عنوان مقاله [English]
Rock specimens having one, two and three cross - sets of single discontinuities and three cross - sets of discontinuities with one set having four parallel discontinuities, in different groups of various orientations (angle between planes of discontinuities and horizontal direction) of 0, 30, 45, 60 and 90 degrees have been prepared. The axial strength of various groups of jointed rock specimens have been tested under different confining pressure of 0, 5, 7, 10, 14 and 20 MPa. Parameters of Ramamurthy's failure criterion including: ratio of uniaxial compressive strength of jointed rock specimens to the uniaxial compressive strength of intact rock specimens (scj/sci), power of aj and triaxial strength factor (Bj) of this research have considerably different from their obtained values using present relationships particularly for higher values of frequency and number of sets of discontinuities, and presence of a dominant joint with orientation angle of 60 degree in the combination of discontinuities. The value of s and triaxial strength factor (mb) in Heok et al. rock mass failure criterion decreases with an increase of number of set and frequency of discontinuities and its minimum value occurs when there is a dominant joint having orientation angle of 60 degree. A new relationship between triaxial strength factor (mb), s and a with scj/sci ratio have been obtained for limestone as ratio of scj/sci can be determined by joint factor (Jf).