rock excavation, underground, different excavation machines, applicability, limitations, theories of rock interaction, cutting tools, pick lacing pattern, various picks, types of excavation machines,

1. ROCK EXCAVATION MACHINES – UNDER
GROUND
U.Siva Sankar
Sr. Under Manager
Project Planning
Singareni Collieries Company Ltd
E-Mail :ulimella@gmail.com or
uss_7@yahoo.com
Visit at:
www.slideshare.net/sankarsulimella
Mechanical Rock Excavation
1

2. Mechanical Excavation Systems
Different mechanical excavation systems, like machines with;
Teeth (Dozer, Shovel, Scraper, Bucket wheel excavator, Bucket chain excavator)
Ripping tool (Coal Plough, ripper, rock breaker),
Pick mounted rotary cutting head/drum (Roadheader, Shearer, Continuous
miner, Surface miner)
Disc cutters and button bits (rock drill, Mobile tunnel miner, Tunnel boring
machine)
Auger tool (Continuous Auger Miner, Surface Auger Miner)
Application of Mechanical Systems
Under Ground:
Continuous Miners, Bolter miners, Auger Miners and shearers for coal or soft
nonmetalics
Boom type miners (road headers in soft to medium hard rocks)
Rapid excavation equipment (Mobile tunnel miners,Tunner borers, raise borers,
and shaft sinking rigs) for soft to medium hard and hard rocks)
Surface:
Rippers for very compact soil, coal, and weathered or soft rock
Bucket wheel and cutting head excavators for soil or coal
Augers and highwall miners for coal
Mechanical dredges for placers and soil
Classification of Underground mechanical excavator by rock type
Hard rock Soft rock
1.Roadheader 1.Roadheader
2.TBM 2.Continuous Miner
3.Mobile Miner 3.Shearer
4.Raise Borer
Comparison of mechanical excavation with drill and blast systems
Advantages Disadvantages
• Generally gives more rapid advance than • Cannot excavate very hard rock
blasting in soft to medium-hard rock.
• High capital cost
• Fewer unit operations
• Require specialist maintenance
• Smoother excavation profiles
• Not as flexible
• No blasting damage to surrounding rock
• Inherently safer
2

3. Parameters influencing applicability of mechanical miners
The decision to introduce a mechanical miner is generally based on the
predicted performance of the selected machine in the given geological and
operational conditions.
Since it is usually not possible to change the geological conditions, a
thorough study of the geological and geotechnical parameters (rock mass
and intact rock properties) at the feasibility and planning stages should be
carried out to match the machine and operational parameters to the
geological conditions.
Machine considerations
The general technical requirements of excavation machines, in addition to
safety and economy, are selective mining ability, flexibility, mobility and hard
and abrasive rock-cutting ability.
Selective mining ability is the ability to cut selectively in mixed face
conditions so that the mineral can be excavated separately, reducing
dilution.
Mobility means easy relocation of machines from one face to another, when
necessary.
Flexibility means easy adaptability to changing operational conditions,
such as face cross-section shape (horseshoe, rectangular, circular,
etc.), gradient, turning radius and unevenness of the floor.
Machine considerations
Hard and abrasive rock-cutting ability is the most important limiting factor on
the performance of mechanical miners; applications show that strength,
texture, etc., of the geological environment are the basic input parameters for
the selection of mechanical miners and performance prediction. the most
efficient type of tool in hard and abrasive rock.
Geological and geotechnical considerations
Rock mass features (such as joint sets, bedding planes, foliation, hydro
geological conditions, deposit geometry, etc.) and intact rock properties (such
as cuttability, abrasiveness etc).
Operational considerations
Mine layouts and development drivages are planned in accordance with the
mining method, which is selected on the basis of orebody shape and
dimensions and other deposit characteristics.
For reliable, economic operation the characteristics and layout features of
a mechanical miner should reflect whether it is to be used for the
excavation of drifts or for ore/mineral. The layout might be modified for a
particular mechanical miner if necessary.
The back-up equipment (such as muck transportation, support, etc.) selected
for a new mine must be chosen to be compatible with the mechanical miner.
In an existing mining operation, however, the machine might be selected on
the basis of the equipment already in use.
3

