Clay Cracking Research Articles

Study on the effect of deformation and strength characteristics of microencapsulated phase change materials on modified silty clay under dry and wet cycles

To prevent the cracking of silty clay under cyclic wet-dry cycling (W-D), which leads to the increase of deformation and strength attenuation of silty clay, microencapsulated phase change material (mPCM) was used to improve it. The deformation and strength characteristics of silt with different dosages (1 %, 2 % and 4 %) of mPCM and their changing patterns were analyzed and studied by indoor compaction test, crack observation test, consolidation test and straight shear test, and compared with silt without modifier. The results showed that with the increase of mPCM dosage, the optimum water content of silt and the maximum dry density decreased. A 2 % dosage of mPCM inhibited the development of silty clay cracks, reduced crack width and deformation, and increased the compression modulus of the soil samples by nearly 2.3 times. Under dry and wet cycling conditions, the cohesion decay of silty clay is greater than the angle of internal friction. The addition of 2 % mPCM significantly increased the shear strength of silty clay, cohesion by nearly 2.1 times, and internal friction angle by 1.4 times. The mPCM inhibits crack development mainly by regulating the internal temperature field of soil samples, thus improving soil strength. This study provides a reference for inhibiting soil cracking from a new temperature perspective.

Calculation model of depth under quantification of surface morphology of dry shrinkage cracks in red clay

Cracks commonly form in clay owing to water loss, negatively affecting strength and hydraulic properties of soil, leading to rock and soil damage including landslides and dam instability. Understanding the changing patterns of the shrinkage crack depth is crucial for exploring slope infiltration patterns and determining key factors for slope stability. This study suggests a relationship between the surface and depth variations during cracking, and investigates the influence of the surface roughness on shrinkage cracks in saturated red clay. Regression analysis and machine learning algorithms were used to establish a depth prediction model. (1) Based on the surface morphology of shrinkage cracks, they are categorized into three types: linear, curved, and inflectional (linear and curved are the main types). (2) The surface roughness and development rate of surface cracks were positively correlated. (3) Based on the geometric parameters of the crack surface, a prediction model (error within 15%) for crack depth was established using multivariate nonlinear regression, providing a reference for the initial assessment of crack depth. These results provide a better understanding of the development patterns of shrinkage cracks, whose influence on slope stability is critical for mitigating the risks associated with slope instability and other soil failures.

The Effect of Soluble Sugar Degradation on the Evaporation of Compacted Clay

In arid climates, evaporation and water loss in surface soil can lead to the development of shrinkage cracks in the soil. The crack network in contaminated soil sites can become a rapid pathway for the infiltration and transport of contaminations, thereby increasing the range of soil contamination. Dense contaminated clay samples were prepared by using glucose as a representative soluble sugar of domestic source contaminations. Through indoor evaporation simulation tests, the effect of soluble sugar anaerobic degradation on the water loss, deformation, and crack growth of compacted clay was analyzed, and the mechanism of this effect was revealed. The results showed that glucose increased the water-holding capacity of clay, while the anaerobic degradation of glucose decreased the water-holding capacity of clay. Although glucose anaerobic degradation reduced the overall deformation of dense clay, it promoted the development of evaporative cracks on the surface of dense clay. Soluble sugar anaerobic degradation mainly affected the evaporative cracking of clay by “forming hydrogen bonds to reduce the rate of evaporative water loss in clay” and “generating CO2 to alter the structure of the clay”.

Dry shrinkage cracking and permeability of biopolymer-modified clay under dry–wet cycles

Biopolymers efficiently improve the anti-seepage function of compacted clay layers, but research concerning the permeability stability of biopolymer-modified clay during cyclic wetting and drying is scarce. In this paper, the macro–microstructures and the permeability coefficients of biopolymer-modified clay and conventional bentonite-modified clay under dry–wet cycles are comparatively studied. The bentonite modifier is found to increase macro–microscopic cracks under dry–wet cycles, while the xanthan modifier decreases the macro–microscopic fracture rate of the clay. The physical properties of 2% by dry weight xanthan-modified clay are similar to those of 10% by dry weight bentonite-modified clay, but the permeability coefficient of the former is lower by approximately one order of magnitude. After the dry–wet cycles, xanthan-modified clay performed better in leakage prevention than bentonite-modified clay. For low-liquid-limit clay, the recommended mass percentage of xanthan gum was 1.5% considering the seepage resistance safety during dry–wet cycles.

