Geocells are three-dimensional, interconnected cellular geosynthetics widely used to enhance the overall strength of soils. Their foldable structure can cause variations in pocket shape during installation, depending on the extent of extension. Understanding the impact of these shape variations is essential for optimizing reinforcement efficiency and reducing the associated geocell application costs. The aspect ratio, defined as the ratio of the cell's transverse (welded) axis to the longitudinal (wall summit) axis, is proposed to evaluate the degree of extension of the most commonly utilized honeycomb-shaped geocell. A coupled continuum-discontinuum numerical method was employed to investigate the behavior of honeycomb-shaped geocell reinforced soils across various aspect ratios under confined compressive loading. The simulation results indicate that a geocell with an aspect ratio of 1.0 exhibits optimal reinforcement efficiency, and whereas reinforcement efficiency decreases as the aspect ratio deviates from 1.0 causing pocket geometries to flatten. The superior performance of rounded geocells is attributed to their enhanced ability to promote load-bearing in strong contact subnetworks. This results in denser packing structures, higher contact force anisotropy from a microscopic perspective, and greater confinement capacity against deformation from a macroscopic perspective.

Frozen soils exhibit unique mechanical behavior due to the coexistence of ice and unfrozen water, making experimental studies essential for engineering applications in cold regions. This review comprehensively examines laboratory investigations on frozen soils under static and dynamic loadings, including uniaxial and triaxial compression, creep, direct shear, and freeze-thaw (F-T) cycle tests. Key findings on stress-strain characteristics, failure mechanisms, and the effects of temperature and time are synthesized. Advancements in microstructural analysis techniques, such as computed tomography (CT), scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), and mercury intrusion porosimetry (MIP), are also summarized to elucidate the internal structural evolution of frozen soils. While significant progress has been made, further efforts are needed to better replicate complex environmental and loading conditions and to fully understand the interactions between multiple influencing factors. Future research should focus on developing novel experimental techniques, establishing standardized testing protocols, and creating a comprehensive database to enhance data accessibility and advance frozen soil research. This review provides critical insights into frozen soil mechanics and supports validating constitutive models and numerical simulations, aiding infrastructure design and construction in cold regions.

The main problem in expansive soil treatment with steel slag (SS) is the relatively slow hydration reaction that occurs during the initial period. To circumvent this, SS-treated expansive soil activated by metakaolin (MK) under an alkaline environment was investigated in this study. Based on a series of tests on the engineering properties of the treated soil, it can be reported that SS could enhance the strength and compressibility of expansive soil, with strength increasing by approximately 108 % for SS contents exceeding 10 % compared to 3 % lime-treated soil, and the compression index reducing by 20 %. Further addition of MK plays a dual role, enhancing strength for higher SS content while excessive MK leads to strength reduction due to insufficient pozzolanic reactions and hydration product transformation. Expansive and shrinkage behaviors are notably improved, with a 5 % increase in SS content reducing the free swelling ratio by 0.66 %-5.9 %, and the combination of 15 % SS and 6 % MK achieving a nearly 300 % reduction in the linear shrinkage ratio. Microstructural analysis confirms the formation of hydration gels, densification of the soil structure, and reduced macropores, validating the enhanced mechanical and shrinkage resistance properties of the SS-MK-treated expansive soil. Additionally, to develop predictive models for mechanical and the content of hardening agents (SS and MK), the experimental data are processed utilizing a backpropagation neural network (BPNN). The results of BPNN modeling predict the mechanical properties perfectly, and the correlation coefficient (R) approaches up to 0.98.

