To investigate the coupled time effects of root reinforcement and wet-dry deterioration in herbaceous plant-loess composites, as well as their microscopic mechanisms, this study focused on alfalfa root-loess composites at different growth stages cultivated under controlled conditions. The research included measuring root morphological parameters, conducting wet-dry cycling tests, and performing triaxial compression tests and microscopic analyses (CT scanning and nuclear magnetic resonance) on both bare loess and root-loess composites under various wet-dry cycling conditions. By obtaining shear strength parameters and microstructural indices, the study analyzed the temporal evolution of the shear strength and microstructural characteristics of root-loess composites under wet-dry cycling. The findings indicated that the alfalfa root-loess composite effective cohesion was significantly higher than that of the plain soil in the same growth stage. The alfalfa root-loess composite effective cohesion increased during the growth stage in the same dry-wet cycles. The alfalfa root-loess composite effective cohesion in the same growth stage was negatively correlated with the number of dry-wet cycles. The fatigue damage of the soil's microstructure (pore coarsening, cement hydrolysis, and crack development) increased continuously with the number of dry-wet cycles. However, due to the difference in mechanical properties between roots and the soil, the root-soil composite prevented the deterioration of the soil matrix strength by the dry-wet cycles. As the herbaceous plants grow, the time effect observed in the shear strength of the root-soil composite under the action of dry-wet cycles is the result of the interaction and dynamic coordination between the soil-stabilizing function of the herbaceous plant roots and the deterioration caused by drywet cycles.

A set of direct shear tests on the soil-geotextile interface (SGI) were conducted using a temperature-controlled constant normal stiffness (CNS) direct shear apparatus. This was done in order to evaluate the effects of normal stiffness, initial normal stress, soil water content, and temperature on SGI shear behavior and microdeformation patterns. The observations indicate that all shear stress-shear displacement curves demonstrate strain-hardening characteristics, with SGI cohesion and friction angle increasing at higher normal stiffness and lower temperatures. At freezing conditions, water content significantly affects the interface friction angle, while this effect is minimal at positive temperatures. Normal stress increases with higher water content, lower temperatures, and higher normal stiffness. Shear stress initially rises with normal stress before decreases, with a more pronounced rise under sub-zero conditions. Normal stress shrinkage shows a positive correlation with normal stiffness. Micro-deformation analysis of soil particles at the interface indicates significant strain localization within the shear band, which is less pronounced under sub-zero temperatures compared to positive temperatures. These patterns of normal displacement vary across analysis points within the shear band, with the macroscopic normal displacement reflecting a cumulative effect of these microscopic variations.

Malan loess is widely distributed on the Chinese Loess Plateau and poses great challenges to geotechnical, ecological, and agricultural practices due to its unique structure and collapsibility. It is essential to understand the evolution of these properties with depth to assess soil stability and reduce engineering risks in the area. This study investigates the mechanical properties and microstructural evolution of Malan loess with depth and employs multivariate statistical methods to explore their complex interrelationships. Oedometer-collapse tests reveal a 94.2 % reduction in collapsibility coefficient (delta s) from 0.0722 at 1 m to 0.0042 at 9 m, indicating a significant reduction in collapsibility with increasing depth. According to the results of the direct shear test, it showed that the shear strength initially decreases and then increases due to the combined effect of the water content and dry density. Scanning electron microscopy (SEM) images reveal the densification of the loess structure, with changes in particle contact from point to face contact and the evolution from macropores to mesopores and small pores as depth increases. Quantitative analysis by Avzio showed a decrease of 61.5 % in macropores area and an increase of 62.5 % in small pores area. The results obtained by Pearson's correlation analysis and random forest model showed that among these microstructural characteristics, the total pore area (%IncMSE = 22.77 %) is the most important factor influencing the collapsibility properties of loess and water content (%IncMSE = 17.72 %) acts a key role in controlling shear strength. Additionally, compared to traditional methods, the random forest model offers a more insightful understanding of nonlinear relationships and multifactorial coupling effects. These findings provide scientific guidance for geotechnical engineering in loess regions, aiding in risk mitigation and promoting sustainable construction.

