The Impact of Engineering-geologic Conditions on the Development of Railway Subgrade Design Solutions

Abstract

An analysis of hydro-meteorological and engineering-geological conditions of the Russia's Eastern Siberia and the Far East is provided in the article.

Full text

Procedia Engineering 189 ( 2017 ) 752 – 758
1877-7058 © 2017 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of the scientific committee of the International conference on Transportation Geotechnics and Geoecology
doi: 10.1016/j.proeng.2017.05.118
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Available online at www.sciencedirect.com
Transportation Geotechnics and Geoecology, TGG 2017, 17-19 May 2017, Saint Petersburg,
Russia
The impact of engineering-geologic conditions on the development
of railway subgrade design solutions
Alpysova V.A.a, Bushuev N.S.a, Shkurnikov S.V.a, Shulman D.O.a
*
aEmperor Alexander I St. Petersburg State Transport University. 9, Moskovsky av., St. Petersburg, 190031, Russia
Abstract
An analysis of hydro-meteorological and engineering-geological conditions of the Russia’s Eastern Siberia and the Far East is
provided in the article.
To assess the disruptive effect of earthquakes on the railway track elements a unified parameter is selected – the magnitude of
admissible stress σr. A multi-factor research is conducted for the fixed seismicity value of 8 points. The analysis of stability is
based on the formula by G.M. Shakhunyants accounting for seismicity.
Basing on the analysis performed the optimal design solutions for embankments with account of soil conditions and earthquake
effects are proposed. Recommendations for the embankment structure’s optimization are given.
© 2017 The Authors. Published by Elsevier Ltd.
Peer-review under responsibility of the scientific committee of the International conference on Transportation Geotechnics and
Geoecology.
Keywords: Subgrade, permafrost soil, seismicity, seismic resistance, damping layer, multiple classification analysis
1. Main text:
The country’s economic and social development is based on the creation of an integrated system of transport
routes engaged in passenger and freight transportation by different kinds of vehicles. Currently, the center of
economic activity in Russia is shifting towards Eastern Siberia and the Far East. This is due to two main reasons:
* Corresponding author. Tel.: +7 (812) 570-76-88.
E-mail address: vera.alpysova@yandex.ru, 2009bushuev@rambler.ru, 3123810@mail.ru, shulman@pgups.ru.
© 2017 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of the scientific committee of the International conference on Transportation Geotechnics and Geoecology

