| dc.description.abstract | This research performed a series of direct shear tests of gravel material under various conditions of normal stress and degree of saturation to study the properties of shear strength, sound waves and vibration waves. A spectrum comparison method of waves is proposed in this paper to distinguish and to filter the sound waves and vibration waves generated in the process of shearing. According to the results of experiments, it is found that within the area smaller than 15Hz, the magnitude of sound waves increased apparently compared to that of background noise and this can be seen as the apparent frequency or main frequency of this gravel material. The magnitude within this frequency area varied slightly in spite of the variation of water content. As to the spectrum of acceleration of vibration waves, similar apparent frequency was found before 15Hz by comparing the experimental data at the earth stage of shearing with that right before the period of failure. Furthermore, some other secondary frequencies were found at the same position of sound spectrum. This showed that there exists a close relationship between sound waves and vibration waves. To examine the shear strength properties of gravel in this study, the sound waves and the acceleration of vibration waves larger than 15Hz were filtered.
From the experimental results, it is found that larger sound pressure of air dried gravel will be caused at failure for larger normal stress. But the sound pressure of partially saturated gravel is smaller than that of air dried gravel. According to the relationships between shear stresses at yielding or failure with normal stress, it is recognized that the yielding stress of air dried gravel is about 76% of failure shear stress, and this value decreased to 74% for partially saturated gravel. Therefore, the shear stresses related to the acceleration signals may be used to realize the yielding premonition. Furthermore, after yield, the acceleration signals increased slightly and last continuously. But the sound signals only show some apparent values at failure. Because the sound signal is weak and its energy dissipates easily, so only few strong signals at failure remained. Conversely, the acceleration signal does not decrease apparently, so it can be combined with the sound signal to distinguish the yielding and failure of gravel. | en_US |