ABSTRACT
A crucial element of a tunnel lining design in metro tunnels is the time and the way till the final lining will begin to spall due to the high temperatures, which may be developed during a fire. Although the structural elements of the tunnel lining are considered inflamable, in a real fire situation the concrete lining can be spalled largely, sometimes perhaps entirely, with very serious consequences on cost and safety of people. The spalling rate of concrete as well as the spalling depth are two main values that cannot be measured since they are affected by a series of factors including mechanical properties, permeability of concrete and age of concrete. A lot of research has taken place in order to calculate the spalling of the concrete using numerical models, which however is not validated sufficiently by the test results. So the target of the specific research is to investigate experimentally the rate and the depth of spalling for several types of concrete under high temperatures. On this purpose specimen of all types of concrete that can be found in metro tunnels were manufactured and exposed at high temperature in a special furnace which has the ability to simulate all kind of fire scenarios and at the same time monitor the spalling depth and time. The temperature of the exposure was selected after modelling of a 25 MW fire in a metro tunnel. The modelling simulated the distribution of the temperature along the tunnel in case of a 25MW fire and representative values of the temperature for 10, 20, 50 and 100m away from the fire ignition were selected.
