Underground excavations for the development of infrastructure, mining operations, waste management etc. require support measures to ensure stability both during their construction and operational phases, which highly depends on the rock mass strength and deformability. Discontinuities within the rock mass are intrinsic features which determine said strength and deformability and affect the excavation stability. Several defining parameters demonstrate that rock mass variability has significant control in the material response during an excavation, especially in sedimentary rocks. In this paper, the Thornhill Sandstone is examined by applying numerical analysis and its mechanical response is investigated under several scenarios with varying excavation geometries, stress conditions while incorporating the influence of discontinuities explicitly within the numerical model. A two-dimensional parametric analysis is performed by applying the Finite Element Method (FEM) and integrating Discrete Fracture Networks (DFNs). More specifically, four different excavation geometries and three different in situ stress regimes are investigated. Drawing on the results, this paper provides insights for tunnel design optimisation when layered rock masses are encountered during an excavation in various underground stress environments with different opening geometries.
The ever-increasing urban population across the globe, the requirement to reach greater depths for mining operations, the development of waste management or storage facilities etc. require implementing underground excavations to solve complex engineering problems and promote sustainable development. Underground excavations, however, are structures requiring support measures in most cases to ensure the excavation stability both in short- and long-term conditions. The opening stability is influenced by various aspects, including the properties of the host rock mass, the excavation geometry, the depth of the overburden etc. Underground structures aid in furthering a community’s long-term sustainability and resilience when a holistic approach and smart planning is incorporated in the design, obtaining positive results in both socio-economic and environmental aspects of development [1]. However, it is important to understand what the ground response as well as the ground/support interaction is going to be to ensure the stability of the underground opening. For the purposes of this research, we are investigating the influence of macro-scale rock discontinuities to assess potential excavation instabilities across a range of different discontinuity patterns that may be encountered when excavating within layered rock masses with an emphasis on sedimentary rocks.