ever, that the nomographs were of limited use in
tremely costly procedure. Ledge excavation is rela-
conditions where several different soil materials
tively expensive because of the need to blast to
were present, the geometry of the pipeline was
break up the material for removal. The situation
nonstandard, or the ambient temperature profiles
is exacerbated because frost penetrates much
were erratic. With the advent of more powerful
deeper in ledge than it does in granular soils. This
personal computers, we felt that an FE program
results from two factors: first, the ledge has a
would offer the designer more flexibility in choos-
higher thermal conductivity than soil, and sec-
ing shield design based upon the conditions pres-
ond, because it has no moisture content, it has no
ent.
latent heat (the energy used when changing the
The city of Berlin, New Hampshire, situated in
phase of a material, e.g., changing water to ice). It
the White Mountain range of northern New
can be seen that an effective shielding method
Hampshire, has a population of about 12,000. The
that would allow a shallower burial depth than
town's geography is mountainous with large
would otherwise be necessary would have the
areas of shallow ledge throughout. The Berlin
potential to save a substantial amount of money
water department approached CRREL to see if
and resources. U.C. Industries, Inc. expressed an
we could offer any advice on the freezing prob-
interest in the concept of frost-shielding and be-
lems they were experiencing with their water dis-
came a partner with the water department to pro-
tribution system.
vide guidance and insulation for the project as
The water in the distribution system is from
well as to be the technology transfer point of con-
two sources: the Ammonoosuc Filter Plant and
tact to private industry.
the Androscoggin Treatment Plant. The Ammo-
This report describes the numerical design and
noosuc plant gets its water off the bottom of a
construction of a 20.3-cm (8-in.) shielded water
reservoir, and the Androscoggin plant is supplied
line in Berlin, New Hampshire. The ongoing
from the Androscoggin River. The Ammonoosuc
project will evaluate its performance and adjust
plant only filters and chlorinates the water, but
the design procedure accordingly as data are
the Androscoggin plant provides a full range of
evaluated.
treatment. During the winter, the water leaving
the Ammonoosuc plant tends to be roughly 2C
warmer than the water leaving the Androscoggin
NUMERICAL MODEL
plant.
The distribution system itself is old, with many
The physical dimensions of the pipeline and
of the lines made up of small galvanized 2-in. to
surrounding material are used to construct an FE
6-in. (5.1 to 15.2-cm)-diam. pipes. A large portion
mesh (Fig. 1). Only half of the physical configura-
of these pipes are buried in or on top of ledge,
tion needs to be modeled, since the other half will
tend to be very shallow, and are prone to freez-
be identical to the modeled half. A mesh is there-
ing. The frost penetration in this area of New
fore constructed that represents one side of a ver-
Hampshire can be 1.5 m (5 ft) or more. The prob-
0
lem is so acute that from January through March
the water users on lines prone to freezing are
asked to run their water continuously. They are
0.5
given an abatement on their water fees by being
billed on the average of the previous three months'
usage rather than on their actual usage during
1.0
the freezing period. This causes a situation where,
during the winter months, water is being run
through the system just to prevent freezing. The
1.5
cost of this water is in effect subsidized by all the
users. The excess water is discarded into the sewer
system, where it puts a greater load on the sewer
2.0
treatment system and therefore increases treat-
ment cost.
The city is in the process of upgrading its wa-
2.5
ter system to correct this situation. The presence
Figure 1. Example of a finite element mesh.
of shallow ledge, however, makes this an ex-
2
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