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RE: Frost line issues

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Title: RE: Frost line issues

Correct, the new soil cover does act as insulation, and the frost penetration is measured from the new surface (including the sides of slopes)

Another consideration is whether or not the soil is susceptible to expansion due to frost. The mound of compacted fill should not contain fines, and will therefore be free draining.  If the soil below is also all granular, the need for depth  for frost protection  is minimal.  On the other hand, if the soil below contains significant clay or silt, then one wants to be sure that all bearing surfaces are below the freezing line.

I'm not terribly familiar with Mongolia, but in Northern Ontario, frost penetrations of 3 metres or more are not unknown.  If the depth of the new mound is less than the frost depth, the footings need to go into original soil.  The designer may also be trying to get below the root-affected zone of the original top soil.

> I am seeking advice regarding footings and the frost line.  I
> am aware that
> footings need to be founded below the design frost line.  If
> a tank for
> example is placed on a mound of compacted fill, is the frost
> line measured
> from the new ground surface local to the tank, or from the
> existing ground.
> I suspect from the new ground level, as the backfill
> insulates the existing
> ground.  I saw a strange sketch, which shows tank foundations
> being carried
> through the backfill and well into the existing ground, for a
> project being
> considered in Mongolia.
> Any comments regarding the frost line would be appreciated -
> here in Perth,
> Western Australia, it rarely falls below 5° outside!