Sublevel stoping..Underground mining methods

Hassan Z. Harraz
hharraz2006@yahoo.com
2014- 2015
This material is intended for use in lectures, presentations and as
handouts to students, and is provided in Power point format so as to
allow customization for the individual needs of course instructors.
Permission of the author and publisher is required for any other usage.
Please see hharraz2006@yahoo.com for contact details.
Topic 4: Underground Mining Methods
 Sublevel Stoping

Outline of Topic 4:
 Considerations on the method
 Conditions for application of the deposit
 Characteristic of Sublevel Stoping Method
 Application
 Development
 Sublevel overhand
 Sublevel underhand
 Slot
 Configuration of stopes
 Drawpoints
Prof. Dr. H.Z. Harraz Presentation
sublevel stoping
2
We will explore all of the above in Topic 4.

Sublevel Stoping
Considerations on the method:
 the sublevel stoping is considered a method of extracting
medium to large scale;
 other names for the method (variations): bighole open
stoping, long-hole stoping or blasthole
sublevel stoping
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Conditions for application of the deposit:
ore resistance: moderate to high;
resistance of the host rocks: moderate to high;
forms: tabular or lenticular, thick (6 - 30m) and extensive lengthwise;
Diving:> 45, preferably 60o- 90o;
good uniformity of grades and thicknesses of ore;
depth of deposit: moderate, preferably <1.2 km.
Sublevel stoping: configuration method in stopes where the ore is detonated by drilling a fan
or parallel; large part of the ore is removed from the stope as it is being detonated, leaving
open stope.

Two versions are common to the method:
 using range in drilling (drilling-ring version) in production, with small
diameter holes (2-3 "). Here, only the drift to be the sublevel open
stope when working on;
 using parallel drilling (drilling parallel) production, with holes of
large diameter (up to 7.5 ") and greater length. Should open a
horizontal slot for positioning the drill. This is done by extending the
drift of the sublevel across the width of the stope.
sublevel stoping
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Drilling in range (drilling-ring)
sublevel stoping
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Figura 2
Drilling Parallel (multi-level blasthole stoping)
sublevel stoping
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higher panel: Bighole open stoping
sublevel stoping
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Characteristic of Sublevel Stoping Method
Advantages
 Moderate to high productivity per man-shift
 Moderate cost of mining (relat = 0.4.)
 Moderate to high production rate
 Suitable for mechanization
 Low exposure to unsafe conditions
 Possibility of simultaneous unit operations
 Average recovery (75%); Moderate dilution (up to 20%).
Disadvantages
 Slow, complex and costly development (though part is done in ore)
 Non-selective method
 Drilling long production requires careful alignment (small deviation in the
holes)
 Great takedowns that can cause excessive vibration, displacement of air
and structural damage.
sublevel stoping
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Applications:
 the main criterion for application of the method is to have
competent ore and host rocks, regular limits for ore and the
footwall slope that exceeds the angle of repose of the
fragmented ore (> 50o overall)
 drill, blast and loading are done independently;
 large of the ore is removed from the stope as it is being
detonated, leaving open stope.
 a recovery can reach 100% if the pillars can be recovered;
sublevel stoping
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The method can operate with Sublevel (fig. Below)
without recovery or Pillars.
sublevel stoping
10

Development:
 ramps and shafts in the footwall,
 transport routes to the base of the stope ore, ore or barren;
 ascending raises are open for connection to the upper level
and allow ventilation;
 development options :
overhand ...
underhand ...
sublevel stoping
11

Sublevel underhand
12
Sublevel overhand
sublevel stoping

Sublevel underhand
sublevel stoping
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sublevel stoping
14
Slot
initial

Slot:
is a space for the
expansion of the rock
where the extraction
begins in the conventional
stope sublevel. The slot
will the level of the roof of
the stope extraction. It is
opened from a slot raise
and can be executed in
various ways
(conventional raising, raise
boring, ...).

Developmental sequence?
slot raisethe stope
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development
slot…
Stope production …
sublevel stoping
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Configuration of stopes
The geometry of the stopes and pillars must
adapt to the spatial distribution of ore.
The position and shape of the pillars will be
determined by geotechnical data and rock
mechanics models for mass. The height of the stope
typically not exceeding 150 meters away.
Later fill (backfill) of stopes can be done to
improve support walls and pillars of recovery.
Cablebolts are also used.
sublevel stoping
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Intermediate slopes of the stope can cause stability
problems in the hangingwall and dilution.
sublevel stoping
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The definition of the total volume and shape of the stopes is
of great importance for the SLOS method. Larger stopes generally
have higher productivity, but higher risk of instability and increased
dilution.
One of the most commonly used options for scaling stopes is the
empirical approach called "stability graph method."
In this method, an open stope stability is expressed in terms of two
parameters: hydraulic radius (RH) and the stability number N ', both
relating to the ceiling or side wall of the excavation.
Referências para o “stability graph method”:
The stability graph method for open-stope design; Underground Min.
Methods: Eng. Fundamentals and International Case Studies, 2001,
W.A.Hustrulid & R.Bullock; Chapter 60, p. 513-520.
sublevel stoping
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The hydraulic radius of a face or side wall of the stope equals the
surface area of the face divided by its perimeter.
RH = Área / Perímetro
O número de estabilidade N’ é obtido a partir de:
 Q is the rate of geomechanics classification of NGI (Norwegian
Geotechnical Institute) Prof. Dr. H.Z. Harraz Presentation
sublevel stoping
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Configuration of stopes...
Graph of stability: the values calculated for HR and N 'define
whether a particular face will be stable, unstable or suffer
subsidence (caving).
sublevel stoping
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Fitting parameters A, B and C :
sublevel stoping
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Example usage method:
Consider a situation where stopes are excavated in competent rock
(RQD = 60), with four dominant joint sets (Jn = 15), which are planar
and without alteration (Ja = 1.0; Jr = 1.0). The ore shows the uniaxial
compressive strength of 120 MPa, while the maximum stress is 24
MPa (determined by numerical models). The critical side to be
analyzed is shown on the next slide. The set of critical joints forms an
angle of 85o with the face of the stope, which has dimensions of 15m x
38m.
Tuning parameters:
Fator A = 0.45;
Fator B = 0.85;
Fator C = 7.0. 5.5
7630
1538
7.100.785.045.0
0.1
0.1
15
60
'





