Anup Kumar Gupta SRF at Departmetn of Environmental Science and Engineering,Indian School of Mines, Dhanbad, India Mine fill is an integral part of mining, different techniques have been used for the same. This presentation is focused on few of the important technique with a descriptive analysis.

1. An introduction to

2. •Mining is a process to extract valuable minerals from the earth’s
crust.
•Coal mining in India is dominated with open cast mining which
accounts for about 80% of total mining while underground mining
is 20%.
•Underground mining is the way to extract the ores from deep,
results in the creation of voids.

3. Why mine fill
 Ensuring long term regional stability
 Limiting excavation exposure
 Waste disposal
 Underground mining creates voids which needs to be
filled to avoid subsidence and for other mine safety
regions
 Provides an option of disposing of waste materials in
underground rather than on the surface

4. Schematic diagram showing how fill preserves confinement at the boundary of an excavation and
assists in mobilising the shear strength along existing joints and arresting potential failure
propagation

5. Disciplines involved in the conception, design,
construction and operation o f mine fill system:
 Mining engineering
 Operating
 Planning
 Mineral processing
 Rock mechanics
 Soil mechanics
 Environmental engineering
 Cement technology
 Pozzolan chemistry
 Mineral chemistry
 Industrial engineering and
 Geology

6. Chapter -2
Basic mine fill material
 Mill tailings
 Aggregate or rock
 Water
 Binder

7. Tailings
• Tailings are the waste produced during mineral processing
(separation of valuable mineral & waste)
• It ranges from clay to sand in particle size
• Use of these processed tailings as a fill material in
underground mine voids will provide a good waste disposal
technique and reduce the surface impact of mining
• Tailings contain various agents like cyanide, lime, acid,
sulfide, arsenic and other heavy metals may as a result of
processing , become unstable, implications of which
should be fully considered in any form of tailing disposal
including mine fill

8. Sources of Mine Fill Tailings
 Mine development waste rock
 Quarry produced rock fill
 Various smelter slag as bulk filling media
 Mine tailings from concentrations
 Heavy media plant rejects
 Dune sand
 Leach pad residues

9. Some of the important features of tailing to be
used as mine fill
 Grain size distribution: This is very important feature as it
determines many of the ultimate properties of the fill
• Void ratio
• Flow properties
• Permeability/percolation rate
• Pumpability
 Mineralogy: Influences other characteristics such as water
retention, strength, settling characteristics and abrasion
action.
 Other properties affected by mineralogy are

10.  Specific gravity (determinant of density of fill)
 Silica minerals(particularly quartz) as it can be very abrasive
and result in high pipeline wear and
 Sulfides which may results in the breakdown of the hydrated
cement in the fill over time
 Particle shape Tailing oxidation and aggregate grading are also
influencing the performance of filling partially

11. Natural sand
 Natural surface sands are also used as fill materials, either
as a sole source for hydraulic fill or supplement tailings in
paste fill.
 Natural sand deposits are formed by fluvial, glacial or
aeolian processes and are often are high in silica with well
rounded particles.
 Sizing between and within deposits can vary widely

12. Rock and Aggregate
Sources:
 Waste rock from open cut operations
 Waste rock from underground development mining
 Quarried rocks and coarse gravels

13.  Huge amount of waste rock is generated where an underground
mine is developed beneath an open cut operation
 The use of rock generally carries a price premium, including
extra rehabilitation at the end of mine life
 It is generally used when other cheaper suitable materials are
not available
 Alluvial sand can also be used , especially if available close
proximity to the mine, but sever ecological damage to river
system result from their recovery
 Moisture content of aggregate is an important parameter and
should be monitored as it can change the water balance of the
fill
 This may cause problems in terms of transportation, drainage
and fill stability
 Uniaxial compressibility strength (UCS) is an important
parameter for the same

14. Water
 Important constituent of the fill either hydraulic or paste
fill
 Presence of salt in sufficient concentration may affects the
fill strength. Laboratory test shows that for both tailings
and aggregate, increase in salinity decrease fill strengths.

