ABSTRACT
Existing rock tunnels may be required to be renovated, which is sometimes referred to as rehabilitated, for an alternative use from their original design function or to be enlarged for alternative future operations. The renovation of an existing tunnel is typically performed by taking the tunnel out of service in order to allow the new works to be completed in a timely manner without undue interruptions. The renovation of historical tunnels should be based on a comprehensive review and full understanding of the original design and construction. Historical tunnels that are planned for decommissioning and have been out of service for an extended period should be inspected by either remote methods if the safe and stability is a possible concern or by direct observations in order to understand the current conditions and integrity of the tunnel. The decommissioning of an existing tunnel commonly requires the effective sealing or plugging of the ends of the tunnel to prevent future access.
