Fines removal during internal erosion results in permeability increase and strength reduction of granular soils. This study examines internal erosion during shearing of granular soils under triaxial loading conditions using a specially designed apparatus and X-ray CT scans. Two gap-graded soil samples with different fines content are tested and scanned multiple times to characterize sample- and pore-scale volume change and fines content using image processing techniques. Results show that internal erosion increases gradually with axial strain and has a complex impact on permeability increase due to the spatial variation of fines content. Triaxial shearing induces both pore contraction and dilation, destabilises the clogging of fine particles, and promotes internal erosion. Also, the erosion of force-supporting fine particles at a high fines content facilitates pore contraction. The progressive internal erosion due to mechanical disturbance leads to the formation of a flow channel from the upstream loading platen throughout the sample, resulting in a dramatical increase in permeability. Overall, this study provides novel insights into the interplay between the hydro-mechanical processes during shearing under constant seepage.
内侵蚀过程中细粒的去除会导致粒状土的渗透性增加和强度降低。本研究使用专门设计的仪器和 X 射线 CT 扫描，研究了三轴加载条件下粒状土在剪切过程中的内部侵蚀。对两种细粒含量不同的间隙级配土壤样本进行了测试和多次扫描，并利用图像处理技术对样本和孔隙尺度的体积变化以及细粒含量进行了表征。结果表明，内部侵蚀随轴向应变逐渐增加，并且由于细粒含量的空间变化，对渗透率的增加产生了复杂的影响。三轴剪切会引起孔隙收缩和扩张，破坏细颗粒堵塞的稳定性，并促进内部侵蚀。此外，在细粒含量较高时，支撑力细粒的侵蚀也会促进孔隙收缩。机械扰动导致的渐进式内部侵蚀会形成一条从上游装载压板流向整个样品的流道，从而显著增加渗透性。总之，这项研究为了解恒定渗流条件下剪切过程中水力机械过程之间的相互作用提供了新的视角。
{"title":"Progressive internal erosion during triaxial shearing: an X-ray micro-computed tomography study","authors":"Zhangqi Xia, Jianfeng Wang, Zhiren Zhu, Wei Hu, Saoirse Tracy, Budi Zhao","doi":"10.1680/jgeot.23.00107","DOIUrl":"https://doi.org/10.1680/jgeot.23.00107","url":null,"abstract":"Fines removal during internal erosion results in permeability increase and strength reduction of granular soils. This study examines internal erosion during shearing of granular soils under triaxial loading conditions using a specially designed apparatus and X-ray CT scans. Two gap-graded soil samples with different fines content are tested and scanned multiple times to characterize sample- and pore-scale volume change and fines content using image processing techniques. Results show that internal erosion increases gradually with axial strain and has a complex impact on permeability increase due to the spatial variation of fines content. Triaxial shearing induces both pore contraction and dilation, destabilises the clogging of fine particles, and promotes internal erosion. Also, the erosion of force-supporting fine particles at a high fines content facilitates pore contraction. The progressive internal erosion due to mechanical disturbance leads to the formation of a flow channel from the upstream loading platen throughout the sample, resulting in a dramatical increase in permeability. Overall, this study provides novel insights into the interplay between the hydro-mechanical processes during shearing under constant seepage.","PeriodicalId":501472,"journal":{"name":"Géotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140322244","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}
Ageing of shaft friction is now an accepted characteristic of displacement piles in sand. However, there is little guidance available on how the associated gains in pile capacity can be incorporated in design. This paper provides an overview of findings from a number of previous high-quality investigations before presenting results from a recent three-year pile testing campaign in the field that targeted aspects of pile ageing to improve understanding of the ageing mechanism. The field testing involved 52 tension tests on pipe piles and specifically examined the influence of installation method (driving, vibration, vibration + driving), pile diameter, steel type and loading history (static and cyclic). These results, taken together with other experimental investigations, show that the development of a welded crust on the pile shaft is a necessary part of the ageing process for steel piles and that the increase with time in the level of constrained dilation under shear on this crust is a primary contributor to ageing of shaft friction. Creep within the sand mass following the disturbance induced by installation can explain the increase in the level of this constraint while stress redistribution and breakdown of arching may also contribute to the phenomenon. Ageing leads to the inference of long-term aged shaft frictions (in tension) of 500mm and 2m diameter pipe piles that are respectively at least 50% and 30% higher than given by the design method in ISO-19901-4 (2024). Additional observations from the field tests relating to the effect of the installation method, steel type and load history on the ageing of shaft friction are made that can assist designers.
