reinforced retaining walls constructed with stabilized silty clay and geogrid reinforcement. Laboratory tests evaluated the physical and mechanical properties of native silty clay, identifying its high water content and poor gradation as primary challenges for engineering applications. A stabilization method incorporating 2 % soil stabilizing liquid, 10 % densifying powder, and 4 % Portland cement was optimized to enhance clay compaction, shear strength, and compressive strength. Model experiments were conducted under varying wall configurations, including natural slopes, stabilized retaining walls, and reinforced stabilized walls with different slope ratios. Results show that the combination of stabilization and reinforcement significantly improved load-bearing capacity, minimized vertical settlement, restricted horizontal displacement, and reduced lateral earth pressure. Comparative analysis of slope ratios revealed that gentler slopes enhanced deformation resistance and reduced geogrid strain. These findings offer practical insights and theoretical support for designing efficient retaining wall systems using stabilized silty clay.