Earth bag building with earth berming

So,  my husband and I are wanting to build a round earth bag house that has a loft and berm up to the height of the loft.  Well actually we would like to build 3 roundhouses with one berm.  I am wondering what kind of extra support is needed for berming or if that is even feasible.   Purpose for the berming is for passive solar. We are I  the mountains with hot dry summers and snowy winters and really wet springs.

More detail will help!

Jamie:

I'm no authority, but looking at other designs, the general issue of having dirt against the outer wall is do-able.  (see my thread on a cistern)

The general issue is dealing with the force of all that dirt so your design needs to resist that force with thick walls or transmit that force.

Ah yes, more detail... so I would like to do kind of a combination of two of Owen Geiger's designs... his Triple Roundhouse and Two Story Round house designs (I would be buying those plans and merging them). So I want to lay the three roundhouses out in the design he shows for the bermed Triple roundhouse design with the buttresses but I would like them a little larger than the diameter's his are (I think his are two 16' and one 24'ish and I would like one 30' and two 20' roundhouses).  Then I would like a loft in each of the roundhouses.  I planned on only berming the height originally designed in his Triple Roundhouse design which is the full back wall to the roof, but with the extra diameter and height I wasn't sure If I would need to pull the two 20's forward a little more to make more of a triangular type shape of the three or just add extra bond-beams and/or rebar or something to help (if positioning can compensate I would rather do that then adding more materials)?  If I used larger bag sizes (width wise) would I need to use the same size for the whole round or can I taper to the standard size in the front?  

Another question - foundation I was under the impression I should dig below the frost line and fill with gravel back to grade then start the stem wall on grade and go up... but a friend has questioned this and says with the berm in mind I should backfill with gravel to about 6-8inches below grade and start the stem-wall inside the trench to keep the house from sliding off the foundation...  I didn't have any rebuttal for that logic... is that a good suggestion or is there a reason for not doing that?