Rapid Forecasting Technology For Rock Mechanics Parameters Based On Digital Drilling

The rock uniaxial compressive strength UCS as well as cohesion c and internal friction angle(p(combined as the c-? parameter)are essential parameters used to characterise rock strength.Accurate measurement of these parameters is necessary for surrounding rock classification,stability analysis and supporting scheme design in underground engineering.The laboratory rock mechanics tests are the main way to determine the above parameters,but there are many problems,such as time-consuming,high cost,and unable to guide the construction in time.At present,there is no field testing instrument that can quickly determine the rock mechanical parameters including rock uniaxial compressive strength and c,?parameters.To solve the above problems,a rapid forecasting technology for rock mechanics parameters based on digital drilling is proposed.The key to implement this method is to develop a digital drilling test instrument and create a quantitative and universal relationship between the drilling parameters and the rock mechanics parameters.In this paper,the following research is carried out in combination with the development of indoor instruments,theoretical analysis and laboratory tests.(1)The response relationship between the drilling parameters and the rock mechanics parameters is clarified.The laboratory rock mass digital drilling test system is developed,and digital drilling tests for different types of rocks such as granite,sandstone and mortar under different control parameters are carried out.The change law of drilling parameters with drilling depth and the response relationship between drilling parameters and rock strength parameters are clarified.Under the common mode of controlling the rotation speed and drilling rate while recoding the torque and thrust,the variation rules of torque M and thrust F versus drilling rate depth Dh are similar,consisting of the following two stages:rising stage and stable stage.M fluctuates slightly around a stable value in the stable stage.This behaviour may be related to rock heterogeneity and the alternating stages of cutting rock.For the same rock,the torque M and the thrust F increase with the increase of the drilling rate V,and decrease with the increase of the rotation speed N.For the same rotation speed N and drilling rate V,the torque M and the thrust F increase with the increase of rock strength.(2)Rock cutting mechanics model based on slip line theory and its application on inversion of c-(p parameterBased on the rock fracture characteristics,a rock cutting mechanical model is developed that does not assume a damaged rock surface.The ultimate cutting load of the rock is derived based on slip line theory,and the relation between the drilling parameters and the c-(p parameter is obtained.Finally,a rock c-? parameter digital drilling measurement method is established.The laboratory rock mass digital drilling test system is used to drill into granite specimens,and the obtained data are compared with the results of theoretical analysis.The mean deviation is 9.08%,which verifies the relation between the drilling parameters and the c-? parameter.In the granite tests,the average difference rate of the internal friction angle from the digital drilling measurement method versus that from the triaxial method is ??=4.27%;for cohesion,it is ?c=8.33%.This proves the effectiveness and the feasibility of the rock c-?parameter digital drilling measurement method proposed in this paper.The theoretical analysis indicates that the ultimate cutting load increases as the ultimate cutting load inclination angle,cutting edge inclination angle,cohesion and internal friction angle increase.The ultimate cutting load is linearly related to the cohesion when the internal friction angle remains constant.(3)Rapid forecasting method for rock mechanics parameters based on digital drillingThe relational model between the drilling parameters and the uniaxial compressive strength is obtained by ?-SVR method,firstly.A predicting method for the uniaxial compressive strength of rock based on digital drilling test technology is established.Combined with the rock c-? parameter digital drilling measurement method,which is established in the third chapter,a rapid forecasting method for rock mechanics parameters based on digital drilling is developed.This method does not require the participation of other tests and can simultaneously measure the uniaxial compressive strength and c-(p parameter of the surrounding rock of underground engineering quickly and accurately.The uniaxial compressive strength can be predicted accurately based on the relational model between the 5 physical parameters and the uniaxial compressive strength.The 5 physical parameters include the rotation speed N,drilling rate V,torque M,thrust F,the ultimate cutting load q of the rock.In the sandstone tests,the Absolute Error MAE of internal friction angle ? from the rapid forecasting method for rock mechanics parameters based on digital drilling versus that from the triaxial method is 1.86°,and the Absolute Error MAE of cohesion c is 3,35MPa.These results prove the effectiveness and the feasibility of the rapid forecasting method for rock mechanics parameters based on digital drilling.