{"title":"An experimental study on factors affecting the ageing of shaft friction on steel displacement piles in sand","authors":"Eduardo M. Bittar, Barry M. Lehane","doi":"10.1680/jgeot.23.00047","DOIUrl":"https://doi.org/10.1680/jgeot.23.00047","url":null,"abstract":"Ageing of shaft friction is now an accepted characteristic of displacement piles in sand. However, there is little guidance available on how the associated gains in pile capacity can be incorporated in design. This paper provides an overview of findings from a number of previous high-quality investigations before presenting results from a recent three-year pile testing campaign in the field that targeted aspects of pile ageing to improve understanding of the ageing mechanism. The field testing involved 52 tension tests on pipe piles and specifically examined the influence of installation method (driving, vibration, vibration + driving), pile diameter, steel type and loading history (static and cyclic). These results, taken together with other experimental investigations, show that the development of a welded crust on the pile shaft is a necessary part of the ageing process for steel piles and that the increase with time in the level of constrained dilation under shear on this crust is a primary contributor to ageing of shaft friction. Creep within the sand mass following the disturbance induced by installation can explain the increase in the level of this constraint while stress redistribution and breakdown of arching may also contribute to the phenomenon. Ageing leads to the inference of long-term aged shaft frictions (in tension) of 500mm and 2m diameter pipe piles that are respectively at least 50% and 30% higher than given by the design method in ISO-19901-4 (2024). Additional observations from the field tests relating to the effect of the installation method, steel type and load history on the ageing of shaft friction are made that can assist designers.","PeriodicalId":501472,"journal":{"name":"Géotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140202313","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}
Xianwei Zhang, Xinyu Liu, Gang Wang, Yiqing Xu, Haodong Gao
Diatomaceous soil has geotechnical properties that differ fundamentally from those of common non-diatomaceous soils due to the presence of diatom microfossils with biological origins. Despite its dominant fines content, diatomaceous soil usually has high frictional shear resistance (approaching that of sand). Currently, the exact role of diatoms in controlling soil strength and underlying mechanisms remain obscure. Here, the frictional strength of diatomaceous soil is evaluated via angle-of-repose and direct simple shear tests on diatom–kaolin mixtures with differing diatom content. The microscale and nanoscale structures are characterised in detail via scanning-electron and atomic-force microscopy to establish how soil structure evolutes with diatom content and shear. For the studied diatom–kaolin mixtures, the angle of repose and internal frictional angle are high and increase with diatom content, especially when diatom content exceeds 20%. Diatom controls the frictional strength through its intricate morphology (cylindrical, saucer and disc shapes), very rough surface (hundreds of times rougher than flaky minerals), and stiff frustules with high Young's modulus. These features increase the particle coordination number and produce interparticle interlockings, both of which prevent particle rearrangement during shear and improve the frictional strength. This paper provides new insights into the multiscale structure of diatoms and improves the understanding of the shear strength of diatomaceous soils.
