Permafrost

48
Thermal Stabilization of Soils in Permafrost Engineering
and the New Techniques for its Realization
Refik M. Bayasan 1 , Anatoly D. Lobanov 2 , Grigory P. Pustovoit 3*
(1.VNIIGAS Institute, Moscow 142717, Russia;2.Inter Heat Pipe Corp., Moscow 117463, Russia
3.Moscow State University, Faculty of Geology, Moscow 119899, Russia;E-mail: egc@geol.msu.ru)
Abstract: Two-phase heat pipes also called seasonal thermo-stabilizers (STS) are widely used
in construction. They are known to be the effective techniques providing stable support for
buildings and structures in cold regions. A STS transfers heat from its underground part
(evaporator) to the aboveground part (condenser) owing to natural temperature difference
between them during a cold season. Active deep cooling of soils results in great increase of
their strength, bearing capacity, resistance to thermal fluxes producing by engineering
structures, and it also protects foundations against frost heave. These well known features
characterize only one aspect of soils thermal stabilization.
The other (not so evident) aspect concerned with foundations reliability has probabilistic
origin. Random variations of natural factors (air temperature and snow cover at first) effect
soils temperature, bearing capacity and stability. Considering this problem in terms of
probabilistic approach and the theory of reliability we have shown that STS application sharply
decreases these negative effects and rises foundations reliability. It permits to decrease safety
factor and foundations cost. The paper presents the numerical results proving the importance of
soils thermal stabilization in this aspect.
We have been working out, manufacturing and applying different types of STS (since
1993). Some of them were presented in our paper for the 6th Symposium in Lanzhou (2004):
vertical thermo-stabilizers with minor diameter (28-54 mm) from steel (TMD-4) and aluminum
alloy (TMD-5); thermo-stabilizers with a flexible bond (crimped metal tube) between
evaporator and condenser (TSF); thermo-stabilizers with horizontal or slightly inclined (1-2
degrees to horizon) evaporators (TSI). The experience has shown that in many cases (e.g. for
engineering structures with high heat release) a soil cooling by those STS is not sufficient.
More powerful cooling units are needed to prevent negative cryological processes and provide
the stability of foundations. For this purpose we have developed new devices – TIP –
thermo-stabilizers with improved productivity (or with increased power). Their technical
parameters and test results are given in this paper, and their operation in the North of Western
Siberia and further applications are discussed. We mean new thermo-stabilizers TIP (as well as
previous STS types) would be useful for the new railway in Tibet.
Key words: permafrost, bases of structures, stability, reliability, thermo-stabilizers.