Geothermal prognoses for tunnels in the Andes / Geothermische Prognose für Andentunnel

Geothermal prognoses were carried out for two tunnel projects in the Andes, each running between Argentina and Chile. Different methods were applied in accordance with the different project phases.
For the feasibility study of a 52 km long railway tunnel, hydrogeological mapping and hydrochemical analyses were carried out as well as isotope analyses on a thermal spring. An attempt to use silica and ionic solute geothermometers produced different results. For the central section of the tunnel temperatures are assumed to reach 50 to 70 °C and further investigations are recommended.
The second tunnel project is now in the design phase. Two investigation phases have been completed including geological/ hydrogeological mapping, water sampling and analysis and core drilling. The geothermal gradient is well known from borehole temperature measurements. The thermal conductivity of the rocks was determined from core samples in a laboratory, and an average heat flow of approximately 100 mW/m² was calculated. During the driving of the tunnel, temperatures of just over 50 °C are expected.