For the headrace Moglicë-Grabovë, part of Devoll Hydropower Project in Albania, two different techniques of tunnelling are planned: DS TBM for the Flysch series starting in Moglicë and Drill & Blast for the Ophiolite section, starting in Grabovë. A major question concerning the tunnelling seems to find the point where DS-TBM excavation from the Moglicë side should stop to “wait” for the Drill&Blast excavation from the Shemsit access tunnel side. Assumed that the so called “block in matrix” rock mass is very unfavourable, respectively disqualifying for TBM excavation. These mixtures of hard blocks embedded in weaker and finer matrix that are very difficult to characterize, frequently challenge the engineering geologists with the characterization, design and construction problems associated with them. Evaluating Block Size Distribution in the BiM rock zone of this project area has been only the first step in characterizing all the geological and geotechnical parameters of the rock mass which will influence a decision that has major economic consequences. CSDCorrections 1.39 is the program used to convert the two dimensional data gathered from thin sections, outcrops, photographs etc. to true three dimensional crystal size distributions (CSD).