ug mechanical excavation

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ROCK EXCAVATION MACHINES – UNDER GROUND

U.Siva SankarSr. Under ManagerProject Planning

Singareni Collieries Company Ltd

E-Mail :[email protected] or [email protected]

Visit at:www.slideshare.net/sankarsulimella

Mechanical Rock Excavation

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Mechanical Excavation SystemsDifferent mechanical excavation systems, like machines with;

Application of Mechanical Systems

� Teeth (Dozer, Shovel, Scraper, Bucket wheel excavat or, 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 tu nnel miner, Tunnel boring machine)

� Auger tool (Continuous Auger Miner, Surface Auger Miner)

Under Ground:

� Continuous Miners, Bolter miners, Auger Miners and shearers for coal or soft nonmetalics

� Boom type miners (road headers in soft to medium ha rd rocks)

� Rapid excavation equipment (Mobile tunnel miners,Tu nner 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 o r coal

� Augers and highwall miners for coal

� Mechanical dredges for placers and soil

Classification of Underground mechanical excavator by rock type

1.Roadheader2.Continuous Miner3.Shearer

1.Roadheader2.TBM3.Mobile Miner4.Raise Borer

Soft rockHard rock

Comparison of mechanical excavation with drill and blast systems

• Cannot excavate very hard rock

• High capital cost

• Require specialist maintenance

• Not as flexible

• Generally gives more rapid advance than blasting in soft to medium-hard rock.

• Fewer unit operations

• Smoother excavation profiles

• No blasting damage to surrounding rock

• Inherently safer

DisadvantagesAdvantages

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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.

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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

Main influencing parameters for excavation

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Density

Discontinuities

Abrasivity

Compressive strength

Other Material properties

Insitu stress condition

Moisture content

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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

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Abrasivity of Rocks

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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

Excavatability Index:

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Table: Mass Strength Number (MS) of rocks

Fig: Joint Set Number (JN) for Rocks

Fig: Joint Roughness Number (Jr) for Rocks

Fig: Relative ground structure (JS) of rocks

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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).

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� 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.

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Classification of Boom Type road Header:Generation:

100 to 1601204th (2000)

10045 to 703rd (1976)

8522 to 372nd (1970)

4091st (1960)

Compressive Strength of Rock to be cut (MPa)

Weight (Tonnes)Generation

Weight:Tucker (1985) classified roadheaders according to weight as: - Light Duty; weight up to 30 t, cutting capabilities up to 70

MPa

- Medium Duty; weight between 34 to 45 t, cutting capabilities up to 100 MPa

- Heavy Duty; weight over 45 t, cutting capabilities up to 150

MPa>75 tIV

50-75 t III

30-50 tII

20-30 t I

<20 t 0

WeightClass

Atlas Copco – Eickhoff established the following classification according to weight (Schneider, 1988);

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.

Classification of Boom Type road Header:

Cutting Action of heads:

� Milling type or Borer Type (axial head), and

� Ripping Type (Transverse head)

Fig: Cutting action of roadheadersa. Ripping type, b. milling type

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Borer type Roadheader


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Borer type Roadheader (Side view)


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Ripper type Roadheader

Ripper type Roadheader

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Fig: Double head or twin Boom 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.

Cutting tools on Roadheader

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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

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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.

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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 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

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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 Miners

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

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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.

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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

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Overview of Continuous Miner machine types vs. Oper ation heights

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.

Lacing pattern on CM Drums

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Fig: Pick Lacing Pattern on Continuous Miner drum f or 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 f or Stone or Hard rocks

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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 coaland 40 to 50mm on drums used for hard rock cutting.

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CM SUMPING SEQUENCE

1

CM SUMPING SEQUENCE

1

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CM SUMPING SEQUENCE

1

CM SUMPING SEQUENCE

2

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CM SUMPING SEQUENCE

3

CM SUMPING SEQUENCE

4

30

CM SUMPING SEQUENCE

5

CM SUMPING SEQUENCE

6

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CM SUMPING SEQUENCE

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CM SUMPING SEQUENCE

8

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CM SUMPING SEQUENCE

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CM SUMPING SEQUENCE

10

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CM SUMPING SEQUENCE

11

CM SUMPING SEQUENCE

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1

SD

SH

CM SUMPING AND SHEAR SEQUENCE

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SD

SH


35

321

SD

SH


4321

SD

SH


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43 521

SD

SH


43 6521

SD

SH


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43 652 71

SD

SH


43 652 71

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SD

SH


8

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� The potential for underground coal production from drilling or augeringmachines 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

Auger Mining:

Fig: Auger Miner for Thin seam extraction

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� 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

� 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 Minin g

Auger Advantages

� 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 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).

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FiG: Surface Auger Mining

• Consisting of single or dual cutting heads with coal being cleared by spiraled flights, creating circular entries

High wall Mining Technology – Auger Type

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DUAL HEAD AUGER

High wall Mining Technology – Auger Type

Fig: Auger Cutter head and Auger Flights

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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).

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.

Coal Ploughes

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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 plowsystems can be operated eitherwith 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.

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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.

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.

Plow Systems

Plow Systems

BASE PLATE PLOWThe plow system using atypical pan line with plow guide and plow chain on the goafside.

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.

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SLIDING PLOWThe 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.

Plow Systems

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.

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.

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�Large diameter drums could have a pre-cutter to aid in rib face control on the longwall face.

Pre_Cutting

Shearer

Fig: Shearer Drums with Radial and Point attack picks

Fig: Side view of Shearer drum

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Fig; 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.

Positioning picks on shearer drums

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Fig. Pick positioning on a shearer drum: (a) profil e view of thedrum (b) lacing of spiral and clearance ring picks

� 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 roadheadercutting 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

Positioning picks on shearer drums

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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

� 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

Mobile Tunnel Miner (MTM)

Fig: Schematic drawing of the cutting technique

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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.

� 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.

Tunnel Boring Machine (TBM)

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

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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 AGfor 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

1

2

3

4

5

Fig: Gripper TBM

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� 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

GrippersCutter head Conveyor

Invert scraper

Front lift leg

Rear lift leg

Thrust cylinder

Main motors

Main body

1. Start boring stroke

2. End boring stroke

3. Start reset stroke

4. End reset stroke

Fig: Cutting cycle of Atlas Copco TBM

Fig: Hydraulic jacks holding a TBM in place.

1. Cutter head2. Front shield3. Main beam4. Gripper trolley5. thrust cylinders6. Belt conveyor7. Ring beam erector structure8. Shortcret

Fig: Gripper Shield

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� 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. (a) Kerf cutter (b) Pineapple cutter.Fig. Disc type cutter.

Different Cutter Heads - TBMs

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

Single Shield TBM

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Double Shield TBM

1. Cutter head2. Shields

2a - Front shield2b - Double shield2c - Rear shield and gripper

Belt conveyorExcavated material removal trolley

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EPBMs

Fig: Schematic representation of EPBM

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Fig: Types of Cutting face of EPBMs

Fig: Schematic representation of EPBM

Cutting head sketch of slurry type shield

Schematic representation of a slurry type shield

machine

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Types of cutting face of slurry type shield