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

The formulation of the fundamental question

Changes in mining methods and an increased focus on productivity driven by Health and Safety standards and labour efficiency, may lead to increased pressure on some mines to investigate alternatives to the conventional hangingwall method of open traversing to establish survey stations in the underground environment. Gillespie alluded to this fact when he stated that “the objections to this method are, the length of time it takes to get the spuds in the roof, and also the difficulty in using them when the roof is high.” [16]. The technology is now available to investigate the viability of introducing an alternative surveying technique to the underground environment in order to improve the efficiency and safety of the surveying process.

A number of authors including Pretorius, Crous [13]and Morton [14] have in the past commented on the apparent reluctance among South African Mine Surveyors to accept the accuracy of a survey station obtained by any other method other than hangingwall traversing. The challenge of this research will be to prove that the establishment of a primary survey network of surveying stations in the sidewall of an excavation of between three and five metres in width will be a safe an accurate alternative to a survey network in the roof of an excavation and still comply with the prescribed minimum standards of accuracy. The results of the proposed research will have to answer the following fundamental question: “Will the precision of position determination by sidewall survey stations⁸ meet the minimum standards of accuracy as specified by Chapter 17 of the Mine Health and Safety Act no. 29 of 1996 in a narrow tunnel environment typical to South African mines?” Should it be determined that the answer to the fundamental question is “yes”, it must be asked

1. 
   “how can this be achieved?” and more importantly;
   
2. 
   “how will such a method contribute to the zero-harm safety policy of a mine?”
   

3. The research outline

The proposed sidewall station survey method will involve the installation of four survey stations drilled and grouted into the sidewall of the excavation at a comfortable height above the floor of the excavation. It is proposed that the position of the survey instrument can be determined by observing angles and distances to four known points. Once the position of the instrument has been determined, the survey will be carried forward towards the advancing face of the excavation or any other position that is required. The viability and accuracy of this alternative survey method has not been tested in mines in South Africa.

It is proposed that survey stations be installed in the sidewall of an excavation and tested to determine the position of the instrument to an acceptable limit of error. It will be necessary to evaluate the impact of the geometry of the placement of survey stations in relation to the unknown point on the accuracy of survey stations installed in this manner. The findings of the test phase will be evaluated in a narrow tunnel environment at a deep level South African mine to determine if the results obtained will meet the current minimum standards of accuracy.

4. Overall objectives

The objective of the proposed research is to determine whether the accuracy of a network obtained from observations made from sidewall survey stations is within the minimum standards of accuracy defined by the Mine Health and Safety Act of 1996 (Act 29) for a Class “A” primary survey network control. In order to investigate the accuracy of the proposed survey method it will be necessary to establish a survey network in a controlled environment where there will be minimal interference with the installation of survey stations and the observations process. The specific objectives of the research were:

1. 
   To establish a survey control network using the accepted method of hangingwall traversing to within the minimum standards of accuracy prescribed for a Class “A” primary survey network.
   
2. 
   To establish on the same site, a survey control network using the sidewall surveying method using a closed traverse method, closing the survey on the point of origin.
   
3. 
   To evaluate the accuracy of closure obtained by the sidewall survey stations with the prescribed minimum standards of accuracy as defined by the MHSA.
   
4. 
   To evaluate the accuracy obtained between the conventional hangingwall survey method and the proposed sidewall survey station method.
   
5. 
   To test the accuracy, safety and efficiency of the proposed survey method in the narrow tunnel environment of a working mine.
   
6. 
   Based on the outcomes of the above points, to determine if the alternative method of surveying is a safe and accurate alternative to standard South African mine survey methods
   
7. 
   To evaluate the associated risks involved in the survey techniques and
   
8. 
   Outline suggested practices to ensure the safety and accuracy of the alternative survey method for practical implementation in South African mines.
   

1.5. Methodology

A service tunnel located under the Doornfontein campus of the University of Johannesburg provided the test site for this research. The tunnel with average dimensions of three metres wide by three metres high, is 160m in length and terminates in a 180m long cross tunnel. The tunnel provided similar dimensions to the narrow tunnel environment found in most South African mines. The tunnel does not carry the normal risks associated with underground mining tunnels as the area is free from ventilation and rock pressure issues and therefore provided a safe, controlled environment with almost no traffic to disturb any work taking place.

