Shrinkage development during soil desiccation

Clayey soils undergo shrinkage during desiccation. When shrinkage is restrained by the boundary conditions or by internal stresses, tensile stresses are generated within the soil body. These stresses eventually produce tension crackswhich create problematic situations in many engineering applications. Presence of shrinkage cracks is significant in many applications such as earth embankments, landfill clay liners, foundations, and road pavements. Desiccation or thermally induced induced shrinkage cracks cause problems in other disciplines as well, for example in mining engineering, agricultural engineering and materials engineering. It is important to understand the shrinking behavior of soil in order to study the desiccation crack development in clayey soils. Free shrinkage of slurry clay was observed in laboratory experiments. Image analysis, along with Particle Image Velocimetry (PIV) technique was used to analyze the data obtained. Relatively small specimens 100 mm longwere used so that strains could be measured to high accuracy.Werribee clay, an expansive clay found in West Melbourne, was used in the experiments. Basic clay properties include liquid limit of 127%, plasticity index of 101 and linear shrinkage of 22%. This paper discusses the relationship between strains (vertical, horizontal, and volumetric), displacements, water content, degree of saturation and void ratio. Shrinkage strain development prior to crack initiation was examined to identify crack failure condition

Evaluation of J integral for clay soils using a new ring test

Fracture behaviour of clay soils is an important area in soil mechanics that needs further development. Currently, there is no test method to determine fracture properties of clay soils during desiccation. The past work has been mostly on the use of fracture toughness as applicable to linear elastic fracture mechanics using external loading of specimens. However, importance of considering likely plasticity in fracture propagation, especially with soft soils, has been highlighted. J integral is an important parameter in elasto-plastic fracture mechanics, which accounts for the change in potential energy with fracture propagation. This paper presents an innovative test method to evaluate the fracture behaviour, in particular to determine J integral, as applicable to desiccating soils. The challenging task of calculating strains and stresses of slurry clays has been dealt with using an image-analysis technique. Starting from the fundamentals of fracture mechanics, J integral is expressed as a summation of several line integrals. The major advantage of the new method is its suitability for wet or slurry soils for which load tests are impossible. Copyright © 2012 by ASTM International

Desiccation cracking in clayey soils: mechanisms and modelling

This paper presents a summary of the work undertaken on desiccation cracking in soils with special reference to the work undertaken by the authors and co-workers at Monash University. All areas of historical field observations, laboratory modelling and identified mechanisms are discussed briefly. Analytical and numerical approaches for modelling of the desiccation cracking and process are discussed. Cohesive crack approach is presented as a viable approach for modelling of desiccation cracking and fracture evolution catering for consistency change of soil during desiccation. It is highlighted that both tensile strength and crack opening displacement increases, thereby increasing the fracture energy of the soil as the moisture content reduces. This modelling approach can be extended to model wetting/drying cycles and to model crack dynamics. Associated moisture transfer modelling also needs to be advanced for a complete solution

Prediction of parallel clay cracks using neural networks – a feasibility study

Cracking in drying clay soil is a common phenomenon especially in arid and semi-arid regions. Proper understanding and reliable prediction of the extent and nature of cracks in clay is vital for the design and construction of geo-infrastructures. While many models have been developed over the years to predict cracking, they are focused on a single crack rather than the whole network. This paper presents a feasibility study on a novel intelligent approach based on artificial neural network to predict the number of cracks in soil for a given combination of input parameters. Initial moisture content, specimen layer thickness and size of the specimen are used as inputs to the model. The output is the number of cracks. The collected database is used to train, validate and optimise the neural network models. The optimisation steps are discussed and analysed as the predicted number of cracks are compared to the experimental ones. A reasonable agreement was found between the experimental and predicted data. The results indicate that the model can be further improved to make more reliable predictions. © 2019, Springer Nature Switzerland AG

Investigation of desiccation cracking using automated digital photography

Desiccation cracking can be heavily detrimental on the performance of clay soils in various engineering applications. Typical engineering applications include compacted clay barriers in waste containment, dam cores, canal liners and road pavements. The evolution of desiccation cracks has not been clearly understood and explained. A series of laboratory tests were conducted using Merri-Creek clay and potato starch. The evolution of cracks was captured by automated digital photography and presented in a time-lapse video format similar to the phenomenon of a blooming flower. To the authors’ knowledge, this is the first time such a video has been produced. Both simultaneous and sequential types of cracking are investigated. The relationship between desiccation rate, average cell area, thickness of the specimen and etc are examined and discussed

