Abstract:
Numerical and experimental investigations were undertaken in this research work to
investigate how a critical state soil model (Modified Cam Clay model) and a frictional
soil model (Mohr-Coulomb model) predict the stress-strain response of coastal clays
of Bangladesh.
The Mohr-Coulomb model was first used to predict the drained and undrained triaxial
shear behaviour of laboratory samples of coastal clays of Bangladesh. The ultimate
behaviour is reasonably well predicted using this model. However this model could
not predict the undrained stress paths of coastal clays.
The Modified Cam Clay (MCC) model using finite element method was used to
predict the stress-strain, pore pressure and effective stress path of coastal clays under
undrained triaxial condition. The MCC model was found to be a good qualitative
predictor of the undrained response of coastal clays. It predicts the elasto-plastic strain
hardening as observed experimentally. The Modified Cam Clay model predicts elastic
response of highly overconsolidated clays before the onset of yield. The inability to
predict elasto-plastic response before the onset of yield is a limitation of the model.
However, the Modified Cam Clay model reallistically predicts the stress-strain and
pore pressure response of coastal clays under undrained triaxial condition and various
overconsolidation ratios.
The Modified Cam Clay model was also used to predict the stress-strain and volume
change response of coastal clays under drained triaxial condition. The stress-strain
and volume change response of coastal clays as predicted by the MCC model matches
well with the drained response of the experimental stress-strain and volume change
data for coastal clays as available in published literature.
An experimental program comprising of a series of model-scale footing and pile
tests was carried out in order to investigate the footing and pile response to axial loads
in coastal clays. The results obtained from these tests were compared to the footing
and pile response predicted using the Mohr-Coulomb and Modified Cam Clay models. The Modified Cam Clay model predictions for the model footing test at
consolidation pressure of 50 kPa and 150 kPa was observed to be nonlinear with a
gradually decreasing slope which closely approximated the experimental data. Similar
nonlinear predictions were observed for the model-scale pile test at consolidation
pressure of 150 kPa.
