8. Analysis of Particle Breakage for Blasted Rockfill Material Under Large Size Triaxial Testing

Breakage of particle is one of the significant factors which modifies the behaviour of rockfill material, and it is also influencing dilatancy, angle of internal friction (φ), stiffness, and permeability. However, the breakage laws of the rockfill material during the shearing remain uncertain. In this paper, the study of the particle breakage analysis of the poorly graded metamorphic rock, viz. schist, phyllite, and quartzite, has been considered. This investigation is based on the one of the consultancy job project of northern part in India for using rockfill material in the concrete face rockfill dam (CFRD). Sliding and roll over are more constrained under a high confining pressure (0.6, 1.2, and 1.8 MPa) rather than crushing of individual particle. Consequently, the contact force between particle to particle significantly increases and considerable amount of particle breakage occurs. During the application of stresses, breakage initiated from lagger size of particles and smaller sizes of particles initiates to rupture under application of confining pressure increases. The fraction of particles lesser than 0.2 mm diameters always added with increasing shearing strain. The amount of breakage showed more with the increasing of cell pressure. The breakage of particles under different confining pressures (stress level) is quantitatively presented as breakage factor, B_f. Breakage factor of rockfill material is to be calculated as per the pre- and post-test particle size distribution curves for all the maximum sizes (d_max) of particle. The effect of confining pressure (σ₃) and d_max on the breakage factor, B_f, is studied by highlighting the plotting between d_max versus B_f for different σ₃ for tested material. From the analysis, it is observed that the breakage factor increases from 3.5 to 11.5% with variation of confining pressure ranging from 0.6 to 1.8 MPa. It is found that the breakage factor increases with increase in d_max and σ₃ for tested rockfill material.