Acta Univ. Agric. Silvic. Mendelianae Brun. 2017, 65, 569-576
Published online 2017-04-30

Discussion on the Safety Factors of Slopes Recommended for Small Dams

Jan Vrubel, Jaromír Říha

Brno University of Technology, Faculty of Civil Engineering, Institute of Water Structures, Veveří 95, 602 00 Brno, Czech Republic

The design and assessment of the slope stability of small embankment dams is usually not carried out using slope stability calculations but rather by the comparison of proposed or existing dam slopes with those recommended by technical standards or guidelines. Practical experience shows that in many cases the slopes of small dams are steeper than those recommended. However, most of such steeper slopes at existing dams do not exhibit any visible signs of instability, defects or sliding. For the dam owner and also for dam stability engineers, the safety of the slope, expressed e.g. via a factor of safety, is crucial. The aim of this study is to evaluate the safety margin provided by recommended slopes. The factor of safety was evaluated for several dam shape and layout variants via the shear strength reduction method using PLAXIS software. The study covers various dam geometries, dam core and shoulder positions and parameter values of utilised soils. Three load cases were considered: one with a steady state seepage condition and two with different reservoir water level drawdown velocities – standard and critical. As numerous older small dams lack a drainage system, variants with and without a toe drain were assessed. Calculated factors of safety were compared with required values specified by national standards and guidelines.


This study is part of project TACR TA04020670 “The Application of Reliability Methods in Dam Safety Supervision of Hydro-Engineering Structures in Relation to Their Safety in an Era of Global Climate Change” and FAST-J-15-2756 project “Evaluation of the Stability of Slopes of Dams of Small Water Reservoirs in Relation to the Requirements of CSN 75 2410”.


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