Tensile fracture in mode I occurs in many geotechnical applications such as in slope stability, d... more Tensile fracture in mode I occurs in many geotechnical applications such as in slope stability, desiccation cracking, borehole pressuremeter testing, etc. The cohesive crack model is a powerful and versatile tool that can be used to numerically analyse mode I fracture, that has had very limited usage in geomechanics to date. This research reports findings from testing on single-edge notched beams manufactured from compacted clay fractured in three-point bending. Specimens were tested at a range of moisture contents to determine several fracture parameters including the parameters defining cohesive cracks. The properties for the cohesive crack were back-calculated by matching the numerically modelled load–load point displacement curve obtained using a hybrid continuum distinct element program with the ones obtained experimentally. It was found that the cohesive crack method could be successfully used in matching the load–load point displacement curves for a range of consistencies of the clay from soft to v...
This article analyses the failure of a 500 mm-diameter cast iron (CI) water pipe that catastrophi... more This article analyses the failure of a 500 mm-diameter cast iron (CI) water pipe that catastrophically fractured in Sydney in 2013. According to metallurgical analysis and finite element simulation, a longitudinal pre-existing crack initiated from the adjacent bell-joint and eventually propagated to a critical length in the pipe barrel over a certain period. There was evidence of leakage prior to the burst incident but information was inconclusive whether it was exactly from this pipe. Fatigue caused by cyclic internal pressure was considered as the predominant factor in leading to crack growth. A numerical model was developed to describe crack growth behaviour using Paris' law, and metallurgical analysis and mechanical tests were conducted to support this investigation. Based on the field evidence and simulation results, the leak-before-break approach might be applicable in CI pipes to avoid severe consequences of trunk main bursts.
This paper presents the results of uniaxial compression tests conducted on quartzite samples. The... more This paper presents the results of uniaxial compression tests conducted on quartzite samples. The tested quartzite samples consisted of 83 mm diameter cores that were cut to a length roughly twice their diameter. The specimens were cored from a depth of between 68-78 m. The stress-strain and acoustic emission (AE) responses were monitored throughout the tests. The results obtained for the intact specimens are believed to be typical, and are in general agreement with the results of other researchers. The tests produced a recognisable AE peak prior to the peak axial strength of the specimen being reached. The axial stress at which this AE peak occurs corresponds to a value of around 90% of the specimen's UCS (unconfined compressive strength). This is due to the formation of new fractures and shear mobilisation of established failure planes prior to failure that emits large amounts of AE energy.
This paper presents a synthesis of mechanisms related to structure development of surficial heavy... more This paper presents a synthesis of mechanisms related to structure development of surficial heavy clay soils. These clay soils develop specific structural features due to wet/dry cycles and desiccation cracking they undergo during soil "ripening". There is substantial field and laboratory evidence to indicate that clay soils generally develop stable structures with stable material properties when they ripen under repeated wet/dry cycles of climatic change. This development occurs as a result of the re-arrangement of the soil particles to minimise the potential or free energy. Available evidence indicates that under field climatic conditions, swelling/shrinkage of clay soils occur predominantly due to water loss from interparticle and interaggregation pores. Vertisols or heavy clay surficial soils can develop special geomorphological features such as gilgai. Mechanisms of gilgai formation are also analysed, and their origin is related to the initial pattern of soil desiccation cracking. The process of shrinkage cracking and associated volume change in soils is explained on the basis of unsaturated soil mechanics theory. Crack patterns are divided into orthogonal and non-orthogonal patterns, and the conditions that lead to the development of these crack patterns are highlighted. Finally, a conceptual approach for modelling of the desiccation cracking process is presented.
The soil-concrete interface shear strength, although has been extensively studied, is still diffi... more The soil-concrete interface shear strength, although has been extensively studied, is still difficult to predict as a result of the dependence on many factors such as normal stresses, surface roughness, particle sizes, moisture contents, dilation angles of soils, etc. In this study, a well-known rigorous statistical learning approach, namely the least squares support vector machine (LS-SVM) realized in a ubiquitous spreadsheet platform is firstly used in estimating the soil-structure interface shear strength. Instead of studying the complicated mechanism, LS-SVM enables to explore the possible link between the fundamental factors and the interface shear strengths, via a sophisticated statistic approach. As a preliminary investigation, the authors study the expansive soils that are found extensively in most countries. To reduce the complexity, three major influential factors, e.g., initial moisture contents, initial dry densities and normal stresses of soils are taken into account in developing the LS-SVM models for the soil-concrete interface shear strengths. The predicted results by LS-SVM show reasonably good agreement with experimental data from direct shear tests.
