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|Title:||The mechanics of pile-soil interaction in cohesionless soils|
|Authors:||Duke University. Department of Civil Engineering.|
Holloway, David Michael, 1946-
Clough, G. Wayne.
Vesić, Aleksandar Sedmak, 1924-
DUKFOR (computer program)
Pile load tests
Piling (Civil engineering)
|Publisher:||Soils and Pavements Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
Abstract: A one-dimensional, discrete element formulation was developed to simulate single pile performance during impact driving and subsequent load testing. The computer program, DUKFOR, combines a multiple-blow wave equation solution with an incremental static equilibrium formulation. Static equilibrium at the end of the simulated blow provides the initial conditions for a subsequent hammer blow or for load test simulation. In this way residual driving stresses are included in the simulation. Nonlinear or bilinear static load transfer properties may be assigned along the shaft and at the pile point. The incremental static equilibrium solution permits arbitrary load test path simulation. Pile tests from two sites were analyzed using DUKFOR: Jonesville Lock and Dam (JLD) near Jonesville, La., where prestressed concrete piles were driven or jetted and driven into dense to very dense, fine silty sands; and Lock and Dam No. 4 (LD4), Arkansas River Project, near Pine Bluff, Ark., where closed-end pipe piles were impact-driven, vibratory-driven, or jetted and driven into medium dense, fine silty sands. Each pile was load tested both in compression and tension. DUKFOR predictions of pile driving (when applicable) and load testing performance were made using fundamental geotechnical assumptions for the resistance distributions. Measured pile capacities were used to backcalculate the appropriate failure parameters for use in the analyses. The shaft load transfer mechanism was described by hyperbolic interface shear test parameters. Hyperbolic point load transfer parameters were developed from LD4 pile test measurements. The DUKFOR predictions of pile performance were generally quite good. Predicted residual point loads for the LD4 test piles were in fair agreement with field measurements. Predicted compression load-displacement behavior was excellent. Tension load-displacement predictions showed the significant effects of residual compression load distribution on tension test performance; however, the displacement predictions at loads near failure were not very good. DUKFOR predicted LD4 load distribution data fairly well, though a "strain-hardening" effect was noted in the load transfer measurements. An axisymmetric finite element code, AXISYM, was developed to provide a direct comparison of analytical results with those of DUKFOR. It was shown that the "strain-hardening" effect could be the result of increasing shear strength due to compression load transfer to the surrounding soil. The opposite effect is predicted by AXISYM for tension loading; the tension load transferred to the surrounding soil reduces confining stress levels and "softens" the pile-soil system response. It was concluded that these tendencies are of minor importance in predicting load-displacement behavior, at least for the pile tests studied. Residual driving load distributions were shown to directly affect pile performance due to the manner in which soil resistance is mobilized. They play a major role in the correct interpretation of pile test results for use in design. DUKFOR is the only method available to predict the residual pile load effects on single pile behavior. Having investigated the analytical capabilities and limitations of the two computer codes, the authors performed parametric studies to establish appropriate stability and convergence criteria. In addition, a parametric study was included to determine the effects of different hammer-assembly-pile-soil system properties on the predicted blow counts and residual load distributions using DUKFOR. Finally, a direct comparison of DUKFOR and AXISYM solution costs was made. In order to obtain load test predictions of comparable accuracy, it was found that the AXISYM analysis was at least 10 to 30 times more expensive in computational effort alone. On the basis of solution capabilities and practical considerations, it is believed that DUKFOR provides the better method.
|Rights:||Approved for public release; distribution is unlimited.|
|Appears in Collections:||Contract Report|
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