Thermo-mechanical behaviour of a kaolin-based clay soil

Abstract

The thermal behaviour of KSS, a low plasticity artificial clay made with kaolin clay, silt, and sand, was investigated in a series of temperature-controlled oedometer tests, at temperatures between 5 °C and 70 °C, and at vertical pressures up to 2.4 MPa. The experiments investigated the effect of over-consolidation ratio (OCR), pressure level, and repeated thermal cycling on thermally-induced volume change. Thermal volumetric strains were found to be dependent not only on OCR but also on pressure level, contradicting previous experimental findings and highlighting the importance of even a small dependency of compression index C c on temperature. Furthermore, thermal volumetric strains were irreversible on heating and cooling even for highly over-consolidated samples. Although irreversibility at high OCR values has been attributed to particle rearrangement and plastic accommodation in the past, an alternative explanation is put forward here, as yielding on the Hvorslev surface is expected to occur on unloading under 1D conditions. The tests also revealed evidence of thermal creep for the initially normally-consolidated samples. The effect of both current temperature and temperature history on the reloading response of mechanically over-consolidated KSS was tested and quantified in terms of their effect on the measured pre-consolidation pressure. The results from these tests were compared to results from the available literature referring to clays of similar and higher plasticity and the comparison highlighted that although soil plasticity can explain the observed quantitative differences between high plasticity soils to a large extent, mineralogy, in addition to structure, may also play an important role for low plasticity soils.