This paper presents the application of the hybrid continuum-discrete element method, i.e. Univers... more This paper presents the application of the hybrid continuum-discrete element method, i.e. Universal Distinct Element Code (UDEC), to simulate soil desiccation shrinkage and cracking. Herein, soil is modelled using a mix-mode cohesive fracture model that combines tension, compression and shear material behaviour. The fracture model considers both elastic and inelastic (decomposed to fracture and plastic) displacement, with the norm of the effective inelastic displacement being used to control the fracture behaviour. The applicability and capability of the proposed approach is demonstrated through numerical simulations of laboratory linearlyconstrained desiccation test. Good agreements with the laboratory observations have been obtained. The dominant influencing factors on soil desiccation cracking have been assessed, several factors including shear strength and tensile strength of soil-base, and soil sample thickness were identified to have a significant controlling influence on desiccation cracking.
Compacted unsaturated soils show distinct behavioural patterns when compared with their saturated... more Compacted unsaturated soils show distinct behavioural patterns when compared with their saturated counterparts, and these behavioural patterns become more and more complex when soil is subjected to wetting, such as swelling or collapse and loss of shear strength. Ignoring these possible complex behaviours of unsaturated soils coupled with varying climatic conditions can lead to inaccurate assessment of the performance of geotechnical structures. Therefore, the accurate prediction of the wetting-induced volume change behaviour of compacted unsaturated soils is a key step in understanding and modelling unsaturated soil behaviour. Of the different constitutive models introduced to date which can define the wetting-induced volume change behaviour of compacted unsaturated soils reasonably satisfactorily, the MPK framework for the volumetric constitutive behaviour of compacted unsaturated soils proposed by Kodikara ( ) has shown favourable results with its direct relationship to moisture variation. This approach provides a practical approach, where reliance is placed on the variations in the moisture or degree of saturation as input. From this perspective, this study evaluates the volumetric behaviour of compacted unsaturated soils due to various wetting state paths, and the results are compared with the predictions of the MPK framework. The results show that the MPK framework is capable of predicting wetting-induced volume change behaviour, including the wetting-induced yielding of compacted unsaturated soils.
Volumetric behaviour is a fundamental consideration in unsaturated soil constitutive modelling. I... more Volumetric behaviour is a fundamental consideration in unsaturated soil constitutive modelling. It is more complex than when the soil is saturated, as unsaturated soils exhibit a range of responses such as swelling and collapse under wetting and shrinkage and cracking during drying. While significant advances have been made, it is still difficult to generally explain all patterns of behaviour. This paper presents a new framework for modelling volumetric response of unsaturated soils with emphasis on compacted soils. The framework uses void ratio (e), moisture ratio (ew), and net stress (p) as the main constitutive variables and suction as a dependent variable. This choice of ewas a main constitutive variable is theoretically sound and is more attractive than the use of suction, which is relatively difficult to measure and displays significant hysteresis during drying and wetting. The framework incorporates the well-known compaction curve making it easily applicable to practical situations. Within the overall e–ew–p space, the operative space is constrained by three main surfaces; namely, loading–wetting state boundary surface, tensile failure surface, and the saturated plane. The conceptual basis for these state surfaces is described and the framework is qualitatively validated against observed behaviour of compacted soils.
Tensile cracking due to desiccation and fracture properties are of great importance in clay liner... more Tensile cracking due to desiccation and fracture properties are of great importance in clay liners, earth dam engineering, waste contaminant systems, and mine tailings. This paper presents restrained shrinkage test results and analyses of consolidated desiccating soil, and compares results with numerical analyses using the computer program Universal Distinct Element Code (UDEC). The cohesive crack method was used as it is more appropriate than linear elastic fracture mechanics for soil cracking at high moisture contents with the likely presence of plasticity during fracture. The variation of the radial stresses on the inner ring with water content was used to model mode I cracking and gather fracture properties of the propagating crack. The model was validated on kaolin clay tested under restrained ring shrinkage and was compared with various test results and results from the literature. The test could be a valuable tool in determining fracture properties during desiccation.
