Moisture-induced degradation of clay-bearing sandstone

Monitoring of structures in shaly rock formation

Shaly rock formations, particularly those rich in expansive clay minerals, pose unique geotechnical challenges for infrastructure development. These formations are susceptible to volumetric swelling and deformation when subject to water ingress, mechanical stress and salt concentration, which can lead to progressive structural damage over time. The long-term swelling effect of shale formation in combination of cyclic thermal and environmental changes induce additional stress on the structure in contact with the shale. This paper illustrates the use of a long-term monitoring program aimed at assessing crack growth and crack propagation of an underground structure situated within shale-dominated geological environments in Southern Ontario, Canada. Real-time continuous data was collected over an extended period to reveal any correlations of seasonal thermal and moisture changes and the deformation of the structure. Furthermore, short-term stress responses were determined based on crane live load tests. These provided insight into the dynamic responses of the structure. The analysis of the time-series data led to the establishment of displacement and strain threshold limits, which ultimately enhanced the structure’s long-term performance and safety. The findings highlight the importance of continuous monitoring in predicting long-term structural responses and support the development of early warning systems and mitigation strategies.

Mechanical degradation of limestone under thermo-chemical–mechanical coupling

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.

Degradation and recovery of hierarchy in soil desiccation cracking: insight from discrete-element method simulations

Soil desiccation cracking typically exhibits a hierarchical structure in homogeneous materials but is often disrupted by inherent heterogeneities. The processes governing the degradation and potential recovery of this hierarchy remain poorly understood. This study investigates these mechanisms using an advanced three-dimensional discrete-element method (DEM) model that explicitly simulates surface evaporation and internal moisture transfer to simulate sequential crack propagation. By introducing non-shrinkable inclusions at varying contents (0–30%) to represent heterogeneity, it is revealed that increased inclusion content degrades the hierarchical pattern, shifting crack initiation to multiple points and favouring Y-shaped junctions (∼120°) over perpendicular intersections. A critical inclusion content of 10% is identified, marking the threshold where stress influence zones of inclusions significantly overlap. Below this threshold, initial hierarchy loss can recover during subsequent drying. Once exceeded, the hierarchical breakdown is permanent. The degradation and recovery of hierarchy are fundamentally governed by the evolution of the internal tensile stress field, which transitions between a progressive state (promoting hierarchy) and a concentrated state (disrupting it). These findings provide novel micromechanical insights into cracking patterns and advance the predictive modelling of desiccation cracking in natural, heterogeneous soils.

Progressive Damage of Sandstone and Shale Under Heating and Cooling Cycles: Implications for Stratified Rock Slope Stability

Research on Multiscale Simulation Methods for Thermal Response of Cemented Sand–Gravel Dams

Cemented sand and gravel (CSG) dams have been widely applied due to their simple construction and use of local materials. With the increasing occurrence of extreme weather events, temperature has become an important factor affecting the safe operation of dams. To investigate the temperature stress response of CSG dams under low-temperature conditions and achieve cross-scale analysis, an adaptive macro–meso finite element method is proposed. Through an iterative “solution–evaluation–mesh adjustment” procedure, meso-scale modeling is performed in high-stress regions, and the results are compared with those obtained using the conventional submodeling method. The results show that, under low-temperature conditions, temperature gradients and thermal stresses are mainly concentrated near the dam surface, with limited influence on the interior, while hydraulic load remains the dominant controlling factor. The local stress distribution patterns obtained by the two methods are generally consistent, and both can reflect stress concentration near the aggregate–mortar interfaces. The proposed method can characterize local meso-scale responses within a global computational framework, providing a reference for cross-scale analysis of the temperature response and the identification of local unfavorable stress regions in CSG dams.