Abstract This report presents the results of a synthesis on the design and analysis of ground improvement for liquefaction mitigation. The synthesis included an industry survey concerning the practice of ground improvement for liquefaction mitigation. Participation in the survey was solicited by advertisements in several trade magazines and by e-mail for the DFI membership. The survey participants numbered 150. Their professional roles include consulting engineers, specialty contractors, design engineers, government engineers, and academicians. They represent a variety of geographical areas including North/Central/South America, United Kingdom, Middle East, Caribbean, Hawaii, Japan, India, Egypt, France, Australia and New Zealand. Upon completion of the survey, several professionals in the field of liquefaction and ground improvement were interviewed for them to elaborate on the survey results. The interviews are included in the Appendix of this report. Financial support for the project was provided by DFI and Dan Brown and Associates PC. The concept of the liquefaction mitigation synthesis was developed by DFI’s Ground Improvement Committee in recognition that: (a) The results of recent research and post-earthquake reconnaissance have challenged previously long-held beliefs about liquefaction and associated mitigation techniques, and; (b) The DFI membership and the engineering/construction industry are interested to know if and how engineers and designers are subsequently adjusting their practice in consideration of recent research and post-earthquake reconnaissance. For more detailed information on recent research and post-earthquake reconnaissance, presentations are available from the State-of-the-Art Forum: Liquefaction Consequences and Mitigation that was held in St. Louis in 2012. A commentary of the state-of-practice in ground improvement for liquefaction mitigation (prepared by DFI’s Ground Improvement Committee) is included in this issue of the DFI Journal. The author would like to thank the participants of the survey and especially Mr. Mike Jeffries, Dr. Les Youd, and Dr. Ikuo Towhata for their willingness to share their expertise in interviews. The author also acknowledges Mary Ellen Bruce of DFI, Billy Camp of S&ME, Inc., and Marty Taube of DGI Menard (and Chair of DFI’s Ground Improvement Committee) for their significant contributions.
摘要:本报告介绍了一项关于缓解液化的地基改善设计和分析的综合结果。该综合报告包括一项关于为减轻液化而进行的地面改善实践的行业调查。该调查是通过若干贸易杂志上的广告和DFI会员的电子邮件征集的。参与调查的人数为150人。他们的专业角色包括咨询工程师、专业承包商、设计工程师、政府工程师和学者。他们代表了不同的地理区域，包括北美/中美洲/南美洲、英国、中东、加勒比海、夏威夷、日本、印度、埃及、法国、澳大利亚和新西兰。调查结束后，我采访了几位液化和地基改善领域的专业人士，请他们详细阐述调查结果。采访情况载于本报告的附录。该项目的资金支持由DFI和Dan Brown and Associates PC提供。减轻液化综合概念是由国际发展部的地面改善委员会提出的，因为它认识到:(a)最近的研究和震后侦察的结果对以前长期以来对液化和相关减轻技术的看法提出了挑战;(二)发展基金会员及工程/建造业有兴趣了解工程师及设计师有否及如何因应最近的研究及震后勘测而调整他们的工作。有关最近研究和地震后侦察的更详细信息，可参见2012年在圣路易斯举行的“最先进论坛:液化后果和缓解”的介绍。关于缓解液化的地面改善实践状况的评论(由DFI的地面改善委员会编写)收录在本期DFI杂志中。作者要感谢调查的参与者，特别是Mike Jeffries先生、Les Youd博士和Ikuo Towhata博士愿意在采访中分享他们的专业知识。作者还对DFI的Mary Ellen Bruce, S&ME, Inc.的Billy Camp和DGI Menard的Marty Taube (DFI的地面改善委员会主席)的重要贡献表示感谢。
