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

6.5. Conclusion

From the three case studies conducted in working underground mines it can be concluded that the sidewall station method can be applied in various forms to obtain good comparative results with the conventional hangingwall survey method. It is clear that certain parameters of geometry and observation protocol must be adhered to in order to obtain accuracies that will meet the prescribed minimum standards of accuracies for a Class “A” survey. It has been found that the method provides a saving in time and offers a reduced risk exposure profile to the survey crews. Although time and safety considerations may be considered as trivial when compared to the impact of introducing a new underground surveying method, the impact of these findings on the safety and efficiency on the mine surveyor is of significant importance.

In the next chapter the compliance of sidewall survey stations with MHSA accuracy requirements will be investigated. A risk analysis of the method and observation protocols will be investigated to ensure that the sidewall station method can be accepted as an accurate alternative to hangingwall survey networks. In order to complete a risk analysis of the sidewall station method the current standard procedures and guidelines available in industry will be analysed in order to provide a detailed procedure for the safe and accurate installation of sidewall survey stations in South African mines.

7. . A critical analysis of current international practice: lessons towards developing South African standard mine survey procedures

7.1. An overview of international wall survey standard procedures

This chapter will evaluate international practice and procedures used to establish wall stations in mine tunnels. In Chapter 6 it was found that the current two station method used in Australian mines in some cases do not meet South African Mine Health and Safety Act minimum standards of accuracy. It is therefore important to evaluate the method of surveying and identify the current strengths and weaknesses of the method. The evaluation will be in the form of a critical analysis of current standard procedures that is commonly available. The method of surveying remains the same in most cases as it consists of a preparation phase, followed by the installation of control which is then observed and finally stored. The analysis will use these five main headings:

• 
  Preparation;
  
• 
  Installation;
  
• 
  Observation;
  
• 
  Calculation; and
  
• 
  Data Storage
  

This analysis will be followed by a SWOT analysis of the methods used in order to better understand the strengths and weaknesses of the current methods and investigate improvements for the sidewall station survey method.
The standard procedures obtained can be divided into two main branches, the “Australian wall station method” as described by Jaroz and McCormack, these standards include:

• 
  Byrnecut at Palabora Mining Company
  
• 
  Kibali Gold Project in the Democratic Republic of the Congo (DRC)
  
• 
  Norwegian method also used at the Cambourne School of Mines. [97]
  

and the standards of GMSI, a company based in South Africa that uses proprietary software based on the same method of surveying:

• 
  South Deep Gold mine
  
• 
  GMSI “minemarkup” software notes
  

Finally the standard Leica freestation software procedures and recommendations will be analysed.

7.2. Phase 1. Preparation

7.2.1 Safety considerations

It is required by all of the various standards investigated that a work inspection and risk assessment be made before any work is commenced. In most cases specific reference is made to the stability of ground. In the case where the network should be extended into the workings of the mine it is required that the control used should be “checked and adjusted stations” [148]

7.2.2. Equipment used

Battery Operated Drills: All the current methods of survey station installation require the use of a battery operated drill for the installation of survey stations.
Survey instruments: The Western Australia survey standard describes the minimum requirements of instruments, defining the angular measurement to have maximum standard error of 5 seconds and a maximum standard distance error of 3mm to 5mm. [149]. The Gijima standards as well as the standards of both PMC Byrnecut Project and the Kibali Gold Project describes the use of the Leica 1200 instrument which is generally a single second instrument.
Targets: McCormack describes a wall station stainless steel stem 200mm in length and 7.5mm in diameter that can be inserted into the 12mm diameter aluminium sleeve. The stem has a bayonet attachment to fit a Leica prism. [110]. Ludvigsen describes a similar method taught in Norway as a stainless steel expansion bolt that is screwed into a 8mm hole drilled into the sidewall of an excavation and glued into place. A brass adaptor is screwed into the bolt and a prism attached to the adaptor. [97]

7.3. Phase 2. Installation

1. Survey Station installation

According to a Kibali Gold Project standard the installation is done in the following manner: [148]. A number of similarities between this project standards and the PMC Byrnecut Project standards exists.

• 
  “A collar hole approximately 10mm deep is drilled using a 16mm drill”
  
• 
  “a 10mm hole is then drilled sufficiently deep to ensure that all dust accumulating in the hole will not prevent the sleeve from fitting in the hole”
  
• 
  “Once the hole is cleaned the sleeve can be inserted in the hole and glued in place”
  

As described in Chapter 6 the method employed at South Deep makes use of a plastic expansion plug that has a threaded insert into which a survey prism can be screwed. [150]

7.3.2 Positioning of survey stations (wall stations)

According to standards used at Kibali, specific care must be taken in the selection of the position of the wallstations with reference to the grade line of the end and the possible position of future junctions that may destroy the wallstations. [148]. Similarly in a policy paper by Gijima Americas it is advised that survey stations should be clustered in a staggered pattern in order to provide more flexibility to the operator for the setup position of the freestation. [151]

7.3.3 Marking the point

The Australian Survey and Drafting regulations require each station to be “adequately referenced and substantially marked” as requiring that the control point to be placed in a position where it is not likely to be damaged. [44]. The PMC Byrnecut Project and Kibali Gold Project survey practices describes in detail the methods to be employed to ensure that this is done consistently. [152]. In accordance to South African mine surveying practice at South Deep mine the sidewall survey station is numbered with a numbered copper disk, similar to the disks used in hangingwall surveys and the number painted on the sidewall. Oxidization as well as blasting fumes will eventually tarnish the copper disk and fade the paint obscuring the number. Regular maintenance should be done on the station numbers when the check survey is performed in order ensure that they remain legible.

7.3.4 Protecting the point

Kibali Gold Project survey standards require a rubber cover such as a conveyor belt from the McGarf Laser alignment system. [148], a similar method is employed at PMC Byrnecut Project. This is a low cost solution making use of recycled material and an effective practice. At South Deep gold mine, no special protection is given to the survey point, although the selection of the position of the points is made in such a manner as to ensure that the point will not be damaged.