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

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Chapter 1Introduction

“No work shall be done if it cannot be done safely” [1] this statement, from the Standard Operating Procedure of a South African mining company, summarizes the main purpose of this research. In South Africa the zero-harm principle is the over-riding philosophy governing every aspect of work performed in the workings of a mine. The previous Minister of Mineral Resources, Minister Shabangu, in an address at the launch of a rescue drill unit for Collieries, stated that the South African mine health and safety performance remains a cause for concern and that the Department of Mineral Resources “pursue the ideal of “Zero Harm” relentlessly” [2]. According to the safety statistics for 2013 “The major contributors to these accidents were underground mine fires, rockfalls and trackless mobile machinery.” [2]. The stated object of the Mine Health and Safety Act is to identify, eliminate and control risks and entrench the rights of workers to refuse to enter a working place or perform work is exposed to risk.

In this context zero-harm is intended to be a commitment to zero fatalities and zero injuries to mine employees, the community and the environment. In the extreme, unforgiving underground environment found in South African mines, in which the conditions make logical thought and the performance of relatively simple tasks difficult, Mine Surveyors need to adapt technology and techniques to perform their allocated duties safely, fast and accurately. Metcalfe remarked in a textbook on Mine Surveying that “…it is ironical that the most trying branch of underground surveying is that where the greatest accuracy and care are required.” [3].According to Livingstone-Blevins the fundamental difference between mine surveying and other branches of surveying is the “mitigation of risk”, the gravity of the consequences of “not getting it right” may prove to be fatal [4].

1. Mine surveying – an overview

Mine surveying has been defined by the International Society of Mine Surveyors as “the art of making such field observations and measurements as are necessary to determine the positions, areas or volumes of natural and man-made features on the earth's surface” [5]. The Mine Surveyor is responsible for accurately determining the position of all mining excavations relevant to surface infrastructure and boundaries as well as all other adjacent mining excavations. It is the role of the Mine Surveyor to accurately represent these positions on the working plans of a mine. Young remarked that “One of the most important phases of mine surveying and probably what requires most care is a survey for openings to connect two given or assumed points.” [6].

Mine surveying has been used as the method of referencing the surface features of a mine with underground excavations since the earliest of times. One of the oldest known tunnels is Hezekiah's tunnel or the Siloam tunnel in Jerusalem, completed around 700 BC [7]. This tunnel was 533m long and designed to transport water into Jerusalem. The tunnel remains one of the earliest examples of tunnelling in the world. The tunnel of Eupalinos in Samos, Greece, was excavated in the sixth century BC to serve as an aqueduct. This tunnel was also known to have been excavated from both ends and is considered to have been one of the first to be aligned using geometric principles.
The principles for aligning underground excavations have changed very little during the years while the purpose of alignment has remained the same, namely, to establish a safe connection between excavations with the minimum amount of error in the shortest time possible. Schofield differentiated between surface and underground surveying by stating that “the essential problem in underground surveying is that of orientating the underground surveys to the surface surveys, the procedure involved being termed a correlation…thus underground control networks must be connected and orientated into the same co-ordinate system as the surface networks” [8].
The role of the Mine Surveyor in South Africa is regulated by the requirements of the Mine Health and Safety Act (MHSA). This Act prescribes the minimum standards of accuracy allowable for the accuracy of the position of mine surveying stations as represented on the prescribed underground plans of a mine and prescribes that all excavations must be accurately represented in relation to mining- and mineral rights boundaries, objects on the surface that will require protection as well as any underground excavations that could pose a hazard to workers. Such hazards include areas where there is a possibility of the accumulation of noxious gas, water or mud, should an unplanned holing¹ be made into such an excavation. Johnson remarked on the importance of accurate and safe alignments of mining excavations by observing that:

“Too much stress cannot be laid on the importance of the care to be exercised in running connections, as there is nothing the mining surveyor’s reputation depends on more directly than his uniform success in this matter. In fact a failure in such a case may involve a large loss to his employer, … an error in many cases cannot be remedied, but results in permanent injury to the mine.” [9].