Spatial uncertainty quantification of desiccation cracks in clays with limit state-adjusted linear elasticity

Spatial uncertainty quantification of desiccation cracks in clays with limit state-adjusted linear elasticity

Study on Crack Development in Red Clay from Guangxi Guilin with Different Clay Grain Content

In order to study the influence of different clay contents on the fractality of red clay, specimens having four different water contents were prepared. The cracking characteristics of the specimens were observed at 20 °C and 60 °C. Image J software was used to measure and calculate the crack area, crack ratio, crack length and width of each sample. The test results showed that the development of cracks in red clay could be divided into three stages: crack generation, crack development and crack stabilization. The clay particle content, temperature and water content have significant effects on crack development, and from the test analyses, it was determined that for construction in the Guilin area, it is necessary to pay attention to drainage protection.

Effect of initial water content and dry density on the self-healing of desiccation cracks in compacted hipparion red clay

The self-healing of desiccation cracks in compacted clayey soils is important for mechanism revelation of cracking behavior in compacted soils. Although the crack self-healing behavior has been found, the influence of soil physical indices on it is still unclear, especially initial water content and dry density of specimen. This study aims to identify and evaluate the effect of initial water content and dry density on self-healing of desiccation cracks. Firstly, a series of desiccation tests were conducted on compacted Hipparion red clay specimens under different initial conditions. Secondly, the two-dimensional morphology of desiccation cracks and strain field changes on specimen surface were examined using the pore and crack analysis system and digital image correlation techniques. The result shows that the desiccation cracks on specimen surface exhibits self-healing behavior during drying. Based on the observed crack self-healing behavior, the desiccation cracking of compacted Hipparion red clay undergoes four stages including initiation, development, self-healing, and stabilization. During the self-healing stage, the critical water content for occurrence of crack self-healing and the crack self-healing amount referring to the crack ratio reduction from peak value to the stable value, are dry density dependent and water content dependent variables. In particular, the higher the initial water content and the lower the dry density of compacted specimen are, the larger the crack self-healing amount is. This crack self-healing difference in specimen with different initial conditions is caused by the vertical anisotropic shrinkage of substrate soil below non-propagating cracks due to its pore structure difference. This study provides a new perspective on the mechanism of desiccation crack in clayey soils affected by initial conditions.

Influence of Clay Content on Crack Evolution of Clay–Sand Mixture

Clay particles have an important influence on the cracking of clay–sand mixture, but the quantitative relationships between the clay content and crack evolution of the clay–sand mixture are still not clear. In order to explore the crack evolution process of the clay–sand mixture under different clay content conditions, we prepared nine groups of saturated clay–sand mixture samples with different clay contents and carried out drying experiments and Brazilian tests. The geometric dimensions and development forms of soil cracking were quantitatively analyzed by taking pictures of the sample cracks, image processing, and weighing the variation of the soil mass at the corresponding time during the drying process. The results showed that when the clay content was greater than 50%, the development process of the clay–sand mixture cracks can be divided into three stages: the formation stage of main cracks, the generation stage of the autonomously derived secondary fractures, and the stage of cracks widening. When it was less than 50%, the cracks in the development process of clay–sand mixture cracks had the characteristics of short length, dense crack spacing, no main cracks, and no obvious stage. The clay could add the tensile strength of the mixture and restrain crack development. The clay content had a significant effect on the shrinkage cracking and crack development process of soil, which shows that with the increase in the clay content, the tensile strength increases and restrains the crack development; the crack rate increases continuously and the width of cracks become larger; the lower the clay content, the lower is the crack rate and the smaller is the average crack width. The water content of samples with different clay soil contents all nonlinearly decreased with the increase in drying time, and the corresponding residual water content increased with the increase in the clay soil content at the same time. The water content of initial cracking, stable crack length, stable crack width, and stable block of the clay–sand mixture increased with the increase in the clay content, and the water content of the stable crack length was the same as that of the stable block number.

