Pathegama G Ranjith | Monash University (original) (raw)

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Papers by Pathegama G Ranjith

Energy reviews, Mar 1, 2023

Water Air and Soil Pollution, Jan 25, 2020

Wellbore integrity during Carbon Dioxide (CO2) storage in deep aquifers is a major problem as the... more Wellbore integrity during Carbon Dioxide (CO2) storage in deep aquifers is a major problem as the currently used well cement will lose its integrity at higher temperatures and eventually leads to CO2 leakage into the atmosphere. Researchers have conducted several studies in order to find a proper well cement material and have tested several types of geopolymers mixing fly ash and different type of cements with an alkaline solution curing in different temperatures. This paper presents a study on geopolymer composites made from fired siltstone, slag as well as alkaline liquid which were cured at temperatures ranging from 23°C to 80°C. Five different types of geopolymer were prepared with ratios of fired siltstone (to 700 oC) and slag as 0:100, 20:80, 30:70, 40:60 and 50:50, separately. After preparing samples with various proportions under different temperatures, the mechanical properties of them were compared. The experimental results reveal that optimum curing temperature range is 50 to 70°C and addition of higher proportion of slag would help geopolymer gain better performance on mechanical strength compared to other geopolymer materials.

Geomechanics and geophysics for geo-energy and geo-resources, Jul 25, 2020

Advances in environmental engineering and green technologies book series, 2018

Geotechnical Testing Journal, Jan 12, 2017

The Goodman jack is widely used to measure the deformation modulus of rock in the field. Although... more The Goodman jack is widely used to measure the deformation modulus of rock in the field. Although some corrections have been proposed for the jack in the research literature, the accuracy of the test remains unsatisfactory, and the results of the Goodman jack test are lower than the actual values. Based on the corrections proposed in the literature, we reported on two factors which may lead to a lower value of the Goodman jack test: one was the non-full rock/platen contact when the borehole is under- or over-sized (relative to the standard borehole with a diameter of 76.2 mm), and the other was the upper limitation on the applied hydraulic pressure. First, a numerical simulation was carried out to investigate the impact of the borehole diameter on the rock/platen contact and the calculated rock modulus. The results showed that when there is a deviation of 0.6 mm in the borehole diameter, the calculated rock modulus may be 2 to 5 times lower. Based on the results of numerical simulation, a borehole diameter-related correction is proposed for the tests in under- or over-sized boreholes. Second, to ensure that the rock responds elastically during the test, we analyzed the stress around the borehole, and based on the Mohr-Coulomb and tensile failure criteria, deduced the upper limitation for the applied hydraulic pressure. The results of a case study in a coal mine suggest that the pressure limitation is controlled by the initial stress in the field and the rock strength, and influenced significantly by the loading direction of the jack. Finally, based on the observations in the present research, a new procedure is suggested for the Goodman jack test, which may be helpful in improving the accuracy of in situ testing.

Geomechanics and Geophysics for Geo-Energy and Geo-Resources

Abstract This paper experimentally examines the time-dependent mechanical behaviours of frac sand... more Abstract This paper experimentally examines the time-dependent mechanical behaviours of frac sand at high compressive stresses. A series of instant and sustained one-dimensional compression tests was performed on Jordan sand, White sand, and Genoa sand, and three grain size distributions for each frac sand were tested. The acoustic emission events related to sand crushing were monitored by piezoelectric sensors for understanding sand breakage during compression. The results show that Genoa sand with 25% weaker anorthite mineral grains show much more grain breakage and higher plastic and creep strains at high compressive stresses than the pure quartz Jordan and White sand. Wider grain size distributions tend to result in larger plastic strains than narrower size distributions but provide better crushing resistance and smaller creep deformation. Cyclic and creep load stages only slightly increase grain breakage compared with instant loads, but result in higher plastic and creep strains. Two creep stages were found in the time-dependent deformation of sand and can be satisfactorily depicted with the Riemann–Liouville fractional calculus model at different stress levels, with sand’s fractional derivative of increases from 0.28 to 0.35 as sand grains are gradually crushed. Lower viscosity coefficients are found in Genoa (~ 15e4 MPa*s) than White and Jordan sand (> 20e4 MPa*s). The time-dependent deformation of sand proppant has a significant implication on the long-term conductivity of sand packs, which can reduce the hydraulic conductivity by about 40%–90% after a one-year duration. The results warrant considering frac sand’s long-term deformation when choosing frac sand as proppants in hydraulic fracturing. Article Highlights Weaker Genoa sand shows 50–150% higher plastic and creep strains than Jordan and White sand at high compression. Wider grain size distributions result in larger plastic but smaller strains creep in sand at sustained loads. Creep strain is depicted by fractional calculus with an increased derivative from 0.28 to 0.35 as sand is crushed.

