Energy technologies, which work by extracting or injecting fluids in the ground, such as geothermal energy systems or underground liquefied gas storage, may induce seismic events, see e.g., [1]. In the Netherlands, induced earthquakes are continuously recorded from the Groningen gas field, with the largest magnitude ever recorded of ML 3.6 at Huizinge. Even though the magnitude of these events is not high, compared to natural earthquakes, damage to the built environment is still caused because of the shallow depth of the events and site amplification, especially where soft soils are encountered [2]. Proper quantification of the induced seismic risk requires better understanding of the response of soft soils to these repeated short events, covering a range of frequencies from 1 to about 20 Hz. This motivated the development of a new advanced dynamic equipment to experimentally investigate the coupled response of soft organic clays and peats from the typical deltaic areas of the Netherlands.
Direct simple shear (DSS) apparatuses are preferred usually to investigate the soil behaviour under cyclic and dynamic loading. Among them, a number of multi-directional DSS setups have been developed to investigate the soil behaviour under multidirectional loading [3, 4, 5, 6, 7, 8]. Applying multi-directional loading to soil specimens in the laboratory is a keystone for elucidating the cyclic and dynamic soil response, as several studies have shown that the cyclic and post-cyclic response of soils is affected by multiple loading directions [6, 9, 10, 11, 12]. However, traditional DSS devices have a number of shortcomings, which are inherited by multi-directional DSS devices. The main deficiency of the DSS device is that the shear stress acting on the lateral side of the specimen cannot be controlled, and hence, a homogeneous stress state cannot be achieved, in spite of the common assumptions. Lateral stresses cannot be measured either in traditional setups, which leaves a knowledge gap on the stress state and the stress path of the sample.
In addition, the majority of laboratory element tests are performed by imposing “slow” undrained cyclic loads, to try to guarantee uniform water pressure distribution within the sample, for the sake of interpretation and modelling. However, seismic events encompass much higher loading frequencies than typically available, with loading rate effects playing a key role in the response of soft soils such as organic clays and peats. In order to fully understand the cyclic behaviour of soft soils, “fast” cyclic tests are crucial.
The innovative multidirectional shear device, developed in the section of Geoengineering at TU Delft (Cyclic-Dynamic shear simulator for Organic Soft Soils, CYC-DOSS), was designed to overcome some limitations of previous equipment. The underlying idea is to abandon the homogenous stress-strain state assumption and monitor the response with local sensors, which allows conditioning a num
{"title":"A new experimental setup to investigate the cyclic response of soft soils under induced earthquakes","authors":"Ching-Yu Chao, Wout Broere, Cristina Jommi","doi":"10.59490/seg.2023.635","DOIUrl":"https://doi.org/10.59490/seg.2023.635","url":null,"abstract":"Energy technologies, which work by extracting or injecting fluids in the ground, such as geothermal energy systems or underground liquefied gas storage, may induce seismic events, see e.g., [1]. In the Netherlands, induced earthquakes are continuously recorded from the Groningen gas field, with the largest magnitude ever recorded of ML 3.6 at Huizinge. Even though the magnitude of these events is not high, compared to natural earthquakes, damage to the built environment is still caused because of the shallow depth of the events and site amplification, especially where soft soils are encountered [2]. Proper quantification of the induced seismic risk requires better understanding of the response of soft soils to these repeated short events, covering a range of frequencies from 1 to about 20 Hz. This motivated the development of a new advanced dynamic equipment to experimentally investigate the coupled response of soft organic clays and peats from the typical deltaic areas of the Netherlands.
 Direct simple shear (DSS) apparatuses are preferred usually to investigate the soil behaviour under cyclic and dynamic loading. Among them, a number of multi-directional DSS setups have been developed to investigate the soil behaviour under multidirectional loading [3, 4, 5, 6, 7, 8]. Applying multi-directional loading to soil specimens in the laboratory is a keystone for elucidating the cyclic and dynamic soil response, as several studies have shown that the cyclic and post-cyclic response of soils is affected by multiple loading directions [6, 9, 10, 11, 12]. However, traditional DSS devices have a number of shortcomings, which are inherited by multi-directional DSS devices. The main deficiency of the DSS device is that the shear stress acting on the lateral side of the specimen cannot be controlled, and hence, a homogeneous stress state cannot be achieved, in spite of the common assumptions. Lateral stresses cannot be measured either in traditional setups, which leaves a knowledge gap on the stress state and the stress path of the sample.
 In addition, the majority of laboratory element tests are performed by imposing “slow” undrained cyclic loads, to try to guarantee uniform water pressure distribution within the sample, for the sake of interpretation and modelling. However, seismic events encompass much higher loading frequencies than typically available, with loading rate effects playing a key role in the response of soft soils such as organic clays and peats. In order to fully understand the cyclic behaviour of soft soils, “fast” cyclic tests are crucial.
 The innovative multidirectional shear device, developed in the section of Geoengineering at TU Delft (Cyclic-Dynamic shear simulator for Organic Soft Soils, CYC-DOSS), was designed to overcome some limitations of previous equipment. The underlying idea is to abandon the homogenous stress-strain state assumption and monitor the response with local sensors, which allows conditioning a num","PeriodicalId":473465,"journal":{"name":"Symposium on Energy Geotechnics 2023","volume":"50 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135646684","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Katia Galindo, Leonardo Guimarães, Cecília Lins, Analice Lima
Injection of CO2 and water in saline aquifers or oil reservoirs causes changes of pressure, saturation and concentrations that affect the state of stress and promote chemical reactions in the host rock, resulting in porosity and permeability variations. It is therefore a coupled hydro-mechanical and chemical (HMC) problem. Numerical simulation of multiphase and multicomponent flow of CO2, oil and water with mechanical coupling allows realistic modeling of the reservoir and cap rocks. Carbonate reservoirs are geological formations composed mainly of minerals such as calcite and dolomite which can dissolve or precipitate in the medium when injecting a fluid of chemical composition and temperature different from those of the fluids initially contained in the rock. Water-weakening due to matrix acidification of carbonates is a well-known phenomenon that can be modeled by including mineral concentrations as state variables in the stress-strain behavior of the material.
