Geostatistical assessments can be used for understanding the distribution of regionalized variables (ReVs) in any spatial study. Many researchers have used the theory of ReVs for different modeling purposes such as hydraulics, mining deposits, etc. In this paper, ReV technique is used for understanding the mechanical variation properties of rock zones under sampled and unsampled conditions in sewer tunnels for Istanbul. This study has been carried out for three different rock properties that are compressive strength, rock quality designation (RQD), Schmidt hammer hardness, and one rock cuttability property, net cutting rate. In order to define ReVs distribution, first semivariogram functions are determined and then kriging maps are generated for identifying the regional dependence. Furthermore, it is possible to make estimations for every point within the study area, and prepare maps for the interpretation of regional features of the ReV concerned. Net cutting rate is a cuttability property of rock, which can be regionalized and compared with the mechanical properties of rocks. This can be used for predicting the performance of excavator. (C) 2002 Elsevier Science Ltd. All rights reserved.