TM 5-852-4/AFM 88-19, Chap. 4
U. S. Army Corps of Engineers
Figure 7-1a. Permafrost and frost probing techniques (by CRREL).
(Probing to frozen ground.) of the Corps of Engineers (in
frozen zones the entire length of the casing should be
the early 1950's), in Greenland by the Arctic Construction
perforated. Since frost action can progressively lift the
and Frost Effects Laboratory (in the mid-1950's), in a
casing, heave prevention measures should be employed
number of North American locations by CRREL (in the
(chap 5).
44
16
b. In the fall the elevation of groundwater
late 60's) , in Scandinavia as reported by Gandahl ,
and in Canada by the Saskatchewan Dept.
of
begins to decrease as soon as the ground begins to
116
35
and the Division of Building Research,
Highways
freeze (fig. 2-4) . Water standing in an observation well
National Research Council of Canada. Advantages are
freezes at the top when the frost line reaches it.
simplicity, economy, and avoidance of electrical
Because the ice is frozen to the pipe it does not drop with
complexities. Potential disadvantages are (a) lack of
subsequent lowering of the water table. It has been
thermal correspondence of the sand in the tube with the
observed that after ice in such wells is cut through at a
surrounding soil, with resultant errors, (b) expansion of
later date, the water in the well drops below the level of
the inner tube and inability to withdraw it under certain
freezing as suction is released and thereafter remains
freezing conditions, and (c) lack of detailed thermal
unfrozen (provided the well is covered) unless the frost
gradient data.
line reaches the new depth. Consequently, adequate
time should be provided for equilibrium to develop once
the ice is cut and the suction released, before readings
7-6. Monitoring groundwater.
are accepted as valid.
a. Simple observation wells have generally
proven to be the most reliable method of monitoring
groundwater elevations. To prevent cutoff of water by
7-4
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