User's Manual

RIOTRONIC X+

User Manual

Burden and spacing designs are influenced by:

 Design powder factor

 Blast-hole diameter

 Rock mass properties (and particularly, the properties of the strongest, most

massive rock penetrated by blast-holes)

 Required fragmentation, displacement and muck pile looseness required (these

being strong functions of the type of digging equipment employed)

 Geometry of the block to be blasted

Rule of thumb #2:

Burden lies in the range of 24-36 diameters.

In places where the rock is strong and either massive or blocky, conservative values of

burden and spacing should be selected. When blasting weak or closely fissured rocks, on the

other hand, satisfactory results are obtained by using larger blast-hole patterns. In benches

that consist of thick beds of both strong and weak rocks, burden and spacing are restricted

by the fragmentation produced in the strongest or most massive bed encountered.

As the length (along the face) to width (normal to the face) ratio of a blast block decreases

below about 1.0, the blast becomes a trench type shot, a blast in which progressive relief of

burden and the required degree of muck pile looseness are less likely to be achieved.

To overcome this potential problem, burden and spacing in ramp blasts should be smaller

than in blasts that shoot to a long sub vertical face.

All too often, burden and spacing are rounded off to the nearest meter or half meter for

convenience when it comes to marking out. In nearly every situation, the best pattern is not

‘to the nearest half meter’. For example, the optimum pattern for a blast is found to be 7.6 m

x 9.8 m, but the mine operator wants it simple so he opts for an 8 m x 10 m pattern. This

produces unacceptable muck piles, so he tries a 7 m x 9 m pattern. This results in excellent

digging, but his costs have increased significantly. Lower costs could be achieved by using

“non-standard” dimensions.

In areas where the burden is too large, explosion gases find it difficult to break the burden

rock and heave it towards the face. Consequently, high pressure gases from the explosion

tend to be bottled up within blast-holes for excessive periods of time.