2016 – Calculation of the Probability of Failure of Impervious Concrete Lining of Plunge Pools Loaded by High-Velocity Jet Impact

M. Mahzari

An analytical approach is presented to calculate the pull-out probability of failure of concrete lining of
plunge pools. The concrete lining is aimed to protect the plunge pool against scour where a scour hole may
endanger the stability of the dam foundation. Uplift and pressure loading of the jet are major actions on
the concrete lining. Ground anchors are used to stabilise the lining against these actions and the governing
mode of failure is the pull-out (tensile failure) of these anchors. While the anchoring design for static uplift
is straightforward, dynamic jet action introduces remarkable complexity into the design. The adopted
methodology is based on a stochastic modelling of the high velocity jet action. A bi-linear power spectral
density function is assumed based on the laboratory measurements on the scale physical models done by
the others. This loading mainly reflects the turbulent pressure fluctuations where the jet impacts the plunge
pool floor. Response of the lining, idealised as a single degree of freedom, is calculated by the random
vibration procedures which provides the most realistic structural analysis methodology. It is assumed the
lining is impervious and hence no dynamic under-pressure is developed. The analysis results provide a
probabilistic description of the anchor tensile force which enables the designer to compute the probability
of failure of the anchors knowing their ultimate strength.

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