Mechanised tunnelling in urban areas

摘要

Successful tunnelling in major cities requires a great understanding of the urban environment: Dense infrastructure on the surface, surface and subsurface utilities, man-made ground, and the natural geological medium. While the first three components may, to a certain extent, be documented and can be investigated with relative ease, the last element, i.e. the ground, remains the most difficult element to correctly interpret. Due to the diverse origin and history of the ground in each city environment, no two natural deposits are exactly alike with regard to physical properties and behaviour. Other hazards associated with tunnel construction in urban areas include poor ground conditions, presence of groundwater, shallow overburden (often approaching feasibility limits), and potentially damaging ground settlements induced by tunnelling. As wisely pointed out by Peck, the engineering properties of the ground cannot be specified, they can only be investigated, determined, and coped with under the physical conditions to which they may be subjected. No two jobs are exactly alike. Yet the designer must design and oversee the construction of a project that serves its purpose safely and economically.