{"title":"Causes of the high friction angle of diatomaceous soil: microscale and nanoscale insights","authors":"Xianwei Zhang, Xinyu Liu, Gang Wang, Yiqing Xu, Haodong Gao","doi":"10.1680/jgeot.23.00230","DOIUrl":"https://doi.org/10.1680/jgeot.23.00230","url":null,"abstract":"Diatomaceous soil has geotechnical properties that differ fundamentally from those of common non-diatomaceous soils due to the presence of diatom microfossils with biological origins. Despite its dominant fines content, diatomaceous soil usually has high frictional shear resistance (approaching that of sand). Currently, the exact role of diatoms in controlling soil strength and underlying mechanisms remain obscure. Here, the frictional strength of diatomaceous soil is evaluated via angle-of-repose and direct simple shear tests on diatom–kaolin mixtures with differing diatom content. The microscale and nanoscale structures are characterised in detail via scanning-electron and atomic-force microscopy to establish how soil structure evolutes with diatom content and shear. For the studied diatom–kaolin mixtures, the angle of repose and internal frictional angle are high and increase with diatom content, especially when diatom content exceeds 20%. Diatom controls the frictional strength through its intricate morphology (cylindrical, saucer and disc shapes), very rough surface (hundreds of times rougher than flaky minerals), and stiff frustules with high Young's modulus. These features increase the particle coordination number and produce interparticle interlockings, both of which prevent particle rearrangement during shear and improve the frictional strength. This paper provides new insights into the multiscale structure of diatoms and improves the understanding of the shear strength of diatomaceous soils.","PeriodicalId":501472,"journal":{"name":"Géotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139851672","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}
B. Caicedo, M. J. Chaparro, J. P. Castillo Betancourt, M. Cabrera, P. Delage, P. Lognonné, B. Banerdt
The dynamic properties of loose sands under low stresses have been poorly investigated because of the higher order of magnitude of stress levels in terrestrial geotechnical structures. However, low densities and low stresses prevail in the sandy surface deposits of some other rocky planets, making low stress conditions relevant for extra-terrestrial soil mechanics. This is the case of Mars, on the surface of which a seismometer has been placed during the InSight mission. In this context, a dynamic shear rheometer was used to measure the shear modulus and damping ratio of a Martian regolith simulant under very low stresses to improve the interpretation of the InSight dataset on surface materials. This paper also revisits the grain contact stiffness and the overall modulus of a random packing of identical spheres, based on the Hertz-Mindlin contact theory. A micromechanical model accounting for the effects of both grain roughness and slipping in the soil degradation curve is proposed. The results of the model show a good agreement with experimental data, capturing the non-linear transition from low to high-shear strains. The model hence provides a new framework for a better understanding of the behaviour of granular materials in low gravity (extra-terrestrial) conditions.
{"title":"A micromechanical model for estimating the shear modulus and damping ratio of loose sands under low stresses. Application to a Mars regolith simulant","authors":"B. Caicedo, M. J. Chaparro, J. P. Castillo Betancourt, M. Cabrera, P. Delage, P. Lognonné, B. Banerdt","doi":"10.1680/jgeot.23.00244","DOIUrl":"https://doi.org/10.1680/jgeot.23.00244","url":null,"abstract":"The dynamic properties of loose sands under low stresses have been poorly investigated because of the higher order of magnitude of stress levels in terrestrial geotechnical structures. However, low densities and low stresses prevail in the sandy surface deposits of some other rocky planets, making low stress conditions relevant for extra-terrestrial soil mechanics. This is the case of Mars, on the surface of which a seismometer has been placed during the InSight mission. In this context, a dynamic shear rheometer was used to measure the shear modulus and damping ratio of a Martian regolith simulant under very low stresses to improve the interpretation of the InSight dataset on surface materials. This paper also revisits the grain contact stiffness and the overall modulus of a random packing of identical spheres, based on the Hertz-Mindlin contact theory. A micromechanical model accounting for the effects of both grain roughness and slipping in the soil degradation curve is proposed. The results of the model show a good agreement with experimental data, capturing the non-linear transition from low to high-shear strains. The model hence provides a new framework for a better understanding of the behaviour of granular materials in low gravity (extra-terrestrial) conditions.","PeriodicalId":501472,"journal":{"name":"Géotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139852612","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}
Xianwei Zhang, Xinyu Liu, Gang Wang, Yiqing Xu, Haodong Gao
Diatomaceous soil has geotechnical properties that differ fundamentally from those of common non-diatomaceous soils due to the presence of diatom microfossils with biological origins. Despite its dominant fines content, diatomaceous soil usually has high frictional shear resistance (approaching that of sand). Currently, the exact role of diatoms in controlling soil strength and underlying mechanisms remain obscure. Here, the frictional strength of diatomaceous soil is evaluated via angle-of-repose and direct simple shear tests on diatom–kaolin mixtures with differing diatom content. The microscale and nanoscale structures are characterised in detail via scanning-electron and atomic-force microscopy to establish how soil structure evolutes with diatom content and shear. For the studied diatom–kaolin mixtures, the angle of repose and internal frictional angle are high and increase with diatom content, especially when diatom content exceeds 20%. Diatom controls the frictional strength through its intricate morphology (cylindrical, saucer and disc shapes), very rough surface (hundreds of times rougher than flaky minerals), and stiff frustules with high Young's modulus. These features increase the particle coordination number and produce interparticle interlockings, both of which prevent particle rearrangement during shear and improve the frictional strength. This paper provides new insights into the multiscale structure of diatoms and improves the understanding of the shear strength of diatomaceous soils.
