Piping flow erosion in water retaining structures: inferring erosion rates from hole erosion tests and quantifying the failure time
Résumé
The piping flow erosion process, involving the enlargement of a continuous tunnel between upstream and downstream, is a major cause of water retaining structures. Such a pipe can be imputed to roots or burrows. The coefficient of erosion must be known in order to estimate the remaining time to failure and to downstream flood. The Hole Erosion test is a laboratory experiment especially suited to estimate a priori this geotechnical parameter. We propose therefore simplified expressions for the remaining time to breaching accounting for this erosion parameter. We established that the radius evolution of the pipe follows a two-parameters scaling law. The first parameter is the critical stress. The second parameter is the characteristic time of piping erosion, which is a function of the initial hydraulic gradient and the coefficient of erosion. We establish here new mechanically based relations for water retaining structures. The time to failure and the peak flow are related to the two basic parameters of piping failure: the coefficient of erosion, and the maximum pipe diameter prior to roof collapse and breaching. Orders of magnitude of the coefficient of erosion and the erosion rate are finally inferred from 18 case studies.
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