Guidance for partial face excavation machines - VMT GmbH

Abstract
Guidance for partial face excavation machines
Nod Clarke-Hackston
VMT GmbH
Jochen Belz
VMT GmbH
Allan Henneker
Surex Pty Ltd
For the construction of tunnels and other underground structures, extraction of the exact amount of material is of
paramount importance both economically and for engineering purposes. In the Sequential Support Method (NATM)
immediate (sequential) and smooth support by means of shotcrete, steel arches, lattice girders and rockbolts, either
singly or in combination are used; cutting of the precise (albeit sometimes of complex geometry) profile is an
integral part of the method.
In order to save unnecessary excavation and provide better information to the machine operator, VMT GmbH has
developed a system to support precise excavation of the tunnel profile when using roadheaders or other partial face
cutting machines. This paper outlines the principles of this system with examples from Australia, Germany, Sweden
and Spain and will cite examples of typical savings achieved.
History
Roadheaders were first developed for mechanical excavation of coal in the early 1950’s. Today their application
areas have expanded beyond coal mining as a result of continual performance increases brought about by new
technological developments and design improvements. The major improvements achieved in the last 50 years
consist of; steadily increasing machine weight, size, and cutterhead power, improved design of boom, muck pick- up
and loading systems, 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 service life. Roadheaders are the
most widely used underground partial-face excavation machines for soft to medium strength rocks, particularly
sedimentary rocks. They are used for both development and production in the soft rock mining industry (i.e. main
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haulage drifts, roadways, cross-cuts, etc.) particularly in coal, industrial minerals and evaporate 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. It is chosen
over other possible tunnelling methods principally because of its application advantages which include free excavation
area, considerable flexibility in regard to unforeseen changes in geological and hydrological conditions, flexibility in terms
of cross-sectional changes, and rapid mobilization with readily available, unsophisticated and relatively inexpensive
excavation equipment.
General
All rock and soil has, to a greater or lesser degree, the inherent ability to support itself or stand freely for a certain
amount of time. Strong rock can remain free standing for hundreds of years while the self-supporting ability of rocks and
soils of weaker types is relatively short-lived and measured in minutes rather than hours, days or years.
For the construction of tunnels and other underground structures, extraction of the exact amount of material is of
paramount importance both economically and for engineering purposes. In the Sequential Support Method (NATM)
where immediate (sequential) and smooth support by means of shotcrete, steel arches, lattice girders and rockbolts, either
singly or in combination are used; cutting of the precise (albeit sometimes of complex geometry) profile is an integral part
of the method.
Figure 1 Complex geometrical profiles
Extraction of too much material is costly and can affect the calculations for temporary support. Over extraction
also results in the need for additional costly material to fill any void between the actually excavated ground and the
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designed permanent lining. Under excavation necessitates reworking of the area to enable preformed supports to be
erected. The rate of excavation also has to be adjusted to the setting rate of the shotcrete.
Figure 2 Precise cutting for girder placement Figure 3 Initial shotcrete coating
When using a roadheader one of the main problems affecting the precise cutting of the face is visibility of the
cutterhead. Frequently the amount of dust produced, or residual shotcrete in the air, is such that the operator is
unable to see the position of the cutterhead. Marking of the face area to be excavated is time consuming for the
survey crew and it takes place in an area where stability of the working area is at its potentially most vulnerable.
Even if the machine is positioned correctly and has a limit on the movement of the cutterhead there is a tendency for
the machine to move as a reaction to the cutting force applied by the machine.
In order to save this unnecessary excavation and provide better information to the machine operator, VMT GmbH
has developed a system to support precise excavation of the tunnel profile when using roadheaders or other partial
face cutting machines.
Figure 4 Poor atmospheric conditions
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Operating Principle
The operating principle is based on determination of the position and orientation of the body of the roadheader with
respect to a Total Station mounted on the tunnel wall and sighting to two shuttered prisms located on the body of the
machine. Rotation of the body of the machine is monitored by a dual axis inclinometer. Movement of the cutter arm and
the position of the cutterhead itself is determined from sensors (Rotary and Linear encoders) mounted either in or on the
arm. Values from these sensors are taken from the machines PLC or by means of direct output from the sensors.
