At 11:40 AM 1/8/05 -0800, you wrote:
>on the matter of frost heave,
I'm enraged, . . . well maybe only mildly irritated . . . . :-)
>1. I am beginning to understand that what is called "frost heave", is
>the process whereby freezing soil at the surface of the ground can only
>expand UP as the water freezes.
Royce,
In a perfect world, where all soil is the same and frozen to the
same degree, frozen soil wants to expand in all directions equally and any
soil that is restrained, that is has no room to expand because other matter
occupies all adjacent space, will seek to displace something weaker than
itself (ie, with less resistance to displacement) in order to expand. (For
this discussion let's deal with only horizontal and vertical forces.)
The weight and frictional forces holding a fence post in the ground
are weaker than the force of frozen soil looking for expansion space.
Since the expansion acts equally in all directions the soil all around the
post will act with opposite but equal forces on each of the four sides so
the net horizontal movement, the displacement, will theoretically be Zero.
The top of the post has no force other than gravity acting upon it,
and if the bottom of the post is below the frost line, there are
theoretically no expansion forces working upward on that so again the net
theoretical displacement is zero. This is why fence posts don't float out
of the ground, they are basically in a state of equilibrium where the force
of gravity is equalled by the resistance of the soil below.
If, however, the bottom of the post is over freezing soil which, as
I said, is looking for matter to displace in order to expand, the forces
holding the post in the ground (gravity and soil friction) will be ovecome
by the force of frost expansion acting upward and it will displace (jack)
the post however much necessary to accomodate its expansion. That's frost
heave.
Regards,
Harry
