Formation Of Desiccation Cracks Research Articles

Drainage Characteristics, Capillary Barrier Effect, and Diversion Length of Flat Earthen Roof of Historical Kemaliye Houses

ABSTRACT Kemaliye houses stand out as remarkable examples of Anatolian architecture, renowned for their distinct mixed construction method and the utilization of diverse and sustainable materials. The flat earthen roof, constructed using local soils and traditional techniques, adds to the unique character of these houses. However, due to the need for roof maintenance, particularly in winter, residents have adopted modern roofing methods. In order to preserve the architectural integrity of historic houses, research into the mechanisms and performance of flat earthen roofs using local materials and original construction techniques is essential. To achieve this objective, original materials, and construction techniques were investigated with 1D infiltration laboratory tests and analyzed using numerical modelling. The results indicated the existence of a capillary barrier effect on the roofs. Additionally, water balance and diversion length of the roof is obtained through experimental study and numerical analysis. Furthermore, numerical analyses indicated that the capillary barrier effect may be reduced or weakened as a result of frost heave and the formation of desiccation cracks. Understanding these phenomena is a vital step in developing effective solutions for preserving and maintaining roofs in their original architectural form.

Impact of Vetiver Plantation on Unsaturated Soil Behavior and Stability of Highway Slope

Due to cyclic wetting and drying, the hydro-mechanical behavior of unsaturated soil is impacted significantly. In order to assess the soil strength parameters, knowing the unsaturated behavior is important. Soil moisture content is an important parameter that can define the shear strength of the soil. Most of the highway slopes of Mississippi are built on highly expansive clay. During summer, the evaporation of moisture in the soil leads to shrinkage and the formation of desiccation cracks, while during rainfall, the soil swells due to the infiltration of water. In addition to this, the rainwater gets trapped in these cracks and creates perched conditions, leading to the increased moisture content and reduced shear strength of slope soil. The increased precipitation due to climate change is causing failure conditions on many highway slopes of Mississippi. Vetiver, a perennial grass, can be a transformative solution to reduce the highway slope failure challenges of highly plastic clay. The grass has deep and fibrous roots, which provide additional shear strength to the soil. The root can uptake a significant amount of water from the soil, keeping the moisture balance of the slope. The objective of the current study is to assess the changes in moisture contents of a highway slope in Mississippi after the Vetiver plantation. Monitoring equipment, such as rain gauges and moisture sensors, were installed to monitor the rainfall of the area and the moisture content of the soil. The data showed that the moisture content conditions were improved with the aging of the grass. The light detection and ranging (LiDAR) analysis was performed to validate the field data obtained from different sensors, and it was found that there was no significant slope movement after the Vetiver plantation. The study proves the performance of the Vetiver grass in improving the unsaturated soil behavior and stability of highway slopes built on highly expansive clay.

Effects of geometry of soil specimens on the formation of desiccation cracks

Desiccation cracks in soils are important in engineering structures that need hydraulic integrity such as earth dams, and containment facilities. At the element test level, such cracks are a hindrance when the volume change of the soil specimen needs to be measured during the test. One such test is the volumetric shrinkage test where the volume of the soil specimen needs to be continuously determined together with its mass change as the soil specimen dries. The soil specimen may deform non-uniformly. Previously hazardous and cumbersome methods using mercury or wax are needed to determine the volume of soil specimens that deform non-uniformly, but the advent of 3D scanning and photogrammetry enables the volume of non-uniform soil specimens to be measured quite accurately. However, such techniques cannot accurately determine the volume of the deformed soil specimen once cracks start appearing in the soil specimen. Volumetric shrinkage tests are commonly conducted for cylindrical soil specimens. This paper investigates the geometry (shapes and dimensions) of soil specimens other than cylindrical on the formation of desiccation cracks. Bentonite is used as the test soil as it experiences large volume change on drying. The test results provide guidance for the geometry of a soil specimen to be used in the volumetric shrinkage test.

