Stabilization of Angular-Shaped Riprap under Overtopping Flows
Riprap is mostly used to prevent erosion by flows down the steep slopes in river engineering. A total of 53 stability tests performed on angular riprap with a median stone size ranging from 15 to 278 mm and slope ranging from 1 to 40% are used in this study. The existing equations for the prediction of medium size of angular stones are checked for their accuracy using the available data. Predictions of median size using these equations are not satisfactory and results show deviation by more than ±20% from the observed values. A multivariable power regression analysis is performed to propose a new equation relating the median size with unit discharge, bed slope, riprap thickness and coefficient of uniformity. The proposed relationship satisfactorily predicts the median angular stone size with ±20% error. Further, the required size of the rounded stone is more than the angular stone for the same unit discharge and the ratio increases with unit discharge and also with embankment slope of the riprap. Keywords—Angularity, Gradation, Riprap, Stabilization
Prediction of riprap stone size under overtopping flow using data-driven models
ABSTRACT Rock riprap is commonly used to protect levees, embankment dam, steep channels, and other structures being vulnerable to deteriorative erosion caused by overtopping flow. A review of the literature in this context indicates that over 24 riprap design expressions exist to predict the stone size in the riprap layer. However, each equation was originally derived on the basis of limited data sets under certain experimental conditions. In this investigation, Gene-Expression Programming (GEP), Model Tree (MT), and Evolutionary Polynomial Regression (EPR) were evaluated to estimate riprap stone sizing by virtue of 102 experimental data sets. Efficiency and performance of GEP, MT, and EPR approaches for training and testing stages were analysed and discussed. Results analysis revealed that the EPR technique provided an accurate prediction of riprap sizing in testing stage compared with other selected data-driven models as well as the empirical equations. The robustness of the developed data-driven predictive techniques was verified through the external validation: the selected data-driven models are definitely valid, have the strong capability to predict the riprap stone size which was not achieved by a chance. The prediction uncertainties of the data-driven models were quantified and compared with the selected empirical equations.
Coefficient Of Friction In Conduits With Large Roughness
Results of experiments of friction losses in conduits with large roughnessformed by spheres and hemispheres in different concentrations are used as abasis for the determination of the reference datum. This enables the computationof the friction loss for this type of roughness without further experimentalwork. A mathematical model for the computation of friction coefficient, applicableto conduits with roughness elements of any shape and based on the coefficientof drag, is presented. The model has been successfully tested by experimentsin channels both with uniform and with random roughness size and shapeincluding experiments with natural river stones up to 150 mm high.