Rock fracture identification with measurement while drilling data in down-the-hole drills

The structural characteristics of rock mass are crucial for the planning and construction of geotechnical engineering. Traditional methods for obtaining rock mass fracture locations rely on expensive drill core sampling and analysis tests. The testing period is long and affects normal on-site construction. In this study, a self-developed measurement while drilling (MWD) system was used to conduct drilling experiments in a limestone mine. Firstly, a method was developed to extract effective drilling data from the entire process of MWD data. Then, a comparative analysis was conducted between the obtained effective drilling data and borehole images. The study revealed significant responses of thrust force, rotation torque, air quantity, and penetration rate to rock mass fractures. The appearance of fractures leads to a varying reduction in both thrust force and air quantity, while rotation torque and penetration rate show a significant increase. Finally, the Composite Fractures Index (CFI) was established to identify rock mass fractures based on the response characteristics of these four drilling parameters and rock mass fractures. The results indicate that the CFI can effectively identify the location of fractures in the rock mass. It offers a dependable engineering surveying solution for real-time and accurate identification of rock mass fractures.