ENGINEERING-GEOLOGICAL CLASSIFICATION OF THE UPPER AND MIDDLE QUATERNARY ROCKS OF TOMSK

L. A. ROZHDESTVENSKAYA

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

The rapid pace of industrial and civil construction, the introduction of new structures and industrial methods, and the introduction into the practice of foundation design of calculation methods based on limiting states create the need for broad engineering-geological investigations and, first of all, for generalizing the available engineering-geological material and construction practice on various genetic types of rocks. In the Construction Norms and Rules [1] issued in 1962, a table of standard and calculated soil characteristics is given, which the authors recommend using for approximate calculations of foundations, while at the same time pointing to the need to refine the cited characteristics in accordance with the local features of the rocks of a given region. In separate works (2, 3, 4), already during the discussion of the 1962 draft SNiP, statements were made about the need to create regional standards in addition to the existing all-Union ones. Construction practice in Tomsk confirms these statements—the soil characteristics given in SNiP cannot be used in designing structures under local conditions. To obtain these characteristics for the Tomsk region, the conditions of occurrence, granulometric, mineralogical, and chemical composition of the rocks and their physical-mechanical properties were analyzed. In doing so, use was made of engineering-geological investigation materials collected in past years, natural exposures (Lagerny Sad, Kashtak, Sinii Utes, exposures along ravines), and boreholes drilled specially for this purpose (III and IV). The data obtained made it possible to compile an engineering-geological representation of the territory of Tomsk (Table 2).

In the Tomsk area, Quaternary rocks, including loessial rocks, are widely distributed; they are represented mainly by loams, sandy loams, sands, and clays of various genesis. They compose terraces of the Tom and Ushaika rivers of different ages and, in part, the western slope of the lake-alluvial plain of the Tom–Yaya watershed. The age of these rocks has been determined in accordance with the available stratigraphic schemes [5, 6, 11] and the results of the investigations carried out.

Thus, as the terrace scheme shows (Fig. 1), by morphological features two low floodplain terraces of the Tom River of Upper Pleistocene age \((Q_3)\) are distinguished quite clearly: the first, 8–12 m high, and the second, 20–25 m high, as well as a complex of high terraces. The low terraces, as will be shown below, are rather clearly separated

Table 1

Continuation of Table 1

in composition and properties of the rocks. The high terraces—the third, 40–50 m high, and the fourth, 60–80 m high—are separated to a certain extent conventionally: they are weakly expressed in the relief and, as will be shown below, are similar in the general section of the terraces and in the composition of the rocks. In terms of height, on the basis of the unified scheme [5], both terraces may be assigned to the Middle Pleistocene \((Q_2)\). In analyzing the deposits of the high terraces, two types of rocks are clearly distinguished (Fig. 1): the upper type—mantling loess-like rocks, and the lower type—the terrace deposits proper. In the mantling rocks, in turn, two horizons are distinguished, differing in age and genesis: the upper one—the superimposed terrace of the Tom River, of Upper Pleistocene age \((Q_3)\), and the lower one, of Middle–Upper Pleistocene age \((Q_{2-3})\), represented by deposits of lacustrine–bog facies [9], also widely developed within the Tom–Yaya interfluve (the lower loess horizon [7]). Among the mantling loess-like rocks of the Tom–Yaya interfluve, rocks of the upper loess horizon \((Q_3)\) of problematic genesis are also widespread.

Below are given the composition and conditions of occurrence of the listed genetic types of deposits.

Alluvial deposits of the terraces of the Tom River

The first terrace \((Q_3)\) is developed in the northern part of the city and partly in the southern part, extending as a narrow belt along the Tom River.

The general section of the terrace is represented by the following horizons:

1. Dark-gray and gray heavy loams and clays with thin interbeds of light loams and sand. In the marginal part of the terrace these correspond to fill soils and humified loams, locally peats—the floodplain facies. Thickness 5.0–7.0 m.

2. Sand or sandy loam of greenish-gray color, fine-grained, silty. This bed sometimes passes gradually into gravel–pebble deposits of siliceous composition, or the boundary between them may be sharp (channel facies). In the first case the thickness of these rocks reaches 8–10 m; in the second, up to several centimeters. The basement of the terrace consists of dense Tertiary clays and sands.

According to grain-size composition, on the basis of data from 60 analyses, the loams belong predominantly to heavy silty varieties. The silt content ranges from 55.0 to 70%; sand, 5–20%; clay, 18–35%.

The mineralogical composition is given in Table 1. As this table shows, the dominant minerals in the heavy fraction are ore minerals, epidote, zoisite, and green hornblende. The content of ore minerals decreases markedly downward through the section; epidote and zoisite remain almost constant; green hornblende increases sharply from 9.0 to 24.6%. The light fraction is represented by quartz and feldspars. The finely dispersed fraction, determined by staining methods, thermal analysis, and electron microscopy, consists mainly of hydromica with an admixture of chlorite and organic matter, with inclusions of individual kaolinite grains.

