Assessment of cast-in-situ FRC linings for high-speed railway tunnels with respect to fatigue and cracking

Report, 2018

This report presents the results of a pre-study aimed at investigating a number of critical aspects identified for the execution of a fibre reinforced concrete lining in relation to the construction of high-speed railways in Sweden. The work carried out focused primarily on the study of fatigue performance of FRC and on the structural response of the tunnel lining under the actions of various loads including air pressure and suction, shrinkage and temperature changes.
In the first part of the report a literature review was carried out to examine the state-of-the-art of fatigue of FRC and derive some qualitative relations to evaluate the risk of fatigue failure due to cyclic loading of the tunnel lining (106 cycles). Subsequently, the tunnel lining was modelled using the commercial finite element software DIANA and non-linear analyses were carried out to determine the risk of cracking and the potential crack widths for a number of load cases.
The main results of this pre-study showed that fibres can provide a small enhancement of the fatigue performance of FRC compared to plain concrete for moderate fibre dosages of up to 1.0% vol. Nevertheless, the effect of reverse loading and existing cracks on the fatigue behaviour of FRC are largely unexplored and require further investigation. It was also found that cyclic loading due to the air pressure and suction from passing trains produced a maximum stress variation of about 10% of the concrete tensile strength, thus posing no risk for fatigue failure provided the concrete lining is uncracked. Conversely, non-uniform shrinkage and temperature gradients were able to induce cracking. In cracked conditions, the air pressure and suction were sufficient to produce excessively large cracks, thereby posing a risk for the fatigue life and durability of the tunnel.