The Block Cave Mining Method

Block caving is a large-scale underground mining method applicable to the extraction of low-

grade, massive ore bodies. With the amount of literature available on block caving this report

identifies the need to provide a simple understanding of the process. Understanding a

production process of a block cave mine is an important aspect before getting involved with

technical aspects of the mine. This report attempts to give an introduction into the production

process of a block cave mine and also an understanding about block caving.

The document has been split into four chapters,

Chapter One gives a basic understanding of the method and highlights the considerations that

have to be made before the implementation of a block cave mine.

Chapter Two gives an introduction into the production process involved in a block cave mine by

taking into account four major levels involved in production. The production process has been

described in the form of a flow chart for simple understanding of the process.

Chapter Three outlines the significance of production control and production management in

order to increase productivity of the mine.

Chapter four outlines some of the safety and risks involved in a block cave mine and the

necessary precautions to be taken in order to increase safety.

This report has been intended to provide a simple understanding of the block cave mining

method and the production process involved. This report is advocated towards a layman in

block caving in view of getting an impression about the block cave mining method.

Contents

Chapter One - Introduction

1.1 Block Caving

Block caving is an underground mining method applicable to the extraction of low-grade,

massive ore bodies with the following characteristics:

large vertical and horizontal dimensions,

a rock mass that will break into pieces of manageable size, and

a surface that is allowed to subside.

These rather unique conditions limit block caving to particular types of mineral deposits. Block

caving is used for extracting iron ore, low-grade copper, molybdenum deposits, and diamond-

bearing kimberlite pipes.

1.1.1 Block Caving Method

A large slice of material is blasted at the base of the ore body which creates an instability within

the orebody, inducing the breakdown and mobilization of ore to the production level through

the breakdown of ore and waste due to the natural pattern of breakages, development of

stresses in the active caving area, and the low strength of the rock mass. The size and shape of

the undercut depends on the characteristics of the rock mass.

Excavations are created at the production level at base of the orebody to draw out the broken

material. A large amount of development expenditure is required to set up the facilities to

break the lowest level of the ore body, and all the broken rock is extracted out of the block cave

through a system of drawbells. Once the caving is initiated, operating cost of the block cave is

very low - comparable to the operating costs in open pit mining.

Once caving is initiated, production can be ramped up until the production rate is almost equal

to the caving rate. The undercut is advanced in the horizontal plane to create greater areas of

caving for increasing the production.

Rock breakage occurs only in the caving areas, induced by undercutting, and has low drilling

and blasting cost; some amount of blasting may be required at the drawpoints1 to break some

of the large rocks coming through the drawbell, especially during the initial stages of draw.

Most block caves these days are highly mechanized with large number of large LHDs (load-haul-

dump machines) working at the lower levels, though smaller orebodies can also be caved and

extracted using gravity draw systems with orepasses2 and slushers3.

The development of a conventional gravity flow system of block caving involves

Figure Conventional Gravity Flow System

http://technology.infomine.com/reviews/BlockCaving/assets/images/BlockCaving1.jpgSource:

Infomine Block Caving

1A spot where gravity fed ore from a higher level is loaded into hauling units

2A vertical or inclined passage for the downward transfer of ore

3A mechanical drag shovel loader

an undercut where the rock mass underneath the block is fractured by blasting;

drawbells beneath the undercut that gather the rock into finger raises4;

finger raises that draw rock from drawbells to the grizzlies;

a grizzly level where oversized blocks are caught and broken up;

a lower set of finger raises that channel ore from grizzlies to chutes for train loading - the finger

raises are arranged like the branches of a tree, gathering ore from a large area at the undercut

level and further channeling material to chutes at the haulage level; and

a lowermost level where ore is prepared for train haulage and chute loading.

