Cut-off wall in foundation of reservoir dam and tailing dam: comparative evaluation

Cut-off wall is used to prevent seepage in foundations of embankment dams of reservoirs and tailing dams. Under the action of external loads, they may be subject to stresses comparable with strength of the wall material. There is a risk of loss of the wall both tensile strength and compressive strength. To decrease stresses, the cut-off wall is made of clay-cement concrete more deformed as compared to material concrete. To compare conditions of operation and strength of the cut-off wall in foundation of the reservoir dam and the cut-off wall in foundation of the tailing dam, there was fulfilled the study of their stress-strain state. Abstract rockfill dam 100 m high with geomembrane face was considered. A 2 m thick cut-off wall is located under the dam upstream slope: it crosses the layer of deformed foundation 15 m thick and is embedded in rock. Mohr–Coulomb model was used for description of behavior. Computations showed that the cut-off wall of the tailing dam performs in less favorable conditions than the cut-off wall of the reservoir dam. It is subject to greater by value vertical and horizontal loads. Due to pressure of slimes, it is subject to several times as much by value vertical compressive stresses. The value of stresses is highly dependent on deformation of the foundation soil. To provide strength, the deformation modulus of the cut-off wall should not exceed the foundation soil deformation modulus by more than 4 times. In spite of the fact that the tailing dam cut-off wall is subject to greater horizontal loads, it has less displacements than the reservoir dam cut-off wall. It was revealed that this is explained by more favorable stress state of soil in foundation of the tailing dam.