This paper describes the design, development, calibration and validation of a novel soil-structure contact stress sensor. The new sensor design combines a novel operating principle, fibre Bragg grating (FBG) strain sensing and data-driven mapping techniques to create a multi-axis contact stress sensor that is both economical and suitably robust for deployment in underground construction applications. The instrumentation process is informed using a ‘virtual twin’ of the sensor in which synthetic data is generated by extracting and interpolating virtual FBG strains obtained from a large number of 3D finite element calculations. A physical prototype is subsequently developed to demonstrate proof of concept. Results from laboratory validation tests give confidence in the sensor's ability to provide accurate contact stress measurements in typical soil-structure interface shear applications. In particular, the novel sensor structure and operating principle was shown to achieve excellent measurement of effective normal stress. The new sensor design harnesses many of the inherent benefits of FBGs including immunity to electromagnetic noise and water ingress, and the use a single lightweight cable and connector, which significantly simplifies installation on site compared to electrical multi-axis sensors.
{"title":"Development of a new soil-structure contact stress sensor for underground construction applications","authors":"Jack Templeman, Brian Sheil","doi":"10.1680/jgeot.23.00202","DOIUrl":"https://doi.org/10.1680/jgeot.23.00202","url":null,"abstract":"This paper describes the design, development, calibration and validation of a novel soil-structure contact stress sensor. The new sensor design combines a novel operating principle, fibre Bragg grating (FBG) strain sensing and data-driven mapping techniques to create a multi-axis contact stress sensor that is both economical and suitably robust for deployment in underground construction applications. The instrumentation process is informed using a ‘virtual twin’ of the sensor in which synthetic data is generated by extracting and interpolating virtual FBG strains obtained from a large number of 3D finite element calculations. A physical prototype is subsequently developed to demonstrate proof of concept. Results from laboratory validation tests give confidence in the sensor's ability to provide accurate contact stress measurements in typical soil-structure interface shear applications. In particular, the novel sensor structure and operating principle was shown to achieve excellent measurement of effective normal stress. The new sensor design harnesses many of the inherent benefits of FBGs including immunity to electromagnetic noise and water ingress, and the use a single lightweight cable and connector, which significantly simplifies installation on site compared to electrical multi-axis sensors.","PeriodicalId":508398,"journal":{"name":"Géotechnique","volume":" 12","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141825842","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}
Surface roughness and coating hardness of underground pipelines are expected to play decisive roles in their axial pullout behaviour, which is an important aspect of pipeline design. Existing guidelines and previous studies underestimated or ignored these effects, resulting in potentially unsafe design. To address this problem, the current study conducted nine large-scale physical modelling tests on pipes in dry and dense sand. Five steel pipes with varying normalised roughness (0.04-1.01) and coating hardness (32.6-59.0 HRA) were used and instrumented with a novel type of film-like piezoresistive sensors for measuring soil-pipe contact pressure. The measured pullout resistance of rough pipes is 2.70-2.85 times of smooth pipes, significantly greater than the value specified in current design guidelines (i.e., 1.17 times). This substantial increase stems from an increase in interface friction coefficient (accounting for 72-79%) and a contact pressure increase induced by constrained dilation and soil arching (contributing the remaining 21-28%). Regarding coating hardness, a critical hardness was observed (around 35 HRA). Due to equivalent roughness from particle embedding, pipes with hardness below this value exhibited similar behaviour to rough pipes. Finally, a new and simple method was proposed for calculating the pullout resistance with consideration of the effects of roughness and dilatancy.
