Enhancing soil sample preparation by thermal cycling

Abstract

The fabrication of soil samples of uniform density is a fundamental problem in laboratory and physical experiments. A novel technique that relies on a systematic increase of density induced by thermal cycling is presented here. The principle is simple; when the sample is heated the grains and their container undergo thermal expansion and this leads to the settling of the material due to the differential thermal expansion between the grains and the container and the metastable nature of the granular assembly. This change in fabric is not reversible upon cooling down of the sample, so the newly formed fabric can be used for experimental testing. Moreover, the soil fabric can be incrementally enhanced using successive thermal cycles of heating–cooling. In this paper, the change of void ratio is investigated in two carbonate sands, a silica sand and glass ballotini. The effect of particle morphology and initial density on the thermal-induced mechanisms of grain rearrangement is discussed. On the basis of experimental results we hypothesise that thermal cycling enables laboratory samples to be produced with enhanced densities and better soil–boundary interfaces, which is critical to help interpretation of data in experimental and numerical tests.