Freeze-thaw (FT) cycles significantly affect soil permeability and could cause geological and environmental disasters. This study investigated the influence of FT cycles on the permeability of compacted clay through triaxial permeability tests, considering freezing temperature, cycle number, water content, and confining pressure. Scanning electron microscopy and nuclear magnetic resonance tests were performed to analyze the microstructure and pore characteristics of the clay during FT cycles. The results show that the hydraulic conductivity of the clay decreases significantly at high confining pressures due to soil consolidation. When the confining pressure exceeds 150 kPa, the impact of FT cycles on hydraulic conductivity becomes negligible. The increased number of FT cycles, exposure to lower freezing temperatures, and higher water content lead to more pronounced soil structure damage, resulting in a substantial increase in hydraulic conductivity. FT cycles cause macropores and microcracks to form and increase the average pore radius, creating preferential seepage pathways. Correlation analysis indicates that the increase in macropore content under various FT cycles is the primary reason for the increased hydraulic conductivity. Based on the modified Kozeny-Carman equation, a prediction model is developed to effectively estimate the hydraulic conductivity. These results provide valuable insight into the damage mechanism of clay permeability in seasonally frozen regions from a microscale perspective.

Expanded Polystyrene (EPS) granular lightweight soil (ELS) is an eco-friendly material made of EPS particles, cement, soil, and water. This study investigates the modification of ELS using a silane coupling agent (SCA) solution to improve its performance. Various tests were performed, including flowability, dry shrinkage, unconfined compressive strength (UCS), triaxial, hollow torsional shear, and scanning electron microscopy (SEM) analysis, to evaluate the physical and mechanical properties at different SCA concentrations. The results show that the optimal SCA concentration was 6%, improving flowability by 13% and increasing dry shrinkage weight by 4%. The UCS increased with SCA concentration, reaching 266 and 361 kPa after 7 and 28 days, respectively, at 6% SCA. Triaxial and shear tests indicated improved shear strength, with the maximum shear strength reaching 500 kPa, internal friction angle rising by 4%, and cohesion reaching 114 kPa at 6% SCA. Hollow torsion shear tests showed that 6% SCA enhanced stiffness and resistance to deformation, while reducing the non-coaxial effect. SEM analysis revealed that SCA strengthened the bond between EPS particles and the cement matrix, improving the interfacial bond. This study highlights the potential of modified ELS for sustainable construction.

Groundwater is widely distributed in various rock and soil media and underground structures. Groundwater seepage inside the silty-fine sand layer causes infiltration erosion, leading to uneven settlement and cracking damage to the foundation and its structures. An analysis was conducted on the mechanisms of flowing soil and piping, and it was pointed out that flowing soil is caused by the effective gravity of sand particles, resulting in the floating and failure of sand particle groups due to the permeability greater than that of sand particles; Pipe surge refers to the migration and loss of movable fine particles, and the formation of water inflow channels through the interior of the silty-fine sand layer. Propose technical measures to improve the physical and mechanical properties of silty-fine sand layers and prevent infiltration damage through grouting. The mechanism of infiltration, splitting and compaction grouting was explained and analyzed, and the grouting materials such as plant glue modified cement sodium silicate, geopolymer, microbial solution, nano silica sol, emulsified asphalt, polyurethane, etc. were discussed and sorted out, aiming to contribute to improving the quality of silty-fine sand layer engineering projects.

As one of the world's most fragile and sensitive ecological regions, Xizang risks significant environmental damage from using traditional materials, including cement and lime, to improve and reinforce loose accumulated sandy soil slopes. To address this issue, this study utilized a low-concentration biodegradable polyvinyl alcohol (PVA) solution combined with sisal fibers (SFs) to stabilize loose accumulated sand in southeastern Xizang. A series of physical, mechanical, and microscopic analyses was conducted to evaluate the properties of the treated sand. The results indicated the following. 1) The stress-strain curves of the improved samples exhibited an elastic-plastic relationship. Failure was observed in two stages. At a strain of 3% or less, the samples demonstrated elastic deformation with a linear increase in stress, whereas the deviator stress increased rapidly and linearly with an increase in axial strain. Once the strain exceeded 3%, the deformation became plastic with a nonlinear increase in the stress-strain relationship, and the growth rate of the deviator stress gradually decreased and leveled off. 2) Under varying confining pressure conditions, the relationship curve between the maximum (sigma 1-sigma 3)max similar to sigma 3 for both untreated loose accumulated sandy soil and soil improved with the PVA solution, and the sisal fiber was approximately linear. 3) The SFs created a skeletal-like network that encased the soil particles, and the hydroxyl functional groups in the PVA molecules bonded with both the soil particles and the fiber surface, thereby enhancing the interfacial properties. This interaction resulted in a tighter connection between the soil particles and SFs, which improved the stability of the structure. 4) The incorporation of a PVA solution and SFs significantly enhanced the mechanical strength and deformation resistance of the loose accumulated sandy soil. The optimal ratio for the improved soil was SP = 3% and SL = 15 mm, which increased the cohesion from 24.54 kPa in untreated loose accumulated sandy soil to 196.03 kPa. These findings could be applied in engineering practices to improve and reinforce loose accumulated sandy soil slopes in southeastern Xizang and provide a theoretical basis for such applications.

