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

2.9. Summary of the findings in this chapter

In this chapter a literature review was made on historic and current legislation, standards, procedures and accepted guidelines in use in the Mine Surveying industry. It was illustrated that the accuracy of survey plans can have a direct impact on the health and safety of those people employed in the mining industry. Financial losses caused by poor alignment as a result of incorrect or inaccurate surveying techniques can be substantial and have in some instances lead to a loss of life. In order to ensure that the correct procedures and acceptable standards of accuracy are at all times maintained in South African mines, the Mine Health and Safety Act have dedicated an entire chapter of the Act to Mine Surveying. In addition to the legal requirements that the responsible surveyor must comply with, a number of corporate driven Standards and Procedures have been introduced at most mining operations in the recent past. The limits of accuracy defined by the MHS Act compares favourably with those defined at various international mining and tunnelling projects. The limits of accuracy defined by the MHSA will be used to evaluate the accuracy of the proposed new method of surveying.

In addition to the Legislation, Standards and Procedures prescribing the accuracy and methodology of surveying in an underground environment, the health and safety of workers has become increasingly important in recent years. The literature reviewed has indicated a focus on the safety of workers working-at-heights in excess of 1.5 metres from the ground and defines in detail the safety procedures to be followed where such work takes place. The installation of survey stations in the hangingwall of an excavation falls within the accepted definition of working-at-heights . In addition to the aspect of working-at-heights , literature has indicated that the use of light metals in the construction of surveying equipment, with specific reference to aluminium ladders typically used where survey stations are installed, could complicate the installation of survey stations even further. The study of industry Standards and Procedures indicates that the prevention of risk in the form of working-at-heights and the use of light metals in a hazardous environment has become very important.
The most feasible cost effective method of ensuring that no impact is made on the productivity of survey crews, would involve removing surveyors from the risk by introducing the use of survey stations installed at a convenient height in the sidewalls of excavations.

A review of the factors influencing the accuracy of a survey was made and the following conclusions were drawn: Visibility, air flow, working-at-heights and production pressure will all have an influence on the integrity of an underground survey network.

In the controlled environment where the proposed method of survey will be evaluated the influence of external factors such as production pressure, temperature differences, visibility and refraction will be minimal to non-existent before testing the assumptions under realistic mining conditions. Such a method would allow the evaluation of the survey technique based on results not influenced by external factors. It will be argued in a later chapter that the use of sidewall survey stations will efficiently address most of these external factors.

3. Surveying Technology Review

1. Technological advances in Instrumentation

The advancement of technology for surveying underground excavations during the years has played an important role in the improvement of the accuracy of alignment, but none more so than in the past 20 years. Hodges et al observed that the demands on the mine surveyor to ensure the accuracy of surveying have increased in response to the ever increasing depth of mining coupled with the mechanization of the mining process. While in the narrow and confined tunnel environment “Survey measurements which are comparatively straight forward on the surface, can assume inordinately difficult proportions in a mine… Furthermore, the extreme environmental conditions underground, coupled with limitations in time and space, make accurate and reliable measurements difficult.” [88]

In a presentation at CONSAS in 1982 Hodges and Smith described the state of evolution of surveying instruments. According to Hodges and Smith, by 1968 an electronic distance measuring device such as the WILD Di-10, could be mounted on a normal opto-mechanical theodolite to facilitate distance measuring. Among the first of these instruments was the Wild Tachymat TC-1 which could store “over 1800 blocks of data can be recorded on one cassette” [89]. The authors remarked upon the reduction of size in circuitry and increase in storage capacity [88] predicting that “the production of fully integrated system, combining electronic measurement of both distance and angles, and incorporating micro processors which enable automatic computation … was the next logical development.” [88]. Accordingly the advantage of such instruments that could measure and record data was recognized in the early 1960’s with the development of the Fennel theodolite, and the evolution of the total station , where by “…1977, at the XV FIG congress in Stockholm, four new total station instruments featuring data recording were introduced,…incorporating microprocessors to control the instrument, perform the necessary computations and output data for recording and processing.” [88] These developments were indicators of the type of instrument that would be available by the end of the 1980’s : “a total station could be defined as a single instrument which is capable of measuring all the field data that a surveyor needs and recording this data automatically.” [88]
In his publication Ryder discussed the requirements of technology incorporated in the monitoring instruments used in the study of rock mechanics for tabular hard rock mines in South African mines. [90], arguably requirements that have the same relevance to surveying technology [90]:

