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

Fracture evolution of micritic bioclastic limestone under Brazilian splitting: a comparison between natural and water-saturated states

The tensile strength properties and the initiation and propagation of tensile cracks within micritic bioclastic limestone–which forms the surrounding rock mass at the tunnel exit of the Altash Water Conservancy Project–pose a threat to engineering stability. To investigate the differences in tensile strength and stress-induced crack evolution under natural and water-saturated conditions, a comparative experimental study was conducted using Brazilian splitting tests coupled with acoustic emission (AE) monitoring. The results demonstrate that, compared with natural specimens, saturated limestone exhibits a 16.54% reduction in tensile strength. The failure process can be categorized into three distinct stages: compaction, quasi-linear elasticity, and unstable crack propagation. Furthermore, AE analysis indicates that while overall AE activity decreases following water saturation, the proportion of tensile cracks increases from 92.30% to 95.14%. Conversely, under natural conditions, shear cracks are more active and initiate earlier. Microscopically, the high content of bioclasts and associated complex interconnected pores (e.g., body cavity and secondary dissolution pores) endow the rock with remarkable hydrophilic and water-retention characteristics. Coupled with the presence of the abundant hydrophilic mineral illite, these factors collectively exacerbate water-rock interactions, driving the significant degradation of the rock’s mechanical properties from both material and structural perspectives.

Moisture-induced degradation of clay-bearing sandstone

Clay-bearing sandstones used in the construction of historic monuments, churches, and castles are highly susceptible to contour scaling, which manifests as fractures parallel to the exposed facades. Repeated wetting–drying cycles accelerate material degradation through stiffness reduction and hygric deformation induced by swelling clays. This in turn alters the hygro-thermal (HT) properties of the stone. In this study, a scalar damage variable is employed within the framework of continuum damage mechanics to characterize the evolving damage state under the influence of moisture fields. The most critical climatic conditions that lead to degradation are first identified through hygro-thermal simulations. Subsequently, a fully coupled hygro-thermo-mechanical (HTM) model is developed to account for both moisture transport and material degradation. The results demonstrate that contour scaling can occur solely due to moisture cycling, even in the absence of freezing or salt crystallization effects. As such, subsurface zones of damage localization and a water-accumulation layer emerge that align well with on-site observations, pointing at potential damage mechanisms such as contour scaling.

Deterioration Mechanism and Constitutive Model of BFRC Corroded by Acid Rain

To elucidate the long-term degradation mechanism of basalt-fiber-reinforced concrete (BFRC) subjected to acid rain corrosion, this study conducted mechanical tests on BFRC specimens with a fiber content of 0.15% under simulated acid rain (pH = 3.0) over 0–120 corrosion cycles. Results reveal a nonlinear evolution in both compressive and splitting tensile strengths—an initial decrease, subsequent increase, and final gradual decline—with peak values attained at 60 and 30 cycles, respectively, corresponding to maximum enhancements of 20% and 45% relative to the initial strength. Microstructural analyses (SEM-EDS) identify a three-phase deterioration process: chemical dissolution (surface decalcification), competitive pore filling coupled with C-S-H decalcification, and expansive cracking induced by ettringite formation. Integrating the experimental data and degradation mechanisms with maturity theory, a dynamic constitutive model incorporating corrosion cycles is developed. The model accurately predicts the time-dependent mechanical degradation of BFRC under acid rain exposure, providing a theoretical foundation for durability design and assessment of fiber-reinforced concrete in corrosive environments.

Laboratory simulation of the ground desiccation network cracks and comparison with field patterns

Thermal Shrinkage and Cracking Behavior of Foamed Lightweight Soil under Temperature Cycling and Region Minimum Service Temperature Range: An Experimental and FDEM Study

Foamed lightweight soil (FLS) subgrades in cold regions are highly susceptible to temperature-induced shrinkage cracking, compromising long-term durability. This study investigates the coupled effects of silty clay content, temperature cycling, and service temperature range on FLS shrinkage behavior and crack evolution through laboratory tests and finite–discrete-element method (FDEM) simulations. Experimental results show nonlinear accumulation of shrinkage strain under cyclic thermal loading, with 20% silty clay significantly enhancing stability. Analysis of variance identifies silty clay content as the dominant factor over temperature cycling frequency. FDEM simulations reveal strain localization and crack initiation under heterogeneous temperature fields, with cracks evolving in three stages: initiation, rapid propagation, and stabilization. Lower minimum service temperatures play a dominant role in accelerating crack development and structural deterioration. Integrating experiments and simulations clarifies how key material and environmental factors govern FLS thermal shrinkage, providing a preliminary reference for crack-resistant design and long-term reliability assessment of FLS subgrades in cold regions.

Degradation trigger mechanism in compacted loess under seepage-stress coupling: correlated with microstructural evolution