Estimation of the diameter of the rip rap for protection of the base of longitudinal walls in rivers with well-graded granular bed

Abstract

In river hydraulics, turbulence and flow velocity represent a great challenge in the implementation of riverbank protection structures, due to the dragging of material and deterioration that is generated on these structures. The objective of this research is to estimate the optimal rip rap diameter as a scour protection measure for longitudinal walls in rivers with well graded granular bed. The study is developed through physical modeling in a hydraulic channel made of acrylic, varying the slope conditions between 1 and 2.5 % and flow rates between 0.017 and 0.030 m3/s, measuring the flow velocity and the dragging capacity of limestone rocks with diameters of ¾", 1", 1 ¼", 1 ½". Likewise, the equations of Highways, Mynord, U.S Department of Transportation, U.S geological Survey and R.A Lopardo were validated. The development of the research shows that the Mynord equation is more adjusted to the experimental conditions, in which for velocities higher than 0.8 m/s the entrained diameters are ¾" and 1", and that the U.S geological Survey equation establishes the smallest diameter of the rockfill, putting at risk the stability and effectiveness of the rockfill as a protection structure. The research represents a significant contribution to the development of hydraulic works, since it establishes the diameters of the rockfill arrangement, according to the flow material dragging velocity.