Rossella Petti, Claudia Vitone, Maurizio Iler Marchi, Michael Plötze, Alexander Puzrin
The present study contributes to develop a novel eco-friendly solution for the mechanical stabilisation of dredged marine sediments by using mussel shells, i.e., another highly impacting waste of marine origin, in partial replacement of cements. Which are the underlying chemo-mechanical interactions affecting the evolution of such mixtures? Can the mussel shells replace cement without compromising useful geomechanical and geochemical properties of the stabilized sediments? Can such mixtures still be modelled as soils when it comes to their geotechnical design and analysis? The paper answers these questions by assessing the mechanical performance of the mixtures formed by sediments stabilised with three types of cement and a mussel shell powder and comparing it with that of the same sediments when treated with cement only. Multiple beneficial effects of the use of mussel shell powder, as peculiar source of calcium carbonate for its biogenic origin, have been demonstrated: it acts as a void filler, enhances the electrolytic exchanges between sediment and cement, and increases the contact area between the mineral particles promoting the chemical hydration reactions. As a result, for fixed replacement ratios, the original mixtures still exhibit soil-like behaviour consistent with traditional geomechanics and even better performances than the control mixtures.
{"title":"Use of shells for the mechanical stabilisation of sediments: a valuable geomechanical perspective?","authors":"Rossella Petti, Claudia Vitone, Maurizio Iler Marchi, Michael Plötze, Alexander Puzrin","doi":"10.1680/jgeot.22.00383","DOIUrl":"https://doi.org/10.1680/jgeot.22.00383","url":null,"abstract":"The present study contributes to develop a novel eco-friendly solution for the mechanical stabilisation of dredged marine sediments by using mussel shells, i.e., another highly impacting waste of marine origin, in partial replacement of cements. Which are the underlying chemo-mechanical interactions affecting the evolution of such mixtures? Can the mussel shells replace cement without compromising useful geomechanical and geochemical properties of the stabilized sediments? Can such mixtures still be modelled as soils when it comes to their geotechnical design and analysis? The paper answers these questions by assessing the mechanical performance of the mixtures formed by sediments stabilised with three types of cement and a mussel shell powder and comparing it with that of the same sediments when treated with cement only. Multiple beneficial effects of the use of mussel shell powder, as peculiar source of calcium carbonate for its biogenic origin, have been demonstrated: it acts as a void filler, enhances the electrolytic exchanges between sediment and cement, and increases the contact area between the mineral particles promoting the chemical hydration reactions. As a result, for fixed replacement ratios, the original mixtures still exhibit soil-like behaviour consistent with traditional geomechanics and even better performances than the control mixtures.","PeriodicalId":501472,"journal":{"name":"Géotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140299893","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}
Backward erosion piping (BEP) has been recognized as a major cause of failures in water-retaining structures. However, the fundamental mechanisms controlling the phenomenon are not well understood. This research applies the theory of rate processes to develop a constitutive relationship between energy density of the seepage flow and the erosion rate of soils during the evolution of BEP. The resulting equation is used to analyze four datasets of previously reported experimental observations. The mechanical parameters estimated through the proposed model fall into the ranges of values that were reported in the literature. To validate the proposed approach, the constitutive model was incorporated into a multiphase numerical framework to simulate evolution of BEP in embankment soil and compared with reported experimental observations. The numerical framework with the proposed constitutive model is shown to be capable of reproducing both the observed evolution of local hydraulic gradients and pipe progression in the structure.
