Effect of excavation stages on stress and pore pressure changes for an underground nuclear repository
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ORIGINAL PAPER
Effect of excavation stages on stress and pore pressure changes for an underground nuclear repository A. K. Verma & M. S. Saini & T. N. Singh & Avi Dutt & R. K. Bajpai
Received: 2 February 2011 / Accepted: 22 August 2011 / Published online: 16 September 2011 # Saudi Society for Geosciences 2011
Abstract This paper provides a brief overview of evolution of deformations, stresses, and pore pressures due to different excavation stages during construction of an URL. Excavation of a rockmass develops damage zone of finite width around the excavated zone which is associated with changes in permeability and affect the fluid flow mechanism. In this study, a coupled hydromechanical (HM) analysis for a water saturated porous rock mass has been done which is caused by sequential excavation and backfill of vertical disposal pit of an URL. For this purpose, an Atomic Energy of Canada Limited’s in-floor concept for a deep geologic repository suitable for Indian condition has been used. Changes in rock deformations, stresses, strains and mechanically induced pore pressure in an undrained condition, during excavation, as well as those caused by mechanically induced rock deformations after backfill of the disposal pit have been modeled. A three-dimensional finite difference tool FLAC3D (Itasca Consulting Group Inc. FLAC-3D 1997) has been used for the analysis.
A. K. Verma (*) Center for Research on Energy Security, The Energy and Resources Institute, Delhi, India e-mail: [email protected] M. S. Saini : A. Dutt Institute of Technology, Banaras Hindu University, Mumbai 400085, India T. N. Singh Department of Earth Sciences, Indian Institute of Technology-Bombay, Mumbai 400076, India R. K. Bajpai Repository Programme Section, Bhabha Atomic Research Center, Mumbai 400085, India
Keywords Hydro-mechanical . Underground geological repository . Flac3D . Coupled analysis . Pore pressure
Introduction Development of nuclear power in the 1950s was hailed as a major technological advancement providing an unlimited source of cheap power, without the shortcomings of finite hydrocarbon and hydroelectric resources (Witherspoon and Bodvarsson 2001). The disadvantages associated with highlevel waste (HLW) in the short-term are due to exposure of radiation and significant heat generation. Hence, there is a need to isolate it from the wider environment and to keep the wastes cool until ready to dispose. While in the longterm, release of heat and radiation from the wastes into the environment tends to induce chronic impacts and hence it needs to be permanently isolated for longer periods. The space between the canisters containing the spent HLW wastes and the excavation is to be backfilled with a material selected in such a way that the backfill constitutes an engineered barrier with especially designed characteristics. In most envisaged designs, expansive clays have been chosen as the most adequate material on its own or in combination with other materials as it regains the original stresses after saturation (Booker and Savvidou
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