The dynamic properties of intact sandstone samples subjected to axially cyclic loading under confining pressures conditions in the laboratory are presented. Five sets of confining pressures

10

20

30

40

50 MPa

were employed by MTS-815 Rock and Concrete Test System. Tests were conducted on dry sandstone samples obtained from areas near “5•12” 2008 Wenchuan Earthquake location with axial loading frequency of 1 Hz and different amplitudes corresponding to different confining pressures. Results demonstrate that: (1) With increased confining pressure

the residual axial and volumetric strain of the rock samples and the residual volumetric strain when dilatancy occurred both become larger. (2) The rock samples subjected to dynamic cyclic loading responded with a significantly higher initial strength and stiffness at higher confining pressures than at lower confining pressures; and the stiffness decreased more rapidly at lower confining pressures than at higher confining pressures. (3) When the stress ratio (Rs) is larger

the sample failed after fewer cycles under confining pressure conditions. (4) The failure modes of the samples are shear failure and the localized band is wider upon dynamic loading.