A comprehensive understanding of the fracture's effects on wave propagation is a necessary prerequisite for estimating the dynamic behavior of fractured rock masses. This study presents a series of ultrasonic experiments on the multifarious effects of open fractures on the propagation characteristics of waves, considering various geometric parameters of fractures. The results indicate that fractures disrupt the waveform and attenuates the wave amplitude and velocity. With the increase of fracture width, the amplitude of transmitted wave and the dominant frequency of transmitted wave decrease, while the transmit time of wave in the sample increases. An increasing fracture dip angle generally leads to the increase of wave amplitude and dominant frequency, while reduces the transmit time of wave. As the fracture spacing increases in the testing range, the wave amplitude increases, while the wave frequency exhibits an opposite tendency. Comparing with the experimental results in the cases of single and multiple fractures, it is confirmed that the attenuation effect and the low-pass effect of fractures on wave propagation are enhanced quickly with the increase of fracture number.

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The Brazilian split test was performed on two groups of limestone samples with loading directions vertical and parallel to the bedding plane, and the response laws of the electrical resistivity and acoustic emission (AE) in the two loading modes were obtained. The test results showed that the Brazilian split test with loading directions vertical and parallel to the bedding showed obviously different results and anisotropic characteristics. On the basis of the response laws of the electrical resistivity and AE, the damage variables based on the electrical resistivity and AE properties were modified, and the evolution laws of the damage variables in the Brazilian split test with different loading directions were obtained. It was found that the damage evolution laws varied with the loading direction. Specifically, in the time-varying curve of the damage variable with the loading direction vertical to the bedding, the damage variable based on electrical resistivity properties showed an obvious damage weakening stage while that based on AE properties showed an abrupt increase under low load.

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