



 
Tim, I would use an approximation to make the calculation easier. My approximation is that the topsoil is a cylinder od diameter 24 feet and thickness 8 inches and the fill is half a cylinder of radius 24 feet and depth 40 inches. The volume of a cylinder is π r^{2} h where r is the radius and h is the height. You want the volume in cubic yards so change the dimensions to yards before making the calculation.
Harley  


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