后向侵蚀管道（BEP）已被认为是导致蓄水结构失效的一个主要原因。然而，人们对控制这一现象的基本机制还不甚了解。本研究应用速率过程理论，建立了 BEP 演化过程中渗流能量密度与土壤侵蚀速率之间的构成关系。所得方程用于分析之前报告的四个实验观测数据集。通过拟议模型估算出的力学参数与文献报道的数值范围一致。为了验证所提出的方法，将构成模型纳入多相数值框架，模拟路堤土壤中 BEP 的演变，并与报告的实验观测结果进行比较。结果表明，采用所提议的构成模型的数值框架能够再现观测到的局部水力梯度演变和结构中的管道进展。
{"title":"Backward erosion piping in geotechnical infrastructure: a rate process perspective","authors":"Zhijie Wang, Caglar Oskay, Alessandro Fascetti","doi":"10.1680/jgeot.23.00259","DOIUrl":"https://doi.org/10.1680/jgeot.23.00259","url":null,"abstract":"Backward erosion piping (BEP) has been recognized as a major cause of failures in water-retaining structures. However, the fundamental mechanisms controlling the phenomenon are not well understood. This research applies the theory of rate processes to develop a constitutive relationship between energy density of the seepage flow and the erosion rate of soils during the evolution of BEP. The resulting equation is used to analyze four datasets of previously reported experimental observations. The mechanical parameters estimated through the proposed model fall into the ranges of values that were reported in the literature. To validate the proposed approach, the constitutive model was incorporated into a multiphase numerical framework to simulate evolution of BEP in embankment soil and compared with reported experimental observations. The numerical framework with the proposed constitutive model is shown to be capable of reproducing both the observed evolution of local hydraulic gradients and pipe progression in the structure.","PeriodicalId":501472,"journal":{"name":"Géotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140299682","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}
Mechanized tunnel excavation in soils causes over-excavations, potentially leading to large amounts of spoil and settlements at ground level. An accurate estimation of over-excavations is crucial in the pre-design phase for assessing costs, determining the appropriate excavation method and choosing the muck management strategy. Currently, the estimation is based on experience and data from similar projects, but it becomes difficult when project conditions are heterogeneous. Alternatively, finite element analyses are time-consuming and not suitable for early design stages and, therefore, simplified tools are needed. In this paper, the authors present a simplified approach putting in relation face extrusion with estimated spoil mass and face volume loss. This approach, conceived for deep tunnels, is the extension to the case of mechanized tunnelling of a hydro-mechanical coupled meta-model derived from finite element numerical analyses for tunnels in clayey soils excavated by using conventional techniques (i.e. without any use of tunnel boring machines). The model has been validated against field data relative to a case study. The approach can be used in the early design process to identify tunnel boring machine characteristics and provide preliminary cost estimates. Additionally, during the construction phase, the method can be employed to interpret monitoring data and pre-design mitigation measures for unforeseen soil profile variations.
{"title":"Mechanized deep tunnel excavation in saturated clayey soils: a pre-design hydro-mechanically coupled method for the assessment of both spoil and face volume loss","authors":"Luca Flessati, Claudio di Prisco","doi":"10.1680/jgeot.23.00294","DOIUrl":"https://doi.org/10.1680/jgeot.23.00294","url":null,"abstract":"Mechanized tunnel excavation in soils causes over-excavations, potentially leading to large amounts of spoil and settlements at ground level. An accurate estimation of over-excavations is crucial in the pre-design phase for assessing costs, determining the appropriate excavation method and choosing the muck management strategy. Currently, the estimation is based on experience and data from similar projects, but it becomes difficult when project conditions are heterogeneous. Alternatively, finite element analyses are time-consuming and not suitable for early design stages and, therefore, simplified tools are needed. In this paper, the authors present a simplified approach putting in relation face extrusion with estimated spoil mass and face volume loss. This approach, conceived for deep tunnels, is the extension to the case of mechanized tunnelling of a hydro-mechanical coupled meta-model derived from finite element numerical analyses for tunnels in clayey soils excavated by using conventional techniques (i.e. without any use of tunnel boring machines). The model has been validated against field data relative to a case study. The approach can be used in the early design process to identify tunnel boring machine characteristics and provide preliminary cost estimates. Additionally, during the construction phase, the method can be employed to interpret monitoring data and pre-design mitigation measures for unforeseen soil profile variations.","PeriodicalId":501472,"journal":{"name":"Géotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140322176","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 proper estimation of stresses generated by train passage is of fundamental importance for the serviceability and longevity of railways, and yet very limited knowledge is available where the track substructure is built on a jointed rock mass. The present study introduces an analytical solution for estimating the ground stresses arising from moving wheel loads, causing a change in the three-dimensional stress state in the track formation, in relation to the stress variation with depth and along the longitudinal track section, i.e. the direction of train passage. Based on 21 case histories, an array of field measurements and numerical simulations covering a wide range of freight tonnage, train speeds, and different formation conditions, were considered to validate the proposed analytical solution. The proposed methodology (analytical solution) was then applied to a jointed rock subgrade to determine the normal and shear stresses acting along a specific discontinuity plane. The main analytical outcome demonstrates that the orthogonal vertical and shear stresses present different and phase-shifted history plots for homogeneous ground conditions with principal stresses rotation. However, conversely for a jointed subgrade, the normal and shear stresses along the discontinuity have the same history plot pattern and are in phase. As a practical guide, the results from this study would help to define which cyclic loads should be applied in laboratory tests to simulate realistic traffic patterns of trains travelling over a jointed rock subgrade.
