STABILITY OF SEDIMENT PARTICLES ON CHANNEL BOUNDARY

Abstract

The work reported in this thesis is an experimental investigation regarding the stability of coarse noncohesive sediment particles placed on the periphery of a trapezoidal channel. The main objective was to determine the shear stress distribution on the bed and the sides of the channel under incipient motion condition for different sediment sizes in order to examine the adequacy of Lane's method. Experiments were performed in a trapezoidal channel 10.0 m long, 0.40 m wide and having a constant side slopes of 1V : 2H. Uniform sediment of three different sizes i.e., 2 mm, 4 mm and 5.16 mm were used. The data were collected for the incipient 'nation conditions on the bed and sides of the channel. The incipient motion condition was iden-tified only by visual observations. Velocity distribution profiles were used to estimate the distribution of boundary shear stresses. Data for the incipient motion condition on the bed show a satisfactory agreement with the relationship propo-sed by Yalin-Karahan's [6] for stable channel design. The experimental values of maximum shear stresses both on the bed and the sides were found to be more are less same as given by Lane [16]. However, the experimental depths of flow under incipient motion conditions were higher than those predicted from Lane's [16] method. The possible reasons for this discrepancy have been identified in this thesis. It has been found that the ratio of the limiting shear stress on side to the limiting shear stress on bed III i.e., K is not a unique function of 8 and 0 as suggested by Lane 116]. Here 8 is the side slope, 0 the angle of repose of given sediment size. The experimental values of K were different and it was found that the value of K also depends on B/D ratio besides, 8 and 0. The boundary shear stresses both maximum and average have been represen-ted as a function of B/D. The data from other investigators Ghosh and Roy 19], Nakagawa et.al, [11] and Flintham and Carling 15] has also been utilised in this analysis