In cold and arid saline areas, the mechanical properties of soils are usually significantly affected by some complicated conditions, especially the coupled effects of the freeze-thaw-dry-wet (F-T-D-W) cycles and soil salinization. This study experimentally investigated the effect of F-T-D-W cycles on the shear performances and microstructures of silty clay that was salinized during wetting processes. Three types of soil samples with different dry densities were designed: (1) silty clay samples without salt (Category I); (2) silty clay samples with salt (Category II); and (3) silty clay samples that were salinized during wetting processes (Category III). Direct shear and scanning electron microscopy (SEM) tests were carried out, the variations in the shear strength, surface deterioration, and shear parameters (e.g., cohesion and internal friction angle) were analyzed, and the degradation mechanism was revealed. The results show that the F-T-D-W cycles and soil salinization significantly affect the shear strength of soils, especially for the samples with low dry densities. The shear strengths of soil samples with and without salt (Categories I and II) decrease as the F-T-D-W cycles increase. Besides, the cohesion of soil samples increases with dry density and declines with the F-T-D-W cycles due to the appearance of cracks and bond failure among soil particles. In addition, there is a threshold number of F-T-D-W cycles to significantly reduce the cohesion of soil samples, and the threshold numbers for soil samples Categories I and II are six and three, respectively. The repeated expansion and shrinking of soils accelerate the damage to the soil structure, which results in a decrease in cohesion and interparticle force. However, when the concentration of salt solution in soils exceeds the saturation concentration, a new denser soil skeleton is formed by the soil particles and surrounding salt crystals, which improves the shear strength of the soil samples. This study could provide deep insights into the shear performance and microstructures of silty clay exposed to F-T-D-W cycles. (c) 2024 American Society of Civil Engineers.

Natural loess has poor engineering properties because of its own loose and porous nature. To meet the needs of engineering construction, this study attempted to add silica micro powder mixed with cement into loess to improve its mechanical properties. The direct shear test, triaxial shear test, and scanning electron microscope (SEM) test were used to evaluate the strength characteristics and micropore structure modifications of silica micro powder and cement stabilized loess. The results showed that the addition of silica micro powder alone increased the shear strength of loess, while when silica micro powder was mixed with cement, the improvement in strength increased significantly. 3% cement with 10% silica micro powder is the optimum content to stabilize loess. The shear strength of the stabilized loess for 28 days under 200 kPa confining pressure was 2255 kPa, which was 34.9% higher than that of plain loess. Under the same cement content, the cohesion of loess increased with the increase of silica micro powder content, and the internal friction angle increased first and then decreased. The increase in curing age and the decrease in water content were positively correlated with shear strength, and the prediction formula of shear strength parameters of stabilized loess is established. In the SEM test, through qualitative analysis, it is found that the unreacted silica powder mainly physically filled the pores of loess, while the reacted silica micro powder and cement mainly combine with hydration products, which together enhanced the compactness of loess. From the quantitative analysis, it can be seen that with the addition of silica micro powder and cement, the macropores and mesopores between loess particles are transformed into small pores and micropores, the orientation of pores is enhanced, and the loess structure becomes more compact, which further revealed the mechanism of silica micro powder combined with cement to stabilize loess. The results of this study demonstrate that silica micro powder mixed with cement can effectively improve the mechanical properties of natural loess, providing a promising approach for reinforcing loess in engineering applications.

Bolts play a critical role in landslide disaster prevention and control as an effective slope reinforcement method. Generally, the Poisson's ratio bolt (PR bolt) has a limited effect in controlling large slope deformations, and the negative Poisson's ratio bolt (NPR bolt) has a high constant resistance and adapts to large deformations, which can partially solve the problem of large slope deformations. Static tensile tests were conducted to compare the mechanical properties of PR and NPR bolts. A large-scale field test was conducted to study the differences between the effects of PR and NPR bolts on the soil slope reinforcement. Terrestrial laser scanning was used to monitor the slope damage process and establish a high-precision digital displacement model to reveal the slope deformation evolution law and failure mechanism. In addition, the bolt reinforcement mechanism was analyzed based on data such as soil pressure and axial force. The NPR bolt effectively blocked the transmission of the slope top load, strengthened the internal stress regulation ability of the slope, and prolonged the damage time of the slope. The results provide notable information on the mechanism, macro-mechanical properties, and field engineering applications of NPR bolts.

RegCM4.3, a high-resolution regional climate model, which includes five kinds of aerosols (dust, sea salt, sulfate, black carbon and organic carbon), is employed to simulate the East Asian summer monsoon (EASM) from 1995 to 2010 and the simulation data are used to study the possible impact of natural and anthropogenic aerosols on EASM. The results show that the regional climate model can well simulate the EASM and the spatial and temporal distribution of aerosols. The EASM index is reduced by about 5% by the natural and anthropogenic aerosols and the monsoon onset time is also delayed by about a pentad except for Southeast China. The aerosols heat the middle atmosphere through absorbing solar radiation and the air column expands in Southeast China and its offshore areas. As a result, the geopotential height decreases and a cyclonic circulation anomaly is generated in the lower atmosphere. Northerly wind located in the west of cyclonic circulation weakens the low-level southerly wind in the EASM region. Negative surface radiative forcing due to aerosols causes downward motion and an indirect meridional circulation is formed with the low-level northerly wind and high-level southerly wind anomaly in the north of 25 degrees N in the monsoon area, which weakens the vertical circulation of EASM. The summer precipitation of the monsoon region is significantly reduced, especially in North and Southwest China where the value of moisture flux divergence increases.