2 literature review 2.1 introductionshodhganga.inflibnet.ac.in/bitstream/10603/32884/11/11_chapter...

6

2 LITERATURE REVIEW

2.1 Introduction

Technology is the key to higher production, productivity and safety, which depends on

the mining operations prevailing in the country. A combination of conventional and

modern technology to suit the indigenous condition and environment would give the

best results. The role of this innovative technology of mining by surface miner assumes

high importance due to the increasing complexity of mining operations in mineral

excavation. Application of surface miner is in a very active phase at different coal,

limestone, gypsum, lignite, salt, phosphate, bauxite and iron ore projects around the

globe and India, too, is catching up since early 1990s. The surface miners are machines

made for an efficient, continuous mining operation. No drilling-blasting, selective

mining, less dilution, no further crushing and fragmentation etc are the attractive

features of the surface miner technology. Presently, surface miners are contributing in a

number of projects in various parts of the globe, especially in USA, Russia, Australia

and Bosnia apart from India.

In the last few decades mineral sector in India has achieved a rate of growth higher than

that of the rate of economy (Venkateshan, 2012). By and large, this increase is

attributable to new proven technologies employed. The latest mining state-of-the-art is

the introduction of surface miners for mining soft to medium hard rock. The surface

miner is already a proven versatile machine with cutting capability for compressive

strengths up to 120 MPa (Ghose, 2008). Out of current global population of nearly 300

surface miners in productive use around the world, some 105 machines are operating in

India (Ghose, 2000). In India, coal mining by opencast is much more popular than

underground mining ever since nationalization. While about 60% of world coal

production comes from underground mines and 40% from opencast mines, in India

around 90% of the coal is produced by opencast method and only 10% by underground

methods (Anon., 2011). According to Khare (2008) the production of coal from surface

mining has increased by 2.67 times from 1974-75 till 2004-05. The ratio of coal

production from surface and underground mines was 90:10 in 2011-12

(www.coal.nic.in/Provisional coal statistics). The increasing trend of surface and

underground coal production of the last five years is shown in Figure 2.1. The increase

in overall production

(CIL), surface miners contributed about 103 million tonne of coal production in the year

2010-2011, which was 26% of the total production (Pradhan, 2012).

indicates that surface miners are being applied maximum in limestone deposit. Surface

miners are contributing in large scale in Indian limestone mines too. Statistics of

limestone production of the last five years in India is shown in Figure 2.2

(www.mines.gov.in).

Figure 2.1: Trend of surface and underground coal production in India

Figure 2.2: Production statistics of limestone in India

2.2 Surface Miners and

In surface mining, various attempts were made to develop an economically viable

alternative to conventional drill and blast technology particularly for soft to medium

2007-08

59

398

2007-08

193

in overall production is contributed mainly by the opencast mines.


2011, which was 26% of the total production (Pradhan, 2012).






and Their Development

surface mining, various attempts were made to develop an economically viable


08 2008-09 2009-10 2010-11 2011

59 59 55 52

398434

473 478

underground (MT) opencast (MT)

08 2008-09 2009-10 2010-11 2011

193222

233 238253

7

mines. In Coal India Limited


2011, which was 26% of the total production (Pradhan, 2012). The global scenario






surface mining, various attempts were made to develop an economically viable


2011-12

52

488

2011-12

253

8

hard rocks. A surface miner, also called continuous surface miner, is a technology to

extract, crush and load material in one go. The earliest continuous surface miner used

for excavating and loading soft and loose material was the elevating grader. However,

these machines were unsuitable for stiff material and also cannot negotiate boulders

(Misra, 2007). The design and fabrication of surface miner was ventured based on

mechanical excavation principle.

The first Wirtgen surface miner was introduced in 1983 to gypsum mine in South

Africa. Hofman reported the use of continuous surface miners as a technology for

opencast mines in 1987 (Pradhan, 2012). However, it took another 10 years to make this

technology on roads on mines. By the year 2008 more than 40 surface miners were

employed in limestone mines and around 50 in coal mines in India. The first break

through of surface miner (Wirtgen make – 2100SM) in Indian coal mine was in 1999 at

Lakhanpur coal mines in Mahanadi Coalfields Limited (MCL), a subsidiary of Coal

India Limited (CIL). A total of 47 surface miners (32 Wirtgen, 3 Bitelli, 12 L&T make)

of various sizes and capacities have been deployed in different collieries of MCL,

Central Coalfields Limited (CCL) and South Eastern Coalfields Limited (SECL) during

2010-2011. Bhatt (1995) identified surface miner as an alternative technology for

limestone mining for cement projects in Kutch district of Gujarat state. The surface

miner (Wirtgen make – 1900SM) was used for the first time in India in 1994 at a

limestone mine of Gujarat Ambuja Cement Limited (GACL). This machine proved the

ability of mining and sizing the soft limestone without blasting. In the same year

Madras Cements purchased the first new Wirtgen surface miner 2100SM. Vermeer

make surface miner was used in bauxite mine of National Aluminium Company

Limited (NALCO) on trial basis in hard rock excavation in 2010. The predominant

surface miner makes in Indian conditions are Wirtgen and L&T. Surface miners have

become the standard mining machine in all soft to medium hard limestone and coal

mines and are being used by various Indian mining companies as given in Table 2.1.

The Voest Alpine, Krupp, Wirtgen, Huron Easi and KSM make surface miners are used

with varying degrees of success.

9

Table 2.1: Deployment of surface miners in Indian companies

Sl. No. Company No. of surface miners

(Wirtgen make)

No. of surface miners

(L&T make)

1

2

3

4

5

Ambuja Cements

Madras Cements

India Cements

Coal India Limited

Sanghi Industries

limited

7

5

3

34

-

-

-

-

10

1

The major manufacturers of surface miners, such as Krupp and Wirtgen of Germany

and Voest-Alpine of Austria, have developed new machines from their areas of

technological strength. Thus, Krupp’s KSM is said to have come from the bucket wheel,

Wirtgen’s machines from its road milling equipment and Voest Alpine Surface Miner

(VASM) from its roadheader (Alpine Miner). Wirtgen offers the widest range of models

in the miner market, i.e., 1900SM, 2100SM, 2200SM, 2500SM, 3000SM, 3700SM and

4200SM. In 1987, 4200SM model was tested in several surface mines in the USA.

These machines, for instance 1900SM and 4200SM, are capable of selectively cutting

mineral separated by as little as 0.15 and 0.52 m thickness respectively (Vogt and

Strunk, 1995). Wirtgen, the world’s largest manufacturer of surface miners with widest

range of products and a variety of mining and other typical application experiences, is

the biggest supplier of surface miners in India.

According to Bordia (1987), these machines are suitable for multi-seam coal deposits

and have been successfully operated in all coal classes and partings with compressive

strengths up to 100 MPa and to a maximum cutting depth of 0.6 m. In addition, Wirtgen

surface miners can continuously cut and load at a capacity between 1000 – 2500 t/h, and

are capable of cutting coal, partings, gypsum, limestone, bauxite and other materials as

hard as 6 on the Mohr’s hardness scale. Different mechanical excavation systems and

their characteristics are listed in Table 2.2.

According to Krupp, the KSM models are designed for cutting materials with uniaxial

compressive strength up to 40 MPa, including hard coal, bauxite, phosphate, limestone,

10

oil sand, gypsum, clay and certain stratified or fractured materials where natural defects

assist cuttability.

Table 2.2: Types and characteristics of excavators (after Bordia, 1987)

System Makers UCS

(MPa)

Cutting

depth (m)

Cutting speed

(m/min)

Maximum

capacity (t/h)

BWE

Milling

Shearer

Rotation

Takraf – Russia

Voest-Alpine

Wirtgen/Huron

PWH C-Miner

Voest-Alpine

25

100

150

100

0.2-7.0

0.0-0.6

1.8 – 2.5

NA

NA

0 – 25

0 – 10

60 – 180

1000

2500

2100

1600

NA = not available

2.2.1 Types of surface miner

“Surface miners” basically implies three distinct classes of machines, namely, milling

type, bucket wheel type and ranging-shearer-drum type. The position of the cutting

drum is often decided based on the desired cutting capacity and compressive strength of

rock. Three distinct categories of surface miners are illustrated in the following

paragraphs.

a) Milling type: Milling type surface miners are manufactured by Wirtgen or Bitelli

machines, Easi-Miner from Huron, Man Takraf, L&T and Vermeer Terrain Leveller.

In most of these machines, the cutting drum is positioned below the machine in

between the front and rear crawlers. The Vermeer and Tesmec cutting drum is at the

end of the machine as shown in Figure 2.3; it is also wider than the machine and uses

top-down cutting which allows the cutter teeth to gain penetration without using

machine’s tractive effort.

In Man Takraf surface miner (MTS250 and 1250) and Tenova TAKRAF the cutting

drum is fixed in front of the machine. The milling type miner can cut rocks with

compressive strength in the range of 80 - 100 MPa. It is able to negotiate rocks having

compressive strength of 140 to 150 MPa, with reduced production (Misra, 2007).

Figure 2.3:

b) Bucket wheel type

machine, is marketed

KSM2000), 4 parallel bucket wheels are mounted on a main frame without boom

shown in Figure 2.4. The machine has a theoretical output of approximately 1000

1400 bank cubic meters

the range of 20 to 30 M

Figure 2.4: Front cutting drum surface miner

planning

: Rear cutting drum surface miner (www.tesmec.com

wheel type: This type of surface miner, based originally on Satterwhite

machine, is marketed by Thyssenkrupp Fordertechnik. In this machine

4 parallel bucket wheels are mounted on a main frame without boom

. The machine has a theoretical output of approximately 1000

meters/hour in material of average uniaxial compressive strength

30 MPa.

Figure 2.4: Front cutting drum surface miner (http://www.readbag.com/mine

planning-publications-documents-large-surface-miners)

11

www.tesmec.com)

This type of surface miner, based originally on Satterwhite

by Thyssenkrupp Fordertechnik. In this machine (model

4 parallel bucket wheels are mounted on a main frame without boom as

. The machine has a theoretical output of approximately 1000-

/hour in material of average uniaxial compressive strength in

(http://www.readbag.com/mine-

miners)

12

c) Ranging-shearer-drum type: This type of surface miner is based on underground

drum type continuous miner, represented by Voest Alpine’s VASM-2 and Rahco’s

CME-12. The ranging-shearer-drum type miners can cut rocks up to a compressive

strength of 120 MPa, though their economic range of operation is up to 80 MPa

(Misra, 2007).

Continuous miners can cut and load stronger formations like coal, shale, soft sandstone

and limestone, gypsum, chalk, etc., which cannot be excavated by bucket-wheel

excavators, or ripped by dozer rippers. Amongst the three types, milling type machine

dominates the market globally. A brief comparison of basic technical parameters of the

three types of surface miners based on drum position is tabulated in Table 2.3.

Classification of surface miners based on milling and boom cutting type is given in

Table 2.4.

2.2.2 Cutting action of surface miner

The milling type miner, shown in Figure 2.5, consists of a rotating wide cutting or

milling drum, which has spiral ridges carrying conical picks with tungsten carbide

inserts. The pick flight can be varied to suit the type of material cut. The drum spirals

are in the form of twin helix so that the cut material is pushed towards the drum centre

where it is loaded on a loading conveyor.

Table 2.3: Comparison of technical parameters based on cutting drum position

Parameter Types of surface miner

Middle drum Rear cutting drum Front cutting wheel

Cutting width (mm)

Cutting depth/height (mm)

Capacity

Weight (t)

Installed power (kW)

Manufacturers

250-4200

0-800

5250

1000-5500

7100

0-2900

For all machines output is related to material characteristics

40-190

450-1200

Wirtgen, Bitelli,

L&T and

Huron

135

750

Vermeer, Tesmec,

Voest Alpine

540

up to 3340

Krupp Fördertechnik

& Tenova TAKRAF

13

Table 2.4: Classification of surface miners based on milling and boom type

Milling miner

Drum, centrally Drum, frontal (DWE)

Easi Miner by Huron

SM series by Wirtgen

Continuous Excavators by forester-Miller

WL-50 Excavators by Barber Green Satterwhite

Excavators by Unit rig

C-Miner by PWH/Paurat

KSM4000

Boom miner

Drum Cut header

CME-12 by Rahco

Voest Alpine surface Miner

(VASM)

TB3000 by Dosco, WAV170 by Westphalia

ET-400 by Atlas Copco-Eickhoff

Figure 2.5: Schematic view of middle drum surface miner (www.wirtgen.com)

The conveyor system comprises a wide primary conveyor which picks up the cut and

comminuted material at the cutting drum, as well as a discharge conveyor to discharge

the material onto trucks as shown in Figure 2.6. The discharge conveyor can be adjusted

in height and slewed to both sides. The conveying speed can be varied. The drum or the

machine frame carrying the drum can be pushed up or down between the tracks by

hydraulic cylinders for controlling the milling depth from as low as 10 mm to as high as

610 mm.

