Abstract

The experience gained in the 1999 fire catastrophes in the Tauern (Austria) and Montblanc (France) tunnels, as well as full-scale tests and investigations reveal the effect of high temperatures on the weakening of rock structures in tunnels. The effect of high temperature on tunnel lining has been studied profusely. Investigations are less numerous on the effect on rock mass, and these have focused on the reduction in the strength and the variation of the elastic behaviour of the rock with temperature. This research focuses on limestone samples from boreholes made for a road tunnel in the south zone of the Catalan Pyrenees (Spain). It has been observed that for certain geochemical compositions, some rock samples explode violently when heated to certain temperatures. This phenomenon is not considered in international regulations and, therefore, it is not considered in the design, operation, or performance of emergency services. A description of the potentially explosive rock is given. The activation temperature and the geochemical composition before and after an explosion are determined. The results facilitate the early identification of this type of material, and the implementation of safety measures in the early stages of the life cycle of this type of infrastructure.

1 Introduction

The experience gained in the 1999 fire catastrophes in the Tauern (Leitner 2001) and Montblanc tunnels revealed the effect of high temperatures on the weakening of tunnel structures. The effect of high temperature on the tunnel lining has been studied profusely (Bamonte et al. 2016; Prochazka and Peskova 2008). In the case of the effect on the rock mass, investigations are less numerous: some studies on rocks exposed to high temperatures are specifically focused on tunnel safety, such as Smith and Pells (2008, 2019) on sandstone tunnels in Australia, or Nordlund et al. (2014) on igneous rocks in Sweden. Full-scale tests were performed by Keski-Rahkonen et al. (1986). As a general overview, an increase in temperature causes a decrease in uniaxial compression strength and elastic modulus, an increase in volume and porosity, as well as cracking and spalling phenomena in surrounding rock.

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