{"title":"Dynamic stress analysis of rock joints under railway loading","authors":"Marlisio Oliveira Cecilio Junior, Buddhima Indraratna, Cholachat Rujikiatkamjorn, Rakesh Sai Malisetty","doi":"10.1680/jgeot.23.00301","DOIUrl":"https://doi.org/10.1680/jgeot.23.00301","url":null,"abstract":"The proper estimation of stresses generated by train passage is of fundamental importance for the serviceability and longevity of railways, and yet very limited knowledge is available where the track substructure is built on a jointed rock mass. The present study introduces an analytical solution for estimating the ground stresses arising from moving wheel loads, causing a change in the three-dimensional stress state in the track formation, in relation to the stress variation with depth and along the longitudinal track section, i.e. the direction of train passage. Based on 21 case histories, an array of field measurements and numerical simulations covering a wide range of freight tonnage, train speeds, and different formation conditions, were considered to validate the proposed analytical solution. The proposed methodology (analytical solution) was then applied to a jointed rock subgrade to determine the normal and shear stresses acting along a specific discontinuity plane. The main analytical outcome demonstrates that the orthogonal vertical and shear stresses present different and phase-shifted history plots for homogeneous ground conditions with principal stresses rotation. However, conversely for a jointed subgrade, the normal and shear stresses along the discontinuity have the same history plot pattern and are in phase. As a practical guide, the results from this study would help to define which cyclic loads should be applied in laboratory tests to simulate realistic traffic patterns of trains travelling over a jointed rock subgrade.","PeriodicalId":501472,"journal":{"name":"Géotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140322312","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}
Chengshun Xu, Chong Yue, Xiuli Du, Ke Liang, Bing Wang, Guoxing Chen
A series of undrained cyclic torsional shear tests were conducted to investigate the effect of cyclic loading frequency on the liquefaction characteristics of saturated sand using the hollow cylinder apparatus. The test results show that the dilative and contractive tendencies of various saturated sands are not only related to the physical properties of sand, but also affected by loading frequency. Under low-frequency loading, the saturated sand has a dilative behaviour, excess pore water pressure fluctuates after initial liquefaction and soil maintains the ability to resist liquefaction to some extent after the initial liquefaction. The liquefaction mode in terms of stress-strain relationship generally performs as the “cyclic mobility”. However, under the high-frequency loading, the saturated sand has a contractive behaviour, excess pore water pressure generally keeps stable after the initial liquefaction. The liquefaction mode in terms of stress-strain relationship generally exhibits as “cyclic instability”. The deformation caused by low-frequency loading is significantly larger compared with that caused by high-frequency loading. At higher loading frequencies, the phase transformation stress ratio increases with the increase of loading frequency, and gradually approaches the failure stress ratio.