Investigating the impact of sample desiccation on Itrax XRF core scanner signal reproducibility

AbstractSediment samples tend to dry out during storage and are, therefore, stored refrigerated at about 4°C after wrapping in plastic foil. During XRF core scanning however, the samples must be taken out of their cover, increasing the risk of drying and formation of desiccation cracks on the surface. Because scan times can often amount to several hours and at highest resolution may take over a day to complete, the core will progressively dry out during scanning. With this study we aim to increase our understanding of how this slow drying of the samples during scanning and storage influences the XRF signal because of changes in water content, sediment surface topography, and the development of small, but slowly expanding cracks in the sediment core. Results show that the desiccation of samples during scanning and storage influence the XRF measurements in several ways. Most importantly, slow desiccation of the cores results in both a general lowering of the sample surface, and a shortening of the core due to shrinkage. Larger distance between sediment surface and detector leads to increased noise levels and poor reproducibility for many elements, while the shrinking of cores may shift individual data points between runs, resulting in poor reproducibility and offsets between datasets obtained at different times. Moreover, the loss of light elements, such as hydrogen and oxygen, can influence the matrix effect, especially for organic‐rich sediment. Because the XRF signals of individual elements are affected to different degrees, these changes may induce artificial shifts and biases in many elemental ratios commonly used for paleoenvironmental reconstruction.

Improving soil resilience to drought climate by an eco-friendly approach

With the intensification of global warming, the increasing extreme drought climate has seriously threatened the stability of critical geotechnical infrastructure. This study proposes a novel, eco-friendly approach to improve soil resilience to drought climate. In order to verify the feasibility and durability of the proposed approach, a series of simulated climatic wetting-drying (WD) cycles were carried out using four sets of soil specimens treated with different W-OH (an eco-friendly polymer) concentrations. During this period, the water evaporation history, desiccation cracking process, WD cycle durability and microstructure evolution of soil specimens treated with different W-OH concentrations were investigated. The results reveal that the W-OH modification has a significant suppression effect on the whole process of soil evaporation, which can effectively prolong the soil evaporation time of constant rate stage and falling rate stage. The addition of W-OH not only significantly reduces crack ratio, total crack length, and average crack width, but also slows down the crack growth rate. Compared with untreated soil specimen, the treatment with low concentration of W-OH (2% and 4%) can effectively mitigate the formation of desiccation cracks, while the treatment of higher concentration of W-OH (6%) can directly prevent the occurrence of such cracks. The microstructure analysis results indicate that the W-OH can transform the soil structure into a denser state through two ways of bridging and encapsulation, which significantly increases the migration resistance of pore water and improves soil strength properties. This investigation is expected to improve fundamental understanding of soil-atmosphere interactions under eco-friendly polymer modification and provides insights into the potential application of eco-friendly polymer modification in enhancing soil resilience to extreme drought climate.

The physics of desiccation cracks 2: Modeling and prediction of the crack patterns

This paper extends the experimental results of our companion paper by modeling and predicting the onset and pattern formation of desiccation cracks in geomaterials (Ruoyu et al., 2023). Thin-layer silt samples in controlled atmospheric conditions were tested to obtain the surface strain maps with the digital image correlation (DIC) method during dehydration. Support experiments, including consolidation and displacement-controlled triaxial tests, were conducted for the properties of geomaterials. These experimental results were used to validate a viscoplastic theoretical model by comparing cracks and singularities locations that distribute following the Cnoidal wave pattern. A critical value exists in the viscoplastic model that determines the number of singularities, which accurately predicts the number of cracks in the experiment. The critical values contain two crucial parameters: rate sensitivity and λ. Rate sensitivity describes the rate-dependent stress–strain relation, while λ shows the ability of pore pressure redistribution under the external mechanical loading rate. These results provide a new view to analyze the desiccation cracks considering the rate-dependent viscoplasticity.

Crack development in a physical model of undisturbed expansive soil slope and core sample under wet-dry cycles

Cyclic wetting and drying in expansive soil slopes results in the formation of desiccation cracks and irreversible structural changes which can cause substantial reduction in overall soil strength leading to slope instability. This study investigates the structural and crack development in a physical model of undisturbed expansive clay slope and small core sample subjected to five wet-dry cycles. The surface distribution and vertical extent of cracks in the slope model was measured during the various drying and drying cycles. The crack intensity factor, which quantifies surface cracks increased with increasing wet-dry cycles and became constant in the third cycle. Vertical cracks whose bases are connected by near horizontal cracks or cracks parallel to the slope developed to a maximum depth of 28 cm in the physical model. The shallow depth and orientation of these cracks along the slope may be a contributing factor for the shallow infinite slope failure in expansive soils. In addition, suction and water content measurements were made during various cycles. Changes in suction occurred to a depth of 28 cm, and the maximum suction increased with increasing cycle number. The results also demonstrate boundary and size effects on crack formation.

