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An economical means for removing high overburden led to the development of the Wheel Excavator. The objective of the Excavator is to move more material farther, and at a lower cost, than is possible with other types of stripping equipment.
The instability of the upper half of our over-burden, such as sand, grovel, and the like, makes working a dragline near an open face a very hazardous operation. This unstable condition also makes it very important and necessary to deposit the dug material a considerable distance beyond the open pit to prevent slides.
The Wheel Excavator technique of stripping overcomes both of these objections. The Excavator is operated on top of the coal bed and it is capable of spoiling the unstable overburden as for back from the open pit as the second previous shovel spoil. The overall height of the spoil is lowered, thereby eliminating sliding of the spoil. The "high wall sliding" problem is also eliminated through the use of the excavator. Coal recovery is greatly improved, as no coal is lost through burial of a sliding spoil.
The Wheel Excavator not only overcomes the problem of overburden removal and cost, but is also a very definite assist to land reclamation. The spoil piles are much more regular in size and contour than those produced by dragline or shovel alone. The hard rock and shale removed by the shovel is at the bottom of the pile and the original loose top material is returned to relatively the same position, thus make the reclamation problem much easier. In many cases we have found the crop and grazing value of reclaimed areas greater than that prior to the stripping operation.
Irregular or fluctuating out-put in Strip Coal Mining has become a problem because of the unequal stripping depths. The overburden height has gradually increased over the years, yet the coal bed thickness has unfortunately remained the some.
Moving a given quantity of overburden does not uncover a uniform tonnage of coal when the overburden thickens. As a result, our mining equipment and organization, geared to peak production, may not be utilized to their fullest rating.
