Approach
Insulation to protect utility lines has been used
The project was divided into three phases. In
in an ad hoc manner throughout the world. The
the first phase, an insulated shield design was
practice was formalized most notably in Norway,
developed, through numerical modeling, for a
where Per Gunderson has been instrumental in
water line buried in ledge in Berlin, New Hamp-
this effort by developing nomographs that pro-
shire. Phase two consisted of constructing, moni-
vide guidance on shield designs. The Norwe-
toring, and evaluating the design developed in
gians have also collocated sewer, power, and do-
phase one. In this phase as well, a second design
mestic water lines within the shield, providing a
was developed, based upon the performance of
heat source that allows even shallower burial
the first shield, and installed at another test site in
depths (Gunderson 1975, 1989). Gunderson's
Berlin. Phase three is the technology transfer and
work encouraged CRREL to pursue the shielding
commercialization of the results.
research, with the added flexibility that the FE
program gives in determining shield configura-
Designing a shield
tions where soil parameters, climate, and pipe
A brief overview of designing a shield is pre-
designs can be varied.
sented below. Each step is looked at in more detail
The project ran from 1993 to 1997 with two
in the context of this study later in the report.
shielded 0.203-m (8-in.) pipelines constructed by
The general procedure used in designing a
the City of Berlin Water Works. The shields were
shield is first to decide the depth that is desired for
designed by CRREL, with engineering consulting
the pipe. This is frequently dictated by physical
and insulation provided by OwensCorning.
constraints present along the pipeline path, i.e.,
CRREL also monitored the temperatures in and
the presence of ledge or other obstructions, or by
around the shields and performed data reduc-
cost considerations. Then one must decide what
tions and comparisons. In addition to the shield-
type of shield configuration is feasible, based
ed designs, an unshielded pipeline was also mon-
upon the size of the pipe, available insulating ma-
itored as a baseline comparison. The first year's
terials, and site constraints. Here the constraints
shield design and installation are detailed in Cou-
may be the presence of other utilities nearby, diffi-
termarsh (1997), which provides details on the
cult digging conditions, or right-of-way consider-
construction and installation techniques used as
ations. In addition, since the shield design may
well as a first-year assessment of the shield tem-
allow insulation to be laid near the surface of the
peratures. This report reiterates some of the im-
roadway, the type and weight of traffic on the road
portant design and construction details, but the
may necessitate a loading calculation to ensure
reader is urged to refer to Coutermarsh (1997) for
axial loads are properly distributed so the bearing
a more detailed look. This report focuses on the
capacity of the insulation is not exceeded. Under
steps taken to design the shield and performance
some conditions, insulation beneath a roadway
comparisons between the design and actual in-
can cause differential icing on the surface. We
situ temperatures.
placed the insulation no closer than 0.508 m (20
in.) below the surface to minimize the effect of dif-
Objective
ferential icing on the roadway.
The objective of this project is to evaluate,
The physical configuration of the trial shield
through field studies and demonstrations, the
and pipe are then duplicated in the FE mesh, and a
effectiveness and design of insulation shields to
numerical simulation is performed in two steps.
prevent the freezing of water and sewer utility
First, the simulation is run with the influence of
lines buried in the frost penetration zone. Specific
the surface temperature and pipe temperature for
goals include
the climate where the pipe is located. This initial
Evaluating the effectiveness of a finite ele-
run sets the correct temperatures throughout the
ment heat transfer program developed to
mesh. In the final step, the water temperature is
assess various insulation and utility line con-
turned off at a time the designer chooses, which
figurations subjected to any given environ-
simulates turning the water flow off in the pipe.
mental conditions.
The simulation is then run to see if and when the
Evaluating the effectiveness of insulation
pipe temperature reaches 0C (32F). The results
shielding schemes.
of the simulation will indicate whether the design
Evaluating and developing guidance on
is adequate. If it is not, then adjustments are made
construction techniques for installing frost
to the shield, e.g., add more insulation, change the
shields.
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