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Summary of foreign knowledge about the origin and development of EDZ in crystalline rocks - research
Vavro, Martin ; Souček, Kamil ; Staš, Lubomír ; Vavro, Leona
Presented search summarizes findings of foreign research oriented on the origin and evolution of the excavation damaged zone in crystalline rocks with a particular focus on the essential results of experimental projects which were performed in Canada, Sweden, Finland, and Switzerland. The study is divided, excluding the introduction, into seven main chapters of the text, which gradually deal with: (1) definition of key terms, (2) overview of the main underground research laboratories in the world where EDZ assessment was conducted, (3) methods suitable for EDZ description and characterization, (4) main factors influencing the origin of failure around the excavations and time-dependent evolution of EDZ. An overview of important outcomes of EDZ experiments, focusing on the European hard rock laboratories (Stripa, Äspö, Onkalo/Olkiluoto and Grimsel), and their summary are presented in the final two chapters.\nThe review summarizing the published key findings and results of in situ experiments shows, that for rock in lower stress state, i.e. in no spalling environment, the extent and character of rock mass damage is typically dependent on the excavation method. Using mechanical excavation, rock damage zone with thickness less than 3 centimeters can be originated. The microcracks within this zone contribute to the increase of hydraulic conductivity of the rock mass. At some test sites (Äspö, Grimsel), where the tunnel boring machine technology was used, the damage zone was already detected in depth of less than 5 mm.\nOn the contrary, openings excavated by drilling and blasting are characterized by much more extensive damage zones up to several tens of centimeters in width. The damage progressively diminishes with the distance from the opening.
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