4. Main influencing parameters for excavation
Rock
Rock composition
Abrasivity (equivalent quartz content)
Matrix
Density (porosity/dry gross density)
Strength: compressive-tensile-shear
Destruction energy
Post-failure behaviour
Main influencing parameters for excavation
Rock mass
Joint structure: spacing, roughness,
orientation
Anisotropy: orientation, formation
Primary stress conditions
Weathering: type and degree
Hydrothermal decomposition
4

5. Compressive strength
Density
Abrasivity
Discontinuities
Moisture content
Insitu stress condition
Other Material properties
5

6. CM- Continuous Miner, MTM- Mobile Tunnel Miner, TBM- Tunnel Boring Machine
Abrasivity of rock
■ Definition: Abrasivity describes the behaviour of rock
with regard to its „grinding“ effect on metal surfaces,
predominantly picks.
Abrasivity is influenced by
Rock type and composition
Content of hard minerals (quartz, phyrite, hard
silicates)
Grain size of hard minerals
Intergranular bond
6

7. Abrasivity of Rocks
7

8. 8

9. Excavatability Index:
N= Excavatability index
Ms= Mass Strength number
RQD= Rock Quality Designation
Jn= Joint set number
Js= relative ground structure number
Jr= Joint roughness number
Ja= joint alteration number
9

10. Table: Mass Strength Number (MS) of rocks
Fig: Joint Set Number (JN)
for Rocks
Fig: Relative ground
structure (JS) of rocks
Fig: Joint Roughness
Number (Jr) for Rocks
10

11. Fig: Joint Alteration
Number (Ja) for Rocks
Assessment of Cuttability and excavation Index (Kirsten,1982)
Road Header:
Roadheaders are the most widely used underground partial-face excavation
machines for low to medium strength rocks.
They are used for both development and production in soft rock mining
industry (i.e. main haulage drifts, roadways, cross-cuts, etc.) particularly in
coal, sedimentary rocks, industrial minerals and evaporitic rocks.
In civil construction, they find extensive use for excavation of tunnels
(railway, roadway, sewer, diversion tunnels, etc.) in soft ground conditions,
as well as for enlargement and rehabilitation of various underground
structures.
Their ability to excavate almost any profile opening also makes them very
attractive to those mining and civil construction projects where various
opening sizes and profiles need to be constructed.
"Roadheading" machines with a cutter head designed to excavate stone
rather than coal instead of drilling and blasting.
This gives a more continuous process and should give a good drift profile.
The use is limited by the grades involved (maximum 1in 4 (140) and the
hardness of the material to be cut (maximum 60-150 MPa UCS).
11

12. In addition to their high mobility and versatility, roadheaders are generally low
capital cost systems compared to the most other mechanical excavators.
Because of higher cutting power density due to a small cutting drum, they offer
the capability to excavate rocks harder and more abrasive than their
counterparts, such as the continuous miners and borers.
Roadheaders were first developed for mechanical excavation of coal in the
early 50s.
The major improvements achieved in the last 50 years consist of steadily
increased machine weight, size and cutterhead power, improved design of
boom, muck pick up and loading system, more efficient cutterhead design,
metallurgical developments in cutting bits, advances in hydraulic and electrical
systems and more widespread use of automation and remote control features.
All these have led to drastic enhancements in machine cutting capabilities,
system availability and the service life.
Machine weights have reached from 17 tons up to 120 tons providing more
stable and stiffer (less vibration, less maintenance) platforms from which
higher thrust forces can be generated for attacking harder rock formations.
The cutterhead power has increased significantly from 37 kW approaching to
500 kW to allow for higher torque capacities. Modern machines have the
ability to cut cross-sections over 100 m2 from a stationary point.
In comparison to drill and blast methods, the main advantages of
roadheaders are:
One machine is capable of cutting, loading and assisting in the erection of
supports.
Compared with conventional driving, a greater advance per manshift is
obtained.
Roof control is improved since the roof and sides of the roadway are not
shattered by shotfiring.
The machine is very stable, easily controlled and capable of cutting a large
variety of roadway sections and sizes.
It is safer since the men are near to the unsupported strata only during the
erection of supports.
12

