Previous studies have explored using scrap rubber in constructing the ballasted track and showed tremendous potential to mitigate noise and vibration. However, its application for slab tracks has not been extensively investigated. This study intends to utilise scrap rubber in the base layer of the slab track; however, the high stress below base layer of the slab track may render its use unsuitable. The addition of scrap rubber would improve the damping performance but reduce the elastic modulus and cause excessive settlement of the track. This paper utilises an experimental programme comprising static and cyclic triaxial testing and numerical analyses to assess the suitability of four mixes, viz. mix-A (soil), mix-B (soil mixed with rubber), mix-C (polyurethane-treated soil), and mix-D (polyurethane-treated soil mixed with rubber), as a base layer in slab tracks. The laboratory investigations reveal that the best performance in terms of improved damping ratio and resilient modulus, and lowered excess pore water pressure and vertical strains are shown by mix-D. These experimental test findings were supplemented with the results from three-dimensional full-scale finite element analyses, which showed a drastic reduction in the vibration levels of the track with mix-D as a base layer instead of conventional lean-mix concrete.
{"title":"Laboratory and numerical analyses on polyurethane-scrap rubber reinforced base layer","authors":"M. A. Farooq, Sanjay Nimbalkar","doi":"10.1139/cgj-2023-0583","DOIUrl":"https://doi.org/10.1139/cgj-2023-0583","url":null,"abstract":"Previous studies have explored using scrap rubber in constructing the ballasted track and showed tremendous potential to mitigate noise and vibration. However, its application for slab tracks has not been extensively investigated. This study intends to utilise scrap rubber in the base layer of the slab track; however, the high stress below base layer of the slab track may render its use unsuitable. The addition of scrap rubber would improve the damping performance but reduce the elastic modulus and cause excessive settlement of the track. This paper utilises an experimental programme comprising static and cyclic triaxial testing and numerical analyses to assess the suitability of four mixes, viz. mix-A (soil), mix-B (soil mixed with rubber), mix-C (polyurethane-treated soil), and mix-D (polyurethane-treated soil mixed with rubber), as a base layer in slab tracks. The laboratory investigations reveal that the best performance in terms of improved damping ratio and resilient modulus, and lowered excess pore water pressure and vertical strains are shown by mix-D. These experimental test findings were supplemented with the results from three-dimensional full-scale finite element analyses, which showed a drastic reduction in the vibration levels of the track with mix-D as a base layer instead of conventional lean-mix concrete.","PeriodicalId":505159,"journal":{"name":"Canadian Geotechnical Journal","volume":"97 50","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139612662","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}
E. Lande, Stefan Ritter, Kjell Karlsrud, S. Nordal
This paper presents two case studies dealing with undesirable impacts of overburden drilling of casings for end bearing piles to bedrock. Monitored pore-water pressures and ground settlements are used to document and assess the influence from rotary percussive drilling with "down-the-hole" (DTH) hammers. The studies show that drilling with high-pressure air driven DTH hammers may cause considerable erosion and soil volume loss adjacent to the drill bit and along the casing resulting in settlements of the surrounding ground. The risk of soil volume loss increases when the drilling is carried out in erodible soils like silt and fine sands. The volume loss is found to be caused by a combined air-lift pump effect and a Venturi suction effect. Monitoring pore pressures in the vicinity of the drilling may be used to reduce soil volume loss and prevent damaging settlements. Results from drilling with water-driven DTH hammer showed significantly less ground settlements and influence on pore pressures compared to using an air-driven hammer. The study suggests that the drilling parameters flow rate and penetration rate, and the cross-sectional area of the pile casing can be combined in a non-dimensional methodology to assess the mass balance of drill cuttings when drilling with water flushing. A design framework is suggested to guide overburden drilling in urban settings to reduce potential impact on the surroundings.
