The behaviour of a gap graded sand with mixed mineralogy

The compression and shearing behaviour in mixtures of soils of different granulometries and/or mineralogies has been researched extensively. The focus of the research has been to identify the key factors that might lead the behaviour to change from transitional to not transitional, where transitional behaviour is characterised by non-convergent compression paths and critical state lines that might be non-unique. A review of mixtures of different soils revealed a complex pattern of behaviour, in which transitional behaviour can be caused by relatively small changes in the proportion or nature of the soil particles. It was then assumed that the mineralogy of the matrix composed by larger grains determines the mode of behaviour. If there is a strong and stiff matrix made of quartz sand particles either larger than or at least of a similar size to the other component, then non-convergent compression paths and/or not unique CLSs are likely to occur. This paper presents the results of triaxial and oedometer tests on a range of mixtures of a quartz sand and a carbonate sand, but with a larger weaker carbonate sand component. As predicted, no transitional behaviour was seen in any mixture.