In this paper, a total number of 363 rock-socket load tests are compiled into a database – DUT/PileROC/363 and analyzed in a consistent manner. This database is used to evaluate the variability of predictions of mobilized resistances (fs and qb), loads Qa at settlements w = 5–20 mm and 0.5%–2% of socket diameter, and Q-w curves. For fs, qb and Qa, the results are characterized as the mean and coefficient of variation (COV) of the ratio of measured over predicted values. It is observed that (1) both shaft shearing and end bearing can be mobilized at small displacements when good construction and inspection procedures are followed, (2) the majority of empirical models for fs and qb are too simplistic and the resulting predictions are highly dispersive (COV > 0.6), (3) the prediction quality does not necessarily improve with an increased level of model sophistication, (4) rock mass modulus Em is crucial for predicting Qa and Q-w curves, (5) predictions of Qa by one nonlinear and two side-slip design methods are of medium dispersion (COV = 0.3–0.6), and (6) only the nonlinear design method produces Q-w curves that resemble the shape of measured curves in load tests.
{"title":"Development and Use of Axial Load Test Databases for Analysis and Design of Soft Rock Sockets","authors":"Xiaoyong Ye, Chong Tang, K. Phoon, Jinbo Chen","doi":"10.1139/cgj-2024-0155","DOIUrl":"https://doi.org/10.1139/cgj-2024-0155","url":null,"abstract":"In this paper, a total number of 363 rock-socket load tests are compiled into a database – DUT/PileROC/363 and analyzed in a consistent manner. This database is used to evaluate the variability of predictions of mobilized resistances (fs and qb), loads Qa at settlements w = 5–20 mm and 0.5%–2% of socket diameter, and Q-w curves. For fs, qb and Qa, the results are characterized as the mean and coefficient of variation (COV) of the ratio of measured over predicted values. It is observed that (1) both shaft shearing and end bearing can be mobilized at small displacements when good construction and inspection procedures are followed, (2) the majority of empirical models for fs and qb are too simplistic and the resulting predictions are highly dispersive (COV > 0.6), (3) the prediction quality does not necessarily improve with an increased level of model sophistication, (4) rock mass modulus Em is crucial for predicting Qa and Q-w curves, (5) predictions of Qa by one nonlinear and two side-slip design methods are of medium dispersion (COV = 0.3–0.6), and (6) only the nonlinear design method produces Q-w curves that resemble the shape of measured curves in load tests.","PeriodicalId":9382,"journal":{"name":"Canadian Geotechnical Journal","volume":null,"pages":null},"PeriodicalIF":3.6,"publicationDate":"2024-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141270281","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jiahao Wang, Li Shi, Honglei Sun, Yuanqiang Cai, Yanming Yu
Canadian Geotechnical Journal, Ahead of Print. Vacuum preloading is a commonly adopted method for improving soft ground. During the preloading period, the applied vacuum pressure is constant or multistaged, implying that the vacuum pump must work continuously with constant or increasing operating power. To reduce the energy consumption of the vacuum pump, a new loading strategy of cyclic vacuum loading was proposed in this study, whereby the pump is periodically switched on and off, and hence the vacuum pressure ascends and descends accordingly. To guide the design of cyclic vacuum preloading, a large-strain radial consolidation theory incorporating the shifting of the consolidation status of ground soil from normally consolidated to overconsolidated (and vice versa) was established in the present study. Based on the established theory, the treatment effects of cyclic vacuum loading can be quantitatively determined, including the ground settlement and the degree of consolidation, while the energy consumption can be simply determined by multiplying the power by the operating time of the vacuum pump, which works only during the ascending stage of cyclic vacuum pressure. Two cases of the cyclic vacuum preloading strategy were evaluated herein, that is, the complete cyclic vacuum loading and combined cyclic/constant vacuum loading cases. Finally, experimental tests were conducted to demonstrate the energy-saving effect of cyclic vacuum preloading. Compared to the conventional vacuum preloading strategy (i.e., constant vacuum pressure), the energy consumption of the cyclic vacuum loading strategy can be drastically reduced (80% reduction), while the treatment effects remain basically unaffected.