13. Classification of Boom Type road Header:
Generation:
Weight (Tonnes) Compressive Strength of
Generation Rock to be cut (MPa)
1st (1960) 9 40
2nd (1970) 22 to 37 85
3rd (1976) 45 to 70 100
4th (2000) 120 100 to 160
Weight:
Tucker (1985) classified roadheaders according to weight as: Class Weight
- Light Duty; weight up to 30 t, cutting capabilities up to 70 0 <20 t
MPa I 20-30 t
- Medium Duty; weight between 34 to 45 t, cutting capabilities II 30-50 t
up to 100 MPa III 50-75 t
- Heavy Duty; weight over 45 t, cutting capabilities up to 150 IV >75 t
MPa
Atlas Copco – Eickhoff established the following classification according
to weight (Schneider, 1988);
Classification of Boom Type road Header:
Neil et. al (1994) refer roadheaders as small size up to 30 t, midsize between
30 to 70 t and large size between 70 to120 t.
Cutting Action of heads:
Milling type or Borer Type (axial head), and
Ripping Type (Transverse head)
Fig: Cutting action of roadheaders
a. Ripping type, b. milling type
13

14. Borer type Roadheader
Borer type Roadheader
14

15. Borer type Roadheader (Side view)
Borer type Roadheader
15

16. Ripper type Roadheader
Ripper type Roadheader
16

17. Fig: Double head or twin Boom Roadheader
Cutting tools on Roadheader
Radial picks are generally suitable for cutting soft to medium hard rocks and
coal.
Forward attack picks are also termed tangential picks, together with point
attack picks due to the orientation of their tool axis. Such picks can also be
used for cutting soft to medium hard rocks.
Point attack picks, also known as pencil point tools, have been increasingly
employed in medium to hard rock cutting and become an inevitable tool on
medium and heavy duty roadheaders.
17

18. Table; Factors influencing Cutting performance
Fig. Comparison of cutting
performance (Gehring, 1989)
Cutting Mechanism in transverse head Roadheaders:
Pick spacings around the cutting head are defined as line spacing (SL) and
circumferential spacing (Cs) as shown in Fig.
Line spacing is the distance between the cutting lines along the length of the
cutting head and depends mainly on the depth of cut and cuttability of material
being cut.
Circumferential pick spacing is the angular distance between the picks
measured perpendicular to the axis of rotation, which is mainly related to the
angle of wrap, head diameter, line spacing, total number of picks, tool-holder
size and additional space required for water sprays.
Fig. Line and circumferential spacings on a cutting head. Fig: RH Cutting Action
18

19. Fig. Lacing patterns of the first (unequal) and the second (equal) cutting heads.
Fig. Breakout patterns of the experimental cutting heads.
Manufacturing of equal spacing circumferential picks is not possible due to
overlap of cutter picks. The performance of equal spaced picks is good in
terms of breakout, vibration studies, but overall performance is not as good
as unequal patterns.
Pick consumption rate (pick/solid bank m3) varies from 0.049 to 0.044. If the
rock is very abrasive or the pick consumption rate is more than 1 pick/m3,
then roadheader excavation usually becomes uneconomical due to frequent
bit changes coupled with increased vibration and maintenance costs.
19

