In the planning phase, the entire surface area is usually divided into mining panels which are later mined and reclaimed with a particular sequence. Panel dimensions and their relative orientations affect in-pit waste haulage distance, stripping ratio, production efficiency, and facility layout. Generally, for the same production rate of coal, reduction of panel width will reduce in-pit waste haulage distance. Increasing panel width, on the other hand, is fundamental for increasing the mining capacity, decreasing the stripping ratio, and reducing the number of sharp changes in production rate as mining moves from one panel to the next.
Let us consider a large surface coal mine where there is only one coal seam, and the layers of overburden and coal are regular and horizontal.
x = panel width (km)
H = Overburden thickness (m)
h = coal seam thickness (m)
φ = overall pit slope at working face
α = overall slope of waste
β = Overall slope at both sides of the working pit.
s = in-pit safety distance (km)
L = average in-pit waste haulage distance (km).
L can be expressed as a linear function of the panel width x:
L = ax + b, km
The first term in the stripping ratio expression represents the bore-hole stripping ratio. It is the minimum value for overall stripping ratio. The second term however is inversely proportional to x. The total stripping ratio can thus be reduced by increasing the panel width. It is clear at this point that an economically desirable balance between the cost effects of stripping ratio and in-pit waste haulage distance can be achieved by selecting a panel width such that the total stripping cost is minimum.
Proposition 1: When deviating from the optimal panel width Xo, increasing it by an amount of Δx causes a smaller increase in the stripping cost than decreasing it by the same amount; i.e.,
if Δx = x2 – x0 = x0 – x1,
then Δy1 = y1 – ymin > Δy2 = y2 – ymin
Proposition 2: The larger the deviation of panel width x from the optimal value X0, the bigger is the difference between the stripping cost at left side of X0 (narrowing the panel) and the stripping cost at the right side (widening the panel),i.e.,
if x12 – x0 = x0 – x11 = Δx1 < Δx2 = x22 – x0 = x0 – x21
then y21 – y22= Δy2 > Δy1 = y11 – y12
A critical step in developing long-range mining plans in large surface coal mines is dividing the surface area into mining panels. We show in this paper that during this process different panel sizes will result in different stripping costs and an optimal panel width corresponding to the minimum stripping cost exists. A formula and an equivalent graphical method for this optimal panel width is developed.