The safe disposal of coal ash produced from power stations involves the assessment of rates of pr... 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.
The 6th International Conference on Computational Methods (ICCM2015), Mar 29, 2015
The soil compaction is one of the most common activities of civil construction. It is applicable ... more The soil compaction is one of the most common activities of civil construction. It is applicable to construction of fills, dams, roads and embankments. The compacted soils can be subjected to various external and environmental loading after construction. The external loading can arise from superstructure loading, moving traffic and overburden soils. The environmental loading can come from the interaction of surficial soils with the atmosphere in forms such as wetting and drying. Under the combination of these loadings, the compacted soils display complex patterns of behaviour such as swelling, collapse, tensile cracking and swelling pressure development against buried nonyielding bodies. The current approaches for predicting the behaviour of compacted soils during subsequent external and environmental loading are, on one hand, are very complex, and on the other hand, are not entirely satisfactory. The seminar will present a new framework for predicting the behaviour of compacted soils under these loadings, referred to as MPK (Monash-Peradeniya-Kodikara) Framework (Kodikara, 2012). More recent experimental results supporting the framework will also be presented.
A mix-mode cohesive fracture model considering tension, compression and shear material behaviour ... more A mix-mode cohesive fracture model considering tension, compression and shear material behaviour is presented, which has wide applications to geotechnical problems. The model considers both elastic and inelastic displacements. Inelastic displacement comprises fracture and plastic displacements. The norm of inelastic displacement is used to control the fracture behaviour. Meantime, a failure function describing the fracture strength is proposed. Using the internal programming FISH, the cohesive fracture model is programmed into a hybrid distinct element algorithm as encoded in Universal Distinct Element Code (UDEC). The model is verified through uniaxial tension and direct shear tests. The developed model is then applied to model the behaviour of a uniaxial compression test on Gosford sandstone. The modelling results indicate that the proposed cohesive fracture model is capable of simulating combined failure behaviour applicable to rock.
Laboratory testing methods are constantly being developed to simulate true field conditions in co... more Laboratory testing methods are constantly being developed to simulate true field conditions in controlled laboratory environment. The aim of laboratory testing methods is to reproduce specimens which accurately replicate field performance in terms of mechanical behavior of pavement materials under applied loads. Compaction is the most common soil stabilization technique in ground improvement and pavement construction works. Among the available laboratory compaction methods, impact method followed by the static method are the most commonly used procedures. Since the nature and approach of these two compaction methods is fundamentally different, an investigation on the effect of using these techniques on the mechanical performance of pavement materials prepared by each of these methods is essential, so as to better understand both these compaction methods. In this regard, two types of recycled Construction and Demolition (C&D) materials suitable for pavement applications, being Crushed Brick (CB) and Recycled Concrete Aggregate (RCA) were selected. Laboratory specimens were prepared using the two above-mentioned procedures. Different aspects of geotechnical characteristics of the specimens, including aggregate breakage, changes in soil-water characteristics, stiffness and resilient characteristics, etc., were investigated. The outcomes of this research indicate that the influence of method of compaction must be considered when interpreting the laboratory test results for field design purposes.
