A testing method for rock c-φ parameter based on digital drilling test technology

The accurate measurement of rock cohesion c and internal friction angle φ (hereinafter referred to as the c-φ parameter) is the basis of optimizing the design of underground engineering support and information construction. The traditional indoor test method has the characteristics of cumbersome testing steps,long cycle and high cost,and cannot carry out in-situ measurement. Therefore,it is necessary to develop an accurate and fast on-site testing method for rock c-φ. Digital drilling testing technology provides a new way for accurate and fast prediction of rock c-φ in-si- tu,and the key is to establish the quantitative relationship between drilling parameters and rock c-φ. According to the fracture characteristics of rock cutting,a rock cutting mechanics model without prior assumption of failure surface is proposed. This model makes up for the deficiency of the existing rock cutting mechanics model that assumes the failure surface as a plane and thus differs from the actual characteristics of the failure surface in rock cutting. The ultimate cutting force is deduced on the basis of the slip-line theory. Based on this,the relationship between drilling parameters (DP) and c-φ parameter (hereinafter referred to as the DP-cφ relationship) is established. In this paper,the digital drilling test is carried out by using the self-developed digital drilling test system. Compared with the results of theoreti- cal analysis and laboratory test,the average difference is 8. 44% ,which verifies the rationality and correctness of the rock cutting mechanics model and the DP -cφ relationship. Therefore,a digital drilling measurement method for the rock c-φ parameter is proposed. Compared with the results of this method and traditional triaxial method through labo- ratory tests,the average difference rate of cohesion and internal friction angle obtained by the two methods are less than 10% ,which proves the feasibility and effectiveness of the digital drilling method proposed in this paper. The method is convenient and fast,and can realize in-situ measurement of the c-φ parameter of the rock mass in the field.