Ground Control in Mining: Challenges with Slope Stability and Blasting Operations
Contributor:
Mining IQ Editorial
Posted: 10/08/2012 12:00:00 AM EDT | 0
While new technologies continue to develop , geotechnical engineers are constantly faced with managing high risk environments and overcoming challenges associated with poor slope stability and ground control regulations.
Mining IQ recently spoke with Tim Rees, Lead Geotechnical Engineer for Open Cut operations at Newmont Boddington Gold Mine which is roughly a 750 000 ounce a year gold mine in Western Australia, to discover the specific challenges his geotechnical team have overcome in order to maintain overall slope integrity and the tools that are needed to ensure mining operations are able to operate within an acceptable level of risk.
Challenges facing the Newmont Boddington Gold Mine geotechnical team in order to maintain safe working slopes in a dynamic mining environment
One of the biggest challenges at Newmont Boddington Gold Mine is that it is a very hard rock and in most cases is 200 MPa. As a result a large amount of energy and explosives are needed to break the rock in order for it to be fragmented enough to be diggable to keep dig rates high.
According to Tim Rees, the pressure to keep dig rates high and maintain a fast rate of drilling and blasting in this type of environment, is the number one challenge the geotechnical team has to maintain safe working slopes
“The biggest issue is always going to be production pressure to get the shots drilled, loaded and fired as quickly as possible, but still being able to maintain a good wall in the process. Unfortunately because we are trying to fracture the rock enough to be diggable we put a lot of explosive energy into the wall which generates blast induced damage,” he said.
For Mr Rees, it’s a balancing act between making the dirt diggable but also maintaining a safe and stable slope.
“We have to use small diameter holes close to the wall and it takes a lot longer to drill and blast which again feeds back into my first point about the production pressure. We prefer to drill large diameter holes to complete benches quite quickly in order to keep up with the shovels, but unfortunately the nature of the small diameter holes means a lot more drilling and therefore a lot more pressure from production to get shots fired and turned around quickly,” he said.
Ground Control Management strategies: how to manage conflicts and overcome productivity pressures
Mr Rees believes communication and regular meetings with all teams involved in the process is something that all mine sites need to implement in order to ensure mitigation of the risks associated with maintaining high slope angles.
Mr Rees also believes training also plays a major part, as it creates awareness about the specific hazards facing teams during the process.
“Within the geotechnical group we also try to get our staff to do a rotation to the drill and blast engineering group and so we can understand each other’s jobs to improve our coordination and planning,” Mr Rees said.
High definition or high speed cameras
These cameras can be used to film the blast to get a much better sense of what’s going on. There used to be this idea that detcord was an instantaneous explosive but in reality it does actually travel at a certain speed while it looks instantaneous when it’s fired to the naked eye. But when you look at it with a high speed camera you can actually see it burning at 7000 meters per second. So being able to slow things down and watch how these explosives go off is useful to see how the rock mass is behaving and assists in being able to see structures open up and explosive gasses escape.
Vibration monitoring
Basic vibration monitors can be used to see when you fire a shot, how much vibration is going into the wall and how much damage we are doing via vibration as opposed to the explosive gasses.
Electronic denotation systems
This has really assisted us in being able to get very accurate timing of when the blasts are fired and slowing down the blasting as it gets closer to the wall, allowing the rock time to move away from the wall and reducing that amount of energy likely to cause damage.
Monitoring systems
We’ve got quite an extensive monitoring network but also the radar really assists us to be able to monitor walls after a blast to see if there is any relaxation. As we trial different slope designs we can test to see quite accurately how are those walls standing up over a long period of time. If they are, perhaps we can afford to go steeper.
Working with Drill and Blast teams to achieve optimal fragmentation
As previously highlighted, communication between all teams is critical in order to maximise optimal fragmentation and stable slopes.
Posted: 10/08/2012 12:00:00 AM EDT | 0
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In the current industry climate, ensuring the efficiency and effectiveness of mining strategies is critical in making the most out of the mining boom while it lasts. An important part of this process is the development and implementation of sustainable strong ground control management plans, to ensure an optimum slope angle is achieved in order to extract ore more effectively.
While new technologies continue to develop , geotechnical engineers are constantly faced with managing high risk environments and overcoming challenges associated with poor slope stability and ground control regulations.
Mining IQ recently spoke with Tim Rees, Lead Geotechnical Engineer for Open Cut operations at Newmont Boddington Gold Mine which is roughly a 750 000 ounce a year gold mine in Western Australia, to discover the specific challenges his geotechnical team have overcome in order to maintain overall slope integrity and the tools that are needed to ensure mining operations are able to operate within an acceptable level of risk.
Challenges facing the Newmont Boddington Gold Mine geotechnical team in order to maintain safe working slopes in a dynamic mining environment
One of the biggest challenges at Newmont Boddington Gold Mine is that it is a very hard rock and in most cases is 200 MPa. As a result a large amount of energy and explosives are needed to break the rock in order for it to be fragmented enough to be diggable to keep dig rates high.
