In situ tests such as standard penetration test (SPT) and cone penetration test (CPT) are often conducted to evaluate the probability of earthquake-induced liquefaction. However, the models adopted have seldom attempted to utilize SPT and CPT data simultaneously. In this study, a side-by-side SPT-CPT database at historical earthquake sites is established; then, a Bayesian network model is constructed to predict the probability of soil liquefaction based on this database, with which the SPT and CPT data are utilized simultaneously. Next, comparative studies are undertaken to illustrate the superiority of the Bayesian network-based probabilistic soil liquefaction model developed over other models, in terms of six SPT- and CPT-based conventional liquefaction models in the literature and two Bayesian network-based models. It should be noted that the liquefaction sites with two in situ tests are scarce and side-by-side SPT-CPT data can be incomplete, which leads to challenges in applying the Bayesian network model developed. To address this problem, correlations between SPT and CPT data are analyzed, and these correlations are further included in the Bayesian network model; as a result, a modified Bayesian network model is reached. Finally, the influence of the proportion of missing data in the incomplete SPT-CPT data on the liquefaction prediction accuracy is discussed.
{"title":"Probabilistic Evaluation of Earthquake-Induced Liquefaction Using Bayesian Network Based on A Side-by-Side SPT-CPT Database","authors":"Han Xiao, W. Gong, C. H. Juang","doi":"10.1139/cgj-2023-0455","DOIUrl":"https://doi.org/10.1139/cgj-2023-0455","url":null,"abstract":"In situ tests such as standard penetration test (SPT) and cone penetration test (CPT) are often conducted to evaluate the probability of earthquake-induced liquefaction. However, the models adopted have seldom attempted to utilize SPT and CPT data simultaneously. In this study, a side-by-side SPT-CPT database at historical earthquake sites is established; then, a Bayesian network model is constructed to predict the probability of soil liquefaction based on this database, with which the SPT and CPT data are utilized simultaneously. Next, comparative studies are undertaken to illustrate the superiority of the Bayesian network-based probabilistic soil liquefaction model developed over other models, in terms of six SPT- and CPT-based conventional liquefaction models in the literature and two Bayesian network-based models. It should be noted that the liquefaction sites with two in situ tests are scarce and side-by-side SPT-CPT data can be incomplete, which leads to challenges in applying the Bayesian network model developed. To address this problem, correlations between SPT and CPT data are analyzed, and these correlations are further included in the Bayesian network model; as a result, a modified Bayesian network model is reached. Finally, the influence of the proportion of missing data in the incomplete SPT-CPT data on the liquefaction prediction accuracy is discussed.","PeriodicalId":505159,"journal":{"name":"Canadian Geotechnical Journal","volume":"34 S15","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140422928","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 cone penetration test (CPT) is one of the most popular in-situ soil characterization tools. However, the test is often difficult to conduct in soils with high penetration resistance. To resolve the problem, a rotary CPT device has recently been adopted in practice by rotating the rod to increase the penetrability, particularly in deep dense sand. This study investigates the underlying mechanism of the rotation effects from a micromechanical perspective using models based on the discrete element method (DEM). With rotation, the cone penetration resistance (qc) decreases by up to 50%, while the cone torque resistance (tc) increases gradually. These results are also used to successfully assess existing theoretical solutions. The mechanical work required during penetration was observed to keep rising as the rotational velocity increased. Microscopic variables including particle displacement and velocity field show that rotation reduces the volume of disturbed soil during penetration and drives particles to rotate horizontally, while contact force chain and contact fabric indicate that rotation increases the number of radial and tangential contacts and the corresponding contact forces, forming a lateral stable structure around the shaft which can reduce the force transmitted to the particles below the cone, thus decreasing the vertical penetration resistance.
