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Abstract The critical failure characteristics of sandstone experiencing change stresses from three-dimensional loading to confining stress unloading and to axial impact，are investigated by the improved split Hopkinson pressure bar(SHPB) with axial static pressure and confining pressure. The results show that：(1) The critical failure characteristics of sandstone under external impact is influenced obviously by axial static pressure；and the impact strength first increases and then decreases as the axial static pressure increases. (2) The stress-strain curve of sample under coupled static and dynamic loading is a typical class I curve when without axial static pressure and the axial static pressure is 20% of uniaxial compressive strength. (3) With the increase of axial static pressure，the stress-strain curve changes to the typical class II curve gradually. In the failure process of sample，the energy change law is from disturbed energy absorption to elastic stored energy release，which can reflect the mechanism of interactions between high static stress and dynamic disturbance in the process of rockburst. The results can provide a test support for the further research of rockburst mechanism. The surface displacement field is monitored by digital speckle correlation method(DSCM). The surface displacement field results show that the samples present whole expansion characteristics under conventional impact loading；but under the axial static pressure of 72 MPa，the samples present the interaction of tension-shear failure and expansion failure，which reflects the effect of axial static pressure on the fracture mode of dynamic failure surface of sample.
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2012, Vol. 31 
