The uncertainty in the grain-based model

such as grain shape

size and spatial distribution

has a significant effect on the reliability and reasonability of numerical simulation for rocks. Based on the Voronoi model in UDEC

two modified Trigon models were proposed and realised through the built-in programming language FISH. Meanwhile

the effects of grain shape

iteration and random seed on the macroscopic response and failure mode of the coal sample were analysed in uniaxial compression test. The results showed that the effects of iteration and random seed on uniaxial compression strength and deformation of coal samples depended on the grain shape. For the two Trigon models

the influences of iteration and random seed were similar. However

for the Voronoi model

the influence of random seed was greater than that of iteration. Furthermore

the type

number and development of cracks were mainly affected by the grain shape. The failure modes of the coal sample were determined by the grain shape

iteration and random seed. Hence

the reliability of numerical simulation in the UDEC grain-based model can be improved by considering the real grain shape

grain size and spatial distribution of rocks.