3D deformation and strain fields in drying kaolinite obtained from tracking internal bubbles using X-ray CT and ANN

AbstractDrying fine-grained sediments experience shrinkage and desiccation cracking that may dramatically alter their mechanical and hydraulic properties. This study adopts X-ray computed tomography (CT) to monitor the three-dimensional (3D) internal deformation and strain fields, and their relationships with desiccation crack formation, for drying kaolinite samples contained in plastic containers. Two kaolinite samples, one dried at room temperature and the other oven-dried at 60 °C, were CT scanned at several intervals during the drying process. From sequential CT scans for the same sample, entrained gas bubbles were extracted and used as tracking markers for deformation and strain field measurements. Since the bubble morphology continuously changed during the drying process, an artificial neural network (ANN) model was developed to link bubbles in sequential scans for the same sample. The tracking algorithm was trained with manually linked bubbles and optimised by comparing different combinations of bubble information, e.g. bubble location, size and shape. The drying samples experienced primarily vertical displacement before the air-entry value, while horizontal displacement occurred during vertical crack formation. Internal vertical and horizontal strains were generally uniform, indicating a limited impact of non-uniform sample drying and substrate constraint.

Ir–Ru Electrocatalysts Embedded in N‐Doped Carbon Matrix for Proton Exchange Membrane Water Electrolysis

AbstractMore active electrocatalysts for H2 and O2 evolution reactions, efficient membranes, and robust porous transport layers (PTL) are required for designing advanced proton exchange membrane water electrolysis (PEMWE) systems. An N‐doped carbon matrix is introduced in this study to surpass the existing Ti PTLs. One‐step pyrolysis results in the carbonization of polyaniline films to the N‐doped carbon matrix, simultaneous formation of desiccation cracks and IrxRuy nanoparticles, and partial impregnation of the synthesized particles into the carbon matrix. The embedded IrxRuy nanoparticles are firmly bound to the surface of the carbon matrix, inhibiting the dissolution and detachment of the nanoparticles during the O2 evolution reaction (OER). The cracks in the carbon matrix allow the steady transport of the produced O2, comparable to conventional PTLs. After optimizing the Ir and Ru contents of the nanoparticles based on the electrocatalytic performance, Ir88Ru12 embedded in the N‐doped carbon matrix is found to be the most suitable catalyst for enhancing the OER performance of the PEMWE system with negligible degradation. These findings can potentially contribute to the industrial application of PEMWE. Relevant electrochemical systems with membrane electrode assemblies, such as fuel cells and CO2 reduction systems, can be modified using the suggested structure.

Maize Yield Response, Root Distribution and Soil Desiccation Crack Features as Affected by Row Spacing.

Plant density is among the most critical factors affecting plant yields and resource use efficiency since it drives the exploitation of the available resources per unit area, root distribution and soil water losses by direct evaporation from the soil. Consequently, in fine-textured soils, it can also affect the formation and development of desiccation cracks. The aim of this study, carried out on a sandy clay loam soil in a typical Mediterranean environment, was to investigate the effects of different row spacings of maize (Zea mais L.) on yield response, root distribution and the main features of desiccation cracks. The field experiment compared bare soil and soil cropped with maize using three plant densities (6, 4 and 3 plants m-2), obtained by keeping the number of plants in a row constant and varying the distance between the rows (0.5-0.75-1.0 m). The highest kernel yield (16.57 Mg ha-1) was obtained with the greatest planting density (6 plants m-2) with a row spacing of 0.5 m; significantly lower yields were recorded with spacings of 0.75 and 1 m, with a decrease of 8.09% and 18.24%, respectively. At the end of the growing season, soil moisture in the bare soil was on average 4% greater in comparison to the cropped soil and was also affected by row spacing, decreasing with the decrease in the inter-row distance. An inverse behaviour was observed between soil moisture and both root density and desiccation crack size. Root density decreased to the increase in soil depth and to the increase in distance from the row. The pluviometric regime occurred during the growing season (total rainfall of 343 mm)-resulted in the formation of cracks of reduced size and with an isotropic behaviour in the bare soil, whereas in the cultivated soil, the cracks were parallel to the maize rows and increased in size with decreasing inter-row distance. The total volume of the soil cracks reached a value of 135.65 m3 ha-1 in the soil cropped with a row distance of 0.5 m, and was about ten times greater in comparison to the bare soil and three times greater in comparison to a row spacing of 1 m. Such a volume would allow a recharge of 14 mm in the case of intense rainy events on soil characterised by low permeability.

