UNDERGROUND DEVELOPMENT

Rapid development for cave mines

John Chadwick looks deeper intomechanical cutting technologies

being developed in a veryinteresting program

Rio Tinto has partnered with

Herrenknecht, Atlas Copco and Aker

Wirth following a long and detailed

selection process to develop new shaft sinking

and horizontal development machines (IM,

April 2010, p5). Pursuing this in logical order,

let us look first at Herrenknecht and its Shaft

Boring System (SBS).

For those unfamiliar with this company,

better known in civil mechanised tunnelling,

Herrenknecht has more than 30 years

experience in this field. It is headquartered in

Schwanau, Germany. At this facility there is the

capacity to manufacture 15 Tunnel Boring

Machines (TBMs for tunnel diameters over

6 m). Since 1977, the companys machines have

bored more than 850 km of traffic tunnels.

Dr. Christian Frenzel, Mining Applications

Herrenknecht, told IM the company has been

getting involved in equipment for sinking

vertical shafts, raise and boxhole drilling for

some time. We have a couple of references

for the Vertical Shaft Sinking Machines (VSM).

These are mainly civil shafts, but one pre-sink

for a mine shaft has been undertaken as well.

The further developments aim for a muck

discharge system, which allows hoisting of

skips to the surface to overcome depth

limitations of slurry systems.

The shaft sinking jumbos have not been

built yet, but have been fully developed. The

actual drill systems have been built several

times for similar applications.

The SBS is designed for the mechanised

excavation of deep vertical blind shafts in hard

rock. The semi-full-face sequential excavation

process is accomplished by a rotating cutting

wheel excavating the full shaft diameter in a

two-stage process for one complete stroke. An

overview of the system is shown overleaf.

The first stage of the excavation process is

to cut a trench to a depth of one stroke with

the cutting wheel rotating around its

horizontal axis. The wheel is pushed

downward in the shaft direction. Then the

machine will excavate the entire bench (face)

area by slewing the rotating cutting wheel

180 around the shafts vertical axis.

The SBS machinery consists of three major

areas of equipment and operation, which are

(working up from the bottom):

Shaft boring equipment with excavation,muck transport and gripping system as well

as equipment for primary rock support and

probe drilling

Primary platform decks for SBS supplyinfrastructure and power packs

Secondary platform decks for final lininginstallation, muck handling and services

extension.

Presenting this machine at this years SME

Annual Meeting1, Herrenknechts Werner

Burger explained that the cutting wheel

circumference and periphery of both sides is

equipped with appropriate cutting tools and

muck buckets to excavate the rock and remove

the cuttings while rotating. Excavation and

muck removal is a continuous process. The

cuttings are guided along internal muck

channels and discharged by gravity onto a

centre arranged secondary conveying system.

A full mining cycle consists of the

following steps:

Trench excavation (plunging) Bench excavation (slewing) Extend SBS support legs Retract and reset main gripper system Adjust SBS vertical alignment with rear

gripper system

Activate main gripper system. The cutting wheel has a diameter that

equals the excavation diameter of the shaft. It

is equipped with disc cutters at the periphery

and the side areas. The front-loading disc

cutters are 483 mm in diameter with a narrow

cutter ring design.

The cutting wheel layout follows the

principle of a bucket wheel. At the periphery,

the bucket-lips are arranged so they pick up

the cuttings from the bench during the

rotation of the cutter wheel. Once in the

buckets the rotation of the wheel lifts the

muck, which at a certain position starts to slide

along internal muck channels towards a

stationary muck ring hopper arrangement.

Here the muck is finally discharged into the

loading area of the vertical conveyor running

up the centre of the machine.

First stage of rock support is the application

Artist's impression of the Modular Mobile Mining (MMM) machine

MAY 2010 International Mining 55

UNDERGROUND DEVELOPMENT

of shotcrete close to the face, below the dust

shield. The shotcrete nozzles slew with the

cutting wheel, which allows the nozzles to

apply a complete ring of shotcrete while the

bench excavation occurs.

The second step is to install the rock bolts

behind, above the dust shield. This is a non

slewing area so all activities can take place

while excavation is proceeding.

For both pre-excavation grouting and probe

drilling, there are two pivoting probe drill units

in front below the dust shield. Retractable

platforms are installed to access the bench for

installation of standpipes and blow-out

preventers.

