Material degradation in tunnels

Degradation of materials used in tunnel construction can cause damage and eventually lead to tunnel closure. To support tunnel owners and their consultants in identifying, preventing, and stopping these failure mechanisms, the COB network has described more than fifteen types of damage along with instructions for maintenance and (non-destructive) inspection techniques.

Currently, it is not possible to implement predictive maintenance or to reliably determine the actual scope of a tunnel renovation project. This is due to gaps in fundamental knowledge about failure mechanisms. The Degradation Committee of the COB tunnel programme focuses on the deterioration of materials used in tunnel construction. The research includes for example the corrosion of reinforcement and the reduction of fire resistance. These kinds of mechanisms can often be detected by the damage they cause. This report gives a detailed overview of typical types of damage that indicate degradation mechanisms.

PART 1 describes the types of damage that can occur in tunnels. Each page provides a photo, the description, its major causes, when and where it can occur, and what the consequences and risks are. For each type of damage preventive measures, forensic tools, and sensoring and monitoring techniques are presented as well as a brief description of how the damage can be repaired and maintained. PART 2 of this document describes the forensic tools, mostly non-destructive, which can be used to investigate the nature and severity of each type of damage.

Together with this document, the committee developed a Fault tree tunnel degradation, in which failure mechanisms related to the degradation of materials are discussed. This instrument should serve as a basis for entering into discussions with managers about the recognizability and prevalence of these mechanisms. And also ‘Principles and methods for protection and repair of concrete structures’ was developed. This document contains an overview that indicates products and systems for the protection and repair of concrete structures (NEN-EN 1504-9) and how often they are used in the Benelux, what the costs are and how sustainable the solution is. These documents are also available on this knowledge base. 

The Degradation Committee focuses on topics such as corrosion of reinforcement and the fire resistance of materials in tunnels. In older tunnels, degradation can lead to leakage and compromise the integrity of the entire structure.