Stress-strain Behaviour of Remoulded Lias Clay

Abstract

This work is concerned with laboratory investigations of the behaviour of remoulded Lias clay under different stress paths, Basic mechanical properties of the soil were determined and were used in a theoretical study of its stress-strain behaviour based on the strain-hardening plasticity concept and time-dependent strains. Remoulded samples of Lias clay were prepared in a specially developed 100 mm diameter tall oedometer; triaxial and oedometer tests were carried out on 70 mm diameter specimens. Stress-controlled tests were carried out using a specially developed dead loading system in which corrections could be made for change in cross-sectional area of the samples. The results indicated that the initial mixing (preparation) water content and the one-dimensional consolidation stress-history of the soil affect its subsequent stress-strain behaviour: an increase of the effective mean stress of the order of four times the original consolidation stress is needed to eliminate the stress-history of the soil. The void ratio - mean effective stress plots for isotropic and anisotropic consolidation cases are parallel, and in the latter case approach the state-of-failure line (C.V.R.) as the value of q/p increases. A linear relationship between shear strains from drained and undrained compression tests was obtained which, in conjunction with shear strains from constant stress ratio tests could be used to predict shear strains for any stress increment resulting in plastic strains. It was also found that plastic strain increments and undrained stress paths (for isotropic and anisotropic cases) were not predicted well by the Modified Cam-clay Model, It was confirmed also that the plastic strain increment vector is stress-path dependent; this implies that there is no unique plastic potential surface for a given soil, but its shape is stress-path or stress-history dependent.