On the required thickness of the grout curtain under dams

Zhang, S and Johansson, F. (2021) On the required thickness of the grout curtain under dams. In: ICOLD Symposium on Sustainable Development of Dams and River Basins. New Delhi, 24th - 27th February 2021

Abstract: To reduce the water leakage and the uplift pore pressure in the rock foundation, grout curtains are often constructed under dams. However, the design of grout curtains has long been based on empirical knowledge. When designing the grout curtain, focus was mainly given on closing the curtain and limiting the leakage, without considering the thickness of the curtain. However, a too thin grout curtain could lead to high gradients, which with time could result in internal erosion of degraded grout and fracture infilling materials. This could lead to poor performance and durability problems, potentially jeopardizing the dam safety and increasing the cost for remedial measures. In this paper, three design criteria are discussed for determining the required thickness of the grout curtain, including water loss reduction, uplift pore pressure reduction and internal erosion of degraded grout and fracture infilling materials. Analyses on the required thickness are made for a typical concrete gravity dam. The results show that the required thickness is significantly affected by the internal erosion of fracture infilling materials. These results show the need for a more refined design approach for the grout curtains based on the suggested criteria.