Micromechanical mechanisms of microstructural evolution governing mechanical response of frozen sandy clay under true triaxial stress conditions

Fracture behavior and constitutive modeling of rock-concrete contact surfaces with different roughness under freeze–thaw cycles

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.

Anisotropic behavior of high liquid limit clay subjected to two maximum drying stress paths

Dynamic Mechanical Properties and Constitutive Model of Saturated Frozen Soil with Different Pore Ratios

This study investigates the dynamic stability of frozen soil slopes subjected to strong disturbances such as blasting. Dynamic compression tests were conducted on saturated frozen clay specimens using a split Hopkinson pressure bar system. The effects of strain rate (100–700 s−1), temperature (−15°C, −23°C, and −30°C), and pore ratio (0.30, 0.24, and 0.18) on the mechanical behavior were systematically examined. The propagation of stress waves and the dynamic stress–strain responses were analyzed. Results show that as the strain rate increases, the arrival times of the incident, reflected, and transmitted wave peaks advance, and the time to reach peak energy, stress, and strain decreases. This trend is consistent across all tested temperatures and pore ratios. Both lower temperatures and higher pore ratios lead to increased specimen strength and a marked shortening of the plastic plateau stage in the stress–strain curves. Based on the experimental results and the effective stress principle for saturated soils, a damage-enhanced constitutive model was developed within the Zhu-Wang-Tang constitutive framework by incorporating a wave-impedance term. This term links microstructural changes (ice content and cementation) to macroscopic strength, effectively characterizing the coupled effects of strain rate, temperature, and pore ratio. The model predictions show good agreement with the experimental data, providing a theoretical basis for the dynamic analysis of frozen soil engineering.

From Pore Expansion to Throat Extension: Effects of Freezing Temperature on Microstructural Evolution and Dynamic Strength Decay in Sandstone

Repeated freeze–thaw (F–T) action, together with dynamic disturbances, can progressively weaken rock masses in cold regions. However, how freezing temperature affects the relationship between microstructural evolution and dynamic strength decay remains insufficiently quantified. This study investigated yellow sandstone subjected to F–T cycles at freezing temperatures of 0, −3, −5, and −20 °C. CT-based 3D reconstruction and Split Hopkinson pressure bar (SHPB) tests were combined with grey relational analysis (GRA) to characterize pore-structure evolution, dynamic strength decay, and their relationship. The results indicated that lower freezing temperatures promoted increases in pore connectivity and structural complexity. After 60 F–T cycles at −20 °C, connected porosity increased from 11.15% to 18.67%, while the ratio of connected porosity to total porosity increased from 51.1% to 85.7%. At an impact pressure of 0.3 MPa, the dynamic strength after 60 cycles decreased by 9.51%, 20.9%, 38.1%, and 61.5% at 0, −3, −5, and −20 °C, respectively. Among the examined microstructural parameters, average throat length had the highest overall grey relational grade (0.821), suggesting that throat development is closely associated with dynamic strength decay. Lower freezing temperatures enhanced pore-ice expansion and unfrozen-water migration, promoting pore enlargement, throat extension, and crack connection. These results quantitatively link pore-network evolution to dynamic strength decay under different freezing temperatures, providing a microstructural basis for assessing the dynamic deterioration of sandstone in cold regions.

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.