{"title":"Experimental study on the influence of cyclic loading frequency on liquefaction characteristics of saturated sand","authors":"Chengshun Xu, Chong Yue, Xiuli Du, Ke Liang, Bing Wang, Guoxing Chen","doi":"10.1680/jgeot.21.00384","DOIUrl":"https://doi.org/10.1680/jgeot.21.00384","url":null,"abstract":"A series of undrained cyclic torsional shear tests were conducted to investigate the effect of cyclic loading frequency on the liquefaction characteristics of saturated sand using the hollow cylinder apparatus. The test results show that the dilative and contractive tendencies of various saturated sands are not only related to the physical properties of sand, but also affected by loading frequency. Under low-frequency loading, the saturated sand has a dilative behaviour, excess pore water pressure fluctuates after initial liquefaction and soil maintains the ability to resist liquefaction to some extent after the initial liquefaction. The liquefaction mode in terms of stress-strain relationship generally performs as the “cyclic mobility”. However, under the high-frequency loading, the saturated sand has a contractive behaviour, excess pore water pressure generally keeps stable after the initial liquefaction. The liquefaction mode in terms of stress-strain relationship generally exhibits as “cyclic instability”. The deformation caused by low-frequency loading is significantly larger compared with that caused by high-frequency loading. At higher loading frequencies, the phase transformation stress ratio increases with the increase of loading frequency, and gradually approaches the failure stress ratio.","PeriodicalId":501472,"journal":{"name":"Géotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140299523","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}
Jingmin Xu, Luorui Zheng, Geyang Song, Dingwen Zhang, Brian Sheil, Alec M. Marshall
Urban tunnelling projects pose significant risks to the integrity of nearby structures due to ground movements induced by the excavation process. Embedded walls are commonly employed as a protective measure to mitigate these adverse effects. This paper presents a comprehensive numerical investigation into the effects of embedded walls on tunnelling-induced ground displacements, aiming to provide insights and recommendations for optimal embedded wall design. The study assesses the impact of varying embedded wall length and horizontal distance from the tunnel on soil settlement and horizontal displacements. Results demonstrate the complex interplay between embedded wall length, horizontal distance, and ground movement patterns, and the highly non-linear influence of key parameters on embedded wall efficiency (i.e. its ability to reduce settlements). A preliminary design chart is proposed to guide engineers in determining the appropriate horizontal location and depth of embedded walls to effectively reduce tunnelling-induced ground displacements. The findings contribute to a better understanding of embedded wall performance in the context of tunnelling and provide valuable guidance for the practical design and implementation of protective measures in urban areas.
{"title":"Effects of embedded walls on tunnelling-induced sandy ground displacements: a numerical investigation","authors":"Jingmin Xu, Luorui Zheng, Geyang Song, Dingwen Zhang, Brian Sheil, Alec M. Marshall","doi":"10.1680/jgeot.23.00307","DOIUrl":"https://doi.org/10.1680/jgeot.23.00307","url":null,"abstract":"Urban tunnelling projects pose significant risks to the integrity of nearby structures due to ground movements induced by the excavation process. Embedded walls are commonly employed as a protective measure to mitigate these adverse effects. This paper presents a comprehensive numerical investigation into the effects of embedded walls on tunnelling-induced ground displacements, aiming to provide insights and recommendations for optimal embedded wall design. The study assesses the impact of varying embedded wall length and horizontal distance from the tunnel on soil settlement and horizontal displacements. Results demonstrate the complex interplay between embedded wall length, horizontal distance, and ground movement patterns, and the highly non-linear influence of key parameters on embedded wall efficiency (i.e. its ability to reduce settlements). A preliminary design chart is proposed to guide engineers in determining the appropriate horizontal location and depth of embedded walls to effectively reduce tunnelling-induced ground displacements. The findings contribute to a better understanding of embedded wall performance in the context of tunnelling and provide valuable guidance for the practical design and implementation of protective measures in urban areas.","PeriodicalId":501472,"journal":{"name":"Géotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140202309","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}
Literature studies are evidencing the counterposed effects of vegetation on soil hydraulic behaviour. Besides, root effects at the microscale are rarely quantified for direct correlations with phenomenological observations due to the complexity of adopting up-scaling factors. This study explores the microstructural causes behind the observed changes in vegetated compacted clayey sand's hydraulic and volume change behaviour. To this aim, laboratory experiments were carried out on compacted samples seeded with Cynodon dactylon. Significant changes in soil water-saturated permeability, water retention and shrinkage upon drying were observed after root growth. Laboratory measurements were complemented with quantification of root morphological features and observations at the microscale at different soil hydraulic states. X-ray scans and mercury intrusion porosimetry allowed covering seven orders of magnitude of pore sizes, shedding light on soil fabric changes at the soil-root interface and the clay aggregate scale. The effects of roots on the soil pore size distribution consisted of multi-physics phenomena: fissure generation, void clogging, and soil aggregation due to roots’ chemical interaction. Furthermore, a good correlation was found between the normalised volume of roots and the micro-pores volume. This new expression was included in a framework to predict soil water retention behaviour considering the aggregated structure and soil-root hydro-chemical interactions.