{"title":"Liquefaction Mitigation Synthesis Report","authors":"T. Siegel","doi":"10.1179/dfi.2013.002","DOIUrl":"https://doi.org/10.1179/dfi.2013.002","url":null,"abstract":"Abstract This report presents the results of a synthesis on the design and analysis of ground improvement for liquefaction mitigation. The synthesis included an industry survey concerning the practice of ground improvement for liquefaction mitigation. Participation in the survey was solicited by advertisements in several trade magazines and by e-mail for the DFI membership. The survey participants numbered 150. Their professional roles include consulting engineers, specialty contractors, design engineers, government engineers, and academicians. They represent a variety of geographical areas including North/Central/South America, United Kingdom, Middle East, Caribbean, Hawaii, Japan, India, Egypt, France, Australia and New Zealand. Upon completion of the survey, several professionals in the field of liquefaction and ground improvement were interviewed for them to elaborate on the survey results. The interviews are included in the Appendix of this report. Financial support for the project was provided by DFI and Dan Brown and Associates PC. The concept of the liquefaction mitigation synthesis was developed by DFI’s Ground Improvement Committee in recognition that: (a) The results of recent research and post-earthquake reconnaissance have challenged previously long-held beliefs about liquefaction and associated mitigation techniques, and; (b) The DFI membership and the engineering/construction industry are interested to know if and how engineers and designers are subsequently adjusting their practice in consideration of recent research and post-earthquake reconnaissance. For more detailed information on recent research and post-earthquake reconnaissance, presentations are available from the State-of-the-Art Forum: Liquefaction Consequences and Mitigation that was held in St. Louis in 2012. A commentary of the state-of-practice in ground improvement for liquefaction mitigation (prepared by DFI’s Ground Improvement Committee) is included in this issue of the DFI Journal. The author would like to thank the participants of the survey and especially Mr. Mike Jeffries, Dr. Les Youd, and Dr. Ikuo Towhata for their willingness to share their expertise in interviews. The author also acknowledges Mary Ellen Bruce of DFI, Billy Camp of S&ME, Inc., and Marty Taube of DGI Menard (and Chair of DFI’s Ground Improvement Committee) for their significant contributions.","PeriodicalId":272645,"journal":{"name":"DFI Journal - The Journal of the Deep Foundations Institute","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126185897","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}
Abstract Deep foundation designs for service limit state are still deterministic in the current AASHTO LRFD Specifications. To address this deficiency, a performance-based reliability design methodology is developed using the Monte Carlo statistical techniques. In the proposed methodology, the design criteria are defined in terms of the allowable displacement. The spatial variability of soil parameters is considered in the proposed methodology by modeling soil parameters as random fields. Failure is defined as the event that the induced displacement exceeds the limiting displacement. The probability of failure by Monte Carlo approach is the ratio of the number of unsatisfactory performance events to the sample size. Three numerical examples are given to illustrate the application of the proposed methodology for laterally loaded and axially loaded drilled shafts, respectively. The spatial variability and correlation of soil properties were shown to exert significant influences on the foundation design.
