We describe a new technique for measuring the deformation and load bearing capability of large intact and jointed in situ rock specimens under applied uniaxial stress. The specimen configuration is an equilateral triangular prism of constant cross section with one end still connected to the rock mass. The free end of the specimen is loaded by a triangular flat-jack package. Displacements are monitored along and across joints; strains are measured on the surface of the specimen.
Forty-six tests have been performed at five sites on solid and jointed specimens over a range of effective diameters from 6 to 50 in.; on surfaces with orientation ranging from horizontal to nearly vertical; and on a wide variety of rock types including granites, sandstones, amphibolites, and chloritic schists. The technique has been used to measure the effect of specimen size on the strength of intact rock and frictional characteristics such as maximum and residual shear stress, normal and shear stiffness, and friction angle on natural joints with surface areas up to 750 square inches.