Abstract: The laboratory mechanical test is carried out on limestone of Tongzi Tunnel on LanzhouHaikou Highway, and the numerical simulation of loading and unloading rockburst test is carried out by threedimensional particle flow program particle flow code（PFC）, which helps to obtain the meso failure characteristics of rock samples under different stress states. The results show that: (1) The rock stress variation, particle displacement, bond failure characteristics and energy variation of rock during loading test show 3 stages, i.e. elastic stage, yield stage and failure stage. (2) With the increase of initial stress, the loading strength of rock increases, and the ultimate strain of rock increases. (3) The greater the stress, the greater the rockburst strength during the unloading test, resulting from stress concentration inside the rock induced by the stress transfers from the unloading surface to the interior during rock failure; with other conditions unchanged, the higher the initial stress, the greater the unloading rockburst strength; and the increase in radial stress will have a more adverse effect on the stability of the chamber rock. (4) The failure modes of rock under loading and unloading conditions are quite different.

Key words: rockburst, tunnel, laboratory mechanical test, numerical simulation, PFC3D, flat , joint model, loading, unloading