Spalling Mechanism: Key for Structural Fire Resistance of Tunnels

Abstract

The need to consider tunnel safety, especially with respect to fire, has been highlighted in the past by various severe tunnel fires that have occurred throughout Europe. This article provides a general overview of the current rules and regulations governing the fire resistance design of tunnel structures. Subsequently, the engineering perspective is presented, focusing on the assessment of fire severity and the resulting thermal loading on the tunnel structure, which may result in spalling of concrete. Thereafter, a scientific perspective is provided, reflecting recent advances made in numerical calculations with respect to the spalling mechanism. From the numerical results and comparison with observations from full-scale tests, it is concluded that thermal restraint is dominant for spalling. Spalling is triggered by the buckling of concrete layers loaded with strains imposed by temperature, which is a new perspective for future scientific research and innovative engineering solutions.

Keywords:

• tunnels
• concrete
• fire safety engineering
• structural fire resistance
• full-scale testing
• spalling mechanism
• finite element model

Acknowledgement

With reference to the examples of best practice the authors would like to acknowledge the commissioning parties Lantis, formely known as the Holding Company Antwerp Mobility (BAM) and the municipality of Amsterdam as well as the collaboration with amongst others the Netherlands Organisation for Applied Scientific Research (TNO), Efectis and the Leipzig Institute for Materials Research and Testing (MFPA).

With respect to the scientific research findings the authors would like to thank the Netherlands Organisation for Scientific Research (NWO), domain Applied and Technical Sciences (TTW), formerly known as the Dutch Foundation for Applied Sciences (STW), for financially supporting the research project nr. 07045 on “Explosive spalling of concrete” by Eindhoven and Delft Universities of Technology.

Disclosure statement

No potential conflict of interest was reported by the authors.