When LHDs are used, the development required is considerably less complex and involves

Undercut Levelhttp://www.edumine.com/xcourse/xblock101/docs/figures/images/10002x.jpg

Extraction LevelSource: Infomine Block Caving

4Steeply sloping openings permitting caved ore to flow down raises through grizzlies to chutes

on the haulage level

an undercut where the rock mass underneath the block is fractured by blasting;

drawbells constructed between the undercut and extraction levels;

an extraction level with drawpoints at the base of drawbells; and

an ore haulage system to collect, crush and transport the ore out of the mine.

Underground Mining Methods

Unsupported

Artificially Supported

Pillar SUpported

Shrink Stoping

Bench and Fill Stoping

Room and Pillar

Sublevel Mining

Longwall Mining

Sublevel and Longhole Open Stoping

Block and Panel Caving

VCR Stoping

Cut and Fill Stoping

1.1.2 History of Block Caving

Late 19th century: precursor to modern block caving developed in the Pewabic iron ore mine,

Michigan, USA

Early 20th century: the block caving method developed in the USA for iron ore and then copper

mining in the western states

1920s: block caving started in Canada and Chile

Late 1950s: block caving introduced into southern African diamond mines and then chrysotile

asbestos mines

Late 1960s: LHD vehicles developed for underground mining

1970: LHDs used with block caving at El Salvador mine, Chile

1981: mechanised panel caving introduced in the primary ore at El Teniente mine, Chile

1990s: planning of the new generation of block caves with larger block heights in stronger

orebodies (e.g. Northparkes, Palabora)

2000s: planning and development of super block caves under existing open pit mines (Grasberg,

Chuquicamata, Bingham Canyon) and at great depth (Resolution Copper)

http://www.edumine.com/xcourse/xblock101/docs/figures/images/10003x.jpg

Source: Infomine Block Caving

1.2 Management Organizational Chart

Mine Manager

Technical Services Superintendent

Technical Services Superintendent

Mine Superintendent

Human Resource

Logistics

Electrical

Mechanical

Cave Development

Cave Production

Ventilation

Projects

Geo-Technology

Geology

Survey

Long Term Planner

Short Term Planner

Design

The organizational chart might differ based on the requirements of a specific mine.

1.2.1 Managerial Responsibilities:

Mine Manager is responsible for the overall management, direction and coordination of the

mine and related operations. Mine Managers are also intended to provide the technical

leadership in the area of underground mine engineering.

The focus of the Mine Manager should be on the following subjects

Ensuring underground mining activities are conducted in accordance with the Occupational

Health and Safety Act and Regulations and environmental standards

Complying with all safety requirements

Observing all company policies and procedures

Assisting with the development of production targets

Ensuring production targets are met or exceeded

Developing schedules, budget and ensuring these are controlled and managed effectively

Monitoring production results on a progressive basis and preparing monthly progress and

variance reports

Maintaining effective working relationships with Contractors, Suppliers and Service Providers,

and ensuring adherence to contractual requirements

Developing a sense of continuous improvement

Ensuring appropriate training programs are in place to meet safety and production

requirements

Maintaining knowledge of current statutory requirements and industry best practices and

ensuring compliance at all times

Interphases with other managers and superintendents as part of the management team

Reviewing mining methods

Implementing optimisation programs where appropriate

Managing manpower levels to achieve their performance

1.3 Parameters to be considered before the implementation of cave mining

Twenty five parameters that should be considered before the implementation of any cave

mining operation are set out in Table 1. Many of the parameters are uniquely defined by the

orebody and the mining system.

No.

Parameters

Considerations

1

Cavability

Rockmass Strength

Rockmass Structure

In situ stress

Hydraulic radius of orebody

Water

2

Primary Fragmentation

Rockmass strength

Geological structures

Joint/fracture spacing

Joint condition ratings

Stress or subsidence caving

Induced stress

3

Drawpoint Spacing

Fragmentation

Overburden load and direction

Friction angles of caved particles

Practical excavation size

Stability of host tockmass

Induced Stress

4

Draw Heights

Capital

Orebody geometry

Excavation stability

5

Layout

Fragmentaion

Drawpoint spacing and size

Method of draw

6

Rockburst Potential

Regional and induced stresses

Rockmass Strength

Structures

Mining Sequence

7

Sequence

Cavability

Orebody geometry

Induced stresses

Geological environment

Influence on adjacent operations

Rockburst potential

Production requirements

Water inflow

No.

