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The Construction of Transport Infrastructure on Permafrost Soils
Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 189 (2017) 421 – 428
Transportation Geotechnics and Geoecology, TGG 2017, 17-19 May 2017, Saint Petersburg, Russia
The construction of transport infrastructure on permafrost soils Vladimir M. Ulitskya, Elena V. Gorodnovab * a
Sc.D, Tech. Professor, Head of Chair, Laurette of the State Prize of the Russian Federation, Emperor Alexander I St. Petersburg State Transport University, the Chair “Soils and Foundations”, 9 Moskovsky pr., Saint Petersburg, 190031, Russia b PhD, Tech. Docent, Emperor Alexander I St. Petersburg State Transport University, the Chair “Soils and Foundations”, 9 Moskovsky pr., Saint Petersburg, 190031, Russia
Abstract The issues associated with freezing and thawing of soils in the subsoil of a complex of port facilities including transport infrastructure have been considered. The solution of thermal-physical problems of freezing, frost heave and thawing of soils has been made in spatial domain; the results of calculations are compared with the practical values. Numerical simulation of the problem of stability of structures on permafrost soils allowed predicting a possible soil thawing depth in time and optimizing the use of modern thermal insulation materials. The proposed calculation methods will provide reducing cost of development of transport infrastructure and port facilities under construction in the important northern regions of Russia. © 2017 The Authors. Published by Elsevier Ltd. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the scientific committee of the International conference on Transportation Geotechnics and (http://creativecommons.org/licenses/by-nc-nd/4.0/). Geoecology. Peer-review under responsibility of the scientific committee of the International conference on Transportation Geotechnics and Geoecology Keywords: Railroad bed; soil freezing and thawing; permafrost soil; freezing boundary; transport infrastructure; numerical modeling
1. Introduction The prediction of possible thawing of permafrost soil bulks during exploitation of a large range of structures in the conditions of the Far North according to the regulatory documents is not in good agreement with observation results. The new methods of numerical modeling of the freezing-thawing processes are in good agreement with long-term observations of these processes. The account of the prediction of settlements during thawing of permafrost soils in the
* Corresponding author. Tel.: +7-921-339-8174; fax: +7-812-314-9013. E-mail address: [email protected]
1877-7058 © 2017 The Authors. 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.2017.05.067
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Vladimir M. Ulitsky and Elena V. Gorodnova / Procedia Engineering 189 (2017) 421 – 428
subsoil of foundations of buildings and transport structures allows optimizing costs of their construction and subsequent operation. Moreover, application of numerical modeling helps to define reference values of stresses and strains in soils and superstructures. The obtained results of numerical calculations meet the requirements of the standards of the world geotechnical practice for design according to ultimate states. 2. The background information 2.1. The Northern Sea Route and adjacent coastal areas It is known that the Northern Sea Route is the main traffic artery in the Arctic that integrates European and Far Eastern seaports into a single transport network. The Russian legislation defines the Northern Sea Route as "the historically developed Russian national unified transport communications in the Arctic". One of the indicators of the level of development of the Arctic navigation is the volume of cargo traffic, which is defined by the following factors: the cargo base, the icebreaker support, the composition of the cargo fleet, existence of the transport and costal infrastructure sufficient for the support of navigation. The Arctic ports are currently a weak link of the Northern Sea Route. To solve this problem there is a goal of the state Arctic policy to provide navigation safety in the sea ports and their approaches as well as to construct the sea ports infrastructure [1]. The most important prospect to promote the Northern Sea Route is to develop the Arctic shelf deposits and create significant port infrastructure, which is required for intake, storage and loading of hydrocarbons for shipping to Russia and abroad. The Yamal Peninsula is one of the most important strategic regions of Russia. Commercial development of the Yamal gas fields and adjacent water areas is essential for substantial growth of the Russian gas production after 2010. "Yamal LNG" Project envisages the construction of an LNG plant using the reserves of the South Tambey field. However, Yamal is characterized by rather poorly developed transport infrastructure, and the industrial development of the region is impossible without adequate development of railway traffic. Nowadays a significant amount of cargo is delivered to the Yamal Peninsula by sea during the summer season navigation. To provide all-year-round cargopassenger traffic and shipping a new railway "Obskaya – Bovanenkovo" is being built to the Yamal Peninsula. During the design of railways perennial natural processes are taken into account, therefore, designers need to know what processes happen in the roadbed and track superstructure in the long term for several decades. This is especially important in the permafrost soil zone, where more than 5,000 km of Russian railway lines are laid. 2.2. The Problems of development of