Authors: M. A. Perras and M. S. Diederichs
1st Canada-US Rock Mechanical Symposium, Vancouver, Canada: May 29, 2007
Abstract
A new 10.3-km by 14.44-m diameter TBM-driven tunnel is under construction beneath the Canadian City of Niagara Falls, Ontario, descending through the entire stratigraphy of the Niagara Escarpment, including dolomites, limestones, sandstones and shales. The tunnel will run for much of its length through the Queenston Formation and will encounter mixed face conditions, block ground, horizontal and inclined shear surfaces, and high horizontal stresses, as well as unique challenges, such as swelling, vertically variable hydrological conditions and topographich effects beneath a buried gorge.
This large project provides the backdrop for a study of large-scale heterogeneity and anistropy in geology, material properties and stress conditions, and the impact on excavation performance and rock-support interaction. An understanding of the digenesis, glacial preconditioning, erosion and structural development of the existing rock mass will help in reconstructing the complex stress regime, including vertically discontinuous lateral stresses and macro-structural components, laterally extensive shear lamellae and inclined shear structures near topographic extremes.
This paper will discuss the geological origins of these features through by numerically modelling past glaciations and subsequent erosion in highly heterogenous laminated ground. It is the relationship between this complex stress history of the Niagara Region, from glacial loading in the Pleistocene to post-glacial erosion, using numerical models will allow for a better understanding of the mechanics involved in fracture formation under these loading and unloading conditions. The model results indicate that deformation can extend out from the gorge up to 1000 m in some of the geological formations.
