The aim of this study is to investigate the rheological behavior of jointed rock masses involved in large space-time scale deformational processes. The analysis is based on both, an experimental approach consisting of an analogue laboratory testing approach which allowed to investigate the mechanical behavior of hypothetical rock masses with different joint characteristics with overlapping effects of creep along these interfaces. Several uniaxial strength and creep lab-tests were performed on artificial specimens of concrete mixtures whose rheological properties were selected according to physic-analogical scaling criteria. The specimens were realized to represent both intact rock and jointed rock masses. Different geometrical configurations were adopted to reproduce pervasive joint sets. The laboratory results were analyzed considering the jointed rock mass as an equivalent continuum medium with a visco-plastic rheological behavior. The study allowed to correlate the major mechanical properties of the jointed rock masses to both the properties of the intact rock and the geometrical configurations of joints.
Jointed rock masses present a very complex rheology, strictly related to their discontinuous, heterogeneous and anisotropic nature. As a consequence, the overall rock mass stress-strain behavior is strictly controlled by properties of both intact rock and discontinuities (Sridevi & Sitharam 2000; Sitharam et al. 2001; Peng & Zhang 2007).
In the study of gravity induced deformations affecting the natural rock mass slopes at a large space-time scale the joint sets play a fundamental role on the creep processes which drive the deformational phenomenon. More in particular, the rheological properties of rock, the structural setting, the jointing conditions and the joint alteration strongly influence of creep phenomenon and the consequent time-stress deformations (Chigira 1992).
In the case of the above mentioned phenomena a discrete solution for representing the involved rock mass is not reliable due to the difficulty of taking into account all the joint sets and their properties. This encourages to consider the rock mass as a continuum medium (Ramamurthy 1994; Sridevi & Sitharam 2000; Sitharam et al. 2001; Martino et al. 2004; Esposito et al. 2007; Discenza et al. 2011), i.e. in which the properties of the joints and of the rocky matrix are merged to obtain equivalent parameter values referable to the jointed rock mass. According to such an approach, rock mass strength and stiffness can be obtained by rheological models that take into account the geometrical and mechanical properties of both intact rock and joints.