Figure 5 Determination of Cutterhead Position
There are two modes of operation: tracking mode allows fast and continuous distance measurements, lock mode allows
the following of moving prisms. The continuous measurements are only interrupted by directional controls to the back
target. The servo-motorized Total Station - Leica TCA 1203 is mounted on a bracket at the tunnel wall. Every 0.5
seconds the PLC sends data on the horizontal and vertical angles and the length of the cutter arm (kinematics of the road
header). The position of the cutter head is calculated in the road header coordinate system and then transformed into the
global coordinates of the tunnel project. Thus the cutter head position relative to the tunnel axis is known and may be
continuously displayed graphically in the operator cabin, since the tunnel profile is maintained at right angles to the tunnel
axis.
When the theodolite does a directional control check, the tracking mode is switched off and the standard measuring
program is activated. This enables a higher accuracy of distance measurement can be obtained, but it is not possible to
track the target. The average duration of the measurement cycle for the directional control is 25 seconds.
The data from the Total Station is transmitted to the Guidance PC on the road header via a pair of radio modems, one
mounted next to the Total Station the other mounted on the body of the roadheader.
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Sophisticated software enables the project surveyor to easily set the system parameters for the machine, enter the Designed
Tunnel Alignment Data (DTA) into the program as well as each of the individual profiles to be excavated. A simple
change in the profile icon enables the machine to rapidly change its excavation sequence in line with the project’s
requirements
Equipment
The major components are mounted on the body of the machine itself. These include the Main Industrial PC, remote
display and trackball control devise in the control cab, UPS, Central Box, 2 x Shuttered Prisms, Dual Axis Inclinometer
and Local Radio Modem. Additional components; the Leica TCA 1203 motorized Total Station, the Remote Radio
Modem and the Backsight Target Prism are mounted on the tunnel wall. Power for the machine components is supplied
from the machine via a UPS. The Total station and Remote Radio Modem are usually powered from the tunnel lighting
circuit.
The Ruggedized Industrial PC, UPS, Central Box and Dual axis inclinometer are all securely mounted on the body of
the machine in an area that gives the maximum protection to these components. The Shuttered prisms are typically
mounted on the roof of the operators cab to give maximum viewability, however due consideration to the alignment of the
tunnel should be taken into account when choosing these locations and to the sighting of positions for the Total Station. A
continuous line of sight between the shuttered prisms and the total station is needed throughout the excavation cycle. The
Machine body should be surveyed prior to installation of the shuttered prisms and inclinometer unit so that the main axis
of rotation can be determined, the position of the prisms measured and the inclinometer be correctly zeroed.
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Figure 6 System Components
The Shuttered prisms are standard survey prisms enclosed in a protective housing with a motorized protective shutter.
The shutter, activated by the software of the SLS system, is only opened for the duration of the angle and distance
measurement to the respective prism. This eliminates confusion of prisms or other reflective objects it also helps to keep
the prism surfaces clean. The individual prisms can be connected by a bus system.
A fluid damped dual axis inclinometer for determination of inclination of the roadheader. The damping behaviour of the
inclinometer can be adapted to the vibration range of the mounting position, in addition the inclinometer is equipped with
a temperature sensor for temperature compensation.
The main computer is a ruggedized industrial PC which is housed in a special Stainless Steel enclosure which is fixed
on anti-vibration mounts between the housing and machine body. The mounting location is chosen to give maximum
protection for the unit. A UPS is supplied to maintain the appropriate power to the PC in the event of fluctuating power
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eing available from the machine. The PC uses the latest Windows Operating system. A remote display for operator is
installed in a prime viewing location in the operators cab. Easy access to functions is via track ball control. A remote USB
connector is available for attaching a keyboard for initial data entry and for memory device attachment.
The Central Box interfaces between the various sensors of the system and converts these outputs for suitable entry into
the Industrial PC. Control signals from the Industrial PC are also converted for transfer to the sensors such as the shuttered
prisms.
Radio Modems are used to connect the components on the machine with those on the tunnel wall as the use of cables in
such a consistently changing working environment would be problematic.
The Local Radio Modem is mounted on the machine and effects Wireless Data Communication between SLS-PC and
Total Station whilst the Remote Radio Modem is mounted next to the Total Station with clear path for radio signals.
Wireless reception is controlled by the SLS-software. The Remote Radio Modem receives the data from the Local Unit
and transfers them to the Total Station. In case of power failure it changes automatically into battery mode and sends an
alarm signal to the SLS-PC.
The principle measurement tool for the SLS-TM system is a Motorized Leica Total Station Model TCA 1203 with
Automatic Target Recognition (ATR). Automatic fine pointing to the prisms speeds up measurements and improves
productivity. A Standard, round retro-reflective prism is used as a rear backsight target. It is recognised and measured by
the ATR target recognition unit of the Total Station and is used to check the bearing of the Total Station. A comparison
between the Backsight Target and Total Stations’ positions during each measurement cycle is used to give a warning in
case of movement of either outside of any preset limits.
