Abstract
An experimental study on Ypresian clays –one of the potential deep formations in Belgium for the geological disposal of heat-emitting radioactive waste– was undertaken to systematically study its thermal properties and coupled hydro-mechanical response during fast heating pulse tests. An accurate characterisation of the thermal properties is required for assessing the near-field perturbations around disposal galleries that the sedimentary host rock formation will undergo. A new experimental cell adapted to apply the high in situ stresses and with thermal flux sensors was used to directly measure the thermal conductivity at different sample orientations (heat flux orthogonal and parallel to bedding planes). A clear influence of the degree of saturation – despite being close to saturation – and anisotropic features on thermal conductivity have been detected. The study was complemented by performing fast heating pulse tests under constant volume on a new and fully-instrumented axisymmetric cell. The cell allowed recording the pore pressure build-up and dissipation along a heating pulse and under water-undrained conditions.
Highlights
An adequate characterisation of the thermal properties and coupled thermo-hydro-mechanical response of soils and rocks is required in energy geotechnics, in the design of energy geo-structures, energy geostorage and deep geological disposal of heat-emitting radioactive waste [1,2,3,4]
One of the main challenges when testing Ypresian clays is to restore the high in situ stresses at the depths of retrieval before thermal testing. This way, opening of fissures and gaps along bedding planes during retrieval, which affect the correct determination of the thermal conductivity, are minimised [7]
The current paper presents selected thermal results of an extensive experimental study performed on Ypresian clays using novel experimental setups
Summary
Within the context of radioactive waste repositories, the following deep sedimentary clay host formations are currently considered: Boom Clay / Ypresian clays (Belgium), Opalinus Clay (Switzerland) and CallovoOxfordian Clay (France). In some of these formations, in situ heating tests have been already used to detect the thermal impact and determine the thermal conductivity by back-analysis [5,6]. One of the main challenges when testing Ypresian clays is to restore the high in situ stresses at the depths of retrieval before thermal testing This way, opening of fissures and gaps along bedding planes during retrieval, which affect the correct determination of the thermal conductivity, are minimised [7]
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