Physics And Chemistry Of The Earth, Parts A/b/c, Dec 1, 2019
Advancement of knowledge on the behaviour of unsaturated soil through constitutive modelling is a... more Advancement of knowledge on the behaviour of unsaturated soil through constitutive modelling is an area of active research within the geotechnical community. Given that most of the Earth surface can be considered unsaturated and most of the geotechnical infrastructures constitute of compacted soil, advancements in predictive modelling are needed for reliable management of geo-infrastructures. Moreover, the complex processes of soil collapse, shear failures and excessive soil swelling underneath artificial and (or) natural structures necessitates continuous monitoring or periodic assessment of relevant field parameters. To address this problem, geophysical and proximal optical sensing methods can be utilised for high-density spatial characterisation of relevant soil properties and features for monitoring of geotechnical structures. In this paper, we combined knowledge in unsaturated soil behaviour on the basis of the recent Monash-Peradeniya-Kodikara (MPK) framework and surface/subsurface soil characterisation using proximal soil sensing techniques and discrete sensing for ground-truthing to envisage a combined observation and predictive modelling paradigm for geo-infrastructures. We discussed the concepts by demonstrating its usefulness in predicting potential landslides and slope stability issues. The overarching impact of the ideas discussed in this paper is expected to generate new research priority areas that can be highly beneficial in monitoring geo-infrastructures subjected to climate loading. Furthermore, we identified future research areas that can provide modern benefits of geophysical techniques in geotechnical problems. In particular, we note that developments in pedophysical transfer functions relating soil resistivity to commonly utilised geotechnical soil properties can be highly beneficial to geotechnical practitioners involved in monitoring of critical geo-infrastructures. Geohazards such as landslides usually occur under conditions of
Offshore pipelines play a significant role in transporting energy resources such as crude oil and... more Offshore pipelines play a significant role in transporting energy resources such as crude oil and natural gas from offshore platforms to processing facilities. The on-bottom stability of offshore pipelines is influenced significantly by the geotechnical conditions at the seabed. Pipeline would undergo a number of thermal cycles during its operational life. At the end of each thermal cycle, some part of the expansion would recover, whereas the irrecoverable expansion would accumulate at the free ends and cause the pipe to move axially in one direction, known as Axial Walking. The test results from the Monash Advanced Pipe testing System (MAPS) imply that pipe axial walking would induce relative movements of the soil below the pipe. Since the pipe-soil interaction is extensively influenced by the soil response, the portion of the soil below the pipe which undergoes shearing, characterised as the Shear Zone, is significant for pipe axial walking assessment and thus needs to be investigated thoroughly. This paper presents an investigation into the behaviour of soil within the shear zone in pipe axial walking problems. Cyclic direct simple shear tests on soft clay at low normal stress are performed as applicable to axial walking problems. The soil response in the shear zone is characterised as undrained, partially drained, or drained based on cyclic shearing rates and the relationship between residual peak shear resistance and shearing rate is investigated. Finite element analyses are also conducted to capture the behaviour of soil within the shear zone, utilising advanced constitutive soil model. Based on the results from both experimental work and numerical analysis, a set of data is established which can be applied in the calibration of large-scale pipe axial walking modelling, and provide guidance on the design practice of offshore pipelines when considering on-bottom stability in axial direction.
Tensile fracture in mode I occurs in many geotechnical applications such as in slope stability, d... more Tensile fracture in mode I occurs in many geotechnical applications such as in slope stability, desiccation cracking, borehole pressuremeter testing, etc. The cohesive crack model is a powerful and versatile tool that can be used to numerically analyse mode I fracture, that has had very limited usage in geomechanics to date. This research reports findings from testing on single-edge notched beams manufactured from compacted clay fractured in three-point bending. Specimens were tested at a range of moisture contents to determine several fracture parameters including the parameters defining cohesive cracks. The properties for the cohesive crack were back-calculated by matching the numerically modelled load–load point displacement curve obtained using a hybrid continuum distinct element program with the ones obtained experimentally. It was found that the cohesive crack method could be successfully used in matching the load–load point displacement curves for a range of consistencies of the clay from soft to v...
This article analyses the failure of a 500 mm-diameter cast iron (CI) water pipe that catastrophi... more This article analyses the failure of a 500 mm-diameter cast iron (CI) water pipe that catastrophically fractured in Sydney in 2013. According to metallurgical analysis and finite element simulation, a longitudinal pre-existing crack initiated from the adjacent bell-joint and eventually propagated to a critical length in the pipe barrel over a certain period. There was evidence of leakage prior to the burst incident but information was inconclusive whether it was exactly from this pipe. Fatigue caused by cyclic internal pressure was considered as the predominant factor in leading to crack growth. A numerical model was developed to describe crack growth behaviour using Paris' law, and metallurgical analysis and mechanical tests were conducted to support this investigation. Based on the field evidence and simulation results, the leak-before-break approach might be applicable in CI pipes to avoid severe consequences of trunk main bursts.
This paper presents the results of uniaxial compression tests conducted on quartzite samples. The... more This paper presents the results of uniaxial compression tests conducted on quartzite samples. The tested quartzite samples consisted of 83 mm diameter cores that were cut to a length roughly twice their diameter. The specimens were cored from a depth of between 68-78 m. The stress-strain and acoustic emission (AE) responses were monitored throughout the tests. The results obtained for the intact specimens are believed to be typical, and are in general agreement with the results of other researchers. The tests produced a recognisable AE peak prior to the peak axial strength of the specimen being reached. The axial stress at which this AE peak occurs corresponds to a value of around 90% of the specimen's UCS (unconfined compressive strength). This is due to the formation of new fractures and shear mobilisation of established failure planes prior to failure that emits large amounts of AE energy.
