Jayantha Kodikara
Monash University, Civil Engineering, Faculty Member
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A new mathematical model is presented that describes the shrinkage curve of environmentally stabilized soils. Environmentally stabilized soils are defined as those that have undergone a sufficient number of wet–dry cycles to reach a... more
A new mathematical model is presented that describes the shrinkage curve of environmentally stabilized soils. Environmentally stabilized soils are defined as those that have undergone a sufficient number of wet–dry cycles to reach a stable soil structure. The model is applicable for fitting to soils that exhibit all typical zones of soil shrinkage behaviour and to those soils that do not exhibit structural and (or) residual shrinkage behaviour. The fitting parameters in this model are directly related to features of the shrinkage curve and have direct relevance to soil mechanics theory and practice. The model is applied to data from 20 different datasets reported in literature with excellent fitting achieved. This model is extended to incorporate the effect of net stress, creating a surface describing soil volumetric behaviour in response to changes in water content and net stress.
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Expansive clays are found in many countries worldwide, and they exhibit inherent volume change during the seasonal moisture variation causing cracks, heaves, and damages to the overlying pavements. Chemical stabilisation is one of the... more
Expansive clays are found in many countries worldwide, and they exhibit inherent volume change during the seasonal moisture variation causing cracks, heaves, and damages to the overlying pavements. Chemical stabilisation is one of the most used approaches to treat the expansive clay subgrades. Cement, Lime and Fly ash are the most commonly used stabilisers, in which fly is cheaper and a by-product obtained from the coal power plant. This paper reviews fly ash stabilisation on various clay types, including low plasticity clays, high plasticity clays, silty clays, organic clays, and peats. The review begins with the properties of fly ash, followed by the characteristics of fly ash stabilised subgrades. The micro-level mechanism, physical, mechanical, and hydraulic characteristics of stabilised pavements are presented graphically for the Class C, and F fly ashes. The micro-level studies reveal that the pozzolanic reaction is stronger than the cation exchange during the fly ash stabilisation. The unconfined compressive strength (UCS), California bearing ratio (CBR) and resilient modulus (Mr) increased with the fly ash addition and curing time for most soft soils except peat clays. Based on the mechanical and hydraulic characteristics, using 15% class C fly ash with 7 days of curing is recommended for optimum performance. Although few research studies confirm that the leachate limit of stabilised soil is within the acceptable limit, further studies are required to investigate the uptake of heavy metals and other certain carcinogenic contaminants. This study will provide key information for researchers and Engineers on the selection of fly ash stabilisation measures for expansive subgrades.
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Tensile failure in soils caused by desiccation cracking is of great importance in many geotechnical applications such as earth dam engineering, design of clay liners for waste contaminant systems, agricultural engineering, and... more
Tensile failure in soils caused by desiccation cracking is of great importance in many geotechnical applications such as earth dam engineering, design of clay liners for waste contaminant systems, agricultural engineering, and environmental remediation. Currently, the majority of tests used for tensile strength measurement are based on external loading and few studies have measured soil tensile strength during the desiccation process. This study uses the restrained ring test as a method to determine the tensile strength in desiccating clay soils by isolating the initiation of a single crack. Four clay soils with varying shrink/swell potentials were tested and analyzed to predict their tensile strength during desiccation. Using image correlation or particle image velocimetry, information on shrinkage displacement and void ratio development were examined. An incremental non-linear elastic analytical model was used to explain the experimental behavior successfully.
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The measurement of density or void ratio during the compaction of geomaterials (soils and unbound granular materials) in the field during road construction is essential for superior performance. The specifications adopted by the road... more
The measurement of density or void ratio during the compaction of geomaterials (soils and unbound granular materials) in the field during road construction is essential for superior performance. The specifications adopted by the road authorities worldwide are exclusively based on density. However, estimating density evolution proximally or non-destructively is challenging. Conventional field-based density measurement techniques are hazardous, slow to use and are point-based measurements. This study developed a novel methodology to estimate the density of geomaterials non-destructively in real-time during the compaction process. The methodology included measuring the surface deformation using Light Detection and Ranging (LiDAR) systems attached to rollers and developing physics-based 1-Dimensional and machine learning (ML) based constitutive models to relate the measured parameters to the density. The developed methodology was validated in an indoor environment where a large soil box...