Centrifuge model studies on desiccation cracking behaviour of fiber-reinforced expansive clay

In this study, randomly distributed fiber reinforcement on the desiccation cracking behavior of expansive clay was investigated. Modeling considerations for the desiccation cracking behavior of unreinforced and fiber-reinforced clay was established using dimensional analysis. A custom-designed setup consisting of a specimen container, heating assembly, and digital image acquisition system was designed, calibrated, and used in the present study. A series of desiccation cracking tests were performed on unreinforced and fiber-reinforced expansive clay in a balanced beam geotechnical centrifuge. The test setup performance was evaluated by conducting tests at varying gravity levels and performing modeling of models. Digital image analysis and particle image velocimetry techniques were used to obtain qualitative information about the cracking of clay under the influence of fiber reinforcement and the varying thickness of the clay layers. The specimens reinforced with fibers exhibited improved cracking resistance than unreinforced clay specimens. The results indicate that the desiccation cracking of clays can be successfully modeled in a geotechnical centrifuge, highlighting the fact that this study is the first-ever such study. This knowledge can be used to study the behavior of critical geotechnical structures, especially clay barriers of landfill cover subjected to desiccation cracking.

Autogenous sealing of a cavity in bentonite clay: an x-ray computerised tomography study

Autogenous closure of cracks in clay during wet−dry cycles is usually observed through digital photography or x-ray, or inferred from changes in hydraulic conductivity. Samples in almost all experimental studies of clay self-sealing carry networks of cracks, making it challenging to control initial conditions of healing or to separate processes operating over a single crack from those pertaining to interaction between cracks. Furthermore, most observational studies are based on before-and-after images with little sense of the pace of crack closure. This paper reports a set of x-ray computerised tomography observations of a single artificial cylindrical hole, as a proxy for a crack, in consolidated, close-to-saturation bentonite samples, undergoing further hydration. The sample is scanned at different times and the scans analysed by image processing. The results show that water chemistry, pre-consolidation pressure and vertical boundary conditions all significantly affect the pace and extent of hole closure. The pace of hole closure is found to follow a logarithmic function when the sample is unconstrained vertically. Autogenous closure appears to be due mostly to osmotic swelling. This suggests that the latter may form the basis for developing constitutive relationships and evolution functions for sealing of cracks in swelling clay undergoing wet−dry cycles.

Shrinkage cracking and strength deterioration of red clay under cyclic drying and wetting

Taking the red clay from Guilin, China as the object, this paper prepares red clay samples with different initial water contents, extracts the crack parameters from the images on the samples under cyclic drying and wetting through image processing, and analyzes the laws of crack development. In addition, parallel red clay samples were subject to shrinkage tests and direct shear tests under the same cyclic drying and wetting. Based on the test results, the authors discussed the laws of shrinkage deformaiton and strength change for the samples under cyclic drying and wetting, and examined the relationship between cracking, shrinkage properties, and strength detiroation of the red clay. The results show that: (1) With the growing crack rate, the volume shrinkage ratio constantly declined; the area shrinkage ratio was generally decreasing, but the decrement was not obvious in local places (in some places, the area shrinkage ratio even increased); the shrinkage coefficient generally declined, (2) Through the five dry-wet cycles, it was learned that the cohesion and internal friction angle of red clay strength can be quantified using the crack rate. This finding lays the basis for judging soil strength based on crack rate, and solving actual engineering problems with the red clay.

A work on reticulated patterns

A work on analyzing and modeling reticulated pattern is told through a personal point of view, showing its development trough many people inputs, including that of Yves Couder. The question of how to describe a reticulated pattern as Ficus religiosa leaf veins and make a physical model reproducing it, led to study cracks in colloids or clay, city streets plans, gorgon skeletons and variation in fern vein patterns.

