Frost Shielding Protection of a
Water Line, Berlin, New Hampshire
BARRY A. COUTERMARSH
construction of the shield, methods used during
INTRODUCTION
construction to handle the 2- 8-ft (0.6- 2.4-m)
In areas that experience freezing temperatures
extruded polystyrene insulation boards that make
for any appreciable time, protecting water lines
up the shield, and the temperature sensor layout
from freezing is a major consideration in the de-
we used to monitor the shield's performance. The
sign and construction of water systems. The nor-
project will be used to assess the performance of
mal procedure is to bury the systems below the
both the FE program and the insulation shield
anticipated frost penetration depth. The presence
under in-situ conditions.
of ledge above this depth can greatly increase the
cost of burying the system. This is not only be-
Background
cause of the expense of blasting and removing the
This frost-shielding project was developed un-
rock but also because frost penetration is deeper
der the Corps of Engineers, Civil Works, Con-
in areas of ledge, requiring an even deeper pipe
struction Productivity Advancement Research
burial depth to protect against freezing.
(CPAR) program. Under the program, the City of
Frost shielding is the practice of protecting the
Berlin, New Hampshire, Water Works and U.C.
water line from freezing by adding extruded poly-
Industries, Inc., a manufacturer of extruded poly-
styrene insulation to retard the heat loss from the
styrene insulation, are partners with CRREL in
water within the line. It has the potential of re-
demonstrating the concept of insulating water
ducing the burial depth of the system from what
lines to protect them from freezing. The project
would normally be necessary. Balanced against
has essentially two components. The first is to
the increased cost of the extruded insulation is
develop a shield design using a CRREL-devel-
the decreased depth required for safe burial of
oped FE program. The second is to construct and
the pipe and thus savings in both the volume and
assess the performance of an in-situ shield based
cost of removed material.
upon the numerical design. More information
The major impediments to routinely insulating
about the finite element program is available in
lines are the lack of performance data and design
Coutermarsh and Phetteplace (1991a, 1991b).
guidance for the shield configuration and insula-
The practice of frost-shielding utility lines has
tion thickness. A finite element (FE) computer
been used most notably in Norway, where Per
program at CRREL can model two-dimensional
Gunderson has been instrumental in its develop-
frost penetration into the ground and describe
ment. He has developed nomographs to estimate
both numerically and visually the temperature
the shield configuration and thickness using cer-
regime expected in and around any potential
tain environmental parameters. The Norwegians
shield design. This FE program allows the de-
have also pioneered collocating sewer lines within
signer to model several different insulation con-
the same shield as water lines. The warmer sewer
figurations and perform "what-if" types of calcu-
lines supply heat to the shield, which helps to
lations against expected temperature conditions.
keep inside-shield temperatures above freezing
This report illustrates its use in the design of
(Gunderson 1975, 1989).
an insulation shield for an 8-in. (20-cm)-diam.
It was the success of Gunderson's work that
water line in Berlin, New Hampshire, in an area
encouraged us to further investigate the concept
where ledge is present to the surface. It details the
of frost shielding in this country. We felt, how-
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