Preliminary Experimental Study on the Cross-Specimen Borehole Applicability of Identical Rock-Mass Characteristics Using Built-In Multi-Sensor MWD Monitoring for a Roof Bolter

Built-in multi-sensor measurement-while-drilling (MWD) modules on roof bolters can record torque, thrust, rotational speed, and displacement during drilling. This study examines whether identical rock types produce consistent MWD responses when tested through different boreholes in separate composite specimens. Three laboratory-scale composite specimens containing yellow sandstone (YS), dark-colored red sandstone (DCRS), and light-colored red sandstone (LCRS) were drilled with the same integrated rig, and the sensor responses and specific energy were compared using descriptive distributions, mean values, and relative differences. The results descriptively indicate that torque and thrust respond more clearly to lithological changes than rotational speed, while torque is generally the most stable indicator. Under nominally identical lithological conditions, responses varied across boreholes in separate composite specimens, with reported relative differences reaching approximately 30% in some comparisons. Because one borehole was drilled per specimen, this preliminary study identifies a cross-specimen reproducibility limitation only; it does not estimate within-rock-mass variability or validate a transferable prediction model. The practical implication is limited to showing that single-borehole formulas should not be transferred without calibration, while normalization, hierarchical modeling, and larger multi-borehole validation remain future research directions.