ANALYSIS OF ENERGY FOR ROTARY DRILLING IN WEATHERED GRANITE FORMATION
风化花岗岩地层旋转钻进中的能量分析

Rotary drilling is a dominant way in geotechnical engineering borehole surveying.Based on the principle of conversation of energy,the energy for rotary drilling has been analyzed.Besides,a hydraulic rotary drill R-20 instrumented with a drilling process monitoring(DPM)system has been used for site investigation on weathered granite formation;and drilling energy is further analyzed based on the monitored data.The result shows that the penetrating energy in drilling is mainly kinetic energy dependant.The distribution of energy for rock failure is related with the strength characteristics of the penetrated formation.The kinetic energy is more than 98 percent and energy from effective thrust force is less than 2 percent when drilling in slightly weathered rock or fresh rock.However,the energy from the effective thrust force reaches to more than 22 percent,apparently increases with the increase in weathered degree of rock when drilling in soil or very strongly weathered rock.It shows that kinetic energy of drilling system and energy of effective thrust force can reflect the characteristics of the penetrated formation,which can provide theoretical foundation for identification of formation using penetrating energy in real-time.