The intense pace of economic development of the territories within the permafrost region continues to increase steadily. Under the effect of different types of development all or some of the components of the natural environment, including the geocryological conditions, can change, resulting in transformations of the natural complex as a whole. 'The geological environment' is defined as an essential constituent of the natural environment. We address it in several aspects as far as various types of economic activity are concerned: 1) as the engineering-geological environment in which different structures are developed and operate; 2) as a source of mineral resources; 3) as the geological environment, the most important component of the natural complex as an animal and human habitat.
Engineering geocryology as a branch of geocryology studies the freezing ground of the Earth's crust as an environment for human life and activity. Among the main problems of engineering geocryology is the engineering-geological background for design, construction and operation of different engineering structures and undertakings within the permafrost region. The aim is to provide and select the most reliable and economic means of development of an area.
One of the main features of design, construction and operation of engineering structures within the permafrost regions is the necessity to take into account and to regulate heat exchange between the ground, the construction and the environment. Change of ground thermal and moisture conditions in the course of economic development especially in connection with the temperature going through 0°C, causes changes of ground composition, of structural properties as well as of strength, bearing capacity and compressibility, of heaving and shrinkage stresses and deformations in freezing and thawing ground, of workability within the permafrost zone as far as excava tion work and mining are concerned, of intensity of thermal erosion, icing, thermokarst, solifluction and other cryogenic processes and phenomena which can turn some terrains into badlands.
Observational data show that the mean annual increase of length of ravines developing in frozen ground reaches tens and even hundreds of metres and that hundreds of cubic metres of thawed soil are removed from one running metre of the northern sea coasts (the height of the shore cliff is about 10 m). Solifluction processes can cause creep of deposits on slopes over a distance of some tens of metres (when the viscous-flow strains in thawing soils take place). Settlements due to warming under constructions can reach tens of centimetres and more. Thermokarst processes lead to ground subsidence and to paludification of large areas. Change of the depth of seasonal freezing and thawing and consequent change of groundwater regime often cause activation of icing processes. Thus, for example, formation of 60 icings with a total area of 107 km2 was observed on one section of a road in Central Yakutiya during one winter season. And finally, activation of frost heaving processes appears not only in the uplift of the ground surface but also in the increase of differential heaving on the surface, as a result of technological change of ground temperature regime.
Thus there exist specific conditions for construction or for any other economic activity within the permafrost regions. Therefore attempts to apply the standard methods and techniques for construction usable outside the permafrost zone to the regions where frozen ground is widespread often lead to inadequate and sometimes even to catastrophic consequences and almost always to unnecessary labour, material and input of time. Thus P.D. Bondarev, A.I. Dementyev and other researchers inspecting buildings constructed within the permafrost region on frozen ground in the city of Vorkuta and in Vorkuta District found that about 80% of the buildings had unallowable deformations (Fig. 17.1). About 30% of all the stone buildings inspected had catastrophic deformations and needed overhaul. Among 1230 buildings inspected in Yakutsk, Chita, Vorkuta and the Buryat Republic around 63% turned out to have deformations (Fig. 17.1). About 30% of all the dwelling-houses on the Arctic coast are deformed. Losses through the overhaul and reconstruction of damaged buildings are as much as 10% of their total cost. The main reason for deformations are permafrost thaw settlement or ground heaving during freezing.
According to TsNIIS* data the extent of railway sections disturbed by heaving processes is about one third of the total extent of the deformed
*Tsentral'nyy Nauchno-Issledovatel'skiy Institut Transportnogo Stroitel'stva [Central Research Institute for Transport Construction]
sections. About 90% of all the resources allotted for repairing the railway bed are used for control of heaving processes. Highway and railway construction cause considerable icing formation. Thus the quantity of icings on some sections of the BAM railway has increased 50-70%. The cost of icing-prevention structures within the Tynda-Urgal section alone is as much as 5 million roubles .
Investigations show that an unjustified approach to the designing of a number of dams in the rivers of Magadanskaya Oblast' caused thawing in the foundations of the crests of the dams, formation of talik zones inside the dams and water permeating through them.