HR
N
sublevel stoping
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The point (N ', SR) graph shows the stability at the boundary between the
stable and unstable areas, which indicates that the hydraulic radius is
maximum 5.5 wise dimension to be applied to the stope.
sublevel stoping
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The point (N '= 10.7, HR = 5.5) in the stability chart
sublevel stoping
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If the stope has a setting that indicates high possibility
of subsidence, there are alternative design to make it more
stable.
Example: lower your volume or leave pillars inside the stope ...
sublevel stoping
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Another alternative to improve stability: strengthen (s)
face (s) of the stope with cablebolts ...
The stopes can also receive fill (backfill) after
extraction of the ore.
sublevel stoping
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Filling of stopes* ...
 Fits relief and redistribution of stresses in the massif.
 To be left empty, the stopes can begin a process of caving when they
started is hard to stop and much of the infrastructure and mine reserves
can be lost.
 Common fillers are CHF (cemented hydraulic fill) and Paste Fill. One
advantage of the paste fill is that there is little water to drain, compared to
CHF.
 Once the stope is empty, it is blocked at the bottom, with the construction
of barricades (bulkheads).
 It is also equipped with vents which connect with the inner part of the
stope and allow water drainage.
 The stope filling in a short period of time produces great pressure on
bulkheads, which can rupture, with risk to facilities and staff.
 Paste fill is safer because in the event of breakage of bulkheads material
spreads over shorter distances, due to the lower amount of water in the
composition.
*Sloane, L., 2010. Sublevel open stoping: design of the O640, L651 and N659 sublevel open
stopes in the 3000 orebody of the Mount Isa copper mines, Queensland, Australia.
Department of Mining, University of Pretoria.
sublevel stoping
28

To investigate the differences
between the stope volume designed /
performed and estimate the dilution
involved in the process, there are now
the CMS (Caving Monitoring System)
devices.
Laser devices are making a scan of the
internal void of the stope.
A definition for dilution:
Dilution = (sterile ton produced) / (ton of ore Planned)
sublevel stoping
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The number of stopes,
dimensions and mining sequence
must relate to the programmed so that
suffice 60% to 80% of the stopes
developed to perform it daily
production.
The remaining stopes should be
available for production if any of the
planned stopes are out of action.
Stopes also provide extra flexibility to
maintain a relatively constant level of
power plant.
Inside view of a stope already plowed 
sublevel stoping
30

Drawpoints
Excerpted from:
Wise, J. J., 1982, “Loading and hauling equipment for use in caving
and sublevel stoping”. Design and operation of caving and sublevel
stoping mines. p.683-691.
Drawpoints are basic elements of development methods
used in sublevel stoping, sublevel caving, block caving,
shrinkage, VCR and others.
Can be positioned:
-in sublevels production when using sublevel caving-;
-na base level or ore body, when it is used block caving,
sublevel stoping and VCR.
Prof. Dr. H.Z. Harraz Presentation sublevel stoping 31

Drawpoints
sublevel stoping
32

Sublevel Stoping
Predominant equipment used in loading and drawpoints until
the 50s transport:
scrapers / slushers
overshot loaders
transport on rails.
Characteristics of these devices:
long-Change from a local operation to another, which can
lead to low utilization;
-facilities designed to operate in horizontal planes, which
should be interconnected by raising. Raises are expensive
and unsuitable for moving large equipment.
sublevel stoping
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After the 50s:
 ramps access between levels, using equipment on tires
(LHD's) and higher productivity, to load / transport of ores,
personnel and materials.
 Drilling long and large diameter, causing the
mechanization of the structural development of the
drawPoint.
Consequences of the use of equipment on tires:
 Need galleries with larger section because the equipment
is larger;
 development of spiral ramps which slope must be
carefully chosen;
 the management of highways, drainage, better ventilation
and more technical mechanical maintenance.
Sublevel Stoping
sublevel stoping
34

As LHD’s:
 allowed the development of access ramps
steeper (lower development costs) and
provided better equipment utilization;
 used along with drills on tires, simplify
development of drawpoints, reducing the
execution time (see Figs. next slide).
Sublevel Stoping
sublevel stoping
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Basic factors for the system on tires:
 drawpoint drifts enough to LHD's width;
 Ventilation suitable for diesel;
 large interval between drawpoints;
Long-system transport in various dimensions, or
orepass leading to long transport system in lower
levels;
 Several sites distant work (for diesel engines).
Sublevel Stoping
sublevel stoping
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Sublevel stoping..Underground mining methods

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