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Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
To account for the aging setup effects, the interface frictional
resistance coefficient, expressed by
β′
factor in this study, has
been increased until correlations are obtained between predicted
and field measurements. This has been shown by the blue line in
Fig. 7. The difference between the two green and blue lines in
figure is assumed to be representing all the contributing factors
to soil setup that are not effective-stress related. Such factors are
referred to as “aging” in this study, and as explained, the
β′
factor is assumed to account for it. Figure 7 shows that the
contribution of dissipation of EPWP is 75% while the
contribution of aging is 25%.
Figure 6.Radial effective stress changes with timealong the pile shaft.
Figure 7.Increase in pile shaft capacity in numerical model.
5 CONCLUSION
The construction site ofFajr II utility plant,Mahshahr, Iranis
selected to study the different components contributing to the
setup effects using an elasto-perfectly plastic axisymmetric
FEM model. Theadopted FEM model is capable of effective
stress analysis and consideration of PWP effects and has been
used to simulate the cavity expansion resulted from pile driving
and subsequent dissipation of EPWP. The focus of study was to
distinguish the effective stress-dependent and independent
factors influencing the setup in layered strata. The findings of
the study are listed below:
-An empirical equation for calculation of shaft capacity
after setup is presented for the study area.Two equations
also are proposed as upper and lower bounds.
- The numerical model predictions compare well with field
measurements.
-The generation of EPWP as a result of cavity expansion
and subsequent dissipation with time has been predicted
reasonably well.
-The variation of interface shear strength reduction factor,
β′
is considered to represent the setup component
attributed to aging.
-In the layered media of the study site, the contribution of
dissipation of EPWP and aging to soil setup has been
estimated 75% and 25%, respectively, at about 50 days
after initial drive.
6 ACKNOWLEDGEMENTS
The authors would like to thank Amirkabir University of
Technology (AUT), Fajr Petrochemical Co., and Machine Sazi
Pars Co., for financing the extensive dynamic and static load
tests of this study.
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