Analysis of reasons for a negative state of buildings and structures within the permafrost regions, show that from 15 to 30% of emergencies are associated with mistakes made in the preparation of the engineering-geo logical support for building sites, i.e. in the characterization of the geocryological conditions. A substantial percentage of deformations is associated with mistakes in design and with violation of operating conditions. Only the correct expert consideration of geocryological conditions of the territory and the justified selection of the design will make it possible to prevent unforeseen deformations of buildings and structures and to provide for their reliable operation. There are numerous examples of successful development of buildings and structures on permafrost. These buildings are supplied with central heating, hot water and have all modern conveniences. An example is Norilsk at 69° N in an area of extensive permafrost, and Mirnyy, a centre of the diamond mining industry, Vorkuta and many other cities are also good examples (Fig. 17.2).
Four types of economic development are usually recognized in engineering geocryology, characterized by specific effects on permafrost and the geocryological surroundings:
1) regional development of large areas within the permafrost zones connected with profound changes of natural conditions (construction of large water storages and hydroelectric water-power stations, destruction of extensive forests and forestation, drainage of swamps, etc.);
2) economic development of the permafrost regions through different types of construction (civil, industrial, highway, hydro-technical constructions, etc.);
3) development for the mining industry and of underground constructions in the permafrost regions;
4) agrobiological types of development (development and amelioration for the purposes of agriculture).
It is obvious that effective development is impossible without considering technological changes of the geocryological conditions, without special measures intended to control geocryological processes so as to prevent, to eliminate or to limit any dangerous consequences. In this connection it is necessary to carry out a complex of scientific work including: a) study of the existing geocryological situation of the area to be developed; b) study of the possible technological impact on the geocryological environment; c) forecasting of changes in the geocryological conditions associated with this impact; d) elaboration of measures aimed at environmental protection. All this scientific work listed above should be carried out before the period of active development of the region and the beginning of capital construction.
The main aim of the study of the existing geocryological situation is to
establish the main features of the distribution, formation and dynamics of seasonally frozen ground and permafrost and of the geocryological processes, to compile geocryological maps and to model natural geosystems for the purposes of geocryological forecasts. At the same time, in A.V. Kudryav-tsev's opinion, it is not sufficient only to note the existing geocryological situation when studying geocryological conditions but it is necessary also to find out the nature of its formation and development, to establish and to assess the role of the particular natural factors in formation of the temperature regime and other geocryological characteristics of the upper ground layers. Then, knowing the character of the natural complex as a whole during the proposed development of the area we can predict the possible change in geocryological conditions. The geocryological survey procedure is the best way to carry out this kind of scientific research (see Chapter 16).
Technological impact causes various changes in geocryological conditions such as increase or decrease of mean annual ground temperature, and of seasonal or perennial ground thawing or freezing. And it is necessary to work out the systematization (typifying) of technological impacts to establish the direction and extent of the effect of economic development on the permafrost conditions. Most of the proposed schemes for classifying technological impact are based on the assessment and separation of deliberate impacts from the spontaneous ones. Thus, for example, spontaneous climatic changes which can take place over large areas as a result of a number of ecological disturbances have assumed great importance for the harmonious exploitation and protection of the environment in the permafrost regions. The applied impacts are usually divided into mechanical, physical, chemical, biological and others according to their nature, with the first being specified loads, the others being specified impacts.
The consequences of technological loads and impacts depend on the duration and the size of the area where they occur. According to duration they can be continuous, as determined by the length of time the newly created technological landscape has existed in the designated state and regime or, for example, by the time of the operation of the construction; temporal-taking place for a number of years (for example, during the period of survey, preparation for construction and construction itself) and pulsed with a duration of not more than one season (for instance, a single modification of snow thickness and density, consolidation and deformation of moss-shrub cover, release of water on the surface, etc.). As a rule pulsed impacts do not cause changes of the permafrost as a whole but lead usually to a change of seasonal thawing depth. Temporal and especially continuous impacts can cause a change of ground heat state at greater depths even leading to the complete thawing of the permafrost.
The thickness of the technologically changed permafrost depends strictly on the size of the area affected. Now it is generally agreed that there exist point, linear and areal disturbances of natural landscapes during the development of an area.
