Influences of PSD curve and vibration on the packing dry density of crushed bentonite pellet mixtures

Crushed high-density bentonite pellet mixture has been proposed for filling up gaps in the deep geological repository for disposal of high-level radioactive waste (HLW), due to its swelling capacity and easily to be handled. In this regard, for the long term safety evaluation of a deep geological repository, it is of great importance to investigate the packing behavior of the crushed bentonite pellet mixtures for achieving an adequate bulk dry density of the engineering barrier system. In the present work, crushed high-density GMZ bentonite pellets (1.94-1.95 Mg/m3) with different sizes were produced. Particle size distribution (PSD) curves of pellet mixtures were established using the distribution modulus method (DMM) and the mixing ratio method (MRM). A series of packing density tests were conducted by free fall packing with or without vibration. Results show that the PSD curves of pellet mixtures had great influences on the packing dry density, which first increased and then turned to decrease with increasing distribution modulus q (or the coarse/fine mass ratio αcf). In the meantime, vibration during packing process can significantly improve the packing dry density and this vibration effect is relative to the composition of the pellet mixture.