This statement still holds true today. The error in the direction or gradient² of a mining excavation can cause large financial losses due to the loss in production caused by re-development and non-adherence to tight production schedules and also the financial and legal applications incurred with the loss of life that could result from unplanned breakthroughs³ into hazardous areas.
The Mine Surveyor has a number of responsibilities that need to be executed on a daily basis to exacting limits of error⁴. These daily “production” responsibilities include “staking-out” of construction lines to control the direction and gradient of development ends⁵ (tunnels). Deviation of these direction and grade lines from the mine design could lead to costly and in some cases permanent, damage to the mine infrastructure, that will require expensive re-development or a change to the original mine design.
It is therefore by implication important that the accuracy of the primary survey network falls within the prescribed minimum standards of accuracy and crucial that the survey network is established in accordance with the correct mine design. Livingstone-Blevins argues that any deficiency in the accuracy of a survey network “ripples through to other processes” with the potential of exposing the mine to risk [4].
Mine surveyors do not have the luxury of being able to “close” their networks, any alignment and gradient error will only be confirmed when the development end breaks through at the position it was aimed at. In the case of a narrow tabular deposit, the primary survey network is extended underground via transfer of direction in the shaft and then the network is extended on each level of the mine workings. A primary survey network is established on each level and will only be verified once the survey is joined with another primary network on a different level. Normally such verification will only occur if the surveys are joined by the secondary survey that is extended into a raise or winze line. The “correlation” between the surface and underground workings will most likely only be confirmed in the case of a breakthrough between levels or when an independent check survey⁶ can verify the original survey.
Cawood remarked on the fundamental changes in the legal framework in which the Mine Surveyor operates. This legal framework defines the manner in which data is collected, processed, presented and reported [10]. The Mine Surveyor must ensure that all surveying work undertaken will satisfy the Mine Health and Safety Act as well as to the required Standards and Procedures determined by his employer. In the current international social- and legal environment, most mining companies have adopted a “zero-harm” principle in all the activities they engage in. A zero-harm policy requires all employees to adhere to all regulations and corporate requirements in accordance with the MHSA Section 22 and 23(1) these policies normally include the “…right to leave any working place whenever: (a) circumstances arise that,….appear to that employee to pose a serious danger to the health and safety of that employee…” as well as the right to refuse to perform dangerous work or entering an area where the possibility of unmitigated risk may be present [11] . According to the MHSA Section 91 “Any person, including and employer, who contravenes, or fails to comply with, any; (a)provision of this act…(c) ….commits and offence and is liable to a fine or imprisonment as may be prescribed...” [11]. Safety in the Mine Surveying context must be recognized to have two distinct aspects namely the safety of the surveyor and survey crew with relation to work procedures and equipment and secondly, the safety of mine employees and the public. This second aspect can only be adequately addressed by ensuring the accuracy of the survey network established by the surveyor.
Traditionally surveying stations have been installed in the roof or hangingwall⁷ of mining excavations. In most instances the roof of the excavation would not be more than two metres high, but with the introduction of more efficient methods of tramming rock such as track-bound locomotives and large trucks the dimensions of tunnels have in most instances increased to be in excess of three metres. When the height of the roof of an excavation increases to a point where the roof cannot be reached without the assistance of a ladder or mobile lifting equipment, the task of installing survey control becomes fraught with hazard. In general any work performed at a height greater than 1.5m is defined as “working-at-heights”. Such work is strictly regulated by company specific on-mine safety standards. These standards have been developed to reduce the incidence of potentially fatal accidents caused by persons falling from heights.
This increased focus on safety has arguably had a direct impact on the number of survey stations that a surveyor can install in a production shift. The height factor reduces the visibility of survey control, hampers the identification of survey points and impacts on the accuracy of centring the instrument and target within acceptable limits. A combination of these factors can cause an error to be transferred to the accuracy of subsequent survey stations leading to an unacceptable limit of error in the position of survey stations.
The advancement of technology used for the surveying of underground excavations during the years has rapidly improved the accuracy of survey networks but none more so than in the past 20 years.” With the continuous reduction of the size of circuitry coupled with the simultaneous improvement of micro processing power allowing the use of increasingly sophisticated computing software able to perform complicated calculations in the field with minimum effort [12]. Although Hodges and Smith noted that by 1968 an electronic distance measuring devices could be mounted on a normal opto-mechanical theodolite to facilitate distance measuring, total station technology was not fully accepted by the South African mine survey community until the mid 1990’s. Modern surveying technology has made the features such as Electronic Distance Measuring, on-board software and electronic recording and downloading standard on most survey instruments.
The increased speed and accuracy of observation offered by such instruments can improve the speed of work of Mine Surveyors thereby assisting in improving their productivity. Any delay in the production process as a result of the installation of survey control can impact negatively on the bonuses paid to production crews. Pretorius and Crous remarked on this fact in their paper, arguing 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]. Metcalfe made a rather pointed observation regarding this matter “underground officials of limited imagination, not realizing the ultimate purpose of a survey…are apt to take a narrow view….” [3] As a result any perceived delay in the production process caused by the surveyor will be viewed in a very poor light by the production crews and may very likely the relationship between the surveyor and the production crew in that working end.
In South Africa the perceived lack of suitably qualified Mine Surveyors within the industry has caused an increase in the pressures placed on those surveyors employed on a mine. It has become essential for a surveyor to complete the installation of survey stations in the shortest possible time in order not to impact on the drilling and blasting process while still ensuring that the accuracy of the survey will be within the prescribed minimum standards of accuracy, thereby maintaining the integrity of the survey network. It is becoming increasingly common to find that first-order survey work is done by semi-skilled operators without the necessary in-depth theoretical surveying background. Most of these surveyors do not have a qualification higher than NQF Level 7 or a first degree. In some overseas mining operations the new technology has enabled non-survey personnel such as mining supervisors to be able to take survey and alignment observations with minimal training, reducing the need for a qualified surveyor to visit the working end on a daily basis.
Adapting existing surveying technology and techniques to the underground mining environment could have a significant impact on the improvement of the speed of installing survey stations while at the same time decreasing the associated exposure to working-at-heights by the mine surveying crew.
The South African mining industry has always been perceived to be responsive to research and adapt to new mining technology, but in contrast, the South African Mine Surveying community [14] has been relatively slow to consider alternative surveying techniques to replace [15] the tried and tested methods of surveying that have been used extensively over the past 100 years. Morton commented on this phenomenon by stating that: “Resection has never been accepted by the majority of surveyors as a reliable method of obtaining a “fix”. This is due to the fact that unless the problem of resection is fully understood, serious errors may be introduced and not detected during calculation.” [14].
Presently most underground mines in South Africa still make use of technology that would not be unfamiliar to a surveyor from a hundred years ago. Pretorius and Crous argued that “Surveyors will agree that they are quite commonly guilty of a form of professional jealousy…a reluctance to change from a tried and trusted system, … This attitude is more often than not short sighted , as the time spent in acquiring the new and better technique might be more than compensated for in the subsequent efficiency resulting from the latter.” [13].

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