Slope Stability Assessment of Earthen Hydraulic Structures at the Dychów Pumped-Storage Power Plant Using Electrical Resistivity Tomography and Finite-Element Modelling: Implications for Ageing Critical Energy Infrastructure

Background: Pumped-storage hydropower (PSH) plants remain a cornerstone of grid stability and renewable-energy integration in Europe, yet a large share of the European fleet is ageing and was built under design codes that predate modern geotechnical standards. The Dychów pumped-storage power plant (ESP Dychów, 88 MW, Lubusz Voivodeship, western Poland), in service since the 1930s, is classified as part of the national critical energy infrastructure. Its earthen retaining structures have a documented history of surface mass movements – including the 1997 landslide on the frontal dam, which damaged around 60 m of the crest road and the powerhouse – and require recurrent safety assessment in complex glaciotectonic settings. Methods: Electrical resistivity tomography (ERT) performed in a gradient array was combined with hydrogeological observations and finite-element slope-stability analyses in ZSoil. Two cross-sections were examined – the earthen frontal dam of the upper reservoir and the embankment of the derivation channel feeding the reservoir – each with four calculation variants and two groundwater scenarios. The shear-strength reduction technique was used to obtain the “global” safety factor SF. Results: SF equals 1.75 for the frontal dam and ranges from 1.80 to 2.10 for the channel embankment. Parametric reduction of the internal friction angle of saturated medium sand yields limit values of φ = 12.3° (dam) and φ = 20.3° (embankment), clearly below realistic in-situ values. Conclusions: Both structures comply with the safety threshold F ≥ 1.50 specified for Class I hydraulic engineering structures. The presented non-invasive ERT–FEM workflow offers a cost-effective tool for the periodic reassessment of ageing PSH infrastructure, supporting its continued role in balancing variable renewable generation in decarbonising power systems.