The mechanics of a saturated silty loess with a transitional mode

Problems of identifying unique normal compression and critical state lines have been found in gap-graded soils and also some silty soils, a mode of behaviour sometimes known as ‘transitional’. Loess is a typical silty soil that covers up to 631 000 km² in China and is of great significance as a result of the large number of engineering projects under construction. To examine the potential transitional behaviour in loess, an extensive series of carefully controlled oedometer tests and triaxial tests on intact and reconstituted specimens were carried out. Loess specimens with a wide range of initial void ratios were reconstituted using different preparation methods. Intact specimens were taken from two depths, but their natural variabilities were not significant and could be neglected, apart from their difference in the initial void ratios. The results have highlighted the features of transitional behaviour in this loess, not only in reconstituted but also intact states, and in particular that there is an influence of the initial density of this loess on its normal compression and critical state lines. Two factors, m and P, as proposed by earlier research, were used to quantify the degree of transitional behaviour. These indicate that this silty loess has a significant degree of transitional behaviour. The intact specimens possibly have an even more pronounced transitional degree than the reconstituted ones, although this is difficult to confirm because of the limited range of initial specific volumes of the intact specimens. The effects of structure on the mechanics of the intact silty loess have also been identified by comparing the behaviour of the intact and reconstituted soils, and the paper discusses the difficulties of doing this for a soil without a unique intrinsic behaviour.