Abstract

Hydropower plays an important role in the context of the energy transition contributing to the reduction of the CO2 emission through a permanent power production as run-of-river scheme as well as for energy storage as pump-storagescheme. Nowadays large hydropower plant designs comprise tunnel, cavern and shaft excavation work known as head race and pressure tunnel or pressure shaft. The powerhouse is often placed within a large underground cavern. The results of a ground investigation phase including the determination of in-situ parameters derived from tests in boreholes drilled from the surface are crucial for a preliminary design of the hydropower plant. Additional in-situ measurements are frequently carried out within an exploratory tunnel to confirm the first predictions and to characterize in detail the mechanical and hydraulic properties of the rock mass. Solexperts portfolio of in-situ well tests comprise the assessment of hydraulic properties vs. depth through hydraulic testing of isolated borehole sections along the borehole axes, the determination of geomechanical parameters like deformation- and Young’s modules through borehole dilatometer tests and rock stress measurements conducting hydraulic mini-frac tests. Plate load tests which use surficial loading are performed in small tunnels or test adits to measure the deformation characteristics of a rock mass on a larger scale.

Abstract

Seismic activity and related rockbursts are currently one of the most dangerous threats negatively affecting work safety and continuity of operation in Polish underground copper mines. Taking into account the experience to date, it can be clearly stated that current technical and organizational tools do not make it possible to eliminate mining tremors, however, by taking appropriate actions, it is possible to minimize the threat and partially control it, e.g. by active de-stressing the rock mass. However, developing an appropriate schedule of preventive activities is still a burning issue. This is due to the random nature of mining-induced seismic phenomena which makes it impossible to accurately predict the place, energy and time of the seismic event. A breakthrough could be the use of stage-based large-scale numerical modelling based on which it would be possible to track stress changes with ongoing exploitation and locate areas of increased seismic risk. This study presents the results of large-scale three-dimensional FEM-based numerical modelling enabling tracking of changes in stress distribution with the progress of exploitation. Then stress distribution and areas identified as prone to instability occurrence were correlated with the areas of high-energy seismic tremors manifestation. Models were prepared at monthly intervals, and validated with the use of measurements obtained with underground geomechanical monitoring systems. As preliminary analyses show, well-validated numerical models can be the basis for estimating seismic risk and may be useful at the stage of designing methods for preventing active rockbursts and seismicity prevention.