Study On Rock Strength Test Method And Rockburst Weakening Mechanism Based On Digital Drilling

With the rapid development of underground engineering such as mine roadway and traffic tunnel to the deep,rock burst as a deep disaster phenomenon occurs more and more frequently.In the high stress environment,there is a stress concentration area in the surrounding rock,where a large of energy is accumulated.Under the impact forces of excavation disturbance,blasting and earthquake,the accumulated strain energy of surrounding rock is suddenly released,which leads to rock rupture and ejection,that rockburst occurs.Therefore,reducing the stress concentration is an important way to maintain the stability of surrounding rock.For high stress surrounding rock,pressure relief is an effective measure to reduce the stress concentration.Borehole pressure relief is a commonly used pressure relief method in underground engineering.Under high stress environment,the rockburst weakening effect of borehole pressure relief rock is affected by borehole parameters and rock strength.Rock compressive strength is an important mechanical parameter reflecting the rock strength.Therefore,the real-time acquisition of rock strength is the basis for the evaluation of rockburst tendency and control effect.The traditional indoor uniaxial compression test is time-consuming and costly,and it is impossible to obtain the compressive strength of rock in situ.However,digital drilling technology is an effective way to solve this problem.Its premise is to establish the quantitative relationship between drilling parameters and rock compressive strength.At present,the research on the relationship between drilling parameters and rock uniaxial compressive strength mostly does not consider the influence of the rock crushing area between the cutting edge and the cut rock on the bit,and there is no evaluation research on the rockburst weakening effect of high stress surrounding rock based on digital drilling.Based on this,this paper studies through the combination of theoretical analysis and laboratory test,and mainly makes the following progress:(1)The relationship model between drilling parameters and rock equivalent compressive strength is establishedConsidering the influence of the rock crushing area between the bit cutting edge and the intact rock on the size and transmission direction of cutting force,a rock cutting mechanics model is established based on the cutting theory and balance principle.Besides,the relationship between drilling parameters and crushing pressure(DP-σ0)are obtained.Combined with the laboratory rock digital drilling test results,the relationship model between drilling parameters and rock equivalent compressive strength(DP-σc)is established.What’s more,the effextiveness of DP-σc relationship model is verified by test data.(2)The response rules of cutting torque and cutting efficiency under different parameters are clarifiedBased on the DP-σ0 relationship,the effects of bit parameters and crushing pressure on bit cutting torque and cutting efficiency are analyzed.The theoretical analysis results show that the bit cutting torque increases with the increase of bit inclination,cutting angle and bottom friction angle,and the bit cutting efficiency increases with the increase of bit inclination and cutting angle,while decreases with the increase of bit bottom friction angle.What’s more,the crushing pressure has a significant impact on the bit cutting torque and cutting efficiency,that the bit cutting torque and cutting efficiency increase with the increase of the crushing pressure.(3)The evolution rules of the rock stress and energy before and after drilling is clarifiedUsing the deep rock nonlinear mechanics test system,the rock dynamic performance tests of different rock burst types before and after drilling are carried out under the true triaxial loading.The test results show that drilling can effectively improve the rock stress peak when impact failure occurs,and the more the number of drilling holes,the greater the rock stress peak.Besides,drilling can effectively reduce the energy released when the specimen is subjected to impact failure,and the more the number of boreholes,the less the energy released.(4)The weakening mechanism of rockburst by borehole pressure relief technology is revealedThrough the analysis of the rock dynamic performance test results,the weakening mechanism of borehole pressure relief technology on rockburst is revealed.After drilling for the high stress rock,a fracture zone is formed around the borehole,and the fracture zones around multiple boreholes are connected with each other,forming a large pressure relief fracture zone.The rock strength in the pressure relief fracture zone is obviously reduced,which can reduce the peak value of stress concentration,transfer the stress concentration area to the deep,and reduce the impact risk.The formation of pressure relief fracture zone changes the rock mechanical properties and reduces the ability of rock to store strain energy,so as to reduce the possibility of impact failure.(5)The evaluation method of rockburst weakening effect based on digital drilling is establishedBased on the DP-σc relationship model established in this paper and the weakening mechanism of borehole pressure relief technology on rockburst,the evaluation method of rockburst weakening effect based on digital drilling is established.The rockburst tendency and control effect of surrounding rock are evaluated by using digital drilling test technology,and the drilling evaluation of rockburst weakening effect of high stress rock is realized,which provides technical support for on-site surrounding rock support design and construction.