Detection methods for strength deterioration and structural characteristics of fractured rock based on digital drilling

Abstract

Fractures ubiquitously exist in strata, and large-scale fractures can cause low bearing capacity and poor stability in rock masses and can sometimes lead to hazards such as roof falls and collapses in mines and tunnels. The foundation of the control of surrounding rocks and effective prevention of such hazards is to be able to accurately determine the structural characteristics of fractures and strength parameters of rocks. Traditionally, testing is carried out mainly through indoor compression tests and borehole inspection, which require drilling of the surrounding rock on site and core testing indoors. The effective in situ and accurate detection of the structure and strength properties of surrounding rock has become a challenge. Digital drilling testing of rock mass is a new approach to solve the above problems and future research direction. In this study, a multifunctional rock mass digital drilling test system is used to perform tests on different types of fractured rocks. The response of drilling parameters to fracture parameters is analysed, and a strength deterioration evaluation index for fractured rock based on drilling parameters is established. Then, the response mechanism of the strength deterioration rate while drilling in the fracture zone is defined, and a model for identifying fracture parameters based on drilling is established. Furthermore, an in situ detection method for fractured rock properties based on digital drilling is proposed. The results of the validation test show that the average difference ratio between the equivalent compressive strength measured by the drilling test and the laboratory compressive test is 3.97 %. The strength degradation of the fractured rock is significant, with a maximum strength degradation rate of 82.1 % obtained through drilling. The average identification accuracies of the fracture position and width are 2.56 mm and 0.85 mm, respectively. The identification accuracy of rock properties while drilling is high, which proves the effectiveness of the prediction model while drilling. This study can provide a theoretical and methodological basis for the accurate in situ prediction of rock properties in underground engineering fields, such as mine roadways, transportation tunnels, and hydraulic tunnels.