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

Phase 5. Storage and presentation

7.5.1. Record keeping

The South African MHSA is currently not regulating the storage of survey records. In the previous MINE HEALTH AND SAFETY ACT, 1996 (ACT NO 29 OF 1996) Chapter 12.4 the keeping and storage of survey records were described. The standard procedure at PMC Byrnecut Project requires documented notes of surveys be kept and communicated at handovers between the contractor and mine. [152]. It is required by these standards that all electronic survey data be copied on to a domain server. Read and write access to the database is provided to the contractor. All calculations must be retained as a hard copy together with a list of co-ordinates and filed. This process is also required in the Kibali Gold Project standards. The New South Wales and Western Australian standards require records to be “maintained manually on either field-book or other stable material, electronic text or image…” and requires regular updates in the case where file formats may change. [44].

7.5.2. Pickup⁴² instructions

A “pick up” instruction would describe the method of measuring the excavation position and volume using tacheometry. According to the Kibali Gold Project standard instructions only a “single face” resection needs to be made [148]. This minimum standard of accuracy for measuring according to the MHSA is a Class “C” survey or localized survey. No such definition could be identified within any of the Australian standards. The accuracy of the position of the outlines of an excavation is not as critical as the accuracy of a survey station. The conclusion made from the procedures described in the PMC Byrnecut Project and Kibali standards is that it is assumed that a poorer accuracy fix will be achieved with a single face observation.

7.6. Check surveys

Check surveys are considered an essential part of maintaining the integrity of a survey network. In the mining environment where closures are not always possible, a check survey normally consists of taking long observations bypassing any intermediate survey stations and closing on a survey base close to the face of the current workings. Wherever possible, survey base closures are made between different levels of the mine. Alternatively the survey is closed on the same point of origin. A further check on the bearing closure is made by gyroscope. Any deviation or error propagated by the survey network can be identified by the gyroscope azimuth determination and the network is normally adjusted to this gyro bearing.

1. Accuracy

The Survey and Drafting directions for Mine Surveyors in New South Wales, Coal, [44] requires accuracies for control and subsidiary surveys to satisfy a standard of accuracy as described by the Inter-governmental committee on surveying and mapping standards and practices for control surveys Special Publication 1. [39]. Similar codes such as the Survey and Drafting directions for Mine Surveyors in New South Wales, Metalliferous and Extractive industries developed by Safework Australia, the Recognized Standard 10 for Mine Surveying and Drafting, Coal mining Safety and Health Act 1999 issued by the State of Queensland , Department of Employment, Economic Development and Innovation, 2011. Direction 3.3.1. requires “conditions to achieve a standard of accuracy as prescribed in ICSM, Sp1 to achieve class “D” or better…via the formula r=c+(d+0.2) where” [44]:

“r” is the length of maximum allowable semi-major axis in millimetres

“c” is an empirically derived factor represented by historically accepted precision, in the case of a Class “D”, this value is 50, categorized as a “lower class survey

“d” is the distance to any station in km, with a minimum value of 1km

[39]
In the case of the test survey conducted at Anglo Platinum mines where a distance of 638metres was surveyed, the Australian standards would be calculated as follows:

Table . ISCM standards of accuracy for 1 kilometre.

[157]
When compared with the South African Mine Health and Safety Act requirements for the same distance the minimum standard of accuracy would be calculated as: [11]

Table . MHSA standard of accuracy for 1 kilometre

[157]
The Code of Practice for Mine Survey, second edition, issued by the Government of Western Australia, Department of Mines and Petroleum Resources Safety requires a “standard of accuracy to be 1:5000 or better” [149], which for 1000 metres will mean a minimum standard of accuracy of 200 millimetres, in which case the two-point resection tested in Chapter 6 would have met the required standards of accuracy.

7.6.2. Methods of check surveying

Hutchinson remarked that the standard practice used in a random setup method for grade installation was to “overshoot day to day surveys…with longshot surveys…” [122]. According to the Survey and Drafting directions for Mine Surveyors in New South Wales [44] an underground baseline shall be established in a “suitable position and of at least 250metres in length…” [44]

Control survey checks are required to be carried out in order to maintain the accuracy and precision of a survey. Although currently not a requirement of the Mine Health and Safety Act, a check survey remains the only method of ensuring the integrity of a survey network. According to PMC Byrnecut Project standards it is required that a “check survey be conducted regularly and any adjustments will need to be documented” [152] McCormack recognizes the importance of a check survey when using the wallstation method “does not eliminate the need for resurveys” [110]
The use of a gyroscope to check and control the bearing transfer of the network. The setup method described by McCormack is a modified Weisbach setup between two known points, developed by the Camborne School of Mines and adjustments made following the gyroscope results. [110]
The Western Australian Code of Practice for Mine Survey requires a loop closure or where that is not possible, a two-way check traverse closing within the accuracies of 1:5000 as defined. [149].

7.