Numerical modeling for evaluating grout curtain depth and providing a new approach for calculating the efficiency based on installation position of piezometers around sealing system

Abstract

Drilling and grouting to seal the dam foundation, and also the abutments are very time and money consuming; therefore, this should be done with high accuracy. The grout curtains may be attached to impermeable layer, in which case they are called non-hanging grout curtain. If the impermeable layer under the dam foundation is not accessible, the grout curtain will be hanging. The depth of the hanging sealing curtains depends on the efficiency projected by the designers. In this study, the authors have considered a model of an earth dam with a height of 180 m. The impact of depth on the performance of hanging and non-hanging grout curtains was studied using seep/w software and analyzing more than 200 sections, and the rate of efficiency change against depth was displayed for both types of sealing curtains. In hanging grout curtains, up to the depth as one-third of the length of the grout curtain, the rate of efficiency changes increases as the length of the grout curtain (∆e/∆d) increases. However, from the above depth onwards, the rate gets decreasing with a smooth slope. In non-hanging grout curtains, up to 20% of the length of the permeable layer, the efficiency rate of grout curtain increases, and from 20 to 90% of the length of the permeable layer, the efficiency rate is constant; however, in the last 10% of the depth, the efficiency rate shows a sudden increase. Furthermore, the impact of the effective radius of the grout penetration on the efficiency rate was also investigated by increasing the thickness of the grout curtain in both types. This test showed that with the increase of the effective radius of the grout penetration, the efficiency of a sealing curtain also increases. In this study, the authors also provided a strategy to help to install the piezometers in positions while the results of calculated performance from equations based on the seepage and equations based on the piezometric pressure get equal.