Advanced continuous drilling for depth-dependent mechanical properties mapping in graded rocks

Accurate rock property assessment is crucial for successful engineering projects in sectors such as water management, power generation, transportation, resource extraction, and mining. This study explores the potential of continuous drilling as a semi-destructive technique for evaluating the mechanical properties of functionally graded rocks altered by weathering and acid treatment. Conventional methods often miss subtle property changes caused by environmental factors, but continuous drilling provides real-time data on parameters like torque and thrust force, enabling depth-dependent property mapping. Experiments were conducted on composite and acid-treated Asmari limestone samples using a custom portable drilling machine. The device, equipped with a T-shaped chisel bit, maintained constant penetration and rotation speeds, capturing changes in thrust and torque as the drill progressed. Tests on composite samples demonstrated sensitivity to shifts between different rock types, highlighting the method’s ability to detect interfaces and structural weaknesses. Field tests confirmed its ability to measure gradual changes due to weathering. Acid-treated limestone exposed to hydrochloric acid showed a significant reduction in mechanical properties: UCS decreased by up to 45%, internal friction angle reduced by 8 degrees, and cohesion dropped by 35% from surface to core. Porosity increased with acid exposure, ranging from 24.3% in the outermost layer to 9.3% in deeper layers. These findings align with existing research on acid-induced degradation of carbonate rocks. Continuous drilling offers a valuable, real-time method for assessing depth-dependent rock properties, enhancing understanding of rock stability and weathering for applications in conservation and modeling.