A microstructural rock model based on the distinct element method employing the Subspring Network contact model with rigid, Breakable, Voronoi-shaped grains (SNBV model) is proposed. The model consists of a mesh (3D Voronoi tessellation) of rigid, breakable, Voronoi blocks. The SNBV model is a microstructural rock model because it is a discrete model that can mimic rock microstructure at the grain scale. SNBV material mimics the microstructure of angular, interlocked, breakable grains with interfaces that may have an initial gap and can sustain partial damage. The model embodies the microstructural features and damage mechanisms that occur at the grain scale: initial microcrack fabric; heterogeneity-induced local tension; and intergranular and transgranular damage. The heterogeneity-induced local tension can be introduced in a controlled fashion that is not tied directly to the shape and packing of the grains and the interface stiffnesses. The synthetic material exhibits behavior during direct-tension and triaxial compression tests that matches the behavior of compact rock. The material can be calibrated to match the standard material properties and characteristic stresses of pink Lac du Bonnet granite. The material properties consist of Young's modulus and Poisson's ratio corresponding with uniaxial compression and Young's modulus corresponding with direct tension, as well as tensile strength, crack-closure stress, crack-initiation stress, secondary crack-initiation stress to mark the onset of grain breakage, crack-damage stress, and compressive strengths up to 4 MPa confinement. The model is suitable for studying the grain-scale micromechanics of brittle rock fracture.

Erosion and seepage control is a prime concern for embankments, dams, and other hydraulic structures constructed with alluvial sandy soil due to its highly porous characteristics. Permeation grouting has been a popular solution for controlling seepage situations in such structures. In this study, unconfined compression tests and triaxial tests were performed to determine the strength properties of grouted alluvial sandy soil located in the Ganges-Brahmaputra-Meghna delta. A simple method was devised to prepare cylindrical grouted samples with water-cement ratios (W/C) of 2:1, 3:1, 4:1, and 5:1. Here, unconfined compressive strength test results revealed that the highest compressive strength of the grouted sandy soil samples was achieved at the 2:1 W/C ratio at all curing ages. Different failure patterns are observed for different W/C samples during unconfined compressive tests. Furthermore, triaxial tests were conducted on the grouted samples prepared at the 2:1 W/C ratio under consolidated undrained conditions. Dilation occurred during the volume change, and the pore pressure decreased with increasing confining stress. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy were conducted to discern the microstructural behavioral changes and the chemical characteristics of the grouted sandy samples, respectively. Here, SEM images revealed a reduction in porosity with decreasing W/C ratio and increasing curing age. Permeation grouting leads to a reduction in permeability without disturbing the soil microstructure. Therefore, permeation grouting is a very effective technique for improving the mechanical behavior of grouted alluvial sand.

The degradation of soil structure in sandy regions undermines soil functionality and poses a significant threat to environmental sustainability. The incorporation of Pisha sandstone, a natural soil amendment, has been recognized as an effective intervention to reduce soil erosion and expand arable land in the Mu Us Sandy Land, China. However, the microstructural stability and resilience of amended sandy soil formed by mixing Pisha sandstone with sandy soils remain inadequately understood. This study aims to evaluate the effects of Pisha sandstone addition on the microstructural stability of sandy soils. Four amendment rates of Pisha sandstone (16.7 %, 33.3 %, 50 %, and 100 % w/w) and five water content levels (40 %-80 %) were tested. Key parameters related to microstructural stability and structural resilience were assessed using amplitude sweep and rotational shear tests via a rheometer. Results indicated that soil shear resistance (tau LVR, tau max, tau y), storage modulus (G'YP) and viscosity (eta 0) decreased with the addition of Pisha sandstone, attributed to its lubricating effect and swelling properties. Additionally, Pisha sandstone enhanced physical elasticity (gamma LVR) and structural recovery of sandy soil under conditions of low disturbance. However, when water content exceeded 50 %, the fluidity of the amended sandy soil increased with Pisha sandstone addition. The sandy soil with a Pisha sandstone addition rate of 16.7 % exhibited optimal structural elasticity, shear resistance, and stiffness. These findings provide valuable insights into the enhancement of sandy soil structural stability using Pisha sandstone, offering a scientific foundation for refining amendment ratios and advancing agricultural management practices.

