Hoang Bao Khoi Nguyen, Md. Mizanur Rahman, Andy B. Fourie, Zenon Szypcio, Katarzyna Dołżyk-Szypcio
{"title":"Discussion: How particle shape affects the critical state, triggering of instability and dilatancy of granular materials–results from a DEM study","authors":"Hoang Bao Khoi Nguyen, Md. Mizanur Rahman, Andy B. Fourie, Zenon Szypcio, Katarzyna Dołżyk-Szypcio","doi":"10.1680/jgeot.21.d.016","DOIUrl":"https://doi.org/10.1680/jgeot.21.d.016","url":null,"abstract":"","PeriodicalId":55098,"journal":{"name":"Geotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135874938","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Xianze Cui, Dazhou Wu, Hongxing Wang, Shengyong Ding, Yong Fan
Pore features and seepage characteristics of mixed granular materials are of great significance in many subjects, including engineering, for instance geotechnical engineering, petroleum extraction, hydrogeology, environmental science and hydraulic engineering. In this paper, two types of mathematical models are proposed that consider different packing methods for porosity and permeability – namely, the filling model (FM) and the replacement model (RM). On this basis, incomplete coverage (overlap between large and small grains during the replacement process) is considered as the ‘replacement model considering incomplete coverage’ (RMCIC) and the ‘replacement model considering incomplete coverage and roundness’ (RMCICR). Roundness is considered in the ‘filling model considering roundness’ (FMCR), the ‘replacement model considering roundness’ (RMCR) and the RMCICR. Four kinds of natural sand are chosen as the source material, with median grain sizes of 1733, 1050, 449 and 190 μm. All models can be divided into two components – one in which the porosity decreases with large grain ratios and the other in which the porosity increases. When roundness is considered, the RMCICR model has the largest porosity, and the FMCR model has the lowest porosity. In addition, the porosity increases when roundness is considered for all models in this study. The porosity in the RMCICR model better coincides with the test results, which can be explained by the consideration of both incomplete coverage and roundness. The order of porosity values is as follows: RMCICR, RMCR, RMCIC, RM, FMCR and FM. Permeability presents a tendency similar to porosity – that is, permeability decreases first and then increases. Moreover, the slope in the declining stage is relatively small, and the slope in the ascending stage is relatively large. The ratio of large grains to minimum porosity and permeability has significant differences. The results suggest the effectiveness of previous mathematical models.
{"title":"Pore features and seepage characteristics of natural gap-graded sand with two size distributions","authors":"Xianze Cui, Dazhou Wu, Hongxing Wang, Shengyong Ding, Yong Fan","doi":"10.1680/jgeot.21.00213","DOIUrl":"https://doi.org/10.1680/jgeot.21.00213","url":null,"abstract":"Pore features and seepage characteristics of mixed granular materials are of great significance in many subjects, including engineering, for instance geotechnical engineering, petroleum extraction, hydrogeology, environmental science and hydraulic engineering. In this paper, two types of mathematical models are proposed that consider different packing methods for porosity and permeability – namely, the filling model (FM) and the replacement model (RM). On this basis, incomplete coverage (overlap between large and small grains during the replacement process) is considered as the ‘replacement model considering incomplete coverage’ (RMCIC) and the ‘replacement model considering incomplete coverage and roundness’ (RMCICR). Roundness is considered in the ‘filling model considering roundness’ (FMCR), the ‘replacement model considering roundness’ (RMCR) and the RMCICR. Four kinds of natural sand are chosen as the source material, with median grain sizes of 1733, 1050, 449 and 190 μm. All models can be divided into two components – one in which the porosity decreases with large grain ratios and the other in which the porosity increases. When roundness is considered, the RMCICR model has the largest porosity, and the FMCR model has the lowest porosity. In addition, the porosity increases when roundness is considered for all models in this study. The porosity in the RMCICR model better coincides with the test results, which can be explained by the consideration of both incomplete coverage and roundness. The order of porosity values is as follows: RMCICR, RMCR, RMCIC, RM, FMCR and FM. Permeability presents a tendency similar to porosity – that is, permeability decreases first and then increases. Moreover, the slope in the declining stage is relatively small, and the slope in the ascending stage is relatively large. The ratio of large grains to minimum porosity and permeability has significant differences. The results suggest the effectiveness of previous mathematical models.","PeriodicalId":55098,"journal":{"name":"Geotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136017521","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mohsen Kamali Zarch, Limin Zhang, S. Mohsen Haeri, Zhengdan Xu
