Experience in Engineering-Geological Mapping of the Territory of Tomsk
Abstract Generated abstract
This paper presents an engineering-geological mapping and zoning study of Tomsk intended to support urban planning and reduce delays in site investigations. Using accumulated geological, hydrogeological, and engineering-geological data from construction surveys, together with observations of geomorphological and physicogeological processes, the authors characterize the city’s Tom River terraces by soil composition, groundwater conditions, bearing capacity, and hazards such as waterlogging, frost heave, ravine growth, and slope instability. The study identifies relief dissection, variable groundwater occurrence, heterogeneous bearing soils, and associated geological processes as the main factors controlling construction conditions. It proposes a threefold zoning of urban districts into areas requiring no engineering preparation, areas suitable only after drainage, grading, runoff control, or slope stabilization, and areas unsuitable for construction, providing a practical basis for municipal design and engineering-preparation work.
Full Text
Experience in Engineering-Geological Mapping of the Territory of Tomsk
G. A. Sulakshina, L. A. Rozhdestvenskaya
(Presented by the scientific seminar of the Department of Hydrogeology and Engineering Geology)
With the present scale of construction work, the timely and high-quality performance of engineering-geological investigations required for substantiating designs of structures is of especially great importance. In the appeal of the participants of the All-Union Conference of employees of design organizations to all engineers, architects, and design technicians, it is noted that one of the reasons for the lag in the development of district-planning projects is the untimely execution of survey work, including engineering-geological work. The solution of this problem, evidently, can be achieved by the advance compilation of engineering-geological maps for areas of proposed construction and, first of all, for the territories of large cities. This task can be solved especially simply because, in the territories of large cities and industrial centers, various engineering-geological works have been systematically carried out for many years at individual construction sites. The collection of materials from such investigations and their generalization in the form of a map of engineering-geological conditions for construction can serve as the basis for preparing planning projects and engineering preparation of urban territories.
Below is presented the experience of compiling engineering-geological maps for the territory of the city of Tomsk.
Over the course of several years, staff members of the Department of Hydrogeology, Engineering Geology, and General Geology of the Tomsk Polytechnic Institute, in cooperation with the regional administration for construction and architecture, carried out the collection of factual geological material in design and other organizations of the city, as well as observations of physicogeological phenomena developed on its territory.
A detailed study of the collected materials on the geology, hydrogeology, and engineering geology of the city showed that construction conditions in different districts of the urban territory differ sharply. This is clearly illustrated by the engineering-geological characterization of the city presented below.
In accordance with the basic principles of engineering-geological zoning, the engineering-geological characterization of Tomsk was based on geomorphological subdivision, proposed—
by B. V. Plotnikov (Fig. 1), according to which seven terraces of the Tom River, elongated in a northwestern direction, can be traced within the territory of the city of Tomsk. An analysis of the engineering-geological features of the territory with respect to the composition and properties of the soils and to physico-geological phenomena, carried out for the individual terraces, made it possible to outline the following features of six terraces.
I terrace
The general composite section of the loose strata of the first terrace, within the limits of the compressible stratum thickness of 10–15 m, is characterized by an alternation of the following varieties:
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Fill soil of extremely varied composition (loams or sandy loams with inclusions of plant remains, brick, gravel, gristle, etc.), with lenses of peaty deposits and horizons of buried soils. Thickness 1.5–8.0 m.
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Silty and humified loams, with lenses of silt and peat. Thickness 1.0–8.0 m.
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Light sandy loams with interbeds of sand and with inclusions of gravel, underlain by sand and gravel. Water-saturated; in boreholes they flow. Exposed to a depth of 10–15 m. At foundation embedment depths of 2.20 and 4.0 m, the bearing soils are fill soils and silty loams.
The physico-technical properties of the bearing soils have not been studied. This is one of the tasks requiring resolution in the near future. The physico-technical properties of the silty loams are characterized by high values of natural moisture content and porosity coefficient and by low allowable loads, on the order of 1.25–1.5 kg/cm² (Table).