The objective of this work is to characterize synthetic carbonate rocks through microtomography and petrography techniques, focusing on a comparative analysis before and after load application and degradation with a reactive fluid [1]. The synthetic rocks were subjected to physical characterization (mineralogy, computed tomography and porosity) and mechanical characterization (uniaxial compressive strength and Brazilian tests) before and after the dissolution process. The petrographic analysis verified an increase in both intergranular and intragranular porosities after dissolution. The microtomography analysis quantified the maximum increase in porosity, from 11.8% to 41.3% in the two-dimensional analysis and 31.6% to 52% in the three-dimensional analysis of the porous structures. Furthermore, the pores were quantified according to their area, and data was obtained on the orientation of the pores, providing insight into the preferred paths of fluid flow. It was also observed that the microtomography technique was an effective tool for characterizing fractures in the samples before and after dissolution [1].
Dissolution tests were also performed in a modified oedometer cell adapted to measure horizontal stress. The dissolution phase was conducted using water and an acid solution to evaluate the influence of the pH on the mechanical behaviour of the samples. When the sample in the oedometric cell is exposed to an acid solution under constant vertical load of 400kPa, vertical displacement takes place (volume decrease of the sample) and horizontal stress increases (Figure 1). The synthetic rock used in this experiment is mainly composed by calcite, with small additions of calcium hydroxide, and the reactive fluid is water acidified with acetic acid (with 10% concentration). This material is manufactured in laboratory in order to have greater control of its constituents and reproducibility of experimental results. During the acidification phase of the experiment, the sample was
{"title":"Minerals Dissolution Effect on the Mechanical Properties of Synthetic Carbonate Rocks","authors":"Katia Galindo, Leonardo Guimarães, Cecília Lins, Analice Lima","doi":"10.59490/seg.2023.648","DOIUrl":"https://doi.org/10.59490/seg.2023.648","url":null,"abstract":"Injection of CO2 and water in saline aquifers or oil reservoirs causes changes of pressure, saturation and concentrations that affect the state of stress and promote chemical reactions in the host rock, resulting in porosity and permeability variations. It is therefore a coupled hydro-mechanical and chemical (HMC) problem. Numerical simulation of multiphase and multicomponent flow of CO2, oil and water with mechanical coupling allows realistic modeling of the reservoir and cap rocks. Carbonate reservoirs are geological formations composed mainly of minerals such as calcite and dolomite which can dissolve or precipitate in the medium when injecting a fluid of chemical composition and temperature different from those of the fluids initially contained in the rock. Water-weakening due to matrix acidification of carbonates is a well-known phenomenon that can be modeled by including mineral concentrations as state variables in the stress-strain behavior of the material.
 The objective of this work is to characterize synthetic carbonate rocks through microtomography and petrography techniques, focusing on a comparative analysis before and after load application and degradation with a reactive fluid [1]. The synthetic rocks were subjected to physical characterization (mineralogy, computed tomography and porosity) and mechanical characterization (uniaxial compressive strength and Brazilian tests) before and after the dissolution process. The petrographic analysis verified an increase in both intergranular and intragranular porosities after dissolution. The microtomography analysis quantified the maximum increase in porosity, from 11.8% to 41.3% in the two-dimensional analysis and 31.6% to 52% in the three-dimensional analysis of the porous structures. Furthermore, the pores were quantified according to their area, and data was obtained on the orientation of the pores, providing insight into the preferred paths of fluid flow. It was also observed that the microtomography technique was an effective tool for characterizing fractures in the samples before and after dissolution [1].
 Dissolution tests were also performed in a modified oedometer cell adapted to measure horizontal stress. The dissolution phase was conducted using water and an acid solution to evaluate the influence of the pH on the mechanical behaviour of the samples. When the sample in the oedometric cell is exposed to an acid solution under constant vertical load of 400kPa, vertical displacement takes place (volume decrease of the sample) and horizontal stress increases (Figure 1). The synthetic rock used in this experiment is mainly composed by calcite, with small additions of calcium hydroxide, and the reactive fluid is water acidified with acetic acid (with 10% concentration). This material is manufactured in laboratory in order to have greater control of its constituents and reproducibility of experimental results. During the acidification phase of the experiment, the sample was ","PeriodicalId":473465,"journal":{"name":"Symposium on Energy Geotechnics 2023","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135647640","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Inge De Wolf, Man Xu, Cristina Jommi, Stefano Muraro
Peatlands have been recognised to provide a natural carbon sink thanks to waterlogged conditions, which keep summertime temperatures relatively low, increase their water holding capacity, decrease the organic soil decomposition rate by creating anoxic conditions and eventually keeping high water table. However, unfavourable environmental conditions due to increasing temperatures and more frequent droughts will reduce water retention of peats and the summertime insulation, in turn increasing their temperature sensitivity and their decomposition rate [1]. As a result, peatlands may start inverting their positive cycle and emitting greenhouse gases, including CO2 and CH4 [2], which suggests better investigating how increasing climate stresses will affect the efficiency of peats in the greenhouse gases cycle and CO2 sequestration.
Some evidence of gas production from increasing decomposition rate in the Netherlands is coming from continuous pore pressure measurements in saturated layers below the water table, which are monitored to assess the safety of the water defence and the transportation infrastructures. Increasing water pressure in closed piezometers compared to vented ones seem to suggest that gas is produced and capped in the ground, until the breakthrough pressure is reached and the gas vents from cracks opened in the soil matrix. Besides the environmental issues, increasing gas production from decomposition is becoming of concern for the stability of embankments made of organic soils, where the effective stress may be lowered to such an extent to endanger their stability. As a matter of fact, in the last ten years, gas overpressure has been claimed to be a triggering or a contributing factor in few small failures experienced by regional dykes in the Netherlands. In spite of the evidence [e.g. 3] and the risk increasing with heat waves and drought events, the role of gas on the coupled hydromechanical response of organic soils has been seldom investigated nor properly understood yet.
In the section of Geoengineering at TU Delft, a research effort has been undertaken in the last years to investigate in depth the role of gas formation and venting on the coupled hydro-mechanical response of organic layers in the subsoil of water defence embankments. Preliminary laboratory tests performed on peats to fill this gap showed the role of increasing gas content on their compressibility and on the mobilised shear strength at given strains [4, 5]. The volumetric response of peats including gas was tentatively interpreted with a simple non-linear elastic model, which proved able to model the experimental results [6].
