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 7: Underground Mining Methods Longwall Sublevel Caving Block Caving
Longwall; Longwall in coal; Longwall in Hard Rock; Sublevel Caving; Characteristics of the ore body and mining method; Development; Production; Equipments Used; Block Caving, Introduction, Historical evolution of the method, Condition deposit; Principles of the method; Methodology of block caving; Basic issues of geomechanical to the black caving method; Caveability;Mine design Block caving; Fragmentation and extraction control; Subsidence associated; Advantages and Disadvantages of Block Caving
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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.
The extraction proceeds during the strike, with the dismantling of the face done with the aid of explosives.
The ore is disassembled collected with a scraper and taken to a orepass.
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Sublevel
Caving
Topics Characteristics of the
ore body and mining
method
Development
Production
Equipments Used
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Characteristics of the method ...
Sublevel Caving in the process of
fragmentation of the ore is done by explosives
(induced caving) and the ore is detonated with
drilling in ascending fans. The sterile overlying
should crumble as the ore is removed.
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Characteristics of the orebody and enclosing
massive and/or tabular (varying inclinations are allowed);
Diving > 50o case is thin;
competent body with mineral rock wall rock (cover) fractured;
stable development of the footwall to access;
the method requires minimal stability to the ore body, because the
galleries sublevel should be self-supporting piece and can receive
routine bolting;
significant dilution, very little sensitive to fragmentation;
likely surface subsidence;
rock cover must accompany the ore in a continuous felling,
producing subsidence at the surface. The ideal condition is
that the enclosing fragment into larger blocks which ore
disassembled to facilitate flow separation at the extraction
drift.
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Design alternatives for dips and varying thickness of
the ore body
Tabular ore body and thick makes all production galleries are always in
the ore, avoiding fans incomplete perforation (loss of ore), open galleries in
sterile (the roof support problems and expenses), losses along the footwall
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Design alternatives for dips and varying thickness of
the ore body
Losses ore
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Design:
transverse sublevel caving – for thick bodies
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Design: transverse sublevel caving - this case, the galleries of production (drifts) are perpendicular to the
strike of the ore;
- Mining recoveries are greater than the longitudinal layout.
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Design:
longitudinal sublevel caving – for narrow bodies
and sharp dip
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Development in Sublevel Caving
The method requires significant development, being part of ore (in high producing mines, 6% of the
total ore mined comes from developing).
The cost / ton of ore in the development is several times higher than in production. Should
maximize production and minimize development.
The ore body is divided into panels whose height varies from 50 to 250 m in height, depending on
the scale of production and reserves per vertical meter.
Each panel is divided into sublevels spaced 20-30 m (increasing the spacing between sublevels
minimizes the development) which will be issued successively downward.
The lower level of the panel is characterized by a main gallery of transportation that serves all
"orepasses", connecting the premises of the extraction well.
Access to sublevels is accomplished by a ramp situated between the ends of the ore body. The
ramp is linked to gallery transporting each sublevel. This gallery of transporting each sublevel must
accompany the footwall contact at a distance 15-20 m.
In transverse sublevel, crosscuts traverse the deposit, going to the hanging wall; development is in
the footwall. Starting in the transport gallery, galleries are open from distant production center-to-center 15-25 m, parallel to each other, extending to the contact with the footwall. Have dimensions
(width x height) 5x4 m; 6x5 m; 7x5 m.
Sublevel of the galleries, just above the ore is drilled and drilling with longholes in range.
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Production in Sublevel Caving
The production begins when the galleries of a sublevel reach the subsequent
contact.
These galleries do not come into general production while, but should not retreat in a
un-organized way. In some mines, adopts the recoil so that its edges are coarsely
contained in a plane.
In other cases, the recoil is done so that the galleries production of more distant
"orepasses" are the first to reach the main gallery.
Equipment used for production drilling (ascending): carts with two spears, with
sectioned stems and crowns of up to 115 mm. Currently, the drills used are electro-
hydraulic and DTH's.