Parameters

Considerations

8

Undercutting Sequence

Regional stresses

Rockmass strength

Rockburst potential

Rate of advance

Ore requirements

9

Induced Cave Stresses

Regional stresses

Area of undercut

Shape of undercut

Rate of undercutting

Rate of draw

10

Drilling Blasting

Rockmass strength

Powder factor

Rockmass stability

Required fragmentation

Height of undercut

11

Development

Layout

Sequence

Production

Drilling and blasting

12

Excavation Stability

Rockmass strength

Regional and induced stresses

Rockburst potential

Excavation size

Draw height

Mining Sequence

13

Primary Support

Excavation stability

Rockburst potential

Brow stability

14

Practical Excavation Size

Rockmass strength

Insitu stress

Induced stress

Caving stress

Secondary blasting

15

Draw Method

Fragmentation

Practical drawpoint spacing

Practical size of excavation

16

Draw Rate

Fragmentation

Method of draw

Percentage hangups

Secondary breaking requirements

17

Drawpoint Interaction

Drawpoint spacing

Fragmentation

Time frame of working drawpoints

No.

Parameters

Considerations

18

Draw Column Stresses

Draw-column height

Fragmentation

Homogenity of ore fragmentation

Draw control

Height-to-base ratio Direction of draw

19

Secondary Fragmentation

Rock- block shape

Draw height

Draw rate-time dependent failure

Rock-block workability

Range in fragmentation size

Draw control program

20

Secondary Blasting

Secondary fragmentation

Draw method

Drawpoint size

Size of equipment and grizzly spacing

21

Dilution

Orebody geometry

Fragmentation range of unpay ore and waste

Grade distribution of pay and unpay ore

Mineral distribution in ore

Drawpoint interaction

Secondary breaking

Draw control

22

Tonnage Drawn

Level interval

Drawpoint spacing

Dilution percentage

23

Support Repair

Tonnage drawn

Point and column loading

Secondary blasting

24

Extraction

Mineral distribution

Method of draw

Rate of draw

Dilution percentage

Ore losses

25

Subsidence

Major geological structures

Rockmass strength

Induced stresses

Depth of mining

Source: Laubsher

Chapter Two -Production Process

2.1 Block Cave Mining System

In a Block Cave Mine there are four major levels that contribute to the production of the mine.

The levels that have been taken into account here are

Extraction

Undercut

Haulage

Ventilation

In a natural progression of a block cave mine the infrastructure that need to be built before the

start of caving includes

Primary access to the production levels (ramps and shafts)

Extraction level excavations

Haulage and Ventilation level excavations; and

Crushing and ore transport facilities.

While most of these excavations need to be created before the start of caving operations,

construction of some extraction, haulage and ventilation level drifts can be planned just in

advance of actual caving operations.

Each of these levels is given a brief introduction and the production process for each level are

outlined from collecting data from different sources. The information flow in the form of a flow

chart is provided for ease of understanding the process. The information flow chart provided is

implemented from personal experience and its objective is to provide an impression on the

production process of an underground block cave mine.

2.2 Extraction Level

The extraction level is the main production level in a block cave operation. All the ore from the

block cave is drawn through draw points at the extraction level and then transferred to haulage

level through a system of ore passes or a fleet of LHDs. Since this is the main production level, it

is developed and supported to counter the stresses and displacements that can be expected

during the life of the drawpoints at the level.