Drum unit with

diesel engine

Boom

counterweight

Slewing ring

Site illumination

Crawler track, adjustable in height

Operator’s cab

Discharge boom,

slewable and

adjustable in height

Scraper blade with

primary conveyor

Cutting drum, mechanically driven

14

Figure 2.6: Transfer of cut material by conveyor system (www.wirtgen.com)

There is a provision for tilting the drum or the entire machine to give a sloping cut up to

7° (Misra, 2007). The drum chamber is sealed by a hydraulically actuated scraper blade

behind the cutting drum to clean cutting surface. The cutting drum rotates in an up-

cutting direction. The cutting tools are mounted in tool holders welded onto the body of

the drum. The picks (number, arrangement and types) used depend on the machine’s

momentary use and on the properties of the material being cut.

2.2.3 Design features

a) Diesel engine

The surface miners are diesel powered. The engine’s power is transmitted via a robust

belt drive to the drum, ensuring an effective power transmission. Moreover, the other

systems (e.g. track and belt drive) are hydraulically driven.

b) Central cutting drum with mechanical drive

The cutting drum is located in the centre of the machine (most cases), between the four

crawler tracks, shown in Figure 2.7. It is located close to the centre of gravity. The

entire machine weight can thus be converted into cutting force.

15

Figure 2.7: Central cutting drum with mechanical drive (www.wirtgen.com)

This allows cutting of harder materials with good results and at the same time ensures

the stability of the machine. The cutting drum speed can be varied by interchanging the

belt pulleys. The usual range of drum speed, which can be realized with these

changings, vary from 60 to 100 rpm. The belt pulleys are tensioned automatically by a

hydraulic cylinder. This is an energy effective, low maintenance system, minimizing

operating and maintenance costs.

c) Automatic adjustment of cutting depth

The cutting depth is regulated by an automatic leveling system mounted to the machine.

The pre-selected cutting depth is maintained either automatically or can be adjusted

manually. The control system can be connected with:

i. Cable sensors scanning the distance to a reference plate sliding on the surface.

ii. Non-contact ultrasonic sensors measuring the distance to the side plate or the

surface.

iii. Automatic control of transversal slope: The machine is equipped with a slope

sensor to control transversal slope of the cutting surface. It can be used to create

defined slopes, for water drainages for example, on the cutting surface.

iv. Multiplex sensors working with three sensors on one or both sides of the

machine, thus leveling uneven surfaces in longitudinal and transversal direction.

v. Laser sensors working with a transmitter and receiver.

16

2.2.4 Specifications of surface miner

Manufacturing sector plays a vital role for the growth of mining industry. There are

many companies in the world which are manufacturing surface miners, namely, Wirtgen

(SM Series), Huron Manufacturing Co (Easi-Miner), Takraf, L&T, Vermeer, etc.

Specifications of a few prominent models are given in Table 2.5, Table 2.6 and Table

2.7.

Table 2.5: Specification of Takraf (www.takraf.com), L&T (www.larsontoubro.

com) and Bitelli surface miners (Murthy et al., 2009)

Name of Company TAKRAF L & T Bitelli

Model MTS

180

MTS

300

MTS

500

MTS

800

MTS

1250

MTS

2000

KSM

223

KSM

303

KSM

304

SF

202M

Drum width (m)

Cutting depth (m)

Operating speed (m/min)

Rated capacity (m3/h)

Machine power (kW)

3.3

0.70

NA

180

500

4.0

0.875

NA

300

750

4.9

1.050

NA

500

1650

5.6

1.225

NA

800

2000

6.5

1.40

NA

1250

2500

7.4

1.575

NA

2000

2500

2.2

0.35

83

NA

597

3.0

0.30

30

NA

597

3.0

0.40

20

NA

895

2.0

0.25

NA

NA

515

Table 2.6: Specification of Wirtgen surface miner (www.wirtgen.com)

Model 2200SM 2500SM 3700SM 4200SM

Cutting width (m)

Cutting depth (m)

Drum diameter (m)

Fuel consumption (l/h)

Operating speed (m/min)

Travel speed (km/min)

Engine (HP)

Weight (t)

No. of tools

Spacing (mm)

2.20

0.35

1.12

150

-

0-5

800

51.0

76

38

2.50

0.60

1.50

191.5

0-25

0-3.9

1,050

103.0

Depends on

application

3.70

0.60

1.50

284

0-20

0-2.5

1,600

176.0

Depends on

application

4.20

0.80

1.86

284

0-20

0-2.5

1,600

191.4

Depends on

application

Cutting drum drive

Number of tracks

Track drive system

Drum speed (rpm)

Mechanical

4

Hydraulic

60-100

Table 2.7: Specification of Vermeer

Name of Company

Model

Drum width (m)

Cutting depth (m)

Operating weight (ton)

Max. cutting speed (m/min)

Machine power (kW)

2.2.5 Operating method

The operating methods are classified into three categories based on the machine travel

mode illustrated in the following paragraphs.

a) Empty travel back method

The surface miner cuts the material from one end of the pit. The cutting drum is raised

and moved back to the starting end without turning after the completion of the full cut.

The material is not cut during the backward movement

coming back to initial point, the machine is set for a new cut in adjacent strip

Figure 2.8.

Figure

This method is generally adopted for a mine having

because the turning time

Specification of Vermeer and Trencor surface miner

Name of Company VERMEER

T855 T955 T1055 T1255

Operating weight (ton)

Max. cutting speed (m/min)

Machine power (kW)

2.5

0.812

40.8

28

281

3.4

0.812

56.7

20

309

3.4

0.812

61.2

16

317

3.7

0.610

99.8

12

447

methods

operating methods are classified into three categories based on the machine travel

in the following paragraphs.

travel back method

cuts the material from one end of the pit. The cutting drum is raised


The material is not cut during the backward movement, i.e., it travels back emp

coming back to initial point, the machine is set for a new cut in adjacent strip

ure 2.8: Empty travel back method (Pradhan

This method is generally adopted for a mine having a field length less than 200

the turning time is more than the empty travel time. It is also applicable in bad

17

Trencor surface miner (www.trencor.com)

TRENCOR

T1255 3000SM

0.610

99.8

447

3.048

0.660

132.5

35

1230

operating methods are classified into three categories based on the machine travel

cuts the material from one end of the pit. The cutting drum is raised


it travels back empty. After

coming back to initial point, the machine is set for a new cut in adjacent strip, shown in

Pradhan, 2009)

field length less than 200 m

more than the empty travel time. It is also applicable in bad

18

pit-end condition and the machine is not able to turn there or the pit width is not

sufficient to allow the turning of machine at the end of a cut.

b) Turn back method

A surface miner cuts from one end of the area and after the completion of cut the cutting

drum is raised and the machine turns, shown in Figure 2.9.

Figure 2.9: Turn back method (Pradhan, 2009)

This method is generally adopted for a mine having a field length more than 200 m, so

that the time consumption in turning is lesser than empty travel time. This method is

widely used in limestone mines and gives more production.

c) Continuous mining method

Surface miner operates on an even field and continuously cuts the material. The

machine moves with cutting the material and near the pit end, it takes turn with a gentle

angle without raising the cutting drum, so that there is no discontinuity in cutting

operation. The cut area gets an oval shape, shown in Figure 2.10. The mining area is

developed by cutting slice by slice. For each slice the cutting depth only needs to be set

once on the surface miner.

19

Figure 2.10: Continuous mining method (Meena et al., 2008)

After the completion of an elliptical movement, adjacent cut is taken. This continues till

the elliptical turning gets sharp angle. Then machine goes for turn back method. This

can be avoided by overlapping elliptical movement, but the productivity reduces at the

overlapping area.

2.2.6 Other operational features

a) Block operation with ramp cutting

While cutting the block down to its planned level, the surface miner cuts its own ramp.

After completing the cut of the first block, the next block can be started adjacent to the

first one. Since turning on narrow benches is difficult and time consuming, two

alternative operations can be recommended:

i. Turning the machine on an appropriate area outside the ramp.

ii. Reverse the machine after finishing one cut and reposition the surface miner at the

adjacent cut.

As a rule of thumb, the turning radius is 12 multiply cutting width (when cutting harder

rock, the cutting depth has to be reduced) (Dey, 1999; Dutta, 2012).

b) Working Length

The productivity of a surface miner depends on the length of working area. Longer cuts

will enhance the productivity, because only a smaller amount of time is spent in

maneuvering from one cut to the next. The forward speed depends on the following

factors:

i. cutting depth

20

ii. material hardness and structure

iii. type of machine and installed engine power

In standard applications, the appropriate minimum cutting field length should be in the

range of (Dey, 1999; Dutta, 2012):

i. 100 m (hard material, low forward speed)

ii. 300 m (softer material, high forward speed)

2.2.7 Types of loading

a) Conveyor loading

Machine is set to cut by lowering its cutting drum at a predetermined depth, and then

starts excavation with its forward movement and the material excavated is transported to

the discharge conveyor via a primary conveyor. Discharge conveyor is mounted on a

discharge boom that can slew in either side and also the height of the boom can be

adjusted as per requirement, shown in Figure 2.11.

Figure 2.11: Conveyor loading system (www.wirtgen.com)

The cutting drum is followed by a scraper plate, which gathers material left on the floor.

This results in clean and smooth floor without any undulation. This method inherently

involves the loss of time needed for the replacement of a filled up dumper or truck with

an empty one. The efficiency of this operation depends on exact planning of number of

21

dumpers in accordance with their fleeting time, availability of space for maneuvering

the trucks or dumpers at the site of operation, and the drivers’ skill to rightly position

the empty dumpers quickly.

b) Windrowing

The conveyor loading arrangement of the machine is not utilized, i.e., machine is not

fitted with the discharge belt. The scraper plate behind the drum is modified and a door

is provided which allows the cut material to heap behind the machine in a row, shown in

Figure 2.12. Cut material can be loaded later to a dumper by loading equipment like

front end loader and scraper.

Figure 2.12: Windrowing system (www.wirtgen.com)

Though windrowing is independent of the loading and transportation of material, but the

overall efficiency (including fuel efficiency) is more as the machine is devoid of the

discharge belt, thus lighter, more balanced and requires less energy for operation. Thus,

it is the most productive mode of a surface miner. On the other hand it needs more space

to operate than in other modes.

c) Side casting

In this method, the discharge belt dumps the material on the side of the cut being made

by the surface miner, shown in Figure 2.13. The dumped material is later loaded to

dumpers/trucks by loaders and

interference due to loading.

Figure

Each method of loading has its own advantages and disadvantages,

2.8. Windrowing system is best from production

2.2.8 Common maint

Production hampers due to the machine breakdown.

maintenance of surface miner for smooth and regular operation as well

the number of breakdowns. Some common maintenance works and breakdowns of

surface miners experienced in Indian coal and limestone mines is given in Table 2.9.

2.2.9 Application and merits of surface miner

a) Application

The application of surface miner

breaking, crushing and loading are combined in one single operation), maintenance and

supervision – due to the one

dumpers/trucks by loaders and taken away. Here the machine operation is free from

interference due to loading.

ure 2.13: Side casting system (www.wirtgen.com)

loading has its own advantages and disadvantages,

. Windrowing system is best from production view point.

maintenance and breakdown issues

Production hampers due to the machine breakdown. It is imperative to provide proper

maintenance of surface miner for smooth and regular operation as well

breakdowns. Some common maintenance works and breakdowns of


Application and merits of surface miner

surface miners simplifies the mining operation (


due to the one-machine concept.

22

taken away. Here the machine operation is free from

(www.wirtgen.com)

loading has its own advantages and disadvantages, as listed in Table

t is imperative to provide proper

maintenance of surface miner for smooth and regular operation as well as to minimize

breakdowns. Some common maintenance works and breakdowns of


operation (source ground


23

Table 2.8: Comparison of the different loading methods

Loading method Advantages Disadvantages

Direct loading

• No re-handling of

material required.

• Larger working area required for

truck maneuvering.

• Production affected by truck

exchange time.

• Belt wear.

Side casting

• Blending of material in

the mine. Stockpile of

material in the mine.

• No waiting for trucks,

independent operation.

• Restricted to 3-5 cuts wide on each

side of the mine stockpile.

• Belt wear.

• Material has to be re-handled.

• Material prone to absorb water when

lying on the ground.

Windrowing

• No waiting for trucks.

• No belt wear/higher

availability.

• Higher production rates

than conveyor loading.

• Coarser material.

• Better selectivity in

steep inclined seams.

• Large working area required.

• Material has to be handled either by

loader or scraper.

• Material prone to absorb water when

lying on the ground.

Table 2.9: Common maintenance and breakdowns in Indian coal and limestone mines

Maintenance Breakdown

• Regular washing of machine by

water.

• Change of radiator coolant,

engine oil, PTO gear box oil,

milling drum oil, advance drive

gear oil and track gear oil.

• Change/service of PTO filter,

diesel filter, water filter,

coolant filter, hydraulic filter,

air filter and water filter.