A similar model was used to numerically investigate the relevance of gas production and venting on the response of a regional dyke in the Netherlands, where gas bubbles from venting were observed after excavating - unloading - the toe of the dyke during a stress test. Fully coupled three-phases hydromechanical numerical ana
{"title":"Evidence of gas formation and venting in organic soils: experimental evidence and modelling approach","authors":"Inge De Wolf, Man Xu, Cristina Jommi, Stefano Muraro","doi":"10.59490/seg.2023.646","DOIUrl":"https://doi.org/10.59490/seg.2023.646","url":null,"abstract":"Peatlands have been recognised to provide a natural carbon sink thanks to waterlogged conditions, which keep summertime temperatures relatively low, increase their water holding capacity, decrease the organic soil decomposition rate by creating anoxic conditions and eventually keeping high water table. However, unfavourable environmental conditions due to increasing temperatures and more frequent droughts will reduce water retention of peats and the summertime insulation, in turn increasing their temperature sensitivity and their decomposition rate [1]. As a result, peatlands may start inverting their positive cycle and emitting greenhouse gases, including CO2 and CH4 [2], which suggests better investigating how increasing climate stresses will affect the efficiency of peats in the greenhouse gases cycle and CO2 sequestration.
 Some evidence of gas production from increasing decomposition rate in the Netherlands is coming from continuous pore pressure measurements in saturated layers below the water table, which are monitored to assess the safety of the water defence and the transportation infrastructures. Increasing water pressure in closed piezometers compared to vented ones seem to suggest that gas is produced and capped in the ground, until the breakthrough pressure is reached and the gas vents from cracks opened in the soil matrix. Besides the environmental issues, increasing gas production from decomposition is becoming of concern for the stability of embankments made of organic soils, where the effective stress may be lowered to such an extent to endanger their stability. As a matter of fact, in the last ten years, gas overpressure has been claimed to be a triggering or a contributing factor in few small failures experienced by regional dykes in the Netherlands. In spite of the evidence [e.g. 3] and the risk increasing with heat waves and drought events, the role of gas on the coupled hydromechanical response of organic soils has been seldom investigated nor properly understood yet.
 In the section of Geoengineering at TU Delft, a research effort has been undertaken in the last years to investigate in depth the role of gas formation and venting on the coupled hydro-mechanical response of organic layers in the subsoil of water defence embankments. Preliminary laboratory tests performed on peats to fill this gap showed the role of increasing gas content on their compressibility and on the mobilised shear strength at given strains [4, 5]. The volumetric response of peats including gas was tentatively interpreted with a simple non-linear elastic model, which proved able to model the experimental results [6].
 A similar model was used to numerically investigate the relevance of gas production and venting on the response of a regional dyke in the Netherlands, where gas bubbles from venting were observed after excavating - unloading - the toe of the dyke during a stress test. Fully coupled three-phases hydromechanical numerical ana","PeriodicalId":473465,"journal":{"name":"Symposium on Energy Geotechnics 2023","volume":"191 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135647648","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
To tackle the challenges raised by climate change, we need to rapidly switch our energy sources to low-carbon ones for all economic sectors. As renewable energies are intermittent, efficient energy carriers, such as hydrogen, will be needed to meet the energy demand. Green hydrogen is considered to be a promising energy vector for the future. However, in addition to problematics related to its production, safe and large scale storage solutions still need to be developed. The geological formations including saline aquifers and former depleted gas fields offer the largest storage capacities but are more adapted to seasonal or mid-to-long term storage. Conversely, underground salt caverns are well suited for storage/withdrawal cycles as short as daily cycling. These artificial structures, offering exceptional tightness, have already been used for decades for hydrocarbons storage but at seasonal storage/withdrawal cycles. The adaptation to short-term hydrogen storage still requires further studies to ensure the stability of the caverns under such loading conditions. Indeed, rapid cyclic loading conditions may impact the tightness and the integrity of the cavern [1, 6].
Rock salt is polycrystalline material with an essentially viscoplastic behaviour, involving different micro-mechanisms such as crystal slip plasticity and grain boundary sliding. At mechanical loading conditions representative of those operated in storage caverns, the rock salt is characterized by non-linear viscous flow. The activation of grain boundary sliding is necessary to accommodate local plastic incompatibilities between neighbouring grains. It has been shown in uniaxial loading conditions but has not been verified in triaxial conditions yet [2, 4]. The presence of brine also affects the micro-mechanisms involved, with for example phenomena like dissolution-precipitation or diffusional mass transfer along grain boundaries, and can modify the mechanical behaviour [5].
In our studies, we investigate the active micro-mechanisms in synthetic halite through in situ X-ray microcomputed tomography (XR-µCT) analysis and digital volume correlation (DVC) and damage quantification. To reproduce loading conditions representative of those in real salt caverns, we apply different confining pressures with a triaxial cell. This triaxial device, developed recently [3], is adapted to in situ XR-µCT tests. We study the development of damage networks and the evolution of pores during the deformation of rock salt under different confining pressures. Samples of halite are prepared by compaction of pure NaCl powder in dry and humid conditions. It gives samples with different brine contents and allows us to study the effect of brine on the deformation mechanims.
An effect of brine is visible, as the cracks seem to appear earlier in the dry samples. On the µCT scans, cracks start to be visible for a lower strain in the case of dry samples compared to the case of wet samples. For a dry
{"title":"3D microscale investigation of active deformation mechanisms of halite under conditions representative of underground hydrogen storage","authors":"Nina Du, Michel Bornert, Alexandre Dimanov","doi":"10.59490/seg.2023.636","DOIUrl":"https://doi.org/10.59490/seg.2023.636","url":null,"abstract":"To tackle the challenges raised by climate change, we need to rapidly switch our energy sources to low-carbon ones for all economic sectors. As renewable energies are intermittent, efficient energy carriers, such as hydrogen, will be needed to meet the energy demand. Green hydrogen is considered to be a promising energy vector for the future. However, in addition to problematics related to its production, safe and large scale storage solutions still need to be developed. The geological formations including saline aquifers and former depleted gas fields offer the largest storage capacities but are more adapted to seasonal or mid-to-long term storage. Conversely, underground salt caverns are well suited for storage/withdrawal cycles as short as daily cycling. These artificial structures, offering exceptional tightness, have already been used for decades for hydrocarbons storage but at seasonal storage/withdrawal cycles. The adaptation to short-term hydrogen storage still requires further studies to ensure the stability of the caverns under such loading conditions. Indeed, rapid cyclic loading conditions may impact the tightness and the integrity of the cavern [1, 6].
