Chao-Sheng Tang

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.

Although overland flow strongly governs soil erosion and sediment transport, its response to desiccation cracking induced by drying‐wetting cycles is not fully understood. This study addresses this gap through laboratory rainfall simulations on a slope model subjected to three drying‐wetting cycles. Soil moisture and suction were monitored at shallow depth, crack patterns were quantified through image processing, and runoff and sediment yields were measured during rainfall events. Infrared thermography was applied to capture flow velocity and spatial organization. Results show that drying‐wetting cycles accelerated moisture loss, steepened suction gradients, and promoted the initiation and propagation of cracks. Crack ratio and total crack length increased markedly during the first two cycles but stabilized in the third, indicating that the slope surface had reached a state of structural equilibrium. Runoff generation was influenced by both antecedent moisture and crack development: higher initial moisture reduced infiltration capacity and produced rapid, high‐magnitude runoff, while progressive cracking enhanced infiltration and weakened runoff response in later cycles. Sediment yield closely followed runoff intensity, peaking in the second cycle due to the influence of reduced infiltration and structural weakening. Infrared thermography showed that leading‐edge velocity declined during rainfall while the continuity‐derived equivalent runoff depth increased, reflecting different responses of local tracer‐front propagation and integrated runoff generation to evolving flow connectivity and effective hydraulic resistance. Across cycles, leading‐edge velocity rose initially and then declined, consistent with the transition from high antecedent moisture and structural weakening to stabilized crack networks. Spatial indices further confirmed this shift, indicating progressive increases in surface roughness, enhanced flow dispersion, and shortened effective flow paths.

Climate change is increasing the frequency and intensity of extreme climatic events, including droughts, heavy rainfall, cold waves, and heatwaves, which accelerate soil degradation and threaten the safety and sustainability of earthen infrastructure. Conventional soil stabilization methods often suffer from high carbon emissions, limited adaptability, and poor ecological compatibility, highlighting the need for sustainable alternatives. This study therefore proposes a new concept of bioconstruction of buffer barrier (Bio-Barrier) on soil surface to enhance soil climatic resilience via bio-mediated geotechnology, which has emerged as a promising low-carbon approach by exploiting biological processes to improve the hydraulic, mechanical, thermal, and ecological properties of soils. This study comprehensively summarizes four representative bio-mediated geotechnologies for Bio-Barrier construction, namely biomineralization, biofilm, biogas, and biological soil crust, and evaluates their roles in enhancing soil resilience under extreme climatic conditions. The mechanisms governing soil improvement are discussed from hydro-mechanical and bio-geochemical perspectives. Under dry climates, Bio-Barrier improve soil water retention, suppress evaporation, mitigate desiccation cracking, and enhance resistance to wind erosion. Under wet climates, they increase water stability and effectively control rainfall erosion, internal erosion, and coastal erosion. Their performance under cold climates demonstrates considerable resistance to freeze–thaw damage, while under hot climates they provide opportunities for regulating soil thermal properties and maintaining hydro-mechanical stability. The challenges associated with long-term durability, treatment uniformity, environmental sustainability, microbial survivability, field-scale implementation, and multi-physics modelling are critically discussed. Future developments are expected to focus on multifunctional integrated Bio-Barrier systems, climate-adapted microorganisms, environmentally benign bio-mediated pathways, and digitalized thermo-hydro-bio-chemo-mechanical modelling. Bio-Barrier offer considerable potential for developing low-carbon and climate-resilient geo-systems and is expected to play an increasingly important role in prevention and mitigation of extreme climate geohazards, sustainable infrastructure and climate adaptation.

Preferential flow within soil cracks influences land surface hydrological processes, yet direct quantifying preferential flow velocity (PFV) remains challenging. Here, we develop a method for high‐resolution monitoring and quantifying PFV in soil cracks using optical frequency domain reflectometry (OFDR). Building on the flow characteristics of preferential flow, we further establish a quantitative framework that links crack width to PFV through a physically based drag‐partitioning mechanism. Laboratory experiments and field slope monitoring enable continuous and accurate measurement of PFV and reveal a coupled evolution between crack width and PFV during flow flushing. This coupled behavior is interpreted from a dynamical perspective based on redistribution of viscous and form drag. By mechanistically relating PFV to readily measurable crack width, the proposed framework provides a parameterization pathway for improving hydrological models. Incorporating crack‐scale PFV enhances the representation of infiltration and other surface hydrological processes.