Sensitivity analysis and rock strength prediction study of rotary drilling with drilling parameters

Rock property exploration has been a major focus in geotechnical engineering. Among various methods of engineering geological research, drilling exploration is significant. Extensive studies have been conducted on drilling exploration and the prediction of rock strength to investigate the interaction between machinery and rock during rotary cut borehole operations. Indoor drilling tests were conducted on rock materials and mortar materials using a self-developed rotary cut digital drilling system. The system enables comprehensive measurement of drilling parameters, including torque, rotation speed, displacement, drilling pressure, borehole sound pressure level, and water intake pressure. An orthogonal test design was used to evaluate the sensitivity between the subsequent drilling parameters and rock strength. The sensitivity analysis of variance (ANOVA) results showed that the speed of rig control parameters and initial push speed had different levels of influence on four parameter indicators: torque, rotation speed, drilling pressure, and sound pressure level. Particularly, the uniaxial compressive strength of the rock significantly affected all four parameter indices, with sound pressure level being the most sensitive and drilling pressure being the least sensitive. Particularly, the uniaxial compressive strength of the rock significantly affected all four parameter indices, with sound pressure level being the most sensitive and drilling pressure being the least sensitive. The model's validity and the sensitivity of the validated parameters were evaluated using the F-test and t-test methods. Comparative analysis of the predicted rock strength values and the measured values showed a difference rate of less than 10%, indicating the model's predictions were highly accurate and affirming its validity.