A number of processes caused by technological loads and impacts are planned and regulated by engineering design. These processes include, for instance, processes of formation of 'thaw basins' under buildings and structures, with heat release and thaw settlements being permissible within certain limits by design. These processes are contrasted with newly appearing, unplanned weakly regulated ones. Among these processes are, for example, thawing of permafrost within building sites caused by blackening of the surface in the regions of coal mining. Attendant disturbances often represent secondary change following the initial disturbances (being an immediate result of engineering undertakings) as cause and effect. It has been suggested reversible, irreversible and destructive disturbances be dis-tinguised according to the character of the response of the geological environment.
The consequences of technological impact on the natural environment can be shown in a change of landscape-climatic conditions, geodynamic state of the topographic elements, geocryological surroundings, geophysical characteristics, engineering-geological, hydrogeological and other conditions. Depending on the type of economic activity the contribution of every above-enumerated impact will change.
Thus, for example, the consequences of hydro technical construction can show themselves in the change of geodynamic, hydrogeological and geothermic conditions and topography. Specifically, this is a redistribution of large water volumes on the Earth's surface, an elevation of groundwater level with paludification, water sedimentation, ground subsidence, abrasion and thermal abrasion and the formation of new talik zones in water storages and the beds of large water courses, together with the development of karst and thermokarst processes, slides, etc.
The consequences of mineral exploitation can take the form of changes of topography, and of the geodynamic, cryological, hydrogeological and engineering-geological features of an area. All mining causes depletion of mineral resources and a change of the geostatic field of the Earth as a result of the development of working cavities. Besides, underground mining is often connected with ground subsidence, followed in most cases by activation of thermokarst processes with formation of a new hydrological situation and depletion of groundwater resources, with topography transformations and rock waste heaps. Opencast mining is associated with topographic transformations, deep depressions and radical change of the hydrodynamic system, with weathering and breakup of outcropping rocks, slope slides, heaving of pit bottoms and slopes and suffusion. Placer mining is associated with changes of river valley topography, river bed alluvium and mud deposition, and decrease of discharge below the bed and, as a result, freezing of taliks below the river bed.
Ground-based construction (civil and industrial construction, linear construction) is mainly connected with changes of the geothermal, geochemical, hydrogeological, engineering-geological and geophysical environment. And under the influence of engineering construction the temperature as well as the ratio between volumes of frozen and unfrozen ground change, exogenetic geocryological processes (such as thermokarst, icing formation, heaving, solifluction, etc.) become more active, ground water regime changes, chemical water pollution and ground salinization take place and induced physical fields appear.
The character and intensity of technological impacts on permafrost associated with construction of foundations can be controlled. Undesirable consequences can be avoided if techniques for construction and the construction sites are selected adequately and if proper protective measures are applied.
Thus every type of construction or economic development of the terrain causes its own disturbances and technological loads, defining the strategy for engineering-geocryological research and for the particular forecasts. To make up a classification scheme for technological impacts on the environment it is necessary to study experience gained in the course of the development of other areas and to carry out special observations of regime using ground stations and repeated aerial photography.
The quantitative and qualitative characteristics of the change of permafrost conditions under the effect of different types of impact within different areas can be given or geocryological forecasts can be made after performing the geocryological investigations and knowing the character of technological impacts.
The principles and methods for rational use of the geocryological environment of the permafrost areas are selected and developed on the basis of geocryological investigations and geocryological forecast data. The following are the general principles:
- 'free use' without any limitations by geocryological surroundings;
- conservation of the natural heat state of the ground (frozen or unfrozen) using measures for limiting the change of ground temperature regime and the engineering-geocryological processes;
- allowing change of the natural state of the ground (perennial thawing, or more severe temperature regime and new formation of frozen ground) using measures for the control of the processes to avoid negative consequences.
The main ways of achieving these are associated with:
a) limitations on the area of development (a given type of development is allowed only within particular areas);
b) limitations on the construction technology;
c) control of permafrost processes to create the required engineering-geocryological situation;
d) abandonment of the development of a given area (method of prohibition).
Recommendations on the principles and methods of development of the permafrost regions, in accordance with rational siting of industrial installa tions and with technically and economically efficient designs for protection of the terrain, form the basis for the rational use of the permafrost geological environment.
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