The arrangement of drawpoints, drawbells and other excavations on the extraction or

production level is referred to as the extraction level layout. The development of the extraction

level and the drawbells creates two types of pillars. The major apex is the shaped structure or

pillar above the extraction level formed between two adjacent drawpoints but separated by the

extraction or production drift. The minor apex is the shaped structure or pillar formed between

two adjacent drawbells on the same side of the extraction drift.

The drawpoint spacing, the drawpoint width, and the distance between the undercut and

extraction levels are all designed based on the fragmentation expected within the block cave.

The ground support installed in the excavations at the extraction level is based on the

characteristics of the rock mass and the expected stress levels at different locations.

2.2.1. Drawbells

The ideal shape of the drawbell is like a bell, so that ore can flow to the drawpoint. However it

is a compromise between strength and shape. The major and minor apexes must have

sufficient strength to last out the life of the draw. It needs to be established how much

influence the shape of the drawbell has on interaction. It has always been an empirical point

that shaped drawpoints improve ore recovery as the ore should have better flow characteristics

than a drawbell with vertical faces and a large flat top major apex. The time consuming

operation is creating the drawbell. The undercut technique also determines the shape of the

major apex and importantly the shape of the drawbell.

The draw rate from the drawbells is an important factor in that it must provide space for

caving; also it must not be too fast to create a large air gap and possible air-blasts. If the draw

rate is too fast seismic activity will occur. Production must be based on this value and not rely

on economic factors such as short term return on investment that ignores long term

consequences. There is also the fact that a slow draw rate will mean improved fragmentation.

http://1.bp.blogspot.com/-

QS9_mgbfCs4/UG4oJRCZ3VI/AAAAAAAAKrY/OxLwja6s4CA/s1600/rock+flow+1b.jpg

2.2.2 Extraction Level Production Process

Planning

Design

Equipment/People

Decision Making

Ground Support

Drawbells

Drifts

Ground Support

Development

Pathways

Ventilation

Ventilation

Blast

Hang ups

Drawpoint

Undercutting

Secondary Blasting

Ore Removal

LHDs

Ore pass full

Ore Pass

Haulage Level

Secondary Ore pass

Crusher

2.3 Undercut Level

The process of undercutting creates instability at the base of the block being caved. Block cave

mining is based on the principle that when a sufficiently large area of a block has been undercut

by drilling and blasting, the overlying block of ore will start to cave under the influence of

gravity. The process will continue until caving propagates through the entire block surface or to

the open pit above, unless a stable shape is achieved. The purpose of the undercut level is

therefore to remove a slice of sufficient area near the base of the block to start the caving of

the ore above.

The undercut level is developed at the base of the block to be caved. The caving of the block is

initiated by mining an undercut area until the hydraulic radius of the excavation reaches a

critical value. As the broken ore above it will collapse into the void so created. Vertical

propagation of the cave will then occur in response to the continued removal of broken ore

through the active drawpoints. The horizontal propagation of the cave will occur as more

drawpoints are brought into operation under the undercut area.

2.3.1 Undercutting

Undercutting is the most important process in cave mining. As not only is a complete undercut

necessary to induce a cave, but the design and the sequencing of the undercut is important to

reduce the effects of the induced abutment stress. It is essential that the undercut is

continuous and it should not be advanced is there is a possibility that pillars will be left. This

rule which is often ignored owing to the problems in re-drilling holes, results in the leaving of

pillars resulting in the collapse of large areas and consequent high ore losses. The undercut

technique also determines the shape of the major apex and importantly the shape of the

drawbell. Care must be taken that there is no stacking of large blocks on the major apex as this

could prevent cave propagation.

2.3.2 Undercutting Techniques

Conventional - The conventional undercutting sequence is to develop the drawbell and then to

break the undercut into the drawbell.

Henderson Technique - The Henderson Mine technique of blasting the drawbell with long holes

from the undercut level just ahead of blasting the undercut reduces the time interval in which

damage can occur. They have also found it necessary to delay the development of the drawbell

drift until the drawbell has to be blasted.

