Spatial positioning of sidewall stations in a narrow tunnel environment: a safe alternative to traditional mine survey practice

Evaluation of setting-out technologies and techniques

In order to discern between the available options of setting-out excavation control and to provide suggestions for the optimal combination of technology and techniques, it is necessary to evaluate the strengths and weaknesses of the various types of technology suing the SWOT technique. In summary the SWOT analysis of each method is considered and extrapolated into an analysis of the how the weaknesses should be addressed and strengths can be exploited for optimal application.

1.4.The gradient control method.

This method using sidewall pegs is commonly used in mining and well understood. Two pairs of gradepegs are installed at between 3 and 5 metres apart on the gradient of the tunnel. When sidewall survey stations are used as the method of survey control, gradepegs should be installed as separate setting-out control rather than using the sidewall stations which forms part of the survey network [163] [164]. Although not necessary, it is a better solution as it will prevent damage to the network control points due to daily use by the production crew. This method is both elegant in its simplicity and cost efficiency. Gradepegs are used in combination of a number of techniques to provide direction control. A SWOT analysis of the gradestring method follows below:

Table A SWOT Analysis of Gradestrings for gradient control

S
Strength


W
Weakness

The cheapest method requiring no special technology to install.

Visible alignment of the strings provides self-checking (4 string check).

The method is well understood by mining and survey personnel.

The method is elegant in it’s simplicity.

Damage to spads can cause misalignment of the gradient control.

Loss of one spad renders the entire cluster of pegs redundant.

Damage to the gradepegs will require a surveyor to repair the control.

Incorrect interpretation of instructions by mining personnel can lead to off-gradient mining.


OW
Opportunities


TW
Threats

Easy implementation of the method.

Proven technology that is used at most mining operations.

The gradestring method allows the adaptation to new technology.

Gradepegs are easily damaged by blasting and transport activities.

Off-line development can result from misaligned marks and poor installation practices.

Operator error can result in a deviation from the survey instructions.

1.5.Direction control using marks made on the grade strings.

Marks made on gradestrings by ferrules combined with the method of intersecting lines [164] provide an opportunity to be enhanced by applying laser technology to the method.

Table A SWOT Analysis of Gradestrings for direction control.

S
Strength


W
Weakness

Low cost requiring minimal technology, marks are made using tie distances and indicated using washers or ferrules.

Can be installed from first principles requiring no aftermarket software or equipment.

Visible alignment of marks provides a simple check on the alignment.

Tie distances is supplied with the survey instruction to verify the mark positions and facilitate the re-installation of the marks if it is required.

Simplicity in execution makes the method ideal for unskilled operators to use and understand.

Damage to spads will cause misalignment of the gradient and direction of the excavation.

Incorrect interpretation of instructions will lead to off-line mining.

Mis-identification of string offsets or marks will lead to incorrect marking-up of the excavation.

The gradestrings have to be correctly tensioned [165] in order for the direction marks to be aligned correctly.

OW
Opportunities


TW
Threats

A known survey method is adapted to existing technology.

The method of alignment is adaptable to a range of technologies.

Cable-ties provide a cost-effective method of attachment and tension [165] of gradestrings.

Tie-distances to alignment marks by intersecting lines method provides a check on the integrity of the grade pegs.

Grade pegs are sensitive to damage from blasting and tramming activities.

Off-line development will occur if the survey instructions are mis-interpreted.

Any error during the installation or marking-up activity will result in off-line development.

The hybrid method requires training if operators and production personnel.

Survey instructions are required to be detailed and specific to ensure compliance with the layout is met.

4. A review of current laser technology.

Laser technology has been used in mining for decades. With the miniaturization of components and advances in technology, lasers have become affordable and offer a range of solutions to the surveyor. The review focusses on the available technology grouped according to the form of application and evaluates each group of devices according to their respective strengths and weaknesses.

1.6. String suspended lasers.

This group of lasers incorporate a laser in a housing that can be suspended from a gradestring. The device projects a laser beam perpendicular to the suspension string. The gradient of the beam is adjusted by moving the position of a pendulum at the bottom of the device on a graduated scale to the required inclination.

Figure Driftscope device

Below is an example a South African derivative of a suspended laser device [166].

Figure . Suspended laser device (Foton Laser [167] )

These devices require the installation of sidegrades in the wall of an excavation. Gradepegs are installed from the survey network at a specified height above the footwall and treated as construction pegs rather than network stations. From the survey instruction a string is stretched between two survey stations. The person responsible for marking-up measures the pre-determined position from the gradepeg to the position where the laser device must be suspended. This will provide the direction line by projecting a laser beam on the face. By adjusting the pendulum at the base of the device the gradient of the tunnel can be indicated with the direction line. The position indicated by the suspended laser [168] is used to “mark-up” the blast pattern for the excavation. This method requires grade pegs to be installed at 90 degrees to the direction of mining [163] as the device cannot be adjusted in the horizontal plane.

