Geology Reference
In-Depth Information
Figure 14.4.
Construction of apartment block complexes in Yakutsk, Siberia, use concrete pile
foundations. Photograph was taken in July 1973. Many of these buildings are now predicted to fail
by 2030 (see Chapter 15).
permafrost, the end-bearing capacity of piles in ice-rich permafrost is sometimes enhanced
by the use of enlarged base (“belled”) piles (Sego and Biggar, 2000). In coastal communi-
ties and elsewhere where permafrost can be saline, additional problems are encountered
in pile usage because the adfreezing strength is accordingly reduced (Brouchkov,
2003).
Other techniques used to preserve the thermal regime of the permafrost include the
insertion of open-ended culverts into the gravel pad, the placing of insulating matting
immediately beneath both the building and the gravel pad, and, if the structure justifi es
it, the insertion of costly refrigeration units or “Cryo-Anchors” (Hayley, 1982).
Passive cooling is increasingly being incorporated into the foundation design of large
structures and into the stability of waste rock-debris piles. This technique maintains
permafrost by taking advantage of seasonal convection in high-permeability embank-
ments and pads (Goering, 1998, 2000, 2003). For example, Figure 14.5A shows a typical
roadway application where the embankment is built of a highly porous rock layer with
high pore-air permeability. The arrows indicate the pattern of winter pore-air circulation
that might occur. Because the surface would be capped with an impermeable asphalt
layer, internal convection occurs beneath the center of the road. The net result is a
decrease in mean soil temperatures and an upward movement of the permafrost table.
The technique is especially applicable to road, rail, or airport embankments located in
regions of warm permafrost. The same technique can also be applied to hazardous
containment dykes such as around oil-storage facilities and to maintaining the stability
of rock waste material discarded from opencast mining operations (Figure 14.5B).
Another application is its use in maintaining the stability of earthen dams constructed
to contain mine tailings. For example, at the BHP Ekati Diamond Mine at Lac de Gras,
NWT, Canada, the installation of “thermosyphons” (Figure 14.6A, B) permits the trans-
fer of heat between the atmosphere and the central core of the tailing dam, thereby
maintaining it in a frozen state. As a result, the earthen dam is both impermeable to
seepage through the dam and resistant to thaw effects from unfrozen lake water on the
upstream side.
