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原文传递 Extrapolation of Pile Capacity From Non-Failed Load Tests

题名：	Extrapolation of Pile Capacity From Non-Failed Load Tests
作者：	Samuel G. PaikotMSky and Terry A. Tolosko
关键词：	Pile Load Test, Pile Capacity. Failure Criterion, Extrapolation Analysis, Reliability, Non-Failed Load Tests.
摘要：	Static pile load test to failure is the ultimate procedure available to examine the capacity and integrity of deep foundations. Being expensive and time-consuming, the procedure is often substituted for the application of a load to a certain factor (most often two) times the contemplated design load. In fact, only a proof test is carried out while the ultimate capacity and actual factor of safety remains unknown. This procedure results in an uneconomic foundation solution, unknown capacity when modifications are required, and the inability of the engineer to gain insight into the controlling mechanism for improved design. The described state of the practice calls for the ability to reliably estimate the ultimate bearing pile capacity for non-foiled load tests. A practical analytical method is proposed, capable of extrapolating the measured load settlement relations beyond the maximum tested load. The proposed procedure, along with two other possible methods, is evaluated. The procedures are examined through a database of 63 driven piles load-tested to failure. Loading is assumed to be known for only 25%, 33%, 50%, 75%, and 100% of the actual bearing capacity (typically lower than the maximum applied load), and separately for 25%, 33%, 50%, 75%, and 100% of the entire load settlement data points. The limited ‘known* data is then extrapolated using the different methods and the obtained bearing capacity is compared to the actual measurements. For consistency, only one failure criterion ((Davisson) is applied. The obtained results are analyzed statistically to evaluate the accuracy and reliability of the three methods. It is shown that the accuracy of the proposed method is 0.99 ± 0.21 (1S.D.), 0.96 ± 0.27,0.87 ± 0.30, and 0.78 ± 0.33 when assuming 75%, 50%, 33%, and 25% of the data points to be known and 0.99 ± 0.26 (1S.D.), 0.89 ± 0.41,0.74 ± 0.46, and 0.64 ± 0.44 when assuming 75%, 50%, 33%, and 25% of the bearing capacity to be known, respectively. The obtained results for the 63 database cases suggest that even when the predicted ultimate capacity Is four times the maximum actual tested load, the associated risk is zero for exceeding the design load, when using the extrapolated value with a factor of safety of 2.0. All the case histories used in this research relate to driven piles. Even though it is expected to be valid, a detailed examination of the method is required before its safe application to cast-in-place piles. Case history analyses of six load-tested driven piles at two sites are presented. The analyzed cases indicate possible substantial savings when the ultimate capacity well exceeds the maximum applied load. Moreover, the method already demonstrates its enormous importance from aspects of engineering and economics.
报告类型：	科技报告