The evolution of cracks in red clay under wet and dry cycles and its influence on shear strength

Using computer image processing technology and lots of triaxial experiments, the fracture evolution rules and shear strength indexes of red clay in the wet and dry cycles were analyzed, and the functional relationship between shear strength indexes of red clay and fracture density was established. The parameters in slope stability calculation were also discussed by the strength indexes reduction method. The results show that with the increase of the times of dry and wet cycles, the crack density gradually increases and eventually it remains stable. During the first two wet and dry cycles, the crack development of red clay was the most obvious. After the dry-wet cycle, the stress-strain curve of the red clay is weakly hardened and the failure mode is bulging. The shear strength of red clay is significantly reduced by the influence of dry wet cycle. After the first cycle, the attenuation of strength indexes is obvious, and the final strength indexes trend to be stable. The attenuation amplitude of the cohesive force is significantly larger than the internal friction angle. After the wet-dry cycle, the stable value of its cohesion becomes 54% ∼ 57% of the initial value, and the stable value of the internal friction angle becomes 45% ∼ 63% of the initial value, so it is recommended to use the value of the long-term strength index and it is more accurate to calculate the slope stability under dry and wet cycles. Under the action of dry and wet cycles, a quadratic polynomial can be used to fit the functional connection between the crack density of red clay and the index of shear strength.

Mitigation of desiccation cracks in clay using fibre and enzyme

Formation of cracks during desiccation is a natural phenomenon in expansive clay. Mitigation of desiccation-induced cracks is highly beneficial for increasing the life span of geo-infrastructures particularly in hydraulic barriers. Improvement of soil properties using additives is a key method in controlling desiccation crack formation and their influence. This paper presents experimental results for an expansive clay modified with nylon fibre and an enzyme-based product. A series of desiccation cracking tests were carried out with varying fibre contents and a constant enzyme dosage. Three-point bending beam tests were performed to evaluate tensile strength of the modified clay. The additives, fibre and the enzyme were able to alter the crack patterns significantly thereby alleviating the effects of cracks. Furthermore, the addition of enzyme alone increased the tensile strength by about 50% while the combined effect of both fibre and enzyme increased the tensile strength by approximately 100% compared with untreated soil. Based on measurement of crack patterns and other properties of the modified clay, the investigation suggests the potential for the fibre-enzyme addition to mitigate desiccation cracks. Further work needs to be carried out to determine optimal dosing requirements for each additive and investigate the effects of potential interactions between the fibre and enzyme.

Desiccation crack formation and prevention in thin bentonite layers

Desiccation cracks in clay play an important role in many geoenvironmental applications such as clay liners in engineered landfills, preferential flows and contaminant transport. In this study, a comprehensive series of experiments was conducted to investigate the desiccation cracks due to the combined effects of initial water content and layer thickness on bentonite clay. Slurries of bentonite were prepared with initial water contents ranging from 1200 to 2200%. The slurry was placed in a glass Petri dish and dried at a temperature of 30 ± 2°C. Results from the experiments were illustrated in a phase diagram, and it was found that the interplay between the initial water content and layer thickness has a significant effect on the formation and prevention of desiccation cracks. More specifically, a phase boundary distinguishing between cracked and non-cracked samples was obtained in the constructed phase diagram. A theoretical model based on the critical cracking thickness was developed and then was used to predict this observed phase boundary. Furthermore, a detailed morphology of crack patterns was investigated by employing image analysis techniques followed by statistical analyses. Findings from this study have potential use in clay liner design, where bentonite is used as the main material, as well as in other problems associated with drying soils.

Hydrogeological systems of landslides in central part of the Volga-Ural region

The study of landslide massifs made it possible to identify two types of hydrogeological systems that differ by feeding area structure and transit zone. In landslide bodies of Urzhuminan stage, composed by dolomites and marls, hydrogeological systems are simple stratal. The aquifers are localized in fractured marls, which, under the influence of infiltration water seeping through them, have turned into a poorly structured gruss-rock cover, which lies on dense dolomites - water-resistant. The inclined bedding of dolomite layers creates the prerequisites for directed filtration of groundwater towards natural lowering. Here forming areas of ground water discharge as low-water springs. In landslides composed of the Upper Jurassic series clays and marls, hydrogeological systems are distinguished by the prevailing vertical groundwater infiltration in transit zone. Theirs’s water source is shallow lakes formed on the surfaces of landslide terraces. Under water pressure influence of in the lake basins and gravity, infiltration groundwaters leaking through the systems of cracks in clays penetrate to a more dense clay layers which are fluid trap. Here, directly under the lake basin, a dome of groundwater is formed. The flow of groundwater from the dome towards inclined depressions leads to creation of unloading areas. They are presented by permanently wet land (flarks) or low-water infiltration springs that come to the surface at the same hypsometric level.