20. Continuous miner is a mining machine that produces a constant flow of ore from
the working face of the mine. The machine continuously extracts as it is loading
coal with a cutting steel drum and conveyor system.
The continuous miner has been available in some form since the late 1800s. The
first machine to resemble a continuous miner was known as the English Channel
Machine.
Continuous Miners
Though there are many variations in design, continuous miners mostly consist of
five main elements:
A central body to carry all other components mounted on some type of drive
mechanism to provide mobility (most commonly caterpillar tracks).
A "cutting head" usually rotating drum(s) and/or chains with cutting picks
attached
A loading mechanism to pick up cut coal and deliver it into the central part of
the machine
A conveying system, usually a chain conveyor running in a steel trough from
front to rear of the miner
A rear jib section capable of a degree of vertical and horizontal movement to
enable the coal to be delivered into a transport or loaded at a desired point.
Continuous Miners
20

21. Continuous Miners
For extraction of hard rocks,
continuous miner is designed
to have both Ripperveyor
cutter head and chainless
cutter head. The diameter of
chainless cutter head is less
than that of Ripperveyor
Continuous Miner
Rate of drivage –50 meters/day
Production –1500 Tonnes/day
For seams of 1 in 5 gradient
and flatter
Thickness of 3.0 m to 4.0 m
21

22. Continuous Miner
Some continuous miners (at one time almost all) could not cut the full
roadway width in one pass but had to be moved backwards and forwards
and from side to side in order to cut the full profile.
This often results in a very rough rib line (bad for stability and ventilation
flow) and delays the ability to install support into/under freshly exposed
roof for a period. The advantages of the ability to cut the full profile in one
pass was recognized early, but was not easy to achieve.
Cutting forward in a straight line could be readily accommodated, but it is
necessary to be able to turn corners, mostly at right angles, and to be able
to retreat the cutting machine from one roadway to relocate at frequent
intervals.
These factors have proved major stumbling blocks to many developments.
In machines which covered the full face, steering in the vertical plane
could also be a major difficulty.
22

23. The "ideal" continuous miner would:
Be able to cut the full face in one pass
Be easily moveable between locations without dismantling parts
Be able to excavate right angle turns with a minimum radius
Have roof and rib bolters fixed to the machine in a location where each
row of the designed support pattern can be installed without moving the
miner and be installed close to the cut face if necessary
Have adequate space alongside to allow good ventilation of the face area
for efficient removal of gas and dust.
Fig: Mining of
Steep seams with
roadheader and
miller head
(drum-type)
miners
Overview of Continuous Miner machine Manufacturers
23

24. Overview of Continuous Miner machine types vs. Operation heights
Lacing pattern on CM Drums
Fig: Continuous drum with pick boxes
The arrangement of picks on the vanes is called a lacing pattern.
CM drum(10) comprises a cylindrical body(11) having an outer cylindrical surface(12).
Extending from the surface are start vanes with each vane extending angularly and
longitudinally w.r.t. longitudinal axis of the drum.
at the drum end there is clearance ring vane up on the picks are positioned
On each vane number of picks are placed, each pick having leading, trailing and side
faces
Upon rotation each pick follows cutting path with adjacent picks at a spacing of 30 to
100mm.
24

25. Fig: Pick Lacing Pattern on Continuous Miner drum for Coal
25,26- End Rings, 27 Left Web Section, 29 Right web section 28 central web section
Fig: Pick Lacing Pattern on Continuous Miner drum for Stone or Hard
rocks
25

26. Fig: Pick Lacing Pattern on Continuous Miner drum
The picks are placed on each vane at an attack angle of between 400 to
500.
The vanes extend angularly about at an angle 100 to 300
The spacing between picks is 50mm to 90mm on drums used for coal
and 40 to 50mm on drums used for hard rock cutting.
26

