Wellington Dam is an extreme hazard concrete gravity dam located on the Collie River approximately
170km south of Perth. Originally constructed to a height of 19m in 1933, the dam was raised to its
present height of 34m in 1960 by placing significant additional concrete against the downstream face
of the original dam. To ensure a lasting bond along the interface between the original and secondary
concrete, an open slot was formed and later grouted once the temperature of the secondary concrete
was similar to that of the original dam.
A recently completed stability analysis identified that Wellington Dam falls well short of contemporary
dam engineering standards for flood loading. Several assumptions were made during the preliminary
analysis relating to concrete shear strength parameters, bonding between the original and secondary
concrete and drain effectiveness that generated a significant range of results. On this basis, further
investigation was carried out to define the concrete parameters and drain condition at Wellington
Exploratory drilling found that Wellington Dam is cracked from the upper gallery through to the
downstream face. The drilling programme also confirmed that the interface between the original and
secondary concrete has become unbonded and that the gravity dam is behaving like an unbonded
short composite beam. The mechanism causing the observed behaviour of Wellington Dam can largely
be explained by external temperature effects and Alkali Aggregate Reaction, (AAR).
This paper explores the techniques used to investigate the condition of the concrete and illustrates the
relationship between concrete behaviour and temperature and AAR effects within a composite
concrete gravity dam.

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