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Desiccation cracks initiate and propagate during the drying process and healing occurs during the wetting process. However, most of the previous studies only paid attention to the drying-induced crack propagation and the wetting-induced healing behaviour was always neglected. In this paper, a series of wetting tests were conducted on cracked soils under different wetting rates. The crack pattern evolution during wetting was recorded and quantitatively analysed. The results show that the narrow and short secondary and tertiary cracks heal earlier than the long and wide primary cracks during wetting. With the elapsed wetting time, the surface crack ratio and average crack width decrease slowly at first, then rapidly decrease and eventually stabilise. However, at the early stage of wetting, the total crack length almost remains constant. The healing of desiccation cracks in clayey soils is mainly attributed by two factors: wetting-induced swelling and disintegration. Furthermore, the healing degree of desiccation cracks become higher with increasing wetting rate. The healing of desiccation cracks with a lower wetting rate is mainly due to the wetting-induced swelling of soils. However, that with a higher wetting rate is dominated by both swelling and disintegration. • The evolution of soil cracks subjected to various wetting rates was investigated. • The healing degree of desiccation cracks became higher with increasing wetting rate. • Wetting-induced crack healing at a low wetting rate is mainly due to soil swelling. • Both swelling and disintegration dominate the crack healing at a higher wetting rate. [ABSTRACT FROM AUTHOR]

Desiccation crack is an important factor affecting engineering properties of clayey soils. In this study, the effects of compaction state and wetting-drying cycles on desiccation cracking behaviour of a clayey soil were investigated. Nine samples with various compaction water contents and dry densities were subjected to three wetting-drying cycles and the evolution of desiccation cracks was quantitatively described. The results reveal that both compaction water content and dry density play an important role in the development of desiccation cracks. Specifically, for the samples compacted on the dry side, desiccation cracks develop simultaneously. This phenomenon is also observed in samples compacted on the wet side with low densities. However, for the samples compacted on the wet side with high dry densities, desiccation cracks develop sequentially. Moreover, the higher the compaction water content, the faster development of desiccation cracks, and the smaller surface crack ratio, total crack length and average crack width. The higher the dry density, the slower development of desiccation cracks, and the smaller surface crack ratio and total crack length. Furthermore, the development of desiccation cracks can be divided into two stages according to the evolution of crack propagation velocity: (a) crack length extension, where total crack length increases rapidly with little changes in average crack width, and (b) crack width widening, where total crack length no longer changes and average crack width increases until it stabilizes. In addition, surface crack ratio, total crack length and average crack width all show an upward trend as wetting-drying cycles progresses. This tendency is more pronounced in the soil sample with a higher compaction water content and a larger dry density. • Effects of compaction state on soil cracking is investigated. • Three wetting-drying cycles are applied. • Larger compaction water content and dry density, smaller cracking degree. • Crack closure and rerouting during wetting-drying cycles are observed. [ABSTRACT FROM AUTHOR]

Up to now, the correlation between soil evaporation and cracking within a multi-scale perspective remains unclear so far. For this purpose, X-ray computed tomography was used to dynamically capture the 3D cracking process of a compacted clayey soil with evaporation. The proposed image processing methods combining CT image segmentation and digital image correlation (DIC) allowed multi-scale quantitative analysis of the temporal evolution of soil water distribution, regional deformation and crack network upon evaporation. Different mechanisms are defined to explain the development of regional crack networks. Evaporation-mobilised tensile stress leads to cracking in the top part of the soil, with a single-peaked change along drying time in the cracking rate. A similar variation appears in the cracking process of the bottom soil, attributed to the basal friction activated by soil desiccation shrinkage. Besides, the cracking rate of this region is nearly independent of the regional evaporation. As for the middle part of the soil, a double-peaked pattern dominates the cracking rate, as the curling contributes to the formation of new inner cracks and the bottom soil cracks propagate upwards. Furthermore, desiccation cracks developing to a certain extent facilitate the water loss of neighbouring soil bodies, whereas this phenomenon is difficult to present over the whole soil scale. The current outcomes are expected to advance insights into the spatial–temporal cracking mechanism of soils under evaporation. [ABSTRACT FROM AUTHOR]