International Journal of Mining Science and Technology, 2021

International Journal of Rock Mechanics and Mining Sciences, 2021

Abstract Understanding the mechanical properties of α-quartz is of vital importance to rock engin... more Abstract Understanding the mechanical properties of α-quartz is of vital importance to rock engineering because α-quartz is the main component of igneous, metamorphic and sedimentary rocks. Molecular dynamics simulations (MDs) of nanoindentation tests on α-quartz were performed to investigate the effects of indenter tip radius and penetration depth on the mechanical properties of α-quartz. Indentation load-penetration depth (P-h) curves were plotted, from which Reduced Young’s modulus ( E r ) , hardness ( H ) were obtained and these mechanical parameters were then compared with the laboratory nanoindentation results. The mechanical results obtained from MDs are in good agreement with the experimental values. It can be found that E r and H increase with indentation depth at shallow contact depth while they decrease with indenter tip size. To the authors’ knowledge, this is the first MDs of nanoindentation test of hard rock-forming minerals reported and we believe that this study can shed light on the precise measurement of the mechanical properties of rock minerals at micro- and nano-scales.

E3S Web of Conferences, 2020

During CO2 injection into deep saline aquifers, the overlying caprock may be subjected to geochem... more During CO2 injection into deep saline aquifers, the overlying caprock may be subjected to geochemical reactions which can alter the leakage pathways for injected CO2. Thus, it is crucial to identify the supercritical CO2 (scCO2) flow behaviour via fractures in caprock and its permeability to estimate the permanence of injected CO2. The objective of this study is to find the effect of scCO2 flow on fractured caprock permeability. A fractured siltstone sample was saturated in deionized water and conducted scCO2 permeability tests using a high-precision advanced core flooding apparatus under different injection pressures and confinements. Next, the siltstone sample was saturated in 10% w/w NaCl brine and conduced scCO2 permeability tests as described earlier. The results show that the brine-saturated sample has low permeability compared to water-saturated siltstone sample. The reason would be the deposition of evaporites during scCO2 flow through the fractured sample. This is known as ...

Computational Materials Science, 2020

Energy reviews, Mar 1, 2023

Water Air and Soil Pollution, Jan 25, 2020

Wellbore integrity during Carbon Dioxide (CO2) storage in deep aquifers is a major problem as the... more Wellbore integrity during Carbon Dioxide (CO2) storage in deep aquifers is a major problem as the currently used well cement will lose its integrity at higher temperatures and eventually leads to CO2 leakage into the atmosphere. Researchers have conducted several studies in order to find a proper well cement material and have tested several types of geopolymers mixing fly ash and different type of cements with an alkaline solution curing in different temperatures. This paper presents a study on geopolymer composites made from fired siltstone, slag as well as alkaline liquid which were cured at temperatures ranging from 23°C to 80°C. Five different types of geopolymer were prepared with ratios of fired siltstone (to 700 oC) and slag as 0:100, 20:80, 30:70, 40:60 and 50:50, separately. After preparing samples with various proportions under different temperatures, the mechanical properties of them were compared. The experimental results reveal that optimum curing temperature range is 50 to 70°C and addition of higher proportion of slag would help geopolymer gain better performance on mechanical strength compared to other geopolymer materials.

Geomechanics and geophysics for geo-energy and geo-resources, Jul 25, 2020

Advances in environmental engineering and green technologies book series, 2018

Geotechnical Testing Journal, Jan 12, 2017

The Goodman jack is widely used to measure the deformation modulus of rock in the field. Although... more The Goodman jack is widely used to measure the deformation modulus of rock in the field. Although some corrections have been proposed for the jack in the research literature, the accuracy of the test remains unsatisfactory, and the results of the Goodman jack test are lower than the actual values. Based on the corrections proposed in the literature, we reported on two factors which may lead to a lower value of the Goodman jack test: one was the non-full rock/platen contact when the borehole is under- or over-sized (relative to the standard borehole with a diameter of 76.2 mm), and the other was the upper limitation on the applied hydraulic pressure. First, a numerical simulation was carried out to investigate the impact of the borehole diameter on the rock/platen contact and the calculated rock modulus. The results showed that when there is a deviation of 0.6 mm in the borehole diameter, the calculated rock modulus may be 2 to 5 times lower. Based on the results of numerical simulation, a borehole diameter-related correction is proposed for the tests in under- or over-sized boreholes. Second, to ensure that the rock responds elastically during the test, we analyzed the stress around the borehole, and based on the Mohr-Coulomb and tensile failure criteria, deduced the upper limitation for the applied hydraulic pressure. The results of a case study in a coal mine suggest that the pressure limitation is controlled by the initial stress in the field and the rock strength, and influenced significantly by the loading direction of the jack. Finally, based on the observations in the present research, a new procedure is suggested for the Goodman jack test, which may be helpful in improving the accuracy of in situ testing.