{"title":"Performance-Based Reliability Design for Deep Foundations Using Monte Carlo Statistical Methods (DFI Student Paper Competition 2012)","authors":"Haijian Fan, R. Liang","doi":"10.1179/dfi.2012.009","DOIUrl":"https://doi.org/10.1179/dfi.2012.009","url":null,"abstract":"Abstract Deep foundation designs for service limit state are still deterministic in the current AASHTO LRFD Specifications. To address this deficiency, a performance-based reliability design methodology is developed using the Monte Carlo statistical techniques. In the proposed methodology, the design criteria are defined in terms of the allowable displacement. The spatial variability of soil parameters is considered in the proposed methodology by modeling soil parameters as random fields. Failure is defined as the event that the induced displacement exceeds the limiting displacement. The probability of failure by Monte Carlo approach is the ratio of the number of unsatisfactory performance events to the sample size. Three numerical examples are given to illustrate the application of the proposed methodology for laterally loaded and axially loaded drilled shafts, respectively. The spatial variability and correlation of soil properties were shown to exert significant influences on the foundation design.","PeriodicalId":272645,"journal":{"name":"DFI Journal - The Journal of the Deep Foundations Institute","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121054086","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}
Abstract This paper focuses on the thermo-mechanical response of two full-scale energy foundations installed at the new Denver Housing Authority Senior Living Facility in Denver, Colorado. The energy foundations were formed by attaching heat exchanger tubes to the inside of the reinforcement cages of drilled shafts. The heat exchange tubes were connected to a ground-source heat pump system, which circulates a methanol-water mixture through the tubing to absorb or shed heat into the foundation and surrounding soil or rock. Instrumentation was incorporated to assess the heat exchange response of the foundations as well as the thermo-mechanical strains during construction and typical building operation. The temperature changes within the foundations are stable during heating and cooling operations and the corresponding thermal axial strains are within acceptable limits. The thermal axial strain profiles measured for both foundations follow trends expected for end-bearing boundary conditions with greater strains near the top of the foundations (upward expansion). The mobilized thermal expansion coefficients inferred from the instrumentation confirm that side shear stresses provide resistance to thermally induced movements. The results from this study indicate that energy foundations can be implemented in new buildings to gain improved heat exchange capabilities without major impacts on the foundation performance, for little added installation cost.
{"title":"Strain Distributions in Full-Scale Energy Foundations (DFI Young Professor Paper Competition 2012)","authors":"J. McCartney, K. D. Murphy","doi":"10.1179/dfi.2012.008","DOIUrl":"https://doi.org/10.1179/dfi.2012.008","url":null,"abstract":"Abstract This paper focuses on the thermo-mechanical response of two full-scale energy foundations installed at the new Denver Housing Authority Senior Living Facility in Denver, Colorado. The energy foundations were formed by attaching heat exchanger tubes to the inside of the reinforcement cages of drilled shafts. The heat exchange tubes were connected to a ground-source heat pump system, which circulates a methanol-water mixture through the tubing to absorb or shed heat into the foundation and surrounding soil or rock. Instrumentation was incorporated to assess the heat exchange response of the foundations as well as the thermo-mechanical strains during construction and typical building operation. The temperature changes within the foundations are stable during heating and cooling operations and the corresponding thermal axial strains are within acceptable limits. The thermal axial strain profiles measured for both foundations follow trends expected for end-bearing boundary conditions with greater strains near the top of the foundations (upward expansion). The mobilized thermal expansion coefficients inferred from the instrumentation confirm that side shear stresses provide resistance to thermally induced movements. The results from this study indicate that energy foundations can be implemented in new buildings to gain improved heat exchange capabilities without major impacts on the foundation performance, for little added installation cost.","PeriodicalId":272645,"journal":{"name":"DFI Journal - The Journal of the Deep Foundations Institute","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121060676","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}
Abstract Helical anchors provide an accepted means for the support of compressive and tensile foundation loading. Despite their prevalence, the load-displacement and capacity of multi-helix anchors has not been adequately documented. Full-scale uplift loading tests on square shaft multi-helix anchors installed in desiccated Beaumont clay were performed at a well characterized test site. The stiffness and strength of the anchors is characterized, and compared against the variability in undrained shear strength determined in consideration of inherent variability, measurement error, and transformation error. The large-displacement softening behavior exhibited by the test anchors was shown to reflect the in-situ stress-strain behavior of the high plasticity clay, and the amount of softening with post-peak displacement was characterized. The prediction accuracy of design models was assessed using the bias and its statistical characterization, and indicated that the variability in model accuracy lies within the uncertainty in undrained shear strength.
