When NGS ran their Gravity Slope Verification Study in Iowa (GSVS14) only a few deep rod monuments were placed.?ÿ Most were disks in poured concrete posts.
SET IN THE TOP OF A 1 FT (0.3 M) DIAMETER BY 4 FT (1.2 M) DEEP BELLOWED OUT CONCRETE MONUMENT
SURROUNDED BY A 2 FT (0.6 M) DIAMETER BY 0.5 FT (15 CM) DEEP CONCRETE COLLAR CONSTRUCTED
TO SUPPORT GRAVITY MEASURING EQUIPMENT.
They were put in during 2013 and measured in 2014.
My question is, could 4 winters since then of freezing under the shallow collar raise the height of the post?
On the few I have looked at, most show roughly circular cracks at the junction of the post and the collar, which seem to have been poured with no separation, but I haven't seen any large differences in height of the collar versus post.
If they belled the bottom of the pour, that should act against the upward thrust of the frost heave, theoretically.
How much, I'm not sure. We don't have any frost heave here.
Around here is a minimum of 18" deep to insure stability from freeze and thaw.
A Department of Commerce map shows a maximum 55 inches frost depth here, and local building code calls for minimum 42 inch depth for footings.?ÿ The 48 inch post depth would be pretty good.?ÿ I'm thinking about interplay of the belled bottom versus freezing lift under the collar and strength of the collar.
STABILITY: C = MAY HOLD, BUT OF TYPE COMMONLY SUBJECT TO SURFACE MOTION
Most GSVS marks were built to last only during the GSVS project.
They did set a steel rod stability B at regular intervals.