Temperature changes in soils cause fairly large volumetric deformations (contraction or expansion) and 'all-round' stresses (extension or compression); for example, as the temperature falls, the energy of the crystalline lattice grows owing to the lower intensity of thermal movement of its atoms and molecules and to corresponding reductions of the size of the lattice, which is manifested in a certain reduction of the coefficients of linear, a, or of volumetric, av, thermal expansion (Fig. 3.7a). Coefficients of thermal expansion are, apparently, higher in rocks and minerals with a lower energy of the crystalline lattice (Fig. 3.7b). Moreover, since quartz has a high value of coefficient a, then the greater the Si02 content in soils, the larger are their a values (Fig. 3.7c).

Temperature deformations of such a complex and multicomponent physico-chemical system as the ice-containing frozen soil are caused, on the one hand, by temperature deformations of the individual components of the soil (mineral skeleton, unfrozen water, ice) and, on the other hand, by volumetric deformations of frozen soils as a result of phase transitions of water in the range of negative temperatures and by development of such structure-forming processes as coagulation, aggregation and dispersion of

a 10 ,degr"
+1 0

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