• Maintenance of radiator water

leakage and track tensioning

work.

• Thermostat valve removal due to overheat of

radiator.

• Failing of tension pulley bearing.

• Breaking of travelling pump seal, water pump.

• Breaking of pulley bush.

• Picks and pick holders breakage.

• Puncture of brake hose, track motor hose

• Damage of scraper door, track roller

• Damage of radiator bolt, radiator and oil collar.

• Breakage of milling drum drive shaft coupling,

milling drum pulley belt.

• Engine breakdown.

• Damage of steering cylinder key, guide column

cylinder.

The application procedure for a mining permit is faster than for a blasting operation.

Surface miner eliminates primary crushing as the output size is < 80 mm, and thus

energy is saved, which otherwise would have been required for the primary crushing

process. Surface miner

movement of the hauling equipment,

of the hauling equipment.

As a result, operating costs are reduced considerably.

dominates globally in

other ore/minerals as given in Fig

Figure 2.14:

However, it is important to note that surface miners, as claimed by Vogt and Strunk

(1995), are ideally suited to selective mining operations. This is becoming increasingly

important as emphasis is now being placed on keeping mineral losses and dilution to a

minimum. In this regard the KSM4000 is noteworthy for its ability to selectively cut

material up to a thickness of 3 cm.

maximum gradient up to 14

129

6

50

0

20

40

60

80

100

120

140

Lim

esto

ne

Bau

xit

e

Co

al

Su

rfac

e M

iner

s


miner produces a smooth, clean and even floor facilitating the

movement of the hauling equipment, minimizing wear and tear of the tyres and chassis

of the hauling equipment.

As a result, operating costs are reduced considerably. Surface miner application

in limestone mines, though it is applicable in production of various

as given in Figure 2.14 (after www.wirtgen.com)

Application of surface miners in different minerals/ore

is important to note that surface miners, as claimed by Vogt and Strunk



In this regard the KSM4000 is noteworthy for its ability to selectively cut

material up to a thickness of 3 cm. A surface miner has a capacity to negotiate a

maximum gradient up to 14o (Rao and Vilas, 1997).

50

2 1 2

17

2

22

5 1 4 3

Co

al

Oil

shal

e

Mu

dst

on

e

Tu

ff

Iro

n o

re

Sh

ale

Sal

t

Gra

nit

e

Peg

mat

ite

Kim

ber

lite

Ph

osp

hat

e

24


lean and even floor facilitating the

minimizing wear and tear of the tyres and chassis

Surface miner application

stone mines, though it is applicable in production of various

www.wirtgen.com).

Application of surface miners in different minerals/ores

is important to note that surface miners, as claimed by Vogt and Strunk



In this regard the KSM4000 is noteworthy for its ability to selectively cut

A surface miner has a capacity to negotiate a

1 4

22P

ho

sph

ate

San

dst

on

e

Lig

nit

e

Gyp

sum

25

c) Merits of surface miner

Use of surface miner is a simplified mining technology and possesses several

advantages, namely, selective mining, improved productivity and ability to work close

to the habitat/agricultural fields. It is environment-friendly with reduced noise emission,

reduced fugitive dust emission, total elimination of ground vibration, no drilling and

blasting, no fly rocks and no secondary blasting/breaking of boulders. Precise cutting of

designed profiles (slopes, surfaces), stable and clean surfaces/benches with improved

overall availability of the system, reduced operating cost, leading to easier coordination

and process planning during planning, dispatching and maintenance can be obtained by

the use of surface miner. Enhanced ROM-quality, improved exploitation of the deposit,

reduced processing requirement after mining, primary crushing stage can be omitted by

application of surface miner. Gentle loading of trucks due to sized material, low

investment costs in comparison to the range of equipment necessary for conventional

mining, energy efficient system and improved safety are also the advantageous features

of surface miner. Surface miners can maintain the surface of existing haul roads in

virgin rock or in opencast mines. It facilitates higher overall travel speed for haulage

vehicles due to better road surfaces. Benches with fewer cracks reduce the chances of

heating/fire due to breathing of air.

2.3 Mechanical Cutting of Rocks

The application of mechanical excavation of rocks, a non-explosive technique of

mining, is very attractive for many projects because of techno-economic advantages

including improved safety, ease in automation, finished and undamaged excavation

dimensions, lower ground vibrations, etc. Mechanical rock cutting is a prevalent method

today for rock excavation in mining and construction industries owing to several

limitations/constraints faced during drilling and blasting. Numerous mining and

tunneling machines, namely, roadheaders, tunnel boring machines, drills, trenchers,

dredges and continuous surface miners utilize cutting action of picks or bits for rock

excavation. Two types of tools are used for rock cutting, namely, drag bits (break rock

as it moves in a direction parallel to the rock surface) and indenters (break rocks by

pressing normally onto the surface). Rock cutting by surface miner follows the former

type. Drag bits are generally limited to applications in weak to medium strength rocks

and in rocks with low abrasivity characteristics because these bits are more susceptible

26

to breakage and wear than indenters (Hood and Ale, 2000). Conical picks are the

essential cutting tools used especially on surface miners, roadheaders, continuous

miners and shearers and their cutting performance affects directly the efficiency and the

cost of rock/mineral excavation (Bilgin et al., 2006).

Evaluation of surface miner performance is necessary in order to allow any meaningful

comparison between different machines operating under a variety of conditions.

Prediction of cutting rate and pick consumption are fundamental to any machine

performance evaluation.

2.3.1 Cutting action of pick

When a pick attacks a rock medium during cutting, at the point of contact between the

pick and the rock medium, high stresses develop under the pick tip. As the pick is kept

pressed into the rock, pick forces exceed the strength of the material and material is

cracked. Cracks are initiated and propagated through the free surface and laterally into

the rock as shown in Figure 2.15. In the final stage, rock is fragmented whenever one of

the main cracks reaches the free surface (Tiryaki and Dikmen, 2006).

Figure 2.15: Force variation during cutting action by pick (Roxborough et al., 1981)

The cutting process is a continuous repetition of localized tearing. The motion of the

pick is accompanied simultaneously by the communition of rock at the point of contact

and the removal of broken products from the core. During the process of communition

27

resisting force increases and the tearing off of small chips is accompanied by the

ejection of finely pulverized rock from the core with a slight fall in cutting forces. When

a large chip is torn from the mass, the cutting force drops to zero or near zero. If the

fracture leading to tearing has partly extended inside the mass, the cutting force remains

zero or near zero until the tool covers the length of the fracture. In the unbroken part of

the rock mass situated under the tool, high contact compressive stresses develop which

form the cutting forces and cause ejection of coal due to friction as well as wear of the

tool (Pozin et al., 1989).

The tip of a cutting tool performs two functions as it pushes through brittle rock. Firstly,

it initiates breakage ahead of the cutting tool. Major fractures induced in this way result

in the removal of saucer shaped pieces as the rock breaks at a shallow angle both to the

sides and ahead of the tool. Secondly, the cutting tool clears a path through the

remaining material by a profiling action and this occurs as the tool cuts into the sloping

surface left by a major breakage (Hurt and Evans, 1980). Continuous miner/drum

shearers, coal ploughs and roadheaders use picks or plough cutters of a similar design

for their cutting tools.

Rock cutting with typical brittle failure is characterized by chip formation and

separation due to combined action of shear and tensile fracture initiated in a crushing

zone near the tooth tip and propagating into the intact rock (Rojek, 2007). The ability of

excavation machines to operate and cut effectively in hard rock is limited by the system

stiffness and the ability of cutting tools to withstand high forces. Mean and peak cutter

forces are of vital importance for a given rock formation. The force acting on a cutting

tool changes constantly in magnitude during a cutting process due to chipping and

brittle nature of the rock. Mean cutter force is defined as an average of all the force

changes during the course of cutting action. Mean peak force is defined as an average of

the peak forces during the course of cutting action. High forces may result in gross

fracture damage to the tungsten carbide cutting tip, damage the machine components

and exceed the machine’s torque and thrust capacities. However, the most

comprehensive and accepted theories are those of Evans’ (1961, 1972, 1982, 1984a and

1984b) for chisel picks and conical picks and of Nishimatsu’s (1972) for chisel picks.

28

2.3.2 Cutting force estimation

Normal and frictional forces act on the cutting edge of the tool. Frictional forces depend

on normal forces and variable coefficients of friction. The pressure is maximum near the

cutting edge of the tool and diminishes rapidly, in a hyperbolic relation, away from the

tool edge.

One of the earliest theories was developed by Evans (1965) for rock cutting with drag

picks. The pioneering work on coal cutting mechanics performed by Evans (1961), and

Evans and Pomeroy (1966) and extended theoretical works of Evans (1972, 1982, 1984a

and 1984b) were used to establish the basic principles of the cutting process and these

have been widely used in the efficient design of excavation machines such as shearers,

continuous miners and roadheaders. The type of failure (brittle and ductile) during rock

cutting depends on the type of rock. It is assumed that the breakage is essentially tensile

and occurs along failure surface, which approximates a circular arc as shown in Figure

2.16.

Figure 2.16: Tensile breakage mechanism (Goktan, 1990)

Evans demonstrated theoretically that tensile strength and compressive strength were

dominant rock properties in rock cutting with chisel picks and point attack tools as

formulated in Equations 2.1 and 2.2 (Table 2.10). Roxborough (1973) proved that the

experimental forces for chisel picks were in good agreement with theoretical values

calculated using Equation 2.1.

S

R T

α

d

T

cutting

tool

Fc

b

O

α

θf = ½ α

29

Table 2.10: Mathematical relations for estimating cutting forces using different picks

Sl. No. Proposed equation Author

1

12 sin (90 )

21

1 sin (90 )2

t

c

dw

F

σ α

α

−=

− − (chisel picks) (Equation 2.1)

Evans (1965,

1972, 1982,

1984a and

1984b); Evans

and Pomeroy

(1966) 2

22

2

16

( / 2)

tc

c

dF

Cos

π σσ

=φ

(point attack picks) (Equation 2.2)

3 ,

2 cos

( 1)(1 sin( )

uc r t

dwF

n

τ φφ φ α

=+ − + −

(chisel picks) (Equation 2.3) Nishimatsu

(1972)

4 Fc = 2.4 + 0.0064 A Sinθ (Equation 2.4)

Fn = 1.5 Fc

Hurt et al.

(1988)

5

2 2

2

16 ( / 2 )

12 ( ( / 2))

( / 2)

t

t

c

c

c

dF

TanCos

Tan

πσ σ ϕ ψ

ψσ σ ϕ

ψ

+=

++

(point attack picks)

(Equation 2.5)

Roxborough

and Liu (1995)

6

2 24 ( / 2 )

( / 2 )

tc

d SinF

Cos

πσ ϕ ψϕ ψ

+=

+(point attack picks) (Equation 2.6)

Goktan (1997);

Goktan and

Gunes (2005a)

7 2 cos( ) ( )

( 1)[1 sin( )

sc

dw Cos iF

n i

σ ψ αψ α

−=

+ − + −

(Equation 2.7) Bilgin et al.

(2006)

8 4

.

tc

dP

Cos a

π σθ

=

(Equation 2.8) Evans (1984a,

1984b) 9

2

c cP aπ σ=

(Equation 2.9)

Where, i = rock internal friction angle (degree) Pc = total horizontal force (N)

ϕ = tip angle (degree) θ = semi-angle of cone (degree)

a = radius of hole (mm) tσ = rock tensile strength (MPa)

Fn = normal force (kN) sσ = rock shear strength (MPa)

uτ = unconfined shear strength (MPa) w = width of the tool (mm)

φ = angle of internal friction of intact rock α = rake angle (degree)

n = stress distribution factor = 12 -α /5 Fc = cutting force (kN)

,r tφ = angle of sliding friction rock-tool β = 90 - α

cσ = rock compressive strength (MPa) d = depth of cut (cm)

ψ = friction coefficient between cutting tool and rock

30

Another two-dimensional model developed by Nishimatsu (1972) assumed that failure

is purely due to shear and occurs along a plane, shown in Figure 2.17 and expressed as

Equation 2.3 (Table 2.10). According to Guo et al. (1992) Mohr–Coulomb failure

criterion and linear elastic fracture mechanics could furnish a greater insight to the rock

cutting mechanics.

Roxborough and Liu (1995) suggested a modification on Evans’ cutting theory for point

attack tools as indicated in Equation 2.5. Goktan (1997) suggested a modification on

Evans’ cutting theory for point attack tools as indicated in Equation 2.6 and concluded

that the force values obtained with this equation were close to previously published

experimental values and could be of practical value, if confirmed by additional studies.

Goktan (1990) used Evans’ theories to compare the cutting efficiency of point attack

tools and wedge–shaped picks and concluded that the ratio of tensile to compressive

strength was the main parameter governing the relative efficiency.

