Experimental and numerical simulations of jointed rock block strength under uniaxial loading

To simulate brittle rocks, a mixture of sand, plaster of paris, and water was used as a model material. Thin galvanized sheets were used to create joints in blocks made out of the model material. To investigate the failure modes and strength, 30 x 12.5 x 8.6 cm jointed model material blocks having different joint geometry configurations were subjected to uniaxial compressive loading. Results indicated three failure modes: (1) tensile failure through intact material; (2) combined shear and tensile failure or only shear failure on joints; and (3) mixed failure of the above two modes depending on the joint geometry. The fracture tensor component in a certain direction quantifies the directional effect of the joint geometry, including number of fracture sets, fracture density, and probability distributions for size and orientation of these fracture sets. Results obtained from the experiments were used to develop a strongly nonlinear relation between the fracture tensor component and the jointed block strength. The laboratory experiments conducted on jointed model material blocks were simulated numerically using the Universal Distinct Element Code (UDEC). With careful selection of suitable material constitutive models for intact model material and model joints, and accurate estimation and calibration of mechanical parameters of the constitutive models through a combination of laboratory testing and numerical simulations of the intact model material and model joints separately, it was possible to obtain a good agreement between the laboratory experimental and distinct element numerical results.