Abstract Evaporation of water from soils is a three-stage process that has great significance in stress development in exposed geotechnical structures, generation of dusts that can cause environmental pollution and respiratory ailments, and dereliction of land by generating drought conditions. In this study, the factors that influence water evaporation from soil have been divided into two categories: external, referring to atmospheric conditions and interior, covering surficial soil characteristics and water content conditions. Particularly, five different sets of laboratory based evaporation tests were performed using cylindrical (150 mm diameter and 7–28 mm height) samples of clayey soil mixed with quartzite sands (three grainsize ranges: 0.2–0.5 mm, 0.5–1.0 mm, and 2.0–3.0 mm) in weight proportions ranging from 0% to 50% to evaluate the effects of soil texture, mineralogy and initial compactive state on its free water evaporation process at room temperature (20–22 °C) and relative humidity (50 ± 2%) conditions. The evaporation tests were performed using mass loss measurements on soil samples to an accuracy of 0.01 g. Findings show that in the first stage of soil drying, water content decreases continuously with time while the ratio of actual to potential evaporation, E a / E p stays mostly stable. During the falling rate stage, both water content and E a / E p decrease significantly. However, the water content varies but not significantly due to the low value of residual evaporation rate in the residual evaporation stage. Soil with lower sand content starts the falling rate stage at higher water content: 32.52% at added sand proportions of 0% versus 21.87%, 20.65%, 20.45%, 20.26% and 18.34% at added sand proportions of 10%, 20%, 30%, 40%, and 50% respectively. Larger soil sample thicknesses accelerate water evaporation rate and extend the constant evaporation rate stage. Soil particle size was not found to have significant impact on evaporation rate on per unit weight of added soil basis. The evaporation rate increases in direct proportionality to increase in initial water content and dry density. Highlights • Soil characteristics influences moisture evaporation significantly. • Larger soil thicknesses accelerate water evaporation rate. • Higher sand mix proportions lead to larger evaporation rate. • The effect of mixed sand grain size on evaporation is insignificant. • The evaporation rate significantly depends on soil initial compactive state.

Abstract Fiber reinforcement is an effective method for improving engineering properties of soil. However, the interaction mechanism of the fiber and the surrounding soil is not well understood. Based on mechanical analysis of fiber-soil interface under pullout condition, a tri-linear model is proposed to describe the shear stress-displacement relationship. The progressive pullout process of a short fiber in soil is divided into five consecutive phases: (1) the initial pure elastic phase (Phase I); (2) the elastic-softening phase (Phase II); (3) the pure softening phase (Phase III); (4) the softening-residual phase (Phase IV); and (5) the final pure residual phase (Phase V). For each phase, the analytical solutions of the distributions of tensile force, interfacial shear stress and displacement are derived. Through a comparison between the pullout test results of polypropylene fiber (PP-fiber) and the predicted results, the effectiveness of the proposed model in capturing the progressive load-deformation behavior of a short fiber in soil is verified. Moreover, the effects of water content and dry density of soil on the model parameters are analyzed in detail. It is found that the interfacial peak/residual shear resistance and shear stiffness of fiber reinforced soil significantly depend on soil compaction conditions. In general, two transition phases (Phase II and Phase IV) are not evident during the whole pullout process of PP-fiber.

Knowledge of shrinkage mechanism and the accompanied cracking behavior is helpful for better understanding the hydraulic and mechanical performance of clay soil under atmosphere condition. Initially saturated thin clay layers were prepared and subjected to air drying in this investigation. Water evaporation, volume shrinkage, surface crack initiation and propagation processes were monitored during the whole drying period. With application of image processing technique, the geometric or morphological characteristics of crack patterns were quantitatively described. Results show that the water in the clay layer evaporated at a near constant rate and then it began to decline when the water content was close to the air entry value. The clay layer volume shrinkage was contributed completely by vertical subsidence before desiccation crack initiation, and the measured final vertical shrinkage strain was several times higher than the lateral shrinkage strain. In addition, it was found that most of the cracks and volume shrinkage occurred during the constant rate of evaporation period while the specimen was still saturated. Crack initiation and propagation generally took place in three stages and terminated at the shrinkage limit. During the process of crack propagation, the crack intersections reached a stable value first and were followed by crack length and crack width. [All rights reserved Elsevier].

Knowledge of shrinkage mechanism and the accompanied cracking behavior is helpful for better understanding the hydraulic and mechanical performance of clay soil under atmosphere condition. Initially saturated thin clay layers were prepared and subjected to air drying in this investigation. Water evaporation, volume shrinkage, surface crack initiation and propagation processes were monitored during the whole drying period. With application of image processing technique, the geometric or morphological characteristics of crack patterns were quantitatively described. Results show that the water in the clay layer evaporated at a near constant rate and then it began to decline when the water content was close to the air entry value. The clay layer volume shrinkage was contributed completely by vertical subsidence before desiccation crack initiation, and the measured final vertical shrinkage strain was several times higher than the lateral shrinkage strain. In addition, it was found that most of the cracks and volume shrinkage occurred during the constant rate of evaporation period while the specimen was still saturated. Crack initiation and propagation generally took place in three stages and terminated at the shrinkage limit. During the process of crack propagation, the crack intersections reached a stable value first and were followed by crack length and crack width. [All rights reserved Elsevier].