Figure 2.17: Shear breakage mechanism (Goktan, 1990)

Goktan also developed some empirical equations to predict the cutting forces of wedge-

type cutters and studied the effect of rake angle on the failure pattern of high strength

rocks (Goktan, 1992; Goktan, 1995). Nishimatsu (1972) found that shear strength

failure was dominant in cutting high strength rocks as formulated in Equation 2.6.

Fc

Fn F

Shear fracture d

rock

chisel

β

α

r

Φ r,t

r

31

A detailed study was carried out by Bilgin et al. (2000) using numerical modeling

software and a small-scale rock cutting rig to investigate the effect of lateral stresses on

the cutting efficiency of chisel-type cutters. Numerical modeling studies showed that the

lateral stresses dramatically decreased the tensile stresses around the cutting groove up

to a certain level of lateral stresses for unrelieved cutting mode. In that case, a lateral

stress of 1/5 or 1/4 of rock compressive strength in magnitude caused an increase in

cutter force compared to the unstressed condition. However, for relieved cutting mode,

the effect of lateral stresses was less apparent, causing an increase in cutter force around

20–30% more than the unstressed conditions.

General principles of efficient cutting head design to increase excavation productivity

with less cutting head vibration and less wear of cutting components were investigated

in detail (Hurt and MacAndrew, 1981; Hurt et al.,1982; Hurt and MacAndrew, 1985;

Hurt and Morris, 1985; Hurt et al., 1988) in previous National Coal Board, Mining and

Research and Development Establishment (MRDE). They strongly emphasized that

cutter force estimation was the essential part of an efficient cutting head design.

Later works on rock cutting mechanics in MRDE mainly concentrated on the cutting

performance of point attack tools (Hurt and Laidlaw, 1979; Hurt, 1980; Hurt and Evans,

1980; Hurt and Evans, 1981; Hurt, 1988). The results showed that the sharp point attack

tools generated higher forces than wedge tools. In abrasive rocks, point attack tools last

longer than wedge tools and might resist higher forces. Minimum cutting forces were

exhibited by the point attack tool at an attack angle of 50o corresponding to a back

clearance angle of 12o. Radial bits appeared to facilitate coal cutting in the tensile mode,

while point attack bits appeared to fragment the coal with a more complex mode of

failure (Sundae and Myren, 1987). Depth of cut was found to be the most significant

factor affecting specific energy, cutter forces and airborne respirable dust (Roepke and

Hanson, 1984). These were well summarized in Fowell’s work published in

‘‘Comprehensive Rock Engineering’’ (Fowell, 1993). Experimental studies that were

carried out in order to evaluate some coal cutting theories for continuous miners proved

that the normal and cutting forces acting on a cutter increased linearly with depth of cut.

Pick spacing had to be considered relative to depth of cut. The chisel-shaped picks were

32

more efficient than the pointed shape tools at relatively shallow depths of cut. However,

the pointed pick was proved to be consistently more efficient shape at comparatively

deep cutting depths (Roxborough et al., 1981; Roxborough and Pedroncelli, 1982).

2.3.3 Specific energy

Specific energy is one of the most important factors in determining the efficiency of

cutting systems and is defined as the work to excavate a unit volume of rock. In

mechanical excavation studies, some rock properties affecting the specific energy were

investigated by different researchers (Paone et al., 1969; Schmidt, 1972; Dunn et al.,

1993). Detailed rock cutting tests, however, showed that specific energy was not only a

function of rock properties but it was also closely related to operational parameters such

as rotational speed, cutting power of excavation machines and tool geometry. Specific

energy decreased dramatically to a certain level with increasing depth of cut and

decreasing tool angle (Roxborough and Rispin, 1973a; Roxborough and Rispin, 1973b;

Roxborough and Phillips, 1975; Roxborough, 1985). Specific energy depends on depth

of cut/pick penetration. The minimum specific energy is obtained with an appropriate

spacing to depth of cut ratio (Figure 2.18).

Figure 2.18: General effect of cutter spacing on specific energy (Fuh, 1983)

33

Different relations of specific energy and cutting performance based on laboratory and

field investigations are shown in Table 2.11.

Table 2.11: Relationship between cutting performance and rock parameters

Sl. No. Proposed equation Author

1

2

2

cSEE

σ=

(Equation 2.10)

Hughes (1972); Mellor

(1972)

2

2 1/ 30.65 0.41 1.81 2.6SE CI k= − + + ±

(Equation 2.11)

McFeat-Smith and

Fowell (1977); McFeat-

Smith and Fowell

(1979)

3

0.28 (0.974)RMCIICR P= (Equation 2.12a)

2 /3

.100

c

RQDRMCI σ =

(Equation 2.12b)

McFeat-Smith and

Fowell (1979); Bilgin et

al. (1996)

4 e

opt

PICR k

SE=

(Equation 2.13)

Rostami and Ozdemir

(1994); Rostami et al.

(1994); Bilgin et al.

(1997)

5

1c

T

Bσσ

= (Equation 2.14a)

2c T

c T

Bσ σσ σ

−=

+ (Equation 2.14b)

32

c TBσ σ×

= (Equation 2.14c)

SE = 2.4147 (B3)0.4826

SE = 0.5816 +0.0946 (B3)

SE=2.0544Ln(B3) – 7.0031

Altindag, 2003

Where, SE = specific energy (MJ/m3) P = power of cutting (kW)

optSE = optimum specific energy(kW/m3) k = plasticity index

RMCI = rock mass cuttability index ek = energy transfer ratio

ICR = instantaneous cutting rate (m3/h) CI = cone indenter value

B1, B2 and B3 = brittleness T

σ = rock tensile strength (MPa)

cσ = rock compressive strength (MPa) E = modulus of elasticity (GPa)

RQD = rock quality designation in percent

E = secant elasticity modulus from zero load to failure

34

In this study, besides the two rock brittleness B1 and B2 cited in literature, brittleness of

B3 concept (Altindag, 2000a; Altindag, 2000b; Altindag, 2002; Altindag, 2003) were

also evaluated.

2.4 Factors Influencing Cutting Performance

According to the report of the Commission on Rock Borability, Cuttability and

Drillability, International Society for Rock Mechanics (ISRM) (Bamford, 1987;

Roxborough, 1987; Braybrooke, 1988; Fowell and Johnson, 1991), the excavatability of

a rock mass by means of an excavator depends on a numerous geo-mechanical

properties of intact rock and rock mass being excavated and power used. Therefore,

evaluation of applicability and selection of a surface miner for any given operation must

be based on a careful assessment of the properties of the rock environment by practical

evaluation, as downtimes of a mechanical excavation process can reduce the overall

system efficiency below the threshold of techno-economic viability, thus defeating the

whole purpose of its deployment.

The following section details the key intact rock and rock mass parameters that

influence the design, selection and operation of surface miners.

2.4.1 Intact rock parameters

Assessing the cuttability of a rock formation with respect to a mechanical excavation

system is an imprecise area of endeavor (Roxborough, 1987). Nonetheless, several

researchers have developed certain empirical approaches to estimate cutting

performance of machines for different rocks on the basis of a number of properties of

intact rock.

a) Rock density: Dry density is a significant property affecting specific energy while

cutting (Tiryaki and Dikmen, 2006). A rock with higher specific gravity or density will

need higher specific cutting energy (SE). The cutting performance of a machine in terms

of bank volume cut per unit time in a coal seam with specific gravity of around 1.5 will

definitely be higher than that of the same machine in other rocks with comparable

uniaxial compressive strength but specific gravity of about 2.5. The machine

35

performance decreases with increase in density of rock which necessitates decrease in

drum speed. Kahraman et al. (2003) correlated density of the rock to determine

penetration rate of percussive drills. Kirsten (1982) identified rock density as an

influencing parameter in the excavatability assessment of the rock.

b) Moisture content: Moisture content affects the uniaxial compressive strength of the

rock (Fowell et al., 1986). It was observed that both cutting and normal forces

decreased by 40 and 49% respectively, specific energy by 38%, and impact wear of the

cutting tool by 80% when cutting a saturated sandstone sample. The sample showed

68% reduction in uniaxial compressive strength compared to that of a dry sample

(Mammen et al., 2009). Nevertheless, mechanical cutting of some rocks, like certain

varieties of sandstone, sometimes become difficult when they get saturated. Dissipation

of high local stress concentration at the pick-rock interface by pore-water makes pick

cutting difficult in high moisture content rock masses. Moisture content, however,

results into lower pick wear rate (Roxborough, 1987). Presence of moisture also

adversely affects mechanical cutting of those materials which turn sticky if wet, like

consolidated soil, bentonite, and some types of claystone, shale, marl and siltstone.

c) Uniaxial compressive strength: Rock strength is one of the most important

parameters evaluated in rock mechanics (Prikryl, 2001). The compressive strength of

rock is characterized by the maximum amount of stress which a rock can withstand.

Uniaxial compressive strength (UCS) is the most widely used parameter of strength,

deformation, fracture characteristics and cuttability (Erosy and Waller, 1995; Atilla et

al., 2004). Evans (1984b) proposed a cutting theory that used uniaxial compressive

strength and tensile strength as input variables for determining cutting and normal force.

The surface miner manufacturers follow simple conjecture and use uniaxial compressive

strength of rocks as the only yardstick to define the cutting ability of their machines or

to assess the cuttability of rocks with respect to any given machine. Nonetheless, the

productivity of a machine goes down substantially with the increase in compressive

strength of rock to be cut.

36

Tenova TAKRAF surface miners claim to be capable of mining minerals/ores with

compressive strength of up to 80 MPa. On the other hand, the output of KSM2000

amounts to 1400 bm3/h in continuous cutting operation under normal condition up to

uniaxial compressive strength of 40 MPa. According to Bag and Schroeder (1999), the

machine can excavate rocks of uniaxial compressive strength of 80 MPa with a reduced

output, and can even cut small lenses of uniaxial compressive strength up to 120 MPa

with reduced production capacity. The cutting rate of a surface miner drastically drops

with rise in uniaxial compressive strength of rock material to be cut. Figure 2.19 shows

the change in production capacity of the machine with compressive and tensile strengths

of rocks.

Figure 2.19: Performance of KSM with respect to uniaxial compressive strength

(http://www.readbag.com/mine-planning-publications-documents-

large-surface-miners)

At Cloud Break iron ore deposit in Pilbara of Western Australia, the production

decreased significantly from 1050 t/h for rocks of uniaxial compressive strength of 10

MPa to 100 t/h for rocks of uniaxial compressive strength of 100 MPa (Murthy et al.,

2009).

Drop in surface miner performance with the increase in uniaxial compressive strength of

coal in Mahanadi Coalfields Limited (MCL), the biggest user of surface miners in India,

was reported by the Chief Executive Officer, MCL. According to him, “Though the

manufacturers claim to have cuttability capacity up to 80 MPa, it has been observed that

if the compressive strength of rock exceeds

badly affected. Cutting teeth become worn out very quickly and require frequent

replacement” (Upadhyay, 2010). Variation of cutting performance of different models

of Wirtgen surface miners with UCS of rocks is depicted in Fig

Figure 2.20: Cutting performance of Wirtgen surface miner

It has been seen that these

the range of 10 to 80 MPa. Under certain circumstances (e.g. highly fractured material)

even harder material can be cut economically. The cutting efficiency decreases with

increasing strength of the rock

d) Tensile strength:

strength as the main criteria, found wider acceptance for predicting cutting forces in

brittle materials. Thuro (1997

predicting drillability. Murthy

assessment of roadheader.

rock plays role in determining cutting rate and beads wear rate


compressive strength of rock exceeds 50 MPa, productivity of surface miner is



face miners with UCS of rocks is depicted in Figure

Cutting performance of Wirtgen surface miners (

It has been seen that these surface miners are capable of cutting rock with a hardness

80 MPa. Under certain circumstances (e.g. highly fractured material)

material can be cut economically. The cutting efficiency decreases with

increasing strength of the rock as shown in Table 2.12.

: The model used by Evans (1961) for coal, taking the tensile


Thuro (1997) took tensile strength as one of the rock properties for

ty. Murthy et al. (2008) considered tensile strength for cuttability

assessment of roadheader. According to Jain and Rathore (2010

role in determining cutting rate and beads wear rate of diamond wire saw.

37


50 MPa, productivity of surface miner is



ure 2.20.

s (www.wirtgen.com)

s are capable of cutting rock with a hardness in

80 MPa. Under certain circumstances (e.g. highly fractured material)

material can be cut economically. The cutting efficiency decreases with

The model used by Evans (1961) for coal, taking the tensile


) took tensile strength as one of the rock properties for

(2008) considered tensile strength for cuttability

2010), tensile strength of

diamond wire saw.

38

Table 2.12: Cutting rate of surface miner for varied rock strength

(www.wirtgen.com)

Type Strength (MPa) Cutting rate (t/h)

SM2200 Up to 50 750 – 300

SM2500 Up to 80

81 to 100

1550 – 220

220 – 65

SM3700 Up to 80

81 to 100

2550 – 365

365 – 100

SM4200 Up to 70 3400 - 475

e) Point load strength index: Point load test is useful for strength classification of

intact rocks. Hadjigeorgiu and Scoble (1990) developed an excavation index

classification scheme by considering point load strength index as one of the parameters.

