Engineering-Geological Conditions of Construction in the Area of the Sovetskoye Oil Field
Abstract Generated abstract
This paper presents preliminary engineering geological results for the Sovetskoye oil field area in northern Tomsk Oblast, where planned industrial, civil, road, and pipeline construction required early assessment of difficult terrain. Using geological survey data, laboratory characterization of near surface deposits, groundwater observations, aerovisual and ground mapping, and interpretation of aerial photographs, the authors evaluate terrace sediments, soil heterogeneity, corrosivity, waterlogging, and bog types. The study finds that construction conditions are controlled chiefly by the properties of sands, sandy loams, loams, clays, and peat within the upper 10 to 15 m, together with shallow groundwater and widespread bogginess. It proposes an engineering geological zoning into uncomplicated, relatively uncomplicated, moderately complex, and difficult areas, intended to guide preliminary planning for pipelines and industrial or civil structures.
Full Text
Engineering-Geological Conditions of Construction in the Area of the Sovetskoye Oil Field
G. A. Sulakshina, V. A. Vaseneva, E. S. Tsotsur
(Presented by the scientific seminar of the Department of Hydrogeology and Engineering Geology and the Problem Geological Laboratory of TPI)
The discovery of oil and gas fields in the northern districts of Tomsk Oblast raised the problem of the economic development of these vast and hard-to-access territories.
The design of industrial and civil construction, pipelines, and roads requires an engineering-geological characterization of the territory. In order to obtain in advance engineering-geological materials that make it possible to resolve questions of general planning and preliminary design at the early stages of mass-construction projects, geological surveys in promising districts of the oblast are carried out with elements of engineering geology.
Preliminary results of such work, conducted in the area of the Sovetskoye oil field, show that the main factors determining the engineering-geological conditions for developing the territory are: the engineering-geological properties of rocks occurring within the sphere of influence of structures under mass development, i.e., within 10–15 m; the waterlogging and swampiness of the territory.
The area studied is located within the zone of development of three above-floodplain terraces of the Ob River. The geological section within the sphere of influence of structures is represented by modern and Upper Quaternary terrace deposits—an irregular interbedding chiefly of sands and sandy loams, with separate interlayers of clays and lenses of peat in the roof. The sands are fine-grained and silty (according to SNiP II-B 1-62), poorly sorted, predominantly non-suffosional, heterogeneous in moisture content and relatively homogeneous in density. The coefficient of heterogeneity \(K\), according to E. N. Kolomensky [3], for the degree of moisture of the sands of terrace II is 2; for the porosity coefficient, 0.85. The clayey varieties are diverse in consistency—from stiff to flowing-plastic (\(K = 2\)), and heterogeneous in plasticity indices (for the liquid limit \(K = 4.85\)). According to individual data, for soft and flowing-plastic loams of terrace II the cohesion is \(C = 0.28\text{–}0.3\ \mathrm{kg/cm^2}\), the angle of internal friction is \(16\text{–}19^\circ\), and the modulus of total deformation (compression) is \(E_{1-2} = 26\text{–}50\ \mathrm{kg/cm^2}\). Thus, the alluvial terrace deposits developed within the site belong to the category standardized by SNiP II-B 1-62 (Table 1).
The data presented on the heterogeneity of the rocks may be used in determining the scope of work for more detailed investigations.
The corrosivity of the rocks was studied for the territory of terrace II, which is the most promising from the standpoint of development. According to data of E. G. Rudchenko,
Table 1
Characteristics of the engineering-geological properties of rocks
| Geomorphological element | Combination of petrographic rocks according to SNiP I-B 1-62 | Rock | A | W | G | E | B | Wp | Corrosiveness of the rocks (according to polarization curves) |
|---|---|---|---|---|---|---|---|---|---|
| Floodplain | Sandy loams with peat, underlain by sands | Silty sands | 1.48 | — | — | 0.876 | — | — | — |
| Floodplain | Sandy loams with peat, underlain by sands | Sandy loams | 1.82 4 |
— | — | — | — | 17.9 8 |
— |
| Floodplain | Sandy loams with peat, underlain by sands | Loams | 1.8 6 |
— | — | 0.97 5 |
0.9 4 |
20.6 11 |
— |
| Floodplain | Sandy loams with peat, underlain by sands | Clays | 1.74 2 |
— | — | — | 0.64 2 |
23.5 5 |
— |
| I terrace | Sands with interlayers of sandy loams and peat | Sands | 1.69 13 |
13.4 59 |
— | — | — | — | — |
| II terrace | Sands and sandy loams (to 8.0 m), below which are loams and clays | Silty fine sands | 1.92 22 |
13.5 39 |
0.76 16 |
0.57 17 |
— | — | High |
| II terrace | Sands and sandy loams (to 8.0 m), below which are loams and clays | Sandy loams | 1.95 20 |
— | 0.78 20 |
— | — | — | Medium and high |
| II terrace | Sands and sandy loams (to 8.0 m), below which are loams and clays | Loams | 2.0 6 |
— | 0.92 4 |
0.72 5 |
0.63 19 |
18 21 |
Medium, high |
A — bulk weight, W — natural moisture content, G — degree of wetness, E — porosity coefficient, B — consistency index, Wp — plasticity limit.
$$ \frac{1.95}{20}=\frac{\text{mean value of the index}}{\text{number of determinations}} $$
According to M. K. Zubovoi and M. D. Myakotina, the corrosiveness of sandy loams and loams ranges from medium to high, and for sands it is high. Fluctuations in corrosive properties are possible in connection with fluctuations in the groundwater level and changes in the moisture content of the rocks.
