I need to dig a rectangular box hole for a rainwater cistern. The dimensions are 4m x 3m x 2m (13ft x 10ft x 6ft). There is a slope of about 10 degrees, and the dirt will be used at a point of lower elevation. The soil is a mix of clay and residues of bricks.
Given the amount of soil that needs to be removed, I'm looking for the easiest way to excavate this much material. I have a wheelbarrow, shovels, and pickaxe to use for the task. Is there any way I can use the slope itself to make the task easier?