{"title":"Axial behaviour of steel pipelines buried in sand: effects of surface roughness and hardness","authors":"Chang Guo, Chao Zhou","doi":"10.1680/jgeot.24.00001","DOIUrl":"https://doi.org/10.1680/jgeot.24.00001","url":null,"abstract":"Surface roughness and coating hardness of underground pipelines are expected to play decisive roles in their axial pullout behaviour, which is an important aspect of pipeline design. Existing guidelines and previous studies underestimated or ignored these effects, resulting in potentially unsafe design. To address this problem, the current study conducted nine large-scale physical modelling tests on pipes in dry and dense sand. Five steel pipes with varying normalised roughness (0.04-1.01) and coating hardness (32.6-59.0 HRA) were used and instrumented with a novel type of film-like piezoresistive sensors for measuring soil-pipe contact pressure. The measured pullout resistance of rough pipes is 2.70-2.85 times of smooth pipes, significantly greater than the value specified in current design guidelines (i.e., 1.17 times). This substantial increase stems from an increase in interface friction coefficient (accounting for 72-79%) and a contact pressure increase induced by constrained dilation and soil arching (contributing the remaining 21-28%). Regarding coating hardness, a critical hardness was observed (around 35 HRA). Due to equivalent roughness from particle embedding, pipes with hardness below this value exhibited similar behaviour to rough pipes. Finally, a new and simple method was proposed for calculating the pullout resistance with consideration of the effects of roughness and dilatancy.","PeriodicalId":508398,"journal":{"name":"Géotechnique","volume":" 27","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141824646","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}
V. S. Ramakrishna Annapareddy, A. Sufian, T. Bore, Alexander Scheuermann
Suffusion experiments were utilised to quantify the evolving degree of heterogeneity in gap-graded soils. Upward flow was imposed on test specimens comprising a mixture layer with varying finer fraction contents overlaid by a coarse layer. A coaxial permeameter cell enabled the local permeability to be obtained using spatial time domain reflectometry. Three methods (coefficient of variation, Dykstra-Parsons coefficient, and Lorenz coefficient) were employed to quantify heterogeneity based on spatial variability in local permeability. For the two-layered specimen in this study, all three methods demonstrated that suffusion had a homogenising effect with particle migration from the mixture layer to the coarse layer. Detailed insights were obtained from a multi-layered approach, where the Dykstra-Parsons coefficient was found to be more sensitive to spatial variations, while the Lorenz coefficient was less dependent on the amount of data. The key observation was that an increase in heterogeneity led to a reduction in particle migration. This is an important finding as prior studies focused on homogeneous specimens, while this study demonstrates that small amounts of heterogeneity can significantly impact particle migration characteristics. This reinforces the need to quantify the evolving degree of heterogeneity.
{"title":"Quantification of spatial heterogeneity and its influence on particle migration","authors":"V. S. Ramakrishna Annapareddy, A. Sufian, T. Bore, Alexander Scheuermann","doi":"10.1680/jgeot.23.00083","DOIUrl":"https://doi.org/10.1680/jgeot.23.00083","url":null,"abstract":"Suffusion experiments were utilised to quantify the evolving degree of heterogeneity in gap-graded soils. Upward flow was imposed on test specimens comprising a mixture layer with varying finer fraction contents overlaid by a coarse layer. A coaxial permeameter cell enabled the local permeability to be obtained using spatial time domain reflectometry. Three methods (coefficient of variation, Dykstra-Parsons coefficient, and Lorenz coefficient) were employed to quantify heterogeneity based on spatial variability in local permeability. For the two-layered specimen in this study, all three methods demonstrated that suffusion had a homogenising effect with particle migration from the mixture layer to the coarse layer. Detailed insights were obtained from a multi-layered approach, where the Dykstra-Parsons coefficient was found to be more sensitive to spatial variations, while the Lorenz coefficient was less dependent on the amount of data. The key observation was that an increase in heterogeneity led to a reduction in particle migration. This is an important finding as prior studies focused on homogeneous specimens, while this study demonstrates that small amounts of heterogeneity can significantly impact particle migration characteristics. This reinforces the need to quantify the evolving degree of heterogeneity.","PeriodicalId":508398,"journal":{"name":"Géotechnique","volume":" 6","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141831807","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 study introduces a novel, interdisciplinary method that merges fundamental geomechanics with computer vision to develop an advanced hybrid feature-aided Digital Volume Correlation (DVC) technique. This technique is specifically engineered to measure and compute the full-field strain distribution in fine-grained soil mixtures. A clay-sand mixture specimen composed of quartz sand particles and kaolinite was created. Its mechanical properties and deformation behaviour were then tested using a mini-triaxial apparatus, combined with micro-focus X-ray Computed Tomography (μCT). The CT slices underwent image processing for denoising, segmentation of distinct phases, reconstruction of sand particles, and feature extraction within the soil specimen. The proposed approach incorporated a two-step particle tracking method, which initially uses particle volume and surface area features to establish a preliminary matching list for a reference particle and then use the Iterative Closest Point (ICP) method for precise target particle matching. The soil specimen's initial displacement field was then mapped onto the DVC method's grid, and further refined through subvoxel registration via a three-dimensional inverse compositional Gauss-Newton algorithm. The proposed method's effectiveness and efficiency were validated by accurately calculating the displacement and strain fields of the soil mixture sample, and comparing the results with those from a traditional DVC method. Given the soil's compositional and microstructural characteristics, these image-matching techniques can be integrated to create a versatile, efficient, and robust DVC system, suitable for a variety of soil mixture types.
