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

Conclusions and recommendations.

It is concluded that no one method or type of technology will be ideal for all situations. The most practical solution remains the separate installation of a tunnel laser in a position where the risks of damage from normal mining activities are minimized. Lasers have proven to be an accurate and efficient method of direction control that is not affected even in areas with high ventilation currents. [176] The methods and technology must be selected to best suit the cost and production profile of each individual situation. If a single ideal method has to be recommended it would be a hybrid of a long range tunnel laser, combined with gradestrings surveyed in from the sidewall network control. The combination of these techniques has the single biggest advantage of all the methods and technologies discussed. A matrix rating each form current of technology is tabulated here:

Table Application matrix of laser technologies.

A cluster of sidewall stations can be installed on the correct gradient in a similar manner as that already adopted by most mines to install gradepegs. The main concern with using the sidewall stations for a gradient control is that it will be subject to damage when used by the production crew on a daily basis. The method used by Finch [164] and Snap Lake in Canada [163] , where the survey stations are installed in addition to the “mining control” points, provides a practical solution that reduces the risk of damage to the survey control points, albeit time consuming. Small lasers suspended from the grade strings or installed in a sleeve at an oblique angle to the direction of mining have proved to be effective and is accepted practice in Australia and Canada. The greatest criticism to the oblique offsets is that the offset distance does not remain constant and requires great care on the part of the production person marking-up on a daily basis. The method of providing oblique offsets is not new and is used regularly in conventional hangingwall surveys where a cross-cut is broken away. Products for alternative methods of mounting such as tripods, wall brackets and rail attachments exist, that can be installed and turned at an offset to indicate the direction of mining. [167]. According to du Toit of Finch mine, a small laser on a tripod is used by the mining department to align the direction marks on the grade pegs with the laser and aligning the face mark-up with the line projected by the laser [177].
The cost of a laser guidance system or entry level total station when compared to the cost of development in a mine tunnel justifies the application of such technology in the ‘mark-up’ of a tunnel. It is unrealistic to expect consistent accuracy in alignment when using bob-strings and weighted plumb lines to direct the mining of a multi-million rand primary development end. For mechanization and automation of mining to become a reality, guidance systems such as laser scanning, proximity monitoring and “smart” survey stations must be combined to provide accurate “indoor” navigation capability in the mining environment. Factors that will influence the selection of a system will include:

• 
  The cost of equipment (capital outlay)
  
• 
  Importance of excavation (incline shaft or ventilation holing?)
  
• 
  Accuracy requirements of excavation
  
• 
  Is the excavation planned for “breakthrough” into another excavation?
  
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  Skill of operators and surveyors
  
• 
  Willingness to adapt new technology
  
• 
  Availability of power supply
  
• 
  Risk evaluation (potential damage due to tramming or blasting)
  
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  Mining layout (long straight lines or curves and breakaways)
  
• 
  Access to the hangingwall
  
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  Sidewall rock strength and competency (no movement)
  
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  Can the excavation equipment used be adapted to automatic alignment by laser?
  

1.17.An estimation of the cost of technology as a percentage of development cost.

Using basic assumptions the percentage cost for excavations based compared to the cost of technology over a period of a year is tabulated. It is clear from the tabulation that the cost of technology for alignment is less than 1% of the cost of the excavation. The technology for alignment is critical to the control of the excavation. The risk of misalignment of an excavation has major cost implications. It is apparent that the cost of technology will have little impact on the overall cost of excavation while at the same time providing insurance against misalignment events.

Table cost analysis of laser technology.

The following alternatives need to be explored in further research:

1. 
   The use of a “construction grade” total station with an on-board freestation software for marking-up. Construction grade instruments are affordable and offer an accurate alternative for marking-up.
   
2. 
   The application of proximity locators on board of mining machinery to align a drill rig.
   
3. 
   The adaptation of machine-guidance technology used with sidewall station transponders or passive RFID’s to orientate and align drill-rigs to the mine design.
   
4. 
   The suitability of a permanently mounted totalstation mounted permanently for machine guidance and monitoring.
   
5. 
   The adaptation of AR technology for mining construction.
   

In an era where advances in technology and software are continuously updated and refined, it is possible to use laser technology with great effect in mining. The technology has been simplified to such an extent that tasks normally associated with a mine surveyor can be completed accurately by the production crew responsible for marking-up. Although the legal responsibility for direction and grade control will always rest with the mine surveyor, it is current practice on international mines that a member of the mining team are able to operate a survey instrument and software to set-out the control for a tunnel. In the South African context where more mining engineers and technologists are produced on a yearly basis, all with a good grasp of elementary survey knowledge, such persons can perform elementary setting-out procedures. In all cases where a laser device is installed by the surveyor, the time should be taken to assist the production crew with the extension of painted grade and direction lines.

In summary, borrowing from Nieveen, the requirements of a quality intervention should be validity, practicality and effectiveness. These requirements are based on state of the art knowledge (relevance). Interventions will be considered as practical by users if they find the intervention useable and compatible with the intent of the intervention. And lastly the desired outcomes of the intervention must be met. [178]. Applying the criteria outlined by Nieveen [178], a tabulation of the technology intervention for direction and gradient control can be made.

Table Requirements of a quality intervention.

Criterion	Remarks
Relevance	Using the sidewall station method of surveying requires an intervention in the method of setting-out mining excavations. The constant upgrade of laser technology has made alternative methods of setting-out possible.
Consistency	The method or hybrid of methods suggested can be utilized for a number of possible staking-out different types of excavations. A comparison of methods currently utilized has been made and the advantages of each method considered.
Practicality	The hybrid method of setting-out control is expected to be useable in the South African mining environment.
Effectiveness	The effectiveness of the setting-out methods has been successfully tested in different environments.

By adopting the format proposed by van den Akker [179] for design principles, the following concluding statement can be formulated to describe alternative methods of setting-out using sidewall stations; based on the conclusions reached in this chapter:

“If you want to use sidewall stations for the accurate setting-out of mine excavations, then you are best advised to give the selected method the ability to be integrated with laser technology and to do that by installing setting-out control separate from the survey network stations in such a manner that the direction and gradient of an excavation can be accurately controlled because laser technology offers a cost-effective solution for setting-out control.”