27. CM SUMPING SEQUENCE
1
CM SUMPING SEQUENCE
1
27

28. CM SUMPING SEQUENCE
1
CM SUMPING SEQUENCE
2
28

29. CM SUMPING SEQUENCE
3
CM SUMPING SEQUENCE
4
29

30. CM SUMPING SEQUENCE
5
CM SUMPING SEQUENCE
6
30

31. CM SUMPING SEQUENCE
7
CM SUMPING SEQUENCE
8
31

32. CM SUMPING SEQUENCE
9
CM SUMPING SEQUENCE
10
32

33. CM SUMPING SEQUENCE
11
CM SUMPING SEQUENCE
12
33

34. CM SUMPING AND SHEAR SEQUENCE
SD
SH 1
CM SUMPING AND SHEAR SEQUENCE
SD
SH 1 2
34

35. CM SUMPING AND SHEAR SEQUENCE
SD
SH 1 2 3
CM SUMPING AND SHEAR SEQUENCE
SD
SH 1 2 3 4
35

36. CM SUMPING AND SHEAR SEQUENCE
SD
SH 1 2 3 4 5
CM SUMPING AND SHEAR SEQUENCE
SD
SH 1 2 3 4 5 6
36

37. CM SUMPING AND SHEAR SEQUENCE
SD
SH 1 2 3 4 5 6 7
CM SUMPING AND SHEAR SEQUENCE
8
9
SD
SH 1 2 3 4 5 6 7
37

38. Auger Mining:
The potential for underground coal production from drilling or augering
machines has been recognized since at least the 1940s.
These machines could bore into the virgin coal from stabilized entries and
provide access to otherwise sterilized coal reserves.
Auger drills mounted with cutterheads cut and fracture through both
overburden and coal, operating very similar to a drill machine.
The cutting action of an auger differs from other coal cutting machines, such
as continuous miners, in that it exploits the lower tensile strength of coal rather
than overcoming the comparatively high compressive strength of coal.
Therefore, auger drills are able to generate a greater amount of power in
cutting coal than a continuous miner.
This makes augers more efficient in terms of the power needed to cut the coal.
There are Thin seam auger miner for extraction in thin UG seams and Surface
auger Miner for extraction of seams from highwall of open pit mines
Fig: Auger Miner for Thin seam
extraction
38

39. Auger performance is principally governed by two main factors; machine
power and cutter head diameter.
The greater the power available the deeper the penetration and the higher the
mining rate, for the same machine configuration.
The larger the diameter of the cutter head the greater the rate of production
per metre of hole advance and hence the higher the mining rate.
Thin seam miner (TSM) is actually a type of continuous miner that can cut
seams from 0.6m to1.2m height and up to 1.5 m high into a coal seam
situated under a highwall in surface mines
Augers drills used in surface mining can range from 18 to 61 m in length to two
to seven feet (0.6 to 2.1 m) in diameter. The cutter head on the auger bores a
number of openings into the seam, similar to how a wood drill produces wood
shavings. The coal is then extracted and transported up to the surface via the
spiral action of flights. Additional auger lengths or flights can then be added as
the cutter head penetrates and drives deeper down into the bored hole
Auger mining is a low-cost method of recovering coal from horizontal or
slightly pitched seams exposed through geological erosion. The practice of
auger mining is reserved primarily for extracting coal at depths of up to 1,000
feet (305 m).
One of the drawbacks is that once the cutter head enters the coal seam, the
operator is unable to view the cutting action directly and must rely more on a
sense of feel for the machine to determine potential problems.
Auger Advantages
Proven ability to mine a cleaner coal product
Proven selective mining capabilities
Extremely low ground pressure
Heavy duty construction for hard cutting
Remote control capabilities
Proven low cost solutions for Ultra Thin Seam Mining
39

40. FiG: Surface Auger Mining
High wall Mining Technology – Auger Type
• Consisting of single or dual cutting heads with coal being cleared
by spiraled flights, creating circular entries
40