{"title":"A numerical investigation on the effect of rotation on the Cone Penetration Test","authors":"Xiaotong Yang, Ningning Zhang, Rui Wang, Alejandro Martinez, Yuyan Chen, Raúl Fuentes, Jian-Min Zhang","doi":"10.1139/cgj-2023-0413","DOIUrl":"https://doi.org/10.1139/cgj-2023-0413","url":null,"abstract":"The cone penetration test (CPT) is one of the most popular in-situ soil characterization tools. However, the test is often difficult to conduct in soils with high penetration resistance. To resolve the problem, a rotary CPT device has recently been adopted in practice by rotating the rod to increase the penetrability, particularly in deep dense sand. This study investigates the underlying mechanism of the rotation effects from a micromechanical perspective using models based on the discrete element method (DEM). With rotation, the cone penetration resistance (qc) decreases by up to 50%, while the cone torque resistance (tc) increases gradually. These results are also used to successfully assess existing theoretical solutions. The mechanical work required during penetration was observed to keep rising as the rotational velocity increased. Microscopic variables including particle displacement and velocity field show that rotation reduces the volume of disturbed soil during penetration and drives particles to rotate horizontally, while contact force chain and contact fabric indicate that rotation increases the number of radial and tangential contacts and the corresponding contact forces, forming a lateral stable structure around the shaft which can reduce the force transmitted to the particles below the cone, thus decreasing the vertical penetration resistance.","PeriodicalId":505159,"journal":{"name":"Canadian Geotechnical Journal","volume":"55 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140418348","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}
Qingtao Lin, Xu Meng, D. Lu, Jinbo Miao, Zhihong Zhao, Xiuli Du
An empirical model for describing the soil movements induced by tunneling is proposed, then the mathematical relationship between horizontal displacement and vertical displacement is obtained. By analyzing 25 sets of data from field engineering and 35 sets of data from model tests, the formula for the maximum settlement Sv,max(z) is optimized to adapt to different ground conditions. The10modified Gaussian function is developed by introducing the existing width coefficient of the settlement trough i(z) and the optimized11Sv,max(z) to describe the surface and subsurface vertical displacement. Subsequently, the formula for the horizontal displacement is12derived based on the Modified Gaussian function. H(z) representing the position of the oriented point of the soil movement is a variable13in the formula for horizontal displacement. Based on measured results, a logarithmic function and a quadratic polynomial function are14proposed to describe the variation of H(z) with depth in the clay stratum and sand stratum, respectively. Then, the rationality of the15proposed method is validated by 4 sets of in-situ data and 4 sets of test data. Finally, the implementation process of the proposed method16is illustrated, and the inversion results of the ground displacement field in Beijing Metro Line 12 are presented.
{"title":"A unified empirical method for predicting both vertical and horizontal ground displacements induced by tunnel excavation","authors":"Qingtao Lin, Xu Meng, D. Lu, Jinbo Miao, Zhihong Zhao, Xiuli Du","doi":"10.1139/cgj-2023-0519","DOIUrl":"https://doi.org/10.1139/cgj-2023-0519","url":null,"abstract":"An empirical model for describing the soil movements induced by tunneling is proposed, then the mathematical relationship between horizontal displacement and vertical displacement is obtained. By analyzing 25 sets of data from field engineering and 35 sets of data from model tests, the formula for the maximum settlement Sv,max(z) is optimized to adapt to different ground conditions. The10modified Gaussian function is developed by introducing the existing width coefficient of the settlement trough i(z) and the optimized11Sv,max(z) to describe the surface and subsurface vertical displacement. Subsequently, the formula for the horizontal displacement is12derived based on the Modified Gaussian function. H(z) representing the position of the oriented point of the soil movement is a variable13in the formula for horizontal displacement. Based on measured results, a logarithmic function and a quadratic polynomial function are14proposed to describe the variation of H(z) with depth in the clay stratum and sand stratum, respectively. Then, the rationality of the15proposed method is validated by 4 sets of in-situ data and 4 sets of test data. Finally, the implementation process of the proposed method16is illustrated, and the inversion results of the ground displacement field in Beijing Metro Line 12 are presented.","PeriodicalId":505159,"journal":{"name":"Canadian Geotechnical Journal","volume":"69 8","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140424101","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}
R. Karmaker, B. Hawlader, Didier Perret, Rajib Dey
This paper presents large deformation finite element (FE) modelling of penetration of solid cylindrical piles into highly sensitive soft clay. The simulations are performed using a Coupled Eulerian-Lagrangian (CEL) FE modeling technique. The pile is penetrated at a constant rate, and the analyses are performed for undrained conditions to simulate the response during penetration. The soil model considers the effects of strain softening and strain rate on the undrained shear strength. The FE calculated results are compared with available analytical and numerical solutions for idealized soil profiles. Simulations are also performed for two instrumented piles previously installed into highly sensitive clay at Saint-Alban in Québec, Canada. The installation-induced changes in stresses, degradation of undrained shear strength, and tip resistance obtained from FE analyses are consistent with the field test results. Large plastic shear strains develop near the pile, which can significantly remould the soil near the pile shaft. A parametric study shows that a quicker post-peak degradation of undrained shear strength of highly sensitive clay creates a smaller zone of high plastic shear strain near the pile, while the plastic zone is wider for low- to non-sensitive clays.