Drilling targeting the production is made in the form of irradiated fans of the galleries
of the sublevel. The holes made are long (up to 50 m long) and is used in this drilling
process "longholes".
Charging is done by pneumatic devices. ANFO explosive is the most common. In the
case of explosive in cartridge, it uses a similar device, equipped with blades to break
through the cartridge.
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One way to start is
dismantling create a free face
(slot relief) with a hole pattern
up to an inclination of approx.
80 to 90.
Another way is to open the
slot from a raise.
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LHD's perform the loading, transport and unloading of ore in the end "orepasses" being
sublevels designed for better efficiency of loaders.
Drilling operations and loading are performed independently and at different levels.
Due to the large number of galleries sublevel there are many fronts production
The explosive consumption is high due to the fact the dismantling be carried out
against the mass of fragmented rock.
Must be careful in removing the ore from drawpoints (you need to control levels at the
point of load):
removal of the material causes little lower recovery;
removal of too much material causes excessive dilution.
There is a cut-off grade given below which do not remove more ore in crosscut and
should detonate new range.
Production
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Equipment for development and production
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In the design of production drifts, the Sublevel Caving uses the
principles of "gravitational flow" ore dismantled, with subsequent
collapse of the host rocks.
Approaches used to issue a gravitational flow:
A) The physical-scale models B) field experiments in real scale C) models mathematical / numerical.
The solutions found so far are not fully satisfactory from the
standpoint of optimization of the gravitational flow of the ore.
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These models are the oldest, made with particles (e.g., sand),
leaking containers of small size.
A) Example test with physical scale models:
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Two major factors related dilution and ore recovery (*)
Width (c) extraction of the gallery;
Clearance (V) between ranges of production
(*) View Article : Theory and pratice of very-large-scale Sublevel Caving. Underground Min. Methods: Eng. Fundamentals and International Case Studies, 2001, W.A.Hustrulid & R.Bullock. Chapter 46, p.381-384.
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Width (c):
A gallery of production should be as wide as possible;
When the ceiling of the gallery is concave, the flow of
ore is very centralized and inefficient sides, requiring
closer galleries.
The amount of ore away from LHD's increases with
the increase of the height of the gallery production.
Therefore, the height should be as low as possible.
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Examples of ancient settings production galleries...
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Are directly executed in underground mines,
where they put up markers (markers) numbered, to be
retrieved and counted after detonation.
A recent experiment shows that the
flow of ore is mainly formed by the
material above drawPoint, but he is not
very predictable.
(Quinteiro, C R, Larsson, L and Hustrulid,
W A., 2001. Theory and practice of very
large scale Sublevel caving. Underground
Min. Methods- Eng. fundam. and
Intern. Case Studies SME)
B) Real Scale Experiments:
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Experiments on real scale: Recently, Sublevel Caving mines have increased lateral spacing interval
drifts and sublevels.
This has increased production, but also increased dilution.
There are still several outstanding questions about the best production
design in this method.
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There are several numerical models being investigated to explain the influence
of the main variables of the method.
Among the principal's PFC - numerical code developed by Itasca group since
the 1990s PFC = Particle Flow Code.
C) Mathematical / numerical models:
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Principles of choice of the configuration of production galleries: the idea of minimization of production costs leads to employ the maximum vertical spacing
between sublevels (currently around 30m);
essential for maximum spacing between sublevels ... ability to drill and carry long, straight holes
and large diameter factor;
the largest possible diameter hole, which allows drilling and loading, is ideal (the maximum is
now 115mm);
large galleries (7x5m, for example) allow the use of drill pipe and longer rectilinear holes (few
rods provide increased rigidity to the drillstring). There are projects of fans with holes up to 50m
in length;
distance between planes of fans (B):
depends on the hole diameter (D) and the type of explosive.
Initial estimate for ANFO ... B = 20 D.
For higher energy explosives ... B = 25 D.