This paper presents a synthesis of mechanisms related to structure development of surficial heavy... more This paper presents a synthesis of mechanisms related to structure development of surficial heavy clay soils. These clay soils develop specific structural features due to wet/dry cycles and desiccation cracking they undergo during soil "ripening". There is substantial field and laboratory evidence to indicate that clay soils generally develop stable structures with stable material properties when they ripen under repeated wet/dry cycles of climatic change. This development occurs as a result of the re-arrangement of the soil particles to minimise the potential or free energy. Available evidence indicates that under field climatic conditions, swelling/shrinkage of clay soils occur predominantly due to water loss from interparticle and interaggregation pores. Vertisols or heavy clay surficial soils can develop special geomorphological features such as gilgai. Mechanisms of gilgai formation are also analysed, and their origin is related to the initial pattern of soil desiccation cracking. The process of shrinkage cracking and associated volume change in soils is explained on the basis of unsaturated soil mechanics theory. Crack patterns are divided into orthogonal and non-orthogonal patterns, and the conditions that lead to the development of these crack patterns are highlighted. Finally, a conceptual approach for modelling of the desiccation cracking process is presented.
The soil-concrete interface shear strength, although has been extensively studied, is still diffi... more The soil-concrete interface shear strength, although has been extensively studied, is still difficult to predict as a result of the dependence on many factors such as normal stresses, surface roughness, particle sizes, moisture contents, dilation angles of soils, etc. In this study, a well-known rigorous statistical learning approach, namely the least squares support vector machine (LS-SVM) realized in a ubiquitous spreadsheet platform is firstly used in estimating the soil-structure interface shear strength. Instead of studying the complicated mechanism, LS-SVM enables to explore the possible link between the fundamental factors and the interface shear strengths, via a sophisticated statistic approach. As a preliminary investigation, the authors study the expansive soils that are found extensively in most countries. To reduce the complexity, three major influential factors, e.g., initial moisture contents, initial dry densities and normal stresses of soils are taken into account in developing the LS-SVM models for the soil-concrete interface shear strengths. The predicted results by LS-SVM show reasonably good agreement with experimental data from direct shear tests.
This paper presents the application of the hybrid continuum-discrete element method, i.e. Univers... more This paper presents the application of the hybrid continuum-discrete element method, i.e. Universal Distinct Element Code (UDEC), to simulate soil desiccation shrinkage and cracking. Herein, soil is modelled using a mix-mode cohesive fracture model that combines tension, compression and shear material behaviour. The fracture model considers both elastic and inelastic (decomposed to fracture and plastic) displacement, with the norm of the effective inelastic displacement being used to control the fracture behaviour. The applicability and capability of the proposed approach is demonstrated through numerical simulations of laboratory linearlyconstrained desiccation test. Good agreements with the laboratory observations have been obtained. The dominant influencing factors on soil desiccation cracking have been assessed, several factors including shear strength and tensile strength of soil-base, and soil sample thickness were identified to have a significant controlling influence on desiccation cracking.
Compacted unsaturated soils show distinct behavioural patterns when compared with their saturated... more Compacted unsaturated soils show distinct behavioural patterns when compared with their saturated counterparts, and these behavioural patterns become more and more complex when soil is subjected to wetting, such as swelling or collapse and loss of shear strength. Ignoring these possible complex behaviours of unsaturated soils coupled with varying climatic conditions can lead to inaccurate assessment of the performance of geotechnical structures. Therefore, the accurate prediction of the wetting-induced volume change behaviour of compacted unsaturated soils is a key step in understanding and modelling unsaturated soil behaviour. Of the different constitutive models introduced to date which can define the wetting-induced volume change behaviour of compacted unsaturated soils reasonably satisfactorily, the MPK framework for the volumetric constitutive behaviour of compacted unsaturated soils proposed by Kodikara ( ) has shown favourable results with its direct relationship to moisture variation. This approach provides a practical approach, where reliance is placed on the variations in the moisture or degree of saturation as input. From this perspective, this study evaluates the volumetric behaviour of compacted unsaturated soils due to various wetting state paths, and the results are compared with the predictions of the MPK framework. The results show that the MPK framework is capable of predicting wetting-induced volume change behaviour, including the wetting-induced yielding of compacted unsaturated soils.