Advance Undercut - The advance undercut technique means that the drawpoints and drawbells

are developed after the undercut has passed over, so that the abutment stresses are located in

the massive rock mass with only the production drift.

http://www.edumine.com/xcourse/xblock101/docs/figures/images/20103.jpg

2.3.3 Undercut Level Production Process

Design

Planning

Development

Equipment/People

Decision Making

Ground Support

Ventilation

Drifts

Pathways

Undercutting

Ore Removal

Haulage Level

LHDs

Crusher

Muck Removal

LHDs

Ore Pass

Waste Dump

2.4 Haulage and Ventilation Level

The haulage and ventilation levels lie below the extraction level. They need to be developed

with adequate excavations to handle the quantity of broken ore and ventilating air streams

required for the designed production rates, equipment and manpower employed within the

block cave.

Facilities for storing, crushing and conveying the broken ore to the mill need to be developed at

the haulage level. The larger excavations required for the crushers, ore bins and conveyor

transfer stations need to be located outside the zone of influence of the stresses due to the

block cave, and adequate ground support will need to be installed to ensure that the

excavations are stable during their expected life.

The excavations and levels must be placed far enough apart so that there is limited interaction

between numerous excavations created to move the ore from the production level to the

milling facilities at the surface.

2.4.1 Haulage Level

Much of the development of the infrastructure for a block cave operation is completed during

the pre-production stage though some haulage lines and ventilation drifts and raises may be

deferred to later in the life of the block cave. Scheduling the development of haulage and

ventilation drifts needs careful planning so that the required facilities are in-place well in

advance of their requirement. Though there is some flexibility in the development of these

levels since they are different elevations and lie below the extraction level, the preliminary

layouts need to be prepared so that the flow of materials, ore and ventilating air can be

integrated without interruption as the block cave progresses.

http://www.accessscience.com/loadBinary.aspx?filename=720500FG0070.gif

2.4.2 Ventilation Level

Ventilation Levels are normally developed between the haulage and the extraction levels.

During the development phase air is streamed through the undercut and extraction levels to

the working faces and exhausted through the raises to the ventilation level. During production,

air is coursed through the extraction level and exhausted through the ventilation raises to the

exhaust side of the ventilation level. Additional air is provided at the working areas through

ventilation raises which connect to the intake of the ventilation level

2.4.3 Haulage Level Information Chart

Scoop

Ore Removal

Haulage Level

Haul Distance Optimization

LHDs

Crusher

Figure Haulage Level Information Chart

2.4.4 Ventilation Level Information Chart

Auxillary Ventilation

Intake Raise

Exhaust Raise

Fresh Air

Exhaust Air

Drifts

Pathways

Fans/Vent Ducts

2.5 Financial Model

Chapter Three - Production Control

3.1 Departments in a block cave mine involved in Production Control

Design

Planning

Geology

Geo-technology

Ventilation

Maintenance

Cave Development/Production

Survey

Construction

Electrical

Mechanical

Human Resource

Safety

In a Mine Environment each and every department plays a crucial role to keep the Mine

running and to meet the production targets. Problems associated with these departments no

matter how small they may be contribute damage in their own way to dampen the production.

Production planning for block cave operations can be complex. The factors to be considered

include geotechnical constraints, cave shape, draw point development sequence, draw point

productivity, production block limits such as loader capacity and ore pass capacity and variable

shut-off grade mining costs. The nature of the problem also changes during the life of a cave

from initial production build up to final closure.

Overall objective for production planning should be to maximize productivity, some of the

aspects of production planning include

Minimum/Maximum tonnage per period

Maximum total tonnage per draw point

Ratio of tonnage from current drawpoint compared with other drawpoints.

Height of draw of current draw point with respect to other drawpoints

Percentage drawn for current draw point with respect to other drawpoints

Maximum tonnage from selected groups of drawpoints in a period.