Shrinkage cracks of bentonite-zeolite mixtures

Bentonite is commonly used in geosynthetic clay liner (GCL) as well as compacted clay liner (CCL) for containment facilities such as sanitary landfills due to its low permeability. Bentonite experiences significant shrinkage on drying, leading to the formation of desiccation cracks and increasing the likelihood of contaminant leachate from the landfill. Adding granular materials such as fine sand to bentonite canreduce shrinkage and hence shrinkage cracks. Recently, zeolite has been suggested as another possible additive to reduce be shrinkage cracks in bentonite. Zeolite has additional benefits of being able to adsorb heavy metals and when enriched with silver, zinc, or copper, it can function as a biocide. The objective of this paper is to present the results of a study on shrinkage crack formation of bentonite-zeolite mixtures during drying. The evolution of shrinkage cracks of the bentonite-zeolite mixtures on drying was studiedusing image processing. The results show that desiccation cracks are at a minimum when the zeolite content is between 15% and 20%. The finding is useful to design more efficient GCL or CCL when zeolite is incorporated into the bentonite layer.

Variational Approach to Damage Induced by Drainage in Partially Saturated Granular Geomaterials

Within the context of immiscible biphasic flow in porous media, when the nonwetting fluid invades the pore spaces which are a priori saturated with the wetting fluid, capillary forces dominate if the pore network is formed by fine-grained soils. Owing to the cohesion-less frictional behavior of such soils, a capillary force–driven fracturing phenomenon has been put forward by some researchers. Unlike the purely mechanistic tensile force–driven mode-I fracturing that typically has been attributed to the formation of desiccation cracks in soils, attempts to model this alternate capillarity-driven mechanism have not yet been realized at a continuum scale. However, the macro-scale counterpart of the capillary energy associated with the various pore-scale menisci is well-established as the interfacial energy characterized by the soil-water retention curve. An investigation of the possible contribution of this interfacial energy in supplying the dissipation related to fracture initiation is the essence of this work, inspired by the vast literature on gradient damage modeling.

Editorial: Hydromechanical Instabilities in Geomaterials: Advances in Numerical Modeling and Experimental Techniques

study of coupled hydromechanical instabilities, where the notion of mechanical instabilities is enriched 13 by the complementary (and not necessarily independent) notion of hydraulic instabilities, with a key role 14 played by interfaces and coupled hydromechanical phenomena.Geomaterials are intrinsically multi-phase, the porous network being typically saturated by a mixture of Hydromechanical Instabilities in Geomaterials et al. (2009, 2013), to explain the formation of desiccation cracks in soils, an alternate capillarity-driven 73 mechanism is proposed at the continuum scale.We hope that readers will enjoy reading the carefully selected papers on the growing and exciting research 75 area of coupled hydromechanical instabilities in geomaterials.

Desiccation Cracking Behavior of Sustainable and Environmentally Friendly Reinforced Cohesive Soils.

Desiccation cracking of cohesive soils is the development of cracks on the soil surface as a result of a reduction in water content. The formation of desiccation cracks on the cohesive soil surface has an undesirable impact on the mechanical, hydrological, and physicochemical soil properties. Therefore, the main aim of this study is to experimentally and numerically investigate eco-friendly soil improvement additives and their effect on the desiccation cracking behavior of soils. Improvement of soil crack resistance was experimentally studied by conducting desiccation cracking tests on kaolin clay. Biopolymer xanthan gum and recycled carpet fibers were studied as potential sustainable soil improvement additives. In addition, image processing was conducted to describe the effect of an additive on the geometrical characteristics of crack patterns. The results show that the soil improvement additives generally enhanced the soil strength and reduced cracking. Furthermore, a hydro-mechanical model was developed to predict the moisture transfer and onset of desiccation cracks in plain and amended kaolin clays. Data obtained show that the inception of the desiccation cracking and radial displacements were delayed in the improved soil specimens, which is in agreement with the experimental data.