Knowledge of shrinkage mechanism and the accompanied cracking behavior is helpful for better understanding the hydraulic and mechanical performance of clay soil under atmosphere condition. Initially saturated thin clay layers were prepared and subjected to air drying in this investigation. Water evaporation, volume shrinkage, surface crack initiation and propagation processes were monitored during the whole drying period. With application of image processing technique, the geometric or morphological characteristics of crack patterns were quantitatively described. Results show that the water in the clay layer evaporated at a near constant rate and then it began to decline when the water content was close to the air entry value. The clay layer volume shrinkage was contributed completely by vertical subsidence before desiccation crack initiation, and the measured final vertical shrinkage strain was several times higher than the lateral shrinkage strain. In addition, it was found that most of the cracks and volume shrinkage occurred during the constant rate of evaporation period while the specimen was still saturated. Crack initiation and propagation generally took place in three stages and terminated at the shrinkage limit. During the process of crack propagation, the crack intersections reached a stable value first and were followed by crack length and crack width.

Understanding the hydro-mechanical response of soil during drying is significant for predicting and preventing the possible disasters related to drought climate. In this investigation, a novel micro-penetrometer was developed to characterize and quantify the drought-induced soil hydro-mechanical response based on the penetration curves, which present the variation of soil strength along depth. The relationships between the penetration resistance and soil water content, and the penetration resistance and soil suction were initially calibrated. It is found that the penetration resistance increases exponentially with decreasing water content as the soil is subjected to drying, while increases linearly with increasing suction. Before the air-entry value is reached, the drying-induced increment of soil strength is insignificant even a large amount of water is evaporated. During this stage, soil strength and water content along depth are generally uniform, and the increment of soil strength is consistent at any depth. After the air-entry value is reached, soil strength increases rapidly even water content decreases slightly. The distribution of soil strength along depth becomes non-uniform. It generally decreases exponentially with increasing depth due to the drying-induced water content and suction gradient. The predicted water content profile based on the penetration results was compared with the measured one, and good agreement was observed. It indicates that the proposed micro-penetration test can be used to characterize the hydro-mechanical response of soil during drying.

Laboratory tests were conducted to investigate the effect of wetting-drying (W-D) cycles on the initiation and evolution of cracks in clay layer. Four identical slurry specimens were prepared and subjected to five subsequent W-D cycles. The water evaporation, surface cracks evolution and structure evolution during the W-D cycles were monitored. The effect of W-D cycles on the geometric characteristics of crack patterns was analyzed by image processing. The results show that the desiccation and cracking behaviour was significantly affected by the applied W-D cycles: the measured cracking water content theta(c), surface crack ratio R-sc and final thickness h(f) of the specimen increased significantly in the first three W-D cycles and then tended to reach equilibrium; the formed crack patterns after the second W-D cycle were more irregular than that after the first W-D cycle; the increase of surface cracks was accompanied by the decrease of pore volume shrinkage during drying. In addition, it was found that the applied W-D cycles resulted in significant rearrangement of specimen structure: the initially homogeneous and non-aggregated structure was converted to a clear aggregated-structure with obvious inter-aggregate pores after the second W-D cycle; the specimen volume generally increased with increasing cycles due to the aggregation and increased porosity. The image analysis results show that the geometric characteristics of crack pattern were significantly influenced by the W-D cycles, but this influence was reduced after the third cycle. This is consistent with the observations over the experiment, and indicates that the image processing can be used for quantitatively analyzing the W-D cycle dependence of clay desiccation cracking behaviour. (C) 2011 Elsevier B.V. All rights reserved.

When drying a clayey soil, shrinkage and then cracking on soil surface occur due to water loss by evaporation, this phenomenon seems to be temperature-dependent. In the present work, experimental tests were conducted on saturated slurry to investigate the desiccation cracking behavior at three temperatures (22, 60 and 105 °C). The initiation and propagation of desiccation cracks during drying was monitored using a digital camera. By applying computer image processing technique, the surface crack ratio (RSC) which is the ratio of the surface area of cracks to the total surface area of specimen, was defined to quantify crack networks at different water contents. The experimental results show that the initial critical water content (wIC), which corresponds to the initiation of desiccation crack, increases with temperature rise. After the initiation of a crack, the ratio RSC increases with decreasing water content and then keeps almost constant when the water content becomes lower than the critical water content (wFC). By comparing the cracking curve with shrinkage curve, it has been found that the cracking curve, to some extent, reflects the shrinkage properties of soil since the wFC is related to the shrinkage limit and slightly influenced by temperature.

