## 5 Conclusions  
In our study, samples from Prada limestone were heated to temperatures of 105, 200, 300, 400, 500, and 600 \({}^{\circ}\)C and then cooled at a slow rate in air, or by quenching in water. The rocks significantly increased in surface hardness, resistance to indentation (measured by Siever's J value), and in brittleness (measured by the brittleness S\({}_{20}\) value). These measurements combined with the evidence from the DRI index, point to a sustained increase in rock drillability. Variation in drillability with temperature were compared with decay in mechanical (UCS, elastic modulus and Poisson's ratio) and physical (P- and S-wave velocity) properties of Prada limestone. The derived conclusions of our study are listed below:  
1. DRI increased with temperature, implying a change in the drillability category at 500 \({}^{\circ}\)C (from medium to high) and a total increase of 40% at 600 \({}^{\circ}\)C, with no significant differences between cooling methods in the studied range of temperatures.
2. A decrease in DRI at 200 \({}^{\circ}\)C for water-cooled samples is explained by the closure of pores and fissures at that temperature.
3. Temperature influence is remarkable, as SJ tripled and S\({}_{20}\) doubled at 600 \({}^{\circ}\)C the initial values for intact rock. An increase in micro-fissures leads to an increase in the ability to indent represented by SJ, and a drop in resistance to crushing represented by S\({}_{20}\).
4. DRI trend almost copied that for S\({}_{20}\), so thermal variation in DRI is more influenced by S\({}_{20}\) than by SJ.
5. We investigated correlations to predict the variation of SJ and S\({}_{20}\) with temperature from variations in the physical and mechanical properties, and we reported strong correlations between most of the studied variables. The common explanation for these correlations is that variation of the studied properties with temperature is caused by a common thermal damage phenomenon (increase in porosity and micro cracking growth and coalescence) that strongly affects all considered geomechanical parameters.  
In summary, a substantial improvement in the drillability of the rock when heated, measured in terms of DRI value increase, can help improve the efficiency of mechanical excavation. Additionally, the obtained correlations enable quick and easy evaluations of drillability based on basic geomechanical parameters (such as UCS and P- and S-velocities) to support the Tres Ponts Tunnel excavations.  
Conceptualization, V.M.-I., M.E.G., C.H.S., T.M. and R.T.; Data curation, C.H.S. and A.B.; Formal analysis, V.M.-I.; Methodology, V.M.-I., M.E.G., C.H.S. and A.B.; Supervision, T.M. and R.T.; Writing--original draft, V.M.-I.; Writing--review & editing, M.E.G., C.H.S., T.M. and R.T. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
Data Availability Statement: Data is contained within the article.  
The authors wish to acknowledge [PERSON] and [PERSON] from the University of Alicante, for their valuable help on mineralogical and petrographic description of the rock. Additionally, Kreum SA, Ayesa SA, Infrastructures de la Generalitat de Catalunya, S.A.U., and the Lleida regional roads authority (Servei Territorial de Carreteres de Lleida, Generalitat de Catalunya) for providing rock samples. This work was supported by the Department of Geological and Geotechnical Engineering, Universitat Politecnica de Valencia.