AECL Research is conducting investigations at its Underground Research Laboratory (URL) in the Lac du Bonnet granite batholith to assess components of the Canadian concept for nuclear fuel waste disposal deep in the plutonic rock of the Canadian Shield. The Mine-by Experiment, one of nine Operating Phase experiments planned for the URL, incorporates h priori installation of state-of-the-art insu'umentation to monitor the complete mechanical response induced in the rock mass by excavation of a 3.5-m- diameter circular tunnel. This response has important implications in the design of a disposal vault, both in terms of stability of the excavation and in the potential changes in hydraulic conductivity resulting from excavation-induced damage to the rock. The final design of the experiment is based on experience with rock mass monitoring at the URL and elsewhere, detailed characterization of the experiment area, and numerical modelling.
The safe disposal of nuclear fuel waste is one of the many challenging engineering problems facing us today. In most countries that employ nuclear technology, deep underground disposal is considered the most appropriate solution. In Canada, AECL Research is responsible for assessing the plutonic rock of the Canadian Shield as a potential host medium for a nuclear fuel waste disposal vault located at a depth of between 500 and 1000 m. As part of its program, AECL Researchas consreacted an Underground Research Laboratory (IJRL) approximately 120 km northeast of Winnipeg, Manitoba in the Lac du Bonnet granite batholith (Figure 1). The URL provides a well-characterized in situ environment in a previously undisturbed volume of rock for experiments that address issues of importance in assessing the disposal concept, and/or that demonsu'ate elements of the proposed disposal technology.
During development of a disposal facility, knowledge of the response of the rock to excavation will be needed to aid in optimizing many elements of the design, including depth of disposal, layout of tunnels and rooms, excavation method and geometry, spacing of waste containers, and emplacement of seals. The Mine-by Experiment, one of nine Operating Phase Experiments planned for the URL (Simmons 1990), is designed to address some of these issues and, in particular, is aimed at characterizing excavation-induced damage and developing numerical modelling capabilities to better understand rock mass behaviour around an underground opening in massive brittle rock. The premise for the Mine-by Experiment was to locate a volume of rock typical (in terms of geology and su'ess conditions) of potential disposal sites elsewhere in the Canadian Shield, to characterize the rock mass volume and insmament it with state-of-the-art insmamentation, then to excavate a 3.5-m-diameter tunnel through the instrumented volume to measure the excavation- induced response. This type of excavation-response experiment is being evaluated as a potentially important characterization test for developing site-specificonstitutive models of rock response and rock failure at candidate disposal sites. This paper describes the rationale behind the design of the Mine-by Experiment, the final arrangement of the experiment, and the major experiment components.