本研究介绍了一种新颖的跨学科方法，它将基础地质力学与计算机视觉相结合，开发出一种先进的混合特征辅助数字体积相关（DVC）技术。该技术专门用于测量和计算细粒土混合物的全场应变分布。我们制作了一个由石英砂颗粒和高岭石组成的粘砂混合物试样。然后使用微型三轴仪器结合微聚焦 X 射线计算机断层扫描（μCT）对其机械性能和变形行为进行了测试。CT 切片经过图像处理，以进行去噪、不同阶段的分割、沙粒的重建以及土壤试样内的特征提取。所提出的方法采用了两步颗粒跟踪法，首先使用颗粒体积和表面积特征建立参考颗粒的初步匹配列表，然后使用迭代最邻近点（ICP）法进行精确的目标颗粒匹配。然后将土壤试样的初始位移场映射到 DVC 方法的网格上，并通过三维逆合成高斯-牛顿算法进一步细化子体素配准。通过精确计算土壤混合物样本的位移场和应变场，并将结果与传统的 DVC 方法进行比较，验证了所提出方法的有效性和效率。考虑到土壤的成分和微观结构特征，这些图像匹配技术可以集成到一个多功能、高效和稳健的 DVC 系统中，适用于各种类型的土壤混合物。
{"title":"Particle tracking–aided digital volume correlation for clay-sand soil mixtures","authors":"Mengmeng Wu, Jianfeng Wang, Bing Pan, Zhenyu Yin","doi":"10.1680/jgeot.24.00036","DOIUrl":"https://doi.org/10.1680/jgeot.24.00036","url":null,"abstract":"This study introduces a novel, interdisciplinary method that merges fundamental geomechanics with computer vision to develop an advanced hybrid feature-aided Digital Volume Correlation (DVC) technique. This technique is specifically engineered to measure and compute the full-field strain distribution in fine-grained soil mixtures. A clay-sand mixture specimen composed of quartz sand particles and kaolinite was created. Its mechanical properties and deformation behaviour were then tested using a mini-triaxial apparatus, combined with micro-focus X-ray Computed Tomography (μCT). The CT slices underwent image processing for denoising, segmentation of distinct phases, reconstruction of sand particles, and feature extraction within the soil specimen. The proposed approach incorporated a two-step particle tracking method, which initially uses particle volume and surface area features to establish a preliminary matching list for a reference particle and then use the Iterative Closest Point (ICP) method for precise target particle matching. The soil specimen's initial displacement field was then mapped onto the DVC method's grid, and further refined through subvoxel registration via a three-dimensional inverse compositional Gauss-Newton algorithm. The proposed method's effectiveness and efficiency were validated by accurately calculating the displacement and strain fields of the soil mixture sample, and comparing the results with those from a traditional DVC method. Given the soil's compositional and microstructural characteristics, these image-matching techniques can be integrated to create a versatile, efficient, and robust DVC system, suitable for a variety of soil mixture types.","PeriodicalId":508398,"journal":{"name":"Géotechnique","volume":"8 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141655947","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}
Constitutive models are an essential part of computational modelling in geotechnics; they are at the heart of almost all theoretical predictions of geotechnical structures. How the stress-strain (and perhaps time) response of soil (and rock) is represented in these mathematical models is usually the key to successful prediction of the behaviour of geotechnical structures. However, the important details of these models, particularly the idealisations that are made, may be poorly or incompletely understood, or ignored, sometimes at significant cost to the unwary analyst. Indeed, the capabilities and the shortcomings of these models, especially the more advanced models, are not always easy to ascertain. In some cases, determination of the values of the input parameters is not straightforward. Consequently, it may be difficult to determine which model to select for a particular task. This paper explores some of the more important developments in the constitutive modelling of soils and addresses some of these issues of potential concern. The need for such models and the various attributes and capabilities that the commonly used models possess is reviewed. Also discussed is the issue of matching a particular model to the geotechnical problem at hand, which model attributes are required and why. The intention is to place emphasis on the physical basis of these models, rather than explore their mathematical complexity in detail. Some of the constitutive models encoded in the software packages used routinely in geotechnical practice are reviewed, and discussion is also provided on their specific limitations. Examples of practical applications, involving the solution of boundary and initial value problems, are described to illustrate both the advantages and some of the limitations of both commonly used and highly advanced constitutive models.
