I am in the initial design phase to build a 'root cellar' approximately 8' x 10' that will be completely underground, with and 8' useable ceiling height.  On top of this area will sit a shed although not connected to the structure below.

My question has to do with the actual excavation and safety relating to holding the soil back from the work area.  The planned location of the structure does not allow for typical excavation equipment or S.O.P's to be employed, such as pulling back yards and yards of earth from the build site.

The question is:  What is the most cost effective way to do this excavation with a temporary 'hold-back' wall system?

It should be noted that although 'temporary', the 'hold-back' walls can be left in place and back filled over and around.

I was thinking of sinking 4 or 6 10' or 12' Sonotubes with rebar, filling with concrete, then as I excavate around them filling the space between the Sonotubes with 2x4's or 3/4" ply.

What do you think?

Any and all advice is appreciated.

Thanks
Joe