Drill and blast mining is the most commonly used mining excavation method in the world. Drill and Blast mining is extremely popular for numerous reasons, such as its cost, simplicity, and effectiveness. In this article, we’d like to take you through what drill and blast mining is, what are some advantages and disadvantages of utilizing this method, and finally walking you through a typical excavation cycle.
What is Drill and Blast Mining?
The drill and blast mining, as its name would suggest, is a method of mining that begins with drilling holes into rock after careful surveying and developing a plan.
Next, these holes are carefully loaded with explosives. The explosives are then detonated, causing the rock to fracture and crumble.
From there, it is simply a matter of removing the blasted rock, called mucking. When all the blasted rock is removed, you can restart the surveying process all over again.
Advantages and Disadvantages of Drill and Blast Mining Method
Since the drill and blast method is the most widely used method of rock extraction today, it obviously has many different advantages compared to two other common mining methods: cut-and-cover and tunnel boring.
Cut-and-cover mining is a process that begins with digging a trench and a subsequent tunnel (“cutting”), extracting the rock, before then returning the surface to its original state (“covering”). Tunnel boring refers to excavation done with a tunnel boring machine (TBM), which is basically a gigantic circular drill that cuts a tunnel through the rock.
Advantages
- Drilling and blasting is a very versatile method that can be utilized in all different types of rocks.
- Drill and blast requires a lower up-front investment than acquiring a TBM, making it a more economically friendly option.
- Drilling and blasting is an environmentally friendly option that can significantly reduce noise, dust, and visual pollution, and instead isolates any pollution near the tunnel portal.
- Compared to cut-and-cover, the quantity of construction & demolition materials (C&D) is greatly reduced.
- Compared to cut-and-cover, disturbances to local traffic are greatly reduced.
Disadvantages
- Since drill and blast involves the usage of explosives, there is the potential hazard associated with establishing a temporary storage site for said explosives, often called a magazine site. This potential hazard can be mitigated through the planning and site selection process.
- Compared to TBM, drill and blast mining results in higher vibration levels.
Excavation Cycle
Planning
The first step in any mining excavation operation is to plan and survey the land. This allows for the development of a plan that can minimize environmental hazards. This step is of crucial importance for drill and blast mining, since here is where all the calculations around the explosions will be done.
Drilling
Next, blast holes will be drilled into the rock by a drilling rig into the foremost front wall of the tunnel, often called the working face. These holes will be drilled according to the blasting plan developed in step 1.
Loading
Now that holes have been drilled, the next step is to carefully load them with explosives. Detonators are attached to each explosive, and the explosive devices are also attached to each other. The quantity of explosives needed varies, but harder rocks require more explosives.
Blasting
The holes are blasted sequentially, beginning in the center and then cascading outward. Although there can be hundreds of individual explosions, the entire blast sequence should take no more than a few seconds. It’s important to ensure that the explosives don’t detonate at the same time, but go one after another in specified intervals.
Ventilating
Before any rock excavation can take place, the blast tunnel must be properly ventilated. This is because the explosion dispersed large clouds of dust that then mixed with the gases created in the explosion. For obvious health and safety reasons, this air must be ventilated through pipes before anybody can enter the tunnel.
Mucking
Now, it’s time to remove the rock through a process called mucking. Excavators will dislodge any splintered rock that wasn’t completely released by the explosion. Additionally, all the loose rock and rubble will be loaded into dump trucks, either with wheel loaders or conveyor belts.
Securing
Before the process can start all over again, the tunnel must be secured. Depending on the type of rock, there are a bunch of different methods that can be used to secure and stabilize the tunnel and its roof. 3 common methods are wire mesh, arches, and bolts. Wire mesh is great for preventing loose rock from the ceiling from falling on workers below. Bolting is the most common method, where large steel rods are drilled into the tunnel ceiling, which is then secured with a steel plate and a large nut to add stability. In poor conditions, steel arches may be necessary to hold up the walls and roof.
Planning
Now that the tunnel has been secured and is stable, you can then begin the next explosion of the process. Additional calculations and measurements must be made in order to ensure a safe and effective blast. The cycle from planning to securing in drill and blast mining can be repeated multiple times, depending on how big of an extraction operation is needed.
If you and your company are looking for any mining services company, you should look no further than American Mine Services in Boulder, Colorado. AMS has over 50 years of experience in evaluating, designing, and constructing mines and tunnels for a variety of construction needs nationwide. Some projects that we’ve recently been awarded are the Crystal Creek dam improvement project and the Fort Dodge Wall structure solicitation. Please contact us with any inquiries.
