Underground openings in rock excavated using drills and blasting technique are surrounded by a zone with altered properties. The zone can be a conduit for the transport of solutions and radionuclides in a nuclear waste repository. The porosity and microfracturing of the blast samples taken from the walls of the Research Tunnel at Olkiluoto in Eurajoki, Finland, were investigated using the ~(14)C-PMMA method. Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDS) were used to investigate the pore apertures and minerals in porous regions in greater detail. A clear increase in porosity was observed to depths of 10- 30 mm from the surface of the half barrel of blast holes. Damage was observed in the rock texture as several fractures radial to the half barrel. The ~(14)C-PMMA method proved to be a practical and efficient tool for studying the extent and intensity of the damaged rock zone. It effectively filled the gap between macroscopic and microscopic investigation methods and provided quantitative information about nanometre-range porosity which is beyond the scope of most standard methods of microscopic investigation.
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