The reaction of the medium of the rocks considered is neutral or slightly acid \((\mathrm{pH}=7.0–6.5)\). The absorption capacity is from 25.6 to 10.9 mg-eq per 100 g of dry rock.

The second terrace \((Q_3)\) is widespread in the southern part of the city. The university and the post office are located on it. In lithological composition it differs sharply from the first terrace. The composite section of the terrace is as follows:

Schematic of the terraces of the Tom River
(in the vicinity of the city of Tomsk)

Vertical scale: \(m\)
River label: r. Tom

Legend:

• \(Q_3^{III}\) — Deposits of the third above-floodplain terrace
• \(Q_3^{II}\) — Deposits of the second above-floodplain terrace
• \(Q_2^{III}\) — Deposits of the third above-floodplain terrace
• \(Q_2^{IV}\) — Deposits of the fourth above-floodplain terrace
• \(Q_3^{I}\) — Deposits of the floodplain terrace
• \(Q_3\) — Deposits of the Upper [[unclear: horizon name]] horizon of the Vasyugan Formation
• \(Q_{2,1}\) — Deposits of the [[unclear: horizon name]] horizon
• \(T_2\) — Tertiary deposits
• \(P_2\) — Paleozoic deposits
• \(D_2\) — Devonian deposits of the Mirskoy terraces / scarps [[unclear]]

1. Dark-brown and brown loams with interbeds of sands. Laterally they are replaced by fill soils. Their thickness is from 0.5 to 4.0 m. In the marginal part of the terrace, interbeds and lenses of peat up to 3.0 m thick occur.

2. Interbedding of sandy loams, often quicksand-bearing, and fine-grained sands of gray and bluish-gray color. Thickness—up to 12–19 m.

3. Coarse-, medium-, and mixed-grained sand with gravel and pebbles, 3 to 7 meters thick. The basement consists of Paleozoic clay shales.

In granulometric composition the loams contain: clay fraction 10–20%, silt fraction 30–45%, sand fraction 30–50%. The sandy loams are fine-grained, with a clay content from 5 to 10%, silt—from 12 to 45%, sand—from 50 to 80%.

The mineralogical and chemical composition of the terrace has not been studied.

The deposits of the high terraces (III and IV)—($Q_2$) are distributed both in the southern and in the northern part of the city. The third terrace is the customary name for the territory of Mount Kashtak (10, 11, etc.). The fourth terrace includes the area of the Tomsk-I station in the southern part of the city. In the north it is developed in the area of the Tomsk-II station, whence it extends as a broad belt to the northeast. In the west it joins the third terrace.

The complex of deposits of both the III and IV terraces, with a total thickness from 15 to 35.0 m, is represented by sandy loams with interbeds of loams and sands, among which interbeds of bluish-gray clays occur. At the base of the terrace deposits, almost everywhere, lie sandy-pebbly rocks composed of mixed-grained sand and pebbles of quartz and flint up to 1.0 cm in size.

In mineralogical and chemical composition the deposits of the high terraces are similar to one another. In the clay fraction of both terraces, along with hydromicas, an admixture of kaolinite, calcite, and organic matter is noted (Table 1).

Comparison of the composition of the high terraces with the low ones makes it possible to note their complete similarity in the mineralogical composition of the light and heavy fractions, both qualitatively and quantitatively. As is evident from Table 1, the essential difference between them consists in the content of the clay fraction, among the minerals of which there is no kaolinite in the deposits of the first terrace. In addition, the rocks of the first terrace are characterized by a higher absorption capacity.

Cover deposits

The superimposed terrace ($Q_3$) is represented by a complex of typically alluvial rocks lying on the eroded surface of the deposits underlying them. This is clearly visible in the outcrop of the Camp Garden and in sections compiled from mine workings in the territory of the city of Tomsk [7]. The general section and lithological composition of the terrace are fairly uniform. Everywhere—in the outcrops of the Camp Garden, the Blue Cliff, on D. Klyuchevskaya Street in Tomsk, and from boreholes and test pits—the following section is noted from top to bottom: 1. Subsoil loams, degraded. Thickness 0.6–1.2 m. 2. Brown and grayish-brown loams, macroporous, bedded, with columnar jointing, with lenses and thin interbeds of sand. Thickness 3.0–5.0 m. 3. Grayish-brown sandy loam, bedded, macroporous. Thickness 0.5–0.7 m. 4. Brown fine-grained sand, horizontally bedded. Thickness 0.5–2.5 m.

In the loams at a depth of 1.5–2.5 m, fine, well-rounded pebbles occur.