{"title":"Causes of the high friction angle of diatomaceous soil: microscale and nanoscale insights","authors":"Xianwei Zhang, Xinyu Liu, Gang Wang, Yiqing Xu, Haodong Gao","doi":"10.1680/jgeot.23.00230","DOIUrl":"https://doi.org/10.1680/jgeot.23.00230","url":null,"abstract":"Diatomaceous soil has geotechnical properties that differ fundamentally from those of common non-diatomaceous soils due to the presence of diatom microfossils with biological origins. Despite its dominant fines content, diatomaceous soil usually has high frictional shear resistance (approaching that of sand). Currently, the exact role of diatoms in controlling soil strength and underlying mechanisms remain obscure. Here, the frictional strength of diatomaceous soil is evaluated via angle-of-repose and direct simple shear tests on diatom–kaolin mixtures with differing diatom content. The microscale and nanoscale structures are characterised in detail via scanning-electron and atomic-force microscopy to establish how soil structure evolutes with diatom content and shear. For the studied diatom–kaolin mixtures, the angle of repose and internal frictional angle are high and increase with diatom content, especially when diatom content exceeds 20%. Diatom controls the frictional strength through its intricate morphology (cylindrical, saucer and disc shapes), very rough surface (hundreds of times rougher than flaky minerals), and stiff frustules with high Young's modulus. These features increase the particle coordination number and produce interparticle interlockings, both of which prevent particle rearrangement during shear and improve the frictional strength. This paper provides new insights into the multiscale structure of diatoms and improves the understanding of the shear strength of diatomaceous soils.","PeriodicalId":501472,"journal":{"name":"Géotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139791623","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}
B. Caicedo, M. J. Chaparro, J. P. Castillo Betancourt, M. Cabrera, P. Delage, P. Lognonné, B. Banerdt
The dynamic properties of loose sands under low stresses have been poorly investigated because of the higher order of magnitude of stress levels in terrestrial geotechnical structures. However, low densities and low stresses prevail in the sandy surface deposits of some other rocky planets, making low stress conditions relevant for extra-terrestrial soil mechanics. This is the case of Mars, on the surface of which a seismometer has been placed during the InSight mission. In this context, a dynamic shear rheometer was used to measure the shear modulus and damping ratio of a Martian regolith simulant under very low stresses to improve the interpretation of the InSight dataset on surface materials. This paper also revisits the grain contact stiffness and the overall modulus of a random packing of identical spheres, based on the Hertz-Mindlin contact theory. A micromechanical model accounting for the effects of both grain roughness and slipping in the soil degradation curve is proposed. The results of the model show a good agreement with experimental data, capturing the non-linear transition from low to high-shear strains. The model hence provides a new framework for a better understanding of the behaviour of granular materials in low gravity (extra-terrestrial) conditions.
