Some aspects on applied geomorphology in periglacial regions
223
9 "
ARCTIC CASE .....
INTERIOR CASE.
-P"
Horizontal distance from centre line (metres)
12
10
8
6
4
2
0
2
4
6
8
10
12
(September)
"~" .....
---z, "('S~3~e;nb'e;;
FROZEN
.-.
4.4
10
t ~.
14
16
Depth (metres)
Figure 9.12. Theoretical growth of a thaw cylinder around a heated pipe installed in silty ground. The
pipe is 1.21 m in diameter, is located at a depth of 2.42 m and maintains a temperature of 80~ The curves
to the left correspond to conditions similar to those of the arctic coast of Alaska, whereas the curves to the
fight correspond to conditions close to those at the southern limit of the permafrost (Lachenbruch, 1970, in
Cooke and Doornkamp (1974), Figure 9.8).
As a consequence of these difficulties, in permafrost zones, the pipeline was built
suspended on a structure with pillars that penetrated in the ground from 8 to 20 m in depth
(Harris, 1986). In some stretches these pillars are provided with a refrigeration system to
avoid the thawing of the permafrost. The pipe was buffed in permafrost-free zones and in
areas devoid of potential problems (well-drained sand and gravelly areas). Similar
problems are found in the construction of gas pipelines. When possible these are usually
buffed to reduce the explosion hazard and to help the temperature of the pipe raise the
resistance of the steel to the gas pressures (Harris, 1986).
4. 4. Mining
In arctic areas, where mineral resources are abundant, some classical mining practices
have been modified due to the peculiar conditions that the permafrost imposes. The main