Characterizing Excavation Damage in Highly-Stressed Granite at AECL's Underground Research Laboratory

Abstract

Experience at AECL's Underground Research Laboratory (URL) has shown that sparsely fractured rock masses at depths of several hundred metres may be subjected to high in situ stresses and highly anisotropic stress ratios. Under such conditions, an excavation damaged zone (EDZ) may form around an underground opening. The nature and extent of the EDZ are of particular importance in terms of understanding the potential for increased permeability in the near- field. Results of in situ characterization and numerical modeling of a circular test tunnel excavated in highly stressed granite at the URL show that the EDZ is limited to a region within about 0.6 radii from the original perimeter of the tunnel. Within this region, however, the characteristics of the EDZ are highly variable around the tunnel. This paper describes the field characterization of the Mine-by test tunnel, and the interpreted characteristics of the EDZ based on numerical modeling. Results are compared to those from other excavations at the URL, illustrating that the nature of the EDZ can be controlled through tunnel design.