{"title":"Numerical modelling of pile jacking in highly sensitive clays","authors":"R. Karmaker, B. Hawlader, Didier Perret, Rajib Dey","doi":"10.1139/cgj-2023-0320","DOIUrl":"https://doi.org/10.1139/cgj-2023-0320","url":null,"abstract":"This paper presents large deformation finite element (FE) modelling of penetration of solid cylindrical piles into highly sensitive soft clay. The simulations are performed using a Coupled Eulerian-Lagrangian (CEL) FE modeling technique. The pile is penetrated at a constant rate, and the analyses are performed for undrained conditions to simulate the response during penetration. The soil model considers the effects of strain softening and strain rate on the undrained shear strength. The FE calculated results are compared with available analytical and numerical solutions for idealized soil profiles. Simulations are also performed for two instrumented piles previously installed into highly sensitive clay at Saint-Alban in Québec, Canada. The installation-induced changes in stresses, degradation of undrained shear strength, and tip resistance obtained from FE analyses are consistent with the field test results. Large plastic shear strains develop near the pile, which can significantly remould the soil near the pile shaft. A parametric study shows that a quicker post-peak degradation of undrained shear strength of highly sensitive clay creates a smaller zone of high plastic shear strain near the pile, while the plastic zone is wider for low- to non-sensitive clays.","PeriodicalId":505159,"journal":{"name":"Canadian Geotechnical Journal","volume":"22 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140426170","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}
Shear behaviour of soil-structure interfaces greatly affects the performance of geotechnical structures. The soil-structure interfaces in geothermal structures (e.g., energy pile and energy wall) are often subjected to varying temperature and suction conditions. However, there is no constitutive model to simulate the coupled effects of suction and temperature on the shear behaviour of soil-structure interfaces. In this study, a thermo-mechanical model was newly developed based on the bounding surface plasticity framework to predict the thermo-mechanical behaviour of saturated and unsaturated interfaces. A power function was used to calculate the degree of saturation at the interface and improve the evaluation of suction effects on interface shear strength. A linear relationship between temperature and interface critical state friction angle was proposed to incorporate thermal effects. New equations were also proposed to describe the critical state lines (CSLs) in the void ratio versus stress plane (e-lnσ_n^* ) and to model the shearing-induced deformation at various temperatures and suctions. The experimental data from different interfaces in the literature were used to evaluate the model capability. Comparisons between measured and computed results suggest that this model can well capture the coupled effects of temperature, suction and net normal stress on the shear behaviour of interfaces.