Software
The SLS-TM Roadheader Guidance System provides an automated means to minimize operating expenses, while
maximizing the accuracy of cut and minimizing time. This is achieved through use of a highly unique, computer-driven
machine operator’s display screen.
The easy to use Windows software has been carefully configured to make data entry as simple as possible. Initial
setup of the system is implemented through the System Editor data entry pages. Input of the Designed Tunnel Alignment
(DTA) is achieved through the DTA Editor pages where the DTA, in point coordinate table format can be created from the
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principle geometric elements that make up the alignment in both horizontal and Vertical. From the Profile Editor each of
the relevant profiles for the project can again be created from the geometric elements that make up the profile.
Where multiple profiles are to be excavated in rotating sequence they can all be stored in the main program. When the
individual profile is to be excavated its profile is simply called up from the profile editor menu. Access to the various user
levels is password protected. Several language options are available as well as Metric and Imperial unit options.
Figure 7 Main operator display
To aid the operator the background of the main graphical display is colour coded to indicate the time interval since the
last valid survey reading. Although the measurement cycle can be set to an interval as short as every 20 seconds there may
be times when a valid reading cannot be made, when this occurs a change in the background colouring is made to the
operators display. The colours for the background are:-
1. Within initial time interval Grey
2. Time greater than first preset value Yellow
3. Time greater than second preset level Red
The typical time intervals being 3 minutes and 6 minutes.
A full dialogue of the survey positions is available from the survey position screens.
Developments from original system
Since the basic system was created there has been a constant programme of developments, frequently inspired by the
end users of the equipment.
All information that is monitored by the system is saved in the system database. This open platform enable customized
reporting to be made and a comprehensive package of displays of the excavated sections of the tunnel including 3-D views
and volumetric calculations have been created. This enables comprehensive reporting of the excavated profile to be
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created and presented to the owner in a clear concise manner. The full scope of the systems capabilities is still to be fully
realised although its use in providing intermediate “as built” documentation is rapidly gaining popularity with the sites
where the systems is in use.
Figure 8 Profile Viewer – General display Figure 9 Detailed View of section
Extension into excavator and bolter guidance
Having seen the of the guidance control for the roadheader on the Eastlink project in Melbourne, Australia, the
site personnel requested a system to be created for use on a Caterpillar excavator as the application was very similar
to that of the roadheader. This was quickly and successfully implemented.
A further major concern on this project was for the safety of the survey personnel who had to enter the
unsupported face area to mark out the positions for the drilling of the rockbolt support holes. Finding a way to
accurately position the drill of the bolter without physically marking the surface for the various support
classifications was achieved with and adaptation of the roadheader guidance system. Substantial costs savings were
made due to the sequential nature of the use of the roadheader, for excavation and the Bolter for support which
enabled the use of many of the main components of the system including the total station and wireless modems. To
change from one system to the other it is only necessary to switch off the system on one machine and initiating it on
the next machine. The software automatically initiates a survey and calculates the machines position and profile
section to be worked upon.
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Figure 10 Guidance for Bolter used in conjunction with Roadheader system
Benefits reported by end users
It has always been difficult to get precise figures from any project whilst production is still taking place, however
the following favourable comments have been received from the site in Bilbao:-
• “The operators like the system; they can cut a better profile faster than when it is done manually”.
• “As it is no longer necessary to mark up the face by the surveyors there is a time saving of 1½ hours per day
when the machine is not in a none productive mode”.
• “In one section where detailed records of were kept it was found that the more precise cutting achieved with the
guidance system in use enabled a reduction from 600 m 3 to 423m 3 in the amount of concrete in comparison to
and identical section of tunnel excavated without the guidance system”.
REFERENCES
Copur, H., Ozdemir, L. and Rostami, J., 1998, Roadheader Applications in Mining and Tunneling. Mining
Engineering, Vol. 50, No. 3, March, pp. 38-42
Chittenden, N., Müller H., 2004 New Developments in Automated Tunnel Surveying Systems. Proceedings ITA
World Tunnelling Congress 2004, Singapore
Sauer, G., 1990 Light at the end of the tunnel. Construction Technology International in March 1990.
Smith, M., 2006 Face Drilling. Reference Editions Ltd for Atlas Copco Rock Drills AB. 2006 Sweden
White, A., 1993 The Installation of Automated Profile Guidance on a Dosco MkIIB Roadheader. Paper Presented at
Meeting of The Institution of Mining Engineers, May 13, 1993, Nottingham
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