Expansive soil, characterized by significant swelling-shrinkage behavior, is prone to cracking under wet-dry cycles, severely compromising engineering stability. This study combines experimental and molecular dynamics (MD) simulation approaches to systematically investigate the improvement effects and micromechanisms of polyvinyl alcohol (PVA) on expansive soil. First, direct shear tests were conducted to analyze the effects of PVA content (0 %-4 %) and moisture content (30 %-50 %) on the shear strength, cohesive force, and internal friction angle of modified soil. Results show that PVA significantly enhances soil cohesive force, with optimal improvement achieved at 3 % PVA content. Second, wet-dry cycle experiments revealed that PVA effectively suppresses crack propagation by improving tensile strength and water retention. Finally, molecular dynamics simulations uncovered the distribution of PVA between montmorillonite (MMT) layers and its influence on interfacial friction behavior. The simulations demonstrated that PVA forms hydrogen bonding networks, enhancing interlayer interactions and frictional resistance. The improved mechanical performance of PVAmodified soil is attributed to both nanoscale bonding effects and macroscale structural reinforcement. This study provides theoretical insights and technical support for expansive soil stabilization.

Soil-rock mixtures are composed of a complex heterogeneous medium, and its mechanical properties and mechanism of failure are intermediate between those of soil and rock, which are difficult to determine. To consider the influence of different particle groups on soil-rock mixture's shear strengths, based on the mesomotion properties of the particles of different particle groups when the soil-rock mixture is deformed, it is classified into two-phase composites, matrix and rock mass. In this paper, based on the representative volume element model of soil-rock mixtures and the Eshelby-Mori-Tanaka equivalent contained mean stress principle, a model of shear constitutive of the accumulation considering the mesoscopic characteristics of the rock is established, the influence of different factors on the shear strength of the accumulation is investigated, and the mesoscopic strengthening mechanism of the rock on the shear strength of the accumulation is discussed. The results show that there is a positive correlation between the rock content, the surface roughness of the rock, the stress concentration coefficient, coefficient of average shear displacement, and the accumulation's shear strength. When the accumulation is deformed, it stores or releases additional energy than the pure soil material, so it shows an increase in deformation resistance and shear strength on a macroscopic scale.

Due to the detrimental ecological impacts and the exorbitant expenses associated with the cement industry, researchers have sought to find natural, sustainable, low-carbon alternatives to Portland cement for weak soil stabilization. This research used geopolymer based on metakaolin (MK), a natural pozzolanic material with different activator concentrations (NaOH and Na2SiO3), to stabilize loose poorly graded sand soils. The research investigated the effect of different amounts of addition MK (5, 10, and 15 %) on the soil's mechanical properties. Furthermore, the effect of parameters such as the type and concentration of the alkaline solution and curing time (1, 3, and 7 days) on the unconfined compressive strength, failure strain, Young's modulus, California bearing ratio, and direct shear test were evaluated. This research also aims to measure the sub- grade reaction modulus (Ks) by developing and manufacturing a laboratory testing apparatus and steel mold to simulate the natural conditions of sandy subgrade soil obtained from performing nonrepetitive static plate load tests. Additionally, scanning electron microscopy images (SEM) and X-ray diffraction analysis (XRD) were also used to study the microstructural changes and the chemical composition of the stabilized soil samples. The results indicate that the soil samples that were stabilized with MK 10 % and NaOH had notably higher compressive strength (2936 kPa), indicating a denser and less porous structure (improved stiffness stabilized soil) in comparison to the soil samples stabilized with MK 10 % and Na2SiO3 which was (447 kPa). Ultimately, Microstructural analysis showed that, due to the addition of 10 % MK, stabilized soils have a denser and more homogeneous structure.

The service performance of frozen soil is one of the important factors that needs to be considered in designing and assessing the safety of artificial ground freezing projects. We conducted shear tests on ice-containing frozen soil and assessed soil performance and damage characteristics of the ice-frozen soil interface. On the basis of experimental results, we further investigated the damage of ice-containing frozen soil numerically using the finite-discrete element method. Experimental and numerical results show that temperature, the normal load, and moisture content are the primary factors influencing the mechanical properties of the ice-frozen soil interface. The effects of these parameters on shear strength, shear modulus, cohesion, and angle of internal friction were analyzed and discussed. There was a transition from ductile to brittle behavior at the ice-frozen soil interface with decreasing temperature. Transition occurred at higher temperatures in soils with higher moisture content. Because ice and sand differ in terms of stiffness, fractures appeared first at the ice-frozen sand interface. Under continued loading, the specific form of damage and maximum load-bearing capacity varied as a function of the location of the maximum shear stress zone and the ice in the soil. Our research findings provide valuable theoretical insights for the design and evaluation of the safety of artificial ground freezing engineering projects.

Roots can mechanically reinforce soils against landslides, but the impact of their typically random and complex distribution on this reinforcement is not well understood. Here, using a modelling approach based on homogenization theory, we aim to assess the effect of the randomness and complexity of root spatial distribution in soils on the mechanical properties of the soil-root composite and the resulting reinforcement. To do this, we modeled the soil-root composite as a three-dimensional (3D) soil column through which parallel roots penetrate vertically. The unit cell (UC) of the soil-root composites with a nonuniform root distribution was created based on the characteristics of root diameter distributions of Elymus dahuricus measured in the field, and the equivalent elastic modulus and strength parameters of the composites were calculated. The accuracy of the homogenization method was verified by direct shear tests with undisturbed soil-root samples. The results showed that the UC model of the soil-root composites could effectively predict its equivalent elastic parameters. A parametric analysis using the proposed homogenization model showed that roots can mobilize significant soil portions to resist deformation by increasing both the number and complexity of root distributions, even at the same root volume ratio. This makes the stress distribution in the soil more uniform and improves the shear strength of the soil-root composites. The presence of Elymus dahuricus roots significantly improved the shear strength of the soil-root composites, primarily due to an increase in cohesion of 23%. This study presents a new perspective on the development of a constitutive model for soil-root composites and highlights its potential value for engineering applications that use roots to reinforce soils.

