EXPERIMENTAL RESEARCH ON MECHANICS CHARACTERISTICS OF SHALE UNDER DIFFERENT LOADING STRAIN RATES¹⁾

The typical stress-strain curves of shale failure are obtained by triaxial tests. The results show that in the range of strain rate tested the peak strength increases noticeably with the increase of strain rate under low confining pressure (10~MPa, 30~MPa), but it increases only mildly or even stabilizes under high confining pressure (50~MPa). The failure mode of shale evolves from brittle splitting shear failure to single shear failure when decreasing the strain rate and increasing the confining pressure, which means that the brittle characteristics of shale is weakened. The influence of strain rate on energy conversion and damage evolution in shale is also investigated, which enriches both the theory and method for large-scale exploitation of shale gas in China.