Study of desiccation cracking and fracture properties of clay soils

The thesis focuses on the development of shrinkage cracking in clay soils upon drying and the determination of fracture properties of clay soils as applicable to analysis of desiccation cracking phenomenon. The results and conclusions were drawn from comprehensive experimental work analysed drawing from Classical Soil Mechanics, Fracture Mechanics, Unsaturated Soil Mechanics and Mechanics of Materials with the aid of powerful image analysis techniques. Attempts were made to fill the gaps in the existing knowledge related to scope of the thesis as identified by a detailed study on the previous works. Three types of soils were used for the work presented in this thesis: Merri-Creek clay, Werribee clay and milled fine sand. The former two are naturally available materials in the Melbourne region. The last material was sourced from a commercial dealer. Potato starch was also used in desiccation tests as an alternative material to examine the crack patterns different from clays. Qualitative and quantitative studies were carried out using these materials aiming to acquire deeper understanding of the cracking mechanisms. Effects of desiccation rate, specimen thickness and particle size on crack patterns were studied. The influence of stress distribution and flaw distribution on crack initiation was also discussed. Image analysis techniques were used extensively to investigate the deformations of soil particles during drying. Shrinkage characteristics and onset of crack initiation were closely studied with displacement vector fields and strain isochrones. Interesting observations were made during these studies which led to deeper understanding of the subject, especially in relation to the mechanisms of crack initiation and associated modelling approaches. Fracture properties of Werribee clay was investigated using SENB beam test. Fracture toughness, fracture energy of Werribee clay was measured using three methods. An attempt was made to explain the behaviour of these parameters with the water content. Finally, an innovative test method to determine the J-integral was introduced. The test is specially designed to determine the J-integral of desiccating soils

Study of desiccation cracks evolution using image analysis

Desiccation cracking can be heavily detrimental on the performance of clay soils in various engineering applications. Typical engineering applications include compacted clay barriers in waste containment, dam cores, canal liners and road pavements. The evolution of desiccation cracks has not been clearly understood and explained. A series of laboratory tests were conducted using Merri-Creek clay. The evolution of cracks was captured by automated digital photography. It was revealed that under the conditions tested, the cracks occurred sequentially subdividing the overall surface area into cells. The relationship between desiccation rate, average cell area, thickness of the specimen and crack initiation are examined and discussed

Investigation of engineering performance of gravels mixed with additives for unsealed pavement stabilization

A case study was undertaken to assist Central Goldfields Shire Council, Victoria, Australia, in assessing the success of its unsealed road stabilisation program. A section of road was treated in 2009, with different combination of additives (RT20 and Eko-Soil) and then post construction testing was carried out in 2010 to verify the success of the trial. A set of parameters, including California Bearing Ratio (CBR), Unconfined Compressive Strength (UCS), Maximum Dry Density (MDD), and Optimum moisture content was tested after the setting of the additives. The results indicated that Eko-Soil performed better than Reynolds RT-20 in treating the selected site

Evaluation of J integral for clay soils using a new ring test

Fracture behaviour of clay soils is an important area in soil mechanics that needs further development. Currently, there is no test method to determine fracture properties of clay soils during desiccation. The past work has been mostly on the use of fracture toughness as applicable to linear elastic fracture mechanics using external loading of specimens. However, importance of considering likely plasticity in fracture propagation, especially with soft soils, has been highlighted. J integral is an important parameter in elasto-plastic fracture mechanics, which accounts for the change in potential energy with fracture propagation. This paper presents an innovative test method to evaluate the fracture behaviour, in particular to determine J integral, as applicable to desiccating soils. The challenging task of calculating strains and stresses of slurry clays has been dealt with using an image-analysis technique. Starting from the fundamentals of fracture mechanics, J integral is expressed as a summation of several line integrals. The major advantage of the new method is its suitability for wet or slurry soils for which load tests are impossible. Copyright © 2012 by ASTM International

J -integral as a useful fracture parameter for analysis of desiccation cracking in clayey soils

Fracture behaviour of clay soils during desiccation is an important area in soil mechanics that needs further development. The current approach is to use Linear Elastic Fracture Mechanic parameters, such as fracture energy and fracture toughness, measured from load tests for analysis and modelling of crack propagation. However, the importance of taking plasticity of the material into consideration has been highlighted by several researchers. This is especially true for soft and/or slurry clay. The recently developed double ring test is the only test available up to date which enables determination of Elasto-Plastic Fracture Mechanic parameter, J-integral. This is an important parameter, which accounts for the change in potential energy with fracture propagation. Currently, there is no data for J-integral in literature as applicable to desiccation cracking. This paper fills the said gap by presenting a set of J-integral data for Churchill clay and Kaoline clay measured from the double ring test. Values have been calculated for both slurry and compacted clay with corresponding coefficients of linear shrinkage. The challenging task of calculating strains and stresses has been dealt with the use of an image analysis technique. In addition, the path independence for J-integral calculation and the behaviour of J-integral with the moisture content are also discussed