Clay Cracking: A Natural Process Guiding a Design-to-Fabrication Method for Cast Aluminum Panels

Clay cracking, a natural process often associated with material failure, can be leveraged by designers to generate unique forms. When clay dries, a crack pattern emerges that is dependent on factors such as the clay’s water content, thickness, and boundary conditions. This paper presents a method for designing and fabricating cast aluminum architectural panels using naturally formed cracked clay patterns. Casting unique panels with clay has the potential to use less material and energy than traditional sand casting uses. The authors used this methodology to develop and fabricate panels for the Cast & Place pavilion (2017) in New York City.

Expansive Clay Cracking Behavior through Digital Image Correlation

Expansive soils may present cracks arising from the drying process and their evolution can cause irreparable damages to engineering projects. Investigating this phenomenon is vital to understanding its geomechanics. The objective of this article is to present numerical modelling of the formation and propagation of cracks in expansive soil. A desiccation experiment was therefore carried out using an expansive silty clay from Paulista, in northeastern Brazil. The drying process was monitored by measuring the temperature and relative humidity of the air, as well as by capturing images with a camera. The digital images were correlated using the Ncorr numerical tool in MATLAB. As a result, this study made it possible to conclude that the soil cracking dynamics presented a non-orthogonal pattern during the dryness test, while the image treatment made it possible to observe the tendency of cracks to appear and propagate on the soil surface, allowing for the detection of crack growth and propagation trends.

Cracking behaviour of fine-grained soils: from laboratory testing to numerical modelling

Many experimental evidences suggest that desiccation cracks in clay initiate as a result of the mobilization of soil tensile strength. However this mechanical approach disregards the cohesionless and effective stress-dependent behaviour of fine-grained soil. On the other hand recent findings in the literature suggest that effective stress-dependent shear failure criteria would be appropriate to explain the mechanisms of desiccation cracking for tensile total stress states. This work aims at assessing the validity of a shear failure criterion to predict the onset of cracking in clay forms exposed to air drying. Clay forms of various geometries were experimentally subjected to non-uniform hydraulic and mechanical boundary conditions. Time and location for crack initiation are monitored using a digital camera. Cracking experiments are then modelled in a hydro-mechanical framework using an effective-stress shear failure criterion. The comparison of simulations with experimental results for both the time and the location of cracking allows assuming that cracking occurs due to failure in shearing.

Analysis of Factors Influencing Stability of Overlying Soil Layer on Thin Bedrock Based on Crack Development‐Closure Test

The water‐blocking properties of the clay layer at the bottom of the Cenozoic overburden in China are an important factor influencing the safety of thin bedrock coal seam mining. Clay has remolding properties that are unlike the nonreversible characteristics of cracks in brittle rock, and failure cracks in clay can reclose or continue to expand under the influence of different external factors. In this work, the soil layer on top of thin bedrock is the research object, and the influences of the particle composition, water content, soil layer thickness, and crack width on the crack development‐closure state of soil layer are analyzed by the orthogonal test method. Visual analysis shows that the order of influence of each factor on the stability of soil layer is the crack width, particle composition, soil layer thickness, and water content. The stability of soil layer decreases with increasing crack width and sand content and decreasing soil layer thickness; in addition, soil layer stability decreases first and then increases with increasing water content. Further variance analysis shows that the crack width and particle composition are key factors that impact the stability of soil layer and that the soil layer thickness has some influence, while the water content has little effect on the stability of soil layer. In addition, the crack will reclose when the sand content in soil is less than 50% and the crack width is less than or equal to 1.0 mm, and the soil layer is prone to further failure when the sand content in soil is more than 50% and the crack width is greater than or equal to 3.0 mm; when the soil layer thickness is 15.0 cm, its stability is better than when the soil layer thickness is 10.0 cm or 5.0 cm.