Groundwater Control For Underground Construction In High Risk Urban Environments

Underground projects can have significant effects on the hydrogeology of the surrounding region both in the short term (during construction) and the long term (during operation of the infrastructure). Groundwater inflows can cause drawdown which has the potential to have adverse effects on the local and regional hydrogeology including:

• Movement of existing groundwater contamination
• Settlement and subsequent impact to existing infrastructure
• Activation of potential acid sulphate soils and rocks
• Groundwater dependent ecosystems
• Waterway base flows
• Private usage of groundwater
• Management and disposal of variable quality groundwater

This paper will detail the process that is used to characterise the groundwater system and assess the impacts and risks of underground construction for major infrastructure projects. This will be illustrated with examples of how these processes have been implemented on previous and current projects. This will inform project decision makers on best practice to manage the groundwater risks future projects will need to deal with.

Examples of primary and secondary groundwater controls will be described, including:

• Alignment selection considering hydrogeological factors and properties
• Construction methodology and retaining system selection
• Choosing a method of groundwater control
• Grouting, including surface grouting, in-excavation grouting and post-excavation grouting
• Groundwater recharge schemes
• Instrumentation and monitoring