Analysis of the Expansive Clay Hydration under Low Hydraulic Gradient Marcelo Sánchez 1 , María Victoria Villar 2 , Antonio Lloret 3 , and Antonio Gens 3 1 Department of Civil Engineering, Strathclyde University, U.K. marcelo.sanchez@strath.ac.uk 2 CIEMAT, Madrid, Spain mv.villar@ciemat.es 3 Technical University of Catalonia (UPC), Barcelona, Spain Antonio.Lloret@upc.edu, antonio.gens@upc.edu Summary. Engineered barriers made up of compacted expansive clays are a basic component of the systems for the isolation of high-level radioactive waste (HLW). The barrier is initially unsaturated and during hydration the hydraulic gradient varies from high values (i.e. higher than 50000) at the beginning of the wetting to very low values (practically zero when reaching stationary conditions). The values of bentonite permeability are frequently obtained at the laboratory under high hy- draulic gradients (i.e. higher than 15000), necessary to induce a measurable flow. A drawback of this practice is that the applied hydraulic gradients are very far from those (expected) in actual conditions. So, the experimental results obtained might not be realistic in many cases, affecting the reliability of the numerical analysis. To advance in the knowledge of expansive clays behaviour this work presents an exper- imental and numerical study. The hydraulic permeability of FEBEX clay samples has been measured under low injection pressures. This work presents the modelling of infiltration laboratory tests designed to reproduce the thermo-hydro-mechanical conditions of large-scale tests. The evolution of the tests is analysed and discussed in detail using non-standard flow models which consider the presence of a threshold gradient and thermo-osmotic effects. Key words: expansive clays, thermo-hydraulic cell tests, numerical modelling, non- standard flow models 1 Introduction The long-term behaviour of low permeability (expansive) clays under low hy- draulic gradient is not well-know, especially when the hydration takes place under non-isothermal and confined conditions, which are the expected con- ditions in high-level radioactive waste repositories (HLW). A trend to a very low rate of hydration, compared to the expected or predicted one, has been SOFTbank E-Book Center Tehran, Phone: 66403879,66493070 For Educational Use.