15. Cement
 Most widely used cements are hydraulic cements,
comprise a fine powder that reacts with water to bind
particles together as aggregates by hardening from
flowable plastic state to a solid
 Main constituents of cements are:
 Carbon, silicate, aluminum, iron (C, S, A, F)
 The setting and subsequent curing of Portland cement
are mainly due to the hydration of calcium silicates.
 The initial hardening reaction is primarily due toC3S,
C2S

16. Pozzolans
Materials which, though not cementeceous in themselves, contain
constituents that will combine with lime at ordinary temperature in
presence of water from unstable compounds that exhibits
cementing properties
 Fly ash, Slag, Gypsum along with pozzolans are some of the other
components of mine fill
 Admixtures are an adhesive substance added to cement are now
frequently used to enhance the performance of concrete, mortar
and grouts before or after hydration of the mix
 According to ASTM C 125 (2) “ A material other than water
aggregates, hydraulic cement and fiber reinforcement used as an
ingredient of concrete or mortar, and added to the material
immediately before or during its mixing
 Some other ingredients such as rheology modifiers, Hydration
modifiers and durability enhancers are frequently used in mine fill

17. Chapter -3
Geomechanics of mine fill
Mine fill is a complex subject encompassing many
disciplines such as:
 Soil mechanics
 Concrete technology
 Fluid mechanics
 Process engineering

18. Mine backfilling applications and the relevant fill
parameters
 Dry fill (DF)
 Hydraulic fill (HF)
 Cemented hydraulic fill (CHF)
 Paste fill
 Composite fills

19. Fig (a). Hydraulic fill in a typical open stope, (b). Composite fill in
open stope
Fig. (a)
Fig. (b)

20. Dry fill
Relevant features of dry fill are
 Bulk unit weight
 Dry unit weight
 Angle of repose
 Angle of friction
 Particle size distribution (P80, P50, P10)
 Apparent cohesion
 Relative density
 Shear strength
 Arching

21. Hydraulic fill
Relevant features of HF are
 Void ratio and porosity
 Relative density
 Permeability
 Active/passive earth pressure
 Effective stress
 Saturated , submerged and bulk unit weight
 Shear strength
 Seepage, drainage and flow nets or flow paths
 Piping
 Quick conditions, liquefaction
 Arching

22. Cemented hydraulic fill
Cemented hydraulic fill is made by adding binders some of the
relevant features of CHF are
 Void ratio and porosity
 Relative density
 Permeability
 Shear strength
 Arching
 Bulk saturated, submerged, unit weights
 Lateral earth pressure
 Seepage, drainage
 Liquefaction
 Slurry rheology

23. Paste fill
 Paste fill is made by combining the tailings and
binders with a certain amount of water to achieve a
thick mud like consistency
Relevant feature of paste fill are
 Same as for CHF plus
 Paste rheology

24. Shotcrete
 It is used to construct fill retaining walls known as fill
bulkhead. Knowledge in the following areas is considered
necessary to use shotcrete in backfill operations:
 Cement chemistry and concrete technology
 Compressive tensile and flexural strengths
 Concrete and shotcrete mix designs
 Reinforcing fibers and slump

25. Geofabrics-geotextiles
 It is used in engineering drainage systems incorporated
with the shotcrete bulkheads.
 Therefore it is an important field for better backfill
environment

26. Phases of backfill material
Tailings or backfill are not homogeneous medial like soil
it comprises of three different phases i.e., Solid, Liquid
and Gas
If all these three phases are present in tailings then it is
classified as unsaturated tailings
When only two phases namely solid and liquid are
present it is classified as saturated tailings

27. Some volumetric relationships
In order to arrive at some useful volumetric relationships it is
necessary to lump all the solid grains into a solid mass and
alll the liquid into a liquid mass and similarly all the gas
chambers into a separate gas volume. After this lumping of
different phases into separate volumes, the original
tailings will be represented by three separate phases.
Where, V= total volume of tailings (with all three phases)
Vs = some of the volume of all solid grains
Vw = some of the volume of all the water contained between
grains
Va = some of the volume of all air between grains and water
film

28.  Ratio of the volume of all the space between the mineral
grains to the volume of all the mineral grains is called the
void ratio (e).
 It is important property of the fill material as it indicates
the amount of space between the solid particles and their
close proximity
 Ratio of volume of space between the mineral grains to the
total volume is also useful property and called Porosity (n)

29. Degree of saturation
 Ratio between the volume of water filled in the voids to
that of the volume of voids is called the degree of
saturation (Sr)
 This is an indication of the extent to which water is
present in the voids
 For example if the degree of saturation is 80% this
means that 80% of all the pore space is filled with
water, if Sr = 0% sample is completely dry while if Sr=
100% fill is fully saturated and all the pores are filled
with water

30.  Water content of fill
 Water content of a fill sample is the ratio between the
weight of water present in the sample to the weight of
solids, and is given by the following relationship
 Moisture content of fill
 Amount of water present in the tailings is called
moisture content of the sample, it is a fraction of total
weight of solids and water together
 It is very important to differentiate water content and
moisture content to calculate the weights of water and
solids

