scope:

This document is to be used to determine the structural adequacy of existing Tunnels, and their components, in the specific circumstances when a Tunnel Structural Assessment is required by the management processes defined in NR/L2/CIV/084, Management of Tunnels. 

The objective of structural assessments is to establish the degree to which the assets remain safe and capable of fulfilling the structural aspects of their defined functions in their current, or any changed, conditions and environments.

The process of a structural assessment is intended to: 

a) inform management actions that are required to maintain the safe operation and performance of the structure; 

b) determine, check and identify changes in the stability, load bearing capacity, condition and use of structure; 

c) determine whether structures remain safe to carry existing, proposed and abnormal loads; 

d) check the structural adequacy for proposed change in use or loading. 

 This document includes requirements and guidance for: 

• Quantitative Assessment; and 

• Qualitative Assessment. 

This document is not applicable to unlined sections of tunnels. 

This document is not applicable to routine assessments of Tunnels, formerly part of the Bridge Guard 3 programme. For parts of Tunnels where the cover depth is assessed as low, it may be appropriate to carry out structural assessments in accordance with the requirements for an Overline Bridge as set out in NR/L2/CIV/035, Management of Structural Assessment Manual. 

Purpose 

This document provides requirements and guidance for the structural assessment of Tunnels. 

There are risks that the structural adequacy of Tunnels would be compromised by deterioration of material condition or changes in loading actions. Structural assessment is part of a framework of control measures that mitigate the risks such that there is no unacceptable risk to safety and performance.