SCALE MODELLING AND SIMILARITY LAWS FOR THE STUDY OF AN UNDER PRESSURE SETTLING STRUCTURE

摘要

This paper presents the scale model studies of a complex under pressure settling structure, carried out at the Laboratory of Hydraulic Constructions of the University of Liege. Made up of fourteen identical settling chambers placed side by side and the bottom of which is divided into pyramidal hoppers, the structure, totally under pressure, is fed by a vertical shaft. Downstream, the settling chambers discharge into a collector, which ensures the clean water feeding of four penstocks through a free surface basin. Finally, a pipes network, under the chambers, ensures the downstream evacuation of the sand trapped in the hoppers. Using adapted and theoretically justified similarity laws coupled with realistic scales for the models, the hydrodynamic behavior and solid transport phenomena in this complex system have been studied. Special care has been taken to evaluate the trap efficiency, the evacuation system working and the global discharge repartition between the fourteen chambers. Sawdust, plastic balls or very small sand particles have been used to model real sediments. A total of three models, from only one hopper to the full settling structure, have been built, with scales from 1/18.5 to 1/100. According to the results of the studies, the length of the settling chambers has been shortened of up to 38 m, i.e. 2 hoppers, and best use instructions have been suggested for the sediment evacuation system.