Filling of mined-out openings

Dry waste fill

Hydraulic fill

Cemented rock fill (CRF)

Paste fill

Dry waste fill coming from the same stope

Any material size is satisfactory : usually between 60 and 150 mm and up to 300 mm

No transport or specific equipment

Reduced cost

High compaction : up to 50% of volume

Fill is weak

Impossible to control the material gradation (grain size distribution)

Impossible to drive the fill tight against the back

Transport of supplementary waste into the stope or extra waste from the stope doesn’t excluded

Ore body

Stope

Waste

Ore breaking

Wastebreaking

Blast holes

Dry waste fill coming from outside of the stope

material from underground development

1500 m niveau l 12

main shaft

waste pass

fill pass

material from surface quarries

Material size between 60 and 150 mm and up to 300 mm is satisfactory

Material gradation can be controlled

Fill is stronger due to a better size distribution

Volume of fill by stope is controlled

Specific fill passes, storage and other facilities are needed

Underground transport is indispensable

Higher cost

Dry waste fill coming from outside of the stope :placement by gravity

Material size between 60 and 150 mm and up to 300 mm is satisfactory

Material gradation can be controlled

Fill is stronger due to the better size distribution

Volume of fill by stope is controlled

High compaction : up to 50% of volume

Specific fill passes, storage and other facilities are needed

Underground transport is indispensable

Higher cost

Dry waste fill coming from outside of the stope : slinger belt placement

Fill is stronger due to better compaction if gradation of material is proper

Fill can be placed tight against the back

Material size is more restricted ( up to 100 - 200 mm)

Material compaction can reach 20 % to 30 %

Specific equipment is needed

Distance of projection is limited to 6 - 10 m

Dry waste fill : Placement by loading equipment

Fill is stronger compared to gravity placement due to better compaction if gradation of material is proper

Fill can be placed against the back

Material compaction can reach 25 %Material size is restricted to 60 and 150 mm in order to create a strong floor for the LHD

Placement by LHD

Material size between 60 and 150 mm and up to 350 mm is satisfactory

Placement by slusher

Material compaction can reach 30 to 40 %Impossible to drive the fill tight against the backDistance of placement is between 10 and 30 m

Hydraulic fill

mine water storage

aggregate silo

pipeline for cleared water

water recovering device

pumps

backfill

fill feed pipeline

mixer

slurry recovering

discharge

discharge

Material containing :

crushed rock of up to 50 mm, granulated smelter slags of up to 30 mm,sands of up to 2-3 mm,mill tailings of up to 0.5 mm

cement can be added

is mixed with water with ratio varying from 0.6 to 4 parts of water for 1 part of solid (in weight)

pulp is pumped through 150 mm (75 to 250 mm) pipes up to 1500 m vertically and 600 m horizontally

speed of particles 2.5 to 4 m/sec

Hydraulic fill

Direct transport by pipes

High performance of filling up to 400 m3/h

Fill is stronger compared to dry rock fill with gravity placement

Good wall support and working surface are achieved

Good ventilation control

Full automation is possible

Very sensitive to water concentrationWater (up to 75% in fill) has to be pumped after fillingMuddy haulage waysAdditional capital cost (compared with dry rock fill)

Pneumatic fill

car tipper

conveyer belt

feeder classifier

aggregatesilo

air in feed arrangement

conveyer

crushers

backfill

aggregatesilo

fill feed

pipeline

discharge

Material containing :

tailingssmelter slagcrushed rocksandsgravelof 5 to 100 mm in size

is pouched through 203 mm pipes by air at 34 to 138 kPa pressure

Pneumatic fill

Density of filling is better compared with gravitational dry rock fill

No excess water (compared with hydraulic fill)

Improvement of face ventilation

Fill can be placed tight against the back

High dust emissionIncreased pipe wear (increased capital cost) High consumption of compressed air and so energy consumption ( up to 15 kWh/m3 )Difficulty in producing a good working floorEquipment is large and difficult to move

Cemented rock fill (CRF)

High-density or paste fill

Mill tailings including slimes, sand, waste rock or gravel from 0 to 25 mm are dewatered down to 12-15% of water content, classified and concentrated by elimination of light particles.

In resulting mixture the volume of fine material must exceed the pore-volume of the coarse fraction. So the fill material attains a density of 2.1 t/m3.

3 to 6 % of cement is added to form a stronger fill.

Concrete or mud pump is used to transport the material (85% of solids) by pipeline of 60 to 200 mm diameter with a rate of 20 to 50 m3/h.

Placement can by done by air assisted nozzle

Comparison

Young’sModulus inMPa

Compaction in %

Concret 3000-9000 0

Cemented fill 300-6000 3-5

Hydraulic fill 10-60 10-20

Uncemented rockfill 10-30 15-50

Cost of rockfill

where : Crf -cost of rockfill ;cstope - cost of rockfill dumped in to the stope fill rise,

cstope = 0.4 $/tonne of rockfill ;cplacement - cost of placement of the rockfill in the stope by the rock loading

equipment ;

filloftonne/$,ccCplacementstoperf

The waste material is dropped by gravity to the waste pass

At the underground level the waste is trammed from the waste pass and dumped to the fill rise of the stope

Than the fill is placed in the stope by LHD or slusher

Cost of sandfill

Sand and mill residues are stored in silos on the surface

Sand is drawn into the mine through a vertical sans pass

At the underground mixing station the sand is mixed with water to produce a pulp of 70% solids

The pulp is piped by gravity to the stopes to be filled with a rate of 100 m3/hr

The basic cost of sandfill in place assumed to be 2.5 $/tonne of fill

Cost of cemented fill

The fill of a cement/sand ratio of 1/20 to 1/4 is prepared in the mixing tank on the surface

The fill is pumped in to the mine through 51 to 127 mm diameter feed lines placed either in boreholes or shafts with outlets at all of the mining levels

Than the fill is delivered to different stopes by horizontal drifts

filloftonne/$,CRccCcementsfcf

where : Ccf - cost of cemented fill ;csf - cost of sandfill, cstope = 2.5 $/tonne of rockfill ;ccement - cost of cement ; ccement = 80 $/tonneCR - ratio of cement in the fill ; CR = 6 - 12 % for a layer of fill of 0.9 to 1.2m

Preparation of stope for the cemented fill

Stope preparation can include the installation of stringers, stulls, mesh, cables ...

Cost of the mesh is assumed to be 2.3 $/m²

Cost of stringers, stulls, cables is assumed to be 50 % of the mesh cost

Extra labor to install stringers, stulls, mesh is assumed to be 4.5 hr x 2 workers for 5 meters of stope advance