Numerical Investigation of Foundation Drains Performance in Decreasing Uplift Force of Concrete Gravity Dams

General assumption in designing cut off walls is that the seepage be held in a limited amount. In order to control the seepage, the foundation drains are located in parallel to cut off wall at downstream. The main aim of foundation drains construction is to collect seepage water and decrease uplift force. Numbers, distance, and diameters of these drains need technical judgment about characteristics of foundation stones. The depth of drains depends on cut off wall characteristics. In this study, the performance of drains in foundation of concrete gravity dam was investigated using finite element method (FEM) via Seep/w software. Among influential parameters in studying the drain effects, one might consider diameters, center to center distance, and distance of the drains from upstream of dam. In this paper effective parameters on uplift force were analyzed and it was found that increasing the drain diameter had lesser effect on decrease of the uplift force slightly compared to the other parameters. In the other words, selecting the best diameters depends on executive consideration. But decreasing the distance of drains and also their distance from upstream of dam would play an important role in decreasing the uplift force. Focusing to the simulated range of parameters, the drains with 15 centimeter diameter and distance of 3 meters had the optimum performance and the best operation in decreasing uplift force. For validation, the numerical method used in this research was compared with the other analytical methods and the proper agreement with them was observed.