An inclinometer mounted on the same part

of the machine as the cutting wheel is used to

guide the SBS. Burger explains: After the

machine is adjusted to the vertical the

difference between the centre of the shaft and

the centre of the machine will be detected by

scanners. To get an accurate and redundant

position of the machine axis in relation to the

scanned shaft centre, three scanner levels are

planned. If this difference is out of a defined

tolerance a correction to the steering is

needed. Therefore, the machine has to be

tilted outside of the vertical direction.

To support the steering of the SBS out of

the vertical a function in the navigation system

is planned. This shall be implemented by a pre-

calculated point of the machine axis in one

advance direction. By moving the SBS out of

the vertical this pre-calculated point can be

moved onto the planned shaft axis. This

system shall be controlled and calibrated

frequently by independent control

measurements.

SBS concept development has been

completed and detailed engineering has

started. It is expected to weigh some 2,000 t

and require a collar depth of around 55 m. The

target is to at least triple current average shaft

sinking rates, which are 2.5-3 m/d.

Modular Mobile MiningThe challenge presented to Atlas Copco was

to come up with a mechanical cutting machine

for the following conditions:

Could accomplish a vast amount of differenttunnels, tight curves and cross cuts

Be a self-propelled unit between jobs Cut in very high in-situ rock stress

applications

Large convergence expected Generally poor ground In some mines very hot ambient rock Highest possible safety standards.

And it is to be able to progress at at least

twice the speed of the best drill & blast

operations.

Atlas Copco has extensive past experience in

TBMs and other mechanical cutting

innovations. A TBM would not have the

flexibility for tight curves, so the company

dusted off the Mobile Miner idea

(IM, September 2008, p62) of which three

models were made in the late 1980s, early

1990s. Two operated in Australian mines, the

MM120 at Mount Isa and the MM130 with

Pasminco at Broken Hill. The latest (1993) and

most advanced was a civil tunnelling machine

employed in Japan, the Taisei MM130R. This

was an articulated mobile miner, with vertical

boom movement. It has the ability to excavate

a tunnel with a height bigger than the

machine or its cutter wheel, giving space to

rock reinforcement equipment. It was intended

for large tunnels to be excavated in hard rock

and successfully completed a tunnel in granite.

Sverker Hartwig is the man at Atlas Copco

for mechanical cutting and he explains other

considerations that took the concept to the

mobile miner rather than a TBM. TBMs are

considered advantageous for high speed

tunnelling, as it is normally referred to a higher

advance rate, a very smooth profile and a

careful excavation, reducing demands for rock

support. On the other side is the cost of a

TBM, and its very limited possibility to change

profile as well as difficulties handling small

curve radii are all aspects where drill & blast

has a number of advantages. The TBM profile

has strengths and weaknesses. The arched roof

is a benefit, but the non-flat invert is not ideal

for all applications. Cutting crosscuts and

branching is difficult with TBMs, and normally

requires extensive, extra measures. The choice

between the two methods is therefore a

complex exercise involving many different

parameters and complex calculations.

Rio Tinto selected the new Atlas Copco

Modular Mobile Mining (MMM) machine

concept for a number of reasons including the

proven technology of the previous three

Mobile Miners and other commercial products,

combined with the ability to install complete

ground support typical with high rock stress

conditions at approximately 1,500 to 2,000 m

depth.

Atlas Copco, with support from Swiss

company ROWA that specialises in back up

systems for TBMs, is currently advancing the

detail design of the access version of the

MMM. Because of the different requirements

of an excavation system for access tunnels and

that for tunnels on what Hartwig describes as

the footprint, we envision two different

versions of the MMM technology. Both the

access and the footprint versions of the

machine share a majority of key technologies

and systems. Therefore we are able to conduct

a performance confirmation test using a full-

scale version of the access machine that will

mitigate the technical risks for the footprint

version.

It was clear from the beginning that the

machine must operate in a mode where the

cutters follow their own tracks (significant

difference to previous Mobile Miners). So

instead of swinging the cutter head sideways,

when working the cutter head, it must be

advanced straight or almost straight forward.