 Rock salt is polycrystalline material with an essentially viscoplastic behaviour, involving different micro-mechanisms such as crystal slip plasticity and grain boundary sliding. At mechanical loading conditions representative of those operated in storage caverns, the rock salt is characterized by non-linear viscous flow. The activation of grain boundary sliding is necessary to accommodate local plastic incompatibilities between neighbouring grains. It has been shown in uniaxial loading conditions but has not been verified in triaxial conditions yet [2, 4]. The presence of brine also affects the micro-mechanisms involved, with for example phenomena like dissolution-precipitation or diffusional mass transfer along grain boundaries, and can modify the mechanical behaviour [5].
 In our studies, we investigate the active micro-mechanisms in synthetic halite through in situ X-ray microcomputed tomography (XR-µCT) analysis and digital volume correlation (DVC) and damage quantification. To reproduce loading conditions representative of those in real salt caverns, we apply different confining pressures with a triaxial cell. This triaxial device, developed recently [3], is adapted to in situ XR-µCT tests. We study the development of damage networks and the evolution of pores during the deformation of rock salt under different confining pressures. Samples of halite are prepared by compaction of pure NaCl powder in dry and humid conditions. It gives samples with different brine contents and allows us to study the effect of brine on the deformation mechanims.
 An effect of brine is visible, as the cracks seem to appear earlier in the dry samples. On the µCT scans, cracks start to be visible for a lower strain in the case of dry samples compared to the case of wet samples. For a dry","PeriodicalId":473465,"journal":{"name":"Symposium on Energy Geotechnics 2023","volume":"49 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135646688","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Clays and clay soils or shales have attracted a lot of interest in a variety of applications, including the development of geothermal resources [1], energy foundations [2], oil exploration [3], energy storage [4], and the storage of nuclear waste [5]. The continued operation of ground source heat pump installations can lead to considerable long-term settlements, which could negatively affect the adjacent or underlying foundations [1]. Therefore, thermal volume change has been widely experimentally investigated in clays [4, 7, 8, 9]. Especially in [4] the authors studied the thermal and mechanical consolidation of saturated marine clays through laboratory element tests, where excess pore pressures were generated by heating samples at constant water content and then allowed to dissipate. In constant stress creep experiments described in [4] it was documented that thermal creep strains typically increased linearly with log time at rates controlled by the prevailing temperature.
On the other hand, the mechanical time dependency of the stress–strain behaviour of soft soils, especially highly plastic clay, is generally too significant to be ignored [10, 11]. The constitutive modelling of the time-dependent stress–strain behaviour of soils has been an active area of research for five decades and has attracted much attention from the international geotechnical community in recent years as denoted in [12]. In [13] a visco-hypoplastic (VHP) model for normally and overconsolidated clays has been proposed. Probably the most salient feature of hypoplasticity itself is that loading and unloading can be described with only one equation as with the strain and stress rate denoted as and , respectively. The elastic stiffness tensor is represented by ; is the degree of nonlinearity and is the flow rule (direction of hypoplastic strain). The last part of the equation expresses the time-dependent strain rate (i.e. viscous) with the material parameters as the viscosity index and being the compression index. denotes the overconsolidation ratio. As may be observed, the model is not restricted solely to time-dependent clay materials, because does not represent a singularity for the constitutive equation as in other hypoplastic models. The model has been extended in [14] to account for the small-strain stiffness and the mechanical behaviour under cyclic loading. It follows the critical state theory and incorporates a loading surface for the definition of , see Fig. 1A). Time-dependent one-dimensional behaviour of clays is in most cases explained by the isotache framework, which assumes a unique relation between effective stress, strain, and strain rate in compression, shown as loci of constant strain rate in space, see Fig. 1B). The creep deformation at constant effective stress (; Fig. 1C)) corresponds to a decrease in strain rate of the soil (path A to B in Fig. 1C)). Consolidation stress history, represented by swelling along the path AC, causes a marked reductio
{"title":"Thermal and mechanical creep of clay in hypoplasticity","authors":"Merita Tafili, Mohammadsadegh Ashrafi, Torsten Wichtmann","doi":"10.59490/seg.2023.625","DOIUrl":"https://doi.org/10.59490/seg.2023.625","url":null,"abstract":"Clays and clay soils or shales have attracted a lot of interest in a variety of applications, including the development of geothermal resources [1], energy foundations [2], oil exploration [3], energy storage [4], and the storage of nuclear waste [5]. The continued operation of ground source heat pump installations can lead to considerable long-term settlements, which could negatively affect the adjacent or underlying foundations [1]. Therefore, thermal volume change has been widely experimentally investigated in clays [4, 7, 8, 9]. Especially in [4] the authors studied the thermal and mechanical consolidation of saturated marine clays through laboratory element tests, where excess pore pressures were generated by heating samples at constant water content and then allowed to dissipate. In constant stress creep experiments described in [4] it was documented that thermal creep strains typically increased linearly with log time at rates controlled by the prevailing temperature.
 On the other hand, the mechanical time dependency of the stress–strain behaviour of soft soils, especially highly plastic clay, is generally too significant to be ignored [10, 11]. The constitutive modelling of the time-dependent stress–strain behaviour of soils has been an active area of research for five decades and has attracted much attention from the international geotechnical community in recent years as denoted in [12]. In [13] a visco-hypoplastic (VHP) model for normally and overconsolidated clays has been proposed. Probably the most salient feature of hypoplasticity itself is that loading and unloading can be described with only one equation as with the strain and stress rate denoted as and , respectively. The elastic stiffness tensor is represented by ; is the degree of nonlinearity and is the flow rule (direction of hypoplastic strain). The last part of the equation expresses the time-dependent strain rate (i.e. viscous) with the material parameters as the viscosity index and being the compression index. denotes the overconsolidation ratio. As may be observed, the model is not restricted solely to time-dependent clay materials, because does not represent a singularity for the constitutive equation as in other hypoplastic models. The model has been extended in [14] to account for the small-strain stiffness and the mechanical behaviour under cyclic loading. It follows the critical state theory and incorporates a loading surface for the definition of , see Fig. 1A). Time-dependent one-dimensional behaviour of clays is in most cases explained by the isotache framework, which assumes a unique relation between effective stress, strain, and strain rate in compression, shown as loci of constant strain rate in space, see Fig. 1B). The creep deformation at constant effective stress (; Fig. 1C)) corresponds to a decrease in strain rate of the soil (path A to B in Fig. 1C)). Consolidation stress history, represented by swelling along the path AC, causes a marked reductio","PeriodicalId":473465,"journal":{"name":"Symposium on Energy Geotechnics 2023","volume":"74 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135646690","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hilmi Bayraktaroglu, Jose L. González Acosta, Abraham P. Van den Eijnden, Michael A. Hicks
Nonlinear effective stress site response analyses (SRAs) are commonly used to estimate dynamic soil behaviour, seismic wave propagation through the soil medium, and resulting ground motions [1]. These analyses can be used to identify potential hazards (e.g., landslides, settlements, liquefaction) and to estimate dynamic loads on superstructures in areas that are prone to natural or induced earthquakes, which can help with disaster planning and risk mitigation efforts. In this study, the influence of fabric anisotropy, which is induced during the soil formation process, on the response of sand deposits has been assessed through one-dimensional site response and response spectrum analyses (RSAs). First, a novel anisotropic critical state theory (ACST) based semi-micromechanical constitutive model accounting for the effect of fabric anisotropy has been incorporated into a fully coupled dynamic code employing the u-p formulation. Then, the initial fabric anisotropy has quantitatively (both with respect to intensity and orientation ) been changed to imitate different anisotropic formations observed in natural deposits. The proposed numerical procedure shows that fabric effects stemming from the anisotropic nature of sands can significantly influence the dynamic behaviour of sand deposits, leading to significant variations in ground motions and therefore resulting in diverse spectral accelerations at the ground surface.
