| "Curtain grouting is constructed to improve the water-tightness of dam rock foundations to control underseepage. Curtain grouting is executed according to the split-spacing method, in which we construct the next order holes in the middle of the previous order holes. Then, the additional holes are constructed on the position, where we cannot meet the improvement target value in Lugeon value at the final-order of design holes according to the standard for the additional holes construction. And it is judged that it has been improved, when non-exceedance probability of the improvement target value is over 85 to 90% in the final-order holes. The improvement effect of curtain grouting is also evaluated by the check holes in addition to the final-order holes. This means that the check holes have significance as a double check. In this paper, the evaluation of the improvement effect of curtain grouting is made using the results of the final-order holes and check holes at four existing dams. We divide each dam foundation into several zones considering virgin permeability in particular and the layout of design grout holes. The results of curtain grouting are analyzed considering the geology of the dam foundations, virgin permeability, the tendency of improvement due to the progress of the order and the frequency distribution of Lugeon values in each zone. Then, it is classified into four patterns from the viewpoint of virgin permeability and of the results of comparing the improvement effect by the final-order holes and that by check holes, and we discuss the possibility of omission of check holes in each pattern. " |
