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

Considerations for the development of a standard practice unique to South African mine surveying

Lessons learned from the current international survey practices analysed in this chapter as well as the findings made during the research phase will be incorporated into a standard South African survey practice. The following points of learning were observed in the analysis of current international practices.

The primary advantage of a survey network using sidewall survey stations is that the risk of exposure to working-at-heights as well as moving equipment is removed. A sidewall station network has the advantage over conventional survey networks that the number of redundant survey stations is increased and the number of observations is also increased. The sidewall station method provides a more robust determination of position based on a greater number of redundant observations. In addition, the error introduced through poor centring practice for whatever reason is done away with. The software available to the surveyor has improved greatly over the last decade, providing the surveyor with a great number of calculation facilities while “on-the-face” in the underground workings.
The increased storage capacity of modern survey instruments allows a far greater number of observations and stored co-ordinates of known reference points being made available to the surveyor. The simplicity of user interface may in most cases allow non-surveyors to confidently take observations and use instruments to perform day-to-day activities such as marking off that would normally have been the duty of the surveyor or have forced the production personnel to make use of less accurate and inefficient methods of performing these tasks.
The primary lesson learned in the disadvantages observed from current international practice is the seemingly over-reliance on software solutions. The improved computational ability of survey instruments coupled with increasingly complex surveying applications on these instruments allow operators to make observations that may be fundamentally incorrect due to the operator not understanding the underlying fundamental survey principles. These include using poor observation geometry, number of observed points and the care and identification of survey stations. In addition the focus of data storage has moved away from hard copy printouts of observations to a purely electronic storage format. With the development of new data formats and operating systems the risk of losing data as a result of newer operating systems not being able to interpret older data storage formats may present a risk in the retrieval and re-calculation of survey observations if required. Data storage in the electronic format will always be exposed to the risk of corruption or loss due to viruses or hardware failure. It is considered important that a hardcopy of important observations and calculations always be available in the event of data failure or data loss.
The opportunity for Mine Survey practice in South Africa is that the international procedures analysed have a number of important features that can be applied to the South African mining context. The South African MHSA has over the years progressed from a prescriptive based type of Act to the current regulations that are formulated to be more outcomes based. The outcomes based format of the regulations within the Act allows the Mine Surveyor the flexibility to introduce alternative methods of surveying as long as the outcomes (in this case the minimum standards of accuracy) prescribed in the Act are met. The Standards introduced in the Australian mining context are robust, providing clear guidelines with sufficient detail to ensure that the minimum standards of accuracy are met. The guidelines provide strong emphasis on the storage and maintenance of records. In the South African context, the MHSA no longer regulates the storage of survey records. The removal of these requirements from the MHSA could lead to loss of data and information as a result of poor storage protocols and an over reliance on electronic data storage.

7. Conclusion

From the mine standards investigated for freestation type surveying it has become clear that some of the procedures investigated are a verbatim copy of each other with some cosmetic changes. The setup geometry that is defined does not follow any logical or scientific reason, stating only that exceeding the defined parameters may cause error in the positional fix of a resection point.

It is argued that some of the proprietary software investigated was designed for “marking up” a development end or taking direction lines, and then adapted to a surveying package. The software uses only basic triangulation to obtain the coordinates of a point which explains the more rigorous angle parameters to which the user is constrained to. The term “pickup” is assumed to describe the process of offsetting or measuring the profile of the tunnel. The MHSA would define this type of surveying as a Class “C” or even a local survey, which is not accurate enough for survey control networks. The method of using wall stations was described by Jaroz, Shepard and McCormack in the Australian context. By evaluating the standards of accuracy used in Australian mines it can be argued that the method, although meeting Australian standards of accuracy, does not necessarily conform to the minimum standards of accuracy required in South African mines, specifically with reference to the more involved nature of the Australian surveyor in the daily surveying and marking-up procedures. In the case of the standards evaluated it is apparent that in most of these cases the mining layout is that of a board-and-pillar type with wider roadways than the conventional narrow tunnel environment which this research is concentrating on. Such a mining layout can provide opportunities for a better distribution of survey points and longer baseline distances.
The Australian standards investigated are detailed in every aspect and in many cases arguably superior to the current Regulations of the Mines Health and Safety Act of South Africa. A case could be made for the South African Mine Health and Safety Act to be updated and in some cases old regulations reviewed and restored to the current regulations to sufficiently address issues including data storage, maintenance of records and check surveys.
The lessons learned from this analysis will form the foundation for the next chapter and will be combined with the findings of the research in order to develop the body of new knowledge that can be applied to devise a unique and practical standard within the South African context of establishing survey networks in narrow tunnel development in deep level mines. The SWOT analysis undertaken has provided valuable insight into the positive aspects of the wall station surveying method in order to promote this method of surveying as a safe, practical and accurate alternative to conventional hangingwall surveying techniques under most mining conditions.

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