Permafrost

Effect of seismic events on the stability of buildings on
permafrost: a case study
V.P. Vlasov
(North-Eastern Permafrost Research Station, Melnikov Permafrost Institute SB RAS, Magadan, Russia)
Abstract: The paper discusses a special case of building failure in Susuman, the Magadan
Province, north-eastern Russia. The area is in the zone of continuous permafrost and high
seismic activity. Scientific and practical interest was caused by the fact that the building, which
was designed to accept thawing of frozen ground (Principle II in the Russian Building Code
2.02.04-88), had been stable for about 30 years and, then, suddenly began to experience
progressive damage threatening its integrity since the spring of 1998. It should be stressed that
the building had a substantial footing foundation of box type, i.e. with cross strapping by
reinforced concrete strips on the top and bottom.
Investigations found that the cause and specific development of distress were related to the
changes in permafrost conditions on the site after major flooding in 1995. Extensive
suprapermafrost taliks developed which were further enlarged by leaks from water and heat
lines. Resulting seepage flows caused the steady-state thaw bulbs beneath the buildings to
coalesce. This impaired the performance of the supporting soils and foundations. The sensitivity
threshold of the warming and saturated soils to seismic loads increased. At present, the majority
of the buildings that were in the flood zone show signs of settlement-related distortions typical
for dynamic impacts. Several earthquakes with magnitudes 3-4.5 occurred in the region after
the 1995 flood. The results of the macroseismic survey by the Geophysical Service of the
Russian Academy of Sciences indicate that the part of the town where the studied building is
located was often within the epicentral region of these earthquakes. In all these cases, local
residents reported that they heard booming and crackling sounds and felt shaking of the houses
with the walls cracking. According to the Geophysical Service data, the intensity of quakes was
one point higher in those parts of the town where the soils warmed by the flood became
hydraulically connected with the river.
The studied building suffered the greatest settlement and structural damage. Although the
cracks in the walls were repaired they used to appear again after next shocks with the cracks
progressively increasing in width. By the time of inspection in 2004, the building had a cross
crack from the foundation and its end tilted and settled significantly. This caused structural
responses and damages in other supporting members and walls due to excessive soil
deformations. The building was recognized to be in emergency requiring stabilization of the
weakened soils beneath the foundation over the entire depth of thawing. A grouting method was
offered.
Key words: permafrost, degradation of foundation soils, seismic impacts, building damage.
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