{"title":"An energy-saving loading strategy: cyclic vacuum preloading treatment of soft ground","authors":"Jiahao Wang, Li Shi, Honglei Sun, Yuanqiang Cai, Yanming Yu","doi":"10.1139/cgj-2023-0120","DOIUrl":"https://doi.org/10.1139/cgj-2023-0120","url":null,"abstract":"Canadian Geotechnical Journal, Ahead of Print. <br/> Vacuum preloading is a commonly adopted method for improving soft ground. During the preloading period, the applied vacuum pressure is constant or multistaged, implying that the vacuum pump must work continuously with constant or increasing operating power. To reduce the energy consumption of the vacuum pump, a new loading strategy of cyclic vacuum loading was proposed in this study, whereby the pump is periodically switched on and off, and hence the vacuum pressure ascends and descends accordingly. To guide the design of cyclic vacuum preloading, a large-strain radial consolidation theory incorporating the shifting of the consolidation status of ground soil from normally consolidated to overconsolidated (and vice versa) was established in the present study. Based on the established theory, the treatment effects of cyclic vacuum loading can be quantitatively determined, including the ground settlement and the degree of consolidation, while the energy consumption can be simply determined by multiplying the power by the operating time of the vacuum pump, which works only during the ascending stage of cyclic vacuum pressure. Two cases of the cyclic vacuum preloading strategy were evaluated herein, that is, the complete cyclic vacuum loading and combined cyclic/constant vacuum loading cases. Finally, experimental tests were conducted to demonstrate the energy-saving effect of cyclic vacuum preloading. Compared to the conventional vacuum preloading strategy (i.e., constant vacuum pressure), the energy consumption of the cyclic vacuum loading strategy can be drastically reduced (80% reduction), while the treatment effects remain basically unaffected.","PeriodicalId":9382,"journal":{"name":"Canadian Geotechnical Journal","volume":null,"pages":null},"PeriodicalIF":3.6,"publicationDate":"2024-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141255893","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Elastic shear moduli of soil at various temperatures and suctions are important for analysing the serviceability limit state of energy piles and many other structures. Up to now, however, the coupled effects of temperature and suction on elastic shear modulus and the stiffness anisotropy, have not been well understood. This experimental study investigated the anisotropic elastic shear modulus of a compacted lateritic clay. A temperature and suction-controlled triaxial apparatus equipped with bender element probes and local strain measurements was used. Soil suctions from 0 to 300 kPa, and a temperature range of 5 to 40ºC were applied. The results at saturated and unsaturated conditions consistently reveal that the shear modulus is smaller after heating at a given stress and suction. Several mechanisms may contribute to this thermal-induced reduction in shear modulus, such as the heating-induced reduction of interparticle force and air-water surface tension. Moreover, the reduction in shear modulus upon heating depends on the shear plane and the degree of anisotropy changes.
{"title":"Coupled effects of temperature and suction on the anisotropic elastic shear moduli of unsaturated soil","authors":"O. T. Bentil, Kai Liu, Chao Zhou","doi":"10.1139/cgj-2023-0757","DOIUrl":"https://doi.org/10.1139/cgj-2023-0757","url":null,"abstract":"Elastic shear moduli of soil at various temperatures and suctions are important for analysing the serviceability limit state of energy piles and many other structures. Up to now, however, the coupled effects of temperature and suction on elastic shear modulus and the stiffness anisotropy, have not been well understood. This experimental study investigated the anisotropic elastic shear modulus of a compacted lateritic clay. A temperature and suction-controlled triaxial apparatus equipped with bender element probes and local strain measurements was used. Soil suctions from 0 to 300 kPa, and a temperature range of 5 to 40ºC were applied. The results at saturated and unsaturated conditions consistently reveal that the shear modulus is smaller after heating at a given stress and suction. Several mechanisms may contribute to this thermal-induced reduction in shear modulus, such as the heating-induced reduction of interparticle force and air-water surface tension. Moreover, the reduction in shear modulus upon heating depends on the shear plane and the degree of anisotropy changes.","PeriodicalId":9382,"journal":{"name":"Canadian Geotechnical Journal","volume":null,"pages":null},"PeriodicalIF":3.6,"publicationDate":"2024-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141112507","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Conventional