Dynamic forces in penstock due to support movements and deformations of rigid anchor points.Rock falls on penstocks on the surface in steep terrain.Support movements due to earthquake-triggered slides.Relative displacements along active faults.Hydrodynamic pressures due to ground shaking: The magnitude of the pressure depends on the response spectrum of the ground shaking and the natural period of the oscillating mass in the pressurized water system.Earthquakes can cause damage to penstocks by different mechanisms as discussed below: Penstocks and gates of hydro power plants are not intrinsically safe against earthquakes. However, the implications of these observations may not yet have been fully realised elsewhere. The vulnerability of these lifelines is not a new phenomenon. However, in relatively short penstocks with fundamental eigenfrequency of the oscillating water mass in the range of the dominant frequencies of the earthquake ground motion, the situation may be the opposite.ĭamage and failure of buried water and gas mains has been caused by quite a number of earthquakes. As discussed in the subsequent sections, the hydrodynamic pressures due to valve regulation are larger than those due to earthquakes in long penstocks or pressure tunnels with a natural period of vibration of the water of several seconds. It may be argued that in the pressurised water system the water hammer is already investigated and the emergency shut-down of a penstock may cause the maximum hydrodynamic pressures. As earthquakes affect all components of a hydro power plant, hydrodynamic actions also have to be checked for all hydromechanical components. This assumption is acceptable for gates of surface spillways, but not for gates located in tunnels or valves in large diameter penstocks.Īlthough no case is known where a penstock has failed or been damaged during a strong earthquake, the question of earthquake safety still has to be addressed. In general the hydrodynamic pressure according to Westergaard is assumed. Penstocks, plugs of diversion tunnels, gates in bottom outlets, intake structures and spillways, valves and other hydromechanical components of the pressurised water system in hydro power plants have rarely been designed for the hydrodynamic pressures, which may be caused during a strong earthquake. Dr Martin Wieland investigates hydrodynamic pressures in penstocks, bottom outlets, plugs of diversion tunnels and gates of intake structures and spillways caused by earthquakes
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