From academic studies to practical field experiences, from laboratory testing to using a variety of digital tools, the Eurock conference annually explores a varied host of themes important to rock engineering and tunnelling, relevant to underground and surface works, and civil engineering tunnels as well as mines.
Below, we look at one paper of Drill & Blast that discusses research that takes further forward the comparison of most recent rock tunnelling project data against the Norwegian University of Science and Technology’s (NTNU) models for such projects. NTNU is located in Trondheim.
Eurock 2025 was also hosted in Trondheim, Norway, and had 13 themes in a Technical Programme over three days (17-19 June).
The full Eurock event that was open to delegates lasted all week (16-20 June), being topped and tailed by a suite of workshops and technical tours, respectively.
The entire event was organised by the Norwegian national group within the International Society for Rock mechanics and Rock Engineering (ISRM). Also preceding the delegate activities were ISRM administrative meetings.
PRACTICE AND MODELS
Models are gradually updated, such that of the NTNU on predictions of Drill & Blast performance. A paper to Eurock 2025 discussed recent developments of the NTNU Drill & Blast model, based on enhancements to the 2007 basis model, plus drawing in data from recent project practice.
T&TI previously carried a short version of a paper looking at the validity of the NTNU Prediction Model for Drill & Blast tunnelling (T&TI Feb 2024). The paper noted that a number of predictive models for tunnelling were established decades ago by Norwegian researchers and continuously improved, also drawing upon project data for that purpose. The findings suggested the most recent baseline model (2007) was still valid, although suggestions were made for specific areas of trends and developments for further study.
The Eurock paper adds to this work, primarily by drawing upon more tunnelling project data. Two new projects were added to the database, with their specific charging (kg/m3) and drilling data (No of charged holes per blast and cut design). The key difference with these projects, though, was to widen the D&B conditions in the database by adding different geology, equipment, operational crew, tunnel cross-sections, and face lengths. The data came from tunnelling contractors via their reporting systems to authorities.
The paper also notes that project data, which considered a total of 353 individual and new blast rounds, show the same trends as found in the previous research: current blast design differs from the principles in the NTNU model by using more charged drill holes per round; plus, higher specific charging.
It notes that for road tunnel the increase in specific change as doubled in some projects, irrespective of contractor, drillhole diameter, drill length or the rock Blastability Index (SPR). A main hypothesis is, as in the prior research, the view that use of bulk slurry emulsion as a type of explosive in Norwegian tunnelling these days is susceptible to “unintentional over-consumption” or waste, compared to cartridge explosives which were previously dominant, around 20 years ago.
More project-based research is needed though.
But, even before then, it notes that with the current practice in blast design “seemingly” not regarding the SPV is a “matter of big concern”, and that contractors “elect to use more explosives regardless of rock blastability or rock type.” It queries the possibility that a contribution to this apparent approach is how tunnelling contracts are organised, “favouring high production rates and low cost”.
The paper says that higher specific charge should lead to more rock fragmentation, which may help mucking out but rock quality and usefulness for re0use might be affected. It adds that, if this is so, the NTNU model could be adjusted to be more in line with current practice by adjusting the SPR, appropriately with size distribution compared to the original in the model (half to be less than 250mm sieving size).
More broadly, the paper says that the project data studied gives a “rather large variation envelope” and is bigger that the possible output envelope offered by the current NTNU models. However, the paper notes that the NTNU model deals with averages, not projects and their variations – which is a caution urged upon those who might use the model “for risk analysis or a as a guideline in legal disputes in specific projects in the future.”
REFERENCES
- Gjengedal, S., Jakobsen, P.D. & Nilsen, H. R. F. (2025) ‘Current practice D&B tunnelling versus the NTNU prognosis model for D&B blast design – a case study’. Eurock 2025, Trondheim, June 2025
- Jakobsen, P.D., Grøv, E., Bruland, A.; Gjengedal, S. (2024) ‘Validity of the NTNU Prediction Model for D&B Tunnelling’. Rock Mech Rock Eng 57, 781–791. https://doi.org/10.1007/s00603-023- 03585-9
- Jakobsen, P.D., Grøv, E., Bruland, A.; Gjengedal, S. (2024) Validity of the NTNU Prediction Model for D&B Tunnelling. T&TI, Feb 2024