Dey and Ghose (2008) considered point load strength index as one of the key

influencing parameters for determination of cuttability of surface miner. Meena et al.

(2008) correlated the production by surface miner with point load strength index on

different rock types and observed that production was inversely proportional to point

load strength index.

f) Seismic wave velocity: Geophysical techniques involving seismic refraction and

reflection, electrical resistivity and gravimetric and magnetic measurements form an

accepted part of engineering-geological investigation procedures. The measurement of

P-wave velocity is a significant way to determine the mechanical parameters of a rock

mass (Zivor et al., 2011 and Verma et al., 2012). In the field of rock mechanics, the

seismic refraction method is the most popular and is useful for the purposes of rock

mass characterization in surface mines which can lead to the selection of an excavation

system (Atkinson, 1971).

The seismic refraction method is usually used to obtain the field seismic velocity as a

measure of the rippability of a rock mass. This method has been practiced for long time

by bulldozer manufacturers such as, Caterpillar and Komatsu. The use of the seismic

velocity as a predictor of rippability is often shown in the form of bar chart. This bar

chart represents the standard performance of a bulldozer, CAT-D10N with a single

39

impact ripper related to seismic velocity. In general, a material with a seismic velocity

value above 2000 m/s can be considered as marginal ripping to difficult to rip proposed

by Atkinson (1971) as shown in Figure 2.21.

Figure 2.21: Seismic velocity method for determination of excavation possibilities

Wirtgen – circular (1984) suggests that seismic wave velocity assessment can be useful

as a means to predict the cuttability of rock and ores for Wirtgen Surface Miner (WSM).

In this circular the normal criteria for testing rock for its cuttability in mining or

tunneling operation involves parameters like uniaxial compressive strength, Brazilian

tensile strength, resistance to shear, Young’s modulus and abrasivity which are

complicated, time consuming and costly.

Using a seismic wave velocity classification the rock mass is divided into three zones,

namely, residual rock (300 m/s), weathered rock (1220 m/s) and semi solid rock (3050

m/s). Using these criteria, what is rippable by heavy equipment, such as CAT-D10

dozer, is also cuttable by the WSM and that standard shock wave velocities can be

applied to Wirtgen surface miner operations.

However, seismic tests can sometimes lead to a misleading estimation of excavation.

The misleading estimation may be due to many factors such as rock mass condition and

geological features which may require different field procedures in order to obtain

reliable data. When field seismic velocity data is not available an empirical equation,

40

derived from field studies in surface lignite mines owned by Turkish Coal Enterprise,

may be used (Karpuz, 1990).

0.225

F cV =953 σ (R2 = 0.87) (Equation 2.15)

Where,

VF = Field seismic velocity, m/s and

σc = uniaxial compressive strength, MPa.

g) Abrasiveness: More abrasive a rock, more wear and tear it causes on cutting tools of

the machine thus affecting its cutting performance adversely. Abrasiveness of a rock is

expressed in terms of different indices like Cerchar Abrasivity Index (CAI), Schimazek-

F Index, etc. that are determined by testing intact rock samples in the laboratory

following standard procedures. Dey and Ghose (2008), and Origliasso et al. (2013)

considered rock abrasivity as one of the key influencing parameters for cuttability

determination of surface miner. Thuro and Plinninger (2004) discussed the application

of the Cerchar abrasivity index in the estimation of tool wear rates for hard rock

operations. Murthy et al. (2009) considered Cerchar abrasivity index as one of the

parameters to develop cuttability of surface miner.

h) Petrography: Roxborough (1987) stressed that the mineralogy of rock, particularly

its quartz content, is often of a crucial significance to cutting. It has a major bearing on

the rate at which a machine cutting elements wear and blunting of the cutter occurs.

Howarth and Rowlands (1986) developed a model to predict the drillability. This model

depends on textural properties of the rock such as grain shape and orientation, degree of

grain interlocking, and the packing density. Howarth and Rowlands (1987) discussed on

predicting tool wear by considering rock texture and mineral fabric. According to

Tiryaki and Dikmen (2006), pick forces are expected to increase in linear rock cutting

as the texture coefficient increases. Feldspar and quartz content in sandstone were found

to influence specific energy.

2.4.2 Rock mass parameters

a) Discontinuities: Discontinuities within a rock mass may aid mechanical excavation

dependent on their frequency and orientation to cut even stronger material than is

41

normally considered suitable. Presence of joints and other structural features like

bedding planes, cleats and slips, etc., in high frequency along with their length and

degree of openness assist the cutting process, especially when they are favorably

oriented with respect to the direction of cutting. The orientation of discontinuities can

also influence the performance of a cutting machine. Evans and Pomeroy (1966)

demonstrated that the orientation of cleats to the direction of cutting can have an

important influence on cutter performance with drag picks. According to Blindheim

(1979), the most favourable joint orientation for roadheaders in an underground opening

is perpendicular to the tunnel axis (loading axis).

Gehring (1980) claimed that only discontinuity spacing less than 100 mm have a

significant influence on the performance of roadheaders (F-6A, AM-50, AM-100), and

it was found as well that if the machine cuts in highly jointed rock mass, production can

be three times the production in solid rock. It was also reported by Roxborough and

Phillips (1981) that less specific energy of about 0.22 MJ/bcm is required when the

cutting direction of picks is parallel to coal cleats (cleat orientation = 0 degree) as given

in Table 2.13 and shown in Figure 2.22.

Table 2.13: Effect of cutting direction on specific energy (Roxborough and Phillips, 1981)

Cleat

orientation

Mean

peak cutting force, kN

Mean

cutting force, kN

SE

MJ/bcm

0 degree

45 degree

90 degree

134 degree

0.38

0.38

0.50

0.42

0.18

0.16

0.22

0.20

0.22

0.17

0.29

0.26

Braybrooke (1988) claimed that when excavation takes place in jointed rock mass, the

mean peak cutting force decreases rapidly as joint frequency increases. According to

Fowell and Johnson (1991), in strong strata one favourably situated joint plane can

double excavation rates if it allows blocks to drop from the face, and discontinuity

spacing of less than 300 mm are required to make excavation rates independent of the

intact rock properties.

42

b) Rock quality designation: Kirsten (1982) identified rock quality designation for

determining excavatability of the rock. Bilgin et al. (1988) used rock quality designation

(RQD) to estimate the advance rate of a roadheader. Murthy et al. (2009) developed a

relation between block RQD and production by surface miner.

Figure 2.22: Types of fracture in cleated coals (after Roxborough and Phillips, 1981)

c) Schmidt rebound hardness number: Schmidt hammer test was reported to have a

possible use for the prediction of machine performance in mechanical excavation

(Goktan and Ayday, 1993). Shimada and Matsui (1994) used rock impact hardness

number for prediction of drivage/drilling rate. Goktan and Gunes (2005b) determined

Schmidt hammer rebound number for predicting cutting rates for a roadheader.

According to Adebayo (2008), Schmidt hammer rebound number exhibited a strong

correlation with the cutting rate. Schmidt hammer rebound values were correlated with

compressive strength by Atkinson et al. (1986). But, this method is of limited use on

very soft or very hard rocks (ISRM, 1981).

d) Rock mass rating: A number of models were developed relating roadheader

performance to rock mass properties such as the rock mass rating (RMR) and rock

quality designation values (Fowell and Johnson, 1982). Bilgin et al. (1996) utilized

uniaxial compressive strength, rock quality designation and machine power to predict

43

the instantaneous cutting rate. Sandbak (1985) developed a model that utilizes the RMR

value to predict the bit usage in foot.

Based on the above literature review, it may be summarized that the machine cutting

performance is influenced by intact rock and rock mass properties (Figure 2.23).

2.4.3 Machine parameters

Performance of surface miner depends on machine configuration such as cutting tool

configuration (rake angle, attack angle, clearance angle and tip angle, pick lacing, type

of pick (point attack), number of picks, tip material), drum weight, drum width, engine

power, nature of coolant for tips, etc. Operational conditions of machine play important

role in production (Rai et al. 2011). Various machine parameters affect the production

performance apart from intact rock and rock mass properties. Production potential of

surface miner depends on method of working to be adopted, which in turn relies on field

conditions. The mode of loading plays a key role in production. The production

capacities of surface miner depends on face length, depth of cut, machine speed, drum

width, etc., as given in Table 2.14 (Dey, 1999).

Table 2.14: Production capacity of surface miner in different working modes (Dey, 1999)

Method of

working Windrowing mode Conveyor loading mode

Empty travel

back method e

e

W x60SxLxd

L/v + L/vP =

1000

c t e

e

W x60Sxd

L/v+t /L +t /LP =

1000

Turn back

method t

e

Wx60SxLxd

L/v+tP =

1000

c t t

e

W x 6 0S x d

1 /v + t /L + t /LP =

1 0 0 0

Continuous

mining method e

SxvxdxWx60P =

1000 c t

e

W x 6 0S x d

1 /v + t /LP =

1 0 0 0

Where, Pe = estimated production (m3)

L= length of face (m)

d= predetermined depth of cut (mm)

v= machine speed during cutting (m/min)

tt= machine turning time (min)

te= empty travel back time (min)= L/ve

W= working hours available in shift (hr)

S= width of cutting drum (m)

tc= truck changing time (min)

Lt = length of cut to fill one truck (m)

= truck capacity(m3) x fill factor) /

(Sxdxswell factor/1000)

ve = machine speed during empty

travel (m/min)

44

Figure 2.23: Intact rock and rock mass parameters influencing machine performance

Inta

ct R

ock

and R

ock

Mas

s P

aram

eter

s

Inta

ct r

ock

Physi

cal

pro

per

ties

R

ock

stre

ngth

Gra

in s

ize

& i

ts

ori

enta

tion

(Mic

ro)

UC

S

Abra

sivit

y

Den

sity

Rock

type

Igneo

us

Geo

logic

al

feat

ure

s

Poro

sity

Toughnes

s

Quar

tz

Sil

ica

pre

sent

Cem

ent

type

Wat

er

Sed

imen

tary

M

iner

al

com

posi

tion

Anis

otr

opy

(Mac

ro)

Met

amorp

hic

M

odulu

s of

Ela

stic

ity

Sei

smic

wav

e

vel

oci

ty

Reb

ound

stre

ngth

val

ue

Rock

Mas

s

Rat

ing

Dis

conti

nuit

y

char

acte

rist

ics

UC

S

Gro

und w

ater

condit

ion

Str

uct

ura

l

feat

ure

s

Type/

ori

gin

of

rock

RQ

D

Ori

enta

tion

Spac

ing

Wea

ther

abil

ity

Rock

mas

s

45

The broad classification of various machine parameters influencing production

performance are categorized into cutting tool configuration, specifications of cutting

drum, engine power, project strategy and operational experience as shown in Figure

2.24.

2.5 Working Performance of Surface Miners

The present surface miners of Wirtgen, L&T and Krupp make in use in Indian coal,

limestone and bauxite mines are capable of handling rocks having compressive strength

up to 50 MPa. Vermeer surface miner is capable of excavating ore/rock type having

uniaxial compressive strength of 80-100 MPa and can produce 300-1600 t/h on a cutting

width of 3 m and cutting depth up to 70 cm. Bauxite deposit having lateritic overburden

of maximum uniaxial compressive strength of 70 MPa could be handled by surface

miner (Pradhan, 2009). The working performance by different types of surface miners

in different rock formations is given in Table 2.15. Surface miner can cut oil-shale

seams more exactly than rippers (2-7 cm) with deviations about one centimeter

(Sabanov and Pastarus, 2008). Production contribution from surface miners in 2010-11

in CIL was about 103 Mt which was 26 % of total production. Details of surface miners

deployed and production from the same in different subsidiaries of CIL are furnished in

Table 2.16 (Anon., 2011).

2.5.1 Boundary conditions for applicability and selection

a) Applicability

Despite such lucrative benefits of surface miner technology and certain successful

applications in different parts of the globe for mining different minerals/ores, it is yet to

be universally accepted due to the rigid boundary conditions of its applicability. A few

surface miners are principally governed by natural factors that are often beyond human

control.

Application of surface miner very much depends on the rock strength as well as geology

of the deposit. Moreover, the surface miner required controls on some essential factors

to work in the field efficiently. Surface miner can be applicable for the situation where

one or more condition exists as illustrated in the section.