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An alternative method was introduced for predicting the nonlinear p-y curves for monotonic unidirectional laterally loaded single piles in uniform undrained clay. On the basis of numerical studies, closed-form solutions were developed for... more
An alternative method was introduced for predicting the nonlinear p-y curves for monotonic unidirectional laterally loaded single piles in uniform undrained clay. On the basis of numerical studies, closed-form solutions were developed for locating the start of yield (y e ); the ultimate yield point (y u ); and the initial stiffness, K i of the p-y curve. The nonlinear section of the curve between the start of the yield and the ultimate yield point was represented by Bezier polynomials (also known as de Casteljau's algorithm). Using these relationships, a direct method of constructing the p-y curves was presented considering either tension failure or no tension failure of soils. For a typical pile configuration, the resulting load-deflection response was observed to compare favorably with the predictions from FLAC analysis and Matlock.
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With the advent of climate change, it is thought that desiccation cracking of soil will lead to increases in damage to buried infrastructure. Desiccation cracking is a complex phenomenon that historically has been very difficult to model... more
With the advent of climate change, it is thought that desiccation cracking of soil will lead to increases in damage to buried infrastructure. Desiccation cracking is a complex phenomenon that historically has been very difficult to model either numerically or analytically. Therefore, there is a need for knowledge on such models to be advanced rapidly. This paper discusses the introduction of cohesive cracks to model fracture attributable to desiccation. The cohesive crack method does not have the limitations of linear elastic fracture mechanics, namely, that an initial notch must be present and that the bulk material must behave in a linear elastic manner. This paper describes how the cohesive crack method has been successfully used to model laboratory desiccation tests of a clay soil. It is shown that, in addition to the tensile strength, the magnitude of fracture energy specified for the material has an impact on crack propagation. The cohesive crack method is proposed as a tool for the numerical modeling of desiccation cracking in many diverse fields.
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ABSTRACT Mode I fracture is common in geomechanics in desiccation cracking, hydraulic fracture, and pressuremeter testing. The cohesive crack model has been used extensively and successfully in numerical modeling of such fracture in... more
ABSTRACT Mode I fracture is common in geomechanics in desiccation cracking, hydraulic fracture, and pressuremeter testing. The cohesive crack model has been used extensively and successfully in numerical modeling of such fracture in concrete and steel but has not been applied in modeling of soil fracture to the same extent. It is argued that the cohesive crack model may be more appropriate than linear elastic fracture mechanics (LEFM) for soils because it takes into account finite tensile strength and any likely plasticity during fracture. With special reference to the Universal Distinct Element Code (UDEC) computer program, a methodology of using interfaces in the distinct element method (DEM) of analysis to model fracture has been validated herein, and this approach is considered to be useful in geomechanical modeling applications. The methodology is based on the cohesive crack approach and shows how softening laws could be back-calculated from load-displacement curves of test specimens. It has been validated using three geometries: a tension test with a rectangular cross section, a notched three-point bend beam, and a compact tension test. Approximate softening laws for St. Albans clay from Canada are proposed. (C) 2011 American Society of Civil Engineers.
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Climatic events such as precipitation result in unbound structural layers of pavements being in a partially saturated condition during their service life. With unsaturated testing being relatively complex and costly, the presence of... more
Climatic events such as precipitation result in unbound structural layers of pavements being in a partially saturated condition during their service life. With unsaturated testing being relatively complex and costly, the presence of relatively low matric suction in granular geomaterials, practitioners have been reluctant to explore the utilization of unsaturated geomechanics in the analysis and design of the mechanical behavior of pavement structural layers. In this research, unsaturated mechanical characteristics of three types of recycled geomaterials were firstly investigated using repeated load triaxial testing and the incorporation of their soil–water characteristics in the analysis of their resilient moduli response. This was to demonstrate the importance of understanding the unsaturated mechanical behavior of compacted granular material. Next, a virgin compaction surface (VCS) was developed within a moisture content-based framework to interpret the loading, unloading and wetting-induced volume change of the compacted materials. Outcomes of this research, for the first time, extend the application of the well-established Monash Peradeniya Kodikara (MPK) framework, originally developed for fine cohesive soils, to granular materials. A distinctive attribute of the proposed approach is the relative simplicity in the testing methodology by utilizing the conventional geotechnical testing equipment. The findings of this research can be used for estimation of the settlement of a granular structural layer that is compacted, loaded and then wetted through precipitation or flooding.
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This study provides a methodology that can be utilised for identifying pipe sections, which can be considered under high risk of failure. Application of the proposed methodology is demonstrated using a case study involving an in-service... more
This study provides a methodology that can be utilised for identifying pipe sections, which can be considered under high risk of failure. Application of the proposed methodology is demonstrated using a case study involving an in-service large (~1.7 km) critical water main in Sydney, Australia. Geospatial features from Google Earth Pro TM and Google Street View TM were used to assess and quantify typical urban environmental attributes, which can be used for identifying pipe failure hotspot locations. Failure history was used to verify the basis of the methodology developed. It was demonstrated that a sound assessment of the pipe conditions is possible through inexpensive geospatial feature analysis. This development can greatly enhance and reduce costs associated with current pipe condition assessment processes.
