TYPIFICATION OF THE ENGINEERING-GEOLOGICAL CONDITIONS OF THE ALEKSANDROVSKOYE OB REGION

E. S. Tsotsur

(Presented by the scientific seminar of the Department of Hydrogeology and Engineering Geology)

The principal task of engineering-geological investigations is the compilation of an informational engineering-geological model of an area. Such a model must contain, in analytical or synthetic form, all the data needed for solving problems connected with the siting of construction complexes and structures, with assessing the impact of engineering-geological measures on the natural environment, and with planning measures for its transformation. In contemporary practice, engineering-geological maps of conditions and zoning are used for this purpose, supplemented by engineering-geological sections, an explanatory note, and various tables.

The methodology for compiling engineering-geological zoning maps, developed in its basic theoretical principles by N. I. Nikolaev, F. P. Savarenskii (1939), and I. V. Popov (1951, 1969), is based on the successive division of the territory under study into areas possessing ever greater homogeneity in engineering-geological conditions. As a result, each territorial unit possesses continuity and a clearly expressed individuality. On the one hand, this is an advantage; on the other, it is the principal shortcoming of engineering-geological zoning. This shortcoming makes it impossible to extrapolate data to taxonomic units that are of the same type but territorially distinct. Most importantly, on the basis of such engineering-geological zoning it is impossible to develop regional NITU, SNiPs, and standard designs of structures as applied to various kinds of natural conditions. There arises a need for typification and classification of the identified territorially distinct taxonomic units. In this connection, one of the main problems of modern engineering geology is the study of regularities in the variation of engineering-geological conditions and their typification over the territory of our country.

The first step in solving this problem was I. S. Komarov’s (1966) proposal of typological engineering-geological zoning. Typological engineering-geological zoning represents the second stage after engineering-geological zoning according to the methodology of I. V. Popov, in which the typification and classification of the identified units are carried out according to the taxonomic scheme he proposed.

In the opinion of a number of scholars (G. S. Zolotarev, N. V. Kolomenskii, M. V. Churinov, V. D. Lomtadze, E. M. Sergeev, G. K. Bondarik, and others), the basis for typifying an area is the general classification of engineering-geological conditions, which must be based on the classification of individual factors of engineering-geological conditions. The currently existing classifications of factors of engineering-geological conditions contain a whole series of shortcomings, the chief of which is that they have different degrees of detail in subdividing the classified objects into taxonomic units, and therefore their comparison is difficult. Moreover, these classifications contain almost no quantitative assessment of factors. At present it is evident that qualitative subdivision does not characterize the differing significance of the classified objects for engineering purposes, but only indirectly and remotely reflects and evaluates the geological environment in a form that permits their consideration in the design of an engineering structure. Therefore, an important initial stage in studying the problem of typification is the analysis of the engineering-geological conditions of a territory with a quantitative assessment of their factors.

Engineering-geological conditions, as is known, are understood to mean the entire aggregate of natural geological conditions that determine the choice of the district and site for the location of structures, the conditions of their construction, stability, and operation, as well as other forms of economic use of the territory. An important factor of the engineering-geological conditions of the Aleksandrovskoye Ob region is the rocks, which predetermine the character of the relief, the development of physical-geological processes, waterlogging, and at the same time serve as the natural foundation for various structures, as the medium for them, or as construction material. In accordance with the taxonomic scheme of I. S. Komarov (1966), materials from small-scale geological and engineering-geological surveys of the territory of the Aleksandrovskoye Ob region made it possible to carry out a typification of engineering-geological conditions at the rank of districts.

To distinguish the types of engineering-geological conditions, the following criteria were adopted:

1) genesis of rocks;

2) character of the deposits in the vertical section, with a quantitative assessment of the regularities of variability in composition and properties;

3) character of the surface, with a quantitative assessment of the degree of dissection;

4) density of waterlogging of different genetic types of rocks, expressed by the ratio of the waterlogged area to the total area of distribution of the genetic type;

5) depth from the surface to the first aquifer, m.

In accordance with the proposed criteria, within the territory of the study area, with a total area of 30 thousand sq. km, six types of engineering-geological conditions have been distinguished, namely (Table 1): engineering-geological conditions of development of alluvial deposits of floodplains (1), first above-floodplain terraces (2), second above-floodplain terraces (3), combined second and third above-floodplain terraces (4), third above-floodplain terraces (5), and near-glacial deposits of the combined Shirta–Taz horizon (6).

Each of the distinguished types of engineering-geological conditions is characterized by a certain vertical type of section inherent only to it, by the degree of relief dissection, by the density of waterlogging, and by the depth from the surface to the first aquifer.

The proposed typification criteria may be used for studying and comparing the conditions of other districts of Tomsk Oblast and even of Western Siberia, which will help to develop NITU, SNiPs, and standard designs for each type of engineering-geological conditions.

REFERENCES

I. S. Komarov. Fundamentals of an integrated method for the engineering-geological study of plain territories covered by a mantle of Quaternary deposits. Author’s abstract of the dissertation submitted for the degree of Doctor of Geological and Mineralogical Sciences. Moscow, 1966.

I. V. Popov. Engineering Geology. Moscow State University, 1959.

I. V. Popov. Typology of elements of engineering-geological conditions as a basis for their quantitative assessment on maps. Vestnik MGU, 1969, No. 5.