ABSTRACT
Complex underground infrastructure projects frequently require, especially in dense urban areas, the need to build concurrently various elements of different nature, in very reduced spaces. It is critical to determine the type of structure, geometry and construction sequence in order to optimise the design as well as to procure a safe and practical construction, minimizing risks. This paper aims to establish a preliminary design approach, for underground works in close proximity to deep foundations, that considers the construction sequence as the key element to assess and derive the optimal method of construction. For this purpose, a simplified systematic strategy, including flow charts, is proposed. Throughout this procedure, potential geotechnical and structural risks associated with the different construction options considered are identified and discussed. This paper is based on the theoretical case of a vent shaft asset construction, with high interaction effects due to the proximity of its various elements, such as, the shaft itself, the ventilation tunnels (adits), the line tunnels and the headhouse building foundation. A vent shaft is a common infrastructure element within underground railway systems in dense urban environments, and its complexity arises from the number and nature of elements to be built in close proximity. To deal with these complexities is a common challenge on many underground infrastructure projects that are becoming more frequent due to urban space limitations. The paper describes potential problems related to the construction processes and proposes design strategies to evaluate them.
