Modelling the destructuring of soils during virgin compression

INTRODUCTION The important in uence of soil structure on the mechanical properties of soil has long been recognized (e.g. Casagrande, 1932; Mitchell, 1976). The term `soil structure' is used here to mean the arrangement and bonding of the soil constituents, and for simplicity it encompasses all features of a soil that cause its mechanical behaviour to be different from that of the corresponding reconstituted soil. The removal of soil structure is referred to as `destructuring', and this is usually a progressive process. In recent years there have been numerous studies in which a theoretical framework for describing the behaviour of structured soils has been formulated (e.g. Burland, 1990; Leroueil Gens Cotecchia & Chandler, 1997). The authors have also made a study of the virgin compression behaviour of structured soils (Liu & Carter, 1999), and in particular have proposed the hypothesis that, during virgin compression, the additional voids ratio sustained by soil structure is inversely proportional to the current mean effective stress. It was found that this hypothesis gives reasonable predictions of the virgin compression behaviour of many soft structured soils, although discrepancies were observed for some soils. The in uence of destructuring, as well as the development of soil structure on the compression properties of soft clays, have been successfully quanti®ed, and it was demonstrated that the hypothesis may be employed as a basis for formulating a complete stress±strain model for structured soils. In this article, the previous hypothesis is generalized so that the virgin compression behaviour of stiff clay, clay shale and ®ssured clay can also be described accurately. A general discussion on the modelling of destructuring of soils is also given.