The flow dynamics of dry granular flows is significantly affected by a prominent feature of a granular mass known as dilatancy. Although their rheological behaviour has been characterised via friction and dynamic dilatancy laws, the role of dilatancy in a granular flow has not been much appreciated. In this study, using a vane rheometer, an experimental investigation was conducted on uniform glass beads of (d = 3 mm) at different initial relative densities (15 ≤ D r ≤ 66%) and shear rates that span over four orders of magnitude. The flow characteristics in terms of effective friction, volume change, and velocity field were obtained and evaluated. The effective friction shows a descending-ascending pattern corresponding to a transitional behaviour from a velocity-weakening solid-like to a velocity-strengthening liquid-like behaviour. The volume-change measurements show that all specimens dilate and reach almost the same density at each shear rate. The velocity field follows a Gaussian pattern characterized by the slipping velocity at the boundary, the interlayer slippage between particles, and the interlayer disorder of the particles. A new non-monotonic friction law and a dynamic dilatancy law are presented as governing rheological laws based on the inertial number and by introducing an effective dilation coefficient. This effective dilation coefficient successfully captures the role of dilation-induced secondary vortex flows in the dry granular flows.
{"title":"Dry granular flow in a vane shear cell: flow characteristics and rheological laws","authors":"Mohsen Kamali Zarch, Limin Zhang, S. Mohsen Haeri, Zhengdan Xu","doi":"10.1680/jgeot.23.00138","DOIUrl":"https://doi.org/10.1680/jgeot.23.00138","url":null,"abstract":"The flow dynamics of dry granular flows is significantly affected by a prominent feature of a granular mass known as dilatancy. Although their rheological behaviour has been characterised via friction and dynamic dilatancy laws, the role of dilatancy in a granular flow has not been much appreciated. In this study, using a vane rheometer, an experimental investigation was conducted on uniform glass beads of (d = 3 mm) at different initial relative densities (15 ≤ D r ≤ 66%) and shear rates that span over four orders of magnitude. The flow characteristics in terms of effective friction, volume change, and velocity field were obtained and evaluated. The effective friction shows a descending-ascending pattern corresponding to a transitional behaviour from a velocity-weakening solid-like to a velocity-strengthening liquid-like behaviour. The volume-change measurements show that all specimens dilate and reach almost the same density at each shear rate. The velocity field follows a Gaussian pattern characterized by the slipping velocity at the boundary, the interlayer slippage between particles, and the interlayer disorder of the particles. A new non-monotonic friction law and a dynamic dilatancy law are presented as governing rheological laws based on the inertial number and by introducing an effective dilation coefficient. This effective dilation coefficient successfully captures the role of dilation-induced secondary vortex flows in the dry granular flows.","PeriodicalId":55098,"journal":{"name":"Geotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135813382","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Determining earth pressure-induced moments in the active limit state is critical for the safety assessment of retaining structures. While traditional design methods assume a Coulomb's resultant force acting at one-third of the wall height, the literature suggests that the earth pressure distribution depends on the failure mode. This paper presents a rigorous kinematic solution for the ultimate moment acting on a wall undergoing rotation about its base (due to bending failure or overturning). In addition, an approximate static solution is considered. These solutions give a good approximation to the ultimate load. While the kinematic solution is closer to the exact numerical solution, the approximate static solution provides a reliable conservative approximation for common geometric and soil parameters. Its advantage is that it has a closed-form formulation. The kinematic solution is successfully validated against experimental data and is further used to investigate the peculiarities of the rotational failure mode and to evaluate traditional methods. It is found that traditional methods are close to the rigorous solutions and, therefore, reasonably safe. A useful by-product of this study: the formulation of the kinematic solution is versatile and can be applied to various geotechnical problems involving rotation.
