Revolutionizing Friction Pile Design Through the Development of a Multi-Friction Sleeve Device for Direct In-situ Measurement of Interface Strength

通过开发用于直接原位测量界面强度的多摩擦套装置彻底改变摩擦桩设计

• 批准号: 9978630
• 负责人: David Frost
• 金额: $ 18.52万
• 依托单位: Georgia Tech Research Corporation
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-10-01 至 2002-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9978630&HistoricalAwards=false
• 关键词: Revolutionizing; Friction; Pile; Design; Through

***9978630FrostA review of the technical design methods for a range of geotechnicalstructures will confirm that, although many of these systems rely on theinterface strength between soil and man-made construction materials toprovide the necessary load resisting forces, rarely are measurements madeto directly determine the interface strength characteristics. Instead,interface strength parameters are either estimated empirically from othermeasures of strength by applying various correlation and/or correctionfactors or they are interpreted through back-analysis of load tests. Forexample, many prominent direct CPT pile design methods relate the measuredCPT tip resistance to the unit shaft capacity of the pile through one ormore correlation factors. Similar approaches are taken in determining thecapacity of tie-back anchor systems, in estimating the friction acting onpipes during micro-tunneling, and in estimating the friction betweenbackfill soils and sheet piles or other retaining structures. Why have these various design procedures relied on empiricism andback-analysis rather than direct measurement of relevant properties? Theanswer is simply that until very recently, while recognized as asignificant factor in the strength of interfaces, the technology andmethods to quantitatively evaluate the surface roughness of civilengineering construction materials at relevant scales was not available.Fortunately, driven by the need to quantify surface characteristics ofmaterials in other engineering disciplines, the technology and equipment isnow available. This project seeks to exploit this opportunity by applyingthis technology to geotechnical interfaces and thereby providing the basisto revolutionize how pile foundations and other earth structure systems aredesigned and constructed. This project is to develop and evaluate a multi-friction sleeve attachmentto the cone penetrometer (CPT) to permit direct in situ measurement of therelationship between interface strength and surface roughness. Recentresearch has successfully quantified the relationship between interfacestrength and surface roughness in the laboratory. The opportunity nowexists to transfer this knowledge to an in-situ test. Through measurementof the loads transmitted to multiple friction sleeves of increasingroughness assembled in series, the quantitative relationship betweeninterface friction and surface roughness can be measured. This will resultin the ability to directly measure the insitu interface strength, therebyopening the opportunity to revolutionize the design concepts, materials,methods and processes used in foundations, retaining structures, andmicro-tunnels.The proposal outlines a series of tasks ranging from laboratoryexperimentation, numerical analysis, calibration chamber testing, tofull-scale field testing to ensure that the design of the proposedattachment is based on a solid fundamental understanding of the interactionof the penetrometer with the surrounding soil. It is noted that theproposed approach is not to alter existing cone penetrometer design but toadd an attachment that offers new capability for site characterization. Theinterface friction measurements made with the device can be complemented byeither pressuremeter or dilatometer measurements so that reliable estimatesof lateral stress conditions are available for the pile capacity predictionprocedures to be developed as part of this study. ***

* 9978630霜冻一系列岩土工程结构的技术设计方法的审查将证实，尽管这些系统中的许多依赖于土壤和人造建筑材料之间的界面强度来提供必要的负载阻力，但很少进行测量来直接确定界面强度特性。 相反，界面强度参数估计经验，从其他措施的强度，通过应用各种相关性和/或correctionfactors或他们解释通过反向分析的负载测试。 例如，许多突出的直接CPT桩设计方法通过一个或多个相关因素将测得的CPT端阻力与桩的单位轴承载力相关联。 在确定回接锚系统的能力、估算微型隧道开挖过程中作用在管道上的摩擦力以及估算回填土与板桩或其他支护结构之间的摩擦力时，也采用了类似的方法。 为什么这些不同的设计程序依赖于物理学和反分析，而不是直接测量相关的属性？ 答案很简单，直到最近，虽然被认为是界面强度的一个重要因素，但在相关尺度上定量评估土木工程建筑材料表面粗糙度的技术和方法还不存在。幸运的是，在其他工程学科中量化材料表面特性的需求的推动下，现在已经有了技术和设备。 该项目旨在利用这一机会，将该技术应用于岩土界面，从而为彻底改变桩基础和其他土木结构系统的设计和建造方式提供基础。 本项目是开发和评估一种多摩擦套筒附件的锥形硬度计（CPT），允许直接在现场测量界面强度和表面粗糙度之间的关系。最近的研究已经成功地在实验室中量化了界面强度和表面粗糙度之间的关系。 现在有机会将这些知识转移到现场测试中。 通过测量传递到多个串联安装的渐增粗糙度摩擦套上的载荷，可以定量地测量界面摩擦力与表面粗糙度之间的关系。 这将导致直接测量原位界面强度的能力，从而为基础，支护结构和微型隧道中使用的设计概念，材料，方法和过程带来革命性的机会。该提案概述了一系列任务，包括实验室实验，数值分析，校准室测试，进行全面的现场测试，以确保所提议的附件的设计是基于对流量计与周围土壤相互作用的坚实的基本理解。值得注意的是，所提出的方法是不改变现有的锥形流量计的设计，但添加一个附件，提供新的能力，现场表征。该装置进行的界面摩擦力测量可以通过压力计或摩擦计测量进行补充，以便可靠地估计侧向应力条件，用于作为本研究一部分开发的桩承载力预测程序。***