Thermal effects on water retention behaviour of unsaturated collapsible loess

Purpose: Temperature has a significant influence on water retention curve (WRC) because temperature affects surface tension of water and volumetric behaviour of soil. However, in previous studies on thermal effects on WRC, the difference in suction-induced volume change of soil specimen at various temperatures is always insignificant. With increasing temperature, the wetting-induced collapse of loess increases. This study aims to investigate thermal effects on WRC of collapsible loess. Material and methods: A loess from Shaanxi province, China, is tested. Wetting–drying tests were carried out on compacted loess specimens at temperatures ranging from 5 to 50 °C. Thermal effects on water retention behaviour of collapsible loess are analysed. Results and discussion: During the wetting process, volumetric water content at a given suction at 50 °C is 20% smaller than that at 5 °C. This is because when temperature increases from 5 to 50 °C, surface tension of water decreases by 10% and wetting-induced volumetric contraction increases by three times. During drying, the air entry value (AEV) of loess decreases with increasing temperature at a rate of 0.16%/°C. Conclusions: The retention capability of unsaturated loess decreases with increasing temperature. For the tested collapsible loess, with increasing temperature, a combined effect of smaller water surface tension and larger wetting-induced collapse results in a prominent decrease in volumetric water content of loess. Moreover, the decrease of AEV induced by smaller surface tension is partially compensated by effects of larger wetting-induced collapse on AEV.