ok. just modified my driling design.

 

the red tip is a drill. designed to loosen up the ground.

it can retract itself inwards into the circle. so it won't get in way of the buckets (blue).

 

once the ground is loosened up,

of which the first layer of the ground is hard surfaces i'm guessing. (why concentrated drill)

 

then the spinning buckets can do its thing and further start the dig.

 

the yellow is the frame that would hold the spinning mechanism following the power line above.

 

 

however, once it is dugged. where does the soil go?

does it stay or drifted away by the current?

 

why the walls. and draining water ?