In this paper, the problem of estimating the shear strength of discontinuity is presented, which especially occurs in massive and karstified limestones, where discontinuity walls can be extremely rough and irregular, with or without filling material, and for which the current models have proven to be unsatisfactory. A characteristic example of such limestones is the deposit of dimension stone “Kanfanar”, located on the Istrian peninsula in Croatia. For the purpose of developing a model for estimating the shear strength of discontinuity, field research was conducted in which large samples of blocks with natural discontinuities were prepared, as well as samples of filling material in limited conditions, on which detailed laboratory tests of shear strength were performed. Special attention was paid to determining the joint roughness coefficient JRC, the actual contact area between the discontinuity walls, the basic or residual friction angle and the friction angle of the built-in filling material between the discontinuity surfaces. The development of the model for estimating the shear strength of discontinuity was based on Barton’s JRC-JCS empirical model, given the fact that it is one of the most commonly applied models in engineering practice. Based on the results of the tests, a modification of Barton’s JRC-JCS model was made, in such a way that the friction angle of the built-in filling material in the case of discontinuity with a filling was applied instead of the basic or residual friction angle. In addition, for the correct evaluation of the roughness of the discontinuity walls in massive and karstified limestones, it was found that it is necessary to increase the roughness coefficient to values larger than 20, which has been proposed as the maximum so far. Evaluation of the proposed model showed that it is satisfactorily accurate in estimating the shear strength of discontinuity with clay filling material of different states of consistency. ; U radu je prikazana problematika procjene posmične čvrstoće diskontinuiteta, koja posebice dolazi do izražaja u masivnim i okršenim vapnencima kod kojih stijenke diskontinuiteta mogu biti izrazito hrapave i nepravilne, s materijalnom ispunom ili bez nje, a za koje se pokazalo da postojeći modeli ne mogu dati zadovoljavajuće rezultate. Karakterističan primjer takvih vapnenaca jest ležište arhitektonsko-građevnoga kamena „Kanfanar” koje se nalazi na Istarskome poluotoku u Hrvatskoj. Za potrebe razvoja modela za procjenu posmične čvrstoće diskontinuiteta provedena su terenska istraživanja tijekom kojih su pripremljeni veliki uzorci blokova s prirodnim diskontinuitetima te uzorci materijala ispune u graničnim stanjima, na kojima su zatim provedena detaljna laboratorijska ispitivanja posmičnih čvrstoća. Posebna pozornost posvećena je određivanju koeficijenta hrapavosti pukotina JRC, stvarnoj kontaktnoj površini između stijenki diskontinuiteta, baznomu, odnosno rezidualnomu kutu trenja te kutu trenja ugrađenoga materijala ispune između ploha diskontinuiteta. Razvoj modela za procjenu posmične čvrstoće diskontinuiteta temeljio se na Bartonovu JRC-JCS empirijskome modelu, s obzirom na činjenicu da je to jedan od najčešće primjenjivanih modela u inženjerskoj praksi. Na temelju rezultata provedenih ispitivanja modificiran je Bartonov JRC-JCS model tako da je umjesto baznoga ili rezidualnoga kuta trenja primijenjen kut trenja ugrađenoga materijala ispune za slučaj diskontinuiteta s ispunom. Uz navedeno, za ispravno vrednovanje hrapavosti stijenki diskontinuiteta u masivnim i okršenim vapnencima utvrđena je nužnost povećanja koeficijenta hrapavosti pukotina JRC10 na veće vrijednosti od 20, koliko su do sada bile predložene kao maksimalno moguće. Evaluacija predloženoga modela pokazala je zadovoljavajuću točnost prilikom procjene posmične čvrstoće diskontinuiteta s materijalom ispune različitoga stanja konzistencije.