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

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***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. ***