文献研究证明了植被对土壤水力行为的反作用。此外，微观尺度上的根系效应很少被量化以直接与现象观测结果相关联，这是因为采用上规模因素非常复杂。本研究探讨了观察到的植被压实粘土砂的水力和体积变化行为变化背后的微观结构原因。为此，我们对播种了 Cynodon dactylon 的压实样本进行了实验室实验。根系生长后，土壤水饱和渗透性、保水性和干燥收缩率都发生了显著变化。除了实验室测量之外，还对不同土壤水分状态下的根系形态特征进行了量化，并在微观尺度上进行了观察。通过 X 射线扫描和汞侵入孔隙度测定法，可以覆盖七个数量级的孔隙大小，从而揭示土壤-根系界面和粘土团粒尺度上的土壤结构变化。根系对土壤孔径分布的影响包括多种物理现象：裂缝产生、空隙堵塞以及根系化学作用导致的土壤聚集。此外，研究还发现根系的归一化体积与微孔体积之间存在良好的相关性。考虑到聚合结构和土壤-根系的水化学相互作用，这种新的表达式被纳入了预测土壤保水性能的框架中。
{"title":"Effects of vegetation growth on soil microstructure and hydro-mechanical behaviour","authors":"Alessandro Fraccica, Enrique Romero, Thierry Fourcaud","doi":"10.1680/jgeot.23.00163","DOIUrl":"https://doi.org/10.1680/jgeot.23.00163","url":null,"abstract":"Literature studies are evidencing the counterposed effects of vegetation on soil hydraulic behaviour. Besides, root effects at the microscale are rarely quantified for direct correlations with phenomenological observations due to the complexity of adopting up-scaling factors. This study explores the microstructural causes behind the observed changes in vegetated compacted clayey sand's hydraulic and volume change behaviour. To this aim, laboratory experiments were carried out on compacted samples seeded with <i>Cynodon dactylon</i>. Significant changes in soil water-saturated permeability, water retention and shrinkage upon drying were observed after root growth. Laboratory measurements were complemented with quantification of root morphological features and observations at the microscale at different soil hydraulic states. X-ray scans and mercury intrusion porosimetry allowed covering seven orders of magnitude of pore sizes, shedding light on soil fabric changes at the soil-root interface and the clay aggregate scale. The effects of roots on the soil pore size distribution consisted of multi-physics phenomena: fissure generation, void clogging, and soil aggregation due to roots’ chemical interaction. Furthermore, a good correlation was found between the normalised volume of roots and the micro-pores volume. This new expression was included in a framework to predict soil water retention behaviour considering the aggregated structure and soil-root hydro-chemical interactions.","PeriodicalId":501472,"journal":{"name":"Géotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140202284","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}
Huaxiang Yan, Majid Sedighi, A. Jivkov, Abdelmalek Bouazza
Recent laboratory and field experiments have provided evidences of the erosion and piping of clay-based barriers. Predicting these phenomena is essential for the performance assessment of bentonite barriers and containments. This paper presents a non-local multi-physics model for bentonite erosion induced by piping flow that includes swelling, detachment of particles and co-transport of detached particles with piping flow. The erosion is controlled by the balance between the cohesive strength, which depends on the swelling, and the shear force, which depends on the water velocity and chemistry. The accuracy of the model is tested by comparison of simulation results with experimental data from pinhole tests and material erosion in boreholes. It is demonstrated that the model predicts accurately the total mass eroded by the piping flow. For example, the results show that the mass loss induced by piping-assisted erosion during the installation of a bentonite plug can reach 10.3% of the original mass, which may significantly reduce the sealing capacity of bentonite plugs in boreholes. The results of simulations show that the eroded mass depends on the borehole diameter and flow rate. The minimum flow rates required to erode 10% of the original mass are 0.8 L/s and 0.045 L/s for db = 56 mm and 160 mm, respectively. These results demonstrate how the proposed formulations can be used to quantify the piping-assisted erosion of clay barriers, such as buffers, backfills, and plugs considered for geological disposal of higher activity waste, and the sealing of investigation boreholes and abandoned geo-energy wells.