{"title":"Limit-state solutions for the active earth pressure behind walls rotating about the base","authors":"David Perozzi, Alexander M. Puzrin","doi":"10.1680/jgeot.23.00093","DOIUrl":"https://doi.org/10.1680/jgeot.23.00093","url":null,"abstract":"Determining earth pressure-induced moments in the active limit state is critical for the safety assessment of retaining structures. While traditional design methods assume a Coulomb's resultant force acting at one-third of the wall height, the literature suggests that the earth pressure distribution depends on the failure mode. This paper presents a rigorous kinematic solution for the ultimate moment acting on a wall undergoing rotation about its base (due to bending failure or overturning). In addition, an approximate static solution is considered. These solutions give a good approximation to the ultimate load. While the kinematic solution is closer to the exact numerical solution, the approximate static solution provides a reliable conservative approximation for common geometric and soil parameters. Its advantage is that it has a closed-form formulation. The kinematic solution is successfully validated against experimental data and is further used to investigate the peculiarities of the rotational failure mode and to evaluate traditional methods. It is found that traditional methods are close to the rigorous solutions and, therefore, reasonably safe. A useful by-product of this study: the formulation of the kinematic solution is versatile and can be applied to various geotechnical problems involving rotation.","PeriodicalId":55098,"journal":{"name":"Geotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136068308","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this paper, the effect of fabric anisotropy on the critical state behaviour of clays is investigated. An original concept of moving critical state is elaborated by a novel state parameter-based rotational hardening rule that is subsequently used to formulate a complete anisotropic elastoplastic constitutive model for clays. It is shown that some of the distinctive pre-failure and critical state responses of clays can be explained by adopting a non-stationary critical state line. Furthermore, an enhanced definition for the state of the soil is proposed that provides a more realistic correspondence between the shearing behaviour of an overconsolidated clay to its initial consolidation state. The proposed model is validated by simulating the experimental data from triaxial tests on a number of clays.
{"title":"Non-stationary anisotropy-dependent critical state for clays","authors":"Hesam Dejaloud, Mohammad Rezania, Nasser Khalili","doi":"10.1680/jgeot.22.00284","DOIUrl":"https://doi.org/10.1680/jgeot.22.00284","url":null,"abstract":"In this paper, the effect of fabric anisotropy on the critical state behaviour of clays is investigated. An original concept of moving critical state is elaborated by a novel state parameter-based rotational hardening rule that is subsequently used to formulate a complete anisotropic elastoplastic constitutive model for clays. It is shown that some of the distinctive pre-failure and critical state responses of clays can be explained by adopting a non-stationary critical state line. Furthermore, an enhanced definition for the state of the soil is proposed that provides a more realistic correspondence between the shearing behaviour of an overconsolidated clay to its initial consolidation state. The proposed model is validated by simulating the experimental data from triaxial tests on a number of clays.","PeriodicalId":55098,"journal":{"name":"Geotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136233027","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Andrew Kirkham, Aikaterini Tsiampousi, David M. Potts
The thermal behaviour of KSS, a low plasticity artificial clay made with kaolin clay, silt, and sand, was investigated in a series of temperature-controlled oedometer tests, at temperatures between 5 °C and 70 °C, and at vertical pressures up to 2.4 MPa. The experiments investigated the effect of over-consolidation ratio (OCR), pressure level, and repeated thermal cycling on thermally-induced volume change. Thermal volumetric strains were found to be dependent not only on OCR but also on pressure level, contradicting previous experimental findings and highlighting the importance of even a small dependency of compression index C c on temperature. Furthermore, thermal volumetric strains were irreversible on heating and cooling even for highly over-consolidated samples. Although irreversibility at high OCR values has been attributed to particle rearrangement and plastic accommodation in the past, an alternative explanation is put forward here, as yielding on the Hvorslev surface is expected to occur on unloading under 1D conditions. The tests also revealed evidence of thermal creep for the initially normally-consolidated samples. The effect of both current temperature and temperature history on the reloading response of mechanically over-consolidated KSS was tested and quantified in terms of their effect on the measured pre-consolidation pressure. The results from these tests were compared to results from the available literature referring to clays of similar and higher plasticity and the comparison highlighted that although soil plasticity can explain the observed quantitative differences between high plasticity soils to a large extent, mineralogy, in addition to structure, may also play an important role for low plasticity soils.
