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Mine dewatering techniques for open pit and underground mines
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MINE DEWATERING
Dr Martin PreenePreene Groundwater ConsultingJune 2014
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SYNOPSIS
Synopsis
• Water management for mining
• Approaches to groundwater control
• Examples of mine dewatering technology– Open pit– Underground – Shafts
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PRACTICE PROFILE
Preene Groundwater Consulting is the Professional Practice of Dr Martin Preene and provides specialist advice and design services in the fields of dewatering, groundwater engineering and hydrogeology to clients worldwide
Dr Martin Preene has more than 25 years’ experience on projects worldwide in the investigation, design, installation and operation of groundwater control and dewatering systems. He is widely published on dewatering and groundwater control and is the author of the UK industry guidance on dewatering (CIRIA Report C515 Groundwater Control Design and Practice) as well as a dewatering text book (Groundwater Lowering in Construction: A Practical Guide to Dewatering)
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MINE DEWATERING
There are 3 aspects to the design and implementation of mine dewatering
An understanding of:
• Hydrogeology
• Dewatering technology
• Environmental sensitivities
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MINE DEWATERING
There are 3 aspects to the design and implementation of mine dewatering
An understanding of:
• Hydrogeology
• Dewatering technology
• Environmental sensitivities
www.preene.com
RANGE OF APPLICATION OF METHODS
From CIRIA Report C515 (2000): Groundwater Control: Design and Practice
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WATER MANAGEMENT FOR MINING
Water Management
Treatment if necessary
PumpingExclusion
Groundwater controlSurface water control
Diversion Pumping
Disposal to Waste
Environmental Mitigation
Beneficial use
On site Off site
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WATER MANAGEMENT FOR MINING
Water Management
Treatment if necessary
PumpingExclusion
Groundwater controlSurface water control
Diversion Pumping
Disposal to Waste
Environmental Mitigation
Beneficial use
On site Off site
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GROUNDWATER CONTROL
Two main philosophies of groundwater control
• Exclusion: Physical cut-off walls
• Pumping: Arrays of wells or sumps (dewatering)
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EXCLUSION: VERTICAL CUT-OFF WALLS
Cut-off walls penetrate into underlying low permeability stratum
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EXCLUSION TECHNIQUES
• Displacement barriers– Steel sheet-piles
• Excavated barriers– Concrete diaphragm walls– Bored pile walls (secant pile walls and contiguous pile walls)– Bentonite slurry walls and trenches
• Injected barriers– Permeation grouting– Rock grouting– Jet grouting– Mix-in-place methods
• Artificial ground freezing
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GROUNDWATER CONTROL BY PUMPING
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OPEN PIT METHODS
In-pit pumping(sump pumping)
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OPEN PIT METHODS
External deep wells Pumped by submersible pumps
External wellsbehind pit walls
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OPEN PIT METHODS
External deep wells and in-pit wells
External wellsbehind pit walls
In-pit wells
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OPEN PIT METHODS
Horizontal drainsto depressurise slopes
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OPEN PIT METHODS
Cut off wall to exclude waterin key strata
Cut off wall
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OPEN PIT METHODS
Wellpoint system to stabilise granular soils
First stage wellpoints
Second stage wellpoints
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OPEN PIT METHODS
Drainage aditsAnd tunnels
Pumped drainage adit with drain holes
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UNDERGROUND METHODS
• In underground mines, the conventional approach is to use the mine itself to control groundwater, by allowing the workings to act as drains
• Once the water is in the mine it is passed along roadways (by pumping or gravity) to a deeper part of the mine (sump) or shaft bottom, to be pumped out via shaft or decline
• Due to depth there may be a need for staged pumping to get the water out of the mine
• In hard rock mines drain holes may be drilled out from workings
• Important to minimise ‘dirty water’ (that has run along the floor/walls) and segregate ‘clean water’ (that has come straight from drain holes), because the water treatment requirements are different
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UNDERGROUND METHODS
• Where fractured or water bearing zones are encountered, exclusion methods can be used to reduce water inflows. Grouting to seal inflow pathways is the most common approach
• Grouting may be:– Planned or responsive– From surface (limited depth) or from workings (interferes with mining)
• Most common type of grout is cementitious based grouts, but problems with grouting through flowing water and may be washed out before they set
• Specialist chemical ‘water stopping’ polyurethane grouts are available to deal with flowing water but are expensive
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SHAFT SINKING METHODS
• Deep shafts for mining present particular problems:– Depth– Limited space and complex working sequence– May pass through multiple aquifers
• Common to use the exclusion approach– Cementitious grouting (cover grouting)– Artificial ground freezing
• Rare to use external pumped wells apart from for shallow depths through granular soils
• Even with exclusion methods there is a need to remove water from shaft bottom– Too deep to pump in one lift– Water often bailed out in hoisting kibble
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MINE DEWATERING
Dr Martin PreenePreene Groundwater ConsultingJune 2014