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V.A. Alpysova et al. / Procedia Engineering 189 ( 2017 ) 752 – 758
first, a considerable part of raw material resources is located in this area, and second, their geographic location
stimulates the expansion of trade between Russia and countries if the Asia-Pacific (AP) region.
The railway transport provides more than 80% of freight turnover and about 40% of passenger traffic in the
transport system of Eastern Siberia. Development of new fossil deposits, increase in trade turnover between Russia
and AP region as well as growth of transit transportation volumes encourage an improvement of the complex
transport system including railway transport. In order to implement the given task of the transportation increase the
Russian Government has elaborated and approved the Strategy for Railway Transport Development towards 2030,
which involves both construction of new lines and reconstruction of the Baikal-Amur Mainline and Trans-Siberian
Railway.
It should also be noted that the Eastern Siberia and the Far East regions are characterized by complex hydro-
meteorological and engineering-geological conditions, which have a considerable effect on the composition and
volume of survey works, development of design solutions, construction and maintenance of the whole railway
infrastructure.
The Eastern Siberia climate is continental and severe. One can observe significant seasonal fluctuations in cloud
coverage, temperature, and precipitation level. Winter temperatures can reach the value of -40-60°С. In summer the
southern area of the region appears to be relatively hot. It is especially typical of Tyva, Khakassia, and Trans-Baikal.
Here the temperature in July is up to +25 degrees.
The Far East climate modifies from harsh continental (Yakutia, Kolyma areas of the Magadan region) to
monsoon climate (South-East). This is due to the extremely vast territory measured from North to South (almost
3,900 km) and from West to East (2,500–3,000 km). In the South-West part of the region the climate is moderate
with the winter temperature ranging from -32 to -48°С. Winters are usually dry and last for 9 months. Summer
temperatures are quite high: from +12 to +20°С. The annual precipitation is 300–500 mm. In the Southern part of
the region the monsoon climate has a relatively cold and dry winter (from -12 to -20°С) and a wet and cool summer
(+16°С).
Analysis of hydro-meteorological conditions allows for the conclusion that almost all territory of the considered
region is characterized by a lengthy period of negative temperatures of more than -25°С, which lasts up to 9 months
per year, and a short period of positive temperatures (up to +25°С).
In the last decades one can observe a change in the region’s climate with sharper temperature fluctuations,
stronger winds as well as change in the quantity and type of precipitation.
Nowadays, trends in hydro-meteorological shifts are not identified. It is due to a relatively short period of
climatic parameters change, their unstable nature, and lack of data needed to obtain verifiable regularities in hydro-
meteorological modification.
When conducting hydro-meteorological survey one should account for the climatic change data as well as
analyze the reasons for climatic conditions modification and provide their systematization.
What is especially peculiar about the regions of Eastern Siberia and the Far East is the following fact: they are
located within the zone of permafrost soil (Fig. 1) and high seismicity (Fig. 2).
Basing on the comparison of seismicity and permafrost soil maps one can conclude that a share of Eastern Siberia
and practically the whole of the Far East are affected by both factors. Thus, it is strongly recommended to take them
into account when performing design works.
If we consider the seasonal thawing of ground as the main negative factor, we should design the railway subgrade
as an embankment formed by sandy filtering soils in order to preserve the ground in the frozen condition (Design
Principle I).

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Fig. 1. Map of Permafrost Soils Distribution.
Fig. 2. Seismicity Map of Siberia and the Far East.

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V.A. Alpysova et al. / Procedia Engineering 189 ( 2017 ) 752 – 758
The maximum embankment height can therefore be established on the basis of the seasonal thawing depth. The
seasonal thawing depth is identifies in accordance with Construction Code 25.13330.2012 Annex 4 [1]. The
standard seasonal thawing depth is determined by the formula:
݀௧௛ǡ௡ ൌ݀௧௛
ᇱටሺ்೟೓ǡ೘ష்್೑ሻ௧೟೓೘ǡ
ሺ்೟೓ି்್೑ሻ௧೟೓
మ, (1)
where:
୲୦
ᇱ stands for the biggest seasonal thawing depth in a year period, m (established on the basis of field
observations);
ୠ୤ stands for the starting temperature of soil freezing, °С;
୲୦ǡ୫ǡ୲୦୫ǡ stand respectively for the average air temperature in the positive period, °С, and for the duration of
this period, h, adopted in accordance with Construction Code 131.13330 [2];
୲୦, ୲୦ stand respectively for the average air temperature in the negative period, °С, and for the duration of this
period, h, in the year of observation adopted in accordance with meteorological data.
At a first approximation, due to the necessity of preserving the ground in the frozen condition the embankment
height is recommended to be within the limits of 3–6 m, depending on the seasonal thawing depth of the permafrost
soils.
If the negative impact of seismic waves [9, 10] is taken as a primary factor, the embankment height should be
determined by two parameters: the maximum application of damping properties of the embankment and the
provision of its general stability.
Seismic impacts are wave oscillating movements arising in response to the underground strike of the released
energy. It results in the three types of waves: longitudinal waves along the seismic raypath, transversal waves
perpendicular to the seismic raypath acting within the rock mass, and transversal surface waves arising at the surface
of the ‘ground-air’ environment division [11, 12, 13, 14, 15]. The most destructive are transversal waves.
An example of destructive impact of transversal surface waves is showed in Fig. 3.
Fig. 3. Destruction of Track Superstructure as a Result of Seismic Transversal Surface Waves Impact [6].