Effects of desiccation cracks and vegetation on the shallow stability of a red clay cut slope under rainfall infiltration

Red clay, an easily cracking lateritic soil, is extensively distributed in southern China. Cracked red clay slopes often show shallow failures under rainfall, which is challenging to reproduce by finite element methods. This study aims to examine how desiccation cracks and vegetation affect the shallow stability of a red clay cut slope during rainfall. Numerical models of the slope are created using ABAQUS, and an effective approach is proposed to simulate the distribution of desiccation cracks. The reliability of the numerical models and approaches is validated against field surveys. Parametric analysis is then conducted to investigate the influences of rainfall parameters, crack parameters and vegetation parameters on the slope stability. The results demonstrate that the presence of desiccation cracks can cause shallow failure and greatly reduce the factor of safety of the slope. This indicates that control of crack development is important to maintain slope safety. Moreover, the stability of cracked slopes can be obviously improved by vegetation with roots longer than 0.5 m. A tap root system appears to perform better than a fibrous root system. However, shallow-rooted vegetation may also contribute to the shallow stability of the slope by restraining the formation of desiccation cracks.

Experimental Study on the Variation of Surface Widths of Lignite Desiccation Cracks during Low-Temperature Drying.

Significant volume shrinkage and drying cracking of high-water-content lignite will occur during low-temperature drying. To determine the variation behaviors of the drying shrinkage rate and desiccation crack surface width in the process of low-temperature drying, low-temperature and low-humidity drying experiments were conducted, and the variations of the surface widths of the desiccation crack with time and water content of old lignite were examined. The results showed that the slow drying of lignite at low temperatures caused significant volume shrinkage and desiccation crack formation, and the occurrence and development of desiccation cracks were highly nonuniform. Three stages of the variation of surface widths of the desiccation cracks were observed with the water content decrease: an initial rapid increase stage, a second slow decrease stage, and a final stable stage, and the average width of the desiccation cracks increased in a Gaussian function. The higher the evaporation rate and volume drying shrinkage rate, the lower the surface width of the desiccation cracks under low-temperature drying conditions. To achieve safe and green mining, storage, transportation, processing, and utilization of lignite, the moisture content of old lignite should be controlled to be above 13–15%.

A temperature-dependent model for tensile strength characteristic curve of unsaturated soils

Tensile strength is a key parameter controlling the formation of desiccation cracks in soils. Desiccation cracks are triggered in unsaturated soils due to drying imposed by natural processes or engineering applications mainly involving elevated temperatures. However, there is no closed-form model in the literature to capture the effect of temperature on tensile strength. This study presents a temperature-dependent model for the tensile strength characteristic curve (TSCC) of unsaturated soils. The model employs the suction stress characteristic curve (SSCC) to represent the uniaxial tensile strength of unsaturated soils at different water contents and temperatures. The model incorporates the effects of temperature into adsorptive and capillary suction stress components. The temperature-dependent adsorptive suction stress is obtained by accounting for thermal induced changes in suction stress at dry state through the Hamaker constant and the density of water. The temperature-dependent form of capillary suction stress is derived by employing temperature-dependent forms of surface tension, contact angle and enthalpy of immersion. Upon comparison, results from the proposed TSCC exhibited a very good agreement against laboratory-measured tensile strength data for two clayey soils tested at different temperatures ranging from 20 to 60 °C. The presented model can improve the analysis of desiccation cracking in unsaturated soils.

