Mine dewatering is the process of removing water from mines. It is a complex engineering problem that intersects multiple fields of expertise. Geotechnical engineers work alongside mining engineers, hydrogeologists, and environmental engineers to devise cost-effective ways to control the flow of water into mines, redirect it when possible, and remove it when there’s no alternative.
Background History of Mine Dewatering.
Early dewatering efforts were a brute force affair. In the 18th century, Roman and Greek mining was the earliest recorded user of mine dewatering techniques. They used simple drain methods such as gravity driven channels, wooden troughs and a hand-operated bucket system. The Persian Qanat system and medieval Europe also came into existence during this age.
The Industrial Revolution of mines dewatering begins with the invention of the atmospheric steam engine, known as steam-powered pumps in 1712 by Thomas Newcomen. With technological advancement, electric and diesel pumps came into existence in the 20th century, this revolutionized mines dewatering completely by providing more reliable and efficient automated pumping system. ?
In open pit mines, dewatering is primarily concerned with preventing groundwater from entering the excavation area and removing any water that accumulates. This involves lowering the water table around the pit and ensuring that surface water is diverted away from the mine. Techniques such as digging drainage channels, constructing dikes, and using large-scale pumping systems are common practices.
The focus is on removing water that infiltrates through rock fractures and fissures into mine tunnels and shafts. The challenge here is not only to pump out the infiltrated water but also to manage it in a way that prevents it from re-entering the mine. The use of sump pumps strategically placed in low points within the mine is a typical solution. These pumps collect and remove water, directing it to the surface or into treatment facilities. Other method involves a wellpoint, deep point and eductor system.
- Sump Pumping: this involves creating a low point (sumps) where water accumulates before being pumped out. Usually common in open–pit and underground mines. It is quite simple but requires constant maintenance.
- Borehole Dewatering: it involves wells being drilled around the mine to lower the groundwater table before excavation. It prevents water inflow and reduces pore pressure. Grasberg Mine (one of the world’s largest gold mines) engaged deep boreholes to control water inflow in its operation.
- Surface Water Diversion: channels and barriers such as dikes redirect surface water away from the mining area. The world's largest Iron ore mine (Carajás Mine) has an extensive surface drainage system.
- Artificial Recharge & Reinjection: Instead of discharging extracted water, it is reinjected into other areas to maintain regional water balance. Olympic Dam Mine reinjects treated groundwater to minimize ecological disruption.
- Ground Freezing: the area around the excavation is frozen and the soil is transformed into a frozen soil well. This method involves the use of a vertical tube array similar to a wellhead, which continuously circulates coolant to freeze the soil, thereby forming a groundwater barrier.
- Well Points System: This system is usually used to hold down the groundwater level up to 6 meters. A drill-spaced well point around the circumference of the excavation engages a vertical section pipe with a screen hole at the base and is connected to a vacuum pump.
- Eductor System: the method uses venturi tube principle, flexible eductor pumps draw water from depths, utilizing high-pressure fluid (often water) to generate a vacuum.
- Deep well system: uses high-power electrically driven submersible pumps, the system accommodates varying geological conditions.
- Electro–Osmotic method: uses an electric field to remove water from saturated soil, Oil Sands Mining engages this method to dewater highly cohesive oil sand tailings.
Dewatering Plan and Technicality
- Info Gathering: this is the first state, get information about the water table, soil test, and probably historical information.
- Planning: calculate the number of wells required, space distance, well depth, slot size, availability of power, and safe environmental discharge.
- Execution: based on information from stage 1 & 2, choose the right pump. To select the right pump, understand the pump performance, horsepower required, and the head pressure needed.
Importance of Dewatering in Mining.
- Safety and hazard prevention: it reduces flooding risk, slope and wall failures, controls underground mine roof collapses, and mitigates mud rushes and liquefaction
- Enhance Productivity and Efficiency: It reduces equipment downtime and prevents ore dilution.
- Protects the Environment: minimizes contaminated water discharge and reduces Acid Mine Drainage (AMD)
- Improve mine stability and sustainability: it extends the lifespan of the mine and supports slope reinforcement
- Reduces Operational Costs
Mines dewatering is not just about removing water, it is essential for safety, operational efficiency, environmental protection, and cost control. A well-designed dewatering system ensures mines can operate efficiently, safely, and sustainably.
