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

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

This study examines the small-strain shear modulus ( G max ) and water retention behavior of unsaturated sand–silt mixtures with a focus on the effects of fines content (FC), mean net stress ( p n ), and hydraulic hysteresis. A comprehensive experimental program was conducted, incorporating saturated and unsaturated bender element tests, soil water retention curve measurements, and scanning electron microscope imaging. The tests were performed on compacted specimens of Firuzkooh No. 161 silica sand mixed with varying silt contents (0-100%) as fines under p n of 50, 100, and 200 kPa along both drying and wetting paths. Two unsaturated triaxial systems equipped with bender elements and a hanging water column controlled matric suction ( ψ ) via axis translation and water head control techniques. The results revealed significant changes in soil structure and hydromechanical behavior with increasing FC. In contrast to other soil mixtures, clean sand exhibited distinct hydraulic and mechanical behaviors, with G max demonstrating a nonmonotonic variation with ψ . As FC increased, a pronounced reduction in G max emerged at FC of 20%, at which point the soil structure began to transform from a fines-in-sand to a sand-in-fines structure. Notably, the impact of hydraulic hysteresis became increasingly prominent with FC: for mixtures with 10%–100% FC, G max during wetting was higher than during drying at the same ψ levels, whereas an opposite trend was observed for clean sand. Additionally, for sand specimens, the suction stress concept effectively described the variation of G max with ψ , while for sand–silt mixtures (10%–100% FC), an extended framework incorporating the equivalent void ratio into a double hardening mechanism concept was adopted. The consistency between experimental observations and theoretical interpretations suggested that these concepts could provide a robust basis for predicting G max behavior in unsaturated sand–silt mixtures.

Integrated geotechnical assessment of foundation soils using field and laboratory investigations: case of a raw water pumping station in the Gharb Plain (Morocco)

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

Preparation Method of Simulated Deep Sandstone Materials Based on Dual Equivalence of Principal Components and Mechanical Properties, and Quantitative Evaluation of Simulation Effectiveness

Intact deep sandstone cores are scarce, heterogeneous with poorly repeatable, limiting systematic laboratory studies of deep-rock mechanical behavior. This study selected dense sandstone recovered from 1050 m in the Pingdingshan mining area as the prototype system for the development of a targeted-sandstone-constrained screening strategy for simulated deep sandstone. The strategy integrates mineral-composition matching, orthogonal mixture design, mechanical testing, PCA-based comprehensive similarity evaluation, GMM classification, stress–strain curve comparison and fracture-morphology verification. Candidate materials were prepared using a cement–silica-fume matrix with quartz sand, K-feldspar, Na-feldspar, nanoclay and superplasticizer. Results show that the water–binder ratio dominated uniaxial compressive strength, tensile strength and elastic modulus, whereas superplasticizer and nanoclay had secondary effects. The PCA-based index assigned weights of 52.9%, 29.2% and 17.9% to uniaxial compressive strength, elastic modulus and brittleness index, respectively. Among the 25 mixtures sampled, S5 showed the highest mechanical similarity, with a simulation index of 71.65% and a stress–strain curve similarity of 0.958. GMM clustering identified S5 and S10 as the closest high-strength, high-stiffness and high-brittleness group, while S10 better reproduced natural crack geometry. These results indicate that the optimal simulated sandstone depends on the target response and provide a task-oriented route for reproducible simulated deep sandstone.

Micro-to-macro mechanical characterization and constitutive parameterization of marine-terrestrial interface soft soils in the Pearl River Estuary

Thermally induced transition from expansive clay to a frictional granular state: An experimental investigation

Expansive soils pose persistent challenges to geotechnical design due to their high swelling potential and sensitivity to moisture variations. Thermal stabilization has recently emerged as a promising alternative to conventional chemical treatment, yet its implications for soil strength mechanisms remain insufficiently quantified. This study evaluates the effectiveness of extreme thermal stabilization on a high-plasticity, kaolinite-rich expansive clay, specifically focusing on the evolution of its mechanical strength and shear parameters. Soil specimens were subjected to controlled thermal treatment at 200°C, 400°C, and 600°C for durations of 15, 30, and 120 minutes, followed by systematic evaluation through unconfined compressive strength (UCS) and direct shear tests (DST). Complementary analyses of grain size distribution, consistency limits, and compaction characteristics were conducted to interpret the observed mechanical responses. The results demonstrate that increasing temperature induces a substantial transformation of the soil fabric, marked by aggregation of clay particles into stable, sand-sized clusters and a reduction in plasticity index (PI) from 27.0 to 2.94 at 600°C. While extreme heating led to a substantial reduction in UCS; reflecting the loss of cohesive clay bonds; it simultaneously produced a marked increase in shear resistance under confinement, with the internal friction angle rising from 23.15° to 50.19°. Free swell potential was progressively suppressed and effectively eliminated at 600°C, confirming the permanent mitigation of expansive behavior. The findings highlight a fundamental shift in strength mechanisms from cohesion-dominated to friction-controlled behavior, demonstrating that thermally treated expansive clay can function as a granular-like material with high shear resistance under confinement. These results provide critical insight into the rational use of thermal stabilization in geotechnical applications involving expansive soils.