D = 115mm and assuming emulsion as an explosive has been B ≈ 3m.
Number of holes in the array:
should follow the S / B ratio ≈ 1.3; where S is the distance between the ends of
neighboring holes in the same range.
In this case (B = 3m), S is 4m.
Interval between sublevels:
is chosen based on the maximum drilling capacity and the ability to maintain satisfactory
alignment of the holes.
As an example, assume 25m.
Lateral spacing between production galleries:
makes an angle of 70o between the upper gallery of the reference and the midpoint of
the gallery just above the sublevel (this is the angle of minimum theoretical expected to
drive the ore detonated). The center-to-center spacing resulting from side galleries is
approx. 22m (see Figure A1 in the next slide).
This initial configuration (Figure A1) was adapted in the 1990s to become more practical
operational point of view (Figure A2). Prof. Dr. H.Z. Harraz Presentation
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Figura A1 Figura A2
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Principles of choice of the configuration of
production galleries:
For adaptation:
effecting up to 55 lateral holes of inclination. Function of these holes ...
ore fragment lying in the slope of approximately 70 and reduce the
length of (longer) central holes of the fan.
Holes smaller than 55o inclination are difficult to load with explosives,
due to the angle of repose of the ore in drawPoint.
The fans may be vertical or inclined (α generally uses up 70 to 80o to the
horizontal). The steepening improves the stability of the roof drawPoint and
easy access for loading the holes with explosive.
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High production rate;
Many And efficient fronts of simultaneous mining;
Possibility of high degree of mechanization;
Method Safe for operators.
advantages
disadvantages
Dilution may be high (15-30%) and moderate recoveries (75-85%);
subsidence on the surface;
high consumption of explosives;
high cost of development;
intensive drilling and disassemble to generate a suitable granular product to flow ore;
controlling the cut-off level can result in low recovery of ore.
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Block Caving
Block
Caving Prof. Dr. H.Z. Harraz Presentation
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Introduction:
Block Caving* is method in which volumes of rock are left without support and suffer rebate under its own weight; the overlying rock fragments-along with the ore. The fracturing and the disposal of ore are obtained by the action of gravity and efforts resulting from tectonic and lithostatic stress.
* Translation: Allowance for blocks.
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Block caving
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Historical evolution of the method ... End of the century. xix: block caving applied to iron ore mines in
Michigan, USA;
Beginning of the century. xx: block caving applied in the USA for iron ore
and copper states in the west side;
20s: block caving starts in Canada and Chile;
50s: block caving starts in South Africa, diamond mines and asbestos;
Beginning of the 60s: LHD vehicles developed for underground mining;
1970: LHD's used with block caving mine in El Salvador, Chile;
1981: panel mechanized caving introduced in the primary ore of El
Teniente, Chile;
90: Planning new generation of mines with greater height block and ore
bodies more resistant (eg Northparkes, Palabora).
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Operating mines closed and planned using the method …
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Some data using block caving mines...
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Condition deposit Resistance ore: weak to moderate, preferably soft or friable ore with intense
fracturing;
Resistance the wall rock: similar to the ore, distinct interface between /
barren ore;
Diving: vertical is better, but can be flat if the deposit is thick;
shape: large areal extent and thick (> 30 meters);
uniform and homogeneous distribution of levels (suitable method at low
levels);
Depth: moderate (> 500m and <1200m).
Principles of the method ... In block caving method, the ore is moved by subsidence (caving) to a
cavity formed almost always without the use of drilling and blasting. Drilling
and disassemble are used in establishing the initial "enhancement".
The base of the ore is excavated by removing their support, this results in
fracturing of the ore which migrates to the enhanced vacuum and which is
then removed.