The waterlogged character of the territory is marked by the predominance of areas where the first aquifer occurs at depths from 0.0 to 2.0 m and from 2.0 to 5.0 m, and by the presence of waters with general-acid and carbonic-acid aggressiveness.
The construction conditions of the territory are determined to a substantial degree by the development and character of the bogs. Aerovisual and ground observations, as well as
Fig. 1. Diagram of engineering-geological zoning of the area of the Sovetskoye field according to development conditions. Areas: 1 — uncomplicated (level surfaces of terraces I, II, III, with a sandy-loamy–sandy section, aquifer at a depth of 1–9 m); 2 — relatively uncomplicated (type I bogs); 3 — of moderate complexity (type II bogs); 4 — complex (type III bogs, flooded floodplain)
also the interpretation of aerial photographs (scale 1:15,000) made it possible to identify the types of bogs according to feeding conditions and the character of the microlandscapes, and on this basis to assess their trafficability and the conditions for carrying out work according to existing construction classifications (1, 2). The predominance of type I and II bogs with isolated patches of type III bogs has been established (Table 2).
A comprehensive analysis of data on rock composition, waterlogging, and bogginess made it possible to divide the studied territory into areas differing in the complexity of development in connection with the construction of pipelines and civil and industrial structures. Four categories of areas were distinguished:
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Uncomplicated—non-boggy areas of terraces I, II, and III with an even or slightly hilly and sparsely forested surface, composed of interbedded sands, sandy loams, and loams. The rocks are unevenly moist, of medium compressibility, standardized by SNiP II-B 1-62. The depth to the first aquifer is more than 1.0 m.
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Relatively uncomplicated areas—with the development of type I bogs, composed of undecomposed and slightly decomposed peat up to 1.0 m thick, with the aquifer at a depth of 0.5–3.0 m.
Table 2
Classification of bogs
| Geomorphological element | Types of bogs by moisture conditions | Types of bogs by prevailing microrelief | Width of bog, m | Peat thickness, m | Degree of decomposition | Depth to groundwater level, m | Composition of underlying rocks | Types of bogs by foundation conditions (1, 2) |
|---|---|---|---|---|---|---|---|---|
| Floodplain | lowland | main | 250–500 m | 0.5–1.0 | undecomposed | 0.5–2.5 | sands, loams | Possible: construction of embankments 1.5–3.0 m high; laying of pipelines; operation and passage of ordinary equipment with the aid of plank roads, sledges, and roads. |
| Floodplain | lowland | reed-sedge, reed | 500 m | 0.5–2.5 | well and weakly decomposed | 0.0–2.0 | sands, loams | Possible: work and passage of construction equipment only with the aid of mats and sledges; laying of various pipelines. Under the action of loads, the peat spreads. |
| I, II, III floodplain terraces | upland, lowland (small areas) | sphagnum–cottongrass; sphagnum; sedge: main; sphagnum–cottongrass | from 100 m to 3 km | 0.5–1.0 | undecomposed and weakly decomposed | 0.5–3.0 | sands, loams, clayey loams | Possible: construction of embankments 1.5–3.0 m high; laying of various pipelines; operation and passage of ordinary equipment with the aid of mats, sledges, roads; construction of light buildings when the bog is drained or the peat is removed. |
| I, II, III floodplain terraces | upland, lowland (small areas) | sphagnum–cottongrass; sphagnum; sphagnum–birch–cotton grass–sedge–sphagnum | from 300 m to 2 km | 0.5–2.7 | well decomposed, strongly decomposed | 0.0–0.3 | sands, loams | Possible: operation and passage of construction equipment with the aid of plank roads, sledges; laying of various pipelines; construction of light structures when the bog is drained or the peat is removed. |
| I, II, III floodplain terraces | upland, lowland (small areas) | ridge–hollow | 2 km | 1.0–6.0 | strongly decomposed, fluid, sometimes floating mats | water from the surface | loams, sometimes sands | Possible: operation of special equipment or ordinary equipment with floating means. |
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Sites of moderate complexity are Type II bogs, composed of well- and strongly decomposed peat with a thickness of 0.5–3.0 m, with a water table depth of 0.0–0.5 m.
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Difficult sites include Type III bogs with strongly decomposed, water-saturated peat 1–6 m thick and the surface of the floodplain, which is inundated during freshets.
The distribution of sites of varying complexity is illustrated by the scheme of engineering-geological zoning of the territory according to development conditions in connection with the construction of pipelines and civil and industrial structures (Fig. 1).
REFERENCES
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P. P. Borodavkin, V. D. Taran. Pipelines under Difficult Conditions. “Nedra,” Moscow, 1968.
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A. K. Dertsakyan, B. D. Makurov. Crossings of Trunk Pipelines across Bogs. “Nedra,” Leningrad, 1965.
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N. V. Kolomenskii. General Methodology of Engineering-Geological Investigations. “Nedra,” Moscow, 1968.