empirical equations for soil properties prediction tend to be site-specific, exhibiting poor reliability and accuracy. Meanwhile, alternative data-driven methods require large datasets for training. To address these issues, this study proposed a novel multifidelity residual neural-network-based Gaussian process (MR-NNGP) modelling framework. A soil property low-fidelity (LF) prediction model is first trained using abundant LF data collected from worldwide sites for generating preliminary estimation. A high-fidelity (HF) model is subsequently trained on sparse HF data from the specific site of interest for calibrating the LF model to make quasi-site-specific predictions. An infinitely wide NN-inspired NNGP is adopted as the baseline algorithm for training LF and HF models. The compression index of clays is selected as an example to examine the capability of the proposed MR-NNGP. The results indicate that the compression index of clays can be well captured by MR-NNGP, exhibiting superior accuracy and reliability compared with one-shot training without using MR modelling and other baseline algorithms such as GP. The MR-NNGP framework alleviates data dependency and improves model performance through hierarchical modelling on relatively simple correlations using a superior algorithm. Unified LF data and efficient hyper-parameter optimization indicate the flexibility for broader applications in various sites worldwide.
{"title":"Multifidelity-based Gaussian process for quasi-site-specific probabilistic prediction of soil properties","authors":"Geng-Fu He, Pin Zhang, Zhen-Yu Yin, Siang Huat Goh","doi":"10.1139/cgj-2023-0641","DOIUrl":"https://doi.org/10.1139/cgj-2023-0641","url":null,"abstract":"Conventional empirical equations for soil properties prediction tend to be site-specific, exhibiting poor reliability and accuracy. Meanwhile, alternative data-driven methods require large datasets for training. To address these issues, this study proposed a novel multifidelity residual neural-network-based Gaussian process (MR-NNGP) modelling framework. A soil property low-fidelity (LF) prediction model is first trained using abundant LF data collected from worldwide sites for generating preliminary estimation. A high-fidelity (HF) model is subsequently trained on sparse HF data from the specific site of interest for calibrating the LF model to make quasi-site-specific predictions. An infinitely wide NN-inspired NNGP is adopted as the baseline algorithm for training LF and HF models. The compression index of clays is selected as an example to examine the capability of the proposed MR-NNGP. The results indicate that the compression index of clays can be well captured by MR-NNGP, exhibiting superior accuracy and reliability compared with one-shot training without using MR modelling and other baseline algorithms such as GP. The MR-NNGP framework alleviates data dependency and improves model performance through hierarchical modelling on relatively simple correlations using a superior algorithm. Unified LF data and efficient hyper-parameter optimization indicate the flexibility for broader applications in various sites worldwide.","PeriodicalId":9382,"journal":{"name":"Canadian Geotechnical Journal","volume":null,"pages":null},"PeriodicalIF":3.6,"publicationDate":"2024-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141111327","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper presents a comprehensive field investigation on a large-scale deep basement excavation in Shanghai soft soil propped by a multi-support system. Because of its large size, irregular shape, and different excavation depths, the excavation site was divided into Zone A and Zone B to optimize the construction process and improve the construction efficiency. The excavation was constructed using the “bottom-up” (BU) method following the principles of stratification and zone excavation. A notable innovation in this project is the implementation of three different support sub-systems as a multi-support system to accommodate different deformation requirements in different areas. The excavation was densely instrumented to monitor the behaviors of retaining walls, columns, axial forces of struts, and surrounding ground throughout the whole construction process. The wall deformation and ground surface settlement of the three support sub-systems are comprehensively compared to investigate the performances of the three support sub-systems. The comparison of the corner-effect envelope summarized from nine reported cases indicates that the multi-support system can effectively alleviate the spatial corner effects of the excavation. The zoned construction technique in conjunction with the multi-support system presented in this case study provides an efficient and economic approach for large-scale deep excavation in soft soils.
