Non-isothermal coupled effects of bound water content and permeability in sand and clay

The couplings among characteristics of bound water, permeability of soils and temperature largely determine the thermal-hydraulic-mechanical behavior of soils. To study the bound water content and the permeability of soils under non-isothermal conditions, the temperature-controlled laboratory measurements of the bound water content in saturated sand, clay and sand-clay mixtures, combined with the corresponding permeability tests, are carried out in this study based on the bulk density method. It is shown that temperature elevation leads to remarkable decreases of the bound water content, largely depending on the soil particle size and the clay content. The bound water contents under different temperatures measured for the packed soil samples with low and high clay contents are obviously higher and lower than those measured for the samples of dispersed soil particles, respectively, due to the interactions and structures among soil particles. The increases of soil permeability with the temperature elevation are also observed in the tests, which are highly related to the heating-induced and clay-content-dependent decreases of the free-water kinematic viscosity and the bound water content. The thermally induced changes of permeability can be overestimated for the soils with low clay contents and underestimated for those with high clay contents if ignoring the effects of bound water.