Numerical Simulation of Effect of Drain Pipe in Uplift Force, Exit Hydraulic Gradient and Seepage in Gravity Dams

In this study, the effects of diameter and location of drain pipes in uplift force, exit hydraulic gradient and seepage in the foundation of gravity dams are investigated. For this purpose, the SEEP/W software as a subgroup of Geo-Studio software is implemented and foundation of a gravity dam is simulated. The results showed that the existence of drain pipes under the gravity dam, reduce 4, 6, and 9 times of uplift force, exit hydraulic gradient and seepage respectively. Installation of two drain pipes with 0.25L distance from each other and in depth of 0.26D near the dam heel, presents more suitable position respect to uplift force reduction (D is the pervious foundation depth). Also, by defining the best position for the location of drain pipes, it was observed that drainage pipes in these situations reduce 41-67% in the volume of the studied dam and increase the safety factor up to 2 to 3 times against the dam overturning. It is also found that the drainage pipe diameter has less effect on uplift force, exit hydraulic gradient and seepage and and is controlled by the rules of the executive. For validation, the numerical method used in this study was compared with the laboratory method by others and a suitable match was observed.