الفهرس | Only 14 pages are availabe for public view |
Abstract The present study is intended to study the problem of seepage beneath a gravity hydraulic structure when subjected to local scour. Study aims at investigating the effect of scour hole position, length, depth, and shape on the seepage characteristics such as potential along the floor, seepage discharge, and the exit gradient. Flowing water on the bed line downstream of a hydraulic structure may transport the soil particles, forming the stream bed, leading to a local scour which is expressed by existence ofa scour hole. The scour hole takes different shapes, in the present study. Four shapes are considered which are rectangular, trapezoidal, triangular, and segmental circular shape. Formation of this scour hole changes the condition of the downstream. bed, which presents the exit face of seepage, from the straight line to it locally lowered line. Such a change in the seepage exit surface may affect the seepage characteristics beneath the structure and in turn affects its stability and lead it to failure. The problem under consideration here deals with effect of scour hole location, dimensions, and shape on the seepage characteristics represented by the potential head (h) along the structure floor, the seepage quantity (q), and the hydraulic gradient (1) along the exit face. In the present work, the problem of seepage beneath a hydraulic structure followed by a scour hole had been numerically investigated using the finite elements technique. The finite elements model was checked using the analytical solutions for some idealized seepage problems previously investigated and the results were close. Moreover, some cases are verified experimentally using a Hele-shaw model. These cases were chosen to represent different cases of the considered parameters. A computer program, based on the finite elements method, was used to handle with the input and output data. The input data is the location of scour hole with respect to the structure floor (Xs), the lower length of the scour hole (Bs), and the maximum scour deI?th (Ys). The output data is the potential along the floor (h), the seepage discharge (q), and exit gradient (1). Result of the study indicated that formation of scour hole, greatly affects the seepage characteristics beneath such structure, which in turn affects their stability. Also, the obtained results were graphically presented in a dimensionless curves and charts to be easily used by designers and researchers. XI |