Excavation Induced Ground Movements And Risk Management Strategies

As well as the need to maintain stability, retention systems for excavations in urban environments are required to limit ground movements to mitigate adverse impact to adjacent structures. Tolerable ground movements will depend on the circumstances of the site; in particular the proximity and type of adjacent structures and their foundation type, underground services or tunnels and their current structural condition. It is impractical to limit excavation induced movements to zero even though this may be the wish of the adjacent property and infrastructure owners. Therefore, a site specific risk management strategy is essential for the selection, design and construction of an appropriate retention system for a particular set of site circumstances.

This paper provides a brief overview of excavation performance in different types of ground including a review of measured horizontal movements in deep basement excavations in the Sydney region and a literature study of excavations in soils. The paper then discusses prediction methods including analytical, numerical and empirical techniques, impact on adjacent structures and mitigation measures. Two short case studies are then given to illustrate the adopted risk management strategies. The first case study concerns an excavation adjacent to several existing railway tunnels, for which a risk register together with a monitoring system were used to manage the rail authority’s concerns on potential damage to the tunnel linings. The second case study describes the application of damage assessment that enabled the client to be informed of the risks and the selection of the appropriate excavation and retention method to reduce risks associated with excavation adjacent to heritage listed buildings.