{"title":"Understanding effects from overburden drilling of piles – a rational approach to reduce the impacts on the surroundings","authors":"E. Lande, Stefan Ritter, Kjell Karlsrud, S. Nordal","doi":"10.1139/cgj-2023-0404","DOIUrl":"https://doi.org/10.1139/cgj-2023-0404","url":null,"abstract":"This paper presents two case studies dealing with undesirable impacts of overburden drilling of casings for end bearing piles to bedrock. Monitored pore-water pressures and ground settlements are used to document and assess the influence from rotary percussive drilling with \"down-the-hole\" (DTH) hammers. The studies show that drilling with high-pressure air driven DTH hammers may cause considerable erosion and soil volume loss adjacent to the drill bit and along the casing resulting in settlements of the surrounding ground. The risk of soil volume loss increases when the drilling is carried out in erodible soils like silt and fine sands. The volume loss is found to be caused by a combined air-lift pump effect and a Venturi suction effect. Monitoring pore pressures in the vicinity of the drilling may be used to reduce soil volume loss and prevent damaging settlements. Results from drilling with water-driven DTH hammer showed significantly less ground settlements and influence on pore pressures compared to using an air-driven hammer. The study suggests that the drilling parameters flow rate and penetration rate, and the cross-sectional area of the pile casing can be combined in a non-dimensional methodology to assess the mass balance of drill cuttings when drilling with water flushing. A design framework is suggested to guide overburden drilling in urban settings to reduce potential impact on the surroundings.","PeriodicalId":505159,"journal":{"name":"Canadian Geotechnical Journal","volume":"120 38","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139613961","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}
Feng-Juan Tao, G. Ye, Zhen Zhang, Jie Han, Rongjun Zhang, Liu Liu
Soil arching causes stress redistribution in many earth structures, such as pile-supported embankments and buried structures. A localized cyclic surface load (e.g., footing and traffic load) would weaken the arching effect and cause structural safety at potential risk. This paper presents a series of trapdoor tests using transparent soil to investigate the degradation mechanisms of soil arching subjected to a localized cyclic surface load. The particle image velocimetry (PIV) technique was adopted to monitor the inner soil deformations during test. The test results show that soil arching under localized cyclic surface loading first degraded locally on the trapdoor center and then progressed from the center to the entire trapdoor. The soil arching degraded faster within a lower backfill, on a wider trapdoor, and under a higher load frequency of localized surface loading. Owing to the volumetric expansion during trapdoor movement, the average vertical stress with soil arching increased faster under localized surface loading than that without soil arching. After full degradation of soil arching, the stress increment and vertical displacement contours with and without arching effect gradually tended to be similar. Finally, an empirical method was proposed to predict the soil arching ratio under localized cyclic surface loading.
{"title":"Degradation Mechanisms of Soil Arching under a Localized Cyclic Surface Loading","authors":"Feng-Juan Tao, G. Ye, Zhen Zhang, Jie Han, Rongjun Zhang, Liu Liu","doi":"10.1139/cgj-2023-0150","DOIUrl":"https://doi.org/10.1139/cgj-2023-0150","url":null,"abstract":"Soil arching causes stress redistribution in many earth structures, such as pile-supported embankments and buried structures. A localized cyclic surface load (e.g., footing and traffic load) would weaken the arching effect and cause structural safety at potential risk. This paper presents a series of trapdoor tests using transparent soil to investigate the degradation mechanisms of soil arching subjected to a localized cyclic surface load. The particle image velocimetry (PIV) technique was adopted to monitor the inner soil deformations during test. The test results show that soil arching under localized cyclic surface loading first degraded locally on the trapdoor center and then progressed from the center to the entire trapdoor. The soil arching degraded faster within a lower backfill, on a wider trapdoor, and under a higher load frequency of localized surface loading. Owing to the volumetric expansion during trapdoor movement, the average vertical stress with soil arching increased faster under localized surface loading than that without soil arching. After full degradation of soil arching, the stress increment and vertical displacement contours with and without arching effect gradually tended to be similar. Finally, an empirical method was proposed to predict the soil arching ratio under localized cyclic surface loading.","PeriodicalId":505159,"journal":{"name":"Canadian Geotechnical Journal","volume":" 438","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139617803","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}
Q. Zhai, Ruize Zhang, H. Rahardjo, A. Satyanaga, Guoliang Dai, Weiming Gong, Xue-Liang Zhao, Chua Yuan Shen
Small strain shear modulus (G) is an essential parameter for many geotechnical analyses. Most of shallow foundations are constructed in an unsaturated soil and the shear modulus of the unsaturated soil fluctuates because of the precipitation, evaporation, and rising of ground water table. In this paper, a new mathematical model is proposed for the estimation of the shear modulus function (SMF), Gunsat, which defines the relationship between small margin modulus of unsaturated soil and matric suction. In the proposed model, the soil-water characteristic curve (SWCC) in the form of the degree of saturation is used as the input information. There are additional two parameters named n and C, which can be calibrated with the experimental data, are adopted in the proposed model. The estimated results show good agreement with the experimental data from literature. The proposed method can be used to track the tendency of Gunsat and minimize the data points from the laboratory tests.
