Damaged rock zone around excavation boundaries and its interaction with shotcrete

Abstract: When an excavation is carried out in a body of rock, the mechanical, hydraulic and physical properties of the rock surrounding the excavation will be disturbed. The zone in which these occur is called the Excavation Disturbed Zone (EDZ) and must be represented in the quantitative assessment of the near-field host rock. Therefore, numerous investigations of the EDZ have been conducted worldwide and are reported in for example, the International EDZ Workshops of 1996 and 2003. By definition EDZ encompasses both, the zone where the rock is physical damaged (mechanical properties are permanently affected) and the zone where the rock is only disturbed (mechanical properties not significantly affected). The former, i.e. the damaged zone, will impact significantly the overall performance of an excavation since the mechanical properties of this zone are considerably reduced. This zone is referred to as the Damaged Rock Zone (DRZ) and is the focus of this study. The strength and stiffness of this zone are important governing parameters that determine how this zone behaves, as well as how it zone interacts with shotcrete as surface rock support. Despite the fact that much has been covered on the subject of excavation damaged zone, most of these work were mainly focused on, (1) identifying factors that influence the development and extent of the damage zone, and (2) quantitatively measure the extent of the damaged zone. The main goal of these studies was for the reduction of this zone. Since, it has never been possible to completely eliminate this zone what is left is in fact to quantify this zone it terms of its strength and stiffness, in order to visualize how the excavation will perform with the presence of DRZ, including its interaction with the rock support systems, which will ultimately lead to recommendations for support optimization. In this regard only few researchers have gone a step further, from just delineating the damaged zone, to quantitatively estimate the stiffness of this zone. Although it is also desirable to measure the strength of the DRZ, it is at this point in time practically difficult and not to mention the complex physics involved. This thesis, as well as the future research, will focus on the behavior of the DRZ and its interaction with surface rock support. Questions about how the strength and stiffness vary with respect to their position and magnitude around the excavation will also be investigated with the help of numerical methods. In the study reported herein however, the primary focus is on, 1) the literature review aspect and 2) stage one field and experimental work on the DRZ and its interaction with shotcrete.