{"title":"A micromechanical model for estimating the shear modulus and damping ratio of loose sands under low stresses. Application to a Mars regolith simulant","authors":"B. Caicedo, M. J. Chaparro, J. P. Castillo Betancourt, M. Cabrera, P. Delage, P. Lognonné, B. Banerdt","doi":"10.1680/jgeot.23.00244","DOIUrl":"https://doi.org/10.1680/jgeot.23.00244","url":null,"abstract":"The dynamic properties of loose sands under low stresses have been poorly investigated because of the higher order of magnitude of stress levels in terrestrial geotechnical structures. However, low densities and low stresses prevail in the sandy surface deposits of some other rocky planets, making low stress conditions relevant for extra-terrestrial soil mechanics. This is the case of Mars, on the surface of which a seismometer has been placed during the InSight mission. In this context, a dynamic shear rheometer was used to measure the shear modulus and damping ratio of a Martian regolith simulant under very low stresses to improve the interpretation of the InSight dataset on surface materials. This paper also revisits the grain contact stiffness and the overall modulus of a random packing of identical spheres, based on the Hertz-Mindlin contact theory. A micromechanical model accounting for the effects of both grain roughness and slipping in the soil degradation curve is proposed. The results of the model show a good agreement with experimental data, capturing the non-linear transition from low to high-shear strains. The model hence provides a new framework for a better understanding of the behaviour of granular materials in low gravity (extra-terrestrial) conditions.","PeriodicalId":501472,"journal":{"name":"Géotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139792606","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}
Jia-Yan Nie, Yifei Cui, Guodong Wang, Rui Wang, Ningning Zhang, Lei Zhang, Zhijun Wu
The effects of multi-scale particle shape characteristics on small strain stiffness of granular soils remain controversial. This study revisits this topic using well calibrated three-dimensional discrete element simulations incorporating into particle roughness-embedded contact model and realistic shape particles. Based on the numerical simulation results, the multi-scale particle shape effects on the small strain stiffness of sands and magnitude of Hardin's equation parameters are systematically investigated, and the underlying micro-mechanisms are also thoroughly explored. Results indicate that the small strain stiffness increases with the increase of particle overall irregularity due to the increased mechanical coordination number, while decreases with the increase of particle surface roughness because of the decreased contact normal stiffness. And the constant term and void ratio term parameters of Hardin's equation increases and decreases linearly, respectively, with the particle overall regularity, while reduces and grows with the particle surface roughness, respectively. Furthermore, the stress exponent is almost unchanged with the particle overall regularity, while increases with the particle surface roughness which determines the relative proportions of contacts under asperity dominated, transitional and Hertzian stages. The study helps to advance our cross-scale understanding of multi-scale particle shape information in relation to small strain stiffness of sands.
{"title":"A comprehensive numerical investigation of multi-scale particle shape effects on small strain stiffness of sands","authors":"Jia-Yan Nie, Yifei Cui, Guodong Wang, Rui Wang, Ningning Zhang, Lei Zhang, Zhijun Wu","doi":"10.1680/jgeot.23.00118","DOIUrl":"https://doi.org/10.1680/jgeot.23.00118","url":null,"abstract":"The effects of multi-scale particle shape characteristics on small strain stiffness of granular soils remain controversial. This study revisits this topic using well calibrated three-dimensional discrete element simulations incorporating into particle roughness-embedded contact model and realistic shape particles. Based on the numerical simulation results, the multi-scale particle shape effects on the small strain stiffness of sands and magnitude of Hardin's equation parameters are systematically investigated, and the underlying micro-mechanisms are also thoroughly explored. Results indicate that the small strain stiffness increases with the increase of particle overall irregularity due to the increased mechanical coordination number, while decreases with the increase of particle surface roughness because of the decreased contact normal stiffness. And the constant term and void ratio term parameters of Hardin's equation increases and decreases linearly, respectively, with the particle overall regularity, while reduces and grows with the particle surface roughness, respectively. Furthermore, the stress exponent is almost unchanged with the particle overall regularity, while increases with the particle surface roughness which determines the relative proportions of contacts under asperity dominated, transitional and Hertzian stages. The study helps to advance our cross-scale understanding of multi-scale particle shape information in relation to small strain stiffness of sands.","PeriodicalId":501472,"journal":{"name":"Géotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139829022","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}
Jia-Yan Nie, Yifei Cui, Guodong Wang, Rui Wang, Ningning Zhang, Lei Zhang, Zhijun Wu
The effects of multi-scale particle shape characteristics on small strain stiffness of granular soils remain controversial. This study revisits this topic using well calibrated three-dimensional discrete element simulations incorporating into particle roughness-embedded contact model and realistic shape particles. Based on the numerical simulation results, the multi-scale particle shape effects on the small strain stiffness of sands and magnitude of Hardin's equation parameters are systematically investigated, and the underlying micro-mechanisms are also thoroughly explored. Results indicate that the small strain stiffness increases with the increase of particle overall irregularity due to the increased mechanical coordination number, while decreases with the increase of particle surface roughness because of the decreased contact normal stiffness. And the constant term and void ratio term parameters of Hardin's equation increases and decreases linearly, respectively, with the particle overall regularity, while reduces and grows with the particle surface roughness, respectively. Furthermore, the stress exponent is almost unchanged with the particle overall regularity, while increases with the particle surface roughness which determines the relative proportions of contacts under asperity dominated, transitional and Hertzian stages. The study helps to advance our cross-scale understanding of multi-scale particle shape information in relation to small strain stiffness of sands.
