Anirban Sen, Business Line Manager – Underground Division, Epiroc Mining (India), explores the technologies, methods and benefits of modern intelligent face drilling equipment, the reasoning behind selection of ‘smarter’ face drills for Civil Tunnelling and Mining Houses, and why use of intelligent systems to control face drills is finding increasing interest.
Drill & Blast Method: Civil Tunnelling vs Mine Development
Drill & blast remains a very common method of tunnel excavation in medium to hard rock situations for both civil and underground mining applications. From its early roots in the early 1900’s the method has evolved in both the drilling equipment technology and in the blasting agents used.
What has changed significantly over the years is the advance rates possible with new and more efficient technologies and methods. Figure 2 shows how the introduction of new drilling technology has allowed greater productivity during the last century.
When we look deeper into how civil tunnelling and underground mine development has followed the technology development of face drills, there is a significant divergence in the early 1990’s. Whilst civil tunnelling has embraced the world of computerised control systems, the mining industry seems to have stalled (with a few exceptions on both sides) and remained with the second generation of face drilling equipment. There are no real fixed answers as to why. Certainly, in some countries there are underground mines that are using similar technologies as their civil tunnelling brothers, but for the most part this is not the case.
Civil tunnel projects are typically short in length, with most being no longer than 2 to 3 years in duration (variable due to length of tunnel etc).
Because of the short time for a tunnel project, it is very rare for project owners to construct the tunnel themselves. Rather, they will employ the services of a civil contractor, with a detailed tender for bidding being issued. Typically these tender contracts carry strict guidelines when it comes to overbreak and underbreak, as well as time to complete the project. Often failure to fulfil these guidelines will result in severe penalties, and could mean the difference between a profitable project for the contractor or a terrible loss.
In all major civil tunnelling markets, there are many contractors and the competition between them is fierce. Any edge that a contractor has over another can mean winning or losing the tender. Perhaps that is why the civil tunnelling industry has been actively driving face drilling equipment suppliers for more advanced equipment. The ability to squeeze out additional advance rates or ways of guaranteeing control on the final tunnel profile can only enhance the chances of securing a contract. Hence, speed, quality and safety are highly sought after qualities for a face drilling machine.
Underground mining also has its fair share of contractors, with development contracts being awarded for such tasks as decline and ore drive accesses. The period of these contracts is also relatively short, with typical time periods of 1 to 3 years. However, the terms of contracts rarely have tight constraints on overbreak. Also, development contracts are typically on a price per metre advanced – as opposed to a total price for a fixed tunnel length. Perhaps, these subtle differences are such that they prevent the drive to implement new technologies.
Another possible reason for the differences in technology levels is due to the level of focus that is brought to bear. For a civil tunnel, full attention is given to the working face, and face utilisation is given top priority. To that end, monitoring and subsequent fine tuning of each segment of the drill & blast cycle is possible to achieve good management. Through this focus, it is possible to introduce new technologies successfully.
For an underground mine, however, there are many activities underway simultaneously in different locations. Development drilling, cable bolting, scaling, development mucking, hauling, development charging, production drilling, production charging, raise drilling, services, exploration drilling are some examples. To measure and rationalise each process is perhaps beyond the capability of most mines. The result is that mines will tend to stick with known technologies, methods and equipment. Advancements in mining industry equipment, as a result, tend to be gradual and within existing control technologies.
- Both civil tunnelling and mine development are performing the same task – creating a tunnel to get from point A to point B.
- The basic drill & blast cycle is very similar with differences based on size and technologies of the equipment used.
- Typically, civil tunnels are larger in dimension though this is not always the case as hydroelectric race tunnels can be relatively similar in dimension.
- Mine development tunnels tend to have sharper turning radii and steeper depth changes than their civil counterparts.
- Civil tunnels are often required to have a design life of many years, whereas mine development tunnels are usually required to last the life of the mine.
- Mining operations typically have multiple headings on many levels, whereas civil tunnels have 1-2 headings per face drill. For civil applications, this means that the face drill has lower utilisation due to lack of available face.
Intelligent drilling & drilling accuracy
Intelligent drilling refers to face drilling equipment that has a computerised control system. What is important to define is that there is a big difference between the previous generation of “computerised” equipment using Programmable Logic Control (PLC) and the modern computer software driven systems.
