Practical methodology for the design and management of instability in hard rock tunnels

The stability of rock faces in underground facilities is critical when considering their lifespan as well as the health and safety of the operatives working within them. Recent years have seen an evolution of new techniques for inspecting tunnel faces and options available to remediate instability - the Lidar technology is becoming more readily available and necessary for assessment of the stability of rock faces. However, rockbolts and sprayed concrete remain the most commonly used solutions within underground facilities in Scotland. These have to be suitably specified to ensure their required design life can be achieved and, as such, detailed site investigation must be carried out prior to their installation. Factors such as groundwater flows and chemical aggression are variables that can potentially be considered when specifying levels of corrosion protection for rockbolts or the drainage requirements of a sprayed concrete system prior to application. In order to ascertain the exact position or pattern of rockbolts, a classification and analysis and of the geological conditions on site has to be carried out to inform the design of a stabilisation system. Critical analysis showed that the majority of the engineering works associated with remediating instability in hard rock tunnels is based on engineering judgement rather than governing standards which makes it difficult for stakeholders to suitably manage problems with instability, and rely heavily on consultants for advice. In an attempt to address this, this study aims to provide the stakeholder’s geotechnical engineers with a best practise methodology framework in dealing with instability in hard rock tunnels, critically reviewing the site investigation techniques used and following up the information flow and geotechnical data management through to the design stage.