46

Figure 2.24: Machine parameters influencing production performance

Mac

hin

e P

aram

eter

s

Cutt

ing T

ools

S

pec

ific

atio

ns

Lac

ing p

atte

rn

Type

of

pic

ks

No. of

tools

Qual

ity o

f

man

ufa

cture

Work

ing

area

Pro

ject

str

ateg

y

Rep

airi

ng o

f

bre

akdow

ns

Oper

atio

nal

exper

ience

Uti

liza

tion (

24/1

6/1

2)

hours

shif

t ti

me

Gra

die

nt

Mai

nta

in q

ual

ity

(sel

ecti

ve

min

ing)

Load

ing

met

hod

No. of

surf

ace

min

ers

Cutt

ing d

rum

wid

th

Oper

atin

g/c

utt

ing

spee

d

Engin

e

rati

ng/p

ow

er

Cutt

ing d

rum

dep

th

Cutt

ing d

rum

dia

met

er

Load

ing

opti

on

47

Table 2.15: Working performance of a few surface miners

Sl. No. Mine Type Condition Production (t/h)

1

2

3

4

5

6

7

8

Limestone mine,

Pannedam, India

(www.wirtgen.com)

Bauxite mine

(www.wirtgen.com)

Frija ore deposit

Guinea

(www.wirtgen.com)

Adanakuruchi, ICL

(Dey and Ghose,

2008)

Limestone, MCL

(Dey and Ghose,

2008)

Lakhanpur, CCL,

India (Pradhan and

Dey, 2009)

Bansundhara

(Pradhan and Dey,

2009)

Talabira

(Pradhan and Dey,

2009)

2500SM

2200SM

2500SM

2100SM

2600SM

2100SM

2200SM

2200SM

Material: Limestone

Density: 2.2 t/m3

UCS: 30 to 50 MPa

Material: Bauxite

Density: 2.2 t/m3

UCS: 30 to 125 MPa

Not available

Material: Limestone

Density: 2.2 t/m3

PLSI: 2.1

Abrasivity: 1.5

Material: Limestone

Density: 2.2 t/m3

PLSI: 2.7

Abrasivity: 1.5

Material: Coal

Density: 1.4 t/m3

PLSI: 1.1

Abrasivity: 0.4

Material: Coal

Density: 1.4 t/m3

PLSI: 1.2

Abrasivity: 0.6

Material: Coal

Density: 1.4 t/m3

PLSI: 1.15

Abrasivity: 0.6

613

250

360

143

210

210

138.6

198

i) Ground topography: Surface miner operates well in flat or mildly inclined deposit.

It cannot at all operate in rough terrain. For application of surface miner ground

preparation is very much essential. The surface should be as level as possible. Topsoil,

large loose stones, trees and roots must be removed. Troughs and hillocks, as well as

steps with a shoulder height of more than 0.4 m must be leveled. In other words, surface

48

miners can finish leveling a clean surface once it has been roughly leveled by some

other means. For mines where the topography is hilly, uneven and rugged, and the rock

is strong, the need of rigorous ground preparation may alone be good enough to put

aside the consideration of surface miner application (Anon., 2010). Joints affect the

stability of slope (Jayanthu et al., 2002; Ajaykumar et al., 2008).

Table 2.16: Production performance of surface miners in Indian coal mines (2010-11)

Company Project Drum size

(mm) Make Population

Coal

production

(Mt)

CCL Ashoka

3800 Wirtgen

1 6.01

2200 4

Piparwar 2200 Wirtgen 1 2.77

SECL

Gevra 3200 L&T 3

22.82 3800 Wirtgen 3

Dipka Exp. 3200 L&T 1

11.72 3800 Wirtgen 2

Kusmunda 3200 L&T 2

4.71 3800 Wirtgen 2

MCL

Basundhara 2100 Wirtgen 2 2.38

Samleshwari 3800 Wirtgen 1

9.19 2100 Wirtgen 1

Belpahar 3800 Wirtgen 1 2.68

2100 Wirtgen 2 2.32

Lakhanpur 3800 Wirtgen 4

13.09 3000 L&T 1

Hingula 3800 Wirtgen 1 1.86

3000 L&T 1 2.78

Ananta

3800 Wirtgen 1 2.45

2200 BITELI 2

3000 L&T 1 4.61

2100 Wirtgen 1

Bhubaneshwari 2200 Wirtgen 2 2.09

Bharatpur

3800 Wirtgen 1

5.51 3000 L&T 1

2100 Wirtgen 2

Lingaraj 3800 Wirtgen 1 2.63

2200 Wirtgen 1 3.12

ii) Ground stability: Surface miners being heavy machines with its load distributed on

its crawler mountings, can operate only on stable ground, and not in unstable,

49

unconsolidated ground, or in ground above subsurface openings that may subside in

course of its operation. They cannot be used for the opencast extraction of locked-up

developed underground bord-and-pillar workings of coal mines. As these machines cut

thin layers of rock in each round, the parting above the underlying void gradually

becomes thinner after each cut. In the process the parting may weaken and subside

suddenly with no prior indication while the machine is cutting. Likewise, they should

not be engaged for mining of limestone or dolomite deposits with karst topography. The

underground water of karst topography carves out crevices, channels and cavities that

are susceptible to collapse from the surface. When enough limestone is eroded from

underground, a sinkhole may develop.

iii) Intact rock parameters: A stronger rock is more difficult to cut. Small changes in

rock properties adversely affect the performance of mechanical excavators (McFeat-

Smith and Fowell, 1977). Uniaxial compressive strength is the most widely accepted

parameter to measure strength of a rock sample, and is usually considered to be the most

useful guide to the performance of mechanical excavation (Brown and Phillips, 1977).

iv) Machine parameters: According to Murphy and Daneshmend (2006), cutting

design of machine has a role in production performance. Machine performance

parameters like cutting rate, pick force, specific cutting energy (SE), pick consumption,

vibration during cutting, etc. that restrict their applications, are strongly related to the

physico-mechanical properties of rocks, such as strength, hardness, toughness,

brittleness, abrasiveness, etc. (Irfan and Dearman, 1978; Bell, 1978; Hugman and

Friedman, 1979; Onodera and Asoka, 1980; Howarth, 1986; Howarth and Rowlands,

1986, 1987; Shakoor and Bonelli, 1991; Ulusay et al., 1994; Tugrul and Zarif, 1999).

Common machine parameters that play significant role in its cutting performance are

cutting tool configuration, rake angle, attack angle, clearance angle and tip angle, pick

lacing, type of pick, number of picks, tip material, drum weight, engine power, loading

options, depth of cut and nominal cutting speed.

v) Other factors: The other factors concerning the applicability of surface miner are

non-sticky material, selective mining requirement of thin seams or thin dirt bands, sized

50

material requirement without using a crusher and environmentally sensitive areas where

blasting is prohibited or restricted.

b) Selection

The common factors considered for selection of surface miner are type, thickness and

inclination of the seam or strata; material characteristics of the deposit; cuttability and

the resultant productivity; working conditions: area available for the maneuverability,

ground conditions, gradeability; stability of the overburden benches; requirement of the

plant in terms of the sized material; climatic conditions and economic feasibility.

The governing criteria for selection of surface miner are geotechnical parameters and

production requirement. Ghose (1996) stated that rock mass classification forms the

backbone of empirical design approach. It is necessary to recognize the caveats implicit

in its application. Majority of research undertaken with mechanical excavation systems

have followed and adopted rock mass classification and made their own site-specific

recommendations. The pioneering system of this type of classification was the

Discontinue Strength Classification propounded by Franklin et al. (1971). This was

followed by Rippability Rating Chart (Weaver, 1975), Excavation Index (Kirsten,

1982), Geological Factors Rating Scale (Minty and Kearns, 1983), Engineering

Classification of Coal Measures (Scoble and Moftuoglu, 1984), Rippability Chart

(Singh et al., 1986), Excavatability Index Rating Scheme (Hadjigeorgiou and Scoble,

1990), Diggability Index (Karpuz, 1990) and Revised Excavatability Graph (Pettifer and

Fookes, 1994).

Barendsen (1970) developed a relationship between specific energy and uniaxial

compressive strength for the machines working with cutting (drag bit) and crushing

(rotary bit) principles respectively. Atkinson (1971) was the first to classify the

excavatability of the rock mass based on the field seismic velocity measurement.

Manufacturers of surface miner compute performance curves based on uniaxial

compressive strength or the ratio of compressive and tensile strength. These indices

have been used either directly or indirectly to select appropriate excavation systems, the

equipment used in mining and assessment of the excavatability (Kramdibrata, 1996).

51

2.6 Cuttability Assessment Models

Many scientists, scholars and researchers developed several empirical approaches using

different parameters to ascertain the suitability of rocks for designing different

mechanical excavation systems, namely,

i. teeth (dozer, shovel, bucket wheel excavator),

ii. disc cutters and button bits (rock drill, full face tunnel boring machine),

iii. ripping tool (coal plough, ripper, rock-breaker) and

iv. pick-mounted rotary cutting head/drum (roadheader, shearer, surface miner).

A few cuttability models are discussed below:

2.6.1 Atkinson (1971)

Field seismic velocity has been widely used as a means to assess rippability and

excavation possibilities without blasting. According to Atkinson (1971), shovel, bucket

wheel excavator and scraper are easily rippable for seismic velocity up to 1500 m/s.

Tractor scraper is marginally rippable up to 2000 m/s.

2.6.2 Franklin, Broch and Walton (1971)

Franklin et al. (1971) suggested a bivariate rock mass classification in which two rock

properties, namely, Fracture Index and Point Load Index play major roles. Fracture

Index is used as a measure of discontinuity and is defined as the average spacing of

fractures in a core or rock mass. These two parameters can be plotted on a classification

diagram to predict rippability as shown in Figure 2.25 where If and Is represent Fracture

Index and point Load Index respectively and this diagram is sometimes referred to as

the graphical method. The classification diagram is divided into three main typical

zones i.e. digging, ripping and blasting. Broken and weak rock masses plot towards the

lower left of the diagram whereas massive and strong ones plot toward the upper right.

The former is easy to excavate using mechanical equipment and the latter requires

blasting.

2.6.3 Gehring (1980)

The Voest-Alpine Rock Cuttability Index (VA-RCI) was developed as a measure to

evaluate a factor describing the cuttability of a rock.

52

Figure 2.25: Discontinuity Strength Classification (after Franklin et al., 1971)

This index has been used by the Voest-Alpine to classify rock for the application of the

Tunnel Boring Machine (TBM) and roadheader as given in Table 2.17.

Table 2.17: Mechanical excavation system in relation to VA-RCI (after Gehring, 1980)

VA-RCI

(mm) Cuttability with TBM Cuttability with roadheader

< 0.5 Moderate performance Not applicable

0.5 - 0.8 Fair to good performance Applicable only when rock occurs in

thin single layer

0.8 - 1.5 Best range of application Heavy machines and strong conical

picks

1.5 - 2.5 Only TBM with single disc

cutters

Medium weight machines with conical

picks

2.5 - 5 Wheels with conical picks

disc cutters for abrasive rock

Medium and light weight machines,

conical picks & drag type picks, best

range of application.

5 - 10

Application of TBM only in

shielded version with drag

type picks

Medium and light weight machines slim

conical and drag type picks.

Point Load Index (MPa)

BLAST TO

FRACTURE

BLAST TO

LOOSEN

RIPPING

DIGGING

M= Medium

EH= Extremely high VL= Very low

H= High L=Low EL= Extremely low

VH= Very high

Fra

ctu

re I

ndex

(m

)

EH

VH

M

2

0.006

VL

L

H

0.02

0.06

0.2

0.6

EH VH M

0.10.003 VL L H 10 1.0 3.0 0.3

53

2.6.4 Kirsten (1982)

Kirsten (1982) identified the parameters influencing the excavatability of the rock,

namely, strength of rock, in-situ rock density, degree of weathering, seismic velocity,

block size, shape of excavation relative to excavating equipment, block shape, block

orientation, joint roughness, joint gouge and joint separation. Kirsten formulated an

Excavatability Index, a similar system like NGI ‘Q’ Index, as below:

N = Ms x (RQD/Jn) x Js x (Jr/Ja) (Equation 2.16)

Where,

N = excavatability index,

Ms = mass strength number (vide Table 2.18),

RQD = rock quality designation (Deere and Miller, 1966),

Jn = joint set number (vide Table 2.19),

Js = relative ground structure number (vide Table 2.20),

Jr = joint roughness number (vide Table 2.21) and

Ja = joint alteration number (vide Table 2.22).

Table 2.18: Mass strength number (Ms) of rocks

Rock Hardness Identification in profile UCS (MPa) Ms

Very soft

Material crumbles under firm (moderate)

blows with sharp end of geological pick and

can be peeled off with a knife. It is too hard to

cut a triaxial sample by hand.

1.7 0.87

1.7-3.3 1.86

Soft

Can just be scraped and peeled off with a

knife; indentations 1-3 mm show in the

specimen with firm (moderate) blows of pick

point.

3.3-6.6 3.95

6.6-13.2 8.39

Hard

Cannot be scraped or peeled with a knife;

hand held specimen can be broken with

hammer end of a geological pick with a single

firm (moderate) blow.

13.2-26.4 17.70

Very hard Hand held specimen breaks with hammer end

of pick under more than one blow.

