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

SWOT analysis of current international survey practice using wall station type surveying methods

In order to evaluate the current international practice where wallstation methods used internationally a Strength-Weakness-Opportunity-Threat (SWOT) analysis has been made based on the standards researched as well as the discussions with surveyors using the method. The variables identified during this analysis will be used in the development of unique guidelines for the installation of sidewall survey stations in the South African mining industry.

1. Strengths

The main strengths of the wallstation method is the ease of use and reduced risk exposure of the survey crew to working-at-heights. The following points are highlighted as strengths of the method:

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  Measuring and offsetting of features, areas and volumes are made easy.
  
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  The practice of using two wallstations is becoming recognized throughout the international community.
  
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  No levelling and centring errors on calculations.
  
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  Incorrectly measured instrument and target heights are avoided.
  
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  Freestation or resection software standard on most instruments.
  
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  Ease of use of software and freestation method.
  
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  A freestation setup is not influenced by strong ventilation.
  
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  No ladder or lifting equipment is required meaning that fewer crew members are required and “working at height” protocols are not required.
  
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  No hangingwall access required means that the risk of exposure is removed.
  
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  Position of the setup can be moved to avoid any potential risk exposure or obstructions caused by mining equipment.
  
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  Two sidewall stations provide more redundancy than one hangingwall peg.
  
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  Wallstation plugs are not made of brass means that the risk of theft of survey stations is reduced.
  
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  Software will identify points that have been damaged, moved, surveyed or identified incorrectly.
  

2. Weaknesses

The main weakness of the wallstation method of surveying has been identified as the risk of error in positional fix created by poor observation procedures. The following points were identified during the evaluation as contributing factors to the weakness of the method:

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  The actual co-ordinated position of a wallstation is dependent on the centre of a specific prism attached to a specific prism attachment and will change if a different prism or attachment is used, making the station unreliable.
  
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  The method requires additional training in the use of the equipment and software and will require sensitization to setup geometry.
  
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  The redundancy of only two wallstations is not sufficient for accurate positioning
  
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  The geometry required for an accurate position fix using two wallstations is restrictive.
  
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  Two station setup calculations are not stored in a user-friendly manner and make manual calculation complicated.
  
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  The calculation is complicated to perform manually making a logic check on the positioning difficult.
  
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  The two wallstation method do not meet the requirements of the MHSA minimum standards of accuracy in all cases.
  
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  The method is accurate for the marking-up of a face but not always for extended control networks if not followed up with a stringent check survey protocol.
  
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  Careful communication between surveyor and crew is required to ensure correct identification of points during observation.
  
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  Obstruction of wallstations by debris can destroy the reference point.
  
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  Damage during installation can damage the thread or inner portion of the sleeve.
  
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  Displacement due to ground movement will render the survey station useless.
  
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  The method is not efficient in areas with poor sidewall conditions where scaling and pressure could destroy or move the stations.
  
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  The method is not accurate when red-laser reflectorless measurements are used as the beam point is not concentrated enough to provide accurate measurements.
  
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  McCormack refers to the fact that the true optical centre of a prism does not remain constant when the target is rotated. [110]
  

3. Opportunities

The following points were identified as areas where the wall stations survey method could be promoted as a preferred method of surveying:

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  A truly “one man” surveying crew is possible.
  
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  The method is compatible with techniques used for laser scanning.
  
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  Additional control points ensure a higher degree of redundancy.
  
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  The wallstation method is compatible with mining equipment such as drill rigs for lining up machinery.
  
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  The method can be taught to mining personnel to perform daily or weekly survey measurements.
  
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  The training of mine surveyors and mining personnel in this method will improve the general body of knowledge of more advanced surveying techniques and may cultivate more research into the application of this method of surveying.
  
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  More mining engineers are becoming available that can use instruments and software in production environment.
  
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  Standard procedures can be applied over most mining operations.
  

4. Threats

The following points were identified as posing a potential risk to the successful implementation of the wallstation surveying method on mines where more traditional methods of surveying are still used.

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  Resistance to change amongst South African Mine Surveyors is perceived to be great.
  
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  The method will have to be proved to be accurate under a greater number of varying environments and conditions.
  
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  The storage of observations and calculation of co-ordinates must be managed.
  
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  Check surveys are critical to the strength of the network.
  
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  The cost of equipment and software can be too great for a small-scale mine.
  
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  The general low level of education of Mine Surveyors and mining personnel in South Africa could impact on the adoption of the system.
  
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  The accuracy of a survey control network can deteriorate fast if not managed during each step of the process.
  
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  The error propagation in bearing must be managed by check surveys and gyroscope azimuth determinations.
  

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