The soils of the I terrace are strongly water-saturated. Groundwater and perched water occur close to the ground surface (0.5–3.0 m), causing waterlogging, ice formations, and frost heaving.
II terrace
In the general section of the soils of the loose strata of the II terrace, the following varieties are observed:
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Fill soil 2.0–5.0 m thick.
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Silty loams and sandy loams with interbeds and lenses of silt and peat.
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Heavy loams—thickness 0.5–4.0 m, with lenses of clays.
Exposed to a depth of 10.0 m. The bearing soils are predominantly fill soils and silty loams. The physico-technical properties of the soils (Table 1), water saturation, and physico-geological phenomena are analogous to those of the I terrace. The degree of study of the II terrace is uneven; its southern half has been studied much less than the northern.
III terrace
For the section of the III terrace, the development of the following soil varieties is characteristic:
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Fill soil up to 2.5 m thick.
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Light loams, replaced by heavy and light sandy loams, and in the southern part by sands. Thickness from 2.0 to 7.0 m.
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Heavy loams, in places macroporous and loess-like. Thickness 1.5–7.0 m.
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Light sandy loams, exposed to a depth of 10 m. The principal bearing soils on this terrace are loams and sandy loams. The characteristics of the physico-technical properties of these soils are summarized in the table. As can be seen from the table, the allowable loads on the bearing soils range on average between 2.0 and 2.5 kg/cm².
The depth of occurrence of groundwater and perched water is more than 3 m from the ground surface. The groundwater regime has not been studied. At the same time, knowledge of it is necessary, since, owing to the highly silty composition of the soils
Schematic geomorphological section
(along the right bank of the Tom River in the vicinity of the city of Tomsk).
Compiled by B. V. Plotnikov, 1957.
Vertical scale 1:500.
Labels in the figure: I terrace; II terrace; III terrace; IV terrace; V terrace; VI terrace; VII terrace; Tom River; development in the southern part of the city of Tomsk; Upper Logernyi Garden; m.
Fig. 1. Schematic geomorphological section (after B. V. Plotnikov, 1957).
Legend:
1 — sands; 2 — sandy loams; 3 — loams; 4 — clay; 5 — pebbles; 6 — Paleozoic clayey shales and sandstones; 7 — fill soil; 8 — silty clays; 9 — buried soils; 10 — modern terrace surface (not eroded); 11 — modern terrace surface (eroded); 12 — boundary of Tertiary deposits; 13 — Paleozoic surface.
Summary table of the physico-technical properties of soils by terraces of the city of Tomsk
| Terrace | Bearing soils | Number of investigated samples | Specific weight, g/cm³ | Unit weight (natural), g/cm³ | Unit weight of skeleton, g/cm³ | Porosity coefficient | Natural moisture | Cohesion, kg/cm² | Upper plasticity limit, % | Lower plasticity limit, % | Plasticity number | Filtration coefficient, m/day | Approximate permissible load, kg/cm² — from–to | Approximate permissible load, kg/cm² — average |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| I | Loams | 27 | 2.16–2.72 | 1.75–2.07 | 1.3–1.74 | 0.59–0.95 | 16.4–37.8 | 0.6–1.0 | 20.0–42.0 | 13.0–30.0 | 7–16 | — | 1.25–2.5 | 1.8 |
