Identification of extension of excavation damage zone by diametrical measurements of p-wave velocity on rock cores delivered from the Kiirunavaara mine (Sweden)

In recent years a lot rock mechanics research has been conducted. One of the main subjects was the Excavation Damage Zone (EDZ). It was of importance because EDZ causes significant changes on mechanical properties, hydraulic conductivity, orientation of the stress field and many other parameters of rock around underground excavations. Some companies like ANDRA (Agence Nationale pour la Gestion des Déchets Radioactifs, France), UK NIREX (United Kingdom NIREX Limited) and SKB (Swedish Nuclear Fuel and Waste Management Co.) involved in the construction of underground spent nuclear fuel repositories have invested significant funds in these researches and extensive knowledge have been obtained in this field. However, most of the research has been concentrated on underground openings excavated with smooth blasting or TBM and very little has been done on drifts excavated in production conditions. Therefore the EDZ is of interest for LKAB (Swedish Co.) and it initiated a research project. Within that project the extent of EDZ was investigated by four different methods – Cross-Hole Seismic, Spectral Analyses of Surface Waves, Borehole Image Processing and Ultra-Sonic method. This thesis work deal with identification of extension of EDZ by diametrical measurements of p-wave velocity (Ultra-Sonic method) on rock cores delivered from the Kirunavaara mine. Diametrical measurements were carried out on cores from two types of rock – iron ore and host rock. To be able to pick up good acoustic signal a couplant have been used. Based on received data two types of analysis have been done – first analysis is based on coefficient of anisotropy, kv, and second is based on ration VPs/VPd. Results obtained during measurements revealed damage of rock in different scale, but the reason which caused that damage could not be identified. In heavily damaged rock the influence of couplant on results was noticed. For that reason some additional tests have been carried out – with saturated sample and Ultrasonic Gel as a couplant to see how large the influence is and to be able to estimate the real velocity of p-wave. Moreover there was a problem with getting signal on heavily damaged rock, therefore some study should be done to identify either it is problem of method or equipment.Validerat; 20101217 (root