Experimental Study of Erosion Process under a Submerged Pipe for Unsteady Flow Conditions

Abstract

River crossing pipelines are the best and economical ways for the transit of any kind of liquids or gases from one side to another side of a river. However, under pipe erosion is a serious problem, which may finally lead to reversal and destruction of the pipeline, especially for the non-buried pipelines. Overturning and destroying the pipeline may cause the release of a significant amount of pollutants into the rivers and cause irreparable damage to the environment, aquatic and humans. Since unsteady flow conditions are generally predominant cause for scouring and sedimentation around the hydraulic structures, therefore this research was conducted to experimentally investigate the under crossing pipeline erosion for unsteady flow conditions using different hydrographs produced in a laboratory flume and clear water condition. The variables were the type of hydrograph and pipe diameter. All hydrographs were designed with the same base time, but different peak discharge and the number of peaks (duplicate hydrographs). The results showed that the depth of erosion under pipeline was significantly and directly affected by pipe diameter and the discharge of the peak of the hydrograph. Duplicate hydrographs for the same base time were found to be effective on erosion due to, the first, the rate of increasing discharge at the beginning of experiments and, the second, the cumulative shear stress- time for the first minutes of starting erosion. Six experiments were also designed to investigate the erosion for steady flow and the results were compared with the corresponding experiments for unsteady flow conditions.