Experimental Investigation of Thermal Volumetric Changes in Clays: Unveiling Hidden Controls

This endeavour investigates the thermally induced volumetric behaviour of fine-grained soils, specifically focusing on the effects of over-consolidation ratio (OCR), plasticity, and stress history. A custom-designed temperature-controlled oedometer cell was used to conduct drained heating and heating-cooling cycle tests on silty clays from Budapest, Hungary. The results reveal that normally consolidated samples exhibit plastic contraction upon heating, while over-consolidated samples show varying responses influenced by their recent stress history and plasticity index. Overconsolidated soil samples with a recent stress history of loading (reloading) predominantly contracted rather than the traditionally expected initial expansion, highlighting the importance of recent stress paths. Plasticity significantly impacts volumetric strain, with higher-plasticity clays exhibiting more pronounced contractions during heating and greater cumulative plastic strain over thermal cycles. The study concludes that a combination of OCR, plasticity, and stress history collectively determine the thermal volume response of fine-grained soils, with implications for the design of thermally robust geo-energy infrastructures.