{"title":"Constitutive modelling in computational geomechanics – 61st Rankine lecture, British Geotechnical Association, 2023","authors":"John P. Carter","doi":"10.1680/jgeot.23.rl.001","DOIUrl":"https://doi.org/10.1680/jgeot.23.rl.001","url":null,"abstract":"Constitutive models are an essential part of computational modelling in geotechnics; they are at the heart of almost all theoretical predictions of geotechnical structures. How the stress-strain (and perhaps time) response of soil (and rock) is represented in these mathematical models is usually the key to successful prediction of the behaviour of geotechnical structures. However, the important details of these models, particularly the idealisations that are made, may be poorly or incompletely understood, or ignored, sometimes at significant cost to the unwary analyst. Indeed, the capabilities and the shortcomings of these models, especially the more advanced models, are not always easy to ascertain. In some cases, determination of the values of the input parameters is not straightforward. Consequently, it may be difficult to determine which model to select for a particular task. This paper explores some of the more important developments in the constitutive modelling of soils and addresses some of these issues of potential concern. The need for such models and the various attributes and capabilities that the commonly used models possess is reviewed. Also discussed is the issue of matching a particular model to the geotechnical problem at hand, which model attributes are required and why. The intention is to place emphasis on the physical basis of these models, rather than explore their mathematical complexity in detail. Some of the constitutive models encoded in the software packages used routinely in geotechnical practice are reviewed, and discussion is also provided on their specific limitations. Examples of practical applications, involving the solution of boundary and initial value problems, are described to illustrate both the advantages and some of the limitations of both commonly used and highly advanced constitutive models.","PeriodicalId":508398,"journal":{"name":"Géotechnique","volume":"27 5","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141665049","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}
Ali Akbar Karimzadeh, Anthony Kwan Leung, Zhiwei Gao
The maximum shear modulus (G0(ij)) of rooted soils is crucial for assessing the deformation and liquefaction potential of vegetated infrastructures under seismic loading conditions. However, no data or theory is available to account for the anisotropy of G0(ij) of rooted soils. This study presents a new model that can predict G0(ij) anisotropy of rooted soils by incorporating the projection of the stress tensor on two independent tensors that describe soil fabric and root network. Bender element tests were conducted on bare and vegetated specimens under isotropic and anisotropic loading conditions. The presence of roots in the soil increased G0(VH) at all confining pressures (p′), as well as G0(HH) and G0(HV) at low p′. However, the trend was reversed at higher p′ because the roots reduced the effects of confinement on G0(ij) by replacing stronger soil–soil interfaces with weaker soil–root interfaces. Roots made the soil fabric and G0(ij) more anisotropic. The proposed model can effectively predict the observed anisotropy of G0(ij) under isotropic and anisotropic loading conditions. The new model also offers a new method for determining the fabric anisotropy of sand based on the anisotropy of shear modulus.