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Abstract. High density polyethylene (HDPE) geomembranes (approximately 8 hectares each) are employed as floating covers at the wastewater treatment plant of Melbourne Water in Werribee, Australia. The anaerobic lagoons at the plant rely... more
Abstract. High density polyethylene (HDPE) geomembranes (approximately 8 hectares each) are employed as floating covers at the wastewater treatment plant of Melbourne Water in Werribee, Australia. The anaerobic lagoons at the plant rely on these HDPE geomembrane floating covers to capture both the biogas and odours. Given the nature of the plant and the harsh environmental conditions, a non-contact inspection method that can cover a vast expanse is the preferred approach for the structural health monitoring and assessment of the cover. This paper presents an exploratory investigation on the use of a quasi-active thermography technique to detect the presence of artificially induced part-through defects on a HDPE geomembrane specimen. The proposed method utilises a naturally occurring heat source (solar radiation) as the thermal stimulus. An infrared thermal camera and a pyranometer were used to record the thermal responses of the HDPE material as a result of solar intensity variation...
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Intelligent compaction (IC) is a technology that uses non-contact sensors to monitor and record the compaction level of geomaterials in real-time during road construction. However, current IC devices have several limitations: (i) they are... more
Intelligent compaction (IC) is a technology that uses non-contact sensors to monitor and record the compaction level of geomaterials in real-time during road construction. However, current IC devices have several limitations: (i) they are unable to visualize or compare multiple intelligent compaction measurement values (ICMVs) in real-time during compaction; (ii) they are not retrofittable to different conventional rollers that exist in the field; (iii) they do not incorporate corrections for ICMVs reflecting variable field conditions; (iv) they are unable to integrate construction specifications as needed for performance-based compaction; and (v) they do not record all the key roller parameters for further compaction analysis. To address these issues, an innovative retrofittable platform with cutting-edge hardware and software was developed. This platform, called the intelligent compaction analyzer (ICA) platform, is effective at calculating conventional acceleration amplitude-base...
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The generation of reference data for machine learning models is challenging for dust emissions due to perpetually dynamic environmental conditions. We generated a new vision dataset with the goal of advancing semantic segmentation to... more
The generation of reference data for machine learning models is challenging for dust emissions due to perpetually dynamic environmental conditions. We generated a new vision dataset with the goal of advancing semantic segmentation to identify and quantify vehicle-induced dust clouds from images. We conducted field experiments on 10 unsealed road segments with different types of road surface materials in varying climatic conditions to capture vehicle-induced road dust. A direct single-lens reflex (DSLR) camera was used to capture the dust clouds generated due to a utility vehicle travelling at different speeds. A research-grade dust monitor was used to measure the dust emissions due to traffic. A total of ~210,000 images were photographed and refined to obtain ~7,000 images. These images were manually annotated to generate masks for dust segmentation. The baseline performance of a truncated sample of ~900 images from the dataset is evaluated for U-Net architecture.
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Hydromechanical behaviour of an unsaturated silt with various suctions and different overconsolidated ratios (OCRs) was investigated through a series of undrained triaxial tests (constant water contents, CW). All the samples were prepared... more
Hydromechanical behaviour of an unsaturated silt with various suctions and different overconsolidated ratios (OCRs) was investigated through a series of undrained triaxial tests (constant water contents, CW). All the samples were prepared from the slurry state. Different OCRs (= 1, 2, 4, and 8 in net stress) were achieved by unloading the samples to 400, 200, 100, and 50 kPa from an initial confining net pressure of 400 kPa. Then the samples were dried to various suctions (0, 100, 200, 300, and 400 kPa). Unsaturated samples with different OCRs were then sheared at CW conditions following the conventional triaxial compression (CTC) paths. Full hydromechanical responses including the changes in deviator stress, stress ratio, volumetric strain, suction, and degree of saturation with axial strain were monitored and are presented in this paper. Some key findings include (i) the critical state for unsaturated soils with different OCRs can be well defined by Bishop’s effective stress; (ii)...
