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原文传递 Evaluation of Static Resistance of Deep Foundations: Phase 1

题名：	Evaluation of Static Resistance of Deep Foundations: Phase 1
作者：	McVay, M. C.; Chung, J.; Nguyen, T.; Thiyyakkandi, S.; Lyu, W.; Schwartz, J. L.; Huang, L.; Le, V.
关键词：	Prestressed concrete bridge elements##Implementation##H-piles##Prestressed concrete piles##Open-ended steel and concrete piles##Static and dynamic load tests##Limestone##Evaluation##Recommendation##Florida Department of Transportation (FDOT)##Standard Penetration Test (SPT)##American Petroleum Institute (API)##
摘要：	The focus of this research was to evaluate and improve Florida Department of Transportation (FDOT) FB-Deep software prediction of nominal resistance of H-piles, prestressed concrete piles in limestone, large diameter (> 36”) open steel and concrete piles, as well as estimation of unit side friction on permanent steel casing for drilled shafts in Florida limestone. To accomplish this the following data was collected, (1) 642 dynamic load tests (DLT) and 33 static load tests on H-piles, (2) 100 DLT tests for prestressed concrete piles in Florida limestone, (3) 50 open-ended steel and concrete piles (22 piles larger than 36-in) from coastal areas in the U.S. and Asia, and (4) 17 cased drilled shafts embedded in Florida limestone. Evaluation of the H-piles revealed that generally, the piles undergo both setup and plugging after driving that is lost after a few restrikes; in addition, long piles undergo skin friction unloading. Recommendations to improve FB-Deep H-pile prediction include averaging Standard Penetration Test (SPT) N values only beneath the pile tip and increasing the limiting N values to 100 for strong limestone layers. In the case of prestressed concrete piles embedded in limestone, (1) weak limestone which for the purposes of this report was classified as N < 45 blows per foot, exhibit unit skin friction values more representative of soil than rock/shelly sand, (2) for competent limestone (N>45) the limiting SPT N value for estimating side and tip resistance should be increased to 100, and (3) the nominal tip resistance should be estimated by averaging the SPT N values within four diameters (or pile width) “B” below the pile tip. For all limestone (weak and competent), a revised unit tip resistance for 4B SPT N averaging is recommended. For all open-ended steel and concrete cylinder piles, it was found that many piles behaved plugged per the static load test results. It was established for both FB-Deep (2015) program and American Petroleum Institute (API - 2011) method that the end bearing was the minimum of inside side friction or unit end bearing acting over the bottom soil plug; in addition, the limiting N value should be increased to 100. Finally, for a permanent cased drilled shaft, the unit skin friction in load tested shafts was found to increase with rock strength to a limiting value of 1.2 tsf; an equation of nominal resistance as well as mobilized resistance as a function of displacement is presented. The contribution of casing in drilled shafts that derive most of their side resistance from the rock socket interface should not be implemented in design, due to strain incompatibility between the cased and uncased portions of the embedded length.
总页数：	212
报告类型：	科技报告