A new modified strength criterion for soft rock masses is proposed in this paper in
order to provide a suitable estimation for soft rock mass strength. The new criterion is based
upon the current compression test data of soft materials of over 150 samples, and available
published data of soft rock strength. It is shown that the proposed criterion estimates reasonable
values of soft rock mass strength. Rock properties and size contribute significantly into the
strength, represented by friction angle and unconfined compressive strength. Examples
exercised reveal that the structure of soft rock masses takes a dominant part in controlling the
strength, which then determines the modelled strength of soft rock masses. The results also
show that the strength of the proposed equation could relatively be higher three times than the
strength of the Hoek-Brown criterion for a massive soft rock mass.