Things you should know about over break in open pit

Things you need to know about wall overbreak in blasting.
Backbreak and radial crushing around the borehole result when the stress produced in the rock by the explosion exceeds the crushing strength of the rock at the crest of the wall. It is pertinent to know that backbreak is a major problem encountered by every mining engineer on site. Excessive backbreak at the perimeter generally results in an overall pit wall angle less than designed, and may result in the need for costly artificial support techniques. In fact failure to properly control blasting at the final pit wall can cost a large open pit mine millions of dollars. Equally important as cost in every industry, is the need to provide a safe working environment. Pit and quarry walls that have sustained substantial backbreak are prone to hazardous rock falls. Therefore, any organization that emphasizes safety will want to control blasting at the limits of an excavation.
Eliminating or minimizing these problems is a task that must be done. There are number of tools available for minimizing the phenomenon. They include
1.Changing the explosive type
2.Changing the blast hole type
3.By decoupling the explosives
4.By decking
5. By changing the burden and spacing
6.Changing the depth of subgrade drilling or stemming height
7.Changing milliseconds delay
The other area to be looked in is the compressive strength, crushing strength and tensile strength of the rock. Special consideration should be given to the orientation of the joints and fractures in the rock. These variables cannot be controlled but must be determined by suitable field and laboratory techniques. Although it becomes very difficult to obtain a classic result, with the half barrel of the wall control holes showing on the face, when adverse geology has been encountered.  Therefore, I would suggest that careful analysis should be done to use the list of solution listed above.