It is a common misconception that the PLC systems of the 80’s and 90’s are even closely related to the true computer control systems of today. PLC systems were unreliable and difficult to troubleshoot, and as a result may be part of the reason why modern computer control systems have had difficulty finding acceptance.
The reality is that the computers used on underground drilling equipment today are built into heavy-duty industrial casings, providing a sturdy and reliable means of controlling a hydraulic system. The in-built features that simplify fault finding and operator functions mean lower downtime and ease of maintenance. Being a software driven system, it is also very flexible with the ability to add new functions and capabilities.
To make a face drill accurate, it is necessary to add sensors on the boom and carrier. Figure 7 shows the sensors that are needed on a typical drilling boom. These sensors monitor angles and lengths, with the information being processed by the control system. Once this is done, the position of the feeds is calculated and displayed for the operator. With a drill plan, the operator can then position the drill holes with greater accuracy and consistency. This accuracy can be made better by the integration of navigation systems with the drill rig control systems that allow the machine to know where it is in 3 dimensions. The best means of providing this navigational accuracy is by utilising a total station that can be controlled from the drill rig itself. Taking the system a step further is to move into full automation of the booms. This gives even faster positioning and accuracy by minimising the human factor.
With today’s equipment and technology, full face drilling automation is still not 100% possible. Typically, the bottom holes (lifters) and some perimeter holes are positioned and drilled manually. The reason for this is due to the possibility of the hydraulic hoses of the feed/rock drill being caught on the ground and damaged. Figure 8 shows an example of a drill plan that could be utilised on a computerised drill rig.
With built-in intelligence consequential drilling accuracy, the modern face drill can achieve impressive advances in efficiency and productivity. By drilling accurately an operation can expect the following benefits:
- Possibility to take longer rounds (ground and tunnel size dependant) due to tighter control on look out angles and burden spacing.
- Leads to faster advance rates because more time is spent drilling than tramming.
- Reduction of explosives used as the number of detonators needed is divided over longer distances per cut.
- Reduced number of holes reduces drilling time due to less drill meters in the face.
- Reduces the amount of explosives due to less charged holes.
- Smoother rock surface after blasting means reduced scaling time.
- Ground support regimes can be optimized.
- Reduced shot/fibre crete used due to reduced surface areas from overbreak and fractured rock surfaces needed to be filled in.
- Reduced vibration damage, especially in bad ground.
- Easier to muck out due to consistent broken rock size.
- Faster advance rates due to more advance per blast.
- Decreased mucking time due to even surface to get full bucket loads.
- Boom stiffness
- Feed bracing force (the force holding the front of the feed against the rock when collaring)
- The drill string plays an important role in achieving hole straightness
Drilling accuracy is finding the most efficient way of excavating a tunnel, with time being the major factor. Time is the main calculation denominator for Net Present Value of a project; this is why intelligent face drilling has become the cornerstone of Rapid Mine Development techniques. Of course, in rapid mine development, an operation must look at all segments of the development cycle and find equipment, technologies, methods, and systems that allow streamlining of the processes. The goal is to reduce development cycle time whilst retaining high safety standards.
Key factors for success
A move towards advanced civil tunnelling face drilling equipment, technologies and methods is not easy. For a mining operation to be successful, the key areas that must be considered are as follows:
- Workforce selection
- Equipment selection
- Underground communication & infrastructure
- Have an open mind
Future of control systems for face drilling equipment
Figure 9 shows some of the machine model series that are currently available from EPIROC Copco (one of the worlds leading mining and civil construction equipment suppliers). What is significant is that EPIROC Copco has chosen to standardise on a base computerised control system across many machine models. This brings efficiency in operator performance, maintenance training, as well as the many benefits mentioned above, which have been attributed to advanced control systems.
The old ways of thinking will change as younger, educated and technologically proficient people join the mining industry. Companies that embrace the new technologies, will have the potential to enjoy better efficiencies that translate into savings. So, mining companies need to evolve or face a slow but certain extinction. Labour costs around the world are rising, and the demand for minerals is following close behind. Industry stakeholders must take the opportunities and lessons learned by the civil tunnelling fraternity so that we too can reap the benefits of increased productivity and efficiency.
The author thanks his employer for permission to publish this work and also acknowledges the various clients, contractors and other providers involved in various projects that have helped deliver high precision drilling. A very special thanks to Epiroc’s technical team in Sweden for supporting me in preparing this paper.