On the Impact of Plastic Fines on the Compaction Characteristics of Sand

Binary mixtures of plastic fines and a non-cohesive host material are used in geotechnical barriers to obtain high shear strength and low permeability. To achieve such properties, the sand grains must form the force chain and the clay must fill the voids of the host material. However, clays are known to affect the grain to grain contacts by forming cohesive membranes. Since engineered barriers are usually compacted at water contents below saturation (Proctor conditions), it is still unclear whether such membranes will form. The aim of the current research is to shed light on the compaction characteristics of such mixtures. Proctor datasets were analysed in terms of skeleton and fines void ratio and optimal water content. Oedometric compression behaviour and limiting void ratios were studied to outline the characteristics of mixtures in a saturated or dry state, respectively. The results show that depending on the mixing ratio, compaction properties can be divided into three different ranges, where either the properties of one of the input materials dominate the behaviour or a transitional range exists that is characterised by a strong mutual influence of both materials. Furthermore, even a small amount of the highly plastic clay was found to influence the properties of the host sand.