{"title":"Maximum shear modulus anisotropy of rooted soils","authors":"Ali Akbar Karimzadeh, Anthony Kwan Leung, Zhiwei Gao","doi":"10.1680/jgeot.23.00496","DOIUrl":"https://doi.org/10.1680/jgeot.23.00496","url":null,"abstract":"The maximum shear modulus (G0(ij)) of rooted soils is crucial for assessing the deformation and liquefaction potential of vegetated infrastructures under seismic loading conditions. However, no data or theory is available to account for the anisotropy of G0(ij) of rooted soils. This study presents a new model that can predict G0(ij) anisotropy of rooted soils by incorporating the projection of the stress tensor on two independent tensors that describe soil fabric and root network. Bender element tests were conducted on bare and vegetated specimens under isotropic and anisotropic loading conditions. The presence of roots in the soil increased G0(VH) at all confining pressures (p′), as well as G0(HH) and G0(HV) at low p′. However, the trend was reversed at higher p′ because the roots reduced the effects of confinement on G0(ij) by replacing stronger soil–soil interfaces with weaker soil–root interfaces. Roots made the soil fabric and G0(ij) more anisotropic. The proposed model can effectively predict the observed anisotropy of G0(ij) under isotropic and anisotropic loading conditions. The new model also offers a new method for determining the fabric anisotropy of sand based on the anisotropy of shear modulus.","PeriodicalId":508398,"journal":{"name":"Géotechnique","volume":"90 24","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141664117","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}
Microbially induced calcium carbonate precipitation (MICP) has emerged as a promising solution for geotechnical issues. However, the role of bacteria in the formation of calcium carbonate (CaCO3) remains incompletely comprehended. In this study, a droplet microfluidic chip was developed to observe the growth process of CaCO3 and bacterial behavior during the MICP process under various bacterial density conditions at the monocrystal-scale. Scanning electron microscope (SEM) was then utilized to analyze the CaCO3 morphology, and Raman spectroscopy was employed to identify CaCO3 polymorphs. Nucleation within microspaces showed a stochastic nature. Within the droplets where crystals formed, all crystals manifested as cubic calcite. Higher bacterial density led to the formation of larger and more irregularly shaped crystals, with crystal size showing a significant correlation with urease activity. In droplets where no crystals formed, higher bacterial density and urease activity resulted in the precipitation of amorphous calcium carbonate (ACC) on the bacterial surface. However, this precipitation pattern differed from the formation of monocrystalline CaCO3. Our results demonstrate that bacteria act primarily as urease secretors to regulate crystal growth during the MICP process, while their role as nucleation sites for crystals remains controversial. This study provides a novel insight into understanding the bio-induced CaCO3 formation mechanism.
{"title":"Role of bacteria on bio-induced calcium carbonate formation: insights from droplet microfluidic experiments","authors":"Jinxuan Zhang, Yang Xiao, Hanlong Liu, Jian Chu","doi":"10.1680/jgeot.24.01107","DOIUrl":"https://doi.org/10.1680/jgeot.24.01107","url":null,"abstract":"Microbially induced calcium carbonate precipitation (MICP) has emerged as a promising solution for geotechnical issues. However, the role of bacteria in the formation of calcium carbonate (CaCO3) remains incompletely comprehended. In this study, a droplet microfluidic chip was developed to observe the growth process of CaCO3 and bacterial behavior during the MICP process under various bacterial density conditions at the monocrystal-scale. Scanning electron microscope (SEM) was then utilized to analyze the CaCO3 morphology, and Raman spectroscopy was employed to identify CaCO3 polymorphs. Nucleation within microspaces showed a stochastic nature. Within the droplets where crystals formed, all crystals manifested as cubic calcite. Higher bacterial density led to the formation of larger and more irregularly shaped crystals, with crystal size showing a significant correlation with urease activity. In droplets where no crystals formed, higher bacterial density and urease activity resulted in the precipitation of amorphous calcium carbonate (ACC) on the bacterial surface. However, this precipitation pattern differed from the formation of monocrystalline CaCO3. Our results demonstrate that bacteria act primarily as urease secretors to regulate crystal growth during the MICP process, while their role as nucleation sites for crystals remains controversial. This study provides a novel insight into understanding the bio-induced CaCO3 formation mechanism.","PeriodicalId":508398,"journal":{"name":"Géotechnique","volume":" January","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141670045","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}
Soils are generally considered anisotropic with respect to hydraulic conductivity, while the evolution of anisotropy condition is unknown for bare and vegetated soils. Therefore, the main goal of this study is to compare the anisotropic hydraulic conductivity of as-compacted, bare, and vegetated specimens. Accordingly, a series of 54 hydraulic conductivity tests were conducted in a custom-made cube triaxial permeameter. The as-compacted specimens were revealed isotropic because the loosely packed preparation procedure resulted in a dominant flocculent structure. However, a fivefold increase in the anisotropy ratio of bare specimens was measured along the isotropic loading path because of the induced surficial degradation zone formed by irrigation and desiccation processes as evident in preliminary observations and crack network analysis. The variations in anisotropy ratio vs. void ratio function of vegetated soil generally fall below the corresponding function of the bare soil. The function was revealed to have a crossed nature, varying from sub-isotropic to super-isotropic states, corresponding to the lower and upper bounds of 0.3 and 3, respectively. It was postulated that vegetation impacts the flow differently by reducing the potential of desiccation cracks, creating preferential flow through the propagation of primary roots and clogging flow channels by secondary roots.
