The Importance of Detailed Groundwater Monitoring for Underground Structure in Karst (Case Study: HPP Pirot, Southeastern Serbia)

Marina Čokorilo Ilić,Marina Ćuk,Igor Jemcov,Ana Mladenović

doi:10.3390/w11030603

Abstract

The establishment of detailed monitoring of quantitative and qualitative parameters of groundwater in the zone of possible interactions between a water-conveyance tunnel and the geologic/hydrogeologic environment is of the utmost importance for assessing the risk of adverse effects and of tunnel performance. The water-conveyance tunnel of the Pirot Hydropower Plant (HPP Pirot) is a good example of applying detailed monitoring in complex geologic/hydrogeologic conditions resulting from the presence of an underground structure. The research scheduling was conditional upon the operating regime of the tunnel (whether it is in or of operation—online or offline). While the tunnel was operating (online), monitoring was conducted at observation wells along the tunnel (approx 15 m distant), a control gate (water losses), springs, and a stream in the vicinity of the tunnel. Areas of the potential hydraulic instability were indicated by synchronous measurements of water level and temperature changes in the observation wells and at the control gate. While the tunnel was offline (empty tunnel) it was possible to access the tunnel, and in situ monitoring proved to be of great importance. Observations of quantitative parameters pointed out hydraulically critical tunnel zones, whilst the qualitative characteristics of groundwater revealed their potential aggressiveness to the concrete lining of the tunnel. The applied methodology shows that a detailed observation program should be an important task of sustainable tunnel management.

Highlights

The presence of an underground structure in a karst can have a considerable impact on the natural status of groundwater and, the groundwater can affect the structure
The main changes in the quantitative and qualitative parameters of groundwater were detected at observation well PP-3, Table 2
Despite the fact that the greatest changes were detected at observation well PP-3, a comparative analysis of that well and PP-1 indicated that the groundwater level largely depended on the operating regime of the tunnel

Summary

Introduction

The presence of an underground structure in a karst can have a considerable impact on the natural status of groundwater and, the groundwater can affect the structure (the two are in constant interaction). Karst areas are risky for constructing underground tunnels, with regard to tunnel stability and water containment [1]. Anthropogenic interventions in such terrains can cause numerous environmental problems, like changes in water quality and quantity, and in groundwater and surface water regimes [2]. These changes occur, in the construction phase, and while the structures are in service. The structures cannot be completely isolated and there is constant interaction with the geologic/hydrogeologic environment. Problems become even more pronounced if such projects are built in complex hydrogeologic systems, with epigenetic, as well as hypogenic karstic systems [3]

Methods

Results

Conclusion