A Study of Capacity Predictions for Driven Piles by Dynamic Pile Testing

This dissertation, "A Study of Capacity Predictions for Driven Piles by Dynamic Pile Testing" by Man-kie, Wong, 黃文基, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled A Study of Capacity Predictions for Driven Piles by Dynamic Pile Testing submitted by Wong Man Kie for the degree of Doctor of Philosophy at the University of Hong Kong October 2006 The ban on the use of diesel hammers for percussive piling works and the introduction of hydraulic hammers in Hong Kong in the mid-1990s have brought unsettling times for the local construction industry. In recent years it has not been unusual to find that the measured set and the temporary compression of piles at final set are beyond the range of the set table of the Hiley Formula. A lack of local expertise in using hydraulic hammers and the absence of an approved pile-driving criterion specifically for the use of this new tool are to blame. Some engineers have responded by imposing more stringent requirements on the pile capacity acceptance test than may be necessary, resulting in over-driven piles and associated damage. To resolve such problems, a pile-driving criterion that is practical and generally applicable to all types of piles is called for. Findings from extensive research overseas has established the general value of Dynamic Pile Testing in assessing pile capacity. Such testing involves the combined use of data collected by Pile Driving Analyzer (PDA) and the analytical tool known as Case Pile Wave Analysis Program (CAPWAP). In Hong Kong, there is considerable scope for the wider use of Dynamic Pile Testing. This thesis reports the results of an in-depth study undertaken to confirm the suitability and potential benefits of such testing under local soil conditions. The test piles selected for this study are those typically used locally. A total of 420 Grade 55C steel H-piles driven by hydraulic hammers between 2002 and 2005 were selected from 22 different projects across the territory with different sub-soil conditions. Between 20m and 60m in length, the test piles are representative of the range commonly found in local construction projects. The results from static load tests were used in this study as a benchmark, and compared to the pile capacity predictions derived from several tools (PDA, CAPWAP, the Hiley Formula and the Modified Hiley Formula) with a view to recommending a reliable and practical method for assessing pile capacity. The study results demonstrated that the CAPWAP method can predict the Davisson limit load accurately. Despite the strong predictive power of CAPWAP analysis, we need for field control purposes a dynamic formula that is reliable and yet more practicable in terms of time and cost. The results of the study show that by calibrating the Hiley Formula with the efficiency of the hammer drop, E, and the coefficient of restitution of the hammer cushion, e, derived from CAPWAP analyses, pile capacity predictions can be made that are close to the CAPWAP predictions and the static load test results. To conclude, the present study has clearly established that PDA, CAPWAP and the "calibrated" Hiley Formula are effective tools for pile capacity assessment and quality control of piling works in Hong Kong. Cost-effective and practical, their combined use would contribute significantly to the overall quality and efficiency of pile driving, thus inducing greater confidence locally in Dynamic Pile Testing. DOI: 10.5353/th_b3710612 Subjects: Piling (Civil engineering) - Testing