Contribution of temperature measurements to the hydrogeological model in the Snowy 2.0 deep tunnels

This paper refers to experiences developed on the deep tunnels design of the Snowy 2.0 pumped-storage hydroelectric project in NSW, Australia. The 27 km long waterway and the Power Station Complex are about 800 m below ground, and in a complex tectonic and lithological setting. Long-term temperature monitoring in boreholes has been used to infer an empirical thermal model along the deep tunnels, which is presented as an example of input data for the ventilation design during construction, and for durability design during operation. An innovative aspect of this paper is related to the graphical interpretative method of borehole temperature logs that is proposed to infer downward or upward groundwater flows and predict the hydrogeological behavior of fractured and faulted zones that cross the tunnel alignment. A large campaign of thermal acquisition boreholes, performed using an ATV probe, identified local anomalies of the geothermal gradient, which were correlated to permeability and pressure data measured in the boreholes, to identify zones of greater permeability that intersect the tunnels. Furthermore, the application of thermal measurements during tunnel excavation is proposed as an additional tool for the prediction of water inflow or identification of zones to be pre-grouted and/or drained. Thematic collection: This article is part of the Leading to Innovative Engineering Geology Practices collection available at: https://www.lyellcollection.org/topic/collections/leading-to-innovative-engineering-geology-practices