小应变剪切模量（G）是许多岩土工程分析的重要参数。大多数浅层地基都建在非饱和土壤中，而非饱和土壤的剪切模量会因降水、蒸发和地下水位上升而波动。本文提出了一个新的数学模型来估算剪切模量函数（SMF）Gunsat，它定义了非饱和土壤小边缘模量与母吸力之间的关系。在提议的模型中，饱和度形式的土壤水特征曲线 (SWCC) 被用作输入信息。此外，模型还采用了名为 n 和 C 的两个参数，这两个参数可根据实验数据进行校准。估计结果与文献中的实验数据显示出良好的一致性。建议的方法可用于跟踪 Gunsat 的趋势，并将实验室测试的数据点最小化。
{"title":"A new mathematical model for the estimation of shear modulus for unsaturated compacted soils","authors":"Q. Zhai, Ruize Zhang, H. Rahardjo, A. Satyanaga, Guoliang Dai, Weiming Gong, Xue-Liang Zhao, Chua Yuan Shen","doi":"10.1139/cgj-2023-0409","DOIUrl":"https://doi.org/10.1139/cgj-2023-0409","url":null,"abstract":"Small strain shear modulus (G) is an essential parameter for many geotechnical analyses. Most of shallow foundations are constructed in an unsaturated soil and the shear modulus of the unsaturated soil fluctuates because of the precipitation, evaporation, and rising of ground water table. In this paper, a new mathematical model is proposed for the estimation of the shear modulus function (SMF), Gunsat, which defines the relationship between small margin modulus of unsaturated soil and matric suction. In the proposed model, the soil-water characteristic curve (SWCC) in the form of the degree of saturation is used as the input information. There are additional two parameters named n and C, which can be calibrated with the experimental data, are adopted in the proposed model. The estimated results show good agreement with the experimental data from literature. The proposed method can be used to track the tendency of Gunsat and minimize the data points from the laboratory tests.","PeriodicalId":505159,"journal":{"name":"Canadian Geotechnical Journal","volume":" November","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139617732","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}
C.W.W. Ng, Yi Le, Sina Baghbanrezvan, Paul Van Laak
Steel catenary risers (SCRs) provide a cost-effective solution for deepwater oil and gas production. However, SCRs are susceptible to potential fatigue failure due to the cyclic motions of floating platforms. Previous studies on the physical modelling of cyclic SCR–seabed interactions have primarily focused on either the continuous cyclic motion of an SCR or a single rest period between two SCR motion packets. However, our understanding of the development of seabed trenches and excess pore pressure and their effects on SCR fatigue during multiple episodes of SCR motion and soil reconsolidation remains limited. This study presents a newly developed model container capable of modelling three-dimensional (3D) SCR motions including heave, surge, sway, and vortex-induced vibration (VIV) in a geotechnical centrifuge. A centrifuge test is conducted to investigate the vertical cyclic SCR–seabed interaction, considering five vertical cyclic motion packets with intervening periods of reconsolidation. The results indicate that ignoring the effects of reconsolidation leads to an overestimation of the fatigue life of an SCR. In this test, the SCR fatigue life is reduced by 18%–23% after five episodic SCR motion packets and intervening reconsolidation.