{"title":"A thermo-mechanical model for saturated and unsaturated soil-structure interfaces","authors":"Sheqiang Cui, Chao Zhou","doi":"10.1139/cgj-2023-0529","DOIUrl":"https://doi.org/10.1139/cgj-2023-0529","url":null,"abstract":"Shear behaviour of soil-structure interfaces greatly affects the performance of geotechnical structures. The soil-structure interfaces in geothermal structures (e.g., energy pile and energy wall) are often subjected to varying temperature and suction conditions. However, there is no constitutive model to simulate the coupled effects of suction and temperature on the shear behaviour of soil-structure interfaces. In this study, a thermo-mechanical model was newly developed based on the bounding surface plasticity framework to predict the thermo-mechanical behaviour of saturated and unsaturated interfaces. A power function was used to calculate the degree of saturation at the interface and improve the evaluation of suction effects on interface shear strength. A linear relationship between temperature and interface critical state friction angle was proposed to incorporate thermal effects. New equations were also proposed to describe the critical state lines (CSLs) in the void ratio versus stress plane (e-lnσ_n^* ) and to model the shearing-induced deformation at various temperatures and suctions. The experimental data from different interfaces in the literature were used to evaluate the model capability. Comparisons between measured and computed results suggest that this model can well capture the coupled effects of temperature, suction and net normal stress on the shear behaviour of interfaces.","PeriodicalId":505159,"journal":{"name":"Canadian Geotechnical Journal","volume":"1 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140426692","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}
Investigations into the temporally evolving stress state below the base of excavations and underground structures are very scarce, in contrast to studies of horizontal earth pressures during the construction stage. Therefore in this work, the measured temporal response in terms of vertical and horizontal effective stresses and displacements below a tunnel slab at the base of an excavation located in a deep sensitive clay deposit is reported. In addition to the measured unloading response over time, the completeness of the site description and complementary measurements enables future benchmarking of numerical models at boundary and element level. Instrument clusters of earth pressure cells and piezometers were installed at three locations in one cross-section. The monitoring data allows the interpretation of effective stress paths and stress ratios, K=σ'h/σ'v, at soil element level covering the construction and the serviceability stages. The in situ stress ratios enable a unique comparison to prior laboratory studies of K during unloading. The data presented herein on the evolution of K corroborate, although approximately, previous studies at laboratory scale. Furthermore, at system level, the monitoring data reveal the intricate interplay between deformations resulting from excavation and pile driving.
与施工阶段对水平土压力的研究相比，对挖掘和地下结构底部随时间变化的应力状态的研究非常少。因此，在这项研究中，我们报告了位于深层敏感粘土沉积中的挖掘工程底部隧道底板下面的垂直和水平有效应力和位移的时间响应测量结果。除了测量到的卸载随时间变化的响应之外，现场描述和补充测量的完整性还有助于未来在边界和元素层面对数值模型进行基准测试。在一个断面的三个位置安装了由土压力传感器和压强计组成的仪器群。通过监测数据，可以解释施工和使用阶段土壤元素层面的有效应力路径和应力比 K=σ'h/σ'v。通过现场应力比，可以将卸载过程中的 K 与之前的实验室研究进行比较。本文提供的有关 K 演变的数据与之前在实验室规模上进行的研究相吻合（尽管只是近似）。此外，在系统层面，监测数据揭示了开挖和打桩造成的变形之间错综复杂的相互作用。
{"title":"Temporal effective stress response of soil elements below the base of an excavation in sensitive clay","authors":"Johannes Tornborg, Mats Karlsson, J. Dijkstra","doi":"10.1139/cgj-2023-0355","DOIUrl":"https://doi.org/10.1139/cgj-2023-0355","url":null,"abstract":"Investigations into the temporally evolving stress state below the base of excavations and underground structures are very scarce, in contrast to studies of horizontal earth pressures during the construction stage. Therefore in this work, the measured temporal response in terms of vertical and horizontal effective stresses and displacements below a tunnel slab at the base of an excavation located in a deep sensitive clay deposit is reported. In addition to the measured unloading response over time, the completeness of the site description and complementary measurements enables future benchmarking of numerical models at boundary and element level. Instrument clusters of earth pressure cells and piezometers were installed at three locations in one cross-section. The monitoring data allows the interpretation of effective stress paths and stress ratios, K=σ'h/σ'v, at soil element level covering the construction and the serviceability stages. The in situ stress ratios enable a unique comparison to prior laboratory studies of K during unloading. The data presented herein on the evolution of K corroborate, although approximately, previous studies at laboratory scale. Furthermore, at system level, the monitoring data reveal the intricate interplay between deformations resulting from excavation and pile driving.","PeriodicalId":505159,"journal":{"name":"Canadian Geotechnical Journal","volume":"72 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140439945","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}
