Impact of Nonplastic Fines Content on the Small-Strain Shear Modulus and Water Retention Behavior of Unsaturated Sand–Silt Mixtures

Strength Anisotropy of Cemented Granular Materials in Low- and High-Stress True Triaxial Tests

Understanding the mechanical behavior of cemented granular materials under multiaxial stress conditions is essential for the safe and efficient design of filtered tailings disposal systems, yet their anisotropic response remains insufficiently characterized. This study examines the strength anisotropy of iron ore tailings and natural sand blends stabilized with ordinary portland cement through low- and high-pressure true triaxial testing. Mixtures were designed using the porosity-to-volumetric cement content index ( η / C i v 0.16 ) to achieve equivalent initial conditions across varying dry unit weights and cement contents. The experimental program comprised unconfined compressive strength tests and true triaxial tests covering stress paths ( b = 0, 0.5, and 1), mean effective stresses (100, 2,000, and 4,000 kPa), and loading orientations ( θ = 0°–180°). The results show that cementation can suppress compaction-induced anisotropy under stresses below the yield threshold, promoting near-isotropic behavior in all directions; however, anisotropy reappears when cement bonds degrade beyond yielding. While both strength and stiffness improved with increasing cement content and dry density, stiffness was controlled primarily by cement dosage and strength by confining stress. Iron ore tailings displayed a larger normalized yield surface ( q / p ′ = 1.2) compared with natural sand ( q / p ′ = 0.8 at 2 MPa). These findings validate the η / C i v 0.16 index as a practical design parameter, enabling engineers to balance compaction effort and cement content to meet performance targets under complex field stress paths.

Experimental and Numerical Study of Water Effects on Mechanical and Fracture Behavior of Sandstone: A Case Study

Water significantly modifies rock mechanical performance and fracture characteristics through water content and water distribution. Nevertheless, the evolution laws of rock mechanical properties and underlying fracture mechanisms under variable water conditions remain incompletely clarified. In this study, uniaxial compression tests were carried out on sandstone samples with diverse water immersion durations. Experimental observations reveal that the uniaxial compressive strength (UCS) and elastic modulus of sandstone follow negative exponential attenuation with prolonged immersion time, with maximum reductions of 50.1% and 25.6%, respectively. Under equivalent water contents, samples featuring dry exteriors and wet interiors possess lower strength than those with wet exteriors and dry interiors. A self-developed numerical code incorporating humidity diffusion effects was subsequently adopted to interpret water-controlled sandstone fracture behaviors. Numerical outputs verify that water-induced softening and heterogeneous water distribution exacerbate rock material heterogeneity and internal stress non-uniformity, triggering tensile microcracks along dry–wet interfaces. As the immersion duration rises, the rock failure mode transitions from shear-dominated mixed failure to tension-dominated failure, and finally reverts to shear-dominated mixed failure. Macroscopic rupture is predominantly governed by the gradual coalescence of tension-generated microcracks. This study offers a theoretical foundation to advance the understanding of water-triggered mechanical degradation and fracture mechanisms in sandstone.

Hydraulic-history effects on the strength and pore structure of compacted claystone: direct comparison between hydraulically processed and directly compacted states

Experimental Investigation on Water-Sensitive Engineering Behaviors of High-Fines Clayey Sand and Quantitative Correlations Between Physical and Mechanical Indices

Clayey sand is a typical transitional coastal alluvial soil controlled by both coarse-grain friction and fine-grain cementation. Current studies focus mostly on remolded samples, lacking systematic understanding of water-induced structural degradation and quantitative physico-mechanical correlations for natural undisturbed clayey sand. In this work, 74 intact undisturbed specimens (0.5–23.0 m depth) were tested via basic physical tests, one-dimensional consolidation and consolidated-undrained triaxial shear tests. Pearson correlation analysis was performed to establish prediction relationships between routine physical indices and mechanical parameters. Results show the soil is classified as SC clayey sand with 39.70% fines and an average natural water content of 23.17%. Natural water content dominates soil engineering performance, presenting strong linear correlations with dry density and void ratio (|r| = 0.90). Higher water content and void ratio increase compressibility and reduce shear strength. The compression coefficient and compression modulus exhibited a consistent nonlinear relationship, reflecting the inherent linkage between these two compression parameters. Burial depth has little influence on soil properties, and plasticity index only serves for soil classification. Mechanistically, increasing moisture may thicken adsorbed water films, weaken interparticle contact and matric suction, and the fine particle-filled skeleton may further enhance the water sensitivity of the soil. The established prediction models support fast evaluation of soil mechanical behaviors, offering theoretical and practical support for geotechnical design of similar coastal clayey sand strata.

Mechanical Response of Fine-Grained Soil-Solid Waste Composites from Large-Scale Direct Shear Tests

Experimental Evaluation of Shear Strength of Soil–Concrete Interface in Carbonate Sands from Northeastern Brazil

This study evaluates the shear strength and geomechanical behavior of the soil–concrete interface in carbonate sands from the coast of Ceará, with particular relevance to offshore wind turbine foundations. Three sands with different calcium carbonate (CaCO3) contents, namely, 10.6%, 22.0% and 30.0%, were tested under applied normal stresses of 50, 100 and 200 kPa. Conventional direct shear tests were carried out to determine soil–soil shear behavior, whereas controlled-interface tests were performed using cementitious specimens with smooth and rough surfaces. The soil–soil tests indicated effective internal friction angles (φ′) between 35° and 38°, with no cohesion. No direct correlation was observed between shear strength and CaCO3 content. Instead, the results indicate that particle size distribution, particularly the proportion of finer fractions, exerted the main control on mechanical behavior. Within the three materials tested, no monotonic trend between CaCO3 content and shear strength was identified, a finding that should be confirmed with a larger sample set. At the soil–concrete interface, shear stress mobilization depended on surface roughness, with the rough surface mobilizing higher shear stresses than the smooth surface. The ratio between the interface friction angle and the soil effective internal friction angle (δ/φ′) ranged from 0.963 to 0.994 for rough surfaces and from 0.859 to 0.951 for smooth surfaces. These findings show the need for site-specific characterization of carbonate sands and for explicit consideration of interface conditions in offshore foundation design, thereby reducing unnecessary structural oversizing.