In terms of granulometric composition, the loams of the superposed terrace have a variegated composition. They are predominantly light, more rarely medium varieties, with a clay content from 10 to 25%, silt from 20 to 60%, and sand from 20 to 60%. In the vertical section the granulometric composition is characterized by an increase in the sandy fraction from top to bottom, confirming the gradual transition of sandy rocks into loamy ones. The age of this rock sequence, on the basis of the Upper Paleolithic site and the find of Elephas primigenius Blum [12], may be accepted as Upper Pleistocene \((Q_3)\).

The mineralogical and chemical composition is given in Table 1. As can be seen from the table, the clay fraction is represented by hydromicas with an admixture of organic matter. In one of the samples, an admixture of montmorillonite was detected by thermal analysis. The absorption capacity is from 6.16 to 13.62 mg-equiv per 100 g of dry rock. The absorbed bases are represented by calcium and magnesium. The reaction of the medium is acidic. The rocks of the superposed terrace are predominantly noncarbonate; the carbonate content by calcimeter is equal to zero in almost all samples.

The upper loess horizon \((Q_3)\) is distributed within the Tom–Yaya interfluve and is represented by typical loess-like yellow-brown and pale macroporous loams, carbonate-bearing, unstratified, with columnar jointing [7]. Their thickness ranges from 0.5 to 13.0 m. In terms of granulometric composition these are heavy and medium varieties, with sand content of 3–15%, silt 60–80%, and clay 15–30%. Their mineralogical composition was not studied by us.

By macroscopic features and granulometric composition, these loams differ sharply from the deposits of the superposed terrace.

The lower loess horizon \((Q_{2-3})\) occurs everywhere both on the high terraces and within the Tom–Yaya interfluve. The thickness of the rocks composing it is usually small, not exceeding 3–3.5 meters within the terraces, increasing on the interfluve to 19.0 m [7]. In lithological composition these are loess-like loams of brownish-gray and dark-gray color, with interbeds and small lenses of fine-grained grayish-brown sand. They are characterized by the presence of a small number of fine macropores and ferruginization along pores and cracks in the form of brown spots and films. On drying, the rocks become very strong. In terms of granulometric composition they belong predominantly to heavy silty varieties. The silt content in them ranges from 60 to 75%, clay up to 30%, with an insignificant amount of sand. The finely dispersed fraction (Table 1) is represented by hydromicas with an admixture of beidellite, organic matter, and chlorite. The hydromicaceous composition of the finely dispersed fraction and the presence of beidellitization are confirmed by the absorption capacity (20.95–24.75 mg-equiv per 100 g of rock).

The material presented confirms the correctness of distinguishing the genetic types of rocks outlined above, which are fairly clearly separated both by conditions of occurrence and by the general section of the deposits, and by a number of characteristics of the rock composition (granulometric composition, composition of the clay fraction, absorption capacity).

In accordance with the data obtained, the distinguished genetic types and lithological varieties of rocks were taken as the basis of their engineering-geological classification.

Analysis of the physical and technical properties of the distinguished varieties, carried out by methods of mathematical statistics with the construction of scatter diagrams for the principal indices, made it possible to draw the following conclusions.

1. No regular change in the principal indices of properties with depth is observed for the distinguished lithological varieties. The limi—

the amplitudes of variation in natural moisture content, unit weight, porosity, and plasticity limits over the area proved to be significant. The absence of any regularity in changes in the properties of the rocks with depth and over the area within the distinguished rock types made it possible to regard these properties as applying to the lithological type as a whole.

1. The analysis carried out of the interrelations between direct and indirect calculated indices showed the presence of a fairly close dependence between the porosity coefficient and the compaction coefficient, and a weak dependence between the compaction coefficient and the lower plasticity limit. The dependence of the shear-resistance indices on moisture content and on the lower plasticity limit is also expressed indistinctly. The dependence between the coefficient of relative collapsibility \((i_m)\) and the moisture content, obtained in 1957 [8], was confirmed. Loess-like rocks having a degree of moisture content \(<0.7\) and a porosity coefficient \(>0.8\) may be prone to additional settlements upon soaking under loads. The coefficient of relative collapsibility under a load of \(2\text{–}3\ \mathrm{kg/cm^2}\) in individual, most highly drained areas varies within the range \(0.02\text{–}0.04\), reaching values of \(0.06\text{–}0.07\) at individual points.

2. Comparison of the indices of the principal properties of loess rocks occurring on different geomorphological elements shows that, both in the ranges of variation of these properties and in their mean values, the loess rocks of the superposed terrace are similar, which confirms the correctness of distinguishing them as a lithological variety.

3. The loams of the lower loess horizon, occurring on different geomorphological units, also have mutually similar property indices and have been distinguished as an independent variety. No collapsibility phenomena have been recorded in these loams.