Table A SWOT Analysis of the Suspended laser.

S
Strength


W
Weakness

Low cost of device allows for individual units deployed to specific tunnels.

Sights possible are possible for ranges >150m [169] under ideal conditions.

Visible alignment [169] of direction and grade line (red or green beam).

The unit is small and portable and can be used in multiple ends [169]

Provides a reference line that is parallel to direction of mining.

The device is capable of providing a direction line and gradient.

The accuracy of the control depends on accuracy of gradepeg placement.

The grade string and direction of mining must be perpendicular to each other.

String tension must be monitored to provide the correct position for the device.

The pendulum must be set to the correct gradient. This is prone to operator error.

Misalignment between the device centre line and beam can occur.

Damage to gradepegs will require a new installation by the surveyor.

Battery failure will require additional batteries to be available to prevent a missed blast because lines could not be taken.

The beam dispersion allows for distances shorter range (<150m)


TW
No independent check can be performed on the beam direction and gradient.


OW
Opportunities

Threats

Easy implementation of the technology.

Direction and grade can be marked off in one setup.

The ease of mounting of the device allows for a faster and more accurate markup.

Standard offsets left and right from direction line can be supplied, making survey instructions easier to understand.

Existing grade string method is familiar to mining and survey personnel.

The direction and grade lines can be indicated and painted in during the laser installation by the surveyor.

Only one person is required for installation and marking-up activities.

Laser technology is still not widely used in mining.

Cost to replace damaged or broken units can be considered to be excessive.

The laser and electronic components can be lost or damaged when used underground.

The calibration of laser must be verified by the supplier of the technology, it cannot be done on site.

Errors in marking-off, line alignment and incorrect use will lead to Off-line development.

Misalignment of gradient can occur if the pendulum device is damaged or incorrectly used.

1.7.In-line Suspended tunnel lasers.

This group of laser devices was developed for the traditional method of mine surveying. The laser is suspended from a string stretched between a conventional hangingwall survey station and a line peg that have been installed in the direction of mining. at a preset vertical angle for gradient (cross or line).

Table A SWOT Analysis of the “in-line” suspended laser

S
Strength


W
Weakness

Affordable technology

Longer sights of up to 150 metres is possible [169]

Visible alignment [169] of the beam provides an easily acquired reference line.

The size of the unit allows it to be removed and used in multiple ends. [169]

The laser provides a reference line in direction of mining allowing for standard offsets to be used.

The technology is used with current methods of survey setting-out, requiring no additional training for operators.

The accuracy is dependent on accuracy of the survey setting-out.

The beam can be misaligned due to incorrect installation procedures.

The device requires access to the hangingwall of the excavation.

Grade control with the device is not possible due to the method of suspension.

Battery failure can cause the device to be inoperable.

The laser provides a shorter range (<150m) than tunnel lasers.


OW
Opportunities


TW
Threats

Easy implementation of the technology is possible.

Direction lines are provided in the conventional manner which is well understood by operators.

Ease of mounting reduces the installation time.

Standard offsets from direction line prevent misinterpretation of survey instructions.

The direction and grade lines can be indicated and painted in during the laser installation by the surveyor, providing a visual reference point to verify the alignment of the laser.

Only one person is required for installation and marking-up activities.

The device cannot be used with sidewall stations without modification.

The method requires the installation of hangingwall survey points.

The device is not ruggedized and may be prone to damage that may require the device to be replaced.

Calibration of the laser has to be done by a service agent.

Misinterpretation of survey instructions will lead to off-line development

Off-line development may result from operator error during the installation and mark-up activities.

1.8.Dual-beam laser devices.

A dual beam laser provides a vertical and horizontal line [166], forming a crossed line on the face of the excavation. Some of these devices are a standard laser with an additional head that can be fitted to split the laser point into a vertical and horizontal line. The device is mounted on a pole, tripod [164], wall bracket or rail mounted bracket [167]. When used in combination with the gradestring method, the device is placed behind the gradestrings to project the required gradient and direction planes through the strings onto the face of the excavation.

Table . A SWOT Analysis of the Dual beam laser.

S
Strength


W
Weakness

The device offers a fast and accurate method of marking-up direction and gradient.

The beam can be projected up to 150 metres under ideal conditions.

Visible alignment with the installed gradeline and direction marks, provides a gradient and direction line on the face of the excavation.

The device is small enough to be transported between ends.

The time required for set-up and alignment is minimal.

A number of mounting options is possible for the device providing flexibility in operation.

