INTERPRETATION OF SCREW PILE LOAD TEST DATA USING EXTRAPOLATION METHOD IN DENSE SAND

Abstract

The basic definition of ultimate pile capacity is the load at which pile penetration keep on
increasing without increasing the applied load (plunging resistance state). The plunging resistance state is
often not achieved due to the limitation of the loading system, especially under dense ground conditions.
Therefore, extrapolation methods were proposed to estimate the ultimate state of the ground (plunging
resistance). However, in case of screw piles, helix deformation can reduce the end bearing capacity and
should be kept in mind while interpreting load test data. In the present study, the extrapolation methods such
as Chin-Kondner and Decourt were used to check the indication of helix plate deformation from the screw
pile load test data. The prediction capability of the ultimate end bearing capacity was also checked at
settlement equals to 10% of helix diameter and at plunging resistance state. Model scale of pile load testing
under dense ground condition was selected to achieve the plunging resistance state. It was observed from the
test results that the Decourt method of plotting could indicate the helix plate deformation. A modified
approach was proposed in Decourt method of plotting to estimate the helix limit load. It was also observed
from the prediction analysis that it would be better to select the ultimate end bearing capacity from the
predicted model curve at settlement equals to 10% of helix diameter. A reduction factor based on load test
results is proposed so that the prediction of extrapolation methods at 10% of helix diameter can be controlled.