Fig. 8.3. Temperature dependence of longitudinal wave velocity vp: (a) - rocks of different composition: 1 - monolithic basalt; 2 - the same, cavernous; 3 - granite, monolithic; 4 - saturated sandstone; 5 - the same, dry (according to O.N. Voronkov, A. Timur); (b) - for soils of different composition: 1 - sand; 2 - silty-clay material; 3 - clay (according to F.F. Aptikayev).
cryogenic heaving, subsidence at thawing, thermokarst, thermal erosion,
Thermal-physical properties of rocks with transfer of thermal energy by conduction are evaluated by three basic characteristics: heat capacity, heat conduction and thermal diffusivity.
Heat capacity is the amount of heat required for a unit of mass or volume to change temperature by 1 °C. The following types of heat capacity are distinguished: specific heat C expressed in Jg"1 K"1, while heat capacity per unit volume Cvol = CP in J irT 3 K ~1. There is also a concept of effective heat capacity Cef taking into account latent heat of phase transition. Thermal conductivity (WnT1 K"') characterizes the capability to convey thermal energy and is equal quantitatively to the heat flow passing through unit of area in unit time, when the temperature gradient is one unit. Thermal diffusivity is expressed by the coefficient (a, m2 s~which serves as an index of temperature field inertia and is related to heat capacity and thermal conductivity by the ratio:
Thermal properties of earth materials are much dependent on composition, structure and state of the materials, i.e. on their genetic features and thermodynamic conditions of their particular setting. Table 8.2 gives data on thermal conductivity and heat capacity per unit volume of rocks, soils, water, ice, air and snow for general comparison and estimation. It should be
284 Composition, cryogenic structure and properties Table 8.2. Thermal properties of earth materials
Thermal conductivity y, Thermal capacity C, Description Wm^K"1 Jm~3K-1
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