The loading direction dependent behaviour of sands, which can be associated with their anisotropic nature originating from the arrangement of the soil inner microstructure, is generally described/idealized using a second order fabric tensor by ACST based models. Similarly, in this study, a contact normal based second order fabric tensor together with a plastic strain driven fabric evolution formulation has been employed to link the influence of the changing inner microstructure to the relevant constitutive formulations. Further details on the fabric formulations and their multilaminate specific extension can be found in ref. [2] and [3]. Although numerous experimental studies have been conducted to investigate the influence of fabric on the undrained response of sands and advanced constitutive models have been developed to account for it, the majority of research efforts involving anisotropy have concentrated on the element test level, while practical boundary value problem (BVP) simulations are usually omitted. In order to ameliorate that trend, the practical aspects of the fabric effects in BVPs will be investigated in the next section.
To investigate the repercussions of incorporating fabric effects, two identical SRAs with different initial fabric configurations, i.e., initially isotropic and anisotropic, have been carried out and the resultant response spectrums are presented in Figure 1. These SRAs were performed for a one-dimensional column of 10 m height with a water table located at m depth, subjected to a seismic l
{"title":"Nonlinear site response analyses for sands: investigating the influence of fabric anisotropy","authors":"Hilmi Bayraktaroglu, Jose L. González Acosta, Abraham P. Van den Eijnden, Michael A. Hicks","doi":"10.59490/seg.2023.643","DOIUrl":"https://doi.org/10.59490/seg.2023.643","url":null,"abstract":"Nonlinear effective stress site response analyses (SRAs) are commonly used to estimate dynamic soil behaviour, seismic wave propagation through the soil medium, and resulting ground motions [1]. These analyses can be used to identify potential hazards (e.g., landslides, settlements, liquefaction) and to estimate dynamic loads on superstructures in areas that are prone to natural or induced earthquakes, which can help with disaster planning and risk mitigation efforts. In this study, the influence of fabric anisotropy, which is induced during the soil formation process, on the response of sand deposits has been assessed through one-dimensional site response and response spectrum analyses (RSAs). First, a novel anisotropic critical state theory (ACST) based semi-micromechanical constitutive model accounting for the effect of fabric anisotropy has been incorporated into a fully coupled dynamic code employing the u-p formulation. Then, the initial fabric anisotropy has quantitatively (both with respect to intensity and orientation ) been changed to imitate different anisotropic formations observed in natural deposits. The proposed numerical procedure shows that fabric effects stemming from the anisotropic nature of sands can significantly influence the dynamic behaviour of sand deposits, leading to significant variations in ground motions and therefore resulting in diverse spectral accelerations at the ground surface.
 The loading direction dependent behaviour of sands, which can be associated with their anisotropic nature originating from the arrangement of the soil inner microstructure, is generally described/idealized using a second order fabric tensor by ACST based models. Similarly, in this study, a contact normal based second order fabric tensor together with a plastic strain driven fabric evolution formulation has been employed to link the influence of the changing inner microstructure to the relevant constitutive formulations. Further details on the fabric formulations and their multilaminate specific extension can be found in ref. [2] and [3]. Although numerous experimental studies have been conducted to investigate the influence of fabric on the undrained response of sands and advanced constitutive models have been developed to account for it, the majority of research efforts involving anisotropy have concentrated on the element test level, while practical boundary value problem (BVP) simulations are usually omitted. In order to ameliorate that trend, the practical aspects of the fabric effects in BVPs will be investigated in the next section.
 To investigate the repercussions of incorporating fabric effects, two identical SRAs with different initial fabric configurations, i.e., initially isotropic and anisotropic, have been carried out and the resultant response spectrums are presented in Figure 1. These SRAs were performed for a one-dimensional column of 10 m height with a water table located at m depth, subjected to a seismic l","PeriodicalId":473465,"journal":{"name":"Symposium on Energy Geotechnics 2023","volume":"50 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135647645","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Sukran Gizem Alpaydin, Yusuf Batuge, Yeliz Yukselen-Aksoy
Introduction
The increasing energy demand and the limited fossil fuel resources make searching for new sustainable clean energy sources. In this regard, it is vital to use energy geo-structures as a renewable and clean energy source. The geo-structures are in direct contact with the soil and cause temperature changes throughout the soil mass.
Bentonite is considered suitable as an engineering barrier in deep geological disposal repositories for spent nuclear fuel, mainly because of its favorable swelling properties and extremely low permeability [1]. It was reported by many researchers that the engineering properties of clayey soils change at high temperatures [2,3]. Therefore, there is a need for soil materials that can maintain their long-term engineering properties under high temperatures. Borates are naturally occurring minerals. They can be found mainly in sediments and sedimentary rocks. The most commercially important boron minerals are tincalconite, colemanite, and ulexite [4].
In the present study, it was tried to improve the compressibility behavior of bentonite by adding colemanite under high temperature. The oedometer tests were performed under a constant temperature (80 ºC) on the bentonite-colemanite mixtures. In this context, samples exposed to short and long-term high temperature (80 ºC) were used and the results were compared with the room temperature results.
