Compression behaviour of natural and reconstituted clays

The intercept of the log(1 + e)-log sigma(v)' straight line is introduced to describe the effect of the starting point on the compressibility of natural and reconstituted clays. It is found that when the effective stress exceeds the remoulded yield stress, the compression behaviour of reconstituted clays is controlled solely by the water content at the remoulded yield stress and the liquid limit. Comparison of the compression behaviour of natural and reconstituted clays indicates that their difference in compressibility is caused by soil structure and the difference in water content at the compression starting point. The compression behaviour of natural clays can be classified into three regimes: (a) the pre-yield regime, characterised by small compressibility, with soil structure restraining the deformation up to the consolidation yield stress; (b) the transitional regime, characterised by a gradual loss of soil structure when the effective stress is between the consolidation yield stress and the transitional stress; and (c) the post-transitional regime, characterised by the same change law in compression behaviour as reconstituted clays when the effective stress is higher than the transitional stress. For the investigated clays, the transitional stress is 1.0-3.5 times the consolidation yield stress. The compression index varies solely with the void ratio at an effective stress of 1.0 kPa for both natural clays in the post-transitional regime and reconstituted clays when the effective stress exceeds the remoulded yield stress, and when compressed in such cases the compression curves of both natural clays and reconstituted clays can be well normalised to a unique line using the void index.