Dynamic mechanical behavior of sandstone with filled joints at varying angles under coupled triaxial static and dynamic loading

Natural or artificially formed rock composite structures with consecutively filled joints at varying angles are frequently disturbed by coupled static and dynamic loads. Understanding the impacts of the confining pressure and joint angle on the dynamic mechanical behavior of rocks is important for the stability of rock mass engineering structures. In this study, seven joint angles and four confining pressures were considered. Dynamic triaxial compressive tests of sandstone with consecutively filled joints were conducted using a split Hopkinson bar (SHPB) apparatus. The test results showed that varying degrees of "strain rebound" phenomena were observed in the stress–strain curves, implying that the jointed samples in the failure stage could still store more elastic energy, which may trigger rock burst accidents in practical engineering. Moreover, the dynamic compressive strength and elastic deformation modulus were proportional to the confining pressure, but showed a trend of slight decrease followed by a noticeable increase with an increase in the joint angle from 0° to 90°. The combined effects of axial pre-stress and confining pressure resulted in different trends in the dynamic peak strain. The plastic deformation moduli of samples with smaller joint angles were insensitive to changes in the confining pressure and smaller joint angles, whereas those of samples with larger joint angles were sensitive to changes in the confining pressure and larger joint angles. In addition, the experimental tendency of the dynamic compressive strength under coupled triaxial static and dynamic loading was in good agreement with the theoretical derivation.