31.  Moisture content (m) is given by the following
relationship
 Solids content (Cw)
 When ratio of the weight of solids to the total weight of
the fill is expressed as percentage is called the solid
content
 It can be represented as

32. Example:
 The wet weight of a fill sample is 225 g and after
completely drying in an oven the weight of the sample
is 175 g. determine the water content and moisture
content
 Solution
The water content = 0.286 or 28.6%
Moisture content = .22 or 22.2 %
Alternatively the moisture content = .222
water content = 0.286

33. Saturated fills, slurries and pastes
 The weight of water = ………………..(1)
 The weight of solids = …………..(2)
 The water content = …..(3)

34. Chapter-4
Fluid Mechanics of Mine Fill
Two main aspects of this chapter are:
 The delivery of mine fill as a high density slurry from
surface to underground , using boreholes and/or pipelines.
The transport mechanism can be by pumping or gravity , or
some combination of both.
 The drainage of water through fill placed underground in
stopes. Since paste fill has very low permeability and rock
fill tends to contain little water, this aspect is of particular
interest for hydraulic fill types.

35. Transport and delivery of fill slurries
 Fill from surface to underground as high-density slurry or
paste typically using a combination of boreholes and
pipelines, frequently using pumps and nearly always using
gravity.
 The topic of interest here is in the properties of the various
high-density mineral suspensions and in particularly their
behaviour in pipelines and boreholes.
 Generally it is necessary to maximise the density of the
hydraulic fill slurry or the paste fill while ensuring that it can
be reticulated to the limits of the underground mine
without the risk of blockages or line breakages.

36. Rheology of Newtonian and non-Newtonian
fluids

37.  A fluid is a continuous substance that will deform or flow in
response to shear stress
 Fluid will tend to take the shape of the surrounding
container.
 Shear stress is the force acting over an area, and the shear
strain will be proportional to the shear stress.
 For a Newtonian fluid the rate of shear strain is directly
proportional to the shear stress. This constant is dynamic
viscosity .
 Water is a classic example of Newtonian fluid – a fluid that
obeys Newton’s law of viscosity.
 Fig 1 shows the shear stress against shear rate for a range of
Newtonian and non-Newtonian fluids.
 Low density mineral slurries behave as Newtonian fluids,
their flow properties being dominated by the water phase.

38. Hydraulic fill slurry behaviour
 Hydraulic fill slurries are prepared from mineral processing
waste streams by partial dewatering and desliming to remove
some of the finest size fractions.
 Modern high density hydraulic fill slurries are mostly
designed to have a density in the range of 45%-50%cv (solid
by volume).
 There should be a critical deposit velocity and settling of
solids for better placement
 Durand (1953) defined the critical settling velocity as:
VD = FL [2gD(s-1)]0.5
Where g= grvitational constant (m/s2)
D= internal pipe diameter (m)
S= specific gravity of particles
FL = Durand settling velocity parameter (%)

39. Fig-3. Limiting settling velocity
parameters (Durand, 1953)

40.  Gilchrist (1988) desctibes four flow regims for hydraulic
transportation in horizontal pipes, these are:
 Homogenous flow: the concentration of the particle is
constant across the pipe cross section generally not the
case when average p: The concentration of particle is not
constant across the pipe cross section. Particles are
suspended by turbulence within the flow.
 Moving bed: The particles move along the pipe invert as a
dispersed bed.
 Stationary bed: A stationary bed of particles remains in
contact with the pipe invert. Above this layer the flow can
be heterogeneous by siltation or moving bed flow.
By the above assumptions Gilchrist concluded that

41.  Deslimed tailings are transported in a fully suspended
heterogeneous regime at velocities greater than the
critical deposit velocity
 At densities below 2.0 kg/l, the flow regime is usually
sliding bed and saltation, and
 At densities above e 2.0 kg/l, the flow regime is typically
homogenous flow

42. Paste fill behaviour
 Paste behaves as a non- settling slurry and therefore does not
have a critical settling velocity.
 In this case flow will occur when the driving head exceeds the
wall shear stress.
 If paste has been delivered at too high a pulp density, flow will
not occur and the paste could block the borehole and pipelines.
 Paste fill flow in pipes and wall shear stress :
 Shear rate is determined from
Where Ύw = shear rate at wall of the pipe (1/s)
V= Fluid velocity (m/s)
D= Internal diameter of pipe (m)
For a typical paste fill system shear rate will range from 25-80/s at
80m3/hr

43.  Wall shear stress is determined from:
 Yield shear stress – effect of pulp density

44. Reticulation design
 Majority of fill delivery systems utilize gravity as the
motive source to deliver high density slurries of pastes
via boreholes and pipes to the working.
 Some mines don’t have sufficient driving head to
achieve delivery to all parts of the mine and high
pressure pumping system are used.
 Process of reticulation design is to match the delivery
volume, slurry densities, pipeline diameter, borehole
diameters and friction loses with the static head and/
or pumping head required to achieve delivery.
 Free fall section is common to both hydraulic and
paste fill where excessive velocity could cause extreme
wear conditions.