26.4-53.0 35.00

53.0-106.0 70.00

Extremely Hard Specimen requires many blows with

geological pick to break through intact

material

106.0-212.0 140.00

above 212.0 280.00

54

Table 2.19: Joint set number (Jn) of rocks

Number of joint sets Joint set number (Jn)

Intact, no or few joints/fissures, and intact granular materials

One joint/fissure set

One joint/fissure set plus random

Two joint/fissure sets

Two joint/fissure sets plus random

Three joint/fissure sets

Three joint/fissure sets plus random

Four joint/fissure sets

Multiple joint/fissure sets

1.00

1.22

1.50

1.83

2.24

2.73

3.34

4.09

5.00

Table 2.20: Relative ground structure number (Js) of rocks

Dip direction* of closer

spaced joint set (in degree)

Dip angle# of closer spaced

joint set (in degree)

Ratio of joint spacing, r

1:1 1:2 1:4 1:6

180/0

0

0

0

0

0

0

0

0

0

0

0/180

180

180

180

180

180

180

180

180

180

180

180/0

90

85

80

70

60

50

40

30

20

10

5

0

5

10

20

30

40

50

60

70

80

65

90

1.00

0.72

0.63

0.52

0.49

0.49

0.53

0.63

0.84

1.22

1.33

1.00

0.72

0.63

0.52

0.49

0.49

0.53

0.63

0.84

1.22

1.33

1.00

1.00

0.67

0.57

0.45

0.44

0.46

0.49

0.59

0.77

1.10

1.20

1.00

0.81

0.70

0.57

0.53

0.52

0.56

0.67

0.91

1.32

1.39

1.00

1.00

0.62

0.50

0.41

0.41

0.43

0.46

0.55

0.71

0.99

1.09

1.00

0.86

0.76

0.63

0.57

0.54

0.58

0.71

0.97

1.40

1.40

1.00

1.00

0.57

0.44

0.35

0.40

0.40

0.42

0.51

0.67

0.90

1.00

1.00

0.90

0.84

0.67

0.59

0.56

0.60

0.75

1.02

1.46

1.40

1.00

* Dip direction of closer-spaced joint set relative to direction of rip/cut # Apparent dip angle of closer spaced joint set in vertical plane containing direction of

ripping/cut

For intact material take Js = 1.0 For r < 0.125, take Js as for r = 0.125

55

Table 2.21: Joint roughness number (Jr)

Joint separation Joint condition Joint roughness number (Jr)

Joints tight or closing

during excavation

Discontinuous joint

Rough or irregular, undulating

Smooth undulating

Slicken-sided undulating

Rough or irregular, planar

Smooth planar

Slicken-sided planar

4.0

3.0

2.0

1.5

1.5

1.0

0.5

Joints open and

remain open during

excavation

Joints either open or containing soft

gouge of sufficient thickness to

prevent joint wall contact after

excavation

1.0

Table 2.22: Joint alteration number (Ja)

Description of gouge

Joint alteration number (Ja)

for joint separation (mm)

< 1.0*

1.0-5.0**

> 5.0***

Tightly healed, hard, non-softening impermeable

filling 0.75 - -

Unaltered joint walls, surface staining only 1.0 - -

Slightly altered, non-softening, non-cohesive rock

mineral or crushed filling 2.0 4.0 6.0

Non-softening, slightly clayey non-cohesive filling 3.0 6.0 10.0

Non-softening strongly over-consolidated clay

mineral filling, with or without crushed rock 3.0

# 6.0

# 10.0

#

Softening or low-friction clay mineral coatings and

small quantities of swelling clays 4.0 8.0 13.0

Softening moderately over-consolidated clay mineral

filling, with or without crushed rock 4.0

# 8.0

# 13.0

#

Shattered or micro-shattered (swelling) clay gouge,

with or without crushed rock 5.0 10.0 18.0

* Joint walls effectively in contact

** Joint walls come in contact after

approximately 100 mm of shear

*** Joint walls do not come in contact at all

upon shear # Values added to Barton’s data

Accordingly, cuttability of rock was classified as given in Table 2.23.

56

Table 2.23: Assessment of cuttability based on excavatability index (Kirsten, 1982)

Excavatability Index (N) Cuttability

1 < N < 10

10 < N < 100

100 < N < 1000

1000 < N < 10000

N > 10000

Easy

Hard

Very hard

Extremely hard, advised blasting

Blasting

2.6.5 Singh, Denby, Egretli and Pathon (1986)

Singh et al. (1986) proposed a parameter referred to as Toughness Index (TI) of rock

which is a derived parameter from the stress-strain curve, and is a measure of elastic

strain energy requirements for deforming with a cutting tool. This is one of the

important parameters in evaluating the cuttability of rock, with a particular reference to

rock cutting machines, such as roadheaders, tunnel boring machines, surface miners and

any excavator using point attack picks (Atkinson et al., 1986; Farmer, 1986). The

toughness index is defined as:

2

1002

cTI xE

σ= (Equation 2.17)

Where,

TI = toughness index (MPa),

σc = uniaxial compressive strength (MPa) and

E = Young’s modulus (MPa).

According to Atkinson et al.(1986), when the toughness index is greater than 27 MPa

the intact rock reaches its limit of cuttability and a field study is necessary to evaluate

the joint pattern which can assist in excavating the rock mass. Table 2.24 shows the

values of TI for a range of rocks.

The overall argument is that the excavation rate of a rock cutting machine is directly

proportional to the energy input and inversely proportional to the rock fracture

toughness provided the efficiency of the process remains constant. If Young’s modulus

is high in relation to strength, the rock is brittle and a proportionately lower strain

energy level will be required to fracture the rock.

57

Table 2.24: Toughness Index of a range of rocks (after Atkinson et al., 1986)

Rock classification

by strength

UCS

(MPa)

Young’s Modulus

(GPa)

Toughness Index

(TI)

Very high strength

High strength

Medium strength

Low strength

Very low strength

-

150.30

116.00

58.51

29.92

-

40.00

29.00

13.36

7.76

-

28.12

23.20

12.81

5.77

Figure 2.26 shows the relationship between rock toughness and production of DOSCO

Mk IIIA rock cutting machines working in coal measure rocks. All the curves indicate

that machine efficiency is exceptionally low since all the values N.η are less than 5kW.

Figure 2.26: Cuttability of rocks based on rock toughness (after Farmer, 1986)

2.6.6 Farmer (1986)

Farmer (1986) proposed the Fracture Index or rock toughness which is defined as the

strain energy available to fracture the rock which is equal to {σc* (∆V/V)} per unit

volume of rock of (σc2 /E) in linear terms. This can be related to the energy input of the

Production – bcm/h

rocks at the top of the strength

range for most generic groups,

some weaker tough rocks

Basalts, weaker igneous

rocks, mudstone, generally

brittle rocks

Ro

ck t

ou

ghn

ess

- M

Pa

Average cutting performance

chalks, brittle weak rocks, weak

limestone, sandstone

Efficient cutting still

machine water jet assisted

Insufficient cutting: blunt

tool: low energy transfer

4 kW

2 kW

1 kW

0.00

0.25

0.50

0.75

1.00

1.25

0 20 40 60 80

58

rock face from the cutting machine which can be expressed as the cutting energy per

unit volume of rock excavated:

2

Energy InputL*

N c

E

ση= =

(Equation 2.18)

Where,

N = power (kW),

η = efficiency,

L* = production (bcm/h),


E = Young’s modulus (GPa).

2.6.7 Roxborough (1987)

Roxborough (1987) correlated specific energy with uniaxial compressive strength for all

sedimentary rocks in a simple equation as follows and classified cuttability of rock for

heavy weight machines as given in Table 2.25.

SE = 0.25σc + 0.11 (Equation 2.19)

Where,

SE = specific cutting energy (MJ/m3) and

σc = uniaxial compressive strength (MPa).

Table 2.25: Selection of excavating (cutting) machine on specific energy values

SE (MJ/m3) Cutting performance for heavy weight machines

25-31 Machine can cut economically only if occurs in thin bed (<0.3 m)

20-25 Poor cutting performance. Low speed cutting improves stability

17-20 Moderate to poor performance. For abrasive rocks frequent pick

change is required

8-17 Moderate to good cutting performance with low pick wear

<8 High advance rate and high productivity

59

2.6.8 Bilgin, Seyrek and Shahria (1988)

Bilgin et al. (1988) developed rock mass cuttability index (RMCI) relating uniaxial

compressive strength and rock quality designation and estimated the advance rate of a

cutting machine. The advance rate can be predicted as given in Figure 2.27.

RMCI = σc (RQD/100)2/3

(Equation 2.20)

Where,


RQD = rock quality designation.

Figure 2.27: Advance rate verses RMCI

2.6.9 Gehring (1989)

Gehring (1989a, b) proposed that the performance of a rock cutting machine could be

defined as:

L* = k.N/σc (Equation 2.21)

Where,

L* = production or cutting performance (bcm/h),

N = cutter head power (kW),

k = a factor for consideration of relative cuttability or tuning effect between

cutting machine and rock and

σc = unconfined compressive strength (MPa).

RMCI

Ad

van

ce R

ate

(x 1

0 b

m3/h

)

20

15

10

5

0

1200 1000 800 600 400 200 0

60

According to Gehring (1992), this takes account of the cutting action and other factors.

The factor which significantly influences the cutting process and cutting performance is

cutting speed of pick indentation. Later, Gehring (1992) modified his earlier formula as:

k = k1 x k2 x k3

Where,

k1 = relative cuttability of intact rock and

= 6 for very tough and plastic rock

= 7 for tough and plastic rock

= 8 for average rock

= 9 for brittle rock

= 10 for very brittle rock

= 10 - 15 for coal

k2 = influence of discontinuity such as joint, bedding plane, etc. and

= 1 for massive and discontinuity distance > 25 cm

= 1.5 - 2 for layered/fissured, thinner bed rock, discontinuity 10 – 25 cm

= 2.5 for layered/fissured/interbedded rock discontinuity <5 cm

k3 = influence of specific cutting condition and is a function of no sumping,

cutting height, cutter head oscillation, pick array, pick shape. For road-

header its value ranges from 3.5 to 4.5.

2.6.10 Kolleth (1990)

In relation to the use of uniaxial compressive strength as a means of predicting the

applicability of continuous digging, transport and spreading equipment Kolleth (1990)

proposed the following ranges of uniaxial compressive strength for the different

mechanical excavators (Figure 2.28).

2.6.11 Hadjigeorgiu and Scoble (1990)

Hadjigeorgiu and Scoble (1990) developed an Excavation Index (EI) classification

scheme and correlated it with other excavation indices.

61

Figure 2.28: Application of UCS in selecting mechanical excavators (after Kolleth, 1990)

The index was developed combining some rock and geological parameters as given

below:

EI = (Is + Bs).W.Js (Equation 2.22)

Where,

EI = excavation index,

Is = point load strength index,

Bs = block size index,

W = weathering index and

Js = relative ground structure index.

The ratings corresponding to the parameters of EI are listed in Table 2.26.

Table 2.26: Excavation index rating scheme

Class I II III IV V

Point Load Index < 0.5 0.5 – 1.5 1.5 – 2.0 2.0 – 3.5 > 3.5

Is 0 10 15 20 35

Volumetric Joint

Count > 30 30-10 10-3 3-1 1

Bs 5 15 30 45 50

Weathering completely highly moderately slightly unweathered

W 0.6 0.7 0.8 0.9 1.0

Relative Ground

Structure

very

favourable favourable

slightly

favourable unfavourable

very

unfavourable

Js 0.5 0.7 1.0 1.3 1.5

62

2.6.12 Jones and Kramadibrata (1995)

Jones and Kramadibrata (1995) established a relationship between the productivity of

continuous surface miners and uniaxial compressive strength of rocks. It was observed

that the production decreases in lognormal form with increase in uniaxial compressive

strength of rock (Figure 2.29).

Figure 2.29: Relationship between production of surface miners and UCS of rock

2.6.13 Kramadibrata and Shimada (1996)

Kramadibrata and Shimada (1996) have shown a functional relationship between Voest

Alpine Rock Cuttability Index (RCI) and various intact rock, rock mass and machine

parameters as given:

{ } ( ){ }C C t C C CRCI = N/(L*σ ) αf γ*δ/σ ,(σ /σ ),(d/δ),(Ey/σ ),(F/δ*σ ) (Equation 2.23)

Where,

N= rated machine power (kW),

L = production rate (m3/hr),

Cσ = uniaxial compressive strength of rock sample (MPa),

γ = specific weight (kN/m3),

δ= discontinuity spacing (m),

Ey =Young’s modulus (MPa),

F = Schimazek’s abrasivity factor (N/mm) and

63

tσ = tensile strength of rock sample (MPa).

2.6.14 Tiryaki and Dikmen (2006)

Tiryaki and Dikmen (2006) established a relationship between tensile strength and

specific energy (SE) in laboratory scale using linear cutting by picks, expressed in

MJ/m3, of rocks as follows:

SE = 0.67 + 3.12σt (Equation 2.24)

Where,

σt = tensile strength of rock (MPa).

