The transient impact of the resonant flexible drill string of a sonic drill on rock

Abstract

Sonic drilling is a fast and efficient method for the undisturbed sampling of soft soils and is widely used in overburden layer drilling such as in soft soil and gravel. This technique can also be used to quickly drill through bedrock using vibration shock technology with rotary drilling, a process that differs from the general vibratory immersed-pipe/pile method. To date, little has been published at home or abroad regarding how to determine the impact of sonic drill bits on rock to rationally design button bits for highly efficient rock penetration. This paper establishes a mathematical model of a sonic drill with a flexible drill string on rock, succeeds in determining a transient solution for flexible drill string vibrations under complex boundary conditions, and systematically studies the influential impulse factors of the sonic resonant flexible drill string on rock by a button bit. As the bedrock stiffness and order of the resonance increase, the magnitude of the impact peak increases, and the impact duration becomes shorter. As the drilling hole is extended, the drill string becomes longer, and the largest impulse obviously decreases. In addition, the damping increase is approximately proportional to the attenuation inhibition effect on the impact force. Through systematic research on the modeling and determination of the impact of the sonic drilling process, the design theory of sonic drilling can continue to be improved.