Really out of my field, but it would seem that reducing the height would increase the travel distance - so, the incline influences the fuel consumption - there must be a trade-off somewhere less incline greater distance to be travelled, steeper climb - less distance. Does the greater / lesser distance dramatically impact of engine power /fuel consumption requirements?

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

Not sure if this comment is relevant but on a vaguely similiar exercise a few years ago , I managed to prove that INCREASING the fuel consumption optimised my haulage costs. This is because the cost of fuel is a very small part of the total operating cost. Ash must have a very low specific gravity. Have you examined putting larger boxes onto your fleet??

For a small stockpile, I would start by determining bench height. Then determine reasonable area for machinery on top bench. Then work my way down bench by bench until I have volume I need. Then make sure a ramp at 10% grade can go around it.

For a large stockpile, say a mining wastepile for planned pit, geotechnical eng. will determine bench height and maximum number of lifts. I do not see where diesel is an issue. If the facility is to be rehabilitated at end of mine, footprint is really the issue here.

capliard

Ingenieur Minier. QuTbec, Canada.

Here is an interesting link that may be helpful - Caterpillar Haul Road Design

I have a friend who has expertise at economic justifications for conveying versus truck hauling, especially for materials such as CCR. You might think about some conveying solutions to allow a steeper angle. Haul trucks to pile and then conveying. Depends on your budget. Operating budget versus capital expenditure.