{"title":"A novel three-dimensional SCR motion simulator for modelling the catenary riser–seabed interaction in a centrifuge","authors":"C.W.W. Ng, Yi Le, Sina Baghbanrezvan, Paul Van Laak","doi":"10.1139/cgj-2023-0406","DOIUrl":"https://doi.org/10.1139/cgj-2023-0406","url":null,"abstract":"Steel catenary risers (SCRs) provide a cost-effective solution for deepwater oil and gas production. However, SCRs are susceptible to potential fatigue failure due to the cyclic motions of floating platforms. Previous studies on the physical modelling of cyclic SCR–seabed interactions have primarily focused on either the continuous cyclic motion of an SCR or a single rest period between two SCR motion packets. However, our understanding of the development of seabed trenches and excess pore pressure and their effects on SCR fatigue during multiple episodes of SCR motion and soil reconsolidation remains limited. This study presents a newly developed model container capable of modelling three-dimensional (3D) SCR motions including heave, surge, sway, and vortex-induced vibration (VIV) in a geotechnical centrifuge. A centrifuge test is conducted to investigate the vertical cyclic SCR–seabed interaction, considering five vertical cyclic motion packets with intervening periods of reconsolidation. The results indicate that ignoring the effects of reconsolidation leads to an overestimation of the fatigue life of an SCR. In this test, the SCR fatigue life is reduced by 18%–23% after five episodic SCR motion packets and intervening reconsolidation.","PeriodicalId":505159,"journal":{"name":"Canadian Geotechnical Journal","volume":" 9","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139617049","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}
Tengfei Wang, Q. Luo, M. H. El Naggar, Hongyang Liu, Kaiwen Liu
Counterweight retaining walls (CRWs) are a variant of gravity retaining walls that feature a pressure relief platform (RP) on the backfill side to reduce total earth pressure, offering a cost-effective option compared to traditional forms. However, the intricate interactions between CRWs and backfill, coupled with the lack of clear design guidelines, have restricted their use. This study examines the behavior of CRWs in translation mode using three different centrifuge model tests, each with varying fill heights. Observations show a slightly concave slip surface through the wall heel, and a nearly planar slip surface extending from the edge of the RP to the back of the wall in an active limit state. Backfill movement can be classified into translation, sliding, and stable zones. Earth pressure distribution on the upper wall follows a trapezoidal pattern, whereas the pressure on the lower wall exhibits a triangular distribution. Earth pressure on the RP is approximately linear, peaking near the RP's edge. Introducing a friction angle mobilization factor for the potential first slip surface improves accuracy in calculating earth pressure. The tests were replicated to validate the analytical model for earth pressure calculations, using the adaptive finite-element limit analysis method.
配重挡土墙（CRW）是重力式挡土墙的一种变体，其特点是在回填土一侧设置一个泄压平台（RP），以降低总土层压力，与传统形式相比，它是一种具有成本效益的选择。然而，CRW 与回填土之间错综复杂的相互作用，再加上缺乏明确的设计准则，限制了其使用。本研究使用三种不同的离心机模型试验来研究平移模式下的 CRW 行为，每种试验的填土高度各不相同。观察结果表明，在活动极限状态下，通过墙跟的滑移面略微凹陷，而从 RP 边缘延伸到墙背面的滑移面接近平面。回填运动可分为平移、滑动和稳定区。上墙的土压力分布呈梯形，而下墙的土压力分布呈三角形。RP 上的土压力近似线性，在 RP 边缘附近达到峰值。为潜在的第一滑移面引入摩擦角动员系数可提高土压力计算的准确性。通过重复试验，利用自适应有限元极限分析方法验证了土压力计算的分析模型。
{"title":"Centrifuge and analytical modeling of counterweight retaining walls under translation mode","authors":"Tengfei Wang, Q. Luo, M. H. El Naggar, Hongyang Liu, Kaiwen Liu","doi":"10.1139/cgj-2023-0124","DOIUrl":"https://doi.org/10.1139/cgj-2023-0124","url":null,"abstract":"Counterweight retaining walls (CRWs) are a variant of gravity retaining walls that feature a pressure relief platform (RP) on the backfill side to reduce total earth pressure, offering a cost-effective option compared to traditional forms. However, the intricate interactions between CRWs and backfill, coupled with the lack of clear design guidelines, have restricted their use. This study examines the behavior of CRWs in translation mode using three different centrifuge model tests, each with varying fill heights. Observations show a slightly concave slip surface through the wall heel, and a nearly planar slip surface extending from the edge of the RP to the back of the wall in an active limit state. Backfill movement can be classified into translation, sliding, and stable zones. Earth pressure distribution on the upper wall follows a trapezoidal pattern, whereas the pressure on the lower wall exhibits a triangular distribution. Earth pressure on the RP is approximately linear, peaking near the RP's edge. Introducing a friction angle mobilization factor for the potential first slip surface improves accuracy in calculating earth pressure. The tests were replicated to validate the analytical model for earth pressure calculations, using the adaptive finite-element limit analysis method.","PeriodicalId":505159,"journal":{"name":"Canadian Geotechnical Journal","volume":" 5","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139616799","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}
Po Cheng, Fei Liu, Xuejian Chen, Yuhe Zhang, Kai Yao
As the offshore industry moves into deeper water, helical piles are emerging as a potential foundation solution option. A large number of studies have been published to explore the installation torque-capacity correlation. However, in most previous studies, the inherent spatial variability of soil strength was neglected. The present research explores the installation and extraction behavior of helical piles through a large deformation random finite element method. A strain-softening soil constitutive model proposed in past literature is employed to model the soil strength remoulding. The validity of the numerical model used to simulate the installation process and the subsequent uplift process is verified by the installation torque and the uplift capacity, respectively. The spatial variation of soil strength is modeled using random field, and then a series of Monte Carlo simulations are performed to investigate the torque-capacity correlation of the helical piles under different random realizations. The analysis results show that for the helical piles with different penetration depths, the spatially random soil strength markedly affects the torque-capacity correlation. Moreover, a probabilistic analysis of the torque-capacity correlation is conducted, which may be of great interest to engineering practitioners in the design method of the helical pile.
