Use of deterministic and probabilistic slope stability analyses to evaluate tunnel location in landslide-prone areas

Abstract

The inherent complexity of subsurface characterization in mountainous terrains typically results in extensive analyses to optimize tunnel alignments based on parameters such as rock quality, support systems, and groundwater flow. However, limited investigations are performed to determine the influence of slope stability on the selection of tunnel location for alignments relatively parallel to the slope face. One of the major limitations of these investigations relies on the rapidly changing geometry of mountainous environments, which significantly increases the computational cost required to model detailed three-dimensional slopes. As such, slope stability analyses are often idealized using two-dimensional simulations. In this research, a case study of the Eisenhower-Johnson Memorial Tunnel (EJMT) in Colorado is incorporated to determine the minimum distance between a dual-bore tunnel and the face of the slope at which slope stability is virtually unaltered, using two-dimensional numerical simulations. The results from a deterministic and probabilistic analysis of approximately 600 simulations suggest that slope stability increases as tunnel bores are translated to areas of increasing overburden. Specifically, tunnel-slope interaction was minimized past a horizontal distance of 5.5 times the diameter of the tunnels into the slope. Complementary analyses associated with the EJMT tunnel construction, including access roads and a three-dimensional analysis of a tunnel alignment relatively perpendicular to the slope face, are included in this document. The author believes this research provides a general trend that could be applied to other projects with geomechanical properties and slope geometry within the ranges used in this study.