Geomechanics and Geophysics for Geo-Energy and Geo-Resources

Abstract This paper experimentally examines the time-dependent mechanical behaviours of frac sand... more Abstract This paper experimentally examines the time-dependent mechanical behaviours of frac sand at high compressive stresses. A series of instant and sustained one-dimensional compression tests was performed on Jordan sand, White sand, and Genoa sand, and three grain size distributions for each frac sand were tested. The acoustic emission events related to sand crushing were monitored by piezoelectric sensors for understanding sand breakage during compression. The results show that Genoa sand with 25% weaker anorthite mineral grains show much more grain breakage and higher plastic and creep strains at high compressive stresses than the pure quartz Jordan and White sand. Wider grain size distributions tend to result in larger plastic strains than narrower size distributions but provide better crushing resistance and smaller creep deformation. Cyclic and creep load stages only slightly increase grain breakage compared with instant loads, but result in higher plastic and creep strains. Two creep stages were found in the time-dependent deformation of sand and can be satisfactorily depicted with the Riemann–Liouville fractional calculus model at different stress levels, with sand’s fractional derivative of increases from 0.28 to 0.35 as sand grains are gradually crushed. Lower viscosity coefficients are found in Genoa (~ 15e4 MPa*s) than White and Jordan sand (> 20e4 MPa*s). The time-dependent deformation of sand proppant has a significant implication on the long-term conductivity of sand packs, which can reduce the hydraulic conductivity by about 40%–90% after a one-year duration. The results warrant considering frac sand’s long-term deformation when choosing frac sand as proppants in hydraulic fracturing. Article Highlights Weaker Genoa sand shows 50–150% higher plastic and creep strains than Jordan and White sand at high compression. Wider grain size distributions result in larger plastic but smaller strains creep in sand at sustained loads. Creep strain is depicted by fractional calculus with an increased derivative from 0.28 to 0.35 as sand is crushed.

International Journal of Mining Science and Technology, 2021

International Journal of Rock Mechanics and Mining Sciences, 2021

Abstract Understanding the mechanical properties of α-quartz is of vital importance to rock engin... more Abstract Understanding the mechanical properties of α-quartz is of vital importance to rock engineering because α-quartz is the main component of igneous, metamorphic and sedimentary rocks. Molecular dynamics simulations (MDs) of nanoindentation tests on α-quartz were performed to investigate the effects of indenter tip radius and penetration depth on the mechanical properties of α-quartz. Indentation load-penetration depth (P-h) curves were plotted, from which Reduced Young’s modulus ( E r ) , hardness ( H ) were obtained and these mechanical parameters were then compared with the laboratory nanoindentation results. The mechanical results obtained from MDs are in good agreement with the experimental values. It can be found that E r and H increase with indentation depth at shallow contact depth while they decrease with indenter tip size. To the authors’ knowledge, this is the first MDs of nanoindentation test of hard rock-forming minerals reported and we believe that this study can shed light on the precise measurement of the mechanical properties of rock minerals at micro- and nano-scales.

E3S Web of Conferences, 2020

During CO2 injection into deep saline aquifers, the overlying caprock may be subjected to geochem... more During CO2 injection into deep saline aquifers, the overlying caprock may be subjected to geochemical reactions which can alter the leakage pathways for injected CO2. Thus, it is crucial to identify the supercritical CO2 (scCO2) flow behaviour via fractures in caprock and its permeability to estimate the permanence of injected CO2. The objective of this study is to find the effect of scCO2 flow on fractured caprock permeability. A fractured siltstone sample was saturated in deionized water and conducted scCO2 permeability tests using a high-precision advanced core flooding apparatus under different injection pressures and confinements. Next, the siltstone sample was saturated in 10% w/w NaCl brine and conduced scCO2 permeability tests as described earlier. The results show that the brine-saturated sample has low permeability compared to water-saturated siltstone sample. The reason would be the deposition of evaporites during scCO2 flow through the fractured sample. This is known as ...

Computational Materials Science, 2020

Rock mass strength is the most important single parameter required for stability analyses of rock... more Rock mass strength is the most important single parameter required for stability analyses of rock slopes and many other designs of structures in or on rock masses. However, the precise estimation of rock mass strength is extremely difficult due to its heterogeneous nature induced by the presence of joints. Rock mechanical behaviour is greatly influenced by the geometrical properties of the joints, such as their orientation, persistence, surface roughness and degree of interconnectivity. In addition, different hydro-geological conditions can have marked influences on jointed rock behaviour. The main objective of this thesis is to investigate the influences of various joint geometrical properties on the hydro-mechanical behaviour of jointed rock masses. Experimental, numerical and theoretical investigations were carried out to achieve this objective.

The International Conference on Geomechanics, Geo-energy and Geo-resources will be held at Monash... more The International Conference on Geomechanics, Geo-energy and Geo-resources will be held at Monash University (Australia) from 28th to 29th September 2016.

This conference is aimed at promoting discussion of strategies to address challenges in developing geo-energy and geo-resources extraction, and greenhouse mitigation measures through deep earth from the perspective of geomechanics and geophysics.