Granite residual soils (GRS) are often encountered in geotechnical projects in the Guangdong-Hong Kong-Macao Greater Bay Area (briefly written as the Greater Bay Area, or abbreviated as GBA). The rea experiences frequent rainfall, leading to wetting-drying cycles that progressively diminish the shear strength of GRS. This weakening effect is not only significant but also accumulates, exhibiting a direct positive correlation with the number of cycles. Current studies on the soil strength attenuation due to wetting-drying cycles are typically limited to no more than 10 cycles, which is rather insufficient to uncover the long-term water-weakening behaviors and their accumulative impacts on GRS. To address this gap, typical GRS samples were first taken from the GBA and then prepared by making them go through a certain number of wetting-drying cycles (maximum of up to 100). Next, a total of 552 small- and large-scale direct shear tests were conducted to investigate the mechanisms of water-weakening effects on soil internal friction angle, cohesion, and shear strength. The degree of saturation and number of cycles were also examined to see their effects on the cumulation of water weakening. Based on results from the small-scale direct shear tests, a model was developed for assessing the weakening impact of water on soil strength. The accuracy of the model prediction was statistically evaluated. Last, the effectiveness and efficiency of the proposed model were demonstrated by validating against the results from the large-scale direct shear tests.

Macro- and micromechanical interactions between the geogrid and granular aggregates considering particle shape effects are essential for the performance of reinforced soil structures under cyclic normal loading (CNL). Crushed limestone and spherical granular media were mixed to obtain samples with different overall regularities (OR = 0.707, 0.774, 0.841, 0.908, and 0.975). Direct shear tests under CNL were conducted at various overall regularities, normal loading frequencies, and waveforms. Consistent with experiment tests, a discrete-element method (DEM) simulation was performed, incorporating authentic particle shapes obtained through three-dimensional (3D) scanning technology. The results showed that the macroscopic interface shear strength and volume change decreased with an increase in the overall regularity and normal loading frequency. The interface shear strength and deformation under the square waveform are bound to be higher than that under other waveforms. The coordination number, porosity, and fabric anisotropy were used to explain the macroscopic interface shear behavior in relation to the overall regularity. A higher coordination number and stronger contact force were observed with a decrease in the overall regularity. As the overall regularity decreased, the interface integrity and stability became stronger, with the result that the reinforced soil structure can withstand a larger principal stress deflection. Through experimental and DEM analyses, the underlying explanation for the effect of particle shape on the mechanical interaction of reinforced soil was revealed.

Climate change increases the frequency of extreme weather events, intensifying shallow flow-type landslides, soil erosion in mountainous regions, and slope failures in coastal areas. Vegetation and biopolymers are explored for ecological slope protection; however, these approaches often face limitations such as extended growth cycles and inconsistent reinforcement. This study investigates the potential of filamentous fungi and wheat bran for stabilizing loose sand. Triaxial shear tests, disintegration tests, and leachate analyses are conducted to evaluate the mechanical performance, durability, and environmental safety of fungus-treated sand. Results show that the mycelium enhances soil strength, reduces deformation, and lowers excess pore water pressure, with a more pronounced effect under undrained than drained conditions. Mycelium adheres to particle surfaces, forming a durable bond that increases cohesion and shifts the slope of the critical state line, significantly enhancing the mechanical stability of fungus-treated sand. The resulting strength parameters are comparable to those of soils reinforced with plant roots. Fungus-treated sand remains stable after 14 days of water immersion following triaxial shear tests, with no environmental risk from leachate. These findings demonstrated that fungal mycelium provides an effective and eco-friendly solution for stabilizing loose sand, mitigating shallow landslides, and reinforcing coastlines.

The treatment of soil with biopolymers has demonstrated various benefits, including strength enhancement, reduction in the permeability coefficient, and promotion of vegetation. Consequently, numerous experiments have been conducted to evaluate the strength of biopolymer-treated soils. This study aims to evaluate the interparticle bonding strength attributed to the biopolymer network formed between soil particles, focusing on the strength characteristics at the particle scale. Agar gum, a thermo-gelling biopolymer, was selected to assess the strength of biopolymer solutions. Experiments were conducted at concentrations of 2 %, 4 %, and 6 % with varying drying times to account for the differences in water content. The bonding, tensile, and shear strengths of the agar gum polymer solutions were evaluated under different loading conditions. To compare the strengths and meaningful trends observed in the agar gum polymer solution under different conditions. The results demonstrated that for all strength conditions involving the agar gum solution, the strength increased with higher concentrations and lower water content. During the particle size test, the bonding strength was improved up to 160 kPa, and the tensile strength of the agar gum polymer itself was observed to be up to 351 kPa. Furthermore, the UCS test results of the silica sand mixed with agar gum showed an improvement up to 1419 kPa. Among the evaluated strengths, the tensile strength was the highest, whereas the shear strength was the lowest. A comparison between the adhesive strength tests, which evaluated the strength characteristics at the soil particle scale, and the UCS of silica sand mixed with an agar gum solution revealed a similar trend. The shear strength increased consistently with drying time across all concentration conditions, which was consistent with the trends observed in the UCS. These findings suggest that the strength characteristics of soils treated with agar gum solutions can be effectively predicted and utilized for ground improvement applications.