Tensile strength is a crucial mechanical property that governs the initiation and propagation of soil tensile cracks. With the global prevalence of warming effects and extreme climatic events, the recurrent freeze-thaw (F-T) cycles intensify the complex evolutions of soil pore structure and tensile strength in regions with widespread seasonal freezing or permafrost active layers. This study investigates the combined influence of F-T cycles and desiccation on the tensile strength of clayey soils. Specimens with varying compaction water contents (14.5%, 16.5%, and 18.5%) and dry densities (1.5 Mg/m3, 1.6 Mg/m3, and 1.7 Mg/m3) were prepared and subjected to cyclic F-T actions. A direct tensile test apparatus was utilized to measure tensile strength (σ t) along the desiccation path. Additionally, the changes in void ratio (e) and suction (s) during F-T cycles were analyzed to understand the mechanism behind the changes in σ t. Experimental results reveal that as the number of F-T cycles (N) increases, water content (w) declines at a decreasing rate and eventually stabilizes. With increasing N , the tensile displacement at failure and σ t show a pattern of initially decreasing and subsequently rising, with the inflection point typically around 1.5%–2.0% lower than the compaction water content (w 0). Under a few F-T cycles, soils compacted at the optimum water content and on the wet side exhibit higher void ratio and lower suction and σ t compared with dry-side compacted soils. However, this trend reverses with further increasing N. In addition, σ t increases as compaction dry density (ρ d0) rises within all water content ranges, primarily attributed to the significant interparticle cohesion controlled by a dense pore structure. The variation of σ t under F-T and associated desiccation is linked with the microstructural evolution characterized by aggregates, interaggregate pores and water-bridges. It is recommended to compact soils both on the dry side of the optimum water content and at the maximum dry density to enhance the freeze-thaw resistance of earth-works in seasonally frozen regions. • Freeze-thaw cycles with desiccation influence compacted soils' tensile strength. • Variations in void ratio and suction during freeze-thaw cycles govern tensile strength. • Soils with higher compaction water content exhibit greater expansion and shrinkage potential. • Dry-side compacted soils resist freeze-thaw risks better. [ABSTRACT FROM AUTHOR]

Soil curling caused by drying is a common phenomenon in nature, and it can vary depending on different atmospheric effects. To investigate the coupled effects of temperature and relative humidity on soil curling, a sequence of desiccation experiments were performed by using elongated strip soil samples in the laboratory. The soil curling process is divided into five stages: vertical settlement stage, lateral contraction stage, concave-up curling stage, curling recovery stage and convex-up curling stage. In this study, the soil evaporation characteristic and curvature curves are obtained under different temperature and relative humidity conditions. The findings revealed that a lower relative humidity results in a higher evaporation rate and a smaller maximum concave-up curling curvature for soil samples. Additionally, as the temperature increased, the water content associated with concave curling decreased. The maximum concave-up curling curvature was determined by the transition from the appearance of concave-up curling to the maximum curvature of concave-up curling. Under the coupled effect of temperature and relative humidity, all the water content associated with the occurrence of concave-up curling, maximum concave-up and convex-up curling appearance are reduced with increasing temperature and decreasing relative humidity. As the temperature ranged from 20 °C to 40 °C, the maximum concave-up curling curvature initially decreased and then increased. Conversely, the maximum concave-up curling curvature increased within the relative humidity range of 30% to 45%. • The evolution of soil curlings under various temperature and RH was investigated. • Both concave-up and convex-up curling occur earlier with increasing temperature. • The curvature of the concave-up curling increases with increasing RH. • Water content at the start of curling decreases with temperature rise and RH drop. [ABSTRACT FROM AUTHOR]

