Study on the Effect of Inclination of Cutoff Wall Beneath Gravity Dams on Uplift Force

Abstract

A method for preventing piping, or for reducing the exit hydraulic pressure gradient or ground-water seepage is the use of cutoff walls and drainage holes. In gravity dams, cutoff walls are usually made from concrete with a vertical geometry under the dam foundation. Inclination of cutoff walls may be chosen by engineers if it shows a positive effect on the reduction of uplift force. The objective of this study is to investigate the effectiveness of inclined cutoff walls under hydraulic structures, considering the influence of depth, location, and inclination angles of the cutoff wall using the finite element method (FEM). This study compares the efficiency of inclined cutoff walls located under a gravity dam. The cutoffs have angles ranging from 0 to 60 degrees with respect to the vertical direction and are angled in downstream direction. Different positions of cutoff walls with various angles of inclination are used. Results show that minimum uplift force occurs when the cutoff wall is at the heel (upstream) of the dam. With fixed longitudinal cutoff wall placement, inclined walls reduce the uplift force. The effect of an inclined cutoff wall upstream of the dam for reducing uplift force is very high. Although the numerical simulation showed that the inclined cutoff wall was able to reduce the uplift force, it is important to note that the construction of an inclined cutoff wall will be more difficult than the construction of a vertical cutoff wall. Therefore, in future studies, the investigation of inclined cutoff wall construction and their utilization need further analysis. Estimating the project construction costs is an important consideration.