An approach is proposed which permits to estimate rock mass properties as confident characteristic values, both local and average, according to Eurocodes. The approach aims currently to estimate the unconfined compression strength (UCS) of the rock mass based on an adjustment of RQD to probability estimator RQDm. This proves to be possible, based on RQD and the number m of cores counted in RQD. Rock mass UCS can be calculated based on a probability weighting procedure. The validity of the exponential distribution of discontinuities' spacing is tested and an estimation of m is proposed, when data are unavailable. The approach is both theoretically sound and flexible. It allows the estimation of various types of UCS, such as local, average over a region or global. The procedure to follow is demonstrated on data from the exploratory drilling program of Driskos tunnel. A number of conclusions and suggestions result from the process.

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