41. High wall Mining Technology – Auger Type
DUAL HEAD AUGER
Fig: Auger Cutter head and Auger Flights
41

42. Coal Ploughes
Essentially a plough is a large mass of steel, usually of a more or less
triangular shape when viewed from the coal face or goaf sides, fitted with
large "picks" (more like small agricultural plough blade tips) angled from
the steel body towards the coal face.
The plough height is the working height in the seam being mined (possibly
a bit lower if the coal tops can be guaranteed to fall once the coal below is
cut.
These "picks" act in a fashion similar to chisels and break a narrow web of
coal off the face (of the order of 300-400mm thick). In most cases there
are no moving parts on a coal plough.
The plough itself is mounted on the front of the AFC and is pushed into
the face by push cylinders mounted in the supports.
The plough has an endless chain haulage attached to the rear, and is
driven through sprockets on electric drive(s) at the face end(s).
Coal Ploughes
The main advantages of ploughs compared to shearers are:
Cheap
Simple (no moving parts on the cutting machine itself)
Relatively low dust make
Able to keep exposed roof area very small (but a large number of chock
movements would be required to maintain this)
Though only a small web is taken, in the right conditions production rates can be
comparable to a shearer as the plough is operated at a relatively fast speed
along the face.
Some disadvantages are:
Cutting height is fixed
Ability to cut stone is limited
With increasing cutting height, machine stability becomes more problematic
Grading can only be done using the AFC angle
There are safety implications with an exposed chain haulage.
42

43. Plow Systems
Plow systems are intended for coal mining
in flat and inclined seams with the
inclination up to 40° with coal hardness up
to 40 MPa in seams with the height range
from 0.6m to 1.8m
In dependence on seam thickness
and mining conditions plow
systems can be operated either
with powered roof support or with
individual hydraulic support (pit
props)
Mining Machines
Division
Plow Systems
BASE PLATE PLOW
The plow system using atypical pan line with plow guide and
plow chain on the goaf side.
Advantages
• It is very suitable for
extremely low seams from
0.6m.
• Easy access to a tow chain
of the plow.
• High safety while handling
with a tow chain also in
inclinations.
Disadvantages
• Losses due to friction of the plow body
bottom plate on the floor.
43

44. Plow Systems
SLIDING PLOW
The plow system using atypical pan line with plow guide
and plow chain on the face side.
Advantages
• It is intended for
seams from 0.9m to
1.8m.
• Well controllable even
when the floor is rolling.
• Low losses due to
friction by a plow body.
Disadvantages
• It is unsuitable for seams
less than 0.9m.
• Not easy access to a tow
chain of the plow.
• Difficult and dangerous
while handling with a tow
chain.
Plow Systems
Advantages Disadvantages
• It is very suitable for extremely low seams
from 0.6m. • Losses due to friction of the plow body
• Easy access to a tow chain of the plow. bottom plate on the floor.
• High safety while handling with a tow chain
also in inclinations.
BASE PLATE PLOW
The plow system using atypical pan line with plow guide and plow chain on the goaf
side.
44

45. Plow Systems
Advantages Disadvantages
• It is intended for seams from 0.9m to 1.8m. • It is unsuitable for seams less than
• Well controllable even when the floor is 0.9m.
rolling. • Not easy access to a tow chain of the
• Low losses due to friction by a plow body. plow.
• Difficult and dangerous while handling
with a tow chain.
SLIDING PLOW
The plow system using atypical pan line with plow guide and plow chain on the face side.
Shearers
A shearer consists of a machine body containing electric motors, hydraulic
equipment and controls which is mounted over the AFC.
Horizontal cutting drums are mounted on the face side of the machine, laced
with cutting picks and rotating in a plane parallel to the face.
If the AFC is pushed towards the face as the cutting drums are rotated and the
shearer travels along the face, it is able to cut into the face for the full web width,
moving along a snake in the AFC.
This is known as "sumping in".
Once fully into the web, the shearer can advance the full length of the face
cutting out the web.
The snake can also be reversed to cut the wedge shaped portion of coal left
while sumping in.
45

46. Shearer
Large diameter drums could have a pre-cutter to aid in
rib face control on the longwall face.
Pre_Cutting
Fig: Shearer Drums with Radial and Point attack
picks
Fig: Side view of
Shearer drum
46