Volumetric behaviour is a fundamental consideration in unsaturated soil constitutive modelling. I... more Volumetric behaviour is a fundamental consideration in unsaturated soil constitutive modelling. It is more complex than when the soil is saturated, as unsaturated soils exhibit a range of responses such as swelling and collapse under wetting and shrinkage and cracking during drying. While significant advances have been made, it is still difficult to generally explain all patterns of behaviour. This paper presents a new framework for modelling volumetric response of unsaturated soils with emphasis on compacted soils. The framework uses void ratio (e), moisture ratio (ew), and net stress (p) as the main constitutive variables and suction as a dependent variable. This choice of ewas a main constitutive variable is theoretically sound and is more attractive than the use of suction, which is relatively difficult to measure and displays significant hysteresis during drying and wetting. The framework incorporates the well-known compaction curve making it easily applicable to practical situations. Within the overall e–ew–p space, the operative space is constrained by three main surfaces; namely, loading–wetting state boundary surface, tensile failure surface, and the saturated plane. The conceptual basis for these state surfaces is described and the framework is qualitatively validated against observed behaviour of compacted soils.
Tensile cracking due to desiccation and fracture properties are of great importance in clay liner... more Tensile cracking due to desiccation and fracture properties are of great importance in clay liners, earth dam engineering, waste contaminant systems, and mine tailings. This paper presents restrained shrinkage test results and analyses of consolidated desiccating soil, and compares results with numerical analyses using the computer program Universal Distinct Element Code (UDEC). The cohesive crack method was used as it is more appropriate than linear elastic fracture mechanics for soil cracking at high moisture contents with the likely presence of plasticity during fracture. The variation of the radial stresses on the inner ring with water content was used to model mode I cracking and gather fracture properties of the propagating crack. The model was validated on kaolin clay tested under restrained ring shrinkage and was compared with various test results and results from the literature. The test could be a valuable tool in determining fracture properties during desiccation.
The safe disposal of coal ash produced from power stations involves the assessment of rates of pr... 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.
The 6th International Conference on Computational Methods (ICCM2015), Mar 29, 2015
The soil compaction is one of the most common activities of civil construction. It is applicable ... more The soil compaction is one of the most common activities of civil construction. It is applicable to construction of fills, dams, roads and embankments. The compacted soils can be subjected to various external and environmental loading after construction. The external loading can arise from superstructure loading, moving traffic and overburden soils. The environmental loading can come from the interaction of surficial soils with the atmosphere in forms such as wetting and drying. Under the combination of these loadings, the compacted soils display complex patterns of behaviour such as swelling, collapse, tensile cracking and swelling pressure development against buried nonyielding bodies. The current approaches for predicting the behaviour of compacted soils during subsequent external and environmental loading are, on one hand, are very complex, and on the other hand, are not entirely satisfactory. The seminar will present a new framework for predicting the behaviour of compacted soils under these loadings, referred to as MPK (Monash-Peradeniya-Kodikara) Framework (Kodikara, 2012). More recent experimental results supporting the framework will also be presented.
A mix-mode cohesive fracture model considering tension, compression and shear material behaviour ... more A mix-mode cohesive fracture model considering tension, compression and shear material behaviour is presented, which has wide applications to geotechnical problems. The model considers both elastic and inelastic displacements. Inelastic displacement comprises fracture and plastic displacements. The norm of inelastic displacement is used to control the fracture behaviour. Meantime, a failure function describing the fracture strength is proposed. Using the internal programming FISH, the cohesive fracture model is programmed into a hybrid distinct element algorithm as encoded in Universal Distinct Element Code (UDEC). The model is verified through uniaxial tension and direct shear tests. The developed model is then applied to model the behaviour of a uniaxial compression test on Gosford sandstone. The modelling results indicate that the proposed cohesive fracture model is capable of simulating combined failure behaviour applicable to rock.