{"title":"Thermo-mechanical behaviour of a kaolin-based clay soil","authors":"Andrew Kirkham, Aikaterini Tsiampousi, David M. Potts","doi":"10.1680/jgeot.21.00194","DOIUrl":"https://doi.org/10.1680/jgeot.21.00194","url":null,"abstract":"The thermal behaviour of KSS, a low plasticity artificial clay made with kaolin clay, silt, and sand, was investigated in a series of temperature-controlled oedometer tests, at temperatures between 5 °C and 70 °C, and at vertical pressures up to 2.4 MPa. The experiments investigated the effect of over-consolidation ratio (OCR), pressure level, and repeated thermal cycling on thermally-induced volume change. Thermal volumetric strains were found to be dependent not only on OCR but also on pressure level, contradicting previous experimental findings and highlighting the importance of even a small dependency of compression index C c on temperature. Furthermore, thermal volumetric strains were irreversible on heating and cooling even for highly over-consolidated samples. Although irreversibility at high OCR values has been attributed to particle rearrangement and plastic accommodation in the past, an alternative explanation is put forward here, as yielding on the Hvorslev surface is expected to occur on unloading under 1D conditions. The tests also revealed evidence of thermal creep for the initially normally-consolidated samples. The effect of both current temperature and temperature history on the reloading response of mechanically over-consolidated KSS was tested and quantified in terms of their effect on the measured pre-consolidation pressure. The results from these tests were compared to results from the available literature referring to clays of similar and higher plasticity and the comparison highlighted that although soil plasticity can explain the observed quantitative differences between high plasticity soils to a large extent, mineralogy, in addition to structure, may also play an important role for low plasticity soils.","PeriodicalId":55098,"journal":{"name":"Geotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136263778","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Chang Zhao, Yang Xiao, Xiang He, Hanlong Liu, Yi Liu, Jian Chu
Enzymatically induced carbonate precipitation (EICP) is a potential method to alter the hydraulic properties of fractured rocks. The pore-scale in-situ formation of bio-mediated precipitated carbonates in fracture-mimicking channels was investigated experimentally through a visualization platform and microfluidic technology. Image processing was employed to analyze the precipitation behavior. Three representative biogrouting methods (one-phase continuous injection, one-phase staged injection, and two-phase staged injection) and the role of nucleation agents were examined in this study. Results revealed that more amorphous substances formed during one-phase injection process, and the one-phase staged injection method exhibited superior precipitation efficiency, while two-phase staged injection method demonstrated better effectiveness in channel clogging. The addition of nucleation agents resulted in the channel-like precipitation pattern, compared to formation of more crystals in the absence of additives. The hydrodynamic coupling between precipitation and flow velocity was used to explain the mechanisms of fracture sealing. Precipitation and aggregation led to the reduction in microchannel aperture, thereby influencing the flow field. Under flow-induced shearing, the amorphous substances could be transported and settled on the channel surface, leading to a self-enhancing process in channeling. This study provides insights into the microscopic mechanisms of EICP and advances the application of EICP in fracture repairing.
