An experimental investigation of shear strength behavior of a welded bimrock by meso-scale direct shear tests

Bimrocks have been rarely studied due to their inhomogeneous properties, challenges related to specimen preparation and tedious in-situ tests. This study was undertaken in an attempt to determine the shear strength parameters as well as the deformation behavior of a highly welded bimrock using laboratory meso-scale direct shear tests. In addition digital image processing analyses (DIP) and fragmentation fractal dimension (DF) calculations were made to quantify the geometrical and structural properties of the bimrock. It was concluded that the block size distribution of Sille bimrock is scale-invariant and shows fractal fragmentation. Moreover the block sizes have power-law distributions and there is evident skewness in normal distribution. The test results demonstrated that with the increase of volumetric block proportions (VBP), the internal friction angle (phi) of the bimrock increases whereas its cohesion (c) decreases. Strain softening behavior was observed after attaining the peak shear stress for all normal stresses and the VBP values. It is revealed that the normal stress is more effective than the VBP on the development of dilatation/contraction behavior. Lastly, the negative correlation between the DF and the peak shear stress indicated that the shear strength of the bimrock increases while the proportion of relatively small blocks in the specimen decreases.