Sandy soils are prone to engineering issues due to their high permeability and low cohesion in the natural environment. Therefore, eco-friendly reinforcement techniques are required for projects such as subgrade filling and soft soil foundation reinforcement to enhance their performance. This study proposes a synergistic reinforcement method that combines Enzyme-Induced Calcium Carbonate Precipitation with Glutinous rice slurry (G-EICP). The macroscopic mechanical properties and pore structure evolution of reinforced sand were systematically investigated through triaxial permeability tests, unconfined compressive strength (UCS) tests, and microstructural characterization based on Scanning Electron Microscope (SEM) and Micro- Computed Tomography (CT) tests. The results indicate that when the glutinous rice slurry volume ratio (VG) reaches 10%, the UCS of G-EICP-reinforced soil peaks at 449.2 kPa. The permeability coefficient decreases significantly with increasing relative density (Dr), VG, confining pressure (sigma 3), and seepage pressure (p). Microstructural analysis reveals that glutinous rice slurry may promote calcium carbonate crystal growth, potentially by providing nucleation sites, establishing a dual mechanism of skeleton enhancement and pore-throat clogging. The increased incorporation of glutinous rice slurry reduces the number of connected pores, lowers the coordination number, and elevates tortuosity, thereby inducing marked enhancements in both the strength and permeability of the treated soil compared to plain soil.

In response to the environmental challenges posed by conventional expansive soil stabilization methods, this study investigates the low-carbon potential of industrial by-products-cement kiln dust (CKD) and calcium carbide slag (CCS)-as sustainable stabilizers. A comprehensive series of laboratory tests, including compaction tests, free swelling rate measurements, unconfined compressive strength (UCS) evaluations, and scanning electron microscopy (SEM) analyses, were conducted on expansive soil samples treated with varying dosages in both single and binary formulations. The results indicate that the binary system significantly outperforms individual stabilizers; for example, a formulation containing 10% CKD and 9% CCS achieved a maximum dry density of 1.64 g/cm3, reduced the free swelling rate to 22.7% at 28 days, and reached a UCS of 371.3 kPa. SEM analysis further revealed that the enhanced performance is due to the synergistic formation of hydration products-namely calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H)-which effectively fill interparticle voids and reinforce soil structure. These findings demonstrate that the dual mechanism, combining rapid early-stage hydration from CCS with sustained long-term strength development from CKD, offers a cost-effective and environmentally sustainable alternative to traditional stabilizers for expansive soils.

Due to the local geology, expansive soils with weak geotechnical properties pose significant challenges to civil engineering projects. Enhancing soil strength and reducing plasticity are essential for supporting diverse construction endeavors. Given the abundance of lime and natural pozzolana in Algeria, this study investigates their influence on the geotechnical characteristics of clayey soils. The research examines the lime and natural pozzolana impact expansive clay soil's consistency, mechanical properties, classification, and microstructural and mineralogical composition. Soil samples are treated with lime and natural pozzolana at varying percentages (0% to 6% and 0% to 20%, respectively) and cured for 1 and 28 days to assess the effect of curing time. Results demonstrate that incorporating natural pozzolana significantly enhances the properties of lime-treated expansive soil, resulting in improved soil fabric and increased cementitious material production compared to lime alone. X-ray diffraction and microscopic analysis revealed the formation of new pozzolanic products (C-A-S-H) alongside existing C-S-H and C-A-H phases in lime-natural pozzolana-treated soil. The study effectively enhances clay soil's workability and geotechnical properties by combining lime and natural pozzolana, offering promising insights for soil improvement in civil engineering projects.

Dispersive saline soil is a type of water sensitive special soil with the characteristic of instability when encountering water, and its engineering properties are unstable. Therefore, this research proposes the use of environmentally friendly biopolymer guar gum to improve soil dispersivity and explores the feasibility of guar gum in improvement of dispersive saline soil. The mechanical properties of the improved dispersive saline soil were determined through unconfined compressive strength tests and direct shear tests. The influence of guar gum on the dispersivity and physical properties of the soil were investigated by crumb tests, pinhole tests, liquid plastic limit tests and particle size distribution tests. The microstructure and mineral composition of the improved soil were analyzed by X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy tests. Experimental results indicate that 1.5 % guar gum can transform highly dispersive soil into non-dispersive soil after curing 28 days. When the guar gum content increases from 0 % to 4 %, the unconfined compressive strength increases by 81.30 %, and the cohesion and internal friction angle increase by 117.02 % and 32.69 %, respectively. Guar gum is enriched with hydroxyl groups, which form hydrogels in contact with water, and form a cationic bridge with the surface cations of clay particles, the two aspects work together to cement the soil particles, dense soil structure. Guar gum can effectively improve the dispersivity and mechanical properties of dispersive saline soil, and can be used as an environmentally friendly soil modification material.