According to Tim Rees, the pressure to keep dig rates high and maintain a fast rate of drilling and blasting in this type of environment, is the number one challenge the geotechnical team has to maintain safe working slopes
“The biggest issue is always going to be production pressure to get the shots drilled, loaded and fired as quickly as possible, but still being able to maintain a good wall in the process. Unfortunately because we are trying to fracture the rock enough to be diggable we put a lot of explosive energy into the wall which generates blast induced damage,” he said.
Furthermore, while most mines have angled batter walls, the walls at Newmont Boddington Gold Mine incorporate vertical batters which means that the first row of holes are close to the crest of each catchment. As a result there is a much higher likelihood of damaging the crest of the catch-berm, therefore increasing the likelihood of slope failures along on structures and the number of rock falls sourced from crests.
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For Mr Rees, it’s a balancing act between making the dirt diggable but also maintaining a safe and stable slope.“We have to use small diameter holes close to the wall and it takes a lot longer to drill and blast which again feeds back into my first point about the production pressure. We prefer to drill large diameter holes to complete benches quite quickly in order to keep up with the shovels, but unfortunately the nature of the small diameter holes means a lot more drilling and therefore a lot more pressure from production to get shots fired and turned around quickly,” he said.
Ground Control Management strategies: how to manage conflicts and overcome productivity pressures
As there are a number of risks and safety issues associated with maintaining a high angle slope, ensuring that all teams are on the same page and have a concrete understanding of the importance of adhering to ground control management strategies is critical.
At Newmont Boddington Gold Mine, this was achieved by getting all teams together on a weekly basis to discuss strategies to get the rock fragmented enough while the wall stability was maintained during basting. These ‘blast master’ meetings involved drill and blast teams, geotechnical engineers and production engineering and mine operations all communicating and keeping up to date on issues associated with blasting and slope stability.
Mr Rees believes communication and regular meetings with all teams involved in the process is something that all mine sites need to implement in order to ensure mitigation of the risks associated with maintaining high slope angles.
“It’s a great forum for everyone to get a chance to talk about the production priorities and to make sure that we got shots fired in time. We also addressed the factors associated with slope stability. It’s not something that is done at every mine but it’s definitely something I would highly recommend to any mine. It’s in everyone’s interest to be at these meetings,” he said.
Mr Rees also believes training also plays a major part, as it creates awareness about the specific hazards facing teams during the process.
“Our geotechnical group also undertake geotechnical hazard awareness training every year. This goes out to all the staff and crews to ensure they know what the hazards are in the pit but also why we are blasting in certain way to try and maintain a stable slope,” he said.
However despite this, the success of overcoming challenges relating to slope stability ultimately comes down to communication.
“Within the geotechnical group we also try to get our staff to do a rotation to the drill and blast engineering group and so we can understand each other’s jobs to improve our coordination and planning,” Mr Rees said.
New technologies used in order to achieve optimum slope angle
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Tim Rees highlights the specific technologies used in Newmont Boddington Gold Mine in order to achieve relatively steep slope angles with large blasts and how these technologies can help to provide a better understanding of operational limits.
High definition or high speed cameras
These cameras can be used to film the blast to get a much better sense of what’s going on. There used to be this idea that detcord was an instantaneous explosive but in reality it does actually travel at a certain speed while it looks instantaneous when it’s fired to the naked eye. But when you look at it with a high speed camera you can actually see it burning at 7000 meters per second. So being able to slow things down and watch how these explosives go off is useful to see how the rock mass is behaving and assists in being able to see structures open up and explosive gasses escape.
Vibration monitoring
Basic vibration monitors can be used to see when you fire a shot, how much vibration is going into the wall and how much damage we are doing via vibration as opposed to the explosive gasses.
Electronic denotation systems
This has really assisted us in being able to get very accurate timing of when the blasts are fired and slowing down the blasting as it gets closer to the wall, allowing the rock time to move away from the wall and reducing that amount of energy likely to cause damage.
Monitoring systems
We’ve got quite an extensive monitoring network but also the radar really assists us to be able to monitor walls after a blast to see if there is any relaxation. As we trial different slope designs we can test to see quite accurately how are those walls standing up over a long period of time. If they are, perhaps we can afford to go steeper.
Working with Drill and Blast teams to achieve optimal fragmentation
As previously highlighted, communication between all teams is critical in order to maximise optimal fragmentation and stable slopes.
At Newmont Boddington Gold Mine, interaction between drill and blast crews and geotechnical engineers are an essential part of the process, giving both teams an understanding of specific challenges each is facing and how to overcome them.
Tim Rees says that communication can be enhanced between the two teams by presentations outlining specific geotechnical hazards and how they can be addressed.
“It’s important to get out there and speak with the crews that are actually drilling holes. We are trying to do geotechnical hazard presentations fairly regularly about different issues such as slope steeping trials. This gives the crews a sense of why we are making changes and why we are trying different blasting strategies. We usually get quite a lot of people coming up and giving us comments and suggesting ideas and they are usually very appreciate of understanding why we are heading in a certain direction and how it affects them in their job,” he said.
If you would like to learn more about the specific technologies and strategies that are available to assist in developing and sustaining strong ground control management plans, join Tim Rees and other mining industry professionals and Ground Control & Hazard Management in Open Cut Mines in Brisbane, December 2012.
CC Images by Mike Cogh and Terinea IT Support Flickr
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