Normal indentation force model considering the degree of rock breakage for digital drilling
Digital advanced drilling relies on quantitative relationships between measurement-while-drilling parameters and rock characteristics. Yet,quantifying the effect of rock fracture on thrust-one of the key measurement-while-drilling parameters that is pivotal in digital drilling,remains largely unexplored. This paper proposed a cavity expansion theory based on the theoretical model to predict thrust considering the fracture effect on rock strength degradation. The degradation of rock strength by fractures was accounted for by the Hoek-Brown constitutive model. In addition,the model took into account the effect of confining pressure on thrust. The similarity between the indentation process and expansion of simplified cavity shapes was exploited,and the stress and displacement fields were approximated during indentation. This led to quantitative relationships between cutter shape parameters,rock strength parameters,and results from indentation tests including penetration depth and indentation force. To verify the proposed quantitative relationship,two wedge-shaped probes with different geological strength indices were carried out to penetrate the rock,and the test results were consistent with the trend and order of magnitude of the model curve. The reliability of the model was further verified by comparing the prediction results of the model with the experimental data in the literature,and the model in this paper tended to be safer when using penetration force to predict the degree of fracture of the surrounding rock of the tunnel face in actual engineering. Subsequent parametric analysis demonstrated that rock fracture and confinement have opposite effect on the thrust,which necessitates consideration of rock fracture on prediction of thrust. The proposed model serves as a start point to discuss the relationship between the thrust recorded in the field and rock strength parameters thus promoting the realization of digital advanced drilling.
cavity expansionsingle cutter indentation force modelrock fragmentationHoek-Brown failure criterionconfinement
万方数据
维普