3.2. Production Control Major Concerns

3.2.1 Fragmentation

Rock fragmentation is the fragment size distribution of blasted rock material, in caving

operations fragmentation has a bearing on

Drawpoint spacing

Dilution entry into the draw column

Draw control

Drawpoint productivity

Secondary blasting/breaking costs

Secondary blasting damage

Primary Fragmentation

Caving results in primary fragmentation which can be defined as the particle size that separates

from the cave back and enters the draw column. The data to be considered for the calculation

of the primary fragmentation is

In situ rock mass ratings

Intact rock strength

Mean joint spacing and maximum and minimum spacing

Orientation of cave front

Induced stresses

Secondary Fragmentation

Secondary fragmentation is the reduction in size of the primary fragmentation particle as it

moves down through the draw column. The processes to which particles are subjected to,

determine the fragmentation size distribution in the drawpoints. The data to be considered for

the calculation of the primary fragmentation is

The effect of fines cushioning

Draw strategy and draw rate

Rock block strength

Shape of fragments

Frictional properties of fragments

Column height

Fragmentation is the major factor that determines productivity from a drawpoint. Fine material

will ensure high productivity.

3.2.2 Draw control

Draw control is one of the major concerns that need to be optimized in order to increase

productivity of the mine. Geomechanical issues related to draw control have played a dominant

role in efforts to reduce stress and improve fragmentation and reduce dilution.

Draw control is the practice of controlling the tonnages drawn from individual drawpoints with

the object of

Minimising dilution and maintaining the planned ore grade.

Ensuring maximum ore recovery with minimum dilution.

Avoiding damaging load concentrations on the extraction horizon.

Avoiding the creation of conditions that could lead to air blasts or mud-rushes.

The following have to be considered for draw control strategy in order to maximize

productivity,

Any factors observed during the start of caving that will influence the planned caving and

drawdown processes.

Control the draw from the first tonnage into the drawpoint.

Define the potential tonnages and grades that will be available from each drawpoint.

The draw control system must be fully operational.

Confirm that the planned draw strategy is correct.

The recording and analysis of the tonnages drawn, this important aspect is often not treated

with the required respect.

Managing the draw by following the adopted draw strategy.

Define how the control is to be monitored, maintained and audited.

Planning for how the draw column would behave with time.

An estimation of the remaining tonnages and grade for future production scheduling and

planning.

Personnel must be aware of the definition of isolated drawpoint.

Ensure the drawpoints are clearly and correctly identified underground.

There must be reporting system to record and describe why allocated drawpoints have not

been drawn.

Ensure secondary breakings are done effectively and efficiently.

Develop standard procedure for close drawpoints.

Draw control is what block caving is about, the reasons for and the principles of draw control

must be clearly understood by all operating personnel. Preparation of orebody must be done in

a sound way so that preventable problems do not hamper the draw control.

3.2.3 Secondary Breaking

Irrespective of the method of primary blasting employed, it may be necessary to reblast a

proportion of the rock which can then be handled by the loading, hauling and crushing system.

There are four types of problems that cause a need for secondary breaking,

High hang-ups are where a large fragment lies across the entrance to the draw bell up to 19m

above the footwall. This type of hang up is very rare though, and it is more common that this

will only occur up to a distance of 5 m above the draw point floor.

Rock jumble is where several ore fragments of rock smaller than two cubic meters form an arch

in a drawbell. This is found to occur especially in the troat of the drawpoint.

Low hang up is a large fragment of over two cubic metres hanging in the troat or on the floor of

a draw point clocking the flow of ore.

Draw point oversize is any large fragment over two cubic metres on the floor of a draw point

and effectively prevents loading by LHD's.

Some of the techniques that are in use for secondary breaking are as follows,

Concussion blasting

Drill and blast

Emulsion secondary blasting

Robust hydro fracturing breaking system

There are many products on the market today that promise effective secondary breaking of

both hang-ups and boulders, including cone packs, the quick draw system, the boulder buster

and the penetrating cone fracture technique.

