Poor Medium

Higher than 0.100-

usual 0.003

Catastrophic <0.003

0.3-0.1 Medium Laminated Rare and concent and netted big 25-50

0.1-0.3 Ice rich >50 Ditto Medium

0.03- Ditto Ditto Small and 0.01 fine

>0.01 Ditto Ataxitic predetermines the inevitable manifestation of thixotropic properties is a high content of silty and colloidal particles, enrichment of these with organic and organo-mineral compounds and high moisture (ice content) of mineral aggregates. The thixotropy of frozen soils on thawing promotes the washout and soaking processes.

Thermal expansion/contraction is a characteristic property of rock materials observed with changes of temperature and which is characterized by the coefficients of linear a and volume expansion /?, representing, respectively, relative linear and cubic deformations arising due to a temperature change of 1 °C. Their relationship is reflected by the ratio /? = 3a. Thermal expansion/contraction in frozen materials is a key factor in the development of such processes as frost cracking - and formation of ice wedges, weathering and the like. Thermal deformations of frozen soils come about due to temperature deformations of soil components (minerals, rock fragments, water, air, ice), phase transitions water:ice and structural transformations of the material with temperature changes. The linear expansion coefficient of the majority of minerals that compose rock, is within 2-12 x 10~6 °C_1. Within this same range are the coefficients of linear expansion of magmatic, metamorphic and sedimentary-cemented rocks. Ice has higher values of a, of the order 30-60 x 10"6 °C~\ depending on ice structure, angle of the crystal optical axis, temperature interval and the like. The a value of unfrozen water estimated from the density of supercooled water, is 187.5 x 10" 6 °C_1 within the temperature range of 0 to -20°C.

Frost resistance of rocks is defined as their capability to sustain without collapse multiple freezing alternating with thawing. In practice, this characteristic is indispensable for the engineering-geological evaluation of mag-matic, metamorphic and sedimentary-cemented rocks with rigid structural bonds. Frost resistance is estimated by the number of freeze-thaw cycles corresponding to reductions of strength. Usually, there are 25 cycles of tests, with specific studies requiring as many as 50 to 200. For construction purposes the number of freeze-thaw cycles (heating-cooling) resulting in 25% reduction of initial strength or 5% of mass is called the frost resistance point. Use is also made of the frost resistance coefficient Kire - the ratio of the frozen rock compressive strength limit to that of dry samples.

Rock strength diminishes under the influence of negative temperatures with participation of the different factors of temperature, hydration and cryohydration. The most important factor of the frozen rock degradation under the influence of alternate cooling-heating is the cryohydration mechanism which is associated with phase transition of water into ice. Frost resistance of rocks is also dependent on thermal-physical properties and strength of rock-forming minerals, cohesion between individual grains, the type of rock wetting, the structural-textural peculiarities of the rock, degree of alteration etc.

Electric properties

Frozen rocks and soils are imperfect dielectrics, i.e. materials that possess simultaneously the properties of both dielectric and conductor. Under the influence of an electromagnetic field in these materials a directed translational motion of charge carriers (current of conductance) arises which provides their electric conductivity, as well as oscillations of bound charges (current of displacement) which determines their polarization. The chief parameters of electric properties of earth materials, the frozen included, are: specific electric resistance (SER) p or the inverse value - specific electric conductivity a = 1 jp, dielectric constant s, coefficient of polarizabil-ity, r/ etc.

Specific electric resistance (Ohm m) is determined by the capacity of rocks and soils to conduct electric current, i.e. by their electric conductivity (7 = 1/p (Ohm-1 m-1). The chief current-conducting component of frozen, unfrozen, and thawed soils is the pore solution. Its electric conductivity has an ionic origin. The gas phase, monocrystals of ice and rock-forming minerals belong to dielectrics and are characterized by a high specific electrical resistance.

The main cause of reduced electrical conductivity of soils in the frozen a b p,Ohm m a

Was this article helpful?

0 0

Post a comment