The Excavation Disturbed Zone of the Experimental Full Scale Deposition Holes and Research Tunnel at Olkiluoto

Abstract

Three experimental full-scale deposition holes (diameter 1.5 m, depth 7.5 m) were bored in the Research Tunnel at Olkiluoto on the southwest coast of Finland. The disturbance caused in the zone close to the surfaces of the full-scale experimental deposition holes has been characterised by laser profiling to assess surface roughness, and by laboratory studies of rock samples taken from the disturbed zone using scanning electron microscopy (SEM) and two novel methods: the He-gas method to measure permeability and diffusion coefficient, and the Carbon-14 Polymethylmethacrylate method (CPMMA-method) porosity and microfracturing. The Research Tunnel itself was excavated using the drill and blast technique. The results of the studies on excavation disturbance caused by blasting show that there is a fractured zone surrounding the Research Tunnel. Hydraulic studies have indicated a hydraulic skin zone. The disturbed zone close to the surface of the walls of the full-scale experimental deposition holes exhibited increased permeability, higher diffusion coefficients and higher porosity. This paper includes some preliminary results covering the studies of excavation disturbance close to the surface of the walls of the full-scale holes and the excavation disturbance caused by blasting.