Material Characterization and Methods
The Ca-bentonite sample used which is activated with sodium bicarbonate. Colemanite was added to bentonite at a rate of 10% of the bentonite by dry weight. In this context, B10C sample represents a 10% colemanite added bentonite mixture. The liquid limits of bentonite and colemanite are 270% and 37%, respectively. The samples (smaller than 75 μm) were obtained by mixing the mixture powder with tap water at a water content of 1.5 times the pre-determined liquid limit value of the mixtures. The slurries were consolidated under a vertical pressure of 12.5 kPa for 14 days. Samples 70 mm in diameter and 19 mm in height were obtained by trimming. The samples were placed in oedometers for tests at room and high temperature (80 ºC). The experimental system was modified for high-temperature tests. The modified system consists of a conventional apparatus, a heat ring, a thermostat, and a water tank. Thus, by heating the cell water, the temperature of the sample was indirectly increased to 80 °C. For long-term experiments, samples were placed in thermal pools in clamped molds (constant volume). These molds were kept in the thermal pools under a constant temperature of 80 °C for 6 months. Then, the consolidation tests of these samples were performed at 80 °C.
Results and Discussions
The result of the consolidation tests of bentonite mixtures at 80 °C after being kept in the thermal pool for 6 months is given in Figure 1. For comparison, the test results at room temperature and 80 °C are also shown. The comp
{"title":"Compressibility behavior of colemanite added bentonite under short and long-term high temperature","authors":"Sukran Gizem Alpaydin, Yusuf Batuge, Yeliz Yukselen-Aksoy","doi":"10.59490/seg.2023.634","DOIUrl":"https://doi.org/10.59490/seg.2023.634","url":null,"abstract":"Introduction
 The increasing energy demand and the limited fossil fuel resources make searching for new sustainable clean energy sources. In this regard, it is vital to use energy geo-structures as a renewable and clean energy source. The geo-structures are in direct contact with the soil and cause temperature changes throughout the soil mass.
 Bentonite is considered suitable as an engineering barrier in deep geological disposal repositories for spent nuclear fuel, mainly because of its favorable swelling properties and extremely low permeability [1]. It was reported by many researchers that the engineering properties of clayey soils change at high temperatures [2,3]. Therefore, there is a need for soil materials that can maintain their long-term engineering properties under high temperatures. Borates are naturally occurring minerals. They can be found mainly in sediments and sedimentary rocks. The most commercially important boron minerals are tincalconite, colemanite, and ulexite [4].
 In the present study, it was tried to improve the compressibility behavior of bentonite by adding colemanite under high temperature. The oedometer tests were performed under a constant temperature (80 ºC) on the bentonite-colemanite mixtures. In this context, samples exposed to short and long-term high temperature (80 ºC) were used and the results were compared with the room temperature results.
 Material Characterization and Methods
 The Ca-bentonite sample used which is activated with sodium bicarbonate. Colemanite was added to bentonite at a rate of 10% of the bentonite by dry weight. In this context, B10C sample represents a 10% colemanite added bentonite mixture. The liquid limits of bentonite and colemanite are 270% and 37%, respectively. The samples (smaller than 75 μm) were obtained by mixing the mixture powder with tap water at a water content of 1.5 times the pre-determined liquid limit value of the mixtures. The slurries were consolidated under a vertical pressure of 12.5 kPa for 14 days. Samples 70 mm in diameter and 19 mm in height were obtained by trimming. The samples were placed in oedometers for tests at room and high temperature (80 ºC). The experimental system was modified for high-temperature tests. The modified system consists of a conventional apparatus, a heat ring, a thermostat, and a water tank. Thus, by heating the cell water, the temperature of the sample was indirectly increased to 80 °C. For long-term experiments, samples were placed in thermal pools in clamped molds (constant volume). These molds were kept in the thermal pools under a constant temperature of 80 °C for 6 months. Then, the consolidation tests of these samples were performed at 80 °C.
 Results and Discussions
 The result of the consolidation tests of bentonite mixtures at 80 °C after being kept in the thermal pool for 6 months is given in Figure 1. For comparison, the test results at room temperature and 80 °C are also shown. The comp","PeriodicalId":473465,"journal":{"name":"Symposium on Energy Geotechnics 2023","volume":"160 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135646686","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Aidy Ung, Seyed Morteza Zeinali, Sherif L. Abdelaziz
Drained residual shear strength is the parameter used in the back analysis of the reactivated landslides and slip surface test [1,2]. The effects of temperature on residual shear strength were not extensively studied, and the method used to assess such effect across the literatures shows some discrepancies. Any internal or external factor impacting the applied stresses and the mobilized residual shear strength may lead to reactivating landslides. Therefore, considering the aggrevating climate change, it is essential to study the impact of temperature on residual shear strength and establish the best method for measuring this effect. The study by [3] concluded that for smectite-bearing soils, the residual shear strength decreases as temperature decreases. In the thermal ring shear tests conducted by [3], the specimen was first consolidated under the desired normal stress, and sheared in room temperature. Furthermore, the temperature was lowered while shearing and residual shear strength was measured as the specimen continued to be sheared. Changing the temperature during shearing without removing the loading arms from the top cap prohibits the specimen to experience the full thermally-induced volume changes and potentially disrupts the results . On the other hand, the study by [4] concluded that there is no significant effect of temperature on residual shear strength of soil. In [4], the specimen was cooled to 5°C at the beginning of the consolidation stage and was sheared after reaching desired normal effective stress. The main difference between these two described procedures is that [3] changed the temperature as the specimen was sheared, while [4] changed the temperature of the specimen prior to the consolidation stage.
The observed disrepencies within the literature may originate in the method of testing. Therefore, this study aims to investigate whether the instant in which the temperature changes in the testing procedure to determine the residual shear strength impacts the results. The tests are conducted in accordance with ASTM 6467 on two clays: EPK clay (99.3% Kaolinite and 0.7% Zeolite) and Rhassoul clay (70.5% montmorillonite, 29.4% Illite and 0.1% Kaolinite). Three ring shear experiments are performed on each of the selected clays. All the experiments starts with preparing the specimen at the liquid limit and place it in the container to form a specimen. In the first set of experiments, the specimen is consolidated under the first effective stress of 7kPa. Once the primary consolidation under this first load is complete, the temperature of the specimen is changed to the target value of 50°C. After the temperature and the volumetric strains stabilize, the consolidation stages proceed to a maximum vertical stress of about 300kPa and then unloaded back to the first load to initiate the preshearing stage. Preshearing is the step to develop a failure surface by shearing the sample for at least the displacement of one full revolution.
