Determination of Extent of Excavated Damage Zone Around Mined Tunnels using Pre and Post Construction Pore-Water Pressure Response

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* * * *** * Normal* 0* * * * * false* false* false* * EN-US* JA* X-NONE* * * * * * * * * * * * * * * * * * * * * * * * * ** * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * **** /* Style Definitions */*table.MsoNormalTable* {mso-style-name:"Table Normal";* mso-tstyle-rowband-size:0;* mso-tstyle-colband-size:0;* mso-style-noshow:yes;* mso-style-priority:99;* mso-style-parent:"";* mso-padding-alt:0cm 5.4pt 0cm 5.4pt;* mso-para-margin:0cm;* mso-para-margin-bottom:.0001pt;* mso-pagination:widow-orphan;* font-size:12.0pt;* font-family:Cambria;* mso-ascii-font-family:Cambria;* mso-ascii-theme-font:minor-latin;* mso-hansi-font-family:Cambria;* mso-hansi-theme-font:minor-latin;* mso-ansi-language:EN-US;}****The containment of nuclear waste in deep geological repositories (DGR) is the preferred method for long-term disposal of spent nuclear fuel globally. The benefit of a DGR is the presence of both engineered and geological barriers that isolate the repository from the surrounding geological environment. The challenge; however, is that like any underground excavation, the surrounding host rock will be damaged during adit excavation known as the excavated damage zone (EDZ). Damage initiation and fracture propagation occurs with the crack intensity decreasing with distance from the tunnel wall, which has a direct influence on the in situ permeability of the host rock. Currently, assessment of the immediate and temporal changes within the EDZ is carried out through numerical simulation and in full-scale underground laboratories where field tests can be conducted. These underground laboratories rely on physical sampling of the host rock following excavation of test adits as well as non-destructive geophysical methods. Both of these methods have some limitations in their overall efficacy. None of these methods can fully characterize the temporal geomechanical properties of the EDZ on a real-time basis throughout the life of the test facility. ***Recent studies have demonstrated that the response of high resolution piezometers to barometric loading, often referred to as geolysimeters, can be used to characterize both the stiffness and hydraulic conductivity of deep shale aquitards (Smith et al.1,2). The overall goal of the proposed research program is to advance current methods to evaluate the development and extent of the EDZ around tunnels constructed in intermediate geomaterials. The short-term objectives involve conducting comprehensive fundamental and applied research to evaluate the potential use of geolysimeters to: (1) determine the change of the in situ stiffness with time and with distance from the tunnel wall (2) determine the change in the hydraulic conductivity of the host rock within the EDZ with time; and (3) extend the current knowledge of stress rotations during tunnel construction and the impact of the accompanying excess pore-water pressure (poroelastic) response on the overall size and shape of the EDZ. My long-term objective is to help place Canadians at the forefront of tunnel construction technologies and nuclear waste storage.***Knowledge gained from this research program will be a critical component in our ability to assess and bound the potential implications of the EDZ in various host rocks currently planned for DGR construction. The potential users of the results include nuclear management organizations, environmental protection agencies, industry, and governmental decision makers. The model improvements may also be adapted for use in DGRs, in Canada and worldwide, to help inform relevant decisi