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.

The shear stress-shear displacement relationship and shear strength parameters at the pipe-soil interface are crucial for calculating jacking force. To investigate these properties, a series of tests were performed using a large-scale direct shear device to examine the shear mechanics of the steel-sand interface under various conditions. The effects of particle size, normal stress, and slurry concentration on shear performance were analyzed macroscopically. Additionally, the evolution of interface micro-behavior was studied using discrete element software PFC 2D. The experimental results indicate that the particle size of the sand has a significant impact on the shear stress-shear displacement curve of the interface, with smaller particle sizes requiring greater shear stress to achieve stability during shear. The strain-softening degree of sand is affected by normal stress. The shear stress-shear displacement curve is more significantly affected by particle size with the increase of normal stress. By considering different slurry concentrations, it is observed that both the shear stress and the sliding friction coefficient reached a minimum value at a concentration of 14%. The numerical simulation results indicate that particle motion causes changes in the distribution of particle structures. The distribution of particle force chains is relatively dispersed before shear. Particles move vigorously toward the shear interface, and force chains primarily concentrate on the shear interface during shear. Shear stress is transmitted through particle movement, and particle displacement causes shear dilation within the contact zone. Particles essentially cease moving toward the shear interface, and the force chains no longer change once the shear band is formed.

This study explores a novel stabilization technique combining Persian gum (PG), an eco-friendly biopolymer, and glass fiber (GF) to enhance the strength and durability of fine-grained soils under freeze-thaw (F-T) cycles. Specimens were prepared at maximum dry density (MDD) with varying PG and GF contents, cured for 0, 7, or 14 days, and subjected to 0, 5, 7, or 10 F-T cycles. Tests included Standard Proctor compaction, Scanning Electron Microscopy (SEM), Unconfined Compressive Strength (UCS), and Direct Shear (DS). Results demonstrated that GF significantly improved durability, ductility, and strength by enhancing interparticle interaction and friction angle. The results indicated that at an optimum GF content of 1%, UCS and E-5(0) increased by up to 35%. Also, after 10 F-T cycles, UCS decreased by 46% for untreated soil and 36% for treated soil. PG enhanced cohesion through interparticle bonding, which was curing-time-dependent. Specimens with 2.5% PG (optimum content) showed a 133% UCS increase after 14 days of curing but a 9% reduction after 5 F-T cycles, with 70% of total UCS loss occurring in the first 5 cycles. The tests indicated that formation of large and stable soil-PG-GF matrix with improved rigidity, strength, and F-T resistance. The results demonstrated that the suggested soil stabilization method, which utilizes low-cost, eco-friendly materials, was effective.

The shear behavior of gravel-block soil (GBS) is unique and significant for evaluation the failure mechanism of GBS landslide on the Qinghai-Tibet Plateau. This study focuses on interpreting the shear behavior observed in the GBS during large-scale direct shear tests conducted on a landslide in Jiacha County, Tibet, China. The tests considered coarse particle content (CPC), dry density, and moisture conditions. Additionally, a discrete element numerical model, scaled to match the laboratory testing dimensions, was developed to simulate the large-scale direct shear tests on GBS. Results indicated that an increase in CPC improves the strength of the GBS, as it enhances the framework strength through interlocking between gravel blocks and between gravel blocks and the soil mass. The critical CPC for shear failure of the GBS exhibits a decreasing trend as the dry density increases. Furthermore, particle crushing rate (PCR) of the GBS is positively correlated with CPC, vertical pressure, and dry density. The simulation results show good agreement with the test results, providing insights into the damage-shear fracture mechanism of typical GBS under large-scale direct shear tests. The research outcomes provide a theoretical basis for the prevention and control of geological hazards in the Qinghai-Tibet Plateau.

As an innovative technology, transparent soil similar material can actively promote the development of soil model experiments by clarifying the structure, ratio, and strength characteristics. In order to study the factors affecting the mechanical properties of transparent soil materials, fused quartz is chosen as the aggregate material, nano-scale hydrophobic fumed silica is used as the binder, and a mixture of dodecane and No. 15 white oil is employed as the constituent material for transparent soils. In this study, indoor direct shear tests are conducted, and the range method is used to analyze the factors of quartz particle size, binder content and proportion, moisture content and dry density of the mixture solution. The relationship between the strength properties of transparent soil material and the above variables are quantitatively investigated. The results show that the transparent soil similar material can exhibit softening or hardening properties by changing the proportion of influencing factors, which can be suitable to most soils. Dry density has the most significant impact on cohesion while particle size of quartz has the greatest influence on the internal friction angle. The strength parameter of transparent soil has exponential distribution relationship with moisture content and linear distribution relationship with dry density. The cohesion and powder content are distributed exponentially while the internal friction angle and powder content are linearly distributed. As the particle size of quartz increases, the cohesion decreases overall and the internal friction angle increases. The strength parameters of transparent soil have a logarithmic distribution relationship with the unevenness coefficient of particle size and a linear relationship with the curvature coefficient of particle size. This study has established a quantitative control relationship between the key parameters of transparent soil materials and their mechanical properties. The revealed correlations between gradation of particles and strength parameters can serve as a guideline for simulation and visualization techniques based on transparent soils. It is of great significance for the visualization of the evolution mechanisms of geotechnical disasters.