Impact of excavation damage on the thermo-hydro-mechanical properties of natural Boom Clay

Abstract

International audienceBoom Clay has been considered as a potential host-rock for the geological radioactive waste disposal in Belgium. In this context, it is important to well understand the thermo-hydro-mechanical behaviour of this clay around the disposal galleries. In this study, the effect of excavation damage on the thermo-hydro-mechanical properties of natural Boom Clay around the Connecting gallery (excavated in 2002) in the Mol underground Research Laboratory HADES (High-Activity Disposal Experimental Site) was investigated. Several samples taken from a horizontal borehole drilled in July 2012 were tested. The thermal conductivity in three different orientations (perpendicular, parallel, and 45° to the bedding plane) was measured using the needle probe method. The results show a cross-anisotropy of natural Boom Clay and an impact of the excavation damage on the thermal property of samples near the gallery. To further investigate the anisotropy behaviour, bender element tests were carried out under unconfined conditions to determine the small-strain shear modulus also in three different orientations. The obtained results confirm the anisotropic behaviour of Boom Clay. Moreover, the evolution of small-strain shear modulus with the distance from the gallery axis (r) was found to be similar to that of thermal conductivity: the values in the zone near the gallery are lower than those in the far field. From these experimental data, an extent of the excavation damaged zone (EDZ) of 4 m from the connecting gallery axis was determined. Further investigations on the microstructure of several samples taken at different distances r by mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) methods were carried out. Macro-pores of diameter ≥5 μm were identified in the samples near the gallery. The identified macro-pores were related to the effect of excavation damage, and a damage variable was thus defined, allowing a damage model to be developed. The values of the two model parameters have been determined from the observed relationship between macro-porosity and thermal conductivity. Comparisons between the predicted and experimental results in terms of small strain shear modulus and hydraulic conductivity show a reasonable agreement

Studying the thermal conductivity of a deep Eocene clay formation: Direct measurements vs back-analysis results

“…Recently, Refs. [8,9] studied the thermal conductivity of Boom Clay (retrieved from HADES Underground Research Laboratory at Mol, Belgium, at a depth of 223 m) with a needle thermal probe technique at different orientations with respect to the bedding planes. Despite the apparent simplicity and standardisation of the experimental setup used, it is important to highlight that exploring thermal conductivity features on this type of sedimentary rocks with bedding planes is not straightforward.…”

Numerical Simulation on Damage and Failure Mechanism of Rock under Combined Multiple Strain Rates

“…e similar rockburst study was experienced at the Kolar goldfield, India in the 1960s [34]. Moreover, in order to examine the excavation damaged zone (EDZ), many field laboratories were established, such asÄspö Hard Rock Laboratory (HRL) [35,36,37] in Sweden, AECL Underground Research Laboratory (URL) [38,39,40] in Canada, Kamaishi mine [41] and Mizunami Underground Research Laboratory [42] in Japan, Mont Terri Rock Laboratory [43,44] and Grimsel Test Site [45] in Switzerland, Mol Underground Research Laboratory [46,47] in Belgium, and Meuse/Haute-Marne Underground Research Laboratory [48,49] in France. In China, the rockburst studies in the tunneling of Jinping project made significant contributions to the development of rockburst prediction [50,51].…”

A finite difference model for undefined end boundary to analyse the heat transfer in dry sands

“…Contemporary geoenvironmental engineering and practices deal with design and construction of several thermo-active structures such as furnaces, boiler units, forging units, brick kilns and rocket launching pads, buried conduits and electrical cables, air conditioning ducts (Kadali et al 2013), disposal facilities of waste from the nuclear and thermal power plants (Rao and Singh 1999;Krishnaiah and Singh 2004;Delage et al 2010;Dao et al 2015), underground crude oil storage tanks (Mandal et al 2013;Padmakumar 2013;Usmani et al 2015), oil carrying pipelines ( Brandon and Mitchell 1989;Abuel-Naga et al 2008;Lee et al 2010;Manthena and Singh 2001), solar ponds (Velmurugan and Srithar 2008), energy geostructures ( Knellwolf et al 2011;Loveridge and Powrie 2013;Salciarini et al 2013;Yavari et al 2014;Di Donna et al 2016;Faizal et al 2016;McCartney et al 2016), which result in conveyance of thermal energy through the soil mass. Moreover, activities like dissociation of gas hydrates by heating (Feng et al 2015;Song et al 2015Song et al , 2016 and exploitation of oil sand by steam assisted gravity drainage (SAGD) (Elsayed et al 2015;Lazzaroni et al 2016) and also soil-atmosphere interaction ( Heusinkveld et al 2004;Ochsner et al 2007;Cui et al 2013) involve heat migration through soil mass.…”