The Effect of Multi-layer Foundation on Seepage Flow Parameters under the Diversion Dams

In this study seepage factors in two-layered and three-layered foundation of a diversion dam was investigated experimentally. Results showed by increasing the upstream head, outlet discharge increases. The trend of discharge increase was similar and the variations range was high for d50=0.6 mm and d50=1.25 mm, but the range of discharge variations was low for d50=0.24 mm. For two-layered foundations, the arrangement of D50=0.2 mm and D50=1.2 mm with 465mm upstream head was the best performance for piping control. Also the arrangement of D50=0.6 and D50=0.2 mm without cutoff had the least seepage discharge (about 0.266 mlit/s). In the presence of cutoff, the best performance for piping control was obtained for the arrangement of D50=0.6-0.2 mm and the seepage discharge was about 0.066 mlit/s. The arrangements of D50=1.2 mm, D50=0.6 mm without cutoff and D50=0.6 mm, D50=0.2 mm with cutoff had the best performance for hydraulic gradient control which were about 0.002 and 0.0011 for 410 mm upstream head, respectively. For three-layered foundation, the arrangements of D50=0.2 mm, D50=0.6 mm, D50= 1.2 mm and D50=1.2 mm, D50=0.6 mm, D50=0.2 mm showed the best performance for piping control so that piping was happened in 490 and 480mm upstream heads, respectively. The best arrangements in terms of  seepage discharge control, without and with cutoff were respectively (D50=0.2 mm, D50=0.6 mm, D50= 1.2 mm) and (D50=0.2 mm, D50=1.2 mm, D50=0.6 mm) with 410mm upstream head, in which the seepage discharges were obtained about 0.533 and 0.433 mlit/s, respectively. The results of this study showed that the multi-layered foundations could be considered as an effective alternative in reduction of outlet gradient and control of piping and seepage discharge.