Population increase means more mega-cities, growing very fast as “compact cities” for which surface space becomes a priority. This creates a particular urgency to make the underground space of the future cheaper to construct, and more reliable in construction and operational performance. The cost and performance of underground projects is intimately linked to the understanding and management of geologic risk for both construction and life-cycle performance of subsurface facilities. This includes not only expected and unexpected uncertainties, but also the anticipation that urban growth will extend into increasingly fragile and poor quality geotechnical environments, and that the projects will involve larger and deeper openings. This paper assesses the state-of-practice and future possibilities for improved management of geologic risk, including risk avoidance, new materials and methods, ground improvement, life cycle engineering for sustainability, and better subsurface characterization. Some geologic risks have plagued for centuries, e.g., ground water, shallow cover and weathered rock, subsidence and impact on structures, stresses and stress relief, progressive deterioration. New risks have arisen associated with new technologies, unexpected stress-driven ground behavior at increased depth, design for higher water inflows and pressures, and the requirement for larger spans and a variety of excavated shapes. In addition, a better understanding of the spatial variability of soil and rock structure is needed a priori, including application of geophysical and remote sensing techniques. Our site investigations of the future need to be increasingly confirmatory rather than exploratory, and we should plan more effectively for ground improvement before construction.
Svensk titel: UNDERJORDSBYGGANDE, GEOLOGI OCH GEOTEKNISK RISK