how difficult it was to build this with the dirt there. Did they just have extra dirt that they had to get rid of and no where to put it but hidden there? Who knows.
In answer to your question, I would hire some day laborers and procure the necessary shovels and wheel barrows and you be the contractor. There is nothing about this that is more superior than just labor.
I would be careful for electrical, plumbing, and other lines that needs to be identified. I would leave a cone if you will around each pier, you do not want to under cut this structure.