Genetic mechanism of high geotemperature in tunnels in consideration of temperature monitoring and hydrogeochemical analysis.

During the tunnel construction, high geotemperature is a recurrent phenomenon in geothermal anomalous zones, significantly affecting both human resources and equipment involved in the process. The current study takes the Nige tunnel, the tunnel with the highest known geotemperature in China, as a case study to analyze the underlying dynamics of this phenomenon. The geotemperature within the tunnel is monitored during excavation before delving into a detailed analysis of the basic characteristics of the high geotemperatures measured. Subsequently, an investigation is conducted into the hot springs in close proximity to the Nige tunnel, which serves to reveal potential heat sources contributing to the high geotemperature. To further reveal the hydrochemical and geothermal reservoir characteristics of the area surrounding the tunnel and hot spring, a water quality test is performed. Lastly, the study situates its findings regarding the geological genesis of high geotemperature within the context of investigating heat conduction channels. Results demonstrate the coexistence of high water temperature (Water T) and rock temperature (Rock T) in the Nige tunnel, with maximum temperatures recorded as 63.4 °C and 88.8 °C, respectively. This study concludes that the source of deep circulating hot water likely stems from infiltration and combination of atmospheric precipitation and shallow water from the continental environment. Additionally, the geotemperature within tunnels primarily stems from thermal anomalous bodies in the deep crust. The performances may be used as guidance to address similar issues that arise in regions with high geotemperature.

Two-Dimensional Probabilistic Infiltration Analysis in a Hillslope Using First-Order Moment Approach.

A first-order moment analysis method is introduced to evaluate the pore-water pressure variability within a hillslope due to spatial variability in saturated hydraulic conductivity (Ks ) during rainfall. The influences of the variance of the natural logarithm of Ks (ln Ks ), spatial structure anisotropy of ln Ks , and normalized vertical infiltration flux (q) on the evaluations of the pore-water pressure uncertainty are investigated. Results indicate different responses of pressure head variability in the unsaturated region and the saturated region. In the unsaturated region, a larger variance of ln Ks , a higher spatial structure anisotropy, and a smaller q lead to a larger variability in pressure head, while in the saturated region, the variability in pressure head increases with the increase of variance of ln Ks , the decrease of spatial structure anisotropy, or the increase of q. These variables have great impacts on the range of fluctuation of the phreatic surface within the hillslope. The influences of these three variables on the variance of pressure head within the saturated region are greater than those within the unsaturated region, and the variance of ln Ks has the greatest impact. These results yield useful insight into the effects of heterogeneity on pressure head and uncertainty associated with predicted flow field.