Nenskra Dam - Dynamic analysis by means of numerical modelling

Lombardi Ltd was commissioned by Salini-Impregilo SpA to perform the Basic Design of the Nenskra HPP (installed capacity = 280 MW), which will be built on the Nenskra river in the Svaneti region (Georgia), some 260 km north-west of Tbilisi. The HPP foresees the construction of a 130 m high Asphaltic Face Rockfill Dam (AFRD) which has a crest length of 940 m and rests completely on alluvial soils at the valley floor (max. depth = 140 m) and alluvial fan deposits at both abutments (max. depth = 60 m). Due to the seismicity of the Caucasian region, the stability of the dam has been analysed in dynamic conditions. The behaviour of the dam body and its foundation, the asphaltic face, the dam crest and the cut-off wall has been evaluated performing fully nonlinear dynamic simulations, by means of FLAC2D and FLAC3D software. The execution of large scale laboratory tests and in-situ measurements allowed the proper definition of the mechanical parameters for the modelled materials. The dynamic behaviour of the dam was checked for both MCE and OBE earthquakes. The maximum permanent displacements at the dam crest have been evaluated (below 1% of the height of the dam for a MCE earthquake). The permanent displacements under an OBE event have been analysed to verify the serviceability conditions. A detailed analysis of the bituminous facing was also performed by means of the 3D model, to evaluate if the maximum asphalt deformation was concentrated either close to dam abutments or within the dam body. The maximum tensile strain of the asphalt allowed evaluating the potential of cracks onset and the consequent risk of saturation of the dam body. The behaviour of the jointed connection between the head of the cut-off wall and the inspection gallery at the upstream toe of the dam embankment has been verified during both the quasi-static phase (dam construction) and the dynamic loading.
Reference location
Nenskra valley (Svaneti region)
Final client
JSC Nenskra Hydro
Is Consortium
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End of works date
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Civil designs; Consultancy; Special studies