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The coexistence of air and water as a mixture in void spaces in unsaturated soils, makes its mechanical behaviour relatively complex and difficult to be addressed by classical saturated soil mechanics principles. In addition, many... more
The coexistence of air and water as a mixture in void spaces in unsaturated soils, makes its mechanical behaviour relatively complex and difficult to be addressed by classical saturated soil mechanics principles. In addition, many engineering problems encountered in practical situations had some part to deal with unsaturated soils and therefore the clear understanding of various behavioural patterns of unsaturated soils is crucial. To date, a large number of attempts are reported in evaluating the mechanical behaviour of unsaturated soils in different stress spaces. The present study evaluates the deviatoric behaviour of compacted unsaturated soils in deviator stress–specific water volume–mean net stress ($$q, {v}_{\mathrm{w}}, p$$ q , v w , p ) space. The effect of moisture content, confinement and the stress history on the behaviour of compacted unsaturated kaolin subjected to triaxial compression was assessed and the results showed that there exists a critical state surface for c...
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A detailed description of the volumetric behaviour of compacted unsaturated soils is essential for modelling compacted soil behaviour. It is more complex than when the soil is saturated, as unsaturated soils exhibit a range of responses,... more
A detailed description of the volumetric behaviour of compacted unsaturated soils is essential for modelling compacted soil behaviour. It is more complex than when the soil is saturated, as unsaturated soils exhibit a range of responses, such as yielding under loading, swelling and collapse under wetting, and shrinkage and cracking during drying. In unsaturated modelling, (v, s, p) or (v, s, p′) is commonly used as the state space to describe volumetric behaviour, where v (= 1 + void ratio, e) is the specific volume; s is the soil suction; and p and p′ are the mean net and mean effective or skeleton stress, respectively. An alternative approach is to use (v, vw, p) space to describe volumetric behaviour, where vw is specific water volume. In either case, coupled water retention behaviour is needed to describe the overall macroscopic process more completely by including the fourth state variable (vw or degree of saturation, Sr, for the former and s for the latter). Following from wor...
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Pipelines used for water and other services are very important lifelines in modern society. Commonly, these buried pipes are subjected to significant stresses due to external (traffic and earth) and internal (water pressure) loads. As... more
Pipelines used for water and other services are very important lifelines in modern society. Commonly, these buried pipes are subjected to significant stresses due to external (traffic and earth) and internal (water pressure) loads. As many of these pipelines were laid sometime in the last century or earlier, in most cases their condition has deteriorated primarily by electrochemical and (or) microbiological corrosion. Corrosion activity (internal and external) can manifest in various forms, but in many cases will lead to reduced pipe thickness, which in turn leads to an increase in pipe stresses induced by the external and internal loads. Currently available analytical procedures to estimate pipe stresses are based on oversimplifications such as the two-dimensional (2-D) analysis based on Winkler springs, limiting their application to general pipe burial conditions. This paper describes the application of a three-dimensional (3-D) finite element method to analyse a buried pipe subje...
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Dynamic compaction is commonly used to construct structural fills for various geo-infrastructures. Current practice is to specify a minimum dry density and moisture content criterion to be used in the field on the basis of Proctor... more
Dynamic compaction is commonly used to construct structural fills for various geo-infrastructures. Current practice is to specify a minimum dry density and moisture content criterion to be used in the field on the basis of Proctor compaction carried out in the laboratory. However, there are still no practical methods for predicting compacted clay behaviour under expected mechanical and environmental loadings. Current theories are difficult to apply in practice due to difficulties in determining the necessary parameters. In this paper, the recently developed “void ratio – moisture ratio (volume of water / volume of solids) – net stress space” (MPK) framework is extended to cover dynamically compacted soils, with significant supporting experimental evidence. Two types of soils are used: lightly reactive kaolin and reactive Merri Creek clay. As the compaction stress was unknown for dynamic compaction, recompression of soil specimens from compacted soil was used to establish the “loadin...
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The safe disposal of coal ash produced from power stations involves the assessment of rates of production and quality of ash leachate. Laboratory column experiments have been used to obtain data on the ash leachate. The extrapolation of... more
The safe disposal of coal ash produced from power stations involves the assessment of rates of production and quality of ash leachate. Laboratory column experiments have been used to obtain data on the ash leachate. The extrapolation of this data to the field conditions requires theoretical modelling of the underlying chemical leaching and transport mechanisms. In the current paper, a model was developed to simulate the leaching of ash which exists in saturated or near-saturated conditions. The model was applied to simulate the experimental results, and good agreement was obtained between the experimental and model results. In the Latrobe Valley region of Victoria Australia, large quantities of brown coal ash are produced annually in the power station complexes which supply the majority of the electricity requirement for Victoria. One of the principal environmental concerns associated with the management of these facilities is the hydrogeological impact of the disposal of coal ash. ...
