Open Cut » Overburden Removal
The objectives of this project were:
- To conduct a field study at Peak Downs Mine to acquire the following data on the excavation of a typical block:
- Calibrated stereo pair photographs to produce digital terrain models (DTM's) of key stages of the operation
Detailed productivity data including swing counts
- To use the above data to quantify the volumetric and productivity parameters associated with the observed block.
- To use the above information to calibrate 3d-Dig and simulate the excavation of the observed block.
- To set up a model of the complete pit where the standard operating method will result in the dragline being spoil bound, and to study the following alternative strategies:
- Truck shovel pre-strip to remove excess spoil
Dragline spoil pull back to create additional spoil room to accommodate excess spoil
The use of a dragline hopper truck system to remove excess spoil during the second pass operation
The stereo pair photographs were successfully digitised to produce DTM's. The technique is recommended for dragline studies subject to the following cautions:
- Very large control targets must be used. In this study the size of targets used in the spoil were about 700mm square. This size is barely adequate. We would recommend targets of about 1.5m square
- At least 4 targets must be visible in each photograph. Furthermore these must be distributed roughly evenly about the region of interest. Two targets in close proximity may induce errors or result in the inability to orient the photographs. Such problems are best avoided by installing an excess of targets, rather than the minimum.
- When photographing a stereo pair care must be taken to ensure the orienting of the camera axis is approximately the same for both photographs. If there is much divergence it may not be possible to bring them into stereo view when processing. A compass and inclinometer should be adequate for this purpose.
Wherever practical we recommend the use of a light aircraft to acquire aerial photographs. This will avoid most of the problems alluded to above. Furthermore the entire operation can be digitised from just one pair. Using land based photography between 3 and 4 pairs will be required, with subsequently much greater processing time required to digitise. Aerial photography will generally prove to be more accurate and cost effective.
3d-Dig was successfully calibrated and used to simulate the observed block. The block was divided into two sub operations,
- spoil dumping and
- bridge building.
The results were:
|Operation ||Observed |
|spoil dumping ||1779 ||1825 ||0.97 |
|key/bridge ||1835 ||1976 ||0.928 |
The difference between the observed and simulated has been used as a correction factor within 3d-Dig for subsequent simulation. An over estimate of productivity is to be expected as the modelling cannot take account of all operational inefficiencies.
The volumes associated with full strip modelling were:
- First Pass 2,970,000 BCM, area of coal uncovered 66,264m3
- Total 4,820,000 BCM, area of coal uncovered 7,4910m3
- Excess spoil 1,080,000 BCM (included in total above)
All three auxiliary stripping strategies were found to be feasible.
The production statistics are:
Total volume trucked 1080000 BCM
Total truck hours 2823
Total truck kilometres 61780
Total blasted prime 3740000 BCM
First pass dragline stripping:
- Total operating time 797hrs
- Total volume 1391000 BCM
- Rehandle 5800 BCM
- Overall productivity 1745 BCM/op hr
Second pass stripping:
- Total operating time 2707 hrs
- Total volume 4570000 BCM
- Rehandle 2356000 BCM
Overall productivity 1686 BCM/op hr
Dragline Pullback Option
Total volume 1210000 BCM
Total operating time 731 hours
Overall productivity 1662m3/op hr
Coal uncovery operation
Blasted prime 4820000 BCM
- Total volume 2228800 BCM
- Rehandle 5000 BCM
- Total operating time 1350 hrs
- Overall productivity 1650m3/op hr
- Total volume 5152000 BCM
- Rehandle 2870000 BCM
- Total operating time 3220 hrs
- Overall productivity 1600 BCM/op hr
Dragline Hopper Truck Option
Total truck hours 2488
Total truck kilometres 55105
Dragline operation first pass
- Total volume 2230000 BCM
- Volume to hopper 1080000 BCM
- Total dragline hours 1423
- Overall productivity 1567m3/op hr
Dragline second pass as for pre-strip option
The interaction between the dragline and the hopper truck system is a complex one. Due to the lack of information on the stochastic variables associated with the operation of such a system, a somewhat rudimentary analysis has been conducted here. For more detailed knowledge it is recommended that as such data becomes available it should be used to build a more detailed model.
It would be feasible to build a model of the hopper truck system within 3d-Dig and have the system model all aspects of the interacting systems. This would lead to more accurate modelling, particularly in regards to the effect of equipment availability.
3d-Dig is an integrated excavation design, dump design and dragline simulation system. It provides full 3d modelling of all aspects of the dragline operation. The system imports and honours all relevant data on the existing pit topography, coal seams and machine parameters. 3d-Dig presents the user with a perspective view of the topography, via a straight forward mouse driven interface the dragline can be placed and an excavation performed. The user can save data files and hardcopies for each step of the operation, providing 'replay' of the digging sequence and allowing a new analysis to commence at any point.
3d-Dig works by taking a Digital Terrain Model (DTM) of the existing pit. It then removes user designed bodies of spoil to simulate excavation, the DTM is modified to reflect this change and the material is swelled and stored to a material buffer. The user can then define an area within which to dump this material (typically somewhere within a dragline's dump radius, for dragline excavation). The material within the buffer is then numerically dumped, in discrete parcels, onto spoil and the topography is modelled and the resultant topography determined. This process continues until all material in the buffer is placed. 3d-Dig also models the movements required to perform the dragline operation and so calculates productivity. The functionality has been implemented in a flexible manner which also allows for the study of non-dragline systems (bucket wheel, truck shovel etc).
In order to fully model a three dimensional pit operation 3d-Dig must import and maintain a large body of data. Broadly this includes:
- Digital terrain model (DTM) of existing pit
- DTM of design topography
- Coal seam model
- Spoil characteristics (repose angle, specific gravity and swell factor)
- Machine parameters (geometry and performance characteristics)
- Performance log (volumes moved, productivity rates machine movement)