Characterisation of crack development in bimrocks using digital image
correlation
Abstract
Bimrocks feature stiff blocks randomly distributed in a soft matrix.
Despite their wide distribution in nature, their significant effects on
the failure of rock structures such as slopes, mines and tunnels have
not been fully understood. Bimrocks behave differently as compared with
other rock types since they contain mix of blocks of different strength,
size and volume distribution and a matrix of different physical and
mechanical characteristics. The purpose of this study is to investigate
deformation behaviour and crack development trends of bimrocks
containing blocks of different sizes (small <1 mm, medium 2-4
mm, and large 5-8 mm). The Brazilian disc test is performed with the
digital image correlation (DIC) technique being employed for deformation
analysis. It is found that the size of blocks significantly influences
the deformation and failure behaviour of a bimrock. Bimrocks with large
blocks exhibit both tensile cracks parallel to the loading direction and
shear cracks inclined towards the loading direction. Moreover, the
development of fracture process zone (FPZ) is highly dependent upon
block size. In particular, bimrocks with large blocks exhibit obvious
development of FPZ, while no FPZ is observed for those with small
blocks. In fact, the specimens with small blocks cannot be called a
bimrock since they behave similar to a homogenous intact disc specimen
in which a crack splits the disc into two halves in a typical Brazilian
test.