In Situ Digital Testing Method for Rock Quality and Strength Assessment from Drilling Process Monitoring

Rock-mass quality assessment is a fundamental indicator of engineering infrastructure. This paper presents a new index for rock mass quality assessment, which is based on the drilling process monitoring (DPM) technique. Additionally, an empirical equation for estimating the P-wave velocity in rock masses based on the DPM technique is proposed. The reliability of the new index and the empirical equation is validated through comparison with digital DPM data obtained from a 102.27 m deep drillhole. The new methods were further compared with laboratory test results of uniaxial compressive strength, P-wave velocity, and mineral contents of the rock core samples. The results indicate that: (1) the in situ strength profile, based on the new index, consists of three distinct zones, each exhibiting significantly different failure patterns. The penetration rate strongly correlated with the new index and uniaxial compressive strength. The new index is not only a thickness geometry parameter but also a mechanical strength parameter of rock masses; (2) the P-wave velocity of different stratigraphic rock masses can be estimated based on the DPM data; (3) the correlation between rock strength and mineral content is weak. The proposed new index and empirical equation represent significant advancements in drilling practice to become an in situ testing tool for assessing the rock strength profile on-site.