X-ray computed tomography investigation of structures in Opalinus Clay from large-scale to small-scale after mechanical testing

Annette Kaufhold,Gerhard Zacher,Matthias Halisch,Stephan Kaufhold

doi:10.5194/se-7-1171-2016

Abstract

Abstract. In the past years X-ray computed tomography (CT) has became more and more common for geoscientific applications and is used from the µm-scale (e.g. for investigations of microfossils or pore-scale structures) up to the dm-scale (full drill cores or soil columns). In this paper we present results from CT imaging and mineralogical investigations of an Opalinus Clay core on different scales and different regions of interest, emphasizing especially the 3-D evaluation and distribution of cracks and their impact on mechanical testing of such material. Enhanced knowledge of the testing behaviour of the Opalinus Clay is of great interest, especially since this material is considered for a long-term radioactive waste disposal and storage facility in Switzerland. Hence, results are compared regarding the mineral (i.e. phase) contrast resolution, the spatial resolution, and the overall scanning speed.With this extensive interdisciplinary scale-down approach it has been possible to characterize the general fracture propagation in comparison to mineralogical and textural features of the Opalinus Clay. Additionally, and as far as we know, a so-called mylonitic zone, located at an intersect of two main fractures, has been observed for the first time for an experimentally deformed Opalinus sample. The multi-scale results are in good accordance to data from naturally deformed Opalinus Clay samples, which enables us to perform systematical research under controlled laboratory conditions. Accompanying 3-D imaging greatly enhances the capability of data interpretation and assessment of such a material.

Highlights

In the past years X-ray computed tomography (CT) has became more and more common for geoscientific applications and is used from the μm-scale up to the dm-scale
In this paper we present results from CT imaging and mineralogical investigations of an Opalinus Clay core on different scales and different regions of interest, emphasizing especially the 3D evaluation and distribution of cracks and their impact on mechanical testing of such material
Enhanced knowledge of the testing behaviour of the Opalinus Clay is of great interest, especially since this material is considered for a long-term radioactive waste disposal and storage facility in Switzerland

Summary

Introduction

In the past years X-ray computed tomography (CT) has became more and more common for geoscientific applications and is used from the μm-scale (e.g. for investigations of microfossils or pore-scale structures; e.g. Schmitt et al, 2016) up to the dm-scale (full drill cores or soil columns; e.g. Schlüter et al, 2015). Benchtop CT equipment for material and geoscience were developed and are frequently used because almost all geoscientific samples show 3-D features which would be missed when analysing 2-D sections only (e.g. by classical microscopy). These features are for example the abundance of minerals, the location of particular particles towards bedding (or texture in general), the pore system, cracks, and veins. Due to the resolution of μ-CT devices in range of a few μm (Brunke et al, 2008), it is suitable to study sandstones, soils, or other rocks with large particles and less suitable for the characterization of clays.

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