Knowledge of rock alteration can be used to give a reliable zonation of a dam foundation for grouting purposes. Rock alteration does affect both water-loss and the uptake of grout by the rock, and the existence of a close connection between water-loss and grout consumption has been accepted for years. However, the strength of this relationship is still debated and at the same time rock alteration is not considered to be possible indicator of grout consumption. In this study, the effect of rock alteration upon permeability and grout consumption has been investigated using the results of grouting at the Yenihayat Dam in Turkey. Using a geological field study, the alteration categories at the investigation area are identified, and zonation of the dam site according to these categories is made. The need for grouting was determined with the help of these alteration categories and these conjectures are tested using the results of injection work. Furthermore, the relationship between water-loss and grout take is investigated and a linear formula with a moderate explanatory power is established by statistical analysis. The formula also has a physical interpretation. This study shows that zonation according to the alteration degree can be a useful approach for grouting decisions. Similar studies at different sites and on different rock types are needed to verify the validity of this approach. (C) 2000 Elsevier Science B.V. All rights reserved.