| Large diameter drilling in coal seams is one of the most commonly used methods for preventing and controlling rockburst.However,in the context of its widespread application,the industry has highlighted a series of doubts about the effectiveness of rockburst prevention,mainly due to the mutual feedback effect between large diameter drilling and time and incremental mining loads,which restricts the effectiveness of pressure relief and rockburst prevention.This article comprehensively adopts research methods such as theoretical analysis,numerical simulation,indoor experiments,and on-site monitoring to analyze the time-varying characteristics,dynamic load response,and static load response laws of large-diameter drilling.It studies the anti erosion and energy consumption mechanism of pressure relief drilling under different factors,and evaluates its pressure relief effect.The main achievements are as follows.(1)In the initial tense,large diameter drilling varies over time,and the adjustment of surrounding rock structure undergoes three stages: the development of elastic zone,the expansion of plastic zone,and the stable development of fracture zone.The plastic zone and fracture zone are the pressure relief zones of the drilling holes,during which the pressure relief zones between multiple drilling holes are connected and connected,transferring stress and dissipating elastic properties,and playing a role in erosion prevention.(2)Under the disturbance of dynamic load during mining,the weak structure formed by drilling weakens the transmission of dynamic load and dissipates energy.However,as the energy level and disturbance period of external dynamic load increase,the ability of large diameter drilling to attenuate dynamic carrier wave weakens,the ability to weaken dynamic load disturbance decreases,the range of stress concentration area increases,the distance from the high-energy elastic energy area to the drilling hole decreases,the trend of drilling rock movement increases,and the variation amplitude of particle motion speed and acceleration at the bottom of the hole increases,Under high-energy dynamic load disturbance,drilling is prone to dynamic instability and failure.Under high dynamic load disturbance,the degree of damage and fracture of drilled coal samples intensifies,and the acoustic emission events continue to increase with the increase of disturbance period until instability and failure,and the acoustic emission events are mainly high-energy.(3)Under static loading during mining,the plastic zone and fracture zone of the borehole expand and change,and the fracture zone is filled with the borehole,suppressing the expansion of the plastic zone.As the loading speed and stress concentration of the external static load increase,the volume of the plastic zone decreases,the unloading amplitude S1 gradually decreases,the stress increase Q1 and the elastic energy storage rate K1 increase,and the unloading effect,energy consumption capacity,and anti impact effect of the large diameter drilling hole decrease.The drilling hole gradually fails.When the static load is loaded to a certain extent,the elastic energy consumption ratio of the drilling hole approaches 0,and the energy consumption capacity of the drilling hole is lost,Acoustic emission signals appear in the form of "high frequency and low energy" at low loading speeds,while at high loading speeds,acoustic emission signals appear in the form of "high energy and low frequency".(4)The pressure relief ability of large diameter drilling has limitations.The degree of time-varying and incremental dynamic and static loads affects the pressure relief and anti impact effect of large diameter drilling.During plastic deformation of drilling,energy is consumed to relieve pressure and exert the pressure relief effect.However,as the degree of incremental dynamic and static loads increases,the anti impact effect gradually weakens or even fails.Therefore,timely optimization of drilling layout should be carried out to improve the anti impact effect of drilling and reduce the risk of impact. |