45. Steward (1988) provide a design steps to be undertaken for
fill reticulation design.
 These steps are applicable to full flow reticulation design
for both fill types
 The steps are:
 Determine mine fill requirements
 Determine the static pressure head available for delivery
throughout the mine life
 Determine the total pipeline lengths. This may vary for
different working areas of the mine
 Determine the system frictional loses.
 Balance the total frictional loses to the static head by
variations to pipe diameter, slurry density or, rarely energy
dissipation methods

46. Hydraulic fill reticulation design
Van der Walt (1988) lists a number of points to consider when designing a fill
system.
The key generic points are:
 The transport velocity of the slurry must be significantly higher than the
critical velocity to prevent the slurry from settling out
 The transport velocity must be kept as low as possible to minimize friction
losses and pipe wear
 Standard pipe sizes are preferred
 In vertical columns ,the maximum flow rate is at the point where the
frictional losses exactly equal the available potential head
 Flow rate of slurry through the system is determined by the inlet conditions
 Maximum working pressure in the system will be found at the bottom of
vertical columns and will be determined by the frictional losses in the
horizontal columns
 Bursting discs and collection sumps should be provided at the points of
maximum pressure in case blockage in the pipe
 Provision must be made for the flushing of lines before and after filling

47. Calculating friction system losses in hydraulic fill
system
 Higher densities and finer particles are significantly
involved in hydraulic fill
 Cook (1993) proposes that high- concentration(settling)
slurries be considered as consisting of the following
components:
 Vehicle portion, consisting of the finer settling and non-
settling particles and the carrier fluid,
 Suspended load, those solid particles supported by the
yield shear stress within the vehicle portion, and
 Coarse fraction being those particles supported by inter-
particle contact

48.  The friction losses in the reticulation system are a function of
the wall shear stresses
 Cooke (1993) gives the following relationship;
Where:
 w = density of carrier fluid
 Sv = relative density of slurry vehicle
 Vm= mean velocity of mixture
 Fv = friction factor for vehicle portion
 Friction factor for high density finer slurries can be determined from the diameter
and roughness of the pipe, the velocity, apparent viscosity (K), yield shear stress ,
flow behaviour index (n) and density of the mixture
For turbulent flow in the rough pipes, the friction factor is
Where fk=0 and fk are calculated form the colebrook white relationship for smooth
wall and rough wall Newtonian flow respectively:

49. Drainage through hydraulic fill
Drainage analysis
 Can be calculated through Darcy’s law
 Q = KAðH/ðL
 Where
 Q= flow rate out of the stope (m3/s)
 K= fill mass permeability (m/s)
 A= cross sectional area of drawpoint (m2)
 ðH/ðL= hydraulic gradient in the drawpoint (m/m)

50. Testing and measurement
 Laboratory scale rheology
 Yield shear stress and slump test
 Yield shear stress determined by the vane shear
viscometer
 Viscosity measurement
 Pipe loop testing

51. Chapter-5
Introduction to Hydraulic Fill
 Hydraulic fill is a class of mine fill types that are
delivered as high density slurry through boreholes and
pipelines to the underground mine voids.
 The name is derived from the water – born delivery
method.
 Hydraulic fill is most commonly prepared by
dewatering and desliming mineral processing waste
streams and has the following characteristics:

52.  Maximum particle size: less than 1mm and most of the finest
sizes are removed to ensure not more than 10% by weight of
less 10 µm are retained to ensure adequate fill permeability.
 Slurries are made at densities between 40-50%cv (solid by
volume).
 The slurry transport regime is heterogeneous and turbulent at
average velocities higher than the critical settling velocity.
 Hydraulic fill has a permeability in situ in the range of 10-5 -10-6
m/s. excess water used to deliver the solid components to the
stope must drain out of the fill, by vertical gravity drainage
through the fill, decantation and through engineered drainage
facilities at stope access points
 Placed hydraulic fill has a porosity typically around 50%. At
50% porosity (void ratio= 1.0),the bulk density is one half of the
dry solid density; e.g. tailings with a specific gravity of 2.8 will
have a dry bulk density of around 1.4t/m2

