Complex geological mixtures as bimrocks, composed of core block inclusions randomly distributed in a weaker matrix, are challenging issues for a proper characterization in a large scale relevant for rock mass range, as the overall behavior is strongly influenced by the presence of the rock fragments and by their volumetric block proportion. The article presents results from their physical modelling and tests in a large-scale direct shear box with dimensions 1,0x1,0x0,6 m, loaded with stresses in large span. The mixtures of blocks and matrix are modelled for values of volumetric block proportion of 5%, 15% and 35%. Results confirm that higher contents of volumetric block proportion lead to higher angle of internal friction and lower value of apparent cohesion, while the time of failure is longer for a higher volumetric block proportion.
Investigation, testing and characterization of bimrocks is extremely challenging task because of the complex interactive influences of core blocks and matrix properties.
On the current level of development of the geotechnical science, few rare examples from testing of bimrocks in large scale are known. Along with this, it is very difficult to conclude how close is the prognosis of the parameters to the actual conditions which are expected in the phase of exploitation of the engineering structures.
It shall be noted that several conceptual empirical approaches are developed for predicting of overall strength of bimrocks considering the boundary conditions for unwelded and welded bimrocks. However, there is still no widely accepted empirical approach in the rock mechanics community (Sönmez et al., 2009). From the present knowledge, it is clear that the mechanical behavior for unwelded bimrocks depends on properties and relations between the core blocks, as strong rock inclusions, and the weaker matrix (Sönmez et al., 2006 and 2009). Main findings are that strength behavior of the boundary between matrix and core blocks affects the uniaxial compressive strength at rock mass level (UCSm) and it's usually increased when the volumetric block proportion (VBP) is larger.
