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<< Click to Display Table of Contents >> Surface Reshaping Principles of Operation |
  
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<< Click to Display Table of Contents >> Surface Reshaping Principles of Operation |
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The 3d-DigPlus surface reshaping module allows a post mining topography to be reshaped in a manner that reduces slopes, maintains volume balance and ensures the volume balance occurs within localised regions.
The transportation analysis allows a completed design to be analysed and creates a set of transport arcs which quantify and graphically illustrate the required movement of material from cut to fill.
The design of final landforms, which must be produced from the post mining topography, are subject to a range of design criteria including the following:
1.Slope criteria. Slope criteria are often the principle governing design criteria with slopes are set with the intention of controlling erosion on the post mining topography.
2.Drainage criteria. Various criteria may apply to the ponding and free drainage of various parts of the post mining topography.
3.Disturbed footprint limitations. When restating steep spoil and reducing slopes the toe of post mining spoil is pushed out into the surrounding topography and hence the footprint of land disturbed by the mining process increases. Often there will be limits on the extent to which the spoil can be pushed, this may be a result of statutory limits on the disturbed footprint or the presence of infrastructure such as roads and buildings.
In addition to the above criteria any design for a post mining topography must be achievable with the equipment fleet which is to be used for the reshaping process. Most typically bulldozers are used for the reshaping and hence the volume balance must occur within the economic push distance of the dozer fleet.
There are a number of factors which limit the accuracy which can reasonably be achieved in the spoil reshaping process. These include:
1.Limits in the accuracy of the the survey of the post mining topography. This can be particularly important with dragline spoil where the close frequency of individual peaks within a line of spoil can place limitations on survey accuracy.
2.The occurrence of localised swell and compaction during the reshaping process. It is typically assumed that dumped spoil will not swell or compress significantly during the reshaping process and this may typically be the case, however depending on the fragmentation and particle size of the spoil localised swelling and compaction can and does occur.
3.Limits on the means of controlling the equipment fleet during the reshaping process. The use of GPS systems on bulldozers whereby the operator can see the dozer blade position relative to the design surface have greatly improved design compliance. However achieving design compliance requires that a push strategy be implemented from the start of the process which ensures that each parcel of material is transported to the correct location. If major blocks of spoil our pushed in the wrong direction from commencement of the operation the final surface is not likely to comply closely to the design.
The spoil reshaping module has been designed to allow the user to quickly establish a post mining topography where slopes, on average, are sufficiently close to the design slopes and localised a volume balance is assured. Where the design criteria calls for a constant slope, with all areas conforming to this slope, it is generally best to target surface where the average slopes are close to this design criteria. If a design is attempted where every part of a slope is exactly on design criteria this will usually involve substantial additional work and frequently no practical benefit due to the accuracy limitations mentioned above. Provided the average slopes are close to design criteria, and there is localised volume balance, it will generally be possible for the dozer operators to efficiently produce a post mining topography which conforms closely to design criteria.
The spoil reshaping module allows the user to subdivide the design area into regions. Each region is reshaped in turn and volume balance is assured within these regions.
Once a region is defined the user sets various reshaping parameters and the system iteratively reduces the surface slopes by removing material from the high areas of the topography and placing them in the lower areas.
A number of iterations will be required within any region to achieve the desired slope reduction. So the process involves gradually reshaping the surface in a series of steps and slowly approaching design criteria. Generally the first iteration will reduce slopes approximately half way between original and design slopes and all regions are established and treated in this manner. The second and subsequent iterations involve selecting regions in turn and performing slope reductions on them. The following clip illustrates the reshaping process:
The Spoil Reshaping functionality has only a limited number of functions and parameters. Learning the general procedures to apply this system is quite straightforward. However the effect of the various parameters on the form of the reshaped surface is quite subtle and it is important that the user has a good understanding of these effects.Effective design also requires skilful placement of the reshaping regions and a suitable process for repeatedly running reshaping iterations across the full set of regions.
The following topic details the various reshaping parameters and gives some indication of how these affect the form of the reshaped surface. It also gives some general guidance as to how to place reshaping regions and how to iterate the reshaping process between regions to gradually produce the desired design surface. Once these basic processes are understood it will take practice to become proficient in the spoil reshaping design process. The included Spoil Reshaping tutorial guides the user through the process of completing a small reshaping task.