{"title":"A comprehensive numerical investigation of multi-scale particle shape effects on small strain stiffness of sands","authors":"Jia-Yan Nie, Yifei Cui, Guodong Wang, Rui Wang, Ningning Zhang, Lei Zhang, Zhijun Wu","doi":"10.1680/jgeot.23.00118","DOIUrl":"https://doi.org/10.1680/jgeot.23.00118","url":null,"abstract":"The effects of multi-scale particle shape characteristics on small strain stiffness of granular soils remain controversial. This study revisits this topic using well calibrated three-dimensional discrete element simulations incorporating into particle roughness-embedded contact model and realistic shape particles. Based on the numerical simulation results, the multi-scale particle shape effects on the small strain stiffness of sands and magnitude of Hardin's equation parameters are systematically investigated, and the underlying micro-mechanisms are also thoroughly explored. Results indicate that the small strain stiffness increases with the increase of particle overall irregularity due to the increased mechanical coordination number, while decreases with the increase of particle surface roughness because of the decreased contact normal stiffness. And the constant term and void ratio term parameters of Hardin's equation increases and decreases linearly, respectively, with the particle overall regularity, while reduces and grows with the particle surface roughness, respectively. Furthermore, the stress exponent is almost unchanged with the particle overall regularity, while increases with the particle surface roughness which determines the relative proportions of contacts under asperity dominated, transitional and Hertzian stages. The study helps to advance our cross-scale understanding of multi-scale particle shape information in relation to small strain stiffness of sands.","PeriodicalId":501472,"journal":{"name":"Géotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139888969","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}
{"title":"Introduction for the 61st Rankine Lecture","authors":"Mark Randolph","doi":"10.1680/jgeot.23.00600","DOIUrl":"https://doi.org/10.1680/jgeot.23.00600","url":null,"abstract":"","PeriodicalId":501472,"journal":{"name":"Géotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139613737","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 Boschi, Marcos Arroyo Alvarez de Toledo, L. Vila, Josep Maria Carbonell, A. Solé
Soil layering modifies cone penetration measurements when the cone is close to layer boundaries. Transition zone and thin-layer effects appear, complicating interpretation. To help identify the mechanisms underlying transition and thin-layer effects, several series of realistic simulations of cone penetration in layered soils are presented. Cone penetration tests are simulated using fully coupled hydromechanical models solved with the particle finite element method. A constitutive model capable of representing flow liquefaction is employed to explore the effect of embedded layers with different initial state parameter and/or hydraulic conductivity than the host soil. Sensing and development distances for tip resistance and excess pore pressure are examined, as well as the effect of layering on dissipation tests. It is shown how distortion of layer interfaces by the cone is captured, explaining several characteristics of pore pressure and dissipation records. It is also shown that looser soil states may be hidden in the tip resistance trace by simultaneous changes in soil hydraulic conductivity.
{"title":"Coupled hydromechanical modelling of cone penetration in layered liquefiable soils","authors":"Katia Boschi, Marcos Arroyo Alvarez de Toledo, L. Vila, Josep Maria Carbonell, A. Solé","doi":"10.1680/jgeot.23.00164","DOIUrl":"https://doi.org/10.1680/jgeot.23.00164","url":null,"abstract":"Soil layering modifies cone penetration measurements when the cone is close to layer boundaries. Transition zone and thin-layer effects appear, complicating interpretation. To help identify the mechanisms underlying transition and thin-layer effects, several series of realistic simulations of cone penetration in layered soils are presented. Cone penetration tests are simulated using fully coupled hydromechanical models solved with the particle finite element method. A constitutive model capable of representing flow liquefaction is employed to explore the effect of embedded layers with different initial state parameter and/or hydraulic conductivity than the host soil. Sensing and development distances for tip resistance and excess pore pressure are examined, as well as the effect of layering on dissipation tests. It is shown how distortion of layer interfaces by the cone is captured, explaining several characteristics of pore pressure and dissipation records. It is also shown that looser soil states may be hidden in the tip resistance trace by simultaneous changes in soil hydraulic conductivity.","PeriodicalId":501472,"journal":{"name":"Géotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139443349","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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