47. Fig; Positioning picks on shearer drums
Positioning picks on shearer drums
Shearer drums consist of several spiral vanes and a backplate welded on a hollow
drum shell.
The spiral vanes serve for cutting and loading, while the backplate is mainly used
for corner cutting at the face side to relieve the cutting action of the vane picks.
The linear advance of a shearer drum per entire revolution is produced by the
combined cutting actions of the vanes.
Spiral vanes and the backplate provide space for the picks to be mounted on
drums.
Spiral vanes or cutting sequences on shearer drums are also known as ‘starts’,
and the number of starts equal that of the spiral vanes.
The total number of starts on a shearer drum varies(3,4,6) depending on the
shearer drum design
Picks can be classified according to their tilt angles and positions on the cutting
head.
The tilt angle is the angle between the pick axis and a plane perpendicular to the
axis of cutting head rotation (Figure a).
Picks, with their axes perpendicular to the axis of cutting head rotation, are named
traversing or arcing picks, while those mounted on the region closer to the nose
section of the cutting head, with individual tilt angles, are termed gauge picks.
Sumping picks are placed on the nose section of the cutting head with their axes
parallel to the axis of rotation of the cutting head. The last gauge pick on the face
side of the cutting head is known as the corner cutting pick.
47

48. Fig. Pick positioning on a shearer drum: (a) profile view of the
drum (b) lacing of spiral and clearance ring picks
Positioning picks on shearer drums
A modern shearer drum also has three groups of picks cutting the coal
seam while it rotates and transfers coal particles from the face onto the
armoured face conveyor.
The first group of picks that cuts most of the coal-seam, which are
mounted on spiral vanes and correspond to the traversing picks on the
roadheader cutting heads, are named vane picks.
The second group of picks mounted on the backplate section of the
shearer drum, and corresponding to the gauge picks on the roadheader
cutting heads, are termed clearance ring picks.
Today’s shearer drums also have some sumping picks mounted on the
outer face of the clearance ring to provide extra protection for the drum
The arrangement of clearance ring picks on the shearer drum was
reported to be more complicated than that of vane picks
The forces required to cut the coal at a certain depth by a clearance ring
pick were reported to be two to ten times higher than the forces needed to
cut the coal at the same depth by a vane pick
More the wear of the clearance ring picks than others
48

49. Mobile Tunnel Miner (MTM)
Characteristics and advantages
Especially developed for hard rock tunneling
and mining
This method allows for any shape of tunnel
(rectangular, horse-shoe or circular)
The technology requires less cutting force than
a normal TBM
Combines the flexibility of a roadheader and
the power of a TBM
Mobile Tunnel Miner (MTM)
MTM is able to excavate any shape of tunnel (rectangular, horse-shoe or
circular)
MTM works with the “Under cutting Technique” requiring less cutting forces
than with a normal hard rock TBM.
The cutting principle with under cutting disc cutters is highly efficient as it
overcomes the lower tensile strength of the rock instead of higher
compressive strength.
The machine is equipped with a crawler unit and a gripper system.
The unit allows the MTM to move without using the crawler.
The MTM is equipped with 3,4 or 8 arms depending on the size of the tunnel.
The muck is transported to the rear of the machine, similar to roadheader
Fig: Schematic drawing of
the cutting technique
49

50. Tunnel Boring Machine (TBM)
TBM is a full face excavator which cuts rock by means of disc cutters mounted
on a circular revolving cutting head (figure 7.5). The following design
features enable it to cut stronger rock than any other type of mechanical
excavator.
Large mass
Hydraulic stabilising jacks
High cutting force provided by hydraulic thrust rams
Cutting discs for rock breakage by indentation
Because of the size and weight of the typical TBM, they are suitable only for
the excavation of long straight drivages such as civil engineering tunnels.
Tunnel Boring Machine (TBM)
TBM provides a good, circular profile which is good for stability and
ventilation but usually requires a false floor to be laid to create a flat floor
for travel.
Limited by grades involved and grade control can be problematic is some
strata conditions. Not suitable for other than very gradual changes of
direction (typically minimum 500m turning radius although tighter radius
machines can be designed and utilized).
Unlike drill and blast or roadheading methods, tunnel boring machines do
not have the capability to readily vary the dimension of the excavation nor
are they suitable in varying ground conditions.
Disadvantages of TBMs
High capital cost (several million dollars)
Can only cut circular section
Large turning radius (100 m)
Time-consuming to install
Minimum tunnel length of 2 km required to justify installation
50