The cross beam provides an easily understood reference line for control and verification.

Routine maintenance and calibration is required for the device.

Longer distances can lead to a bigger misalignment error if the line is not regularly maintained by a surveyor.

The shorter range (<150m) requires regular line extensions.

Battery failure will prevent marking-up activities from taking place.

The accuracy of the alignment is dependent on operator skill in setup.


OW
Opportunities


TW
Threats

The technology is easy to use.

Laser is a proven technology and trusted for accuracy.

The device allows the control of the direction- and gradient over the installed gradelines.

The device is easy to set-up.

The laser provides a reference line from which standard offsets can be provided.

The direction and grade lines can be painted in and verified every time the laser is used.

The range of the laser beam facilitates a longer time between new setting-out control points.

Only one person is required for installation and marking-up activities.

The device can be damaged and carries a replacement cost.

The device requires alignment calibration.

Off-line development can occur due to alignment error by the operator.

Survey instructions have to be detailed and clear to ensure correct marking-up.

The accuracy of direction and gradient is dependent on accuracy of gradepegs and string tension.

1.9. Sleeve laser devices.

This group of lasers are pocket-sized devices with a pin that can be inserted in a sleeve or specially designed spigot installed in the sidewall of an excavation [169]. A switch mounted in the wall-mounted spigot, switches the laser on when inserted into the wall and switches the device off when removed. By setting-out the required horizontal and vertical angle with a total station, a mark is made on a wall opposite to the direction of the tunnel. The visible laser from the instrument is used to align the drill hole [148]. A sleeve is inserted using a resin epoxy and aligned to the correct line and grade while the epoxy sets [152]. Alternatively it is possible to align the laser by installing a wall bracket in the sleeve in the sidewall. [167] A ‘markup instruction⁵⁰’ provides the necessary information to the production team to take the correct offsets and gradients. At some operations, sleeve lasers are used for short distances less than 20metres to prevent error propagation as a result of the misalignment of the sleeve during the setting of the epoxy in the hole. [164]

Table A SWOT Analysis of the Sleeve laser.

S
Strength


W
Weakness

Affordable technology.

No wires or strings are required for the alignment process.

The device provides an accurate reference line for direction and gradient.

Sights of up to 150 metres are possible. [169]

The laser beam provides a visible reference line for alignment [169]

The device is small and cheap enough to be issued to multiple users.

The device is removed after use and can therefore be used in multiple ends. [169]

The device can be used to turn angles and offsets for breakaway ends. [169]

The device does not need to be mounted “at-height” to prevent damage from transport or blasting activities.

The sleeve position is protected from damage from blasting by a rubber mat cover.

The laser requires to be installed in the sidewall of an excavation. This method of mounting is not ideal to set-out straight lines.

The epoxy used to mount the sleeve requires a setting time during which the sleeve has to be held in position.

The alignment of the sleeve can move during setting period of the epoxy.

The mounting of the laser in the sidewall can only provide oblique offsets for straight development.

The laser has a short range (<150m) of efficiency.

Damage to the sleeve will affect the accuracy of the reference line.

Battery failure will prevent the device from being used.

No alternative check on the accuracy of the reference line is available.

Opportunities

Threats


OW
The device is easy to use.

Laser is a proven and trusted technology.

A laser direction line provides a visual reference line.

The device is ideal for breakaway instructions.

A beam splitter can be attached to the device and used to indicate gradient and direction at the same time.

The direction and grade lines can be indicated and painted in during the laser installation by the surveyor and verified every tie the laser is used.

Only one person is required for installation and marking-up activities.


TW
The survey instructions have to be detailed and clear when used for straight development.

The angle of the laser line requires continuous monitoring of offset distances.

An error in interpretation of survey instructions will lead to off-line development.

The device can be damaged and carries a replacement cost.

The device requires alignment calibration.

The offsets to maintain the correct direction of the tunnel is given by offsets that compensate for the oblique offset of the laser (refer to Figure ). Monitoring by the contract surveyor ensures that each blast “markup”⁵¹ is accurately done and the direction of the tunnel accurately controlled. The surveyor checks the setting-out parameters prior to blasting.

Figure . Oblique offsets diagram.

1.10.Long range mounted laser systems.

Sleeve lasers are used for direction control over short distances, ranging from 20 meters [164] to a maximum of 150 metres [166]. Primary direction control for long, straight tunnels is best achieved by a long-distance laser mounted on the sidewall close to the hangingwall [170]. The laser beam is projected through an alignment screen⁵² to align the beam to be parallel to the design line of the excavation allowing for offsets at fixed distances to the left and right of the line [152]. The accuracy of the line is dependent on the base line and accuracy of work by the surveyor and must be checked regularly [171] and should only require extension after 800metres of development. These lasers are permanently mounted and require protection from blast and incidental damage.

