Interaction between underground works and deep foundations: A risk assessment approach

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. This chapter establishes 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. A risk assessment based on the problem geometry and construction alternatives is presented in the form of a risk matrix. In terms of ground conditions in the soil-structure interaction model, for simplicity, it has been assumed to be constructed in a single stratum in the model geometry, corresponding to a fine soil material with undrained and drained behavior for short-term and long-term scenarios respectively. The chapter aims to improve the understanding of the foreseeable interaction effects in this type of infrastructure for when similar projects are faced in the future. When installing bored piles in close prox