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This paper presents the statistical analyses of pipe failure data on large diameter water mains collected from five Australian water utilities. The analyses were performed to identify the factors that lead to failures of cast iron, steel... more
This paper presents the statistical analyses of pipe failure data on large diameter water mains collected from five Australian water utilities. The analyses were performed to identify the factors that lead to failures of cast iron, steel and ductile iron pipes. Data required for the analyses such as mode of failure, causes of failure, corrosion data, and pit characteristics were obtained from the failure inspection reports provided by Australian water utilities. After studying the failure inspection reports, three main types of corrosion category were identified in the failed pipe sections. Reported corrosion at the time of failure was also used to glean the levels of corrosion that have led to pipe failures. It should be noted that the data reported may not be always totally consistent, but the availability and collection of accurate information on pipe failures is very valuable in advancing pipe failure prediction for pipe asset management.
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Most major urban water utilities in Australia have extensive critical pressure main systems, parts of which have been in service for a century or more. Failure of critical mains has severe impacts in terms of maintaining service levels to... more
Most major urban water utilities in Australia have extensive critical pressure main systems, parts of which have been in service for a century or more. Failure of critical mains has severe impacts in terms of maintaining service levels to customers, loss of fire fighting supply, safety, transport disruption and other social costs, as well as significant financial and reputational implications. A better understanding of the condition, performance and prediction of failure of critical water mains was identified by an international team of partners comprising utilities, research organisations and technology providers. This paper presents details of a global collaborative project developed to undertake research into this issue in partnership with local water utilities, local universities, international water bodies and pipe condition service providers (www.crticalpipes.com). The project scope, governance, activities and likely outcomes are briefly described.
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Offshore pipelines are commonly buried in seabed for protection against damage, for better insulation and to prevent upheaval buckling induced by thermal and pressure loadings. The uplift resistance provided by the backfill soil is an... more
Offshore pipelines are commonly buried in seabed for protection against damage, for better insulation and to prevent upheaval buckling induced by thermal and pressure loadings. The uplift resistance provided by the backfill soil is an important design parameter when determining the correct burial depth for a given pipeline. In this paper, the effect of variability in soil backfill stiffness and operation conditions on the performance of the pipeline upheaval behaviour is investigated. Variations in the soil backfill stiffness, pipe properties and the operational factors such as temperature and pressure are considered to assess the safety of the pipeline probabilistically. An optimized Latin Hyper Cube (LHC) sampling technique is used to draw the sample of soil stiffness, pipe properties and operational conditions from preassigned probabilistic distribution for each variable. Pipeline behaviour was simulated using elastic model, and the interaction was modelled using pipe-soil intera...
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Large sheets of high-density polyethene geomembrane are used as floating covers on some of the wastewater treatment lagoons at the Melbourne Water Corporation’s Western Treatment Plant. These covers provide an airtight seal for the... more
Large sheets of high-density polyethene geomembrane are used as floating covers on some of the wastewater treatment lagoons at the Melbourne Water Corporation’s Western Treatment Plant. These covers provide an airtight seal for the anaerobic digestion of sewage and allow for harvesting the methane-rich biogas, which is then used to generate electricity. There is a potential for scum to develop under the covers during the anaerobic digestion of the raw sewage by microorganisms. Due to the nature of the operating environment of the lagoons and the vast size (450 m × 170 m) of these covers, a safe non-contact method to monitor the development and movement of the scum is preferred. This paper explores the potential of using a new thermographic approach to identify and monitor the scum under the covers. The approach exploits naturally occurring variations in solar intensity as a trigger for generating a transient thermal response that is then fitted to an exponential decay law to determi...
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High-density polyethylene geomembranes are employed as covers for the sewage treatment lagoons at Melbourne Water Corporation’s Western Treatment Plant, to harvest the biogas produced during anaerobic degradation, which is then used to... more
High-density polyethylene geomembranes are employed as covers for the sewage treatment lagoons at Melbourne Water Corporation’s Western Treatment Plant, to harvest the biogas produced during anaerobic degradation, which is then used to generate electricity. Due to its size, inspecting the cover for defects, particularly subsurface defects, can be challenging, as well as the potential for the underside of the membrane to come into contact with different substrates, viz. liquid sewage, scum (consolidated solid matter), and biogas. This paper presents the application of a novel quasi-active thermography inspection method for subsurface defect detection in the geomembrane. The proposed approach utilises ambient sunlight as the input thermal energy and cloud shading as the trigger for thermal transients. Outdoor laboratory-scale experiments were conducted to study the proposed inspection technique. A pyranometer was used to measure the intensity of solar radiation, and an infrared therma...