The mechanism of eros10n m noncohesive soils

Abstract

Reference is made to the surprising fact that the shear stress 7, dueto water flow, needed to start erosion in a sandy bed, is only 1/10 to 2/10 of the resistance to shear s of the monogranular layer of the bed, deduced from Coulomb's law. The erosion mechanisms proposed by some authors are analysed.  A new mechanism is suggested by which the stresses, on the particles, of random fluctuations of drag and lift forces are explicity considered. Using the concepts of the safety coefficient F = s/'f and of the probability P of the beginning of erosion, an abacus is presented which makes it possible to calculate F as a function of P and of the coefficients of variation of s and z7.  lt is thus shown that the fractions 1/10 and 2/10 are but the inverse of the coefficient of safety from 5 to 10. A test is suggested for determining the angle of repose.  Themes for future research are listed.