In order to choose a secondary breaking method with respect to productivity the following

need to considered and evaluated,

Explosive quantities

Labour and Equipment requirements

Fragmentation

Safety

3.2.4 Equipment

3.3 Significance of Production Management

Production management is a necessary part of any mining operation. Mining operations consist

of more than equipment; there are also people, material, processes and systems. With a proper

production control we can

Reduce mining costs and increase mine production

Achieve high face utilization

Improve mine safety

Optimize mine development

Comply with mining plans and performance targets

Increase control over the mining operation

Flexibility in production control

Safety

Design

Construct

People

Underground Mining Strategy

Operate

Technical

Technology

3.3.1 Production Management an Integrated Approach

Block cave planning is a challenging task that is dependent upon effective predictive modeling

of the rock mass and the mining system. The planning methodology of several operations

worldwide does not seem to have an integrated approach to planning. The lack of integration

challenges realistic production plans and potentially results in conservatives using more

resources than needed to achieve desired production targets.

In a research that had been conducted to identify the integration approach towards production,

four main models had been acknowledged in order to sustain the regular mine planning

activities.

Fragmentation Model

Geomechanical Model

Geological Model

Reconciliation Model

Fragmentation Model estimates the ultimate fragmentation that leads to the estimation of

mine design, missing parameters, mining equipment and draw point productivity.

Gemechanical Model inducts the mine design into a three-dimensinal stress analysis that can

simulate effect form a stresses point of view of different mining strategies in conjunction with

the mining plan. The main output of this model will be stress distribution on the cave back,

front cave and induced stresses due to differential draw across the active layout.

Geological Model links data relating to structure lithology and mineralogy with the ultimate

metallurgical recovery. This model aims to build the information towards a geo metallurgical

model that can provide a reasonable estimate of the metallurgical recovery based on the

combination of the composite lithologies.

Reconciliation Model is one of the most important models supporting the mine planning

system. It provides the tools to analyze the historical behaviors of the mine. It can capture

information on the underground mine and will provide a set of reliability measures regarding

the compliance with different production plans. This model also provides the information to

feed the fragmentation and geo mechanical models to calibrate and reconcile the initial

estimates.

Geomechanics Model

Fragmentation Model

Production Targets

Production Sequence

Production Planning

Development Rate

Draw Rate

Draw Method

Reserves Model

Reconciliation Model

Geological Model

Economic Parameters

Chapter Four - Safety

4.1 Safety and Risks

Block cave mining has been termed as a safe mining method primarily due to the limited

number of supervision areas, concentrated work areas, smaller work force requirements and

higher degree of mechanizations. Even with these advantages towards block cave mining

method there are risks involved towards safety and some of these risks have been highlighted

in the report.

4.1.1 Air-Blasts

An air blast is the rapid flow of air through an underground opening flowing compression of the

air in a confined space, most frequently caused by the sudden fall of a large volume of rock. The

air in the void is expelled at high velocity and pressure through available excavations is capable

of even blowing off equipment's.

Preventive measures to be considered in order to minimize the consequences of air blast

include

Maintaing drawpoint drifts, drawpoints covered with ore material.

Maintaining an emergency procedure.

Maintaining permanent seismic monitoring.

Constant communication with personnel.

4.1.2 Rock-Bursts

A rock burst is the uncontrolled disruption of rock associated with a violent release of energy

and can cause significant damage to tunnels and other excavations in the mine. Rock bursts can

be light, medium or heavy depending on the energy released and the volume of rock displaced

into the mine excavations.

Preventive measures to be considered in order to minimize Rock bursts include

Limit stresses induced in the extraction level.

Monitor mine seismicity.

Automate mining equipment to limit the exposure of personnel to the hazard.

Use dynamically capable support systems.

