CHARACTERISTIC WATER CONTENTS OF A FINE-GRAINED SOIL-WATER SYSTEM

This paper critically appraises the limitations of the liquid-limit wa ter content of clayey soils determined conventionally either by percus sion cup or by the cone penetration method. It is shown that the conve ntional liquid limit and plastic limit are arbitrary, strength-based w ater contents and that they cannot represent the plasticity limits, an d that the state of the soil-water system at the conventional liquid l imit does not correspond to a stress-free reference state. The present investigation identifies three characteristic limiting water contents for a soil-water system which have well-defined, unique mechanisms co ntrolling them, namely the free swell limit, settling limit and shrink age limit. Simple procedures for the determination of the free swell l imit and settling limit of natural soils are presented. The settling l imit is shown to be the 'real liquid limit' of any clayey soil. With a number of experimental illustrations, it is clearly shown that the se ttling limit represents the maximum water-holding capacity of clayey s oils and that it corresponds to the stress-free reference state.