Prediction Of Mechanical Properties And Rockburst Tendency Of Deep Hard Rock Based On Digital Drilling Technology

With the deepening of human engineering to the deep earth,the rock burst disaster of deep rock mass has become a common geological problem in underground engineering construction due to the influence of natural causes and human technology.Violent rock burst disasters not only cause huge economic losses,but also bring serious security risks to engineers and technicians.Therefore,the prediction of rock burst tendency has been one of the hot topics in the academic and engineering circles.In this paper,the newly developed digital drilling test system for indoor rock is used to carry out drilling tests of six kinds of rock under different confining pressure conditions.Combined with the basic physical and mechanical tests of indoor rock,the correlation between the parameters of rock while drilling and the strength parameters of rock is analyzed.Based on the analysis model of drill bit,the concept of cutting strength ratio of rock is proposed.The relationship between rock strength parameters and cutting strength ratio obtained based on digital drilling technology and theoretical criterion of rock burst tendency is studied,and a new idea of predicting rock burst tendency in deep depth is put forward.The results are as follows:(1)The variation law of rock parameters with drilling time under different confining pressures is studied.The results show that the variation process of bit torque,cutting force and thrust with drilling time can be divided into rising stage and stable stage,and the variation process of rotational speed with drilling time can be divided into decreasing stage and stable stage.In the ascending(or descending)phase of the curve,the relative slope of drilling parameters with drilling time increases with the increase of confining pressure for the same rock.In the stable stage,the larger the confining pressure,the larger the torque,cutting force and thrust value,and the smaller the rotational speed value of the same rock.Under the same confining pressure condition,the harder the rock,the larger the torque,cutting force and thrust in the stable stage,and the smaller the rotational speed;Conversely,the smaller the torque,cutting force and thrust,the greater the speed.(2)Based on the working principle of drill bit,a force balance analysis model was established to predict rock strength parameters(internal friction Angle,cohesion force)and confining pressure environment.The results show that the average relative error between the predicted and measured values of rock internal friction Angle is less than 10.0%.The average relative error between the predicted and measured values of rock cohesion is 155%,which is a large deviation.The mean relative error between the predicted and set values of confining pressure is less than 15%.(3)The correlation between uniaxial compressive strength and tensile strength of rock samples and internal friction Angle and cohesion is studied.The results show that uniaxial compressive strength and tensile strength are positively correlated with internal friction Angle and cohesion of rock.The ratio of uniaxial compressive strength to tensile strength has no obvious correlation with internal friction Angle and cohesion.The relationship between cutting strength ratio and internal friction Angle,cohesion,uniaxial compressive strength and tensile strength under different confining pressures is analyzed.The results show that there is a good correlation between cutting strength ratio and internal friction Angle,cohesion and strength of rock.Based on this,a new idea for predicting rock strength is proposed.The average relative error between the predicted value of tensile strength and the measured value of laboratory test is 43.7%,which is a large error.The average relative error between the predicted value of uniaxial compressive strength and the measured value of laboratory test is 8.63%,indicating that the prediction is accurate.(4)The rock burst characteristics of rock sample borehole under different confining pressure conditions are studied,and the rock burst tendency is determined from the Angle of energy and stress.The predicted value of internal friction Angle and cutting strength ratio of rock are linearly fitted with rock burst criteria(energy impact index,elastic strain energy index,Russenese criterion,Barton criterion and Hoek criterion)respectively.The results show that the predicted value of internal friction Angle of rock and the empirical equation R~2 of rock burst criteria are all greater than 0.90.The R~2 values of the empirical equation of rock cutting strength ratio,energy impact index and elastic strain energy index are 0.75 and 0.74,respectively,and the R~2 values of the empirical equation of Russenese criterion,Barton criterion and Hoek rockburst criterion are all greater than 0.90.