slightly below the bottom of the pipe. The shield
conservative (i.e., somewhat colder than expected)
was 1.2 m (4 ft) wide and 0.76 m (2.5 ft) high and
boundary condition. The failure criterion used
was built up using 0.051-m- (2-in.-) thick, 1.22-
was that the pipe temperature was not to drop to
2.44-m (4- 8-ft) SSE boards of SP-Formular 250
0C. This criterion was later considered to be too
extruded polystyrene foam insulation. The trench
severe, and it was modified on the second design,
was blasted in ledge slightly wider than the
explained later. The design shown in Figure 4 gave
shield and was backfilled with sand.
results that met this criterion. More details on this
In these first design runs, the surface bound-
design can be found in Coutermarsh (1997).
ary condition was an equation regressed to the
coldest air temperatures that had been found in
2nd Avenue
66 years of records (Fig. 5). It was felt this gave a
In the summer of 1995, a thermocouple (TC)
Figure 4. Physical configuration of Labossiere Street pipe and shield.
Thermocouple locations are indicated by small squares.
20
15
10
5
0
5
10
15
0
7000
8000
9000
1000
2000
3000
4000
5000
6000
Time (hours)
Figure 5. Average daily coldest temperatures regressed to sine
curve and used as design surface temperature during shield design
FE runs.
5
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