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API REPORT 13A Document Information:
Title
Analysis of Centrifuge Pile Tests; Simulation of Pile-Driving
American Petroleum Institute
Publication Date:
Jun 20, 1980
Scope:
INTRODUCTION
Previous studies on the centrifuge have been directed towards
simulating the behavior of a laterally-loaded pile in fine, dry and
saturated sand. After data had been obtained on the model pile,
attention was turned to modelling the soil-pile interaction behavior.
Since the Winkler [continuous reaction elements (springs) distributed
along the pile length] foundation representation is the simplest that
can be adduced, and, moreover, has been found to give adequate results
for design in a variety of foundation problems, attempts were made to
extract a Winkler type of function from the model pile test results.
The pile response is obtained from the output of a series of strain
gauges attached to the pile. In effect these indicate the bending
moment in the pile as a function of length along it. As a consequence,
to obtain the pile-soil interaction behavior at various locations
along the pile, it is necessary to integrate the bending moment
function twice for each level of applied load to obtain pile
displacements (the top displacement is measured and known), and to
differentiate it twice, to get the soil interaction pressure. Then, at
a given point on the pile, the pile-soil interaction behavior is given
by plotting the pressure versus the displacement at various load
levels. A series of such functions at different depths gives the
information required for subsequent analyses.
The troubles with this procedure are well-known. Double integration is
satisfactory and gives a good indication of pile deflections, since
the smoothing process eliminates the effect of random errors in the
measurement of Pile strains. However, double differentiation
exaggerates the same errors, and the resulting pressure function can
be quite erratic. It is necessary to smooth the strain gauge data
first before processing it; various smoothing techniques are available
and have been tried. The results of preliminary attempts at obtaining
a smoothing function are described in a previous report (3).
In the stage of the work reported here, a revised method of analysis
was developed, and applied both to calibration tests of the pile, and
to the tests carried out in dry and saturated sand. The results of
these applications are described below.
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