CPT Based Pile Design

The geotechnical design of a pile foundation is concerned with the determination of the safe magnitude of an external load that the foundation can carry without jeopardizing the stability of the supported structure. In recent years, in-situ sounding tests are becoming a more attractive method to predict pile capacity due to the rapid development of testing instruments, improved understanding of their mechanics and interpretation, and cost efficiency. The cone penetration test (CPT) and its upgraded version, the piezocone penetration test (PCPT), are the most widely used in situ sounding tests to predict pile capacity. This research report compared eight CPT-based and three PCPT-based methods for potential application of the best performer(s) by the Nebraska Department of Transportation (NDOT) to predict pile capacity. Several statistical as well as non-statistical comparison criteria were adopted. According to the evaluation output, the modified (calibrated) Tumay and Fakhroo (1982) method was found to be the best performer for H-piles, and the modified DeRuiter and Beringen (1979) method was found to be the best performer for pipe and precast prestressed concrete piles. For a complete design of pile foundations, the settlement criterion has to be incorporated. The settlement of pile foundations must not exceed a certain tolerable magnitude of settlement to ensure the safety of the structure supported. In this regard, this research project adopted the t – z curve approach to predict pile settlements. Several existing t – z curve approaches based on analytical and numerical techniques were assessed and their relative accuracy was investigated. An easy to use software for the computation of settlement was also developed.