Investigation of the crack and acoustic emission behavior evolution of red sandstone subjected to water

• The increased water content reduces the rock strength, and Young's modulus, in red sandstone specimens. • • The mechanism of rock crack evolution under different water contents was investigated. • • A new precursor characteristic of rock failure was proposed. • • The study can form the basis for risk assessment and disaster prevention based on the water content in the rocks. To explore the influence of water on the crack and acoustic emission (AE) behavior evolution of rock specimen during the deformation and failure, uniaxial compression tests with variable water contents (dry, natural, and saturated state) on red sandstone specimens were systematically conducted in the laboratory. Based on real-time AE monitoring technology and scanning electron microscope (SEM) technology, the crack evolution mechanism in the rock specimen during the deformation and failure was studied. The results indicate that the peak strength of red sandstone in the natural and saturated state is 26.13% and 41.75% lower than that of red sandstone in the dry state. With the increase of water content, the dominant failure pattern of rock specimen changes from tension failure to shear failure. According to the variable characteristics of the AE events rate, the deformation and failure process of rock specimens with the change of water contents can be divided into four stress stages. Moreover, the relationships among the AE events rate, peak frequency, water content and different stress stages were discussed. Approaching to the peak stress, there is an obvious trend of relative decrease of the Ib -value and the phenomenon of “sharp increase” and “sharp drop” in the average AE energy rate. The above-mentioned variable characteristics of AE parameters can be used as a precursor for the instability and failure of rock specimens with different water contents.