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The History and Future of Rock Mass Characterisation by Drilling in Drifting: From sledgehammer to PC-tablet
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.ORCID iD: 0000-0003-1923-044X
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.ORCID iD: 0000-0002-5165-4229
2017 (English)In: Mine Planning and Equipment Selection (MPES 2017): Proceeding of the 26th International Symposium on Mine Planning and Equipment Selection Luleå, Sweden, August 29-31, 2017 / [ed] Behzad Ghodrati, Uday Kumar, Håkan Schunnesson, Luleå: Luleå tekniska universitet, 2017, p. 99-106Conference paper, Published paper (Refereed)
Abstract [en]

In underground construction projects problematic rock mass conditions are one of the major issues causing cost overruns during the excavation phase. Before a tunneling project starts the rock mass is roughly characterized by a pre-investigation. However, in many cases, these pre-investigation does not portray the rock mass characteristics accurately and do not predict local anomalies in the subsurface. Therefore there is a need for new rock mass characterization methods that can reduce uncertainties and improve the overall tunneling process.

In the end of the 1880s, rock mass characterization based on manual drill data was investigated and rock masses were quantified using drillability. Since then, the technology has significantly changed with the introduction of hydraulic rock drills, computerized drill rigs, and advanced rock mass classification systems based on drill parameters. Nowadays, automatic drill logging systems and drilling data processing software packages are widely available and commonly used in Scandinavian tunneling projects.

This technology uses drilling parameters to characterize the rock mass. However, monitored drill parameters are influenced not only by the variations in the properties of the penetrated rock mass but also by the operator and the rig control system that continuously control the applied forces to optimize drilling and prevent jamming. In order to be useful for geomechanical purposes, the drilling data needs to be filtered, normalized and analyzed to refine the rock related response from responses caused by other influencing factors. If successful the data might be used to determine hardness, fracturing and water indicators.

Even though the technology has shown high potential in laboratory tests and field trials, it is not an obvious choice for all tunneling projects. In this paper, the background of the technology are described and the potential for the future outlined, concluding that the technique probably will be used more extensively in the future. 

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2017. p. 99-106
Keywords [en]
Measurement While Drilling, MWD, drilling, rock mass characterization
National Category
Other Mechanical Engineering Mineral and Mine Engineering Other Civil Engineering
Research subject
Mining and Rock Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-68734ISBN: 978-91-7583-935-6 (print)ISBN: 978-91-7583-936-3 (electronic)OAI: oai:DiVA.org:ltu-68734DiVA, id: diva2:1206060
Conference
26th International Symposium on Mine Planning and Equipment Selection, Luleå, Sweden, August 29-31, 2017
Available from: 2018-05-15 Created: 2018-05-15 Last updated: 2018-10-31Bibliographically approved
In thesis
1. Analysis of Excavation Damage, Rock Mass Characterisation and Rock Support Design using Drilling Monitoring
Open this publication in new window or tab >>Analysis of Excavation Damage, Rock Mass Characterisation and Rock Support Design using Drilling Monitoring
2018 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Prior to an underground excavation a site investigation is carried out. This includes reviewing and analysing existing data, field data collected through outcrop mapping, drill core logging and geophysical investigations. These data sources are combined and used to characterise, quantify and classify the rock mass for the tunnel design process and excavation method selection.

Despite the best approaches used in a site investigation, it cannot reveal the required level of detail. Such gaps in information might become significant during the actual construction stage. This can lead to; for example, over-break due to unfavourable geological conditions. Even more so, an underestimation of the rock mass properties can lead to unplanned stoppages and tunnel rehabilitation. On-the-other-hand, the excavation method itself, in this case, drill and blast, can also cause severe damage to the rock mass. This can result in over-break and reduction of the strength and quality of the remaining rock mass. Both of these attributes pose risks for the tunnel during excavation and after project delivery.

Blast damage encompasses over-break and the Excavation Damage Zone (EDZ). In the latter irreversible changes occur within the remaining rock mass inside this zone, which are physically manifested as blast fractures. In this thesis, a number of methods to determine blast damage have been investigated in two ramp tunnels of the Stockholm bypass. Herein, a comparison between the most common methods for blast damage investigation employed nowadays is performed. This comparison can be used to select the most suitable methods for blast damage investigation in tunnelling, based on the environment and the available resources. In this thesis Ground Penetrating Radar, core logging (for fractures) and P-wave velocity measurements were applied to determine the extent of the blast damage.

Furthermore, the study of the two tunnels in the Stockholm bypass shows a significant overestimation of the actual rock mass quality during the site investigation. In order to gain a more accurate picture of the rock mass quality, Measurement While Drilling (MWD) technology was applied. The technology was investigated for rock mass quality prediction, quantifying the extent of blast damage, as well as to investigate the potential to forecast the required rock support. MWD data was collected from both grout and blast holes. These data sets were used to determine rock quality indices e.g. Fracture Indication and Hardness Indicator calculated by the MWD parameters. The Fracture Index was then compared with the installed rock support at the measurement location.

Lastly, the extent of the damage is investigated by evaluating if the MWD parameters could forecast the extent of the EDZ. The study clearly shows the capability of MWD data to predict the rock mass characteristics, e.g. fractures and other zones of weakness. This study demonstrated that there is a correlation between the Fracture Index (MWD) and the Q-value, a parameter widely used to determine the required rock support. The study also shows a correlation between the extent of the blast damage zone, MWD data, design and excavation parameters (for example tunnel cross section and charge concentration).

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2018
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
Keywords
Blast damage, Excavation Damage Zone, EDZ, Measurement While Drilling, MWD, Rock support, Rock mass characterisation, Tunnelling
National Category
Geotechnical Engineering Other Civil Engineering
Research subject
Mining and Rock Engineering
Identifiers
urn:nbn:se:ltu:diva-71402 (URN)978-91-7790-252-2 (ISBN)978-91-7790-253-9 (ISBN)
Presentation
2019-01-15, F1031, F-huset, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2018-11-01 Created: 2018-10-31 Last updated: 2019-01-07Bibliographically approved

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