本文介绍了对采用多支撑系统支撑的上海软土地区大型深层地下室开挖的综合实地调查。由于开挖场地面积大、形状不规则、开挖深度不同，为优化施工工艺、提高施工效率，开挖场地被划分为 A 区和 B 区。开挖采用 "自下而上"（BU）的方法，遵循分层和分区开挖的原则。该项目的一个显著创新是采用三个不同的支撑子系统作为多支撑系统，以适应不同区域的不同变形要求。在整个施工过程中，开挖现场安装了密集的仪器，以监测挡土墙、支柱、支撑轴力和周围地面的行为。综合比较了三种支撑子系统的墙体变形和地表沉降，以研究三种支撑子系统的性能。从九个报告案例中总结出的转角效应包络对比表明，多支撑系统能有效缓解开挖的空间转角效应。本案例研究提出的分区施工技术与多支撑系统相结合，为在软土中进行大规模深层开挖提供了一种高效、经济的方法。
{"title":"Performances of a Large-scale Deep Excavation with Multi-support Types and Zoned Excavation Technique in Shanghai Soft Soil","authors":"Yingjie Jing, Lin Li, Jingpei Li, Haohua Chen","doi":"10.1139/cgj-2023-0719","DOIUrl":"https://doi.org/10.1139/cgj-2023-0719","url":null,"abstract":"This paper presents a comprehensive field investigation on a large-scale deep basement excavation in Shanghai soft soil propped by a multi-support system. Because of its large size, irregular shape, and different excavation depths, the excavation site was divided into Zone A and Zone B to optimize the construction process and improve the construction efficiency. The excavation was constructed using the “bottom-up” (BU) method following the principles of stratification and zone excavation. A notable innovation in this project is the implementation of three different support sub-systems as a multi-support system to accommodate different deformation requirements in different areas. The excavation was densely instrumented to monitor the behaviors of retaining walls, columns, axial forces of struts, and surrounding ground throughout the whole construction process. The wall deformation and ground surface settlement of the three support sub-systems are comprehensively compared to investigate the performances of the three support sub-systems. The comparison of the corner-effect envelope summarized from nine reported cases indicates that the multi-support system can effectively alleviate the spatial corner effects of the excavation. The zoned construction technique in conjunction with the multi-support system presented in this case study provides an efficient and economic approach for large-scale deep excavation in soft soils.","PeriodicalId":9382,"journal":{"name":"Canadian Geotechnical Journal","volume":null,"pages":null},"PeriodicalIF":3.6,"publicationDate":"2024-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141109716","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The construction of basement walls using discontinuous staged berms is based on excavating the central zone of a lot and leaving a lateral berm – which is then removed in phases with unexcavated sections (buttresses) remaining until a concrete wall is completed in the excavated areas. It is a commonly used technique in many nations, but its use is unsupported by regulations or scientific studies. This paper addresses the need for a analysis of this technique and makes a study of the geotechnical parameters of the subsoils where it is applied, as well as the commonly used practices. The research involved over 4000 finite element method calculations integrating geotechnical parameters with construction geometry. The results have enabled the preparation of four stability design charts based on linear polynomial surface adjustment for two project scenarios: with and without surcharge load. This paper proposes the use of these stability design charts for staged bermed excavations in a broad spectrum of soil types and the incorporation of a designer-defined safety level to ensure temporary stability. Additional charts are provided to assess the safety factor of projects once the geometries and geotechnical parameters of the subsoil are known.
