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

**9978630FrostA对一系列岩土结构的技术设计方法的回顾将证实，尽管许多这些系统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抗载荷力，但很少进行测量来直接确定界面强度特性。相反，界面强度参数要么通过应用各种相关和/或校正因子从其他强度测量中经验地估计，要么通过负载测试的反向分析来解释。例如，许多著名的直接CPT桩设计方法通过一个或多个相关因素将测得的CPT桩顶阻力与桩身单位承载力联系起来。在确定回拉锚固系统的承载力、估算微隧道开挖过程中作用于管道的摩擦力以及估算回填土与板桩或其他挡土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经验主义和反向分析，而不是直接测量相关属性？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是不可用的。幸运的是，在其他工程学科中，由于需要量化材料的表面特性，技术和设备现在是可用的。本项目旨在利用这一机会，将该技术应用于岩土工程界面，从而为桩基和其他土结构系统的设计和施工方式提供革命性的基础。该项目旨在开发和评估一种附加在锥贯仪（CPT）上的多摩擦套筒，该套筒可以直接在现场测量界面强度和表面粗糙度之间的关系。最近的研究已经在实验室中成功地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。通过测量传递给串联装配的多个粗糙度增大的摩擦套的载荷，可以定量测量界面摩擦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、挡土结构和微隧道中使用的设计概念、材料、方法和工艺带来革命性的机会。该提案概述了一系列任务，从实验室实验、数值分析、校准室测试到全尺寸现场测试，以确保所提议的附件设计基于对穿透仪与周围土壤相互作用的坚实基础理解。值得注意的是，建议的方法不是改变现有的锥形穿透计设计，而是增加一个附件，为现场表征提供新的能力。使用该设备进行的界面摩擦测量可以通过压力计或膨胀计测量来补充，以便可靠的侧向应力条件估计可用于作为本研究的一部分开发的桩容量预测程序。＊＊＊

***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. ***