Permafrost

due to its effect on hydraulic conductivity. Without a sufficient supply rate of water, growing
microcracks tend to become engulfed by the freezing front before the increasing internal
pressure can cause further fracture. This behavior is generally analogous to the conditions
necessary for ice lens formation in soils and particle trapping at an advancing solidification
front.
We have also conducted laboratory experiments by simulating the thermal regime
associated with (a) one-sided freezing in non-permafrost regions and (b) two-sided freezing of
an active-layer above permafrost. Crack development, rock surface heave, temperature and
pore pressure have been monitored in 10 blocks of siliceous chalk 45 cm high during the course
of more than 20 freeze-thaw cycles. The location of cracking varies according to the rock
thermal regime and generally agrees with the numerical model predictions. With two-sided
freezing of the active layer, cracking commenced at a depth determined by the permafrost table,
and significant ice segregation occurred during thaw cycles. By contrast, in seasonally frozen
rock (1-sided freezing), the location of cracking was more variable and closer to the rock
surface. We are now applying the same laboratory techniques to cylinders of cement and
concrete. By preparing the samples using different frost-prevention techniques such as air
entrainment, we will better understand the environmental conditions that can lead to concrete
foundation fracture and eventual failure.
Keywords: Frost heave, ice segregation, concrete, modeling, fracture.
50
Permafrost Thaw Settlement and Embankment Stability
Ruijie Chen, Wei Ma
(1.Geo-Environmental Engineering, SNC-Lavalin Engineers & Constructors, Toronto, Ontario M
2.State Key Laboratory of Frozen Soil Engineering, CAREERI, CAS, Lanzhou Gansu 730000, China)
Abstract: Permafrost degradation resulting from climatic warming or regional warming has
been observed in areas from Arctic to Qingzang plateau, and from cold to warm permafrost in
the past decades. One of the main consequences of permafrost degradation is thaw settlement
which can be significant for ice-rich permafrost. Permafrost thaw settlement is one of the
most important considerations in design, operation and maintenance of buildings, embankments
and other infrastructures in permafrost areas. Permafrost thaw settlement was discussed in this
paper in terms of thaw settlement susceptibility, settlement estimation, porewater pressure
variation and thawed soil effective strength, with respect to permafrost geotechnical and
hydrogeological properties.
Stability of embankment subject to thaw settlement was assessed in a few different
scenarios. Settlement occurs along with thawing under a free drain condition. In this
condition, embankment instability generally attributes to uneven settlements. For fine-grained
low permeability soils or under a condition with drainage problems, excess pore water pressure
can accumulate in the thawing layer to form a low shear strength soft layer, which can result in
sliding failure of the embankment. Measures to ensure a well-drained condition in the
thawing process to prevent formation of such soft soil layer and for slope supporting were