Micro and macro-structural effects of high temperatures in Prada limestone: Key factors for future fire-intervention protocols in Tres Ponts Tunnel (Spain)

Temperature and cooling methods strongly affect the stability of tunnels drilled in rock masses so condition interventions for fire emergencies. Samples from two horizontal boreholes Prada limestone during design stage Tres Ponts Tunnel Catalan south Pyrenean zone (Spain) are heated 105 to 600 °C, subsequently cooled with air or water simulate extinguishing interventions. Changes chemical composition microstructure, physical properties (open porosity, volume, dry total weight, P S-wave velocity), mechanical (uniaxial compressive strength, elastic modulus, Poisson’s ratio) analysed. Rock weakening is observed even at low temperatures (T < 300 °C). The influence method appeared intermediate 300-400 °C open velocities, modulus show greater variation water-cooled samples. A temperature 500 paramount importance ‘Prada’ as it leads a dramatic increase porosity notable decrease velocities under both methods. Trans-granular micro-crack progression using scanning electron microscope (SEM), samples loss uniaxial strength (UCS), this due connections growing fissures. Thermal damage also when quickly cooled. An ANOVA simple regression analysis performed discard natural location borehole obtained experimental results. Finally, correlations predict UCS P-wave velocity after thermal treatment proposed exponential potential functions help make preliminary decisions tunnel fire. These predictive results on effects will be considered definition future intervention protocols Tunnel.