In establishing generalized property indices within each distinguished lithological variety, the methods of mathematical statistics were used, as indicated above. The values of the principal property indices, generalized compression curves, and shear-resistance indices of the rocks were obtained by the median method. For the calculations, 479 records of laboratory investigations of soils were used. On the basis of the data obtained, an engineering-geological classification was compiled (Table 2).

In order to compare the obtained indices of the properties of soils distributed within the territory of the city of Tomsk with the standard and calculated characteristics given in SN and P II-B1-62 [1], the deformation moduli of the soils and the values of cohesion and the angle of internal friction were calculated. In the calculations, the genetic features of the rocks were taken into account; accordingly, the calculations were carried out separately for the loams of the first terrace and for the loess loams and sandy loams of the high terraces and the watershed slope. As a result, two tables (3 and 4) were obtained, compiled according to the principle of Table 13 of SN and P II-B1-62. In these tables, in calculating the deformation modulus, the well-known formula was used:

\[ F=\frac{1+e_2}{a}, \]

where \(a\) is the compaction coefficient, adopted by us for the load interval from \(0.5\) to \(2.0\ \mathrm{kg/cm^2}\). The moduli of total deformation included in the formulas for calculating deformations of foundation bases according to SN and P are not given in Tables 3 and 4, owing to the present absence, for this territory, of field observations of settlements of structures and trial plate-load tests, as well as because of the approximate nature of the transition from the values of the deformation modulus of the foundation base under a plate to the deformation modulus of the foundation base under the foundations of various structures.

Table 3

Table 4

It is known [13, 14] that the value of the modulus of total deformation, as a rule, considerably exceeds the deformation modulus obtained from compression tests. According to I. A. Agishev [13], “at a porosity coefficient $\varepsilon = 0.4—0.425$, a discrepancy between the two values by a factor of 7 is observed; at a porosity coefficient $\varepsilon = 1.5—1.6$, it gives up to a factor of 2.”

Taking the above into account, until actual values of the moduli of total deformation are obtained, it may be recommended that they be calculated from compression-test data with a coefficient of 2.

Comparing Tables 13 of SN and P and 3 and 4, compiled for local soils, one can see that even when the obtained compression deformation moduli are increased by a factor of 2—3, the standard and local indices differ substantially. The data obtained confirm the need to develop local supplements to SNiP-1962 and, after supplementation and correction on the basis of experimental and field observations of deformations of the foundations of structures, they may be used as such.

LITERATURE

1. Building Codes and Regulations, 1962 (SN and P, and P-B, 1-62).

2. Shvets V. B. Normative and design characteristics of alluvial clayey soils. Bases, Foundations and Soil Mechanics, No. 1, 1962.

3. Egorov S. N. On the question of determining indices of shear resistance and compressibility of cohesive soils from their physical properties. Bases, Foundations and Soil Mechanics, No. 1, 1962.

4. Kuchin M. I. Principal tasks in the study of the loess rocks of Kuzbass and the Ob region for ensuring industrial construction and introducing into practice the calculation of deformations of foundation soils by limiting states. Collection of Scientific Works, TISI, Vol. VII, 1960.

5. Resolutions and proceedings of the interdepartmental conference on elaborating and refining stratigraphic schemes of the West Siberian Lowland. Gostoptekhizdat, 1961.

6. Draft of a unified stratigraphic scale of the Quaternary system, adopted by the standing commission of the ISC on May 12, 1962.

7. Sulakshina G. A., Rozhdestvenskaya L. A., Mikhalchenko B. F., Shumkova T. S. Engineering-geological characterization of the cover deposits of the city of Tomsk and adjacent districts in connection with civil and industrial construction, 1962.

8. Sulakshina G. A., Rozhdestvenskaya L. A., Plotnikov B. V. Engineering-geological characterization of construction conditions in the city of Tomsk. Tomsk, TPI, 1957.

9. Zarina E. N., Kaplyanskaya F. A., et al. The periglacial formation of the West Siberian Lowland. Materials on Quaternary Geology and Geomorphology of the USSR, issue 4, 1961.

10. Chernyshev G. A. New data on the stratigraphy of the Quaternary deposits of the Tomsk Ob region. Collection of Scientific Works, TISI, Vol. VII, 1960.

11. Radugin K. V. Geomorphological section of the Tom—Chulym watershed in the area of the city of Tomsk.

12. Kashchenko N. F. A mammoth skeleton with traces of the consumption of certain parts of this animal’s body as food by modern man. Proceedings of the Imperial Academy of Sciences, Physico-Mathematical Division, Vol. XI, No. 7, 1901.

13. Agishev I. A. The dependence between porosity and the deformation modulus, established by field tests of clayey soils. Bases and Foundations, No. 20, 1957.

14. Samarin I. K. On the compressible thickness of the foundations of hydraulic-engineering structures according to field observations of their settlements. Bases, Foundations and Soil Mechanics, No. 6, 1962.