When drying a clayey soil, shrinkage and then cracking on soil surface occur due to water loss by evaporation, this phenomenon seems to be temperature-dependent. In the present work, experimental tests were conducted on saturated slurry to investigate the desiccation cracking behavior at three temperatures (22, 60 and 105 °C). The initiation and propagation of desiccation cracks during drying was monitored using a digital camera. By applying computer image processing technique, the surface crack ratio (RSC) which is the ratio of the surface area of cracks to the total surface area of specimen, was defined to quantify crack networks at different water contents. The experimental results show that the initial critical water content (wIC), which corresponds to the initiation of desiccation crack, increases with temperature rise. After the initiation of a crack, the ratio RSC increases with decreasing water content and then keeps almost constant when the water content becomes lower than the critical water content (wFC). By comparing the cracking curve with shrinkage curve, it has been found that the cracking curve, to some extent, reflects the shrinkage properties of soil since the wFC is related to the shrinkage limit and slightly influenced by temperature.

Abstract Desiccation cracking process negatively impacts both mechanical and hydraulic properties of clayey soils. Traditional methods applied for the characterization of soil cracking behaviors are mainly based on visual inspections or destructive approaches. The electrical resistivity method provides a non-destructive, sensitive and continuous evaluation of the spatiotemporal variations of many soil physical properties. In this study, an integrated experimental setup is configured to simultaneously capture the evolution of temperature, relative humidity, water content, crack morphology, and apparent electrical resistivity in clay during continuous drying. Apparent electrical resistivity measurements at 1.0 cm electrode spacing are carried out to detect the initiation, propagation and coalescence of desiccation cracks. Image processing quantitatively describes the geometrical characteristics of shrinkage surface crack patterns. Experimental results indicate the strong correlation between the measured apparent electrical resistivity and cracking behavior of soil. As water content decreases during drying, the apparent electrical resistivity of initially saturated clayey soil decreases first before the onset of desiccation cracking, and then transits into the increasing trend. The evolution of apparent electrical resistivity in clayey soil is dominated by two competing effects, with one originated from the volumetric shrinkage-induced closer packing of soil fabric and higher concentration of ions in pore fluids, and another from the evaporation-induced water loss associated with hydration film contraction and desiccation crack insulation. The electrical resistivity method is an effective technique to characterize the development of desiccation cracks, and particularly reliable to map their positions. This study is expected to improve the fundamental understanding of desiccation cracking mechanisms in soils and provide insights on soil characterizations for enhanced stability and performance of earthwork structures. Graphical abstract Image 1 Highlights • ERT technique is effective to characterize desiccation cracking process. • Resistivity decreases first and then increases with decreasing water content. • Initiation of crack leads to sudden high resistivity anomaly. • Resistivity method contributes to early crack detection in earth structure. • Correlations among resistivity, evaporation, shrinkage and cracking were clarified.

Buffer/backfill material in engineered barrier plays an important role in preventing leakage and migrating high-level radioactive nuclear waste (HLW) in geological repository. GMZ bentonite has been proposed as prior buffer/backfill material to be applied in HLW geological repository in China. It is crucial to have a better understanding of the geotechnical properties of this material for optimizing the design and ensuring the long-term stability of the repository. In this paper, the research progress on the geotechnical properties of GMZ bentonite was summarized, including hydraulic conductivity, water retention capacity, thermal physical properties, swelling properties, microstructure, compressibility, multi-fields coupling behavior and long-term characteristics. The following findings are obtained: (1) The basic geotechnical properties of GMZ bentonite are significantly related to the thermal, hydraulic and mechanical boundary conditions, which can be characterized by complex coupling of multi-phase and multi-field; (2) on the premise of meeting the basic requirements of engineered barrier, adding quartz sand and other additives to GMZ bentonite is a currently available and feasible way to improve the geotechnical properties of GMZ bentonite; (3) the observed volumetric deformation and mechanical behavior of GMZ bentonite and mixture under thermal, hydraulic, mechanical and chemical boundary conditions significantly depend on its compaction conditions, relative montmorillonite content and microstructure characteristics; (4) the current researches on GMZ bentonite are mainly limited by traditional laboratory small-scale tests under single-field and single boundary conditions in obtaining single parameter. However, there is still a gap between the simulated environmental conditions in the tests and the real environmental conditions in geological repository. Based on the above understanding and current research shortages in this field, some important research topics were proposed for future work, including multi-field/phase/component coupling characteristics and the mechanisms, long-term performance, large-scale model tests, underground in situ tests, numerical modeling and the constitutive modeling of GMZ bentonite under complex boundary conditions.

Image processing technologies are proposed to quantify crack patterns. On the basis of the technologies, a software “Crack Image Analysis System” (CIAS) has been developed. An image of soil crack network is used as an example to illustrate the image processing technologies and the operations of the CIAS. The quantification of the crack image involves the following three steps: image segmentation, crack identification and measurement. First, the image is converted to a binary image using a cluster analysis method; noise in the binary image is removed; and crack spaces are fused. Then, the medial axis of the crack network is extracted from the binary image, with which nodes and crack segments can be identified. Finally, various geometric parameters of the crack network can be calculated automatically, such as node number, crack number, clod area, clod perimeter, crack area, width, length, and direction. The thresholds used in the operations are specified by cluster analysis and other innovative methods. As a result, the objects (nodes, cracks and clods) in the crack network can be quantified automatically. The software may be used to study the generation and development of soil crack patterns and rock fractures. & 2013 Elsevier Ltd. All rights reserved.