ON THE PREDICTION OF LONG TERM PILE CAPACITY FROM END-OF-DRIVING INFORMATION

During the past 50 years extensive research has been directed at improving the accuracy of bearing capacity assessment by dynamic methods at the time of testing. It has been learned that the change of capacity with time after installation depends on a number of parameters, both soil and pile type dependent. The long-term ultimate pile capacity may range between 50 and 1000% of the end-of-driving capacity. Sometimes relaxation occurs and then the long-term bearing capacity is less than 100% of the end-of-driving capacity. Usually the capacity increases with time due to "setup". While the accuracy of capacity prediction at the time of testing has considerably improved due to electronic measurements and more detailed analysis procedures, reaping the full benefit from this development requires restrike testing with waiting times after pile installation varying from a few hours to several weeks. Unfortunately, this puts a significant scheduling and time burden on the construction process and thus eventually on the owner. It is clear that the full benefits of a fast and inexpensive dynamic test can only be realized if better test procedures can be developed to predict long term capacity from end of driving information. Such procedures would reduce the need for restrike testing with long waiting periods after pile installation. This paper examines the promise and shortcomings of methods that are proposed for service load capacity predictions from end-of-drive tests and compares them with standard dynamic test procedures. A quantitative assessment of the dynamic resistance is also done based on CAPWAP analyses and these values are compared to setup gains considering soil type along the shaft and at the toe. Based on a review of new and existing data bases it is concluded that the most economical test procedure would include a 24 hour restrike test.

Language

  • English

Media Info

  • Features: Figures; References; Tables;
  • Pagination: p. 77-95
  • Monograph Title: CURRENT PRACTICES AND FUTURE TRENDS IN DEEP FOUNDATIONS
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00987883
  • Record Type: Publication
  • ISBN: 9780784407431
  • Files: TRIS
  • Created Date: Mar 9 2005 12:00AM