I have attempted to build ramps (to be able to dump easily with trucks) up to my hoppers, both the wash plant, and the conveyor hopper.
I've attempted this by placing cribs and lock blocks. I can get the construction pieces placed down to gain height, but when I add excavated material to cover the pieces, it always works its way under the pieces and they end being moved out of position, ruining the ramp - and making it impossible to "fix" the piece when prompted by the game because "material has worked its way under the original".