| I | Silty loams | 10 | 2.59–2.72 | 1.51–1.80 | 1.16–1.34 | 1.0–1.22 | 30.6–40.02 | 0.75–0.85 | 27–42.0 | 21.0–28.0 | 7.0–16.0 | — | 1.0 | 1.0 |
| II | Loams and silty loams | 8 | 2.62–2.67 | 1.54–2.0 | 1.06–1.59 | 0.67–1.50 | 23.0–49.1 | 0.8–1.0 | 32.0–49.0 | 18.0–28.0 | 14.0–20.0 | — | 1.0–1.8 | 1.5 |
| III | Light loams, locally macroporous | 8 | 2.64–2.72 | 1.64–1.93 | 1.40–1.59 | 0.71–0.90 | 11.9–21.6 | 0.38–0.82 | 19.0–27.0 | 12.0–17.0 | 7.0–12.0 | — | 1.5–2.5 | 2.0 |
| III | Light, heavy sandy loams, macroporous | 30 | 2.64–2.72 | 1.62–1.99 | 1.45–1.69 | 0.56–0.88 | 8.3–21.6 | 0.20–0.87 | 17.0–25.0 | 14.0–19.0 | 1.0–7.0 | — | 2.0–2.75 | 2.4 |
| IV | Silty sandy loams | 26 | 2.68–2.71 | 1.64–2.11 | 1.47–1.77 | 0.52–0.83 | 8.7–29.2 | 0.3–1.04 | 17.0–27.0 | 15.0–19.0 | 1.0–7.0 | — | 1.5–2.5 | 2.25 |
| IV | Light loams | 8 | 2.63–2.71 | 1.89–2.14 | 1.55–1.78 | 0.48–0.73 | 17.1–24.6 | 0.66–1.00 | 19.0–26.0 | 15.0–18.0 | 7.0–11.0 | — | 1.5–2.0 | 1.9 |
| V | Loess-like loams | 128 | 2.59–2.73 | 1.57–2.07 | 1.37–1.72 | 0.51–0.96 | 5.63–27.6 | 0.2–1.00 | 20.0–33.0 | 10.0–21.0 | 2.0–17.0 | 0.0; 0.7 | 1.5–2.5 | 1.9 |
| V | Loams | 80 | 2.59–2.74 | 1.67–2.10 | 1.31–1.73 | 0.49–0.98 | 11.4 | 0.30–1.0 | 20.0–37.0 | 11.0–22.0 | 7.0–15.0 | — | 1.25–3.0 | 2.7 |
| V | Macroporous sandy loams | 16 | 2.64–2.70 | 1.42–1.90 | 1.39–1.61 | 0.60–0.99 | 5.0–21.3 | 0.19–0.91 | 18.8–25.0 | 15.0–19.0 | 3.0–6.0 | 0.02 | 1.50–2.5 | 2.2 |
| V | Sandy loams | 38 | 2.63–2.72 | 1.65–2.10 | 1.52–1.81 | 0.47–0.79 | 5.0–29.8 | 0.15–1.0 | 13.8–25.1 | 15.22–19 | 01.0–7.0 | — | 2.0–3.0 | 2.6 |
one may expect that a rise in the groundwater level may lead to a decrease in the bearing capacity of the soils to less than 1.5 kg/cm².
IV terrace
The general section of the soils of the loose stratum of the IV terrace is represented by the following varieties:
- Fill soil up to 2.5 m thick.
- Light loams, locally silty, with peat lenses. Thickness from 0 to 3.0–4.0 m.
- Light, silty sandy loams, locally silty, with lenses of sands and light loams. Thickness from 2.3 to 8.5 m.
- Light loams, underlain by sandy-pebble deposits, exposed to a depth of 7–10 m.
The bearing soils at foundation depths of 2.5 and 4.0 m on the IV terrace are predominantly light, more rarely heavy silty sandy loams and light loams of the II and III horizons.
As is evident from the summary table, the permissible loads on the bearing soils average 2.0–2.5 kg/cm², decreasing sharply when they occur below the groundwater level.
The occurrence conditions of groundwater and perched water on the IV terrace are extremely unfavorable. Their depth of occurrence ranges from 0 to 10 m below the ground surface.
The highly silty composition of the soils, water saturation, and surface-runoff conditions contribute to the intensive growth of ravines, widely developed along the slopes of the IV terrace toward the valley of the Ushaika River. The high groundwater level here is also associated with aufeis, waterlogging, and frost heaving observed along the slope of the V terrace.
