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

Evaluation of the accuracy of the sidewall survey station network

The MHSA provides for four specific classes of survey categorized as Class “A”,”B”, ”C” and “Localized”. In order to determine whether the sidewall survey station method will meet the requirements of the MHSA, the following question was posed “Will the sidewall survey station method of surveying be sufficiently accurate and precise to meet the prescribed standards of a Class “A” survey network as defined by the MHSA?”.

It could be that the accuracy of a survey network can be sufficiently accurate to meet the Class “C” or local minimum standards, but would not be deemed accurate enough to be used in the establishment of a primary survey network the requirements of which would be classified as a Class “B” or a Class “A” survey. The fundamental question of the research was to determine whether the sidewall method of surveying would provide accuracies that would meet the requirements of the MHSA. In most cases the main development of a mine will be in the form of a narrow tunnel design. In the regulations the specific definition for the class of survey required for the accuracy of a main haulage survey is not clear enough to make a clear distinction between a Class “B” or a Class “A” survey. The research therefore has aimed at evaluating whether the sidewall station survey method would be accurate enough for a Class “A” survey and whether this minimum standard of accuracy could not be achieved by downgrading the application of the sidewall survey method to alternative surveying applications where the standard of accuracy could be met.
The results of the research have indicated that the minimum standards of accuracy required for a survey network to meet the requirements a Class “A” quality survey can be achieved under specific conditions. It was found that rigid observation protocol must be adhered to in order to ensure the accuracy of a survey. In addition the most important requirement in order to achieve the required accuracy is the observation of a minimum of four reference points during the position determination of a resection point. If only two points are used, the standard of accuracy achieved in a network deteriorates to a Class “C” or localized survey accuracy that can only be used for measuring or reconnaissance surveying. It is suggested that a survey network can be extended up to 750 metres from the last checked points with little deterioration in accuracy, as long as a four point configuration is used in every case where the survey is extended.
As a result of these findings, it is recommended that a check survey should be performed when the sidewall station network reaches a maximum of 750 metres from the last checked baseline. It is also recommended that a check survey baseline be established at the station (near the shaft) of each level of the mine and when a check survey is completed, a new check survey baseline be established that can be readily identified and used for the verification of the accuracy of any further survey work. Mines operating on multiple levels have by definition a number of independent survey networks with the same point of origin, namely the shaft. Due to the nature of underground mining on independent levels, the accuracy of these independent survey networks cannot be determined without performing a closure survey between the two levels. In addition to the problems caused by these “independent” underground survey networks, the error in the alignment of the surface survey network with the underground survey networks could result in misclosures. The use of the gyroscope to verify the accuracy of the underground survey network in relation to the surface survey network is therefore essential not only to check the error in bearing transfer underground but also the error propagation within the underground survey network itself.

4. Conclusion

The results of the research have shown that the sidewall station method of surveying meets the minimum standards of accuracy required for a Class “A” primary survey network as prescribed in the South African Mine Health and Safety Act’s regulations, provided that fundamental survey observation protocol is followed. Observation protocol must ensure that sufficient redundancy is provided for in observations and control points. In the mining industry the accuracy of a survey network has a direct influence on the safety of all employees underground and the protection of the economic asset of the mineral resource. Unplanned holings, mining through boundaries and the sterilization of ore reserves will have a direct financial impact on the life of a mine. The accuracy of any mine survey is regulated by the MHSA and may as a result be check surveyed at the expense of the mine if there is concern regarding the accuracy of the networks [11]. The accuracy of the survey networks of a mine therefore has a direct and significant impact on the safety of mining personnel, the safety of workings and the economic resource.