{"title":"Uplift Performance of Multi-Helix Anchors in Desiccated Clay","authors":"A. Stuedlein, J. Young","doi":"10.1179/dfi.2012.007","DOIUrl":"https://doi.org/10.1179/dfi.2012.007","url":null,"abstract":"Abstract Helical anchors provide an accepted means for the support of compressive and tensile foundation loading. Despite their prevalence, the load-displacement and capacity of multi-helix anchors has not been adequately documented. Full-scale uplift loading tests on square shaft multi-helix anchors installed in desiccated Beaumont clay were performed at a well characterized test site. The stiffness and strength of the anchors is characterized, and compared against the variability in undrained shear strength determined in consideration of inherent variability, measurement error, and transformation error. The large-displacement softening behavior exhibited by the test anchors was shown to reflect the in-situ stress-strain behavior of the high plasticity clay, and the amount of softening with post-peak displacement was characterized. The prediction accuracy of design models was assessed using the bias and its statistical characterization, and indicated that the variability in model accuracy lies within the uncertainty in undrained shear strength.","PeriodicalId":272645,"journal":{"name":"DFI Journal - The Journal of the Deep Foundations Institute","volume":"78 10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127177036","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}
Abstract Drilled shaft foundations usually carry very high design loads, and often serve as a single load-carrying unit. These conditions have created a need for a high-level of quality assurance during and after construction process. During the construction process, different types of anomalies such as necking, soft-bottom gap at the base, voids and soil intrusions can occur. Anomalies throughout the length can significantly reduce the axial load capacity of the drilled shaft. This paper studies the effect of voids inside and outside the reinforcement cage on the strength and structural capacity of drilled shafts. The objective of this research is to quantify the extent of loss in axial strength and stiffness of drilled shafts due to presence of three different types of symmetric voids throughout their lengths; also, to evaluate the potential for buckling of longitudinal bars within the various types of voids. To complete these objectives, fifteen large-scale drilled shaft samples were built and tested using a hydraulic actuator at the Florida International University’s (FIU) Titan America Structures and Construction Testing (TASCT) laboratory. During the static load test, load-displacement curves were recorded by the data acquisition system (MegaDAC). Results show that the presence of symmetric voids outside the rebar cage (void Type C) that occupy 40% of the cross sectional area of the drilled shafts cause 27% reduction in the axial capacity, while the symmetric voids that penetrate inside the core (void Type B) cause 47% reduction in the axial capacity. The findings indicate that the voids Type B decrease the capacity and stiffness of drilled shafts more than other types due to the resulting inadequate confinement of the concrete and reinforcement.
{"title":"Behavior of Axially Loaded Drilled Shaft Foundations with Symmetric Voids Outside and Inside the Caging","authors":"M. Hajali, C. Abishdid","doi":"10.1179/dfi.2012.006","DOIUrl":"https://doi.org/10.1179/dfi.2012.006","url":null,"abstract":"Abstract Drilled shaft foundations usually carry very high design loads, and often serve as a single load-carrying unit. These conditions have created a need for a high-level of quality assurance during and after construction process. During the construction process, different types of anomalies such as necking, soft-bottom gap at the base, voids and soil intrusions can occur. Anomalies throughout the length can significantly reduce the axial load capacity of the drilled shaft. This paper studies the effect of voids inside and outside the reinforcement cage on the strength and structural capacity of drilled shafts. The objective of this research is to quantify the extent of loss in axial strength and stiffness of drilled shafts due to presence of three different types of symmetric voids throughout their lengths; also, to evaluate the potential for buckling of longitudinal bars within the various types of voids. To complete these objectives, fifteen large-scale drilled shaft samples were built and tested using a hydraulic actuator at the Florida International University’s (FIU) Titan America Structures and Construction Testing (TASCT) laboratory. During the static load test, load-displacement curves were recorded by the data acquisition system (MegaDAC). Results show that the presence of symmetric voids outside the rebar cage (void Type C) that occupy 40% of the cross sectional area of the drilled shafts cause 27% reduction in the axial capacity, while the symmetric voids that penetrate inside the core (void Type B) cause 47% reduction in the axial capacity. The findings indicate that the voids Type B decrease the capacity and stiffness of drilled shafts more than other types due to the resulting inadequate confinement of the concrete and reinforcement.","PeriodicalId":272645,"journal":{"name":"DFI Journal - The Journal of the Deep Foundations Institute","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115643462","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}
Abstract In this paper, a reliability-based optimization design method is presented for design of a row of drilled shafts to stabilize an unstable slope while achieving the required target reliability index with minimum cost. In the previous developed deterministic analyses, the drilled shaft stabilization mechanisms for the reinforced slope were taken into account through the concept of soil arching, which was quantified by the load transfer factor in the limiting equilibrium analysis. However, due to the inherent uncertainties of the soil properties and the model error of the semi-empirical load transfer equation, a single value of factor of safety chosen in the deterministic approach may not yield the desired level of reliability. A modification of the deterministic method into a probabilistic method is developed in this paper. The monte carlo simulation (mcs) for the soil properties described by the log-normal distributions was employed to calculate the probability of failure (reliability index β) for the drilled shafts reinforced slope system. The developed theories are coded into a computer program (p-uaslope) for analyzing complex slope profile conditions. Finally, a case study (ohio ath-124 slope) is presented to illustrate the step by step design procedure using the developed probability approach..