Laboratory testing methods are constantly being developed to simulate true field conditions in co... more Laboratory testing methods are constantly being developed to simulate true field conditions in controlled laboratory environment. The aim of laboratory testing methods is to reproduce specimens which accurately replicate field performance in terms of mechanical behavior of pavement materials under applied loads. Compaction is the most common soil stabilization technique in ground improvement and pavement construction works. Among the available laboratory compaction methods, impact method followed by the static method are the most commonly used procedures. Since the nature and approach of these two compaction methods is fundamentally different, an investigation on the effect of using these techniques on the mechanical performance of pavement materials prepared by each of these methods is essential, so as to better understand both these compaction methods. In this regard, two types of recycled Construction and Demolition (C&D) materials suitable for pavement applications, being Crushed Brick (CB) and Recycled Concrete Aggregate (RCA) were selected. Laboratory specimens were prepared using the two above-mentioned procedures. Different aspects of geotechnical characteristics of the specimens, including aggregate breakage, changes in soil-water characteristics, stiffness and resilient characteristics, etc., were investigated. The outcomes of this research indicate that the influence of method of compaction must be considered when interpreting the laboratory test results for field design purposes.
Physics And Chemistry Of The Earth, Parts A/b/c, Dec 1, 2019
Advancement of knowledge on the behaviour of unsaturated soil through constitutive modelling is a... more Advancement of knowledge on the behaviour of unsaturated soil through constitutive modelling is an area of active research within the geotechnical community. Given that most of the Earth surface can be considered unsaturated and most of the geotechnical infrastructures constitute of compacted soil, advancements in predictive modelling are needed for reliable management of geo-infrastructures. Moreover, the complex processes of soil collapse, shear failures and excessive soil swelling underneath artificial and (or) natural structures necessitates continuous monitoring or periodic assessment of relevant field parameters. To address this problem, geophysical and proximal optical sensing methods can be utilised for high-density spatial characterisation of relevant soil properties and features for monitoring of geotechnical structures. In this paper, we combined knowledge in unsaturated soil behaviour on the basis of the recent Monash-Peradeniya-Kodikara (MPK) framework and surface/subsurface soil characterisation using proximal soil sensing techniques and discrete sensing for ground-truthing to envisage a combined observation and predictive modelling paradigm for geo-infrastructures. We discussed the concepts by demonstrating its usefulness in predicting potential landslides and slope stability issues. The overarching impact of the ideas discussed in this paper is expected to generate new research priority areas that can be highly beneficial in monitoring geo-infrastructures subjected to climate loading. Furthermore, we identified future research areas that can provide modern benefits of geophysical techniques in geotechnical problems. In particular, we note that developments in pedophysical transfer functions relating soil resistivity to commonly utilised geotechnical soil properties can be highly beneficial to geotechnical practitioners involved in monitoring of critical geo-infrastructures. Geohazards such as landslides usually occur under conditions of
Offshore pipelines play a significant role in transporting energy resources such as crude oil and... more Offshore pipelines play a significant role in transporting energy resources such as crude oil and natural gas from offshore platforms to processing facilities. The on-bottom stability of offshore pipelines is influenced significantly by the geotechnical conditions at the seabed. Pipeline would undergo a number of thermal cycles during its operational life. At the end of each thermal cycle, some part of the expansion would recover, whereas the irrecoverable expansion would accumulate at the free ends and cause the pipe to move axially in one direction, known as Axial Walking. The test results from the Monash Advanced Pipe testing System (MAPS) imply that pipe axial walking would induce relative movements of the soil below the pipe. Since the pipe-soil interaction is extensively influenced by the soil response, the portion of the soil below the pipe which undergoes shearing, characterised as the Shear Zone, is significant for pipe axial walking assessment and thus needs to be investigated thoroughly. This paper presents an investigation into the behaviour of soil within the shear zone in pipe axial walking problems. Cyclic direct simple shear tests on soft clay at low normal stress are performed as applicable to axial walking problems. The soil response in the shear zone is characterised as undrained, partially drained, or drained based on cyclic shearing rates and the relationship between residual peak shear resistance and shearing rate is investigated. Finite element analyses are also conducted to capture the behaviour of soil within the shear zone, utilising advanced constitutive soil model. Based on the results from both experimental work and numerical analysis, a set of data is established which can be applied in the calibration of large-scale pipe axial walking modelling, and provide guidance on the design practice of offshore pipelines when considering on-bottom stability in axial direction.
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Papers by Jayantha Kodikara