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Methodology of block caving: develop below the panel to be mined, a layout extraction of ore;
above the level of extraction, a horizon of "undercut" (highlight) will provide free
face below the ore body, causing the collapse;
temporary pillars in the "undercut" horizon are removed and the collapse of the ore
starts;
ore haggard blister and fills the void of the "undercut";
remove fragmented material in the extraction horizon, inducing flow of ore and ore
loss of support has not beaten down that is also subject to collapse;
vertical progress of "caving" is related to the extraction of fragmented ore and its
blistering.
During the flow of the fragmented ore is reduced the size of the blocks.
Primary fragmentation is done by natural mechanical process, advantageously in
terms of cost. Sometimes explosive is used in production, making long and spaced
holes to induce fracturing.
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Basic issues of geomechanical to the black caving method:
1) Caveability 2) Mine design 3) Fragmentation and extraction control 4) Subsidence associated
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1) Caveability: The process is still not well understood, but it is known that the main factors
involved.
The caving is principally defined by the rock quality (RMR, Q, etc.) and its
hydraulic radius - RH.
The basic requirement for the method to work is that the rebate (caving) occurs.
The slump of the ore is the result of the action of gravity, being influenced by:
pattern of fracturing the middle ... for good fracturing at least two families cross sub-vertical joints between
themselves and one horizontal family;
stress distribution in the area to be mined.
It is not easy to predict whether the resulting fragmentation which occurs rebate or.
A rule of thumb: For an ore body be subject to abatement, approx. 50% of the fragments should have a maximum size of
1.5m.
There are several geomechanical classifications to forecast caving and fragmentation. The
most commonly used: RMR, Q system, classification of Laubscher (1981) system.
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Geomechanical parameters observed in some mines:
Palabora Mine (copper) in South Africa ... MRMR between 57-70, which is
among the highest values for block caving (this method is not advised when
MRMR >50).
Henderson Mine (molybdenum) in Denver- USA ... with RMR 27-60.
Northparkes (copper-gold) in Australia ... features RMR between 33-54, for Lift
1 (upper part of the ore body).
El Teniente, Chile ... MRMR between 55-74, for various lithologies of the mining
area (andesites, diorites, breccias).
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Note .:
RMR classification
Developed by Bieniawski
Ranges 0-100
Main parameters:
RQD (Rock Quality Designation)
Spacing between discontinuities
Uniaxial compressive strength of rock
Quality of discontinuities
Presence of water in the rock mass
Orientation of discontinuities relative orientation of the
excavation
Rating MRMR (dev by Laubscher,. Page 413 SME book.) Similar to RMR, but includes stress induced by mining and blasting in the calculation of MRMR parameter.
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2) Mine Design : Key elements in establishing the layout of mine ...
2.1) is possible division of the area to be mined :
division separated by pillars of security blocks sequentially to be
mined;
division into blocks without pillars, with continuous mining.
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2.2) Selection of extracting ore system : The extraction system is complex, time consuming and costly preparation. Usually
requires several years of work to be put into production.
a) traditional by gravity system; b) by slusher system; c) by LHD's system.
a) Traditional gravity system - ideal for very fragmented ores: loading and transportation system developed under each block
orepasses are open and finger raises with grids
the level of fragmentation is controlled louvers
Finally enhancement is done in the block which begins the fragmentation and
migration of the ore and racks through the undercut up to the level of transport.
b) By slusher system- for medium or little fragmented ores:
development is simplified by omitting grids level. The cones migration ore bind
directly to points of discharge.
the high wear on the pillars discharge requires very resistant concrete coating.
c) By LHD's system - more modern system, to little fragmented ore: Provides greater productivity drawPoint simpler design eliminates the need for a
orepass for each drawPoint but need area larger tube (strut costs!) Due to the
size of the equipment.
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Systems ore extraction by gravity
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Systems ore extraction by gravity
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Systems ore extraction
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Ore extraction system for LHD's
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Isometric view of a system of extraction of ore per LHD`s :
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Plan view of the level of
extraction of ore to a
system with LHD`s:
Drawpoints
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2.3) Location of permanent facilities The block caving is generally used in low resistance of rocks, but
the developments and openings production (drawpoints, etc.)
must be kept in places where the rock has better quality.
