Loss of soil structure for natural sedimentary clays

A number of oedometer and triaxial consolidated undrained triaxial shear tests were performed on both undisturbed and reconstituted specimens of natural soft clays. Based on a comparison of strength behaviour between undisturbed and reconstituted specimens of soft clays, a new interpretation of the loss of soil structure is proposed. This new definition indicates that the resistance of soil structure disappears completely when the consolidation stress is larger than the yield stress in oedometer compression (i.e. the post-yield stress state). The difference in behaviour of compression and strength between reconstituted and undisturbed specimens in the post-yield stress state is explained as being caused by the difference in water content, whereas the mechanical behaviour in the pre-yield stress state (i.e. consolidation stress smaller than yield stress in oedometer compression) is affected by both the water content and the resistance of the soil structure. Experimental data from mercury intrusion porosimetry for a strongly structured diatomite are also used to verify the dramatic change of microstructure in the vicinity of the consolidation yield stress.