V terrace
The V terrace of the city has been studied most fully. According to data from numerous excavations carried out on the territory of the terrace, the summary section of the soils of the loose stratum of the terrace is as follows:
- A cover stratum of loess-like and macroporous, locally degraded soils. It is represented by light and heavy sandy loams and loams, in individual areas well preserving all the characteristic features of loess-like soils. Thickness 4.0–7.0 m.
- Sands and light sandy loams, replaced in the western part of the terrace by loams and clays. Thickness 3.0–6.0 m.
- Heavy loams and clays, exposed to a depth of 10.0 m.
The composition of the soils of the cover stratum at foundation depths is extremely variegated. In the part of the terrace located south of the Ushaika River, light loams with lenses of heavy, silty loams are predominantly developed.
North of the Ushaika River, loess-like soils predominate on the V terrace, and only in the very northern corner of the terrace, hypsometrically situated lower than the rest of the area, do the loess-like loams pinch out, being replaced by ordinary light loams.
The physical and technical properties of the bearing soils of the V terrace are characterized by highly variegated indicators. The permissible loads for bearing soils vary over very short distances within the range from 1.5 to 3.0 kg/cm². In evaluating individual construction sites, it is necessary to keep in mind the possibility of uneven settlements.
Groundwater within the V terrace occurs at depths greater than 10 m. No physical-geological phenomena are observed here.
VI terrace
The degree to which the VI terrace has been studied is very uneven. Its remnant, located in the southwestern part of the city, has been studied in considerable detail. For most of this territory of the city, detailed
the characterization of the engineering-geological conditions can be given without additional investigations.
The general composite section of the loose soils of the VI terrace is as follows:
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The cover stratum, represented by silty light and heavy loams and sandy loams with lenses of loess-like loams. Thickness 4.07 m.
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Heavy loams and clays. Thickness 1.5–2.0 m.
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Sand with gravel is encountered at a depth of 6.0–9.0 m. The bearing soils are the deposits of the cover stratum, which in composition and properties are analogous to the soils of the V terrace (table).
Groundwater on the gentle parts of the terrace occurs at a depth of more than 10 m.
The strongly silty composition of the loess-like soils, the emergence of groundwater on slopes, and the conditions of surface runoff contribute to the vigorous development of ravines.
From the brief engineering-geological characterization of the individual terraces given above, it is evident that the principal natural factors determining construction conditions in the city of Tomsk, in order of their significance, are:
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Strong dissection of the relief, associated with the presence within the urban territory of the terraces of the Tom River, the valley of the Ushaika River, and a well-developed ravine network.
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The capricious occurrence of groundwater and perched water, encountered at depths from 0.5 to 10 and more meters from the ground surface.
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The variegated composition and properties of the bearing soils, among which all varieties of loose soils are encountered: clays; silty, humified, light, heavy, macroporous non-subsiding and subsiding loams; sandy loams; and sands. The permissible loads of the bearing soils vary over wide limits—from 1.0 to 2.5 kg/cm²—changing sharply over very short distances.
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Diverse physico-geological phenomena associated with the peculiarities of soil composition and the conditions of their watering, which complicate the conditions of construction and operation of structures.
In accordance with the presence of one or another combination of natural factors in the territory of the city of Tomsk as a whole, the following three groups of districts, differing in construction conditions, may be distinguished:
a) districts not requiring engineering preparation;
b) districts suitable for construction but requiring engineering preparation;
c) districts unsuitable for construction.
The first group of districts, not requiring engineering preparation, includes the gentle sections of the high and low terraces with a groundwater depth of more than 3.0 m. Such sections almost do not require grading; the deep occurrence of groundwater eliminates the need for drainage works; physico-geological phenomena are absent.
Most of the loess-like soils distributed in these areas are non-subsiding. Subsiding varieties occur in small patches, are usually characterized by category I subsidence, and require only that the soils be protected from soaking and freezing during construction and that the rules for building operation be observed.