{"title":"Influence of injection methods on bio-mediated precipitation of carbonates in fracture-mimicking microfluidic chip","authors":"Chang Zhao, Yang Xiao, Xiang He, Hanlong Liu, Yi Liu, Jian Chu","doi":"10.1680/jgeot.23.00155","DOIUrl":"https://doi.org/10.1680/jgeot.23.00155","url":null,"abstract":"Enzymatically induced carbonate precipitation (EICP) is a potential method to alter the hydraulic properties of fractured rocks. The pore-scale in-situ formation of bio-mediated precipitated carbonates in fracture-mimicking channels was investigated experimentally through a visualization platform and microfluidic technology. Image processing was employed to analyze the precipitation behavior. Three representative biogrouting methods (one-phase continuous injection, one-phase staged injection, and two-phase staged injection) and the role of nucleation agents were examined in this study. Results revealed that more amorphous substances formed during one-phase injection process, and the one-phase staged injection method exhibited superior precipitation efficiency, while two-phase staged injection method demonstrated better effectiveness in channel clogging. The addition of nucleation agents resulted in the channel-like precipitation pattern, compared to formation of more crystals in the absence of additives. The hydrodynamic coupling between precipitation and flow velocity was used to explain the mechanisms of fracture sealing. Precipitation and aggregation led to the reduction in microchannel aperture, thereby influencing the flow field. Under flow-induced shearing, the amorphous substances could be transported and settled on the channel surface, leading to a self-enhancing process in channeling. This study provides insights into the microscopic mechanisms of EICP and advances the application of EICP in fracture repairing.","PeriodicalId":55098,"journal":{"name":"Geotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135266854","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ci Wang, Conleth D. O'Loughlin, Fraser Bransby, Phil Watson, Zefeng Zhou
Motivation for this paper stems from experimental investigations that consider how the vertical capacity of a horizontal circular plate anchor in clay changes due to consolidation. These experiments produced interesting time-dependent measurements that prompted a follow-on study, designed to explore the underlying mechanisms. The new experimental data indicate that changes in anchor load during consolidation under a fixed anchor displacement is linked to three distinct mechanisms. The first is a ‘stress-relaxation’ reduction in anchor load that occurs quasi-instantaneously after the initial anchor movement stops, with a magnitude that is linked to the average strain rate associated with the initial anchor movement. The second is a local consolidation effect that causes a reduction in anchor load over durations that scale with the anchor diameter. The final mechanism occurs simultaneously with the second, but at a slower rate, such that the resulting increase in anchor load becomes apparent at larger values of time. This increase in anchor load is due to dissipation of excess pore pressures developed in the wake of the anchor during the initial anchor movement. These time-dependent changes are considered relevant for the post-installation capacity of offshore anchors and for the capacity of anchors following a large movement event.
{"title":"Time-dependent processes influencing offshore foundations in clay: an experimental study on plate anchors","authors":"Ci Wang, Conleth D. O'Loughlin, Fraser Bransby, Phil Watson, Zefeng Zhou","doi":"10.1680/jgeot.22.00389","DOIUrl":"https://doi.org/10.1680/jgeot.22.00389","url":null,"abstract":"Motivation for this paper stems from experimental investigations that consider how the vertical capacity of a horizontal circular plate anchor in clay changes due to consolidation. These experiments produced interesting time-dependent measurements that prompted a follow-on study, designed to explore the underlying mechanisms. The new experimental data indicate that changes in anchor load during consolidation under a fixed anchor displacement is linked to three distinct mechanisms. The first is a ‘stress-relaxation’ reduction in anchor load that occurs quasi-instantaneously after the initial anchor movement stops, with a magnitude that is linked to the average strain rate associated with the initial anchor movement. The second is a local consolidation effect that causes a reduction in anchor load over durations that scale with the anchor diameter. The final mechanism occurs simultaneously with the second, but at a slower rate, such that the resulting increase in anchor load becomes apparent at larger values of time. This increase in anchor load is due to dissipation of excess pore pressures developed in the wake of the anchor during the initial anchor movement. These time-dependent changes are considered relevant for the post-installation capacity of offshore anchors and for the capacity of anchors following a large movement event.","PeriodicalId":55098,"journal":{"name":"Geotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135267969","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Assessing the shear strength of coarse granular soils is challenging because testing devices in the laboratory often limit the maximum particle size (d max ). While engineering standards define representative elementary volumes (REV) using the aspect ratio α=X/d max , where X is the characteristic sample size, they often disagree on the minimum α, as the effects of sample scale on shear strength are still not well understood. This paper presents a discrete-element study on the combined effect of specimen size and grading on the critical state shear strength of granular materials. The study covers a wide range of aspect ratios and demonstrates that the macroscopic response is stable for α≥15 - which is significantly higher than the standard requirement of α≥10 for simple shear tests. The granular microstructure is also strongly affected by α and the formation of column-like structures of grains carrying strong contact forces, reaching sample size independent conditions only for α≥20. Such column-like structures are shown to be primarily composed of the largest classes of grains, supporting the fact that grading has no effect on the critical state shear strength and d max correctly serves to scale a granular sample to the size of the testing device.