In the mining industry most corporate policies state very clearly that no production will take place of it cannot be done safely. The matter of safety and efficiency is therefore considered as one entity. It is argued that the accuracy of a survey network is linked to the overall safety aspect of a mining operation, therefore the safety of the mine workings will be at risk as a result of poor survey coverage.
The risks associated with working-at-heights , using lifting equipment and the exposure to working in close proximity to the hangingwall on a lifting platform (ladder or mechanical platform) during the installation process were evaluated. The drive towards zero tolerance of any incident in the mining industry requires demands that all associated risks be evaluated and mitigated prior to the execution of work. It is argued that the sidewall survey station method has been proven as a safer alternative of surveying. This reduced risk profile should assist the facilitation process of managing the change from conventional surveying to the sidewall survey station method.
The focus on safety has had a significant impact on the productivity of the surveyor reducing the effective time spent doing the core work of extending and verifying the survey network and at the same time ensuring the accuracy and integrity thereof. The sidewall survey station method is seen as a method of reducing the risk profile and at the same time freeing up time within a shift that can be spent productively performing core surveying activities.
If the productivity of the survey department is, as a result of the performance of non-core activities, not at an optimal level, the core functions that a surveyor as custodian of the survey database or “void” model will not be executed in a timely and accurate manner. In such a case, the essential maintenance of a survey network, including check surveying, maintenances of reference points, offsetting and updating of the 3D mine void model will be neglected, placing the safety of the operation at risk. Efficiency is therefore considered an essential part of the safety risk profile of a mining operation.
Accuracy and safety should be considered as co-dependent entities in the field of Mine Surveying. The accuracy in survey data assists in the control of risks associated with the lack of accurate spatial information within the mining production and planning environments. In the case where networks have to be established and maintained this must be done within the parameters of legislation and corporate regulations, standards, procedures and guidelines. The adherence to safety is considered as a non-negotiable with severe penalties in cases in which a breach of safety protocols is perceived to have been committed. Safety protocols in the installation of survey pegs dictates the use of ladders, working-at-heights , the operation of mobile lifting equipment, barring of side and hanging walls amongst others.
Today’s surveyor is faced with an ever changing environment where the emphasis on efficiency. Productivity is challenged by the need to achieve complete tasks within an environment where zero tolerance to any form of injury exists. In order to ensure that these requirements are met the surveyor must rely on ingenuity, innovation and technology to work safely, accurately and efficiently. The use of mechanized equipment will probably increase in the future, leading to increased changes to the design of mine access development. Mine designs accommodating mechanized equipment will inevitably require an increase in the dimensions of the access tunnels. As a result of the implementation of new methods of mining, it is becoming difficult on some mines to use the conventional hangingwall method of open traversing to establish survey stations in the underground environment. Gillespie alluded to the fact 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 increase in dimension and increased rates of advance will lead to greater and more frequent demands being placed on the surveyor’s time to ensure the proper alignment of the access tunnels. The use of ladders and working-at-heights demand greater care in the day to day activities of the surveyor and as a result means that less survey work can be completed in a normal shift.
In the study, the efficiency and safety of the sidewall surveying method was compared with the traditional method of hangingwall surveying in order to consider the efficiency of both methods. Conventional hangingwall surveying techniques require the hangingwall to be accessed at three different positions. The hangingwall is accessed during the installation and again when removing targets at the reference point or backsight, the station position and the foresight position. This implies that the hangingwall is required to be accessed by some means on at least six separate occasions. When direction control is placed, the survey crew member remains at height for prolonged period of time and is exposed to a hangingwall which may not be barred⁵³ or safe. In contrast the sidewall survey station method provides an excellent alternative to working-at-heights and is able to avoid or mitigate the risk of exposure to these associated hazards as no contact with the hangingwall is required. The avoidance of the risk of working-at-heights has the additional benefit of leading to increased productivity as a result of the time saved that would be spent in these activities.
As has been indicated in the research a significant saving in time can be expected as a result of not needing to access the hangingwall at any stage during normal surveying activities. This saving in time should in turn provide additional time for the surveyors that would otherwise have been required to locate, setup, access and otherwise manage lifting equipment. It is reasoned that in such a case more time can be spent in selecting safe and optimal positions for reference points and ensuring the quality of the survey network.

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