SMALL DAMS PETITS BARRAGES

5.8.1 Introduction
To prevent failures that can develop through the slopes of embankment dams the slopes
must be flattened to acceptable grades which provide acceptable safety factors, based on the
characteristics of the soil from which it is built.
Stability analysis of a fill dam concerns the determination of the forces exerted on the
dam and analysis of combinations of those forces; of those combinations, the worst case
scenarios are considered in terms of the envisaged failure mechanism.
5.8.2 Critical Cases for Analysis
During construction and life of an earthfill embankment structure the following cases may
occur:
� During construction temporary slopes must always be stable. Furthermore, the outer
slopes must also be stable during development of hydrostatic pore pressures.
� During full reservoir conditions and developed seepage conditions the stability of the
downstream shell is critical. Sufficient drainage systems will improve the stability.
� In case of sudden draw down of water in the reservoir the upstream slope can fail
under saturated earthfill conditions.
Dynamic forces can also develop and must be considered in seismic zones.
5.8.3 Limiting Equilibrium Methods
The two dimensional equilibrium methods are based on the following:
� An embankment cross section is evaluated.
� The earthfill above the slip failure is divided into blocks.
� Each block is analysed for weight and shear resistance and the final safety factor
determined.
For all methods except for the wedge method vertical blocks are selected. For the wedge
method a series of levels are selected and is applicable to the following:
� where a horizontal earth layer with lower shear resistance (e.g. clay with high
plasticity) is situated in the foundation.
� where the foundation consists of rock, the core consists of material with small grains
and the outer zones consist of material with rough grains.
Methods
Various methods as follows were developed in years indicated:
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