{"title":"Modelling the piping-assisted erosion of clay barriers","authors":"Huaxiang Yan, Majid Sedighi, A. Jivkov, Abdelmalek Bouazza","doi":"10.1680/jgeot.22.00421","DOIUrl":"https://doi.org/10.1680/jgeot.22.00421","url":null,"abstract":"Recent laboratory and field experiments have provided evidences of the erosion and piping of clay-based barriers. Predicting these phenomena is essential for the performance assessment of bentonite barriers and containments. This paper presents a non-local multi-physics model for bentonite erosion induced by piping flow that includes swelling, detachment of particles and co-transport of detached particles with piping flow. The erosion is controlled by the balance between the cohesive strength, which depends on the swelling, and the shear force, which depends on the water velocity and chemistry. The accuracy of the model is tested by comparison of simulation results with experimental data from pinhole tests and material erosion in boreholes. It is demonstrated that the model predicts accurately the total mass eroded by the piping flow. For example, the results show that the mass loss induced by piping-assisted erosion during the installation of a bentonite plug can reach 10.3% of the original mass, which may significantly reduce the sealing capacity of bentonite plugs in boreholes. The results of simulations show that the eroded mass depends on the borehole diameter and flow rate. The minimum flow rates required to erode 10% of the original mass are 0.8 L/s and 0.045 L/s for db = 56 mm and 160 mm, respectively. These results demonstrate how the proposed formulations can be used to quantify the piping-assisted erosion of clay barriers, such as buffers, backfills, and plugs considered for geological disposal of higher activity waste, and the sealing of investigation boreholes and abandoned geo-energy wells.","PeriodicalId":501472,"journal":{"name":"Géotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140243329","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}
Permanent ground displacement due to faulting during strong earthquakes threatens stability of civil structures. To protect surface foundations from faulting, several mitigation techniques have been developed. Due to limitations of earlier mitigation strategies for unidentified reverse faulting conditions, this research presents a novel mitigation system, including installing sliders beneath the wings of a V-shaped concrete element, to reduce footing rotation. To evaluate the effectiveness of the suggested mitigation strategy, concrete strength tests, a physical centrifuge test and a comprehensive numerical study for different fault locations and dip angles were conducted for the first time. Results demonstrated that the placement of the sliders beneath the V-shaped wings had a significant effect on dissipating the fault dislocation. Compared to the previous mitigation techniques, the proposed system decreased the foundation rotation from a high value (11o) to a low value (3.2o) for the worst-case scenarios. Furthermore, the friction coefficients among sliders and concrete, the concrete wing inclination angle, length, and thickness were critical parameters to design the optimum proposed system. On the other hand, soil layer thickness and relative density did not significantly affect the footing rotation.