The experimental site was surveyed in the traditional hangingwall traverse method and the survey closed on the point of origin and the co-ordinates balanced. Such a closed traverse is not standard practice in the underground environment, but the accuracy of the conventional survey had to be verified to be within the acceptable minimum standards of accuracy for a primary survey network.
The same route was then re-surveyed using the sidewall station method of surveying, using a minimum of four sidewall stations for each setup. Both surveys were closed at the same point of closure in order to determine the error in closure for the survey. The accuracy of this survey method was compared to the acceptable minimum standards of accuracy for a primary survey network. A comparison was drawn between the positions obtained by the two different survey methods. Data was collected by making observations using a single second total station using only the standard on-board software of the instrument. In order to collect data that would take the following parameters into consideration:

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  The optimal distance between target and instrument setup position;
  
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  the effect of incorrect target alignment and placement of targets with specific reference to the geometry of the setup;
  
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  the effect of incorrect target identification including the effect of observations made by infrared to target as compared with measuring distances using a reflector-less method of observation; and
  
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  the optimal method of sidewall peg installation including the method of:
  

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  Positioning the survey stations for optimal geometrical alignment;
  
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  permanently fixing the point in the sidewall by grouting or friction; and
  
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  Determining the effect of contamination by dirt and oxidization of the sidewall station plugs on the accuracy of observations.
  

The final orientation of the survey network case study was checked for angular closure using observations from a gyroscope to verify the final bearing closure of the proposed survey method, compared to the original survey. A full analysis of the closures obtained was made in order to determine whether the new proposed method of surveying complied with the minimum accuracy requirements for a primary survey network as currently required by the Mine Health and Safety Act.

1.6. An overview of the literature search and further chapters

The following chapters will attempt to review relevant current knowledge in the field of Mine surveying and related industries with reference to techniques, standards, procedures and legislation that impact on current mine surveying practice.

Chapter 2 will be investigate current Mine Survey and other Legislation, Industry Standards and Codes of Practice, both nationally and internationally. As part of the investigation process, recent health and safety incidents in the international mining environment where mine surveying played a contributing role will be discussed. As part of this industry standards review, the effect of external variables such as illumination, refraction, production pressure and the regulation of working-at-heights on the safety, accuracy and productivity of mine surveys will be considered.
Chapter 3 will review the history of developments in survey technology and briefly analyses the range of surveying technology currently available. It is argued that, given the availability of modern survey equipment, the speed and accuracy of surveying has been greatly improved, but at the same time, relatively few alternative methods of surveying have been developed to replace the tried and tested methods of mine surveying that have in most cases been in use since 1900. The conventional methods of obtaining the spatial position of survey points will be discussed and modern applications of technology used in large tunnelling projects and international mining operations are investigated. A number of recent large projects will be discussed with specific reference to the method of surveying used at each of these projects.
Chapter 4 details the setup of the experimental survey network using a standard hangingwall survey as the control. The proposed method of using sidewall survey stations as the basis for establishing a primary underground survey control network will be tested in a controlled environment to evaluate the accuracy of the method. The chapter outlines the controls put in place during the research to attempt to ensure the quality of the survey network and the new proposed method of surveying to be applied will be discussed in detail.
In Chapter 5, the results of the observations made under the controlled conditions of the test facility and the subsequent analysis of this data will be used to evaluate the accuracy of the sidewall survey station method compared to the traditional control survey, prior to being tested in a working narrow tunnel environment. The process of establishing a sidewall survey station network from existing hangingwall control, the extension of such a network and the results of the analysis of the geometry of sidewall stations obtained will be discussed. The minimum standard of accuracy obtained through the two methods of surveying will be compared against the requirements of a Class “A” survey as described by the MHSA.
Chapter 6 evaluates the implementation of the proposed sidewall survey station method of surveying under the real production conditions of a mine. The full scale in a working mine is tested at a deep level South African mine. The method of surveying and any adjustments to the proposed method of surveying will be discussed and analysed in this chapter. The closures obtained by the new method be compared against the minimum standards of accuracy of a Class “A” survey as defined by the MHSA.
Chapter 7 evaluates the current Standard Operating Procedures and Guidelines followed in similar methods of surveying nationally and internationally, with the intention of compiling a proposed guideline relevant to the South African mining context.
Chapter 8 outlines the new knowledge obtained from this research and sets out a guideline to describe the method of establishing and extension of a sidewall survey station network. Factors that could have an influence on the accuracy and safety of the proposed survey method will be discussed. The suggested guidelines include the geometry of survey observations, the placement of survey reference points and the minimum number of reference points to be used to ensure that the minimum standards of accuracy will be obtained during a survey. It is recommended that this chapter be read in conjunction with Appendix 7 which is intended to serve as a proposed outline for a Standard Operating Procedure for sidewall station survey networks on a South African mine.
Chapter 9 evaluates solutions for marking up the direction and gradient control using sidewall stations. The combination of gradelines and lasers as well as alternative technologies is discussed.
The final conclusion and recommendations drawn from the experimental survey and the actual narrow tunnel deep mine test are made in Chapter 10. This chapter attempts to prove that the sidewall survey station method of surveying will achieve comparable results meeting the prescribed minimum standards of accuracy when compared with the accuracies achieved through traditional hangingwall surveying. The final conclusion attempts to answer the question outlined at the start of the thesis: “Will the precision of position determination by sidewall survey stations meet the minimum standards of accuracy as specified by Chapter 17 of the Mine Health and Safety Act no. 29 of 1996 in a narrow tunnel environment typical to South African mines?”

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