A study of completely decomposed volcanic rock with a transitional mode of behaviour

A transitional mode of behaviour is seen in some soils where the specific volumes of samples do not converge to the same values at the same stress state within the ranges of strains that can be achieved in laboratory tests so there are no unique normal compression or critical state lines. This type of behaviour has been found in different soils but not previously in soils resulting from decomposed igneous rocks. In order to investigate the possibility of transitional mode of behaviour in a decomposed volcanic rock, an extensive series of one-dimensional compression and triaxial tests were conducted on samples in reconstituted and intact states. The important features of transitional mode of behaviour in soils have been identified, that is, the presence of non-unique and parallel normal compression and critical state lines. The behaviour of the soil is therefore dependent on the initial specific volume. The degree of transitional behaviour is strong, particularly in the reconstituted samples, but it is less clearly identified in the intact samples due to the small range of initial specific volumes available. These observations indicate that the transitional mode of behaviour, previously seen in sedimentary soils and artificial soil mixtures, can be extended to some weathered igneous rocks. Determining the effects of structure is difficult due to the non-unique intrinsic properties, but nevertheless, the effects of structure have been identified and discussed