{"title":"Reliability-Based Optimization Design for Drilled Shafts/ Slope System (DFI Student Paper Competition 2012)","authors":"Lin Li, R. Liang","doi":"10.1179/dfi.2012.010","DOIUrl":"https://doi.org/10.1179/dfi.2012.010","url":null,"abstract":"Abstract In this paper, a reliability-based optimization design method is presented for design of a row of drilled shafts to stabilize an unstable slope while achieving the required target reliability index with minimum cost. In the previous developed deterministic analyses, the drilled shaft stabilization mechanisms for the reinforced slope were taken into account through the concept of soil arching, which was quantified by the load transfer factor in the limiting equilibrium analysis. However, due to the inherent uncertainties of the soil properties and the model error of the semi-empirical load transfer equation, a single value of factor of safety chosen in the deterministic approach may not yield the desired level of reliability. A modification of the deterministic method into a probabilistic method is developed in this paper. The monte carlo simulation (mcs) for the soil properties described by the log-normal distributions was employed to calculate the probability of failure (reliability index β) for the drilled shafts reinforced slope system. The developed theories are coded into a computer program (p-uaslope) for analyzing complex slope profile conditions. Finally, a case study (ohio ath-124 slope) is presented to illustrate the step by step design procedure using the developed probability approach..","PeriodicalId":272645,"journal":{"name":"DFI Journal - The Journal of the Deep Foundations Institute","volume":"86 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115724945","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}
{"title":"From the Editors and Publisher","authors":"","doi":"10.1179/dfi.2012.012","DOIUrl":"https://doi.org/10.1179/dfi.2012.012","url":null,"abstract":"","PeriodicalId":272645,"journal":{"name":"DFI Journal - The Journal of the Deep Foundations Institute","volume":"51 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122852891","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}
Abstract Open caissons are used for many geotechnical engineering applications. Open caissons may be used as deep foundation elements bypassing weak soils to tip in firm deeper strata, and in rivers and maritime construction to reduce the risk of scour. Open caissons are also used for collecting sewage water through gravity sewer pipe networks or from sewer force mains. In such applications, the design and construction of open caissons require a detailed soil investigation program. In this way, the design and construction plan of an open caisson can be developed with full knowledge of the prevailing subsoil conditions. The engineering and construction techniques are key factors to achieve functional caissons. Based on close observations during construction stages, the current study presents some challenges that were encountered during the construction of two open caissons of internal diameters 20 m and 10 m (65.6 ft and 32.8 ft). This paper describes the procedure followed to alleviate the construction difficulties encountered. Site exploration program and control measures required to satisfy design and construction requirements are crucial aspects. Sinking of open caissons in dense or very dense sands is risky. Incorrect sinking of open caissons may cause extra cost, delay in construction, and harm to nearby structures. Air/water jetting near the cutting edge of an open caisson, outside slurry trench, and/or inside open trench may be used to drive an open caisson downward. Unsymmetrical work around an open caisson may lead to tilting of the caisson. If this occurs, the tilt should be immediately corrected before resuming the sinking process. Improper cleaning of fine materials on the caisson’s excavation bed, and/or inappropriate pouring of underwater concrete may result in a defective concrete seal. The paper contains a series of practical guidelines to assist those intending to use open caissons, and shares good caisson sinking practice with practitioners. Finally, the study aims to understand the difficulties encountered and to anticipate future problems.
