Examination of Proof Test Extrapolation for Drilled Shafts
Ooi, P
Department of Civil and Environmental Engineering, University of Hawaii at Manoa, Honolulu, HI

Chang, B
Geolabs, Honolulu, HI

Seki, GY
Geolabs, Honolulu, HI

(Received 11 June 2001; accepted 4 June 2003)

Abstract
The difference between a load test and a proof test is that in a load test, the foundation is loaded to failure, whereas in a proof test, it is usually tested to the design load times the desired margin of safety, and failure may not necessarily be reached. Paikowsky and Tolosko (1999) presented and examined methodologies for obtaining the ultimate capacity from proof test data for driven piles. Load test data on drilled shafts supporting the H-3 freeway viaduct on the island of Oahu in Hawaii are used to test six extrapolation techniques by incrementally truncating the load versus settlement data and then comparing the predicted with measured capacities. With some limitations, several of these methods can be used to provide very reliable estimates of capacity of drilled shafts from proof tests, verifying the recommendations of Paikowsky and Tolosko. The more reliable methods and their limitations are identified and ways of maximizing the accuracy are suggested. With increased confidence in the use of extrapolation techniques, substantial savings can be realized in the construction industry and the engineering community. Also, in deriving the top-down load-settlement curves for the shafts tested with the Osterberg load cell, a simple method is proposed to account for the elastic compression of the shaft.

Keywords:
deep foundations, drilled shaft, drilled shafts, elastic compression, extrapolation, foundation, load test, Osterberg load cell, proof test, ultimate capacity

Paper ID: GTJ10558
DOI: 10.1520/GTJ10558

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Author Ooi, P Affiliation Department of Civil and Environmental Engineering, University of Hawaii at Manoa, Honolulu, HI Author Chang, B Affiliation Geolabs, Honolulu, HI Author Seki, GY Affiliation Geolabs, Honolulu, HI Author Ooi P, Chang B, Seki GY Title Examination of Proof Test Extrapolation for Drilled Shafts Symposium , Committee on