Objective The drilling quality of anchor boreholes is significantly influenced by the structural planes of weak interlayers within rock masses. Weak interlayers, tending to be hidden hazards within rock masses, affect the drilling stability and efficiency, further influencing the stability and safety of the whole support structure. Once drilled by drill bits, weak interlayers exhibit significant dynamic responses, which reflect the changes in rock mass structures during the drilling.
Methods From the perspective of drilling specific energy, this study conducted digital drilling experiments on rock mass-like specimens bearing weak interlayers using the independently developed measurement while drilling (MWD) system, which allows for real-time and accurate monitoring and recording of drilling parameters such as drilling pressure, torque, rotational speed, and drilling velocity. By analyzing the sensitivity, principal components, and entropy of these parameters, this study assessed their degrees of feedback on the response characteristics of weak interlayers, determining the most significant parameter. Subsequently, this study developed a method to identify the drilling power ratio (the ratio of torque-induced rock-breaking energy to total rock-breaking energy) based on the most significant parameter, achieving the intelligent identification of weak interlayers within the rock mass-like specimens.
Results and Conclusions The results indicate that torque played a pivotal role in rock fracturing while drilling and the identification of weak interlayer characteristics. This parameter exhibited the highest weight and the optimal feedback effect. The drilling power ratio method, with torque variations as the primary characteristics for identification, successfully increased the average accuracy from 72.943% to 88.268% in identifying the thicknesses of weak interlayers. Furthermore, the method to identify dip angles was developed based on drilling power ratios. The calculation results indicate that this method yielded an average accuracy of 90.833% in the dip angle identification of weak interlayers. All these suggest a significant enhancement of the identification accuracy of weak interlayer characteristics. This corroborates the effectiveness of the proposed methodology, providing an accurate and reliable basis for identifying and dealing with weak interlayers within rock masses during actual engineering.
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