The projects that are summarized below are ready to be initiated by RTC, and we are working on securing partners to the projects. For the majority of the projects, we have prepared a draft project plan and budget in cooperation with a technical project leader. If you are interested in any of these projects, please contact us. All projects have been approved by the RTC Board of Directors.
These projects have been identified out of the needs of the mining industry, through interviews with e.g. in-mine and R&D personell. In addition, some project suggestions come from cutting edge development at suppliers, universities or other research organisations, suggesting to test or implement a new tool and/or method that could solve a critical challenge in the business.
The development in mines (drifting) is traditionally not conducted with the aim to optimize the profile of the excavation. Therefore poorly designed blasting may cause a number of problems which will slow down the drifting process and increase the costs. The factors affecting the result of the blasting are listed below while the result of different blast damages is shown in Fig. 1.
In short, the most important factors (for a given rock mass) causing the problems are misplaced holes, hole deviation, too many holes and too much explosives detonated in the round/time interval. Another way of describing the chain of events is:
• More rock to haul
• Increased excavation boundary to support
• Rougher rock surface (face, walls and roof – profile)
• Impairs the possibility to position the drill and to collar, due to a rougher rock surface, rougher face, walls and roof.
• Reduced control of bolt installation leading to an increase in number of installed bolts
- Increased ventilation cost
• Increase of blast fumes which subsequently will increase re-entry time
• If the auxiliary fan is fitted with Variable Speed Drive (VSD), then the fan has to be set at its maximum speed to blow more air to reduce re-entry time. The consequence of this is that the fan will consume more electrical power than the normal setting.
• Blast-damage to ventilation ducting
• Under-break will increase airway resistance and thus will reduce primary fan performance. The fan setting will have to be increased in order to maintain required airflow quantity, which subsequently will increase its power consumption.
- Increased damage to the remaining rock mass due to over-charged contour holes leading to increased need for
• Scaling of blast-damaged rock
• Bolting and surface support
♦ Deviation in the blast hole leads to
- Ore dilution in the case of mining
- Over-break and increased support requirements
Over-blasted excavations are cost-driving with respect to reduced production, due to:
♦ Slower positioning of drills and collaring because of a rougher rock surface (face, walls, roof – profile)
♦ Increased time needed for
- Charging as a larger volume of explosives (more than necessary) has to be pumped into the holes
- Repairing the blast-damaged ventilation ducting
- Mucking and hauling of rock due to over-break
- Scaling due to a larger volume of blast-damaged rock
- Bolting due to an increased number of bolts and the increased complexity during meshing due to the rough rock surface
- Shotcreting and increased amount of shotcrete volume
- Meshing due to
• a more fractured/damaged rock
• larger excavation boundary area due to over-break (blast-induced as well as scaled)
• Slower media handling (pipes, cables and ventilation) due to a rougher rock surface
• Increased rock mass volumes to transport to surface due to the overbreak
However, there can also be some advantages with more blast damage. One of them is reduction of stresses close to the boundary of the excavation making the excavation less prone to strain bursting. The disadvantage with improved control of the contour is that the distance between the contour holes has to be decreased and different charging has to be used for the contour holes and the rest of the holes in the round. There have been a number of studies addressing the listed problems, aiming e.g. to defining the effect of blasting on the remaining rock mass and quantifying the amount of fracturing caused by the blast (e.g. Oriad, 1982; Forsyth & Moss, 1991; Raina et al., 2000 Warneke et al., 2007, Saiang 2008 and a series of studies by SveBefo in the 1990s). In an ongoing project supported by BeFo (Johansson, 2014) the activities are to (i) Forecast the extent of the damaged zone using rock mechanics data and for different geological conditions, (ii) with the aid of MWD-data judge the extent of the damage zone and (iii) Develop a more complete damage zone table including rock type and discontinuities. Furthermore, the objective of another BeFo project (Andersson, 2014) is to investigate the possibility of defining a type section which should be the same along the whole tunnel. The section should therefore accommodate all installations needed for the operation time of the tunnel (electricity, ventilation etc.). Other examples of studies carried out are Jonsson (2014) and SBUF (2014), addressing, e.g. the contour control and the possibility to use the performance requirements and quality in the formulation of contracts for rock excavations. One of the conclusions from these projects was that there is a need for training of the staff working with drilling and it is important to involve the contractors as they have a more comprehensive understanding and experience of the tunneling process than many of the consultants acting as project leaders.
We propose an approach comprising Project A: an inventory project, and Project B: a detailed analysis project which addresses the issue of better contour control during development.
PROJECT A will comprise an inventory of existing knowledge/practice and collection of input data for a detailed analysis of the whole chain of events. This project will also identify the lack of information and input data and propose how to obtain this data. The inventory will consist of a literature survey, an inventory of experience from mines and interviews of key persons in, e.g., the mining companies, contractor companies and the equipment manufacturers, along with a mapping of available data from the mining operations.
Duration: approx. 12 months.
Estimated budget: 50 000 €.
PROJECT B will comprise (i) additional inventory and data collection, (ii) complementary analyses to provide data for the later stages of the analysis of the chain of events caused by different blast designs and (iii) detailed analysis of the whole chain from blast design to the consequences for the working environment, production disturbances etc.
Duration: approx. 30 months.
Estimated budget (with three mines): 325 000 €.
For further information regarding these projects, please contact Johan Hedlin, CEO >>