Conventional statistical analysis does not take into account the spatial coordinates of the control tests (water content, density, etc.). The geostatistical approach, by considering how the values of measured parameters vary from one location to another, takes into account both features: structure and randomness inherent in the core of the dam. This approach has been applied to the core of the LG-3 dam (James Bay project) built with glacial till. After obtaining the variograms, the problems of estimating the mean compaction degree of a given volume have been studied and the following questions have been analysed: What is the distribution of the degree of compaction of the control volume? What is the efficiency of the compaction control tests that were used during the construction of the dam? Is it possible to improve the efficiency of these tests? Keywords: earthfill, compaction test, quality control, statistical analysis.