Abstract:

The compressive strength and deformation parameters of rock materials are important indices of rock engineering. Because a
rock is a typical heterogeneous material, its strength and deformation parameters vary with sample sizes. In this paper, the size effects
of rock materials under different confining pressures were numerically studied using PFC2D code. The simulation results indicate that
(1) rock strength, peak strain and compressive modulus decrease with increasing specimen sizes, whereas the change of specimen size
has little effect on the failure mode of these rock specimens. (2) rock strength, peak strain and compressive modulus increase with the
confining pressures. Among them, the rock strength and peak strain have linear relations with the confining pressures. In addition, the
failure of rock specimens gradually changes from the splitting mode into shear failure mode with the increase in confining pressures.
(3) the increments of rock strength and peak strain for different size specimens at the same confining pressure range are approximately
the same. Meanwhile, these two parameters increase with confining pressures. Therefore, the size effect of the rock strength and peak
strain at high confining pressure becomes weak. In addition, the increasing ratios of compressive modulus for the corresponding
scenarios are similar, which causes the confining pressure to have little impact on the size effect of compressive modulus.

Key words: rock, compressive strength, deformation parameters, size effect, confining pressure