Study on drilling dynamic characteristics and stratum information identification of anchor hole intypical coal-bearing stratum

The rotary drilling of anchor hole in coal seam roof is studied to analyze the dynamic characteristics of the engineering drilling during the drilling process according to the drill-string dynamic theory through numerical analysis, finite element simulation and identification of dynamic response signal, so as to meet the growing demand for intelligent drilling technology in the coal mine.Accordingly, the dynamic model of the drill string is derived and built, and the analytical solution of the dynamic loading force of the drill-string system is obtained, including the calculation methods of axial force, tangential force and torque.In a typical coal seam, the amplitude of the dynamic-loading axial force and tangential force varying with the pressed depth ranges from 0.18 kN to 0.31 kN; the amplitude of the dynamic-loading axial force and the tangential force varying with drilling speed ranges from 0.17 kN to 0.29 kN.The analytical expression of the vibration acceleration of the drill-string system is obtained. Combined with the engineering background of roadway support, it can be concluded that the lateral and longitudinal vibration accelerations of the drill-string system are important indicators for the characteristics of coal-bearing stratum during drilling. Furthermore, with the finite element simulation, the load curve of anchor drill bit rock drilling specimens in four typical coal-bearing strata was analyzed, including the sandstone specimen, coal seam rock specimen, hole sandstone specimen and broken soft coal specimen.As indicated by the simulation results, the drilling load varies significantly with the strength of the rock specimen, and the simulation results in a typical coal seam are basically consistent with the analytical calculation results.In addition, four typical rock specimens from coal-bearing stratum were used for the real drilling test, the vibration signal of the drilling tool is collected and processed by the acceleration sensor, and the effectiveness of the method of identifying the stratum with the vibration acceleration signal is verified. The test results show that, through the vibration signal, the characteristics of typical coal-bearing strata under the conditions of the rotary drilling of the anchor drill bit can be identified quickly and effectively; in particular, under the special working conditions of drilling the cavity development stratum and broken soft coal seam, the stratum can be identified remarkably through the drilling vibration response signal. The research results provide an effective method for dynamically and intelligently detecting underworkings stratum information in coal mine and improving the drilling quality.