Field-scale rock formations (i.e. rockmasses) are composed of sections of intact rock separated by a preexisting joint network. As rockmass deforms, strain accumulates within the intact rock and slip occurs along the preexisting joints. However, the magnitude of strain within the intact rock sections are not necessarily equal everywhere throughout the rockmass due to the presence of the discontinuities. In general, testing representative rockmass specimens in the laboratory is difficult because of the required size. As an alternative, small-scale rockmass analog laboratory specimens can be used to investigate trends in rockmass behavior. This research evaluates the mechanical behavior of rockmass analog specimens of Carrara marble containing two orthogonal sets of smooth joints. Both intact and the jointed specimens were tested under triaxial compression with 1 and 12 MPa of confinement. Axial and radial deformation within each section of intact rock in the specimens were recorded with separate strain gages, and strain gages in these same positions were also attached to intact specimens for comparison. Notable radial strain heterogeneity was observed in the jointed specimens and this heterogeneity was suppressed under higher confinement levels. Strain was also found to localize in intact rock blocks with higher surface area to volume ratios.
Field-scale rock formations are commonly referred to as rockmasses, which are composed of sections of intact rock separated by a network of preexisting discontinuities (Mendes et al., 1966). Such discontinuities can include joints (i.e. fractures), shear zones, faults, and other structural planes (Cui et al., 2020), which are formed from varying stress fields throughout the rockmass's tectonic history (Mandl, 2005). The presence of discontinuities reduces the strength of the rock and affects other aspects of its mechanical behavior (Hoek and Brown, 1997). Rockmasses are more difficult to test in the laboratory compared to intact rock because representative rockmass specimens are typically on the scale of meters. Large triaxial testing apparati are uncommon and typically allow for a maximum specimen diameter of 1 meter, which is not sufficient for many rockmasses with joint spacing of multiple meters (Muschler and Natau, 1991; Natau, 1977; Singh and Huck, 1972; Vergara et al., 2015).