{"title":"Design stability charts for construction procedure of basement walls using staged bermed excavation: a parametric study","authors":"M. Cano, J. L. Pastor, A. Riquelme, Roberto Tomás","doi":"10.1139/cgj-2023-0535","DOIUrl":"https://doi.org/10.1139/cgj-2023-0535","url":null,"abstract":"The construction of basement walls using discontinuous staged berms is based on excavating the central zone of a lot and leaving a lateral berm – which is then removed in phases with unexcavated sections (buttresses) remaining until a concrete wall is completed in the excavated areas. It is a commonly used technique in many nations, but its use is unsupported by regulations or scientific studies. This paper addresses the need for a analysis of this technique and makes a study of the geotechnical parameters of the subsoils where it is applied, as well as the commonly used practices. The research involved over 4000 finite element method calculations integrating geotechnical parameters with construction geometry. The results have enabled the preparation of four stability design charts based on linear polynomial surface adjustment for two project scenarios: with and without surcharge load. This paper proposes the use of these stability design charts for staged bermed excavations in a broad spectrum of soil types and the incorporation of a designer-defined safety level to ensure temporary stability. Additional charts are provided to assess the safety factor of projects once the geometries and geotechnical parameters of the subsoil are known.","PeriodicalId":9382,"journal":{"name":"Canadian Geotechnical Journal","volume":null,"pages":null},"PeriodicalIF":3.6,"publicationDate":"2024-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140982251","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Foam is found to be a special fluid (i.e., gas divided by liquid film) that exists in municipal solid waste (MSW) landfills. As a disconnected phase, the unsaturated flow behavior of foam is significantly different from that of gas in connected phase. In this study, the difference between foam flow and gas flow was characterized through displacement tests in the MSW columns. Resistance factor, which is defined as the ratio of steady pressure drop between foam displacement and gas displacement, is employed to characterize this difference. The effects of foam quality, void ratio, and particle size on resistance factor were studied. The unsaturated permeability curves of foams generated by leachate samples at different depths were measured. The leachate at the middle layer has low surface tension to produce strong foam, while the leachate at the top and bottom layers has high surface tension to produce weak foam. The unsaturated permeabilities of weak foam and strong foam were about 1 and 2 orders of magnitude smaller than that of gas, respectively. The reduction in waste void ratio decreased the resistance factor as the excessive shearing effect in small pores would cause the foam to collapse.
{"title":"Experimental comparison of foam flow and gas flow in municipal solid waste","authors":"Jie Hu, Xiaobing Xu, Meng Meng, Wenjie Xu","doi":"10.1139/cgj-2023-0620","DOIUrl":"https://doi.org/10.1139/cgj-2023-0620","url":null,"abstract":"Foam is found to be a special fluid (i.e., gas divided by liquid film) that exists in municipal solid waste (MSW) landfills. As a disconnected phase, the unsaturated flow behavior of foam is significantly different from that of gas in connected phase. In this study, the difference between foam flow and gas flow was characterized through displacement tests in the MSW columns. Resistance factor, which is defined as the ratio of steady pressure drop between foam displacement and gas displacement, is employed to characterize this difference. The effects of foam quality, void ratio, and particle size on resistance factor were studied. The unsaturated permeability curves of foams generated by leachate samples at different depths were measured. The leachate at the middle layer has low surface tension to produce strong foam, while the leachate at the top and bottom layers has high surface tension to produce weak foam. The unsaturated permeabilities of weak foam and strong foam were about 1 and 2 orders of magnitude smaller than that of gas, respectively. The reduction in waste void ratio decreased the resistance factor as the excessive shearing effect in small pores would cause the foam to collapse.","PeriodicalId":9382,"journal":{"name":"Canadian Geotechnical Journal","volume":null,"pages":null},"PeriodicalIF":3.6,"publicationDate":"2024-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140979752","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Xiaojiao Li, Rui Chen, Liping Huang, Bo Pu, Pei Tai
Ground collapse occurs frequently due to the roof or roof–sides breakdown of shallow cavities, but analytical solutions considering both types of failures remains a challenge and without incorporating the unsaturated characteristics of shallow soils. This study presents an analytical solution for the collapse of shallow rectangular cavities in unsaturated soils. Proposing a critical cover depth to differentiate deep and shallow cavities. Results show that the collapse type (roof or roof–sides) in shallow cavities depends on the width at collapse. It varies significantly with matric suction, displaying two patterns: increasing and stabilizing, or increasing, decreasing and stabilizing. The variation trend of width at collapse with matric suction aligns with that of apparent cohesion, with a peak near the air-entry value when the fitting parameter n is relatively large (such as n = 3 or 4). The air-entry value influences the magnitude rather than the shape of the variation curves. Additionally, shallow cavities with small cover depths tend toward roof failure, while those with large cover depths, especially with significant height, are more prone to roof–sides failure. Increasing surface surcharge can reduce collapse width, shifting towards roof–sides failure, especially with low cohesion or internal friction angle.