{"title":"Challenges and Uncertainties Relating to Open Caissons","authors":"F. Abdrabbo, K. E. Gaaver","doi":"10.1179/dfi.2012.002","DOIUrl":"https://doi.org/10.1179/dfi.2012.002","url":null,"abstract":"Abstract Open caissons are used for many geotechnical engineering applications. Open caissons may be used as deep foundation elements bypassing weak soils to tip in firm deeper strata, and in rivers and maritime construction to reduce the risk of scour. Open caissons are also used for collecting sewage water through gravity sewer pipe networks or from sewer force mains. In such applications, the design and construction of open caissons require a detailed soil investigation program. In this way, the design and construction plan of an open caisson can be developed with full knowledge of the prevailing subsoil conditions. The engineering and construction techniques are key factors to achieve functional caissons. Based on close observations during construction stages, the current study presents some challenges that were encountered during the construction of two open caissons of internal diameters 20 m and 10 m (65.6 ft and 32.8 ft). This paper describes the procedure followed to alleviate the construction difficulties encountered. Site exploration program and control measures required to satisfy design and construction requirements are crucial aspects. Sinking of open caissons in dense or very dense sands is risky. Incorrect sinking of open caissons may cause extra cost, delay in construction, and harm to nearby structures. Air/water jetting near the cutting edge of an open caisson, outside slurry trench, and/or inside open trench may be used to drive an open caisson downward. Unsymmetrical work around an open caisson may lead to tilting of the caisson. If this occurs, the tilt should be immediately corrected before resuming the sinking process. Improper cleaning of fine materials on the caisson’s excavation bed, and/or inappropriate pouring of underwater concrete may result in a defective concrete seal. The paper contains a series of practical guidelines to assist those intending to use open caissons, and shares good caisson sinking practice with practitioners. Finally, the study aims to understand the difficulties encountered and to anticipate future problems.","PeriodicalId":272645,"journal":{"name":"DFI Journal - The Journal of the Deep Foundations Institute","volume":"364 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131912950","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}
Abstract paper presents the results of a full-scale axial compression and tension (uplift) testing program executed on large-capacity helical piles installed in very stiff to very hard clay till soils (i.e. cohesive soils). A total of ten tests including six axial compression tests and four tension (uplift) tests were carried out. The results of the axial compressive and tensile pile load tests and field monitoring of helical piles with either a single helix or double helix are presented in this paper. Helical piles are traditionally used to support light to medium loads (i.e. loads up to 500 kN or 56 tons). However the results of the present study confirmed that helical piles can support significantly higher axial compressive loads up to 2450 kN or 275 tons, which is about 5 times traditional design loads. The study also demonstrated the high tensile capacities of helical piles which was as high as 85% of their compressive capacity. Hence helical piles can provide a viable design option for foundations supporting relatively heavy loads.