{"title":"Sample size effects on the critical state shear strength of granular materials with varied gradation and the role of column-like local structures","authors":"David Cantor, Carlos Ovalle","doi":"10.1680/jgeot.23.00032","DOIUrl":"https://doi.org/10.1680/jgeot.23.00032","url":null,"abstract":"Assessing the shear strength of coarse granular soils is challenging because testing devices in the laboratory often limit the maximum particle size (d max ). While engineering standards define representative elementary volumes (REV) using the aspect ratio α=X/d max , where X is the characteristic sample size, they often disagree on the minimum α, as the effects of sample scale on shear strength are still not well understood. This paper presents a discrete-element study on the combined effect of specimen size and grading on the critical state shear strength of granular materials. The study covers a wide range of aspect ratios and demonstrates that the macroscopic response is stable for α≥15 - which is significantly higher than the standard requirement of α≥10 for simple shear tests. The granular microstructure is also strongly affected by α and the formation of column-like structures of grains carrying strong contact forces, reaching sample size independent conditions only for α≥20. Such column-like structures are shown to be primarily composed of the largest classes of grains, supporting the fact that grading has no effect on the critical state shear strength and d max correctly serves to scale a granular sample to the size of the testing device.","PeriodicalId":55098,"journal":{"name":"Geotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135273381","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Non-coaxiality is one of the key characteristics of soil–structure interfaces that broadly occur in geotechnical engineering. A series of interface tests between gravel and structure was performed to address and model the non-coaxiality behaviors of interfaces subjected to various 3D loadings. Non-coaxiality of the interface was identified during yielding phase subjected to 3D cycling of shear stress and can be captured by non-coaxiality angle. The non-coaxiality angle does not evolve due to 3D cyclic shearing and depends primarily on the magnitude and direction of current shear stress and the direction of the shear stress increment. The shear stress amplitude ratio, shear stress amplitude, shear stress rotation and initial shear stress significantly affect the magnitude and change pattern of the non-coaxiality angle, attributed to varied shear stress and shear stress increment vectors. A unified flow rule for interfaces was established based on 3D interface test analysis. The flow rule perfectly determines the flow direction of kinds of interfaces prior to and at the mobilisation of shear strength under diverse 2D and 3D loading conditions, such as arbitrary shear paths and differing shear stress amplitudes, shear stress amplitude ratios, initial shear stresses, normal stresses, shear strengths, and anisotropy characteristics.
{"title":"Non-coaxiality behaviors and unified flow rule of soil–structure interfaces","authors":"Dakuo Feng, Jianmin Zhang","doi":"10.1680/jgeot.22.00413","DOIUrl":"https://doi.org/10.1680/jgeot.22.00413","url":null,"abstract":"Non-coaxiality is one of the key characteristics of soil–structure interfaces that broadly occur in geotechnical engineering. A series of interface tests between gravel and structure was performed to address and model the non-coaxiality behaviors of interfaces subjected to various 3D loadings. Non-coaxiality of the interface was identified during yielding phase subjected to 3D cycling of shear stress and can be captured by non-coaxiality angle. The non-coaxiality angle does not evolve due to 3D cyclic shearing and depends primarily on the magnitude and direction of current shear stress and the direction of the shear stress increment. The shear stress amplitude ratio, shear stress amplitude, shear stress rotation and initial shear stress significantly affect the magnitude and change pattern of the non-coaxiality angle, attributed to varied shear stress and shear stress increment vectors. A unified flow rule for interfaces was established based on 3D interface test analysis. The flow rule perfectly determines the flow direction of kinds of interfaces prior to and at the mobilisation of shear strength under diverse 2D and 3D loading conditions, such as arbitrary shear paths and differing shear stress amplitudes, shear stress amplitude ratios, initial shear stresses, normal stresses, shear strengths, and anisotropy characteristics.","PeriodicalId":55098,"journal":{"name":"Geotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135273547","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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