Abstract: Aphanitic basalt is one of the main types of surrounding rock widely observed in the cavern group of super large scale underground powerhouse of Baihetan hydropower station, which includes widely-seen hidden microfissures and unfolds special mechanical response characteristics during excavation. With the use of CT scan, high-speed camera, acoustic emission, scanning electron microscopy and other methods, the deformation and failure characteristics, crack propagation and AE evolution of aphanitic basalt were analyzed. Meanwhile, the microscopic failure mechanism was explored. The key outcomes are: The intact specimens with a smooth stress-strain curve instantaneously burst that caused AE signal abnormally concentrated when loaded to peak strength, which was mainly characterized by fragmented failure. The samples with hidden microfissures exhibited a stress-strain curve of “zig-zag” shape and multiple surface spalling and active AE signal during the whole compression process, of which the failure mode was primarily the splitting failure. The samples with macrofissures showed a stress-strain curve of double or multi-peak shape and the failure mode was primarily the shear failure that the preexisting fissures started to partially slip before the peak. After that, the macroscopic rupture surface formed at the first peak which led to AE signal concentrate at the moment when peak stress instantly dropped .The microscopic failure mechanism of aphanitic basalt was mainly characterized by intergranular fracture and transgranular fracture of mineral grains. The research results lay a solid foundation for accurately understanding and scientifically mastering the mechanical response and rupture evolution characteristics of the surrounding rock mass of underground powerhouse caverns of Baihetan hydropower station, and also provide reference and guidance for the understanding of high-stress failure and disaster control of brittle rock masses.

Key words: Baihetan hydropower station, basalt, deformation and failure characteristics, acoustic emission, crack propagation, meso-mechanism