ABSTRACT:
A new 10.3 km by 14.44 m diameter TBM-driven tunnel is to be constructed under 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, blocky ground, horizontal and inclined shear surfaces, and high horizontal stresses, as well as, unique challenges such as swelling, vertically variable hydrological conditions and topographic effects beneath a buried gorge. This large project provides the backdrop for a study of large scale heterogeneity and anisotropy 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 macrostructural components, including laterally extensive shear lamellae and inclined shear structures in the vicinity of topographic extremes It is the relationship between this complex stress history and the general excavation response which is of interest. Stepping through the geological 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.
1 INTRODUCTION
1.1 Engineering geology and forensic modeling A simplified version of a complex geological history, including multi-staged glacial loading and unloading, glacial and fluvial erosion, and glaciofluvial backfilling has been modeled to determine how the stress field has developed, what effects the evolution has had on the sedimentary units and the relative origin and lateral extent of the geological structures which are found to exist.