Figure . Tunnel laser

Table A SWOT Analysis of Long range mounted laser


S
Strength


W
Weakness

This is the most accurate form of laser.

Sights up to 1000 metres are achievable under ideal conditions.

Visible alignment of the reference line is provided.

Using an adaptor the laser can provide gradient and direction line control.

Permanent mounting requires minimal maintenance.

The device operates on external power, not batteries.

The device is mounted out of the way of movement and blasting paths.

The device provides self-checks through target alignment and audible alarms when disturbed.

The installation and mounting must be done by a surveyor.

Routine maintenance of the device and reference line direction is required.

The longer distances of projection can increase the alignment error of the excavation.

The device requires external power.

Damage by equipment and blasting will cause misalignment. [172]

The beam may be dispersed and refracted in a poorly ventilated environment [172]

The laser requires to be placed a safe distance away from the blasting area.

Only one excavation can be serviced per laser.


OW
Opportunities


TW
Threats

Tunnel lasers are proven technology with an excellent track-record.

The laser direction line replaces strings for alignment.

The device is ideal for long, straight development including incline shafts.

Some devices have an audible alarm to warn against misalignment [167].

Beam dispersion and refraction over long distances is prevented by proper ventilation [170]

A longer time between new setting-out control installation is possible.

Only one person is required for installation and marking-up activities.

The device is not ideal for breakaways.

Mounting on the roof or high on the sidewall exposes the crew to the risk of working at heights.

The device is expensive to replace.

The line requires continuous monitoring of offset distances.

An error in interpretation of survey instructions will lead to off-line development.

The device requires alignment calibration.

Off-line development due to alignment or operator error.

1.11.Applications for totalstation technology.

Modern survey total stations can download on-board software in order to perform horizontal and vertical control of mining excavations. Once the instrument has been orientated by the freestation method, control are staked out based the mining layout and provides marking-up reference points for grade and direction lines. Total stations with on-board software are extensively used within the tunnelling environment to align and control the direction of drilling equipment in excavations [173] with an excellent track record. In tunnelling applications, the instrument is used in conjunction with the navigation system of the excavation equipment. Total station technology allows for the updating of the mine design and can provide structural monitoring. The cost of such systems is beyond the normal scope of conventional mining projects, but in the case of excavations where a high degree of accuracy is required this technology is a viable alternative with multiple applications.

Table . A SWOT Analysis of the Total station.

S
Strength


W
Weakness

This is the most accurate form of alignment.

Sights up in excess of 1000 metres are achievable under ideal conditions.

Visible alignment of the reference line is provided.

Gradient and direction line control is immediately referenced to the mine design.

The instrument is transportable

The entire mine design and reference co-ordinates can be stored on the instrument.

A number of setting-out functions can be performed using the instrument.

The equipment is expensive.

The equipment requires fundamental survey knowledge and training to be in place.

The orientation and alignment of the instrument requires training and practice.

Routine calibration of the instrument and reference line direction is required.

The equipment is prone to damage. [172]

Operator error will lead to offline development.

OW
Opportunities


TW
Threats

Totalstations are used in the tunnel construction industry with great success.

Immediate corrections to direction and grade are possible.

It is possible for the control process to be automated.

The instrument can be used for continuous monitoring providing early warning of movement.

The instrument can measure the excavation and report on over-or under break.

The instrument can be remotely accessed and linked into a network.

The device requires mounting on the roof or high on the sidewall to prevent damage.

The instrument is the most expensive of the groups of devices and is expensive to replace.

An error in interpretation of survey instructions will lead to off-line development.

The device requires periodic maintenance and alignment calibration.

Off-line development is a great risk due to incorrect design information and operator interpretation.

1.12.A perspective on developing technologies.

Machine guidance technology is well-known for surface mining operations. The combination of sidewall stations and transponder technology brings the alignment of excavation equipment into the realm of the possible. Studies have been conducted with autonomous vehicles guided in the underground environment proving that the concept is feasible. [174]
Sidewall station reference network combined with transponder or passive RFID systems will make accurate autonomous navigation possible. Such a network will form the foundation for Augmented Reality (AR) - or Mixed Reality (MR) technology such as the devices described by Chmelina [19]. Augmented reality devices can display data such as the mine design, support layout and geological features to the observer on-site and in real time. Combining the spatial reference system with portable data devices such as an iPad or Google Glass [175] the observer’s position can be accurately tracked and data relayed. Linking such device with a photogrammetric device it will be possible for new features to be located and updated within the database. The combination of these technologies will provide the basis for a person to execute a mark-up of an excavation with no visible reference lines. The adaptation of these technologies and spatial reference systems must form basis for further research.

5.