{"title":"Anisotropic hydraulic conductivity of as-compacted, bare and vegetated soils","authors":"Mostafa Gholami, Hamed Sadeghi, Pouya AliPanahi","doi":"10.1680/jgeot.23.00248","DOIUrl":"https://doi.org/10.1680/jgeot.23.00248","url":null,"abstract":"Soils are generally considered anisotropic with respect to hydraulic conductivity, while the evolution of anisotropy condition is unknown for bare and vegetated soils. Therefore, the main goal of this study is to compare the anisotropic hydraulic conductivity of as-compacted, bare, and vegetated specimens. Accordingly, a series of 54 hydraulic conductivity tests were conducted in a custom-made cube triaxial permeameter. The as-compacted specimens were revealed isotropic because the loosely packed preparation procedure resulted in a dominant flocculent structure. However, a fivefold increase in the anisotropy ratio of bare specimens was measured along the isotropic loading path because of the induced surficial degradation zone formed by irrigation and desiccation processes as evident in preliminary observations and crack network analysis. The variations in anisotropy ratio vs. void ratio function of vegetated soil generally fall below the corresponding function of the bare soil. The function was revealed to have a crossed nature, varying from sub-isotropic to super-isotropic states, corresponding to the lower and upper bounds of 0.3 and 3, respectively. It was postulated that vegetation impacts the flow differently by reducing the potential of desiccation cracks, creating preferential flow through the propagation of primary roots and clogging flow channels by secondary roots.","PeriodicalId":508398,"journal":{"name":"Géotechnique","volume":"25 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141705658","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}
Zhang Zheng Cai, Han Ke, Peng Ze Zhang, J. Lan, Peng Cheng Ma, Jie Hu, Bo Xiao, Yunmin Chen
Large phosphogypsum (PG) stacks risk dam failure, with an insufficient consensus on the shear strength parameters for stability analysis. To this end, a combination of scanning electron microscopy (SEM) and triaxial tests was undertaken to investigate the underlying mechanism between crystal structure and shear strength of in situ and remoulded PG samples. The shear strength and deformation of PG were significantly affected by dissolution and recrystallisation. Dissolution weakened the cementation between particles, leading to a stabilisation of approximate 11 kPa under different confining pressures in the initial shear stage. The hardening phenomenon was related to the formation of cluster crystals under saturated conditions. An increase from 1.57 to 1.73 in the critical state stress ratio on remoulded samples occurred as the K0 consolidation time increased from 4 to 28 days. The compressive deformation of PG is accompanied by chemical consolidation, which is mainly impacted by the consolidation conditions (saturation) rather than the consolidation time. In the engineering design of the PG stacks, φ’ could be taken to a higher value at saturation and c’ could be higher when the dry density is higher than 1.2.
