Large Diameter Shafts: A 3d Analysis

The growing population of cities and the consequent need for transportation have led to a rapid increase in underground infrastructure. Accesses for this infrastructure can serve the purpose of ventilation systems, emergency exits or subway stations. Stations demand large spaces for all the facilities and passengers in transit and must be located within a reasonable distance from the main transportation demanding points. The traditional method to build these stations has been the cut-and-cover method. The option of large diameter shafts, excavated by a sequential optimize cycle, has recently been used to locate subway stations in replacement to the traditional solution. In this paper two case studies of these structures for the purposes of subway stations in Brazil and Portugal are presented. Two-dimensional axisymmetric finite element analyses, despite being able to represent both the ground and the lining, are limited to model the sector-construction sequence and inclined geological layers, therefore these conditions on the behaviour of large diameter shaft were evaluated by the means of a parametric set of 3D finite element models with varying the height of the vertical excavation stage, construction sector stages and dip of the geological layers. The results are evaluated in terms of surface settlements, induced stresses and displacement profile.