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To estimate the destructive impact of earthquakes on the railway track elements (subgrade, ballast, sleepers, rails)
a unified parameter has been adopted – magnitude of admissible stress ɐሺሻǡ˃. Research was conducted by means
of multiple classification analysis. As impact factors the thicknesses of subgrade (hsg = 3–21 m), bedrock (hbr = 5–
95 m) and Earth crust (distance to hypocenter r = 10 and 20 km) were selected. Basing on the fact that according to
the Construction Code 14.13330.2011 [4] the calculations for structures are performed when seismicity is estimated
≥ 7 points (MSK scale), research was conducted for the site with seismicity of 8 points [7, 8]. Calculations for stress
are done using the formulae by V.N. Tyupin and E.V. Nepomnyashchikh [3].
The calculations performed have resulted in the regression equation of the following kind:
ݕൌʹʹ͸͵͸͸ǡͲെ͸͹Ͳͻ͸ǡͷή˘ଵെͺͶʹͷͶǡ͹ή˘ଶെ͹ͻͺͶ͵ǡͷ ή˘ଷ൅ͷͻ͹Ͷ͸ǡ͹ή˘ଶή˘ଷǤ (2)
where:
ݕ stands for the optimization parameter – stress σr, Pa;
˘ଵ stands for the influence factor (subgrade thickness);
˘ଶ stands for the influence factor (bedrock soil thickness);
˘ଷ stands for the influence factor (distance to the hypocenter).
All coefficients of the regression equation are significant. So, the greater is the thickness of the soil layers, the
lower is the magnitude of stress acting on the subgrade and track superstructure.
In this case the embankment should be seen as a damping structure located between the bedrock soil and track
superstructure. Moreover, the higher is the embankment, the lower negative impact of longitudinal waves is
conveyed to the track superstructure. Nevertheless, with the embankment height getting larger its general stability
decreases.
To analyze the embankment stability calculations accounting for the seismic impacts and not accounting for them
were performed using the formula of G.M. Shakhunyants [5]:
ܭௗ௬௡ ൌσሺே೔ή௙೔೏೤೙ା஼೔೏೤೙ή௟೔ା்೔ೞ೛೏೤೙ሻ
೙
೔సభ σ்೔೚೑೑ೞ೐೟
೙
೔సభή௄ೞǡ (3)
where:
ܭௗ௬௡ stands for the dynamic stability factor;
ܰ௜ stands for the coercive force in the i section;
݂௜ௗ௬௡ stands for the dynamic friction factor in the i section;
ܥ௜ௗ௬௡ stands for the specific cohesion in the i section;
݈௜ stands for the i section foundation length;
ܶ௜௖ௗ௬௡ stands for the coercive dynamic force in the i section;
ܶ௜ௗ௜௦௣stands for the displacement force in the i section;
ܭ௦ stands for the seismicity factor.
For embankments of 3–21 m height the general trends of the stability factor change have been established
depending on the embankment height, as showed in Fig. 4.

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Fig. 4. The general trends of the stability factor change depending on the embankment height.
The analysis of the embankment stability factor change depending on its height allows to conclude that within the
height ranging from 3 to 9 m the largest percentage of stability factor decrease is observed (~20%); within the height
ranging from 9 to 21 m this value does not exceed 10%.
It should also be noted that at the embankment height of more than 12 m (according to acting standards) it is
required to arrange berms which significantly increases the consumption of soil materials, width of the land strip
needed to construct an embankment as well as the volume of construction work. Thus, the most rational solution for
the embankment height is the range from 3 to 12 m.
2. Conclusions:
1. In Eastern Siberia and the Far East it is recommended to design railway subgrade predominantly on
embankments of 3–12 m height, which allows, first, to keep the soil frozen and second, to decrease the
negative impact of earthquakes on the track superstructure.
2. The optimal embankment structure shall be identified by means of calculation which will account for
hydro-meteorological conditions, trends of their change, conditions of permafrost soil deposits and their
thickness as well as the seismic impacts.
3. If the embankment height is insufficient, one shall arrange additional damping layers within the
embankments in order to decrease negative earthquake impacts.
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