Since only a portion of the face is excavated at

one time, the head has to be retracted out of

the rock and then moved sideways or vertically

56 International Mining MAY 2010

The main sections of the SBS. The cutting wheel,

cutting wheel drive assembly, mechanical machine

support structure, shotcrete and probe drilling

equipment are all in the excavation chamber (1). Then

comes the adjustable front support with slew

bearing/drive assembly cutting wheel support and

dust shield (2). Regular rock support area for rock

bolts (3). The mainframe with gripper carrier, gripper

system and lowering/thrust cylinders (4) with the rear

alignment system (secondary gripper) above. Muck

handling system (5)

in the air and then sumped forward again to

cover the entire drift face. In order to reduce

the lost time for this necessary repositioning,

the machine should have a longer stroke than

the Mobile Miner.

The second issue to address was muck

collection in front of the machine. Atlas Copco

considered roadheader aprons with gathering

wheels/arms and chain conveyors to be more

suitable than the previous Mobile Miner

solution.

Rio Tinto requirements call for extensive rock

reinforcements. So the machine length had to

be stretched in order to provide enough room

for rock bolting and shotcreting equipment.

The rock support is to be installed

simultaneously with rock boring.

The original performance target was an

average of 240 to 360 m/month. Compare this

with the MM130 Pasminco machines best

month of 83 m. For these reasons, we

needed more power, more cutters, and a much

heavier machine for stability, Hartwig

explains.

The basic concept is for a cutter head

mounted in a fork, which can be moved along

the MMMs curved front plate 15. This

movement is normally made under no load.

Then the fork is locked in position, to make

the left, right, or centre cut. The cutter head

can be lifted horizontally 1.5 m for the upper

cuts. The advance for each part cut is a stroke

of 1.75 m. One complete advance of the drift

will require six to eight cuts, after which the

whole machine with trailing back-up system

will move forward for the next set.

Hartwig says this particular machine cannot

cut a lower profile then 4.5 m since thats the

size of the head. However, both larger and

smaller machines can be designed using similar

components. Other modules that can be

added are a cutter head revolving unit that can

tilt the head sideways 30 and also an

articulation [joint] that can be fitted between

the front and rear grippers. These aspects

enable this technology to ideally cover all

present and future requirements of both access

and footprint excavation of horizontal

infrastructure.

The back-up system should be regarded as

a full TBM back-up with all such facilities. It is

crawler based, with individually steerable

crawlers making it possible to negotiate

narrow curves both when boring and when

backing out for repositioning to a new face.

Muck is collected in front of the machine and

is transported to the rear of the back-up by

several conveyors. It can then be delivered to

mine trucks or possibly onto an extendable

conveyor system. The back-up hosts a 2,500

kVA system for the machines variable speed

drive and hydraulic systems. It will also carry

shotcrete pumps, compressors, ventilation fans

and dust suction fans. It will carry materials like

roof bolts, wire mesh, spares, and cutters.

Rio Tinto and Atlas Copco estimate the

average performance of this technology will be

between 10 to 16 m/d.

Like the SBS, the concept development is

complete and detail engineering is underway.

Tunnel boringAker Wirth has been selected as Rio Tinto's

partner to develop the other concept for fast

drift development. The concept chosen is

based on Aker Wirth's experience and

competence in underground hard rock mining

and tunnelling and combines the flexibility of a

roadheader operation with the robustness of a

TBM. This concept uses the learnings of the

previous version that was developed and

tested in the early 1990s. Using the

undercutting technology at the core of the

concept, the Mobile Tunnel Miner (MTM) is

capable of meeting the challenges set out by

Rio Tinto to improve safety and speed in drift

development.

The use of undercutting technology is one

of the key features of the MTM. This type of

cutting rock uses the lower tensile strength of

the rock to excavate it, rather than the higher

compressive strength (UCS). Tests with the

The simplified model of the main beam only shows

how the MMM cutter head must be advanced

straight or almost straight forward. Since only a

portion of the face is excavated at one time, the

head has to be retracted out of the rock and then

moved sideways or vertically in the air and then

sumped forward again to cover the entire drift face

Atlas Copco MMM Parameter Access Version of Atlas Copco MMM

Tunnel width (m) 5.3-6.3*

Tunnel height (m) 5.25-6.1**

Horizontal curve radius (m) 70/30***

Slope () 15

Cutter head size (m) 4.5 x 1.8 (diameter x width)

Cutters number and size 2 x 28 x 483 mm

Installed power (kVA) 2,500 (6/10/16 kV)

Cutter head power (kW) 1,260 at 12 RPM

Cutter head speed (RPM) 0-15, both directions

Forward Thrust static (kN) 3,500

Load per cutter (kN) 183 -270

Machine weight (t) 350

Complete Machine with back-up (t) 675

*Without change of modules **Can be increased by spacers

***30 m with increased tunnel width

Summary data - Access Version of Atlas Copco MMM (all numbers are preliminary)

UNDERGROUND DEVELOPMENT

MAY 2010 International Mining 57

58 International Mining MAY 2010

UNDERGROUND DEVELOPMENT

initial MTM prototype showed that the energy

per excavated m3 rock is about half of the

energy required with full face cutters mounted

on a TBM.

