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Drill cuts used in underground mines The principal patterns mainly used in UG mines are: 1. Pyramid cut 2. Wedge cut 3. Drag cut 4. Fan cut 5. Burn cut 6. Coromant cut 7. Ring drilling

Pyramid cut In this type, four or six shot holes are drived at the middle of the face which at the end to form a cone or pyramid shape. The length of the holes are approximately 15cm more than the other type of holes. The charging is done mainly at the apex of these cut holes, so that it creates a face to fire the next with delays. These cuts are generally used for blasting hard rock mass

Pyramid cut

Wedge cut Here, 2 to 4 pairs of holes are drilled to form a wedge , which is starting from two sides of the drift centre and inclines at an angle less than 45 degree towards the centre to meet the back of the hole along a line. This cut is suitable for uniform, thickly bedded hard rocks. They consume least total quantity of explosives but the depth of pull is restricted by width of drift. Recommended for solid blasting.

Wedge cut

Drag cut This type used for laminated rocks and for controlled blasting in a small cross sectional area to break the rock along cleavage plane. More numbers of shot holes are required in this case compared to other pattern in the same cross sectional area. Since it’s depending on the direction of cleavage planes, not favor for large excavations.

Drag cut - cut holes -trimmers FRONT VIEW END VIEW

Fan cut This is used in laminated strata, mostly soft and covers the face with fan like pattern. Charge in each hole is heavy because each shot has to act for itself. This cut is not recommended for hard ground. Recommended for solid blasting.

Burn cut Parallel holes are drilled at right angles to the face in a cluster form. Some of the holes left uncharged to give relief to the heavy explosives in the charged holes. This cut is effective in hard, brittle, homogenous ground and breaks evenly. The spacing is 1.5 times the diameter of the uncharged hole. The blasting is done in a sequence of hole.

Burn cut

Burn cut The main advantage of this cut are Time is considerably reduced. Easy supervision. Depth is dependent of the size of drift. The blasted material is not projected far.

Coromant cut To achieve greater advance in tunnels or drifts of small area, this new type of parallel hole cut is used. It consists of a slot, which is left unloaded with outer cut holes and location is important. The slot is produced by contiguous drilling of two holes. 20mm drill rod with tapper and special drill bit of 57mm diameter. Depending upon the nature of rock, only one centre hole may be possible. These cuts are mainly used in hard rock formation.

Coromant cut 90mm 115mm 130mm 57mm 180mm

Ring drilling For stopping operation in metal mines, ring drilling is used. Vertical ring drilling, the holes are drilled in vertical plane like a fan to break to a vertical face (sub level stopping). Horizontal, holes are fanned out radially to break to a horizontal face (shrinkage stopping). Short delay interval of 25 millisecond is usually employed between holes in each ring, starting from easiest breaking section in the middle towards the walls.

Drill patterns used in surface mines The drill cuts mainly used in open cast mines are Square cut Diagonal cut Rectangle cut V-cut Staggered V-cut

Square cut

Staggered V-cut