Numerous loess relic sites with cultural and historical values exist in the seasonally frozen ground region of Northwest China. Freeze-thaw action is an essential factor in inducing cracking and collapse of loess relic sites, and the creep behavior of loess also affects its long-term stability. Microbially induced calcium carbonate precipitation (MICP) technology has a promising application in earthen ruin reinforcement due to its environmental friendliness and good compatibility. To evaluate the feasibility of MICP technology for reinforcing loess relic sites in the seasonally frozen ground, triaxial compression tests, triaxial creep tests, and SEM tests were conducted on MICP modified loess after 0, 1, 3, 7, and 9 freeze-thaw cycles. Then, the changing laws of shear strength and creep properties of samples in the freeze-thaw conditions were analyzed. The results show that the MICP technology can enhance the mechanical properties and frost resistance of loess. The shear strength, cohesion, and long-term strength of MICP modified loess are enhanced by 27.8 %, 109 %, and 29.8 %, respectively, under 100 kPa confining pressure, and their reduction is smaller than that of the untreated loess after 9 freeze-thaw cycles; the internal friction angle fluctuates within 1 degrees. Finally, the reinforcement mechanism and freeze-thaw resistance mechanism of MICP technology were revealed. Microbially induced calcium carbonate can cement soil particles, fill interparticle pores, and inhibit the development of pores and cracks caused by freeze-thaw action. The results can provide a theoretical foundation and scientific basis for the long-term stability analysis of loess relic sites reinforced with MICP technology.

In this study, laboratory aging experiments are conducted to examine the aging effect on the interface shear behavior between soil and geomembrane. In the first stage, the geotechnical index and shear strength parameters of the soils are determined through laboratory experiments. The second stage focuses on examining the shear strength behavior of soil-geomembrane interfaces. The study examines commonly used geomembranes in the world, such as high-density polyethylene and thermoplastic polyolefin. Different synthetic waste leachates prepared in laboratory conditions are used to simulate real field conditions. The aging effects of geomembranes are examined by subjecting them to different pore liquids in the curing pool for 16 months. The surface deformations and roughness of the geomembranes used in the experiments are analyzed using scanning electron microscopy and optical profilometer. The study evaluates the effects of soil properties, pore liquids, and aging on the geomembrane surfaces. Soils with more coarser grains exhibited higher interface friction angles. It has been determined that the interface friction angles were significantly adversely affected by all curing liquids. Acidic mine drainage was found to have the most detrimental effect on the interface friction angles of geomembranes, while coal combustion product leachate caused minimal damage. The results from optical profilometer and scanning electron microscopy analysis aligned with the interface direct shear test results, further supporting the findings from the experiments. The study has shown that the design interface friction resistances are not sufficient for geomembranes exposed to chemicals in the long term. This aspect should be taken into consideration when creating design parameters.

Soil-rock mixtures (SRM) from mine overburden form heterogeneous dump slopes, whose stability relies on their shear strength properties. This study investigates the shear strength properties and deformation characteristics of SRM in both in-situ and laboratory conditions. Total twelve in-situ tests were conducted on SRM samples with a newly developed large scale direct shear apparatus (60 cm x 60 cm x 30 cm). The in-situ moist density and moisture content of SRM are determined. Particle size distribution is performed to characterize the SRM in laboratory. The bottom bench has the highest cohesion (64 kPa) due to high compaction over time while the other benches have consistent cohesion values (25 kPa to33 kPa). The laboratory estimated cohesion values are high compared to in-situ condition. It is further observed that for in-situ samples, the moist density notably affects the cohesion of SRM, with cohesion decreasing by 3 to 5 % for every 1 % increase in moist density. At in-situ condition, internal friction angles are found to be 1.5 to 1.7 times compared to laboratory values which is due to the presence of the bigger sized particles in the SRM. The outcomes of the research are very informative and useful for geotechnical engineers for slope designing and numerical modeling purpose.