sublevel stoping..underground mining methods

A short series of lectures prepared for the

Fourth year of Geology, Tanta University

2014- 2015

by

Hassan Z. Harraz

[email protected]

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 [email protected] for contact details.

Topic 4: Underground Mining Methods Sublevel Stoping

mailto:[email protected]





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

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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

MINING METHOD


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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.

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.


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Drilling in range


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Figura 2

Drilling Parallel (multi-level blasthole stoping)


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higher panel: Bighole open 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.


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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;


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The method can operate with Sublevel (fig. Below)

without recovery or Pillars.


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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 ...


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Sublevel underhand

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Sublevel overhand


sublevel stoping

Sublevel underhand


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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 raise the stope


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development

slot… Stope production …


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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.


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Intermediate slopes of the stope can cause stability problems in the hangingwall and dilution.


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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.


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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

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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).


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Fitting parameters A, B and C :


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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. 5.57630

1538

7.100.785.045.00.1

0.1

15

60'

HR

N


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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.


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The point (N '= 10.7, HR = 5.5) in the stability chart


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Configuration of stopes... 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 ...


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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.


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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.


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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)


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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 Prof. Dr. H.Z. Harraz Presentation

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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


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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.


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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


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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


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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


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sublevel stoping..underground mining methods

Education

sublevel stopingconsiderations

sublevel underhandprof

conventional stope sublevel

stope ore

open stope stability

stope extraction

graph of stability

method variations