51. Wide choice of TBMs for rock tunneling with diameter > 14m for different ground
conditions
Open or Gripper type for hard ground
Single shield – hard ground
Double shield – hard ground
EPB (Earth Pressure Balance Machines) – Soft ground, pressure< 7 bar
Slurry and mix-shield – Soft ground with very high water pressure and large
amounts of ground water
Fig: Gripper
TBM
The largest diameter TBM, at 15.43 m, was built by Herrenknecht AG
for a recent project in Shanghai, China. The machine was built to bore
through soft ground including sand and clay.
The largest diameter hard rock TBM, at 14.4 m, was manufactured by
The Robbins Company for Canada's Niagara Tunnel Project.
1 Cutterhead 4 Anchor Drilling Devices
2 Cutterhead Support 5 Wire Mesh Erector
3 Ring Erector
5
2
1
4
3
Fig: Gripper TBM
51

52. A TBM breaks rock with disc cutters mounted on the rotating cutter-head
in such a pattern that they roll against the rock of the tunnel face in a
series of concentric circular grooves or kerfs.
The cutting force is produced by powerful hydraulic thrust rams. Each
disc cutter is free to rotate within its mounting.
The high cutting forces required to break strong rock types produce
equally high reaction forces on the machine.
To maintain contact with the rock and to maintain the optimum spacing
between cutting grooves, the machine is held stable by a combination of
its great mass and by hydraulic jacks (grippers) acting against the side of
the tunnel.
Broken rock is gathered from the floor by scoops mounted around the
perimeter of the cutting head and discharged at the crown of the cutter
head onto a belt conveyor that runs through the center of the machine
Cutter head Grippers Conveyor
1. Start
boring
stroke
2. End
Main boring
body stroke
3. Start
reset
stroke
Invert Front Thrust Rear Main
scraper lift leg cylinder lift leg motors
4. End
Fig: Cutting cycle of Atlas Copco TBM reset
stroke
Fig: Hydraulic
jacks holding a
TBM in place.
1. Cutter head
2. Front shield
3. Main beam
4. Gripper trolley
5. thrust cylinders
6. Belt conveyor
7. Ring beam erector structure
8. Shortcret
Fig: Gripper Shield
52

53. All types of hard rock TBMs excavate rock using disc cutters mounted in
the cutter head.
The disc cutters create compressive stress fractures in the rock, causing it
to chip away from the rock in front of the machine, called the tunnel face.
The excavated rock, known as muck, is transferred through openings in
the cutter head to a belt conveyor, where it runs through the machine to a
system of conveyors or muck cars for removal from the tunnel.
Cutter head of soft rock TBM does not use disc cutters only, but instead a
combination of tungsten carbide cutting bits, carbide disc cutters, and/or
hard rock disc cutters.
Fig. Disc type cutter. Fig. (a) Kerf cutter (b) Pineapple cutter.
Different Cutter Heads - TBMs
53

54. 54

55. Single Shield TBM
1.Cutter head
2.Shield
3.Belt conveyor
4.Excavated material removal trolley
55

56. Double Shield TBM
1. Cutter head
2. Shields
2a - Front shield
2b - Double shield
2c - Rear shield and gripper
Belt conveyor
Excavated material removal trolley
56

57. EPBMs
Fig: Schematic
representation of EPBM
57

58. Fig: Schematic
representation of EPBM
Fig: Types of
Cutting face
of EPBMs
Schematic
representation of a
slurry type shield
machine
Cutting head sketch of
slurry type shield
58

59. Types of cutting face of slurry type shield
59