{"title":"Installation and Performance Characteristics of High Capacity Helical Piles in Cohesive Soils","authors":"M. Sakr","doi":"10.1179/dfi.2012.004","DOIUrl":"https://doi.org/10.1179/dfi.2012.004","url":null,"abstract":"Abstract paper presents the results of a full-scale axial compression and tension (uplift) testing program executed on large-capacity helical piles installed in very stiff to very hard clay till soils (i.e. cohesive soils). A total of ten tests including six axial compression tests and four tension (uplift) tests were carried out. The results of the axial compressive and tensile pile load tests and field monitoring of helical piles with either a single helix or double helix are presented in this paper. Helical piles are traditionally used to support light to medium loads (i.e. loads up to 500 kN or 56 tons). However the results of the present study confirmed that helical piles can support significantly higher axial compressive loads up to 2450 kN or 275 tons, which is about 5 times traditional design loads. The study also demonstrated the high tensile capacities of helical piles which was as high as 85% of their compressive capacity. Hence helical piles can provide a viable design option for foundations supporting relatively heavy loads.","PeriodicalId":272645,"journal":{"name":"DFI Journal - The Journal of the Deep Foundations Institute","volume":"65 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129343435","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}
Abstract The p-y method is one of the most popular methods in pile design and has been calibrated for various boundary conditions using numerical and experimental studies during recent years. Most studies on reinforced concrete (RC) piles have included the impact of flexural nonlinearity, (e.g. nonlinear moment–curvature relations) but not considered associated pile shear deformations when deriving p-y curves from field data. Common p-y curves may be better applicable for piles with flexure dominated failures (e.g. piles with free- head boundary conditions). For piles with fixed head boundaries (i.e. rotation restrained piles) shear deformations could be of significant influence. To study this problem, a coupled shear flexure interaction model for axial-bending-shear behavior coded in OpenSees was applied to a 0.61 m (2 ft) diameter flagpole and a 0.61m (2 ft) diameter fixed head pile specimen to investigate the possible influence of shear deformations to the overall pile responses. The surrounding soil was represented by p-y curves derived from prior large scale testing on piles with similar boundary conditions. Analysis results show that for flagpole piles, shear forces and shear deformations were insignificant. Considerable contributions of pile shear displacements and forces were observed for the fixed head pile, with shear displacements contributing up to 40% of the total pile displacement. Results suggest that nonlinear shear deformations for reinforced concrete piles should be considered for fixedhead or similar conditions, and that currently used p-y curves may underestimate the actual lateral pile displacement and possibly lead to unsafe design for the particular boundary condition.
{"title":"The Influence of RC Nonlinearity on p-y Curves for CIDH Bridge Piers","authors":"L. Massone, A. Lemnitzer","doi":"10.1179/dfi.2012.003","DOIUrl":"https://doi.org/10.1179/dfi.2012.003","url":null,"abstract":"Abstract The p-y method is one of the most popular methods in pile design and has been calibrated for various boundary conditions using numerical and experimental studies during recent years. Most studies on reinforced concrete (RC) piles have included the impact of flexural nonlinearity, (e.g. nonlinear moment–curvature relations) but not considered associated pile shear deformations when deriving p-y curves from field data. Common p-y curves may be better applicable for piles with flexure dominated failures (e.g. piles with free- head boundary conditions). For piles with fixed head boundaries (i.e. rotation restrained piles) shear deformations could be of significant influence. To study this problem, a coupled shear flexure interaction model for axial-bending-shear behavior coded in OpenSees was applied to a 0.61 m (2 ft) diameter flagpole and a 0.61m (2 ft) diameter fixed head pile specimen to investigate the possible influence of shear deformations to the overall pile responses. The surrounding soil was represented by p-y curves derived from prior large scale testing on piles with similar boundary conditions. Analysis results show that for flagpole piles, shear forces and shear deformations were insignificant. Considerable contributions of pile shear displacements and forces were observed for the fixed head pile, with shear displacements contributing up to 40% of the total pile displacement. Results suggest that nonlinear shear deformations for reinforced concrete piles should be considered for fixedhead or similar conditions, and that currently used p-y curves may underestimate the actual lateral pile displacement and possibly lead to unsafe design for the particular boundary condition.","PeriodicalId":272645,"journal":{"name":"DFI Journal - The Journal of the Deep Foundations Institute","volume":"30 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131786820","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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