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

6.4. Palaborwa Mining Company, Copper mine

Palabora Mining Company (PMC) is a copper mine situated in the Limpopo province near the town Palaborwa approximately 500km north east of Johannesburg. The mine started underground operations in 2003 and follows a block-caving layout. The production level is approximately 820m below surface. The dimensions of the development ends accessing the orebody are planned to be 5.6metres wide by 5.8metres high. This height makes direct access to the roof of the excavation difficult. A new decline shaft to extend the life of mine is currently being developed by Byrnecut, an Australian based mining contracting company. The decline³⁹ development surveying is done by an Australian contractor using a two peg freestation method. The mining layout of pillars lends itself to better survey setup geometry and allows for continuous loops of surveys that can be closed as an additional check.

Figure . The mining layout of the copper mine

Source: Mr. J Bezuidenhout PMC

1. Methods and Standard procedures employed

The mine uses standard hanging wall surveying for day-to-day operations. The mining contractor uses a type of wallstation method of surveying described by Jaroz and Shepard [96]. According to the mine standards [147], the surveyor will avoid the use of acute observation angles in order to obtain the strongest geometry possible for the setup. Angles smaller than 60 degrees and larger than 120 degrees are to be avoided. [147], Standards require baselines longer than 25 metres and control should be extended from checked and adjusted stations in order to reduce the risk of error propagation.
The wallstations used, consist of an aluminium tube into which a long brass target holder is placed when targets are placed for observation. The sleeve is recessed deeply enough not to be damaged by blast debris. The station number is painted on the sidewall with high visibility paint and a numbered disk is attached to it.

Figure . Target installed
Figure . Target with attachment


Photographs by H Grobler
The survey peg⁴⁰ and sleeve is protected from blast damage by a rectangular piece of recycled conveyor belt, pinned to the sidewall so that it can be swung out of the way when needed.

2. Closures obtained

The mine has conducted a check survey using hanging wall pegs which to date have yielded good closures with the wallstation method used by the contractor.

Figure . Check survey origin of the contractor

The origin of the check survey was on a hangingwall baseline near the origin of the new decline shaft used to carry the survey into the decline.

Figure . Diagram of the check survey route


Table . PMC Closure calculation
The following tabulation details the temporary points surveyed during the check survey. The first tabulation indicates the uncorrected closure on points A3216C and the contractors point T6 which is the same point. Similarly the end point of the baseline A3121C and T7, indicates an error vector of 50 and 62mm respectively compared to the allowable minimum standard of accuracy of 31mm over the distance of 471metres. Refer to Table .

A gyroscope bearing check was made to compare the closure of the two methods on a set of hangingwall pegs placed for the purpose of the check survey. The closure obtained on the baseline was 44 seconds. This closure is within the MHSA specifications for the minimum standard of accuracy for a bearing closure between points, however the closure is possibly too large for precise shaft sinking. It can be argued that according to the MHSA this survey may have met the standards of accuracy for a Class “B” survey “…any survey carried out for the purpose of fixing main or access development, mine boundaries…” [11]. After adjustment using the gyro bearing and the corrected co-ordinates the closure was recalculated and found to be within the prescribed minimum standard of accuracy error vector calculated above.

Table Final closure obtained

A summary of the gyroscope closure is tabulated below:

Table Gyroscope closure

3. Does this method meet the minimum standards of accuracy?

From the closure it emerges that the accuracy of both survey methods are within the minimum standard of accuracy. According to the Chief Surveyor on site “The standard of accuracy also lies in the execution of the practical “know the practical calculation limits” which would result in a poor survey setup and choice of setup to establish high accuracy surveying. You would not be able to achieve good accuracy if you are not aware of the traps with this method. Thus it might be even posing higher risk to your accuracy.” [147]

4. Is this method a safer method of surveying?

When asked about the safety of the method, the Chief Surveyor replied that “Safety is not negotiable on any mine and in any workplace. This method of surveying has got the lowest risk of injury especially at Palabora where the excavations are so high to reach.” [147]

5. Further advantages or disadvantages of the method?

The Chief Surveyor considers that this method is both fast and safe, but that the check survey is crucial to the accuracy of the network. [147] In addition the method is still seen as a new and untested method by most South African surveyors.