{"title":"Estimation of the installation torque-capacity correlation of helical pile considering spatially variable clays","authors":"Po Cheng, Fei Liu, Xuejian Chen, Yuhe Zhang, Kai Yao","doi":"10.1139/cgj-2023-0331","DOIUrl":"https://doi.org/10.1139/cgj-2023-0331","url":null,"abstract":"As the offshore industry moves into deeper water, helical piles are emerging as a potential foundation solution option. A large number of studies have been published to explore the installation torque-capacity correlation. However, in most previous studies, the inherent spatial variability of soil strength was neglected. The present research explores the installation and extraction behavior of helical piles through a large deformation random finite element method. A strain-softening soil constitutive model proposed in past literature is employed to model the soil strength remoulding. The validity of the numerical model used to simulate the installation process and the subsequent uplift process is verified by the installation torque and the uplift capacity, respectively. The spatial variation of soil strength is modeled using random field, and then a series of Monte Carlo simulations are performed to investigate the torque-capacity correlation of the helical piles under different random realizations. The analysis results show that for the helical piles with different penetration depths, the spatially random soil strength markedly affects the torque-capacity correlation. Moreover, a probabilistic analysis of the torque-capacity correlation is conducted, which may be of great interest to engineering practitioners in the design method of the helical pile.","PeriodicalId":505159,"journal":{"name":"Canadian Geotechnical Journal","volume":" 12","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139624351","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}
Lateritic clay has distinct properties from other clays due to its high sesquioxide content. Its stiffness characteristics have not been well understood, especially when the soil is unsaturated and anisotropic. This study investigated the stiffness characteristics of compacted lateritic clay through suction-controlled triaxial compression tests equipped with local strain measurements. Both vertically and horizontally cut specimens were tested to determine the evolution of stiffness anisotropy during shearing. Three suctions (0, 10 and 150 kPa) and two confining pressures (50 and 200 kPa) were considered. When strains are relatively small (e.g., less than 0.2%), the secant Young’s modulus Esec of vertical specimens is consistently higher than that of horizontal specimens at all suctions and stresses due to the inherent anisotropic structure. The degree of anisotropy increases with increasing suction since suction enhances the stiffness significantly more in vertical specimens than in horizontal specimens. This behaviour may be due to an enhanced force chain in the vertical direction during shearing. As strains increase, the degradation of Esec normalized by the maximum Young’s modulus E0 is almost independent of suction and anisotropy. Lateritic clay has a higher degradation rate than other clays with a similar plasticity index because of its aggregated microstructure.
