Geotechnical Society of Edmonton

NEWS 2008

Posted March 20, 2008

Event March 20, 2008

University of Alberta Student Seminar - Development of EDZ around a niche in the Opalinus Clay

Dr. Salina Yong

In Switzerland, the Opalinus Clay is under consideration as a potential host rock for deep geological disposal of nuclear waste. The construction of an underground opening perturbs the surrounding rock mass and leads to the creation of an Excavation Damaged/Disturbed Zone (EDZ/EdZ). Understanding the processes under which excavation-induced perturbations are created and their impact on the properties of the host rock are important in the context of geological waste repositories. Consideration of an overconsolidated argillaceous host adds mechanical complexities as these materials are inherently transitional and rarely isotropic. Past investigations at the Rock Laboratory indicate the EDZ/EdZ consists of two sets of fractures induced by the excavation of openings perpendicular to the strike of bedding. One set is oriented sub-parallel with the tunnel axis in the sidewalls while the other is oriented sub-parallel with bedding and found above the crown and below the invert. However, few tunnel-wall-parallel fractures were identified in a recent field experiment (EZ-B) conducted at the Rock Laboratory yet rock mass degradation has been nonetheless indicated in other field measurements. In the EZ-B Experiment, a short test tunnel was excavated sequentially and the surrounding rock mass monitored before, during, and after the excavation. In this thesis, excavation-induced perturbations are characterised and influential factors and an appropriate damage criterion are identified. Characterisation of the EDZ/EdZ was achieved through the integration and comparison of field data with numerical modelling results. Under certain kinematic conditions, the role of rock mass heterogeneity dominated over that of intact rock heterogeneity.

Changes in the maximum and minimum principal stress ratio were found to provide an appropriate fit to the rock mass degradation indicated by seismic measurements and the observations of borehole instabilities.

Location: Room 2-118 NREF University of Alberta
Time: 12:30 p.m. - 1:30pm
Date: Thursday, March 20, 2008
Cost: Free

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