Frost Line Depth Under Berms

[JoePE]

Looking for guidance (hopefully a reference) that describes prediction of frost-line depth in detail and specifically below the surface of a berm area. The berm in question has a 30' base and is 12' high. The frost-line in this area is considered to extend 48" below grade. I do not know the soil type or subsurface water conditions, but I don't anticipate any surprises (Boston, MA Metrowest area).

My expectation is that because of the added exposure of its vertical faces, the frost-line in the berm will extend more that 48" below the surface but not down to the frost-line of the surrounding area (16'). Somewhere in between?

Thanks.

 

[LeoSC]

Generally frost depth is assumed to occur at the design frost depth, measured normal to the exposed areas. In this particular case, the soil in the berm would be expected to freeze 4' from the top and 4' from the sides. The soil under the berm itself would freeze 4' measured normal from the face of the berm.