Thermo-Hydro-Mechanical Behaviour of Ypresian Clay
Document typeMaster thesis
Rights accessOpen Access
Deep geological disposal solution of high-level and long-lived radioactive waste has been internationally recognised as the preferred option. On this regard, Belgium investigates two deep clay formations; the Boom clay at Mol located at around 220 m deep, considered the reference host formation, and recently the Ypresian clay located at around 500 m deep, considered as the alternative one. The main objective of this research is to perform a thermo-hydro-mechanical characterisation of Ypresian clay by a comprehensive experimental program, carried out on undisturbed samples taken from Kallo borehole (370 m deep). The characterisation program comprised laboratory classification tests, initial total suction and water retention curves (with chilled-mirror dew-point psychrometer), X-ray diffraction, small-strain shear stiffness properties at different orientations (parallel and perpendicular to bedding planes), and mercury intrusion porosimetry (pore size distribution curve of the intact material). Oedometer tests under saturated conditions using step loading and continuous loading approaches were used to characterise the volume change properties of the intact material (yield stress, pre and post-yield compressibility) at different orientations (loading parallel and perpendicular to bedding planes) and at different temperatures (22 and 80 ºC). The material was put in contact with synthetic water at a vertical total stress of 4 MPa (to restore the in situ stress), and then subjected to drained heating (the material underwent some small contraction on this process). The water permeability properties were determined on constant volume and oedometer cells at different orientations (flow parallel and perpendicular to bedding planes) and temperatures (22, 40, 60 and 80 ºC). Temperature cycling effects on water permeability were also examined at constant vertical stress in oedometer cells. Microstructural changes undergone by the material along the different stress paths followed were analysed by mercury intrusion porosimetry. The microstructural study focused on the double porosity features of the intact material, and how this pore network evolves on loading and heating. A heating pulse and constant volume equipment was calibrated and upgraded, which included the development of new acquisition software, the adaptation of new pore water pressure transducers, and a new controlled-power cartridge heater. Preliminary results of a heating/cooling pulse test were presented and discussed.