Mine Dewatering Strategy: Reaching the Deposit at the face of Surface water

picture @Edo LGA in a Dolomite Quarry

Dewatering operation is one of the most sensitive and continuous operation during raining season.

The approach to this operation depends on the mine design, mining method and other factors including the mine terrain.

Most surface mine can not escape the challenge of surface water inflow but can be overcome through proper dewatering plan.

Dewatering is define as the process of removing unwanted collection of water in the mine. It describe as the approach use in remove water from mine pit so as to gain access to the ore deposit.

In view of surface Mining methods, which involves the extraction of deposit with less overburden thickness. The mining approach adopt in surface Mining methods are such that a cavity is advance into the Earth crust. Such cavity has lower attitude compare to the nearby environment which prompt the collection of water into it.

Mine out area (stope, pit) recieve water from:

1. Surface run-off water

2. Direct precipitation (Rain)

3. Underground water ( water below the mean sea level).

Surface water by hydrogeological survey is the water running along the dipping cause of earth crust whether from nearby river, stream, flood, or other surface appearance water.

Most times this can be water from abandoned pit  closer to the mine area or from gathered surface water.

As have earlier said, mine out area has lower elevation compare to it vicinity, this support the inflow of surface water into the mine.

Taking a sharp look at direct precipitation, surface mine is open directly to the sky, this makes it recieve water droplet during raining season.

Likewise in the view of underground water inflow, water gain access into the mine through fracture and cracks originated from blasting and geological Condition of rock.

Inflow can be from surface accumulation or from underground water.

DISADVANTAGES OF MINE WATER INCLUDES;

1. Stop in mine crude production
2. Damage to mine floor
3. Damage to mine wall and reduce wall strength and stability which can easily support wall failure
4. In the case of dimension block cutting mine, present of water can easily increase the aparture of cracks/fracture which will directly render most of the blocks not marketable
5. In case of rock/ore formation with compromise minerals grains, the dissolution of mineral grains under oxidation reaction may cause some of the grains internal force of attraction to reduce.
Most mineral grains may undergo weathering and leaching off due to acidic water reaction.
6. Ore formation containing sulphide mineral, radioactive minerals and other acidified mineral may likely result into acidic water formation. This becomes dangerous to equipment, plants among others. Pumping in such case become difficult and strategic.

CONTROL STRATEGY FOR MINE WATER.

Thou mine water accumulation is inevitable during raining season as we can't cover the mine cavity/stope/pit with water proof linens. Even if this is possible, can we stop aquifer water or underground inflow from entering the mine???

Since we just need to continue mine operation, below are some dewatering approach and method to reduce mine water challenge in the mine.

1. Use of pump and pump system: This involve the use of whether electric power pump or Diesel engine pump. The use of pump may appear not fully efficient in situation where the mine water inflow condition is continuous. But this is bypass by ensuring pump network is build and also drainage canal is constructed to fasten the flow rate of water in the mine environment. Is of no doubt that electric pump is fast pumping than the diesel pump, thou the challenge of cost and power system may hamper the use of this pump type.

2. Sump and pump system: sump is a hollow basin sunk somewhere around the mine for collecting water and to aid fast pumping.

This approach can be use to allow working access at one section of the mine while pumping is goin on at the other part of the mine.

3. Strategic mining approach: This is a tactical mining progress that involves varying elevation level of the production zone in the mine to avoid water infringement with mining work.

The mine design is such that it provides a working bench with little water inflow challenge.

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STEMMING OPERATION IN VIEW

Stemming in blasting is very important and affect not only the efficiency of the blasting but also the impact of the blasting on the environment.

By simple definition, stemming is a confinement process done by the use of innert materials to confine explosive charge within the drill hole during charging.

The define function of stemming is to:

1. Ensure the explosive charge is confine within the hole socket so as to avoid poor distribution of explosive release shock energy.

2. Prevent the escape of shock wave into the environment and causing airblast and other environmental impact.

Stemming can be top confine or inter-column charge confined.

In case of decking charge pattern, each explosive charge column is separated by innert material to reduce the charge weight and also to ensure effective distribution of shock energy along the hole column.

In the case of decking, stemming is use to confine and to separate upper charge column from the lower charge column.

Stemming materials can be the drill cuttings from the hole or poorly sorted, well-graded gravel or stones.

Use of stones of well-graded nature with particle size ranging from 4mm to 9mm tend to show good confinement than drill cuttings due to it heterogeneity nature that permit the grains interlocking.

Some of the factors that affects stemming length are:

1. Hole diameter

15-30D

2. Bench height/Hole depth

Stemming=0.45-0.55H

3. Burden

Stemming=0.7-1.5B

4. Explosive energy/strength: high strength explosive requires longer stemming length to confine and resist the escape of shock energy to the surface

5. Rock properties: This includes the rock strength, discontinuity nature among others.

Most cases, stemming may be position at point where discontinuity daylight on the hole wall instead of placing booster.

Also, stemming length varies with the strength of rock formation to be blasted.

Hard rocks like granite (>250Mpa) is blast with stemming length varying from 20-30D.

Medium rocks like dolomite:20-25D

Soft rock :15-20D.

Reason why stemming length tend to increase with Rock strength is that, stronger rocks offers higher resistance against the Penetration of released shock energy at detonation. The release wave tends to follow weaker zone instead of fracturing and slabbing the rock mass, in a bit to relieve the detonation pressure, the stemming of short length may be pull out.

This is why, lengthy stemming is needed to confine the Explosive energy within the rock mass.

In the process of selecting lengthy stemming the place of ensuring good and sufficient charge length must also be considered so as to enable good fragmentation.

Blasting with high safety condition, getting good blasting result alongside with good economic factor is what define a successful Blasting

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