Influence of fibers on desiccation cracks in sodic soil

Drying shrinkage of soil contaminated by alkaline solutions in ecologically fragile areas is a key issue that affects the strength, stability, and permeability of contaminated soil. Reinforcement with polypropylene fibers is a common physical treatment method. This paper presents experimental investigations of the shear strength, permeability, formation, and development of desiccation cracks in sodic soil with four different contents of polypropylene fibers: 0%, 2%, 4%, and 8%. The shear strength and permeability coefficient were tested by the SLB-1 triaxial shear permeability tester. Meanwhile, a series of crack images and water content evolution were obtained during free desiccation tests with self-designed monitoring equipment. The dynamic changes in the cracks are then quantitatively analyzed by using digital image processing and geographic information system (GIS) analysis. The experimental results show that shear strength increases and permeability coefficient decreases with the increase of fiber content. The evaporation process with different polypropylene fiber contents has three stages, namely, Stages I, II, and III that are in accordance with the slope of the evaporation curve. However, the polypropylene fiber content has little effect on the total duration of crack development. The crack development process has three stages. The crack ratio, fractal dimension, and average width decrease as the polypropylene fiber content increases. The fractal dimension gradually and linearly increases with time. The fractal dimensions of the cracks are reduced with increased polypropylene fiber content, which indicates that polypropylene fibers can inhibit the development of soil cracking. Because the elastic modulus of the fibers is very high, it is difficult for the fibers to be pulled out from the soil during cracking. Therefore, friction is produced at the interface between the fibers and soil particles, which can inevitably inhibit the relative sliding of the fibers and share the tensile stress caused by the structural shrinkage in the soil. Therefore, polypropylene fibers can dramatically improve the stability and integrity of soil, similar to a “bridge.” In conclusion, these research results provide an important explanation for dealing with alkali-contaminated foundations and soils.

Effects of drying and shrinkage on the mechanical performance of unsaturated fine/medium- grained soils used as heat storage media

Studying the mechanical behavior of heat storage media is vital in the safety and design of most sensible and borehole thermal energy storage systems, which are normally built as part of the sub-structure of buildings with load bearing capabilities. In spite of its importance on the efficiency and performance of heat energy storage systems, the mechanical stability and behavior of heat storage materials, mainly at elevated temperatures, has not been given adequate attention in past studies. On this regard, the mechanical behavior of three unsaturated fine- and medium- grained soils from Germany is studied at elevated temperatures, in view of using the soils as a solid sensible heat storage media. The results show a significant dependence of the mechanical behavior of the investigated soils on moisture content and temperature. Furthermore, an increase in shrinkage of the soil specimens with a decrease in the texture of the soils was observed during heating of the soils. The shrinkage behavior is also corroborated with the formation of minor and moderate tensile desiccation cracks of the specimens, which when unaccounted for can result in the lowering of the heat conduction of the heat storage medium, thus lowering the efficiency of the heat storage system.

Experimental study of the main controlling factors of desiccation crack formation from mud to shale

Numerous studies have been done on the formation mechanism and distribution law of desiccation cracks. However, the formation mechanism of micro-cracks in shale is still unclear. In this study, the most common clay minerals of shale (montmorillonite, illite, kaolinite) were experimentally studied to identify the main controlling factors of desiccation crack formation, and show the influence of these factors on crack geometry. To imitate the process of desiccation crack formation, a diagenetic crack imitator machine and a laboratory air drying were used. The results show that clay content, temperature, and thickness of the clay layer are the main factors that control the crack formation. Our samples suggest that crack width increases with increased montmorillonite content, and decreases with increased kaolinite and illite content. Temperatures of 100 °C and 230 °C induced further desiccation cracks in pure mineral solutions, while the mixed samples did not show any additional crack propagation. Crack width was shown to increase with layer thickness. In addition, 92% of all samples exhibited the three-armed pattern, where the angle distribution was between 90-100 and 170–180°. We further propose that the water content in the dehydration process plays an important role in the formation of cracks, and the crack formation can be divided into four stages. The majority number of cracks occur at the initial and development stages, where the main mono-crack forms and starts to divide. The cracks intersect each other at the complex third stage. Ultimately, at the weak stage the last few random thin cracks might form. The formation of the first crack also depends on clay type and varies in time within an order from early to late: montmorillonite, kaolinite, illite. Based on the visual similarity between diagenetic micro-cracks in shale and mud desiccation cracks, as well as their mechanism of cracks formation, this study may provide a new perspective on the formation of the diagenetic micro-cracks in shale reservoirs and complements previous studies through virality of pure homogeneous and mixed clay samples.