{"title":"Suction and anisotropy effects on the stiffness characteristics of a compacted lateritic clay from small to large strains","authors":"O. T. Bentil, Chao Zhou","doi":"10.1139/cgj-2023-0295","DOIUrl":"https://doi.org/10.1139/cgj-2023-0295","url":null,"abstract":"Lateritic clay has distinct properties from other clays due to its high sesquioxide content. Its stiffness characteristics have not been well understood, especially when the soil is unsaturated and anisotropic. This study investigated the stiffness characteristics of compacted lateritic clay through suction-controlled triaxial compression tests equipped with local strain measurements. Both vertically and horizontally cut specimens were tested to determine the evolution of stiffness anisotropy during shearing. Three suctions (0, 10 and 150 kPa) and two confining pressures (50 and 200 kPa) were considered. When strains are relatively small (e.g., less than 0.2%), the secant Young’s modulus Esec of vertical specimens is consistently higher than that of horizontal specimens at all suctions and stresses due to the inherent anisotropic structure. The degree of anisotropy increases with increasing suction since suction enhances the stiffness significantly more in vertical specimens than in horizontal specimens. This behaviour may be due to an enhanced force chain in the vertical direction during shearing. As strains increase, the degradation of Esec normalized by the maximum Young’s modulus E0 is almost independent of suction and anisotropy. Lateritic clay has a higher degradation rate than other clays with a similar plasticity index because of its aggregated microstructure.","PeriodicalId":505159,"journal":{"name":"Canadian Geotechnical Journal","volume":" 23","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139624549","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}
Bi-directional static loading tests were conducted on two, strain-gage instrumented barrettes installed to 72 m depth in HoChiMinhCity, Vietnam. The barrettes were to support a 16 storey building with 5 basements. The soil profile comprised layers of medium coarse to fine sand, medium clay, firm to stiff clayey soil, and dense sandy silt. The region is experiencing an ongoing land subsidence affecting the upper about 40 m of soil and, on average in the city, the ground surface is currently settling 16 mm/year. The test records were processed by means of effective stress analysis to provide the axial pile force distribution, load transfer functions, and equivalent head-down load-movement curve. The analysis was then used to obtain the equivalent pile-head load-movement response adjusted to the planned 22 m deep basement excavation. Load transfer functions were back-calculated from the test records and indicate that the construction will show somewhat large load-transfer movement. However, because the neutral plane will be below the subsiding layers, below 40 m depth, downdrag is not expected to affect the building. The load response of the barrettes is compared to the results of a BD loading test on a 1.8 m diameter bored pile at an adjacent project.
{"title":"Bidirectional static loading tests on barrette piles. A case history from Ho Chi Minh City, Vietnam","authors":"Tan Nguyen, B. Fellenius","doi":"10.1139/cgj-2023-0098","DOIUrl":"https://doi.org/10.1139/cgj-2023-0098","url":null,"abstract":"Bi-directional static loading tests were conducted on two, strain-gage instrumented barrettes installed to 72 m depth in HoChiMinhCity, Vietnam. The barrettes were to support a 16 storey building with 5 basements. The soil profile comprised layers of medium coarse to fine sand, medium clay, firm to stiff clayey soil, and dense sandy silt. The region is experiencing an ongoing land subsidence affecting the upper about 40 m of soil and, on average in the city, the ground surface is currently settling 16 mm/year. The test records were processed by means of effective stress analysis to provide the axial pile force distribution, load transfer functions, and equivalent head-down load-movement curve. The analysis was then used to obtain the equivalent pile-head load-movement response adjusted to the planned 22 m deep basement excavation. Load transfer functions were back-calculated from the test records and indicate that the construction will show somewhat large load-transfer movement. However, because the neutral plane will be below the subsiding layers, below 40 m depth, downdrag is not expected to affect the building. The load response of the barrettes is compared to the results of a BD loading test on a 1.8 m diameter bored pile at an adjacent project.","PeriodicalId":505159,"journal":{"name":"Canadian Geotechnical Journal","volume":"5 7","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139439326","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}
Changjie Zheng, Jingquan Yang, G. Kouretzis, Xuanming Ding
This paper presents a study on the effect of the degree of saturation of the foundation soil on the vertical seismic response of end-bearing piles subjected to P-waves. The research focuses on nearly-saturated soil, where the air phase is not continuous and air bubbles are dissolved in the pore water, thus can be treated as two-phase material. The response of the two-phase soil-pile system is quantified by means of a rigorous coupled hydromechanical model, which is based on Biot’s theory for poroelastic media and treats the air bubbles-pore water mixture as homogeneous fluid obeying Boyle’s law. Numerical results are used to illustrate the influence of the degree of saturation of the soil layer on the seismic strong motion transferred to the pile head i.e. the capacity of piles to filter seismic wave energy. This work bridges the gap between single-phase and two-phase saturated soil models, which predict profoundly different pile head displacements at incident wave frequencies of practical interest, and elucidates the mechanisms that lead to these differences.
本文研究了地基土的饱和度对承受 P 波的端承桩垂直地震响应的影响。研究的重点是近饱和土，其中的气相并不连续，气泡溶解在孔隙水中，因此可视为两相材料。两相土壤-桩系统的响应通过严格的耦合水力机械模型进行量化，该模型以孔弹性介质的 Biot 理论为基础，将气泡-孔水混合物视为服从波义耳定律的均质流体。数值结果用于说明土层饱和度对传递到桩头的地震强运动的影响，即桩头过滤地震波能量的能力。单相饱和土模型和两相饱和土模型预测的桩头位移在实际应用中的入射波频率存在很大差异，这项研究填补了这两者之间的空白，并阐明了导致这些差异的机理。
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