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With the gradual depletion of shallow resources, the energy exploration depth has been increasing and condition becomes complex. 1 Consequently, the explorations face increasingly harder rocks with higher strengths. Breaking hard rock rapidly in petroleum and mineral exploration is a popular and significant topic. 2-6 However, the current technologies cannot meet the demands of quick drilling. It is necessary to develop a more efficient technology for hard rock exploration. To achieve this goal, the assisted ultrasonic vibration technique (ultra-high-frequency cyclic loading), combined with the traditional drilling method, was first introduced by researchers at Aberdeen University. 7 To implement this technology more effectively, studies were conducted on rock-breaking characteristics under ultrasonic vibrations and optimization of the vibration parameters. The studies conducted by Wiercigroch et al 8 showed that the high-frequency axial vibration significantly enhanced the breaking rates compared to the traditional method. Subsequently, uniaxial compressive strength experiments were conducted on fine granite by Yin et al 9 to demonstrate that there exists a static force threshold for this technology. They found that the optimal value range of static loading was 200-300 N. An

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As a type of ultra-high frequency loading, ultrasonic vibration is an effective way to break the rock at high rates. Exploring the influence of various factors on the loading effect is essential for its effective application to assist drilling. In this study, the damage evolution of granite under ultrasonic vibration with different amplitudes was investigated. The theoretical and numerical simulation models of rock breaking by ultrasonic vibration were established. The research group applied ultrasonic vibration loading to granite using different amplitudes. The damage characteristics were tested by NMR experiment, and the damage evolution was numerical analyzed by Particle Flow Code software. The result shows that the propagation of cracks is positively correlated with the amplitude of ultrasonic vibration. The increase of amplitude magnifies the generation of transverse cracks, which is conducive to the stripping of rock fragments. A threshold value was found for the amplitude, and fractures show different propagation and expansion characteristics at the higher and lower values. Increasing the amplitude magnifies the stress at the crystal defect and speeds up the crack propagation process. The stress wave generated by ultrasonic vibration inside the rock will attenuate with the increase in depth. Increasing the amplitude value will amplify the stress in the influence area, and decrease the size of the area.

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In the construction of mountain tunnels, the increasing proportion of hard rock stratum enhances the difficulty of rock breaking by tunnel boring machine (TBM). As a type of cyclic load with ultrahigh frequency, ultrasonic vibration has the advantages of energy concentration and strong penetration. In the process of rolling and extrusion, the weakening of the rock by ultrahigh-frequency loading can improve the rock crushing efficiency of the TBM disc cutter. In this study, we established a physical model of rock cutting using a disc cutter assisted by ultrasonic vibration and obtained a motion equation. The discrete element software particle flow code (PFC) was selected to construct a heterogeneous granite model to demonstrate the mechanism and development of cracks inside the hard rock under a rolling disc cutter assisted by ultrasonic vibration. The results demonstrate that ultrasonic vibration helps the disc cutter construct a stronger stress field in the shallow layer, which promotes tensile damage of the surface rock. Vibration promotes the development of cracks inside the rock and accelerates the penetration of transverse cracks, which is conducive to the stripping of rock fragments. The addition of ultrahigh-frequency loading also reduces the fluctuation increase of cracks, which makes the operation state of the disc cutter more stable and avoids abnormal damage to tools.