EFFECT OF CUT-OFFS DEPTH RATIO ON UPLIFT AND EFFICIENCY OF FRONT AND BACK FACES OF UPSTREAM CUT-OFF

摘要

Two main problems face the stability of hydraulic structures, piping and uplift. Cut offs are used to increase the horizontal length of seepage under the apron of the hydraulic structures to overcome the effect of both uplift and piping under these aprons. In previous researches it was found that the best position to minimize the uplift under hydraulic structures apron is to use an upstream cut off at the start of the apron and a downstream cut-off at the end of the apron also a modification factor was estimated for the downstream cut off front and back faces length. In this study, an electrical analogue model was used to investigate the effect of the depth of the upstream and downstream cut-off D1 and D2 respectively when the upstream cut-off is at the start of the apron and the downstream cut off is at the end of the apron on the uplift forces along the hydraulic structure and the rear and front faces head drop of both upstream and downstream cut-off. Finding this data a modification factor was estimated for the upstream cut off also the best ratio (D1/D2) that achieves the minimum uplift under the apron. Each of the previous parameters were measured, unit head drop were calculated and compared for the entire cases understudy, the lowest values for uplift were determined and a modification factor for the upstream front and back face lengths was estimated, artificial neural network were trained to find the value of the modification factor for each case using the initial potential difference, the ratios (D1/D2) and [(D1+D2) / Lt]. The ratio between depths of the upstream cut-off D1 and the downstream cut off D2 (D1/D2) ranged from 0.4 to 2.5. 16 models were tested with total number of 48 runs.