4.2 Emergency Response Plan

Prompt action is required to control mine fires, explosions, entrapments, and inundations.

According to the Health, Safety and Reclamation Code for Mines in British Columbia, the Mine

Emergency Response Plan (MERP) should outline essential procedures to be taken in the event

of a hazardous incident.

The MERP will guide personnel in determining the following constraints,

What actions can be taken to prevent an emergency

What precautions would minimize the effects of an emergency

What immediate actions mine personnel should take to contain emergency

Whether mine employees have the skills necessary to carry out the procedures outlined within

the MERP

Who will assume temporary command of the emergency effort

Who is in charge of which parts of the emergency operation

What kinds of special services and mutual aid support are available to sustain rescue actions

How key personnel will obtain information and assess reports to make critical decisions

Effective media relations procedures

An established MERP is critical to a mines ability to contain an emergency before it becomes

out of control. A MERP ensures that supervisory and other personnel know exactly what to do

to prevent and control an emergency.

Mine operators develop standard response procedures for emergency situations by organizing

and preparing personnel to function and respond effectively. Emergency response procedures

include

Assisting personnel in responding quickly and effectively to an emergency

Providing a common set of practices that govern the activities needed for an orderly response

Outlining strategies for early containment and control of an emergency

Establishing common set of rules for training all emergency response personnel

4.3 Refuge Chambers

The need for some form of refuge chamber in underground mines has long been recognized.

Early types were frequently a redundant excavation, which was blocked off to provide an

enclosed space where the atmosphere could be over pressured using compressed air sourced

from the mine system. This basic model has evolved to incorporate more functionality and

increased sophistication. The increasing prominence of diesel-powered trackless equipment

and a greater awareness of the needs of the workplace have provided the impetus to develop

self-contained chambers that can be readily relocated to support the mining operation as it

progresses.

4.3.1 Location

Distance from workplace

Refuge chambers should be sited near active workplaces, taking into account the needs of

people working there and potential hazards they face. It is recommended that the maximum

distance separating a worker from a refuge chamber be based on how far a person, in a

reasonable state of physical fitness, can travel at a moderate walking pace.

Capacity

The primary function of an underground refuge chamber is to provide a safe haven for people

working in the immediate area in the event of the atmosphere becoming irrespirable.

The chamber size should recognize that other personnel such as supervisors, surveyors,

geologists and service technicians may also need to use the facility. The number of such people

in the workings from time to time can require:

Provision for a refuge capacity more than double that determined from the size of the locally

operating crew alone.

Implementation of a system to limit the number of personnel in the area.

Safety of location

A refuge chamber is perceived as the ultimate place of safety in an underground emergency. Its

location should therefore be secure and chosen taking into consideration the below mentioned

conditions

Exposure to hazards

Adequate ground conditions

Safe from accumulation of water

4.3.2 Support of life

Modern refuge chambers typically operate under three separate and complimentary regimes -

stand-by, externally supported and stand alone.

When there is no emergency, chambers operate under stand-by conditions. No survival systems

are activated. The emergency power pack is kept charged an, if fitted, chamber monitoring and

communication systems are enabled.

A chamber is expected to operate under externally supported conditions when there is an

emergency but no disruption to normal electrical, pneumatic and potable water services. These

services, if provided, are available for the continued support of the chamber.

The stand-alone condition arises when a chamber becomes disconnected with total

independence to ensure the survival of its occupants, in the most stress-free manner possible.

http://www.mininghealthandsafety.com/files/page_text/images/7211209396219.jpg

4.3.3 Modern Refuge Chamber Requirements

Capsule

Oxygen Supply System

Air Purification and Temperature and Humidity Adjustment System

Environment Monitoring System

Communication System

Capsule Illumination and Indication System

Power Supply Guarantee System

Survival Guarantee System

Mine Refuge Chamber

5. Future Innovations/Availability in Block Caving

6. Conclusion