Real-time rock strength and fractures determination based on Measurement while drilling method via rock drillability index: an in-situ study

In underground engineering, understanding rock strength parameters is fundamental for rock classification and evaluation, significantly influencing the design and optimization of support systems. Present research emphasizes real-time assessment methods for rock conditions during drilling operations. Employing the dimensionless rock drillability index (I_d) proposed in connection with Measurement While Drilling (MWD), it allows real-time evaluation of geological conditions in the surrounding rock through in-situ drilling tests. This study conducted in-situ drilling tests using both the MWD system and a drilling camera detection system. The results indicate a power function relationship (negative correlation) between I_d and rock strength (uniaxial compressive strength). Furthermore, under various drilling conditions, including the use of Polycrystalline Diamond Compact (PDC) bits and core bits, I_d continues to be a reliable method for assessing rock strength. A comparison of results from the two evaluation methods, I_d and specific energy, demonstrates that the application scope and stability of using I_d to assess rock strength superiors that of specific energy. Significant fluctuations in I_d within rock fracture zones suggest that I_d can accurately predict the presence of such zones. These findings affirm that I_d is stable and widely applicable for assessing the strength of the surrounding rock and predicting the presence of fracture zones.