由于浅层空洞的顶板或顶板侧面破裂，地面塌陷经常发生，但考虑这两种类型的塌陷的分析解决方案仍然是一个挑战，而且没有考虑到浅层土壤的非饱和特性。本研究提出了非饱和土壤中浅层矩形空洞坍塌的分析解决方案。提出了区分深腔和浅腔的临界覆盖深度。结果表明，浅层空洞的坍塌类型（顶面或顶面-侧面）取决于坍塌时的宽度。塌陷宽度随母吸力的变化很大，表现出两种模式：增大和稳定，或增大、减小和稳定。塌陷宽度随垫吸力的变化趋势与表观内聚力的变化趋势一致，当拟合参数 n 相对较大（如 n = 3 或 4）时，塌陷宽度在进气量值附近达到峰值。空气进入值影响的是变化曲线的大小而不是形状。此外，覆盖层深度较小的浅空洞倾向于顶板破坏，而覆盖层深度较大的空洞，尤其是高度较大的空洞，更容易发生顶板-侧面破坏。增加地表附加荷载可减小坍塌宽度，使坍塌趋向于顶面破坏，尤其是在粘聚力或内摩擦角较低的情况下。
{"title":"An upper-bound solution for ground collapse induced by shallow rectangular cavity in unsaturated soils","authors":"Xiaojiao Li, Rui Chen, Liping Huang, Bo Pu, Pei Tai","doi":"10.1139/cgj-2024-0026","DOIUrl":"https://doi.org/10.1139/cgj-2024-0026","url":null,"abstract":"Ground collapse occurs frequently due to the roof or roof–sides breakdown of shallow cavities, but analytical solutions considering both types of failures remains a challenge and without incorporating the unsaturated characteristics of shallow soils. This study presents an analytical solution for the collapse of shallow rectangular cavities in unsaturated soils. Proposing a critical cover depth to differentiate deep and shallow cavities. Results show that the collapse type (roof or roof–sides) in shallow cavities depends on the width at collapse. It varies significantly with matric suction, displaying two patterns: increasing and stabilizing, or increasing, decreasing and stabilizing. The variation trend of width at collapse with matric suction aligns with that of apparent cohesion, with a peak near the air-entry value when the fitting parameter n is relatively large (such as n = 3 or 4). The air-entry value influences the magnitude rather than the shape of the variation curves. Additionally, shallow cavities with small cover depths tend toward roof failure, while those with large cover depths, especially with significant height, are more prone to roof–sides failure. Increasing surface surcharge can reduce collapse width, shifting towards roof–sides failure, especially with low cohesion or internal friction angle.","PeriodicalId":9382,"journal":{"name":"Canadian Geotechnical Journal","volume":null,"pages":null},"PeriodicalIF":3.6,"publicationDate":"2024-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140978422","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Tree roots play a crucial role in hillslope stability, but quantifying their reinforcement remains challenging. This study aims to quantify the root reinforcement provided by Cunninghamia lanceolata across varying slope gradients based on in-situ pullout experiments. A total of 120 soil profiles were excavated to map root distribution across four slope gradients. Subsequently, 304 in situ pullout experiments were conducted encompassing root diameters ranging from 1 to 8 mm. The Root Bundle Model Weibull was calibrated and coupled with root distribution data to quantify reinforcement contributions from a single tree to stands. It was found slope gradient significantly influences root distribution, with steeper slopes harboring coarser and more widely distributed roots. In situ experiments revealed substantial variability in pullout stiffness and peak displacement for roots of the same diameter, with thicker roots exhibiting higher stiffness and greater displacement. Calculations indicate that root reinforcement exhibits an exponential decline with increasing distance from the stem but shows a marked positive association with slope gradient due to the influence on root distribution. Statistical analysis reveals that the area experiencing root reinforcement exceeding 10 kPa on a 40° slope is roughly double that of 0° and 20° stands.
