Permafrost

Geocryological Aspects of Unsuccessful Construction in a Mountainous
Area of the Permafrost Zone
V.P. Vlasov 1 , V.A. Basisty 1,2 I.V. Chegurova 2
(1.North-Eastern Permafrost Research Station, Melnikov Permafrost Institute SB RAS, Magadan, Russia;
2.NPP Gidrogeolog, Magadan, Russia)
Abstract: The paper presents the results of permafrost monitoring on the site of numerous
damages to buildings in the Dukat Silver Mine camp.
The site is typical for the mountainous areas of the Magadan Province, north-eastern
Russia, which is situated in the zone of transition from discontinuous to continuous permafrost.
It is characterized by extremely complicated geological and permafrost conditions. Tectonic
disruptions with faults and steeply dipping bedrock are responsible for the highly variable
thickness of soil deposits (5 to 30 m). The upper bedrock is heavily weathered and consists of
fissured tuff, andesite, siltstone and mudstone that have reduced strengths and are saturated with
water. The overlying coarse colluvial-alluvial and residual deposits are ice-poor to 3 m. Below
this depth, the deposits have high ice contents and their thawing results in settlement of 8-12
cm/m (up to 32 cm/m in some localities and horizons). Large suprapermafrost and open taliks
occur in the area. For such conditions, the active construction method, or Principle II in the
Russian Building Code 2.02.04-88, was selected and the superstructures were designed to
handle differential settlements. This approach however failed to ensure the stability of many of
the buildings. Greater damage occurred to the buildings located in the transition zone from the
unfrozen ground to thawing permafrost. These buildings had to be demolished because of the
danger of collapse. The unsatisfactory performance of the foundations resulted from inadequate
consideration for the permafrost and groundwater conditions on the construction sites with
complex topography where leveling was made by filling the lows. Filling does not provide, in
most cases, thermal protection to the permafrost between heat-generating buildings. Instead, it
promotes the formation of rapidly deepening and widening suprapermafrost taliks due to
infiltration of surface water and leakage from water and heat lines. Seepage flows in the talik
zones intensify thermokarst and lead to subsurface thermal erosion extending into the soils
below the existing buildings. The thaw bulbs under the buildings attain an unsteady state with
chaotic outlines. This causes dangerous unevenness of soil settlement and, consequently,
unacceptable foundation distortions.
Investigations confirm that the reliability of the “structural” method is highly limited.
Experience shows that it is virtually impossible to provide the stability of buildings on
permafrost only by increasing structural strength. For the given conditions, engineering
preparation of the foundation material involving pre-thaw of course soils would have been more
expedient.
Key words: Perennially frozen coarse soils, differential thaw settlement, building damage.
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