{"title":"Testing Procedures on the Assessment of the Effects Temperature on Residual Shear Strength of Soils","authors":"Aidy Ung, Seyed Morteza Zeinali, Sherif L. Abdelaziz","doi":"10.59490/seg.2023.637","DOIUrl":"https://doi.org/10.59490/seg.2023.637","url":null,"abstract":"Drained residual shear strength is the parameter used in the back analysis of the reactivated landslides and slip surface test [1,2]. The effects of temperature on residual shear strength were not extensively studied, and the method used to assess such effect across the literatures shows some discrepancies. Any internal or external factor impacting the applied stresses and the mobilized residual shear strength may lead to reactivating landslides. Therefore, considering the aggrevating climate change, it is essential to study the impact of temperature on residual shear strength and establish the best method for measuring this effect. The study by [3] concluded that for smectite-bearing soils, the residual shear strength decreases as temperature decreases. In the thermal ring shear tests conducted by [3], the specimen was first consolidated under the desired normal stress, and sheared in room temperature. Furthermore, the temperature was lowered while shearing and residual shear strength was measured as the specimen continued to be sheared. Changing the temperature during shearing without removing the loading arms from the top cap prohibits the specimen to experience the full thermally-induced volume changes and potentially disrupts the results . On the other hand, the study by [4] concluded that there is no significant effect of temperature on residual shear strength of soil. In [4], the specimen was cooled to 5°C at the beginning of the consolidation stage and was sheared after reaching desired normal effective stress. The main difference between these two described procedures is that [3] changed the temperature as the specimen was sheared, while [4] changed the temperature of the specimen prior to the consolidation stage.
 The observed disrepencies within the literature may originate in the method of testing. Therefore, this study aims to investigate whether the instant in which the temperature changes in the testing procedure to determine the residual shear strength impacts the results. The tests are conducted in accordance with ASTM 6467 on two clays: EPK clay (99.3% Kaolinite and 0.7% Zeolite) and Rhassoul clay (70.5% montmorillonite, 29.4% Illite and 0.1% Kaolinite). Three ring shear experiments are performed on each of the selected clays. All the experiments starts with preparing the specimen at the liquid limit and place it in the container to form a specimen. In the first set of experiments, the specimen is consolidated under the first effective stress of 7kPa. Once the primary consolidation under this first load is complete, the temperature of the specimen is changed to the target value of 50°C. After the temperature and the volumetric strains stabilize, the consolidation stages proceed to a maximum vertical stress of about 300kPa and then unloaded back to the first load to initiate the preshearing stage. Preshearing is the step to develop a failure surface by shearing the sample for at least the displacement of one full revolution.","PeriodicalId":473465,"journal":{"name":"Symposium on Energy Geotechnics 2023","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135646691","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The effect of temperature on the mechanical behaviour of clay-based geomaterials is relevant in several geotechnical applications (e.g., low enthalpy geothermal systems, energy geostructures and nuclear waste disposal). The mechanical response of (saturated) normally consolidated (NC) clay to temperature variation is not intuitive as the material irreversibly contracts upon heating. Since the thermal contraction observed at the engineering scale does not correspond to the thermal expansion of the clay constituents, both in sign and amplitude, the thermo-mechanical response is usually attributed to temperature-induced changes in the arrangement of clay particles/aggregates (changes in the inter-particle/aggregate porosity) [4] or to the nano-scale thermo-mechanical behaviour of the adsorbed water between clay unit layers (changes in the intra-particle porosity) [3].
Especially for clay minerals with a large amount of adsorbed water, such as swelling clays (tens of % of the total water is absorbed in saturated swelling clay samples), the latter hypothesis has been investigated numerically by molecular dynamics modelling of a layer-water-layer system in non-isothermal conditions [3,8] and experimentally through X-ray diffraction and scattering experiments (XRD, SAXS) [5,6,7].
According to the numerical simulations in [3,8], the free energy barrier between stable system states (the number of adsorbed water layers surrounding a clay particle) decreases with temperature, inducing a possible transition between mobile and immobile water. This nanometric phenomenon may result in a macroscopic volumetric thermal contraction.
A similar picture comes from the in-situ diffraction and scattering experiments [5,6,7], where a slight decrease in clay basal spacing (distance between two consecutive clay’s aluminosilicate layers) is measured for increasing temperature. However, the experiments reported are performed in unsaturated conditions at controlled humidity and cannot be confronted with the fully saturated samples usually employed in geomechanical testing.
Measurements for monitoring nano-scale changes of fine-grained soils in their natural wet states are needed to prove the nano-scale origin of the thermo-mechanical behaviour of clays. Small-angle X-ray scattering (SAXS) has often been used to study particle orientation in compacted saturated clay [1]. Smaller features of the mineralogy and sub-particle behaviour of clays can be instead accessed by X-ray diffraction (XRD) and wide-angle X-ray scattering (WAXS) [2]. In principle, SAXS/WAXS measurements capture the inter-particle and intra-particle distances by measuring the scattered intensity of an X-ray beam hitting a sample.
This research uses combined SAXS/WAXS measurements to monitor nano-scale changes induced in the clay basal distances of several fine-grained natural soils in their saturated state by temperature variations. The experiments were performed with a SAXSLAB Ma
{"title":"Experimental insight into the thermal nanometric response of clays","authors":"Angela Casarella, Georgios Birmpilis, Jelke Dijkstra","doi":"10.59490/seg.2023.647","DOIUrl":"https://doi.org/10.59490/seg.2023.647","url":null,"abstract":"The effect of temperature on the mechanical behaviour of clay-based geomaterials is relevant in several geotechnical applications (e.g., low enthalpy geothermal systems, energy geostructures and nuclear waste disposal). The mechanical response of (saturated) normally consolidated (NC) clay to temperature variation is not intuitive as the material irreversibly contracts upon heating. Since the thermal contraction observed at the engineering scale does not correspond to the thermal expansion of the clay constituents, both in sign and amplitude, the thermo-mechanical response is usually attributed to temperature-induced changes in the arrangement of clay particles/aggregates (changes in the inter-particle/aggregate porosity) [4] or to the nano-scale thermo-mechanical behaviour of the adsorbed water between clay unit layers (changes in the intra-particle porosity) [3].
