NUMERICAL MODELLING OF PILED EMBANKMENTS ON SOFT SOILS

Abstract

This research is about the effect of pile installation process on soil arching development and embankment surface settlement. In addition to this the long term analysis of the influence of creep is also observed. This is a part of AMGISS (Advanced Modelling of Ground Improvement on Soft Soils) project on "Numerical Analysis of Piled Embankments". This dissertation focuses on the influence of pile installation process and the influence of creep in the analysis of piled embankment. The numerical analysis has been performed using an axisymmetric model. The Hardening Soil model has been employed for modelling the material behaviour of the embankment fill, bearing stratum and the soft soil. Pile installation process has been performed using K-pressure method and the analysis has been performed for different K values of the K-pressure and for different pile spacings. For comparison, a drained and undrained analysis for a reference piled embankment has also been performed. The results show that surface settlements and soil arching development from drained analysis are reasonably close to those from undrained analysis. The influence of pile installation on embankment surface settlement and also on differential settlement has been found to be not significant. It also does not show significant influence on the maximum tension in the geosynthetic, soft soil counter pressure and load on pile (efficacy). Similar behaviour has also been observed in the case of embankment constructed on floating piles. The influence of creep on the development of soil arching has been investigated in the case of end bearing pile and floating pile by developing numerical models for different pile spacings. The Soft Soil Creep model is used for modelling the material behaviour of the soft soil. The results have been compared in terms of efficacy, settlements and maximum geosynthetic tension. iv The influence of creep has been found to be very marginal when the embankment is constructed on end bearing piles. On the other hand, when embankments are constructed on floating piles, there is a considerable increase in embankment surface settlement when creep effect is taken into account. The rate of increase in settlement has also been found to be uniform with increase in pile spacing. It does not show significant influence on efficacy in the case of embankment on floating piles. Significant reduction of surface settlement has been obtained when using floating piles compared to embankments without piles. Geogrid does not have any influence in the load transfer mechanism.