• 
  “Robustness and suitable protection against adverse atmospheric conditions (heat, humidity, corrosion;”)
  
• 
  “Simplicity of use;”
  
• 
  “Protection from the environment ;”
  
• 
  “Reliability, minimize the possibility of operator error;”
  
• 
  “Adequate sensitivity, accuracy and reproducibility of measurements;”
  
• 
  “Protection. Robustness and suitable protection against adverse atmospheric conditions (heat, humidity, corrosion);”
  
• 
  “Ease of reading and immediate availability of data;
  
• 
  ‘Minimal interference with mining operations.” [90]
  

In most cases all new surveying instruments used underground comply with these requirements to some extent. New surveying technology has made the following features available on most instruments:

• 
  Electronic Distance Measuring
  
• 
  Higher accuracy of angular measurement
  
• 
  On-board software
  
• 
  Immediate verification of minimum standards of accuracy and accuracy
  
• 
  Electronic recording of data eliminates human error
  
• 
  On-board storage of all data including all observations made and the co-ordinates of survey points
  
• 
  Electronic downloading of observations and surveying data
  

It must be reiterated that even with the obvious advantages of the new technology the mine surveying industry has been slow in adopting this technology. The added speed and accuracy offered by such instruments can significantly improve the speed of work of Mine Surveyors improving their productivity. Pretorius and Crous in an article titled “Standard instructions for Mine Surveyors,” dated 1967, expressed the opinion that the productivity of a surveyor may have a direct impact on the cost structure of a mining operation, stating that “Where salaries and wages form a high percentage of working cost, every hour of productive work lost must be directly reflected on the cost structure.” [13]. Hodges summarized the advantages of surveying automation as “increased productivity, reduced errors, and more efficient use of resources.” [88] It can be argued that the development of surveying instruments, data storage and computational ability has reduced the amount of time required to take observations and improved the speed of calculation. This improvement in the turn-around time of surveying has in turn lead to increased productivity due to reduction in surveying errors and faster calculation times.

In 1984 in a paper authored by Deeth, further improvements in surveying equipment were predicted which “are unlikely to see a significant reduction in size, weight or speed of measurement but will reduce manpower. There already exists the potential to produce a self-tracking self-seeking instrument.” [91] Most of the predictions made by Deeth have proved to be accurate; however continuous development in the speed of measurement and the exponential increase in data storage capacity has taken place. Self-tracking instruments are now used at a number of mining and tunnelling projects. Laser scanning instruments are becoming smaller and cheaper as technology is improved. One of the areas of development where constant improvements are made is in the improved storage and computational abilities of equipment. Deeth argued somewhat ironically that “This type of unit allied to data recording at the point of detail would allow the one man survey team, and a guard dog to protect the otherwise unattended instrument.” [91].

Hodges et al argued that “In order not to impede mining operations and to save time of qualified personnel, it is essential to continuously improve and update mine surveying technology by the rationalization of measurement and instrumentation techniques.” [88] With the introduction of continuously improving technology in the surveying field, coupled with the ever increasing demands of productivity required from a survey office and a lack of qualified surveyors, it has become tempting to argue that with the increased sophistication of technology, the person operating the equipment could be “less” qualified. Cawood remarked that:

“…the myth that sophisticated surveying equipment and increased use of technology require less qualified surveyors or even just ‘operators’, will in the long term damage the long standing professional image of the Mine Surveyor. The contrary is true, namely the more sophisticated instruments become, the higher surveyors must be qualified in order to understand and correct the errors associated with these sensitive devices…” [92].

While it may be argued that the average mine surveyor only understands and therefore uses only a small amount of the applications installed on modern surveying instruments, it should be emphasised that a better understanding of instrument applications is essential to the improvement of the productivity of surveyors. In order to ensure the integrity of the survey profession and the accuracy of survey networks for which mine surveyors are responsible, it is important that surveyors take a critical interest in the instruments and survey methods that they are using to perform routine tasks. Sir David Gill in an address to surveyors stressed that “However perfect an instrument may be (and it is the surveyor’s business to see that it is perfect), it is the surveyor’s further business to look upon it with complete and utter mistrust” [93]

2.