Development of digital twins is emerging rapidly in geotechnical engineering, and it often requires real-time updating of numerical models (e.g., finite element model, FEM) using multiple sources of monitoring data (e.g., settlement and pore water pressure data). Conventional model updating, or calibration, often involves repeated executions of the numerical model, using monitoring data from a specific source or at limited spatial locations only. This leads to a critical research need of real-time model updating and predictions using a numerical model improved continuously by multi-source monitoring data. To address this need, a physics-informed machine learning method called multi-source sparse dictionary learning (MS-SDL) is proposed in this study. Originated from signal decomposition and compression, MS-SDL utilizes results from a suite of numerical models as basis functions, or dictionary atoms, and employs multi-source monitoring data to select a limited number of important atoms for predicting multiple, spatiotemporally varying geotechnical responses. As monitoring data are collected sequentially, no repeated evaluations of computational numerical models are needed, and an automatic and real-time model calibration is achieved for continuously improving model predictions. A real project in Hong Kong is presented to illustrate the proposed approach. Effect of monitoring data from different sources is also investigated.
{"title":"Real-time Fusion of Multi-Source Monitoring Data with Geotechnical Numerical Model Results using Data-driven and Physics-informed Sparse Dictionary Learning","authors":"Hua-Ming Tian, Yu Wang, K. Phoon","doi":"10.1139/cgj-2023-0457","DOIUrl":"https://doi.org/10.1139/cgj-2023-0457","url":null,"abstract":"Development of digital twins is emerging rapidly in geotechnical engineering, and it often requires real-time updating of numerical models (e.g., finite element model, FEM) using multiple sources of monitoring data (e.g., settlement and pore water pressure data). Conventional model updating, or calibration, often involves repeated executions of the numerical model, using monitoring data from a specific source or at limited spatial locations only. This leads to a critical research need of real-time model updating and predictions using a numerical model improved continuously by multi-source monitoring data. To address this need, a physics-informed machine learning method called multi-source sparse dictionary learning (MS-SDL) is proposed in this study. Originated from signal decomposition and compression, MS-SDL utilizes results from a suite of numerical models as basis functions, or dictionary atoms, and employs multi-source monitoring data to select a limited number of important atoms for predicting multiple, spatiotemporally varying geotechnical responses. As monitoring data are collected sequentially, no repeated evaluations of computational numerical models are needed, and an automatic and real-time model calibration is achieved for continuously improving model predictions. A real project in Hong Kong is presented to illustrate the proposed approach. Effect of monitoring data from different sources is also investigated.","PeriodicalId":505159,"journal":{"name":"Canadian Geotechnical Journal","volume":"53 5","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140444374","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 role of particle shape on soil mechanical response has been studied extensively especially through numerical means. The underlying micro-mechanics of how particle shape may affect the soil mechanical responses at element scale remains unclear. Systematic micro-mechanical experiments that consider in-situ tracking of the evolution of fabric during the shearing process is missing. Aided by a miniaturised triaxial apparatus and X-ray computed tomography, this study presents a series of triaxial compression on four granular soils with different particle shapes yet the same mineralogy, grading and initial density. Evolution of three-dimensional soil fabric quantifiers during shearing was captured based on 192 full-field CT images. The results revealed that the initial shearing reduced the packing density without changing the particle packing pattern, followed by particle sliding and particle rotation which redistributed the force chains and formed a new packing pattern to resist shearing, causing strain localisation and reductions in both the contact number and concentration of contacts di-rection. Fabric anisotropy increased before reaching the peak and attained the maximum value as the soil approached the critical state. Particle shape, especially when quantified by overall regularity, or other combinations of descriptors, displayed more significant linear cor-relations with critical-state parameters than by local descriptor.