2.4) Other important aspects ... drawPoint size, spacing (small fragments implies closer drawpoints),
geometry of the pillars, sequence and direction of mining.
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Typical design parameters …
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Typical design parameters …
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3) Fragmentation and extraction control: Fragmentation is difficult to predict and influence
the choice of ore extraction system and spacing
drawpoints.
The rate of ore extraction affects fragmentation:
very rapid extraction : very rapid extraction can create voids near the surface enhancement; fragments of ore become larger because they suffer fewer burdens on the mass of collapsed overlying materials; for better fragmentation stack height of caved ore must be maximized;
very slow extraction : very slow extraction can cause compaction of the ore and restore locally stable structures.
Modes of observation of progress caving: see SME Min. Eng. Handbook, 1992 pg.1820.
Accident Northparkes (1999) by sudden collapse of the ore in the abatement process.
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Examples of fragmentation obtained in some mines…
Mina
Tamanho do
fragmento
médio D50mm
Espaçamento
entre os pontos de
drenagem (m)
Grace 1.500 6,0 x 9,0
Urad 700 9,0 x 9,0
Clímax 350 10 x 10
El Salvador Minério fino
Bell Mine
Com rastelamento Com Trav Carregamento
7,6 x 7,6
12,2 x 12,2
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Examples of fragmentation inferred from borehole...
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Types of fragmentation :
• In situ ... represented by the blocks that are naturally present in the rock before mining activities;
• Primary ... represented by blocks in the vicinity of the cavity abatement and separate themselves from the massive intact when the rebate is started;
• Secondary ... occurs when blocks of primary fragmentation move for drawpoints.
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Examples of fragmentation observed in drawpoints :
Northparkes E26, Austrália Esmeralda Sector, El Teniente Mine, Chile
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Cumulative distribution
of fragmentation observed in
Premier Mine, South Africa
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4) Subsidence associated : subsidence is discontinuous and affects large
areas of the surface;
the final geometry of the subsidence area is quite
varied, depending on ... resistance ore;
resistance overburden;
presence of significant structural features (e.g., dykes, faults);
depth of mining;
natural slope of the surface.
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Examples of subsidence - kimberlites in West Africa
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Examples of subsidence - Mine El Salvador, Chile
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Examples of subsidence - San Manuel Mine, USA
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higher production rate than any other method in underground-coal
High productivity
lower production cost of underground methods, side of the Longwall (e.g., production
costs of $ 6.0 / t in the Premier Mine-South Africa)
High recovery (90% or more), but with significant dilution
production (not development) runs for abatement; i.e. there is no need for drilling and
blasting
can be highly mechanized
good ventilation and security for workers
Advantages of Block Caving
Disadvantages of Block Caving
subsidence and collapse in large scale
high dilution
control resumption is critical to the success of the method
development is slow
costly operations of support
reduction and fragmentation difficult to predict and control
method with little flexibility and no selective
possibility of oxidation of the ore due to the long time of percolation water
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the International Caving Study (ICS) Stages I and II (ICS II sponsors:
Codelco Chile, De Beers Consolidated Mines, LKAB, Newcrest Mining
Limited, Northparkes Mines, Rio Tinto Technical Services, Sandvik
Tamrock, WMC Resources Limited);
the ICS I monograph, Block Caving Geomechanics, published by the
JKMRC, 2003;
Proceedings, MassMin 2000, Brisbane;
Proceedings, MassMin 2004, Santiago, and PowerPoint presentations
made to that conference;
Rock Mechanics for Underground Mining, 3rd edition, by B H G Brady and
E T Brown, 2004;
Block Caving Geomechanics by E T Brown;
Individual works of GP Chitombo, BA Eadie, GE Flores, NJ Harries, E
Hoek, The Karzulovic, DH Laubscher, The Logan, The Moss, IA and I