Page 255 - The Combined Finite-Discrete Element Method

238 TRANSITION FROM CONTINUA TO DISCONTINUA

Figure 7.6 Fracture sequence in 2D combined finite-discrete element simulation of bench blasting;
the last picture shows an enlarged fracture pattern.

is worth noting that the initial finite element mesh employed is a very coarse one. As
the fracture pattern develops, the finite element mesh is refined to accommodate newly
created boundaries (as previously described in this section), while the energy dissipation
mechanisms due to strain softening are controlled in respect to the mesh size.
A typical sequence for a muck-pile formation is shown in Figure 7.7. Initially, fractured
rock forms an unstable column with individual rock blocks moving horizontally and
accelerating downwards under gravity (self-weight). The bottom of the column collapses
first, and this collapse is propagated toward the upper layers of rock. In the next stage the
lower layers of rock decelerate due to confinement induced through boundaries, which
results in contact interaction between rock fragments and intensive energy dissipation.

Figure 7.7 Initial collapse of fractured rock.