The second group of districts comprises areas requiring various kinds of engineering preparation.
These include:
- Gentle sections of the I and II terraces and non-flooded sections of the valley of the Ushaika River (the settlement of Cheremoshniki). The bearing soils at foundation depths of 2.5 and 4.0 m are represented mainly by silty
silty loams and clays with interbeds and lenses of silts and peat, whose bearing capacity is low, usually not exceeding 1.5 kg/cm². Groundwater and perched water in these areas occur high—at depths from the surface of up to 0.5 m and from 0.5 to 3.0 m.
The high groundwater level and moistening by surface waters are associated with waterlogging and frost heaving of roads. Moistening by groundwater from the slope of the III terrace in winter causes icing. For the normal development of industrial and civil construction in these areas it is necessary to:
a) lower the levels of groundwater and perched water;
b) intercept and divert underground flow at the base of the III terrace;
c) put surface runoff in order.
Implementation of the indicated measures will eliminate waterlogging, frost heaving, and icing. The bearing capacity of the soils will not change substantially, since the filtration capacity of the soils is very low.
- Flat areas of the IV terrace. The bearing soils at depths of 2.5 and 4.0 m are represented by water-saturated quick silty sands, whose bearing capacity on average is less than 1.5 kg/cm².
Groundwater and perched water are located at depths from the surface of up to 0.5 m and, in places, from 0.5 to 3.0 m, which, together with surface moistening from the slope of the V terrace, causes icing, frost heaving of roads, and waterlogging.
The necessary engineering preparation of this territory should consist of the following:
a) regulation of surface runoff;
b) underground horizontal drainage of groundwater and perched water.
These measures make it possible to eliminate waterlogging, icing, and frost heaving of roads, and also to raise the bearing capacity of soils from less than 1.5 kg/cm² on average to 2.0 kg/cm².
- Slopes of the III, IV, V, VI terraces with groundwater occurring at depths from the surface of up to 0.5 m and from 0.5 to 3.0 m. Groundwater outlets on the slopes contribute to the development of ravines (in places rapidly growing ones), sliding of slopes, and the formation of frost heave.
The measures determining the possibility of using this territory for construction are as follows:
a) grading of slopes;
b) lowering of groundwater levels;
c) strengthening and filling of ravines, afforestation and sodding of slopes, and construction of check dams.
As special measures to combat landslides in areas important for the city, it may be recommended to prohibit construction on areas where landslides develop, using them for forest plantings, gardens, and parks.
Lowering of groundwater levels may be accomplished by installing predominantly horizontal drainage and, in some cases, by using absorption wells.
- Slopes of the III, IV, V, VI terraces, composed of highly silty soils with groundwater occurring at depths greater than 3.0 m. The highly silty composition of the soils, the disordered runoff of surface and domestic waters, and groundwater outlets at the base of the slopes contribute in places to the catastrophically rapid growth of ravines, which put significant areas of useful territory out of operation.
Use of this territory for construction and park plantings requires the immediate implementation of the following measures—
measures: a) grading of slopes, b) regulation of the runoff of surface and utility waters, c) drainage of groundwater, d) stabilization of ravines; e) strict observance of the rules for carrying out construction work.
- Slopes of the III, IV, V, and VI terraces with a groundwater depth of more than 3.0 m, in places complicated by inactive ravines. The use of these areas for construction purposes presents no difficulties and is associated only with minor grading of slopes and the filling of ravines.
The third group of districts, unsuitable for construction, includes permanently and periodically flooded areas of the valley of the Ushaika River.
The presented scheme of engineering-geological zoning of the territory of the city of Tomsk, reflected on the engineering-geological zoning map, is used by municipal design organizations for preparing the engineering-preparation design for the city territory and for solving a number of specific engineering-geological problems (laying routes for sewers, tram lines, etc.) with a significantly reduced scope of work.