• A new method to measure water content at soil surface is developed based on infrared thermal imaging technology. • The method is based on infrared thermal imaging technology. • For a given over-saturated soil, the interfacial temperature difference is a constant value. • The unsaturated water content is linearly related to the interfacial temperature difference. • The proposed method is validated using a cracked soil sample. In this study, infrared thermal imaging technology is adopted to measure water content at soil surface by calibrating the linear relationship between water content at soil surface and interfacial temperature difference of a given soil type. The method is suitable for the soil surface which is unsaturated. First of all, the theoretical considerations of the new method are introduced. Infrared thermal imaging technology can directly measure soil surface temperature and the difference between the soil surface temperature and the ambient temperature is named as the interfacial temperature difference. For over-saturated soils, at a certain environmental condition, the interfacial temperature difference of a given soil type is a constant value. For unsaturated soils, there is a linear relationship between water content at soil surface and interfacial temperature difference. For the tested four types of soils with different textures, all the values of R2 for the linear fitting are greater than 0.9. Then, the water content at soil surface can be calculated based on the surface temperature measured by the infrared camera. Moreover, in this study, a cracked soil sample with an uneven surface water content field is tested for validating the feasibility of the proposed method. There is a good match between the data measured by the proposed method and traditional oven drying. It indicates that the proposed method can be used to obtain the distribution of water content on the soil surface and may provide a new idea for the future research on the spatio-temporal evolution characteristics of in-situ soil under climate change and provide a new choice for leakage detection of structures like dams, tunnels, etc. [ABSTRACT FROM AUTHOR]

Digital camera was used to record the dynamic process of soil desiccation cracks in real time. With application of image processing technique, the relationship between the strain/displacement field and desiccation cracking were analyzed. Results show that the crack usually occurs at locations where tensile strain concentrates. After the crack is generated, the surrounding strain field and displacement field are rapidly redistributed. The new strain field and displacement field act on the crack again, affecting the propagation direction of the crack. Under the interaction between the strain/displacement field and cracks, the crack tends to intersect with other cracks at right angles and deflection may occur in the development process. The soil is divided into different clods by the cracks. Each clod centripetally shrinks and has a shrinkage center which may move with elapsed drying time. Based on the strain/displacement field, the characteristics of desiccation cracking in local area of soil can be predicted in advance and it can be used to directly judge the activeness of the cracks or clods. The digital image processing technique can effectively obtain the soil deformation without disturbing the soil sample, which offers an available way for understanding the intrinsic dynamic mechanisms of soil desiccation cracking. [ABSTRACT FROM AUTHOR]

Drought-induced soil desiccation cracking has attracted great attention in various disciplines with the advent of global climate change. Accurately obtaining soil crack networks is essential to understand the cracking mechanism. Inspired by recent advances of artificial intelligence (AI) in computer vision, we propose a new automatic soil crack recognition method based a novel network architecture, named Attention Res-UNet. Deep Res-UNet inherits both the advantages from residual learning for training deeper networks and U-Net for semantic segmentation. Moreover, attention mechanism is utilized to alleviate the influences caused by the uneven illumination conditions. Firstly, the soil crack images under different uneven illumination conditions are collected to create a new soil cracking image dataset. Then, traditional method and multiple state-of-the-art deep learning based different semantic segmentation models are tested on our collected dataset. Finally, a professional evaluation standard, which considers both the overall metrics (precision, recall, dice, surface crack ratio) and details (crack total length, average crack width, number of crack segments) of the soil crack features is proposed to evaluate the recognition results of the different models. Extensive experimental results demonstrate the superiority of our proposed Attention Res-UNet approach compared with traditional methods and other deep learning models in recognizing soil cracks under complex environmental conditions. Our method is also suitable for crack recognition of other materials under complex environmental conditions. • Artificial intelligence is used for soil cracks recognition. • Deep Res-UNet and Attention gate is combined for soil crack image recognition. • A professional evaluation standard is proposed to evaluate recognition performance. • Proposed model is superior to other deep learning models in soil cracks recognition. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to review the development and the state of the art in desiccation cracking characterization methods and review the desiccation cracking behaviors of soils. The review begins by briefly introducing in Section 1 the influences of desiccation cracking on soil properties and the significance of studying this topic. Section 2 summarizes the past and existing experimental approaches that have been invented and adopted for soil desiccation cracking investigations at both laboratory and field scales. Various theoretical frameworks formulated to account for the underlying cracking mechanisms are presented in Section 3. Section 4 shows the implementation of theoretical frameworks into mesh-based and mesh-free numerical tools to capture the initiation, propagation, and coalescence of desiccation cracks. Section 5 describes the crack dynamics in desiccating soils, with emphases placed on the coupled process of water evaporation, suction increase, and volume shrinkage, and the crack network evolution. Section 6 discusses major influencing factors of soil desiccation cracking covering soil intrinsic properties, boundary constraints, environmental conditions, and soil admixtures. Finally, a brief summary and proposed prospective research works are presented in Sections 7. [ABSTRACT FROM AUTHOR]