强震期间断层造成的永久地表位移威胁着民用建筑的稳定性。为了保护地表地基免受断层作用的影响，人们开发了多种缓解技术。由于早期针对不明逆断层条件的缓解策略存在局限性，本研究提出了一种新型缓解系统，包括在 V 型混凝土构件的翼下安装滑块，以减少地基旋转。为了评估所建议的缓解策略的有效性，研究人员首次针对不同的断层位置和倾角进行了混凝土强度测试、物理离心机测试和综合数值研究。结果表明，在 V 形翼下方放置滑块对消散断层位移有显著效果。与之前的缓解技术相比，在最坏情况下，所提议的系统将地基旋转从高值（11o）降至低值（3.2o）。此外，滑块与混凝土之间的摩擦系数、混凝土翼倾角、长度和厚度也是设计最佳拟议系统的关键参数。另一方面，土层厚度和相对密度对地基旋转没有显著影响。
{"title":"Reducing shallow foundation rotation due to reverse faulting using predefined shear planes","authors":"M. Baziar, Mir Mahdi Rashedi, A. S. Azizkandi","doi":"10.1680/jgeot.23.00221","DOIUrl":"https://doi.org/10.1680/jgeot.23.00221","url":null,"abstract":"Permanent ground displacement due to faulting during strong earthquakes threatens stability of civil structures. To protect surface foundations from faulting, several mitigation techniques have been developed. Due to limitations of earlier mitigation strategies for unidentified reverse faulting conditions, this research presents a novel mitigation system, including installing sliders beneath the wings of a V-shaped concrete element, to reduce footing rotation. To evaluate the effectiveness of the suggested mitigation strategy, concrete strength tests, a physical centrifuge test and a comprehensive numerical study for different fault locations and dip angles were conducted for the first time. Results demonstrated that the placement of the sliders beneath the V-shaped wings had a significant effect on dissipating the fault dislocation. Compared to the previous mitigation techniques, the proposed system decreased the foundation rotation from a high value (11o) to a low value (3.2o) for the worst-case scenarios. Furthermore, the friction coefficients among sliders and concrete, the concrete wing inclination angle, length, and thickness were critical parameters to design the optimum proposed system. On the other hand, soil layer thickness and relative density did not significantly affect the footing rotation.","PeriodicalId":501472,"journal":{"name":"Géotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140260997","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}
This paper derives a closed-form criterion to assess the risk of flowslide runout in loose frictional soil. The derivations rely on a recently proposed framework to simulate pre- and post-failure motion in infinite slopes. An analytical solution of the coupled differential equations capturing flowslide hydromechanics is obtained by specifying them for a perfectly plastic constitutive law. This result enables a comprehensive examination of the factors that control whether the landslide motion, once triggered, autonomously comes to rest (self-regulating behavior with low mobility) or continues to propagate (self-feeding behavior with high mobility). It is found that the time history of motion is regulated by non-dimensional property groups reflecting the timescale of excess pore pressure dissipation and the inertial properties of the liquefied zone, which are in turn governed by material (e.g., hydraulic conductivity, dilation coefficient, elastic moduli) and slope properties (e.g., thickness, inclination). The solution is used to build charts identifying the critical ranges of soil properties and triggering factors that differentiate between high-mobility and low-mobility flowslides. Most importantly, it is shown that the fate of flowslide motions is predicted by a critical ratio expressed in terms of excess pore pressure and flow velocity, here defined factor of mobility, FM, with values above 1 indicating a self-feeding runout.
{"title":"A closed-form criterion to identify high-mobility flowslides","authors":"Yanni Chen, G. Buscarnera","doi":"10.1680/jgeot.23.00171","DOIUrl":"https://doi.org/10.1680/jgeot.23.00171","url":null,"abstract":"This paper derives a closed-form criterion to assess the risk of flowslide runout in loose frictional soil. The derivations rely on a recently proposed framework to simulate pre- and post-failure motion in infinite slopes. An analytical solution of the coupled differential equations capturing flowslide hydromechanics is obtained by specifying them for a perfectly plastic constitutive law. This result enables a comprehensive examination of the factors that control whether the landslide motion, once triggered, autonomously comes to rest (self-regulating behavior with low mobility) or continues to propagate (self-feeding behavior with high mobility). It is found that the time history of motion is regulated by non-dimensional property groups reflecting the timescale of excess pore pressure dissipation and the inertial properties of the liquefied zone, which are in turn governed by material (e.g., hydraulic conductivity, dilation coefficient, elastic moduli) and slope properties (e.g., thickness, inclination). The solution is used to build charts identifying the critical ranges of soil properties and triggering factors that differentiate between high-mobility and low-mobility flowslides. Most importantly, it is shown that the fate of flowslide motions is predicted by a critical ratio expressed in terms of excess pore pressure and flow velocity, here defined factor of mobility, FM, with values above 1 indicating a self-feeding runout.","PeriodicalId":501472,"journal":{"name":"Géotechnique","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140261366","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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