{"title":"Quantifying Reinforcement of Forested (Cunninghamia lanceolata) Slopes with Different gradients based on In-Situ Pullout Experiments","authors":"Bingli Hu, Lijun Su, Yiding Bao, Qijun Xie","doi":"10.1139/cgj-2023-0473","DOIUrl":"https://doi.org/10.1139/cgj-2023-0473","url":null,"abstract":"Tree roots play a crucial role in hillslope stability, but quantifying their reinforcement remains challenging. This study aims to quantify the root reinforcement provided by Cunninghamia lanceolata across varying slope gradients based on in-situ pullout experiments. A total of 120 soil profiles were excavated to map root distribution across four slope gradients. Subsequently, 304 in situ pullout experiments were conducted encompassing root diameters ranging from 1 to 8 mm. The Root Bundle Model Weibull was calibrated and coupled with root distribution data to quantify reinforcement contributions from a single tree to stands. It was found slope gradient significantly influences root distribution, with steeper slopes harboring coarser and more widely distributed roots. In situ experiments revealed substantial variability in pullout stiffness and peak displacement for roots of the same diameter, with thicker roots exhibiting higher stiffness and greater displacement. Calculations indicate that root reinforcement exhibits an exponential decline with increasing distance from the stem but shows a marked positive association with slope gradient due to the influence on root distribution. Statistical analysis reveals that the area experiencing root reinforcement exceeding 10 kPa on a 40° slope is roughly double that of 0° and 20° stands.","PeriodicalId":9382,"journal":{"name":"Canadian Geotechnical Journal","volume":null,"pages":null},"PeriodicalIF":3.6,"publicationDate":"2024-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140980875","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Guo-Yao Li, Pin‐Qiang Mo, He Yang, Hai-Sui Yu, Yong-Jun Qin
Many geotechnical scenarios involve cavity unloading from a loaded state, particularly in pressuremeter tests, and the unloading data of pressuremeter tests has exceptional attraction as it is less disturbed by the insertion process. However, the analyses for continuous cavity loading and unloading (i.e., cavity initially experiences expansion and then contracts) in critical state soils are rarely studied. To this end, a novel semi-analytical solution based on the unified state parameter model for clay and sand (CASM) is proposed for the whole expansion-contraction of spherical and cylindrical cavities under undrained condition. The problem assumes that the cavity is unloaded after a monotonic loading stage, leading to plastic regions during both loading and unloading periods. The cavity response for the whole expansion-contraction process is investigated, with the total pressure and stress paths at the cavity wall presented and validated against numerical simulation. The developed solution is successfully implemented to interpret both loading and unloading data of pressuremeter tests. The undrained shear strength, in-situ effective horizontal stress and initial overconsolidation ratio are back analyzed by using a curve fitting method based on the proposed solution.
{"title":"Undrained cavity expansion-contraction analysis in CASM and its application for pressuremeter tests","authors":"Guo-Yao Li, Pin‐Qiang Mo, He Yang, Hai-Sui Yu, Yong-Jun Qin","doi":"10.1139/cgj-2024-0011","DOIUrl":"https://doi.org/10.1139/cgj-2024-0011","url":null,"abstract":"Many geotechnical scenarios involve cavity unloading from a loaded state, particularly in pressuremeter tests, and the unloading data of pressuremeter tests has exceptional attraction as it is less disturbed by the insertion process. However, the analyses for continuous cavity loading and unloading (i.e., cavity initially experiences expansion and then contracts) in critical state soils are rarely studied. To this end, a novel semi-analytical solution based on the unified state parameter model for clay and sand (CASM) is proposed for the whole expansion-contraction of spherical and cylindrical cavities under undrained condition. The problem assumes that the cavity is unloaded after a monotonic loading stage, leading to plastic regions during both loading and unloading periods. The cavity response for the whole expansion-contraction process is investigated, with the total pressure and stress paths at the cavity wall presented and validated against numerical simulation. The developed solution is successfully implemented to interpret both loading and unloading data of pressuremeter tests. The undrained shear strength, in-situ effective horizontal stress and initial overconsolidation ratio are back analyzed by using a curve fitting method based on the proposed solution.","PeriodicalId":9382,"journal":{"name":"Canadian Geotechnical Journal","volume":null,"pages":null},"PeriodicalIF":3.6,"publicationDate":"2024-05-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140987422","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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