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Fan cuts are a drilling and blasting pattern used in mining to reach the next free face for drilling. The V-shaped cuts widen the rock face, allowing deeper access. The angle of the fan cut should be above 60 degrees, and blasts should be spaced at least 50 milliseconds apart.
When mining, there are a number of procedures that can be used to create the necessary access through the rock or other substance. Holes are drilled into the surface in a strategic pattern and explosives are inserted to achieve the desired explosion pattern. A fan cut is a type of drilling and blasting pattern used in tunneling that allows mining efforts to reach the next free face, or clear area, for drilling. As drilling continues deeper into the tunnel, the fan cut can again be used to reach the next free wall. The fan cut gets its name from the shape of the holes used, which form an arc or fan pattern across the surface from a series of V-shaped cuts.
Fan cuts are used in situations where the opening at the base of the tunnel for the subsequent drilling action is larger than the tunnel entrance or advance. There must be sufficient width for the drilling equipment to reach into the rock face and be positioned to create angled cuts. In this situation, a series of slanted holes can be drilled in the open face. The holes are placed at angles that will cause the most breaks in the rock face so that the next layer of free wall can be reached.
The V-cuts can be made on top of each other or next to each other, depending on the size of the tunnel and the type of equipment available. The fan cut helps to widen the available rock face by creating a trench that allows deeper and deeper access to the rock face. Fan cutting can be used in conjunction with several other cuts or techniques depending on the structure of the tunnel, the material being drilled and the explosives used.
The angle of the fan cut shouldn’t be very sharp. If sharp angles are required, however, a higher concentration of explosives used in the holes will be required to achieve the desired effect. Ideally, the fan cuts should be above 60 degrees. Cuts can be done in double V or up to quadruple if space is available. The blasts will also need to be spaced at least 50 milliseconds apart to allow enough time for them to bulge and move. This will give the explosion enough impact to move most of the rock.
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