ABSTRACT
The paper presents the in situ testings of the hydraulic hammer productivity upon boulder breaking. There are also factory data regarding hydraulic hammer productivity upon tunnelling and the published data about the hydraulic hammer productivity on concrete tasks. The article contains preliminary research on fracture toughness of rocks, conducted according to the suggested methods by the International Society for Rock Mechanics at the Faculty of Mining, Geology and Petroleum Engineering in Zagreb. The aim of the research is to precisely determine the factors of the resistance to the appearance and advance of fractures within the rock, which should decrease dilemma upon decision when to apply hydraulic hammers upon tunnelling.
