To cite this paper: Int. J. Rock Mech. & Min. Sci. 34:3-4, paper No. 165. Copyright © 1997 Elsevier Science Ltd Copyright © 1997 Elsevier Science Ltd Int. J. Rock Mech. & Min. Sci. Vol. 34, No. 3-4, 1997 ISSN 0148-9062 To cite this paper: Int. J. RockMech. &Min. Sci. 34:3-4, Paper No. 165 A PHYSICAL MODEL STUDY OF JOINTED ROCK MASS STRENGTH UNDER UNIAXIAL COMPRESSIVE LOADING P.H.S.W. Kulatilake ; W. He; J. Um; H. Wang Dept. of Mining & Geological Engineering, University of Arizona, Tucson, AZ 85721, U.S.A. ABSTRACT Jointed rock mass strength is investigated through physical modeling using model material blocks subjected to only uniaxial compressive loading. Jointed model material blocks exhibited different failure modes depending on the joint configurations. Orientation of the joint sets played a significant role related to the modes of failure. It was possible to obtain a strong non-linear relation between the jointed model mass strength and the fracture tensor component to cover the strengths resulting from all the different failure modes observed in the investigation. The fracture tensor component was used to obtain the combined effect of number of joint sets, joint density, and distributions of size and orientation of the joint sets in a chosen direction. Needed future research are suggested to generalize the promising rock mass strength criterion obtained in the performed research. Copyright © 1997 Elsevier Science Ltd KEYWORDS Rock mass strength • physical modeling • discontinuities • anisotropy • scale effects • compressive strength INTRODUCTION A good understanding of the mechanical properties of jointed rock masses is vital to arrive at safe and economical designs for structures built in and on rock masses. The presence of various discontinuities, the inherent statistical nature of their geometrical parameters, and the uncertainties involved in the estimation of their geomechanical and geometrical properties make it complicated and difficult to accurately predict the mechanical properties of jointed rock masses. Some in-situ tests have been carried out to study the effect of size on rock mass compressive strength (Bieniawski 1968; Pratt et al. 1972; Bieniawski, Van Heerden 1975). Heuze 1980 has reviewed the previous work on scale effects on mass strength. The results of these investigations clearly show the reduction of mass strength and modulus with size up to a certain size at which change becomes insignificant. It is important to note that these relations are highly site-dependent, since the scale effect is primarily governed by the fracture network. In these investigations, no attempt had been made to map the fracture network. Results of laboratory model studies (Brown 1970a,b; John 1970; Einstein, Hirschfeld 1973; Chappel 1974) show that many different failure modes are possible in jointed rock and that the internal distribution of stresses within a jointed rock mass can be highly complex. Numerical simulations of jointed rock blocks (Kulatilake 1985; Kulatilake et al. 1993a) based on the finite element method with Goodman's joint element (Goodman et al. 1968) and the distinct element method (Cundall 1988; Hart ISSN 0148-9062