颗粒形状对土壤力学响应的作用已被广泛研究，特别是通过数值方法。颗粒形状如何在元素尺度上影响土壤力学响应的基本微观力学仍不清楚。目前还没有考虑在剪切过程中对结构演变进行现场跟踪的系统微观力学实验。在微型三轴仪器和 X 射线计算机断层扫描技术的帮助下，本研究对四种颗粒形状不同但矿物成分、等级和初始密度相同的颗粒土进行了一系列三轴压缩。根据 192 幅全场 CT 图像，捕捉了剪切过程中三维土壤结构量化指标的演变。结果显示，初始剪切降低了堆积密度，但没有改变颗粒的堆积模式，随后的颗粒滑动和颗粒旋转重新分配了力链，并形成了新的堆积模式以抵抗剪切，从而导致应变局部化，并降低了接触数和接触双向的浓度。织物各向异性在达到峰值之前有所增加，并在土壤接近临界状态时达到最大值。与局部描述符相比，颗粒形状（尤其是通过整体规则性或其他描述符组合进行量化时）与临界状态参数的线性相关性更为显著。
{"title":"X-ray CT quantification of in-situ fabric evolution and shearing behaviour of granular soils of different particle shapes","authors":"Jianbin Liu, Anthony Kwan Leung, Zhenliang Jiang, Karim Kootahi, Zhongjian Zhang","doi":"10.1139/cgj-2023-0416","DOIUrl":"https://doi.org/10.1139/cgj-2023-0416","url":null,"abstract":"The role of particle shape on soil mechanical response has been studied extensively especially through numerical means. The underlying micro-mechanics of how particle shape may affect the soil mechanical responses at element scale remains unclear. Systematic micro-mechanical experiments that consider in-situ tracking of the evolution of fabric during the shearing process is missing. Aided by a miniaturised triaxial apparatus and X-ray computed tomography, this study presents a series of triaxial compression on four granular soils with different particle shapes yet the same mineralogy, grading and initial density. Evolution of three-dimensional soil fabric quantifiers during shearing was captured based on 192 full-field CT images. The results revealed that the initial shearing reduced the packing density without changing the particle packing pattern, followed by particle sliding and particle rotation which redistributed the force chains and formed a new packing pattern to resist shearing, causing strain localisation and reductions in both the contact number and concentration of contacts di-rection. Fabric anisotropy increased before reaching the peak and attained the maximum value as the soil approached the critical state. Particle shape, especially when quantified by overall regularity, or other combinations of descriptors, displayed more significant linear cor-relations with critical-state parameters than by local descriptor.","PeriodicalId":505159,"journal":{"name":"Canadian Geotechnical Journal","volume":"1 7","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139957879","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}
Centrifuge modeling allows granular flows to be simulated under stresses characteristic of full-scale flows, while maintaining repeatability. However, the impact of the Coriolis effect on the run-out behavior of dry granular flows is not fully understood. In this study, using the discrete element method (DEM), we conducted simulations of dry granular flow both with and without Coriolis (dilative and compressive) conditions to analyze the impact of the Coriolis effect on granular run-out mobility, flow structure, and granular interaction. For unsteady flows, the dilative Coriolis force increased the moving distance of the flow centroid by 60%–70% and increased the maximum kinetic energy by 5%–17%, whereas those parameters were reduced by 30% and 2%–9%, respectively, under compressive Coriolis conditions. Results showed that selecting a lower centrifugal acceleration by reducing the rotational angular velocity in physical modeling is ineffective for realizing a weaker Coriolis effect. This study established that using a larger centrifuge could mitigate the Coriolis effect, but that this outcome became less notable as the centrifugal radius increased. Additionally, we suggest a preliminary relation that could be used to correct the results of experimental granular flow final run-out distance obtained using a geotechnical centrifuge.
