Structural associations and types of contact in frozen soils

During freezing of soils and in the frozen state, specific types of contacts and structural associations appear as a result of complicated processes of formation of structure. In hard rocks and in some cemented sedimentary rocks, the chemical relations dominate, whereas in fine-grained soils with high ice content the relations between the separate elements are more often molecular and ion-electrostatic, often called water-colloidal relations.

The formation of structural associations in such multiphase and multi-component dispersed systems as frozen soils always occurs not only between mineral surfaces, but between the surfaces of ice and mineral particles. Moreover, structural associations usually appear not on all the surfaces of elements composing the soil but only in places where they approach, i.e. at contacts. The number and character (nature) of various individual contacts have a certain influence on microstructure and properties of frozen soils. Every type and variety of contact is specified by its mechanism of formation and the nature of interrelating forces and by the geometry and size of contact.

At a first approximation, the whole variety of contacts in soils under negative temperature and with ice inclusions can be divided into point, area and volumetric and their primary feature is the area of contact interaction between organic/mineral particles and ice, and the other contact characteristics are aggregation (distant coagulative), coagulation (close coagulative) and dry (waterless) contacts, which differ in the energy of interaction and the distance between the contacting ice and ground particles (Fig. 4.13). The point contacts are the most common in clastic and sandy soils; the area contacts apply to clay-rich soils, whereas volumetric are typical of supersaturated soils with high ice content, when organic/mineral particles practically 'swim' in the ice, i.e. are entirely surrounded by ice.

The sub-dividing of contacts according to the energy of their interaction largely depends on the distance between the interacting soil particles. For example, when two soil particles directly interact they constitute the most dry and strong (without water or phase) contacts. They have valent and ion-electrostatic interaction and directly bring together the elements of frozen soil; they are divided into types of contacts: dry mineral (mineralmineral), dry mineral-cement (mineral-cementing matter), and dry mineral-

The dry mineral contacts normally appear during diagenetic transformation of soils as a result of an increase of pressure with depth and loss of moisture of clay-rich sediments. 'Cold fusion' of minerals by chemical forces can be another possible way of forming these contacts between mineral particles when the soil freezes in a 'closed' system.

The mineral-cement contacts are formed in the process of recrystalliz-

By extent of contact

By energy of interaction and nature of contacts

Aggregational (long-range coagulation)

Coagulational (short range coagulation)

Dry (dehydrated)

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