53. Mining
methods
Descriptions Key characteristics
Cut and fill Uncemented hydraulic fill placed
in long pours to fill each lift as
mined
•Flat beach angles in the range of 20 (1:30) provide a good working
platform
•Mostly uncemented cap placed to provide hard mucking surface
•Long term drainage facilities designed into the base of cut and fill
mining area
•Suitable for under and overhead methods
•Relatively simple barricade built to contain each fill
Drift and fill Orebody mined as a series of
longer primary stope & secondary
pillars
•Each drift filled tight to the back to provide support for the removal of
adjacent pillar drift
•Cemented fill required to maintain stable side exposure in secondary
drift strong enough for self weight of fill plus any surcharge load from
the back of overbody
Post pillar- cut
and fill
Large plan area mined in lift
leaving slender pillars
•Each lift filled with uncemented hydraulic fill
•It provides a working platform for mining operations
•It provides confinement to the slender pillars, maintaning performance
Bench stoping Small single sublevel stopes
mined and post filled
•Engineered barricades required in all opening at the base of the bench
to retain the fill and permit effective drainage
•Cemented fill required in primary benches
•Flat mucking surface required for extraction of next sublevel
•Waste rock often dumped into secondary benches for disposal
Sublevel open-
stoping
Larger stopes usually mined over
several vertical sublevels and
filled at the end of production
•Engineered barricades required in all openings on each sublevels to
retain fill & permit effective drainage
•Most drainage will report to lowest levels with only minor amounts
higher up in the stope
Table: Use of hydraulic fill by mining method

54. Design
Demand from mining methods
Hydraulic fill is used in a number of different
applications in a variety of mining methods.

55. Preparation of hydraulic fill
 Hydraulic fill is mainly slurry based mine filling where a solid
waste material like tailings, sand or waste rock is used.
 Slurry densities are typically 25-35%cw (solid by weight)
 This includes as well stabilized circuit for slurry transport to the
destination point
 Hydraulic fill plant performs two related functions of dewatering
the slurry and removing the finest fraction of the tailings material.
 The tailings slurry is dewatered to minimise the quantity of water
that will be placed underground and must drain out of the fill
during and after placement
 The slurry density should be between 45-50% cv (solid by volume)
 This is typically greater than 70%cw (solid by weight) or relative
density greater than 1.8
 Hydraulic fill also removes the finest size fractions to achieve the
required permeability targets and so ensure proper drainage

56. Components of hydraulic fill
 Hydrocyclones
 Spiral and rake classifiers
 Drum filters
 Elutriation tanks
 Storage tanks and pachucas
 Delivery system from preparation site to stope

57. Fill containment-design and construction of fill
barricades
 Fill barricade is important to retain the fill solids while
permitting the excess transport water to drain out of
the stope
 Wall must have the structural capacity to withstand the
maximum anticipated lateral pressure that the
hydraulic fill will impose
 Various types of barricaded designs have evolved in
mining districts, some of them are as follows

58.  Waste rock barricade with very limited application in
some cut and fill operations with very low lift hights.
 Timber and permeable hessian barricade
 Arched impermeable concrete masonry block work up to
1m thick over spans of 4m X 4m, with sealing grout,
hatchways and drainage pipes

59. Placement and drainage
 Hydraulic fill placed into production voids such as stope
must be allowed to drain to remove transport water
 Consequence of not meeting this may leads to barricade
failure, allowing a rush of fluidized fill in to the mine
working and cause tragedy
 Earth pressure /or pore pressure loads applied to
retaining barricades must be lower than the design
strength of these structures
 The excess transport water with which the hydraulic fill is
delivered must be able to drain freely from the fill and
from stope
 The excess water should be minimized by : maximizing
slurry placement and reducing, diverting or eliminating
flushing water delivered to the stope

60. Hydraulic fill summary of key issues
 Advantages and limitations of hydraulic fill:
 The risk of inrush and its consequences can be higher in
uncommented hydraulic fill compared to cemented hydraulic
and paste fill operations if badly designed
 The fill placement rate is constrained by drainage rate and
account must always be taken of pouring and resting times and
the establishment of unsaturated filling conditions
 The desliming process reduces the available tonnage of fill
material to be placed underground
 Surface processing plant is relatively simple and low capital cost
but requires effective instrumentation and quality control
systems
 Cement binder is not required in many situations where future
exposure is not required, thus subsequently reduce the cost
compared to paste fill
 Inadequate collection of drainage water can result in poor
roadway condition, damage to vehicles and have major impact
on the ventilation system