 Especially for clay minerals with a large amount of adsorbed water, such as swelling clays (tens of % of the total water is absorbed in saturated swelling clay samples), the latter hypothesis has been investigated numerically by molecular dynamics modelling of a layer-water-layer system in non-isothermal conditions [3,8] and experimentally through X-ray diffraction and scattering experiments (XRD, SAXS) [5,6,7].
 According to the numerical simulations in [3,8], the free energy barrier between stable system states (the number of adsorbed water layers surrounding a clay particle) decreases with temperature, inducing a possible transition between mobile and immobile water. This nanometric phenomenon may result in a macroscopic volumetric thermal contraction.
 A similar picture comes from the in-situ diffraction and scattering experiments [5,6,7], where a slight decrease in clay basal spacing (distance between two consecutive clay’s aluminosilicate layers) is measured for increasing temperature. However, the experiments reported are performed in unsaturated conditions at controlled humidity and cannot be confronted with the fully saturated samples usually employed in geomechanical testing.
 Measurements for monitoring nano-scale changes of fine-grained soils in their natural wet states are needed to prove the nano-scale origin of the thermo-mechanical behaviour of clays. Small-angle X-ray scattering (SAXS) has often been used to study particle orientation in compacted saturated clay [1]. Smaller features of the mineralogy and sub-particle behaviour of clays can be instead accessed by X-ray diffraction (XRD) and wide-angle X-ray scattering (WAXS) [2]. In principle, SAXS/WAXS measurements capture the inter-particle and intra-particle distances by measuring the scattered intensity of an X-ray beam hitting a sample.
 This research uses combined SAXS/WAXS measurements to monitor nano-scale changes induced in the clay basal distances of several fine-grained natural soils in their saturated state by temperature variations. The experiments were performed with a SAXSLAB Ma","PeriodicalId":473465,"journal":{"name":"Symposium on Energy Geotechnics 2023","volume":"73 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135647642","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Decline in well productivity is a widely reported phenomenon and a critical challenge negatively impacting energy and water operations in deep geological reservoirs [1, 2]. A key contributor to this problem is the detachment of in-situ fine particles present in the porous matrix, which will then migrate and travel through the porous formation until getting strained within thin pore throats resulting in pore clogging and therefore permeability damage [3]. The detachment of in-situ fine particle occurs when the mechanical equilibrium of the attaching (i.e., electrostatic and gravity forces) and the detaching forces (i.e., drag and lifting forces) exerted on the particle is disturbed. In geological reservoirs, the equilibrium of in-situ fines can be disturbed as a result of fluid flow velocities, temperature alterations in the porous formation, or reduced ionic strength of the in-situ fluids [4]. Fines migration and straining can also alter in-situ stresses through generating pore pressure changes as a result of permeability damage [5].
Multiple experimental and numerical studies have evaluated the mechanisms involved in detachment, migration, and straining of in-situ fines and the clogging of pore fluid channels [6, 7]. A number of studies have also focused on evaluating temperature-induced particle mobilization [8]. Variations of the electrostatic force with temperature is often explained through the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory [9]. In a saturated porous formation containing in-situ fines, Dielectric permittivity of pore fluid decreases with an increase in temperature, weakening the repulsion between the fine clay particles and the sand surface [10]. As a result, the attaching electrostatic forces are lower under higher temperatures.
This study focuses on developing a theoretical model to evaluate the impact of the size distribution of in-situ fine particles on non-isothermal fluid flow induced fine mobilization in saturated porous media. Expressions for drag force and electrostatic force are obtained based on the DLVO theory considering coupled effects of fluid velocity, temperature, and ionic strength of in-situ fluids. The main parameters adopted in the proposed model are presented in Table 1. The proposed model predicts the maximum concentration of retained fines considering coupled effects from temperatures and pore pressures. Results are valuable for estimating permeability damage and well productivity during enhanced geothermal operations.
{"title":"Fine particle liberation in saturated porous media under non-isothermalfluid flow","authors":"Xinle Zhai, Kamelia Atefi-Monfared","doi":"10.59490/seg.2023.624","DOIUrl":"https://doi.org/10.59490/seg.2023.624","url":null,"abstract":"Decline in well productivity is a widely reported phenomenon and a critical challenge negatively impacting energy and water operations in deep geological reservoirs [1, 2]. A key contributor to this problem is the detachment of in-situ fine particles present in the porous matrix, which will then migrate and travel through the porous formation until getting strained within thin pore throats resulting in pore clogging and therefore permeability damage [3]. The detachment of in-situ fine particle occurs when the mechanical equilibrium of the attaching (i.e., electrostatic and gravity forces) and the detaching forces (i.e., drag and lifting forces) exerted on the particle is disturbed. In geological reservoirs, the equilibrium of in-situ fines can be disturbed as a result of fluid flow velocities, temperature alterations in the porous formation, or reduced ionic strength of the in-situ fluids [4]. Fines migration and straining can also alter in-situ stresses through generating pore pressure changes as a result of permeability damage [5].
 Multiple experimental and numerical studies have evaluated the mechanisms involved in detachment, migration, and straining of in-situ fines and the clogging of pore fluid channels [6, 7]. A number of studies have also focused on evaluating temperature-induced particle mobilization [8]. Variations of the electrostatic force with temperature is often explained through the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory [9]. In a saturated porous formation containing in-situ fines, Dielectric permittivity of pore fluid decreases with an increase in temperature, weakening the repulsion between the fine clay particles and the sand surface [10]. As a result, the attaching electrostatic forces are lower under higher temperatures.
 This study focuses on developing a theoretical model to evaluate the impact of the size distribution of in-situ fine particles on non-isothermal fluid flow induced fine mobilization in saturated porous media. Expressions for drag force and electrostatic force are obtained based on the DLVO theory considering coupled effects of fluid velocity, temperature, and ionic strength of in-situ fluids. The main parameters adopted in the proposed model are presented in Table 1. The proposed model predicts the maximum concentration of retained fines considering coupled effects from temperatures and pore pressures. Results are valuable for estimating permeability damage and well productivity during enhanced geothermal operations.
","PeriodicalId":473465,"journal":{"name":"Symposium on Energy Geotechnics 2023","volume":"48 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135646680","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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