Laboratory Study of Protecting Downstream Slope of Rockfill Weirs Using Stepped Gabions

Abstract

In the present investigation, the stability of rockfill weirs protected by gabions and subjected to overtopping flow rates under the effect of high flow rates have been studied experimentally. Five weir models with different downstream slopes [1V:2.5H,1V:3H,1V:4H,1V:5H,1V:7.5H]were constructed and tested. Fifty eight experiments were conducted for five cases of stepped gabions laying on the downstream slope[ laying gabions with one layer and no connections (M-1),laying gabions with lateral connections (M-H),laying gabions with longitudinal connections (M-V), laying gabions with two layers(M-2),and laying gabions with three layers(M-3)] using three gravel diameters (11.11,15.9 and 22.25)mm.Fromthe data analysis, a set of equations were obtained for the estimation of failure unit discharge in terms of equivalent gravel diameter, relative submerged intensity of gabions, gabions layer solidity, and tangent of internal friction angle of gabions, for each case of gabions laying. A simple method was presented for the design of rockfill weirs protected by stepped gabions in terms of maximum failure dischargewith the help of design charts obtained from the present study.A mathematical model depending on the characteristics of the physicalmodel was derived for each slope giving failure unit discharge values that agree quite well with the experimental values. Comparing results of the present study with those of other investigations shows that rockfill weirs protected by gabions stand much higher failure unitdischarge than earth weirs protected by gabions.