Two areas of development have been

identified:

Access and infrastructure, which include

ventilation and ore handling with an area 20

to 30 m.

Footprint development, which includes the

undercut and extraction levels with an area of

15 to 20 m.

For a typical block caving operation the drift

profile has to be suitable to incorporate a flat

floor, wide enough for the use of standard

mine trucks and LHDs. The four-arm MTM is

particularly suitable for the footprint

development, however for the infrastructure

tunnels, a larger model is required. Therefore it

was decided to increase the number of cutting

arms to six, in order to achieve the required

tunnel dimensions (6 m in diameter), without

compromising on advance rates. The target

was set at a challenging average advance rate

in a single heading of 12 m/d.

The MTM has to be self-supporting, travel

independently with a short turning radius

(< 30 m), suitable for place-changes and high

manoeuvrability. Rock support specifications

include:

Temporary roof support near the face toprevent rock fall

Immediate lining support as close to theface as possible with 50 mm shotcrete and

rockbolting with a 1 m spacing in L1

Installation of mesh and a second layer of

50 mm shotcrete in

L2.

The engineering

process has resulted

in a concept

consisting of the

main six-arm MTM

machine, followed

by three self-propelled

backup cars which contain

all the logistical equipment.

MTM excavation/materialhandlingThe MTM is developed to excavate non-circular

tunnel profiles in hard rock with high flexibility

of movement and short turning radius. The

centre area of the face is excavated with two

inner cutting arms, which move during head

rotation from outside to the centre. The outer

area is excavated with four outer arms, which

move from the centre to the outside.

This cutting principle should create a curved

tunnel face with high stability. A roof

support in the front area

provides protection against rock fall. The front

area of the MTM is accessible for maintenance

and cutter exchange with special tools to

handle the 560 mm diameter cutters.

Excavated muck is collected on a loading

apron, fitted with spinners, to direct the

material to the mouth of the conveyor -

identical to standard Aker Wirth roadheaders.

With regard to Rio Tinto's requirements, the

system provides the following unique features:

The basic six-arm MTM with a logisticalback-up trailer, produces a fully grouted and

bolted tunnel

The MTM is capable of achieving advancerates of 12 m/d in varying rock

classifications

There is no limit in rock strength for theapplication of the MTM system. The

advance rates and wear costs remain

economically acceptable in high strength

rock (>200 MPa UCS)

The system uses the unique and energysaving undercutting principle to excavate

rock

The Aker Wirth MTM can produce differentdrift cross-sections, using one and the same

machine, from rectangular, to horseshoe

and circular shape

Due to its own crawler drive, the system hasrelatively high manoeuvrability and can

travel underground to different faces.

The next step in the development will be a

pilot project where the MTM can prove its

performance in practice. IM

References1. Burger, Werner, Delabbio, Fred and Frenzel,

Christian, Accessing deep orebodies using mechanical

excavation equipment, SME Annual Meeting,

Phoenix, March 2010.

2. Hartwig, Sverker and Delabbio, Fred, New Atlas

Copco tunnel boring machine for accelerating tunnel

construction in deep mining operations, SME Annual

Meeting, Phoenix, March 2010.

3. Hensgens, Werner; Greve, Hans and Delabbio,

Fred; Aker Wirth develops a new machine for rapid

underground mine development. Pending conference

presentation.

Maximum boring diameter 6 m

Minimum tunnel dimensions 5 x 5 m

Average advance rate >12 m/d

Length of MTM 64 m

Minimum curve radius 30 m

Weight of the MTM system including back-up 305 t

Total installed power 1,870 kW

Number of cutting arms 6

Operating torque cutterhead drive 685 kNm

Maximum cutterhead speed 24 rpm

Disc cutter diameter 560 mm

Crawler speed 0-10 m/min

Shotcrete pumping capacity 20 m/h

Number of rockbolting units 2+2

Main technical data of the Aker Wirth MTM