2.6.15 Murthy, Kumar, Jain and Dash (2009)

Considering the various parameters relating to the intact rock, rock mass and machine

design and operating parameters an index, CISM (Cuttability Index of Surface Miner)

was developed (Murthy et al., 2009). The CISM can be determined from the following

equation:

MFCISM =

RMF x IRF (Equation 2.25)

The term RMF represents Rock Mass Factor and is represented by field P-wave velocity

in the rock mass measured in km/s. The term IRF represents Intact Rock Factor and is

given by,

IRF = LVP x SiO2 (Equation 2.26)

Where,

LVP = laboratory P-wave velocity in rock (km/s) and

SiO2 = silica content in rock mass (%).

The term MF represents machine design/operating parameters and is represented by,

MF = EPxCSxCA (Equation 2.27)

Where,

64

EP = total engine power (kW),

CS = cutting speed (m/s) and

CA = total cutting area engaged in cutting rock at any point of time.

This can be calculated from the following equation,

πDCA = W

6 (Equation 2.28)

Where,

D = drum diameter (m) and

W = drum width (m).

It is assumed that at any time only 1/6th

of the circumferential length of drum gets

engaged in cutting the rock. The equation established for machine performance

prediction is:

1b

0NTPH = b (CISM) (Equation 2.29)

Where,

NTPH = Production (tons/hr) and

b0 and b1 = constants.

2.6.16 Dey and Ghose (2009)

Dey and Ghose (2009) developed a nomogram to fathom the suitability of a surface

miner for a given rock mass taking into account a few key influencing parameters,

namely, point load strength index, volumetric joint count, rock abrasiveness and

direction of machine operation with respect to joint orientation. Considering that

machines with higher power can cut stronger rocks, its engine power has also been

rated. Ratings of these parameters are tabulated in Table 2.27. The addition of

appropriate ratings of these four parameters for a given rock mass and one parameter for

an identified model of surface miner gives the cuttability index (CI) for the whole

system.

65

Table 2.27: Ratings of parameters of cuttability index for surface miners

Class I II III IV V

Point load index (IS50) < 0.5 0.5 - 1.5 1.5 - 2.0 2.0 - 3.5 > 3.5

Rating (Is) 5 10 15 20 25

Volumetric joint count

(no./m3)

> 30 30 – 10 10 – 3 3 – 1 1

Rating (Jv) 5 10 15 20 25

Abrasivity < 0.5 0.5 - 1.0 1.0 – 2.0 2.0 - 3.0 > 3.0

Rating (Aw) 3 6 9 12 15

Direction of cutting

respect to major joint

direction

720 - 90

0 54

0 - 72

0 36

0 - 54

0 18

0 - 36

0 0

0 - 18

0

Rating (Js) 3 6 9 12 15

Machine power (kW) > 1000 800-1000 600-800 400-600 < 400

Rating (M) 4 8 12 16 20

The technical feasibility of the system can be appraised from the guideline provided in

Table 2.28.

Table 2.28: Cuttability index and expected surface miner performance

CI 50 > CI 50< CI < 60 60< CI < 70 70 < CI < 80 CI > 80

Surface

Miner

Performance

Very easy

excavation

Easy

excavation

Economic

excavation

Difficult

excavation,

may be not

economic

Surface

miner should

not be

deployed

CI = Is + Jv + Aw + Js + M (Equation 2.30)

Where, Is, Jv, Aw, Js and M are the ratings corresponding to point load index (IS50),

volumetric joint count, abrasivity, direction of cut with respect to major joint orientation

and machine power respectively.

The authors also suggested that the cutting performance of a surface miner (L) may be

estimated from cuttability index (CI), the rated capacity of the machine (Mc) and a

factor for specific cutting condition (k) that varies from 0.5 to 1.0 as follows:

66

c

CIL = 1 - kM

100

(Equation 2.31)

Where,

L = production or cutting performance (bm3/h),

cM = rated capacity of machine (bm3/h),

CI = cuttability index and

k = a factor for consideration of influence of specific cutting condition and is a

function of pick lacing, pick shape etc. and varies from 0.5 – 1.0.

Jones and Kramadibrata (1995), Murthy et al. (2009) and Dey and Ghose (2009)

developed predictive models for surface miner. A comparative study of these models

was conducted to evaluate their relative accuracy. The results of the analyses inferred by

putting input parameters collected from a few Indian coal and limestone mines are

produced in Table 2.29. The predictive model developed by Murthy et al. (2009)

yielded nearest result amongst all the three models.

Table 2.29: Comparative study of predictive models

Mine A Mine B Mine C Mine D

Input

parameters

UCS =19.1 MPa

Density = 1.18 t/m3

IVp = 0.41 km/s

LVp = 1.26 km/s

Engine P = 895 kW

Silica = 0.5 %

PLSI = 1.96

CAI = 0.18

Joint spacing = 3-

10/m3

UCS =23.5 MPa

Density = 1.29 t/m3

IVp = 0.52 km/s

LVp = 2.84 km/s

Engine P = 895 kW

Silica = 0.5 %

PLSI = 1.12

CAI = 0.19

Joint spacing = 3-

10/m3

UCS =35 MPa

Density = 2.49 t/m3

IVp = 2.36 km/s

LVp = 4.20 km/s

Engine P = 450 kW

Silica = 16 %

PLSI = 2.32

CAI = 0.31

Joint spacing = 1/m3

UCS =13 MPa

Density = 2.4 t/m3

IVp = 2.26 km/s

LVp = 3.93 km/s

Engine P=597

kW

Silica = 16 %

PLSI = 0.80

CAI = 0.25

Joint spacing =

1/m3

Actual

production (t/h) 1051 910 140 181

Predicted

production (t/h)

Jones and

Kramadibrata

(1995) 421 310 46 1372

Murthy et al.

(2009) 680 564 174 182

Dey and Ghose

(2009) 448 488 181 287

67

2.7 Limitations of Some Key Cuttability Assessment Models

Assessment of machine performance is an attempt to relate the machine specifications

to the rock conditions, by recording its production rate (or speed of advance), fuel

consumption and pick consumption. Machine specifications are related to the motor

power of the machine and characteristics of the hydraulic or electrical devices which

supply forces to the cutting tools. The machine operational parameters are not

extensively investigated by most of the researchers.

This opens a wide scope for developing new relationships and also fine tuning to some

of the existing relationships between machine, intact rock and rock mass parameters for

achieving desired production performance with surface miners. The limitations of some

key cuttability assessment models for predicting surface miner, proposed by earlier

researchers, are tabulated in Table 2.30. This exercise is required to understand the

existing models and their application regime so that needful modifications can be

attempted to improve productivity by surface miner.

Most of the researchers, considered either intact rock or rock mass parameters with one

or two properties for determining the relations with specific energy, cuttability.

Knowing the available mechanical power for cutting and machine advance enables the

cutting forces at the tips of the cutting tools and the thrust force to be determined.

Therefore, it can be said that the performance of surface miners can be better judged by

utilizing the combination of intact rock and rock mass properties, available machine

power and operating conditions.

There is a lack of research on application of surface miner in particular under varied

rock conditions. Therefore, the objective of the study is to investigate the various intact

rock and rock mass parameters and to assess their influence on the cutting performance

of surface miner and to develop constituent relationships in order to predict the

performance of surface miners for different Indian geo-mining conditions.

68

Table 2.30: Limitations of a few models for cuttability assessment of surface miners

Sl.

No. Researchers Limitations

1 Jones and Kramadibrata

(1995)

The equation developed for prediction of surface

miner production contains only uniaxial compressive

strength of rock. The predicted results using this

equation showed deviation from actual production.

This may be due to non-incorporation of other

influential parameters, namely, machine and rock

mass parameters. The equation thus needs to be

refined by including other controlling factors so that

it can become applicable widely.

2

Kramadibrata and Shimada

(1996)

Kramadibrata and Shimada (1996) derived cuttability

index of surface miner by considering machine

power, specific weight, discontinuity spacing,

Young’s modulus, abrasivity and tensile strength as

functional parameter. Machine operating parameters

were not considered in this model.

3 Murthy et al. (2009)

Murthy et al. (2009) evaluated the cuttability index

of surface miner considering laboratory P-wave

velocity, silica content, in-situ P-wave velocity,

engine power, sweep area in cutting and cutting

speed. This model though yielded reasonable

predictions, needs further refinement by

incorporating the actual cutting area, desired chip

size and operational control with respect to intact

rock and rock mass parameters.

4 Dey and Ghose (2009)

Only a few intact rock and rock mass properties were

considered along with machine power by the

researchers to determine cuttability index. The drum

design and operating parameters were not considered

in this mathematical model. The model developed

also did not yield reliable production estimates.

2.8 Identification of Influencing Parameters

The purpose of identification of the influencing parameters is to understand their

relevance in the performance of surface miner and subsequently, use them for predicting

its performance. Several models were developed by various researchers on different

machines to understand its performance with respect to intact rock and rock mass

parameters. The models covered rock cutting by picks, specific energy, cuttability and

production prediction by different machines (Table 2.31).

69

Table 2.31: Parameters used in different models for predicting machine performance

Parameters 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Models

Evans (1965) ◙ ◙

Barendsen (1970) ◙

Atkinson (1971) ◙

Franklin et al. (1971) ◙

Kirsten (1982) ◙ ◙

Singh et al. (1986) ◙ ◙

Farmer (1986) ◙ ◙ ◙

Roxborough (1987) ◙

Bilgin et al. (1988) ◙ ◙

Gehring (1989) ◙ ◙ ◙ ◙

Hadjigeorgiu and Scoble (1990) ◙ ◙

Jones and Kramadibrata (1995) ◙

Kramadibrata and Shimada (1996) ◙ ◙ ◙ ◙ ◙ ◙ ◙

Tiryaki and Dikmen (2006) ◙

Murthy et al. (2009) ◙ ◙ ◙ ◙ ◙

Dey and Ghose (2009) ◙ ◙ ◙ ◙

Kahraman et al. (2003) ◙

Total 9 3 2 1 1 4 2 2 3 3 2 5 1 2

Legend: 1. Uniaxial compressive strength, 2. Tensile strength, 3. Density, 4. Silica, 5.

Ground structure/ weathering condition, 6. Joints, 7. Rock quality designation, 8.

Seismic velocity, 9. Point load strength index, 10. Modulus of elasticity, 11. Abrasivity,

12. Machine/cutter head power, 13. Machine specifications, 14. Operational condition

The previous research revealed that the most influencing parameters in decreasing order

of importance for prediction of machine performance was uniaxial compressive strength

followed by machine power, joint conditions, tensile strength, modulus of elasticity,

point load strength index, density, seismic velocity, rock quality designation,

operational conditions, machine specifications, silica content and ground structure.

70

2.9 Research Methodology

An in-depth analysis of literature review was carried out in terms of parameters

influencing the performance of rock cutting machines and surface miner in particular as

well as predictive models developed by researchers. Accordingly, a research

methodology was framed in order to meet the objectives mentioned in section 1.3. The

methodology mainly involves identification of various critical parameters that have a

bearing on surface miner cuttability and performance prediction. The critical parameters

are intact rock, rock mass properties, machine and operational parameters identified

through literature review followed by field and laboratory investigations.

A comprehensive analysis through statistical, multiple regression, empirical and

artificial neural network approaches is proposed to be carried out to develop predictive

models for surface miner cuttability and performance assessment. Figure 2.30 describes

the proposed methodology for achieving the stated objectives.

2.10 Research Strategy

The research strategy includes a sandwich approach in which, both field and laboratory

investigations will be carried out for generating relevant data. Coal and limestone mines

(six mines) located in different parts of India will be the study sites. Different models of

surface miners shall be covered in this study. In order to achieve the objectives the

following research strategy will be adopted:

a) Identification of parameters influencing cuttability of rock and machine performance

based on literature review.

b) Establishment of a database of the relevant geotechnical properties, machine design

and performance parameters.

c) Identification of critical parameters for rock cuttability and surface miner

performance prediction.

d) Prediction of rock cuttability for surface miners.

71

Figure 2.30: Research methodology

Geological and

geotechnical parameters

Recognition of need

Research objectives

Scope of work

Surface miner

specifications

Work plan

Literature review

Field investigations

Intact rock and rock mass

Limestone Coal

Surface miner

performance

Intact rock

parameters

Laboratory investigations

Data analysis

Identification of critical parameters

Concept forming, simulation and analysis

Analytical Multiple regression Empirical ANN

Conclusions and recommendations

Evaluation and testing

Development of rock cuttability index

and machine performance prediction

72

e) Establishment of relationships between the geo-mechanical properties of intact rock,

rock mass and performance parameters of surface miners, namely, production, chip

size, diesel consumption and pick consumption.

f) Development of an integrated approach for the applicability, selection and

performance prediction of surface miner in a given site-specific condition.

2 literature review 2.1 introductionshodhganga.inflibnet.ac.in/bitstream/10603/32884/11/11_chapter...

Documents