VCR concept: The term crater in blasting terminology is applied for creation of a surface cavity in a rock mass as result of detonating an explosive charge into it. This blasting concept was initially used as tool to evaluate the capability of an explosive. It gained importance in surface blasting operations, and in the recent past, in underground operation.
Vertical crater retreat (VCR), also known as vertical retreat mining (VRM), reduces the cost of mining wide, steeply orebodies. The stope has a similar shape, but instead of small longholes drilled in fans, large blastholes are drilled vertically from a top sill to break through into a bottom sill on the sublevel below. This allows the ore to be broken into the bottom sublevel in successive horizontal slices using the same blasthole for each successive deck or blast. No slot raise is required.
Only the bottom of each hole is loaded for each successive blast. This breaks off a slice of ore from the bottom of the ore block, which falls into the drawpoint level below, where it can be mucked out. Mucking provides room in the stope for the next blast. Dilution is controlled by removing just enough ore to create a sufficient void for the following blast.
This mining method is particularly safe, because the miner does not enter the area where the ore is blasted. Drilling and loading are done from the top sill. The method also eliminates the need to support the ground in the stope after each blast. Mucking can be done using remote-controlled LHDs.
Blasting by Raydet Vis-a-Vis Detonating Cord Down the Hole Production Drilling Pattern KHETRI AND KOLIHAN MINES KHETRI COPPER COMPLEX Long Hole Drilling 57 mm Diamater hole MALANJKHAND COPPER PROJECT Mine Planning and Equipment Selection Open Cast and Under Ground Mine section Over Hand stoping - Room and Pillar stope drilling and cable bolting Sub Level Caving Method (block caving)
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