[CPEO-MEF] Frost Jacking of Unexploded Ordnance

[Lenny Siegel <lsiegel@cpeo.org>]

[The following article is taken from the Spring 2005 edition of the Army
Environmental Center's newsletter, Fielding Environmental Solutions.
This research is important anywhere the ground freezes, and it should be
considered in remedial decisions at munitions response sites in such
areas. - LS]

Field Tests of Frost Jacking of Unexploded Ordnance 

The U.S. Army Cold Regions Research and Engineering Laboratory (CRREL)
with congressional funding received through the National Defense Center
for Environmental Excellence (NDCEE) and in coordination with the U.S.
Army Environmental Center has completed a study analyzing the extent of
frost jacking (net seasonal upward movement) of buried unexploded
ordnance (UXO) in cold regions where there is frost-susceptible soil and
adequate moisture.  Frost heave (uplift of ground associated with
freezing) occurs when there is frost-susceptible soil, freezing
temperatures, and adequate water supply. Objects in the soil move upward
when the soil heaves. When the frozen soil thaws, the soil often
subsides more than the object, and there is a net upward movement of the
object in the soil.  

In September 2003, eighteen inert ordnance shapes were buried in highly
frost-susceptible soil in Hanover, NH, to determine whether they would
experience frost jacking. The site was monitored through the following
winter and spring. Based on field tests during the winter and spring of
2003-2004 the study concludes that frost jacking of ordnance occurs in
regions of seasonal freezing when the ordnance is buried in
frost-susceptible soil. The ordnance moves upward at approximately the
same rate at which the ground heaves; however, during thaw, the ground
subsides to a greater degree than the ordnance. The larger
ordnance-2.75-inch rockets and 81-mm mortars-buried 24 and 36 inches
deep, moved upward at an average of about 1.5 inches-about four times
the distance as the smaller ordnance (20- and 40-mm projectiles). At
this rate, upward movement of UXO could become a concern within a
relatively short period of time after certified clearance. The largest
ordnance buried, a 155-mm mortar, did not heave-this is most likely due
to its weight counteracting upward forces generated by frost heave.  

Frost jacking may be an important factor in certifying the required
depth of UXO clearance that may affect UXO discrimination and detection
technology requirements. This is important because range areas that have
been cleared to a certain depth may no longer be safe after a period of
time elapses that is sufficient for frost jacking to cause UXO to move
up to a depth where it poses a threat.  

For more information on the frost jacking report contact the U.S. Army
Environmental Center's Technology Hotline at
T2Hotline@aec.apgea.army.mil.  

***

For more information about Fielding Environmental Solutions, see
http://aec.army.mil/usaec/technology/fes00.html.

-- 


Lenny Siegel
Director, Center for Public Environmental Oversight
c/o PSC, 278-A Hope St., Mountain View, CA 94041
Voice: 650/961-8918 or 650/969-1545
Fax: 650/961-8918
<lsiegel@cpeo.org>
http://www.cpeo.org
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