Visualization of Pore-Structural Deformation of Dynamic CT Images of a Leitha Limestone

The deforming mechanism of rocks is an important basis for studying the lithosphere deformation and local tectonic activity, while microstructure of rocks is the key to study its deforming mechanism. Microtomography(Micro-CT), which can obtain high-resolution three-dimensional(3D) digital images nondestructively, make it possible to observe the internal structure of rocks. The dynamic CT technique by using HADES device further enables the observation of the deformation process of rocks. In this paper, a set of 3D dynamic CT images of a Leitha limestone experienced triaxial test have been processed to characterize the evolution of pores by using the concept of cluster of percolation theory. The processing and analysis include:image cropping and masking, image segmentation, quantitative analysis and visualization. The visualization of pores has been carried out by presenting:all pores, the largest cluster, small clusters, and fracture-like small clusters. The results show that:(1) the largest percolating pore is continuously reducing while the sample is compressed;(2) new pores or cracks appear in the upper part of the sample in the early steps of the compression;(3) a shear zone emerges in the lower part of the sample after axial strain over 3.5% and it is represented by a large number of small fractures and/or pores in a zone of a dip angle around 45°. This implies that the deformation of the highly porous rock not only exhibits the formation of compaction bands as observed previously, but also shear deformation. The interesting aspect is that the orientations of small fractures distributed along the shear zone do not accompany the orientation of the shear zone, showing there is no predominant direction. This study reveals the concurrency of compaction band and shear zone by the visualization of catalogued clusters. The reason that the orientations of newly created small fractures along the shear zone do not show the same as that of the shear zone may be caused by the complexity of local microstructures of pores. This is worthwhile to be studied further in future.