{"title":"Investigation of granular flow run-out behavior under dilative and compressive Coriolis conditions using DEM simulation","authors":"Bei Zhang, Wenyang Li, Yu Huang","doi":"10.1139/cgj-2022-0531","DOIUrl":"https://doi.org/10.1139/cgj-2022-0531","url":null,"abstract":"Centrifuge modeling allows granular flows to be simulated under stresses characteristic of full-scale flows, while maintaining repeatability. However, the impact of the Coriolis effect on the run-out behavior of dry granular flows is not fully understood. In this study, using the discrete element method (DEM), we conducted simulations of dry granular flow both with and without Coriolis (dilative and compressive) conditions to analyze the impact of the Coriolis effect on granular run-out mobility, flow structure, and granular interaction. For unsteady flows, the dilative Coriolis force increased the moving distance of the flow centroid by 60%–70% and increased the maximum kinetic energy by 5%–17%, whereas those parameters were reduced by 30% and 2%–9%, respectively, under compressive Coriolis conditions. Results showed that selecting a lower centrifugal acceleration by reducing the rotational angular velocity in physical modeling is ineffective for realizing a weaker Coriolis effect. This study established that using a larger centrifuge could mitigate the Coriolis effect, but that this outcome became less notable as the centrifugal radius increased. Additionally, we suggest a preliminary relation that could be used to correct the results of experimental granular flow final run-out distance obtained using a geotechnical centrifuge.","PeriodicalId":505159,"journal":{"name":"Canadian Geotechnical Journal","volume":"13 22","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140442798","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}
Michael O'Neill, Andrew Grime, M. F. Bransby, Phillip Watson, James Whelan
Drag anchors are often employed in offshore floating facility moorings. The standard drag anchor design approach is based on a deterministic Load and Resistance Factor Design (LRFD) framework that considers characteristic design ‘low’ and ‘high’ estimates of soil strength and other geotechnical parameters, combined with code-specified partial factors. A disadvantage of this approach is that the resulting anchor designs may not achieve a consistent level of reliability. This paper describes a study that addresses this limitation by developing and demonstrating a generalised drag anchor probability of failure analysis framework for inclusion in a Reliability Based Assessment (RBA) of a mooring. A feature of the study is the inclusion of consolidation and cyclic loading effects in the anchor analysis. The study highlights the benefits an RBA approach can offer to the drag anchor design process, including reduced anchor size and preloading requirements, and increased confidence in the anchor design and estimate of anchor performance. For temporarily moored facilities this approach offers the potential to exploit expanded weather windows for operations. For permanently moored floating offshore wind developments this approach may allow adoption of reduced levels of target reliability, thereby reducing costs for systems with a large number of anchors.
{"title":"A Reliability-Based Assessment Framework For Drag Anchors","authors":"Michael O'Neill, Andrew Grime, M. F. Bransby, Phillip Watson, James Whelan","doi":"10.1139/cgj-2023-0552","DOIUrl":"https://doi.org/10.1139/cgj-2023-0552","url":null,"abstract":"Drag anchors are often employed in offshore floating facility moorings. The standard drag anchor design approach is based on a deterministic Load and Resistance Factor Design (LRFD) framework that considers characteristic design ‘low’ and ‘high’ estimates of soil strength and other geotechnical parameters, combined with code-specified partial factors. A disadvantage of this approach is that the resulting anchor designs may not achieve a consistent level of reliability. This paper describes a study that addresses this limitation by developing and demonstrating a generalised drag anchor probability of failure analysis framework for inclusion in a Reliability Based Assessment (RBA) of a mooring. A feature of the study is the inclusion of consolidation and cyclic loading effects in the anchor analysis. The study highlights the benefits an RBA approach can offer to the drag anchor design process, including reduced anchor size and preloading requirements, and increased confidence in the anchor design and estimate of anchor performance. For temporarily moored facilities this approach offers the potential to exploit expanded weather windows for operations. For permanently moored floating offshore wind developments this approach may allow adoption of reduced levels of target reliability, thereby reducing costs for systems with a large number of anchors.","PeriodicalId":505159,"journal":{"name":"Canadian Geotechnical Journal","volume":"225 ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140475882","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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