PRESSURE DEPENDENCY OF RESEDIMENTED NILE SILTY CLAY

Abstract

The investigation of the undrained behavior of Resedimented Nile Silty Clay (RNSC) is of great importance to oil exploration projects at and off the shores of North Coast Egypt, especially at large consolidation stresses. The behavior of RNSC is not studied enough despite its uniqueness due to the dueling effects of the high plasticity of the fine-grained components and its relatively large percentages of sand and silt particles. A program of oedometer and undrained triaxial compression tests has been performed to investigate the effects of consolidation at different stress levels up to 0.5 MPa. The Nile sediments are collected from the field and resedimented in specially fabricated consolidometers to emulate the natural deposition process occurring along the Nile banks. The results are compared to theories of normalized behavior and pressure sensitivity correlations from literature. The effect of isotropic consolidation in triaxial tests is discussed. The undrained shear stress-strain results show significant changes when consolidation stresses exceed the resedimentation pressure in ductility, strains at peak resistance, and post-peak strain softening. The undrained strength ratio (su/σ’vc) decreases with increasing consolidation effective stress from 0.33 at 100 kPa to 0.18 at 500 kPa, which is a faster rate than predicted by correlations from literature.