Ground characterization from digital drilling data with time-series algorithm

Abstract

Drilling a hole uses drill bit to damage and break the geomaterial. The net drilling process essentially can be considered as an in-situ test for understanding the mechanical strength of geomaterials being drilled. Many researchers have attempted to use digital methods to record drilling data to characterize the ground strength conditions. Measurement While Drilling (MWD) and Drilling Process Monitoring (DPM) are two typically digital methods for ground characterization by recording depth-series and time-series drilling data during the penetration of a drill bit into new geomaterials. These two digital methods have emerged as a promising advancement in comparison to conventional geological, physical, and mechanical testing methods while their primary superiorities are attributed to digital data acquisition capabilities and cost-effectiveness. Chapter 1 provides an overview of drilling mechanisms and in-situ testing of geomaterial strength. The MWD system and DPM system are reviewed as methods for correlating drilling parameters with geomaterial properties. However, issues with filtering noise in MWD data and establishing correlations are highlighted, indicating a research gap that this thesis aims to address. Chapter 2 introduces the first use of the time-series algorithm to transfer MWD depth-series data into time-series. The differences between MWD penetration and constant penetration rate are illustrated and examined. Chapter 3 further addresses the interpretation challenges associated with MWD data from hydraulic rotary drilling of three advanced drillholes during tunnel excavation in Chongqing. By employing the time-series algorithm, the quality of MWD data is assessed and improved from 33.9%, 39.6%, and 73.5% to 100% for three drillholes. Chapter 4 presents an approach for rapidly profiling rock mass quality underneath tunnel faces during the construction of the Sichuan-Tibet Railway. The time-series method is used to analyse MWD depth-series data from rotary-percussive drilling of fifteen blastholes, enabling the identification of homogeneous geomaterial boundaries and the quantification of rock mass quality through the recalculation of new constant Specific Energy (SE). Chapter 5 resolves the noise issue embedded in the penetration rate of MWD depth-series data from rotary-cored drilling for site investigation around an old cast iron tunnel in London. The constant penetration rates in the typical layers of London clay are from 0.193 to 0.299 m/min, which is similar to rock materials from other sites with high strength. Chapter 6 examines the DPM time-series data for the characterization of oil shale reservoirs. The elevations of oil shale reservoir characterized by DPM main zoning results are between 1248−1247 m and 1199−1178 m for JK03 drillhole while between 1245−1244 m, 1196−1180 m for JK04 drillhole, respectively. A negative correlation exists between the constant penetration rate and the traditional RQD value. Higher heterogeneity in oil shale results in lower strength (higher constant penetration rate). Chapter 7 develops a portable time-series monitoring system, aiming to determine the anchorage length of anchor cables in slope protection. Chapter 8 concludes the main findings of the thesis and recommendations for future works.