{"title":"Strength behaviour of stacked phosphogypsum incorporating dissolution–recrystallisation equilibrium","authors":"Zhang Zheng Cai, Han Ke, Peng Ze Zhang, J. Lan, Peng Cheng Ma, Jie Hu, Bo Xiao, Yunmin Chen","doi":"10.1680/jgeot.23.00508","DOIUrl":"https://doi.org/10.1680/jgeot.23.00508","url":null,"abstract":"Large phosphogypsum (PG) stacks risk dam failure, with an insufficient consensus on the shear strength parameters for stability analysis. To this end, a combination of scanning electron microscopy (SEM) and triaxial tests was undertaken to investigate the underlying mechanism between crystal structure and shear strength of in situ and remoulded PG samples. The shear strength and deformation of PG were significantly affected by dissolution and recrystallisation. Dissolution weakened the cementation between particles, leading to a stabilisation of approximate 11 kPa under different confining pressures in the initial shear stage. The hardening phenomenon was related to the formation of cluster crystals under saturated conditions. An increase from 1.57 to 1.73 in the critical state stress ratio on remoulded samples occurred as the K0 consolidation time increased from 4 to 28 days. The compressive deformation of PG is accompanied by chemical consolidation, which is mainly impacted by the consolidation conditions (saturation) rather than the consolidation time. In the engineering design of the PG stacks, φ’ could be taken to a higher value at saturation and c’ could be higher when the dry density is higher than 1.2.","PeriodicalId":508398,"journal":{"name":"Géotechnique","volume":"4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141703300","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}
During land reclamation on the reef islands, large amounts of silt-sized coral soils were created by segregation and degradation. The accumulation of silt-sized coral soils is fairy uncommon while the research on the geotechnical properties of the coral silt is very limited. In this study, a systematic experimental investigation on the mechanical behaviour of coral silt obtained from a reclaimed reef island in the South China Sea has been performed, with comparisons to the coral sand collected from the same area. Similar to the coral sand, the coral silt particles also exhibit irregular particle shape and intra-particle pore due to their nature origin. According to the limiting water contents, the coral silt is classified as a low-plasticity clayey silt. Under one-dimensional compression, the coral silt exhibits a much quicker convergence compared to coral sand. Prior to convergence, the compressibility of coral silt is higher. After yielding, the compressibility of coral sand becomes higher due to significant particle breakage. The loose coral silt subjected to undrained shearing at low confining pressures exhibits obvious strain softening behaviour, indicating static liquefaction or flow failure. The critical state and peak friction angles of coral silt are lower than those of coral sand but much higher than those of the other terrigenous clayey silts. A curved critical state line with well-defined horizontal asymptote in the deviatoric stress - mean effective stress plane is identified for coral silt, again indicating higher potential to static liquefaction.
{"title":"On the mechanical behaviour of a coral silt from the South China Sea","authors":"Ting Yao, Ziwei Cao, Wei Li","doi":"10.1680/jgeot.24.00012","DOIUrl":"https://doi.org/10.1680/jgeot.24.00012","url":null,"abstract":"During land reclamation on the reef islands, large amounts of silt-sized coral soils were created by segregation and degradation. The accumulation of silt-sized coral soils is fairy uncommon while the research on the geotechnical properties of the coral silt is very limited. In this study, a systematic experimental investigation on the mechanical behaviour of coral silt obtained from a reclaimed reef island in the South China Sea has been performed, with comparisons to the coral sand collected from the same area. Similar to the coral sand, the coral silt particles also exhibit irregular particle shape and intra-particle pore due to their nature origin. According to the limiting water contents, the coral silt is classified as a low-plasticity clayey silt. Under one-dimensional compression, the coral silt exhibits a much quicker convergence compared to coral sand. Prior to convergence, the compressibility of coral silt is higher. After yielding, the compressibility of coral sand becomes higher due to significant particle breakage. The loose coral silt subjected to undrained shearing at low confining pressures exhibits obvious strain softening behaviour, indicating static liquefaction or flow failure. The critical state and peak friction angles of coral silt are lower than those of coral sand but much higher than those of the other terrigenous clayey silts. A curved critical state line with well-defined horizontal asymptote in the deviatoric stress - mean effective stress plane is identified for coral silt, again indicating higher potential to static liquefaction.","PeriodicalId":508398,"journal":{"name":"Géotechnique","volume":"62 12","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-06-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141347749","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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