territories with seasonally frozen and permafrost soils In geological-engineering terms, the northern regions of Russia are territories with seasonally frozen and permafrost soils. Permafrost soils spread over the most of Siberia and throughout the Arctic coast. The area is about 11 million square km. These specific soil conditions for the world construction practice impose a number of requirements to be taken into account in investigations, design, and workflow management as well as in subsequent maintenance of building structures including the constant post-construction monitoring. In permafrost soil areas there are various permafrost and frozen-soil conditions [2]. One of the authors of this paper has been working in the permafrost soil regions for a long time, as well as in the areas of deep seasonal freezing and the presence of permafrost lenses. In general, as regards deformation nature frozen soils can be divided into the following categories: x Frozen dispersed soils, well cemented by ice with evenly distributed small ice inclusions of sands, sandy clays, loams, clayey rocks. Ice cemented pebbles and other alluvial sediments can be also attributed to the group. x The same soils but with large inclusions of ice in the form of separate layers, wedges and bulks. x Frozen dispersed ice-saturated soils with rock inclusions. x Fractured bedrocks with cracks filled with ice. The characteristic features of the geological-engineering stratum of frozen soils include frost-geomorphological sediments, frost friction, solifluction, the presence of areas with underground ice and massive ice deposits. The areas
Vladimir M. Ulitsky and Elena V. Gorodnova / Procedia Engineering 189 (2017) 421 – 428
where reliable rocks have large slopes increasing a thickness of permafrost dispersive soil bulk, that leads to development of differential settlements of buildings and structures, may be considered risky as well. In the practice of construction on permafrost soils there are some cases of considerable deformations of structures built in very coarse, fractured or eroded rocks due to their thawing. These deformations are typical for very coarse soils with substantial content of ice crusts which envelop large fragments. Considerable settlements may occur in fractured rocks due to thawing. Significant deformations due to thawing are also typical for soft rocks (siltstone, argillite, marl etc.) In frozen state these soils have high strength. However, due to thawing these soils may disintegrate and considerable settlements occur. According to structural and technological features of buildings and structures, geotechnical conditions and the ability to change subsoil properties as required, one of the following principles to use permafrost soils as a subsoil for buildings and structures, generally accepted in Russia, is applied: Principle 1 – permafrost soils are used in the frozen condition which is preserved during the process of construction and the whole specified period of building or structure maintenance; Principle 2 – permafrost soils are used in the thawed condition (thawing of soil is admitted during building or structure maintenance or before construction of a building or structure down to a designed depth). The choice of one or another principle of using a subsoil may also depend on the priority of construction of a structure. For example, while railroads are constructed bridges and conduits may become the barrier objects, which construction completion as well as the start of transportation through them define a completion of the whole road section construction. Quite often principle 2 is applied to the construction of such barrier objects regardless permafrost soil conditions, even if the construction cost in this case is higher in comparison with the application of principle 1. This solution is explained by the fact that while preserving the subsoil in the frozen condition almost always there is a need to provide a technological break between the foundation construction completion and the start of its constructional and operational loading. The duration of this period is determined by the time of adfreezing of the soil and foundation or foundation elements, it ranges from several days to a month or even a longer period (depending on a soil temperature and construction practice). Obviously, such a break is unacceptable according the construction requirements to the whole road section. As a rule, the infrastructure of the Northern ports is to be constructed according to principle I (preservation of the frozen state of soil). In order to substantiate the accepted solutions on implementation of subsoils and foundations for buildings and structures as well as to construct and provide reliable operation of the port area the numerical modeling of this problem was carried out. This modeling is a basic requirement of Federal Law # 384 RF “Technical Regulations for Provision of Safety of Buildings and Structures” enacted in 2010. 3. A thermal regime of a northern port. Simulations of major facilities 3.1. “Thermoground” numerical modeling For complex studying of the problem the numerical modeling was carried out using the software module “Thermoground”, developed by experts of Saint Petersburg State Transport University and Saint Petersburg State University of Architecture and Civil Engineering for solving thermal-physical problems. The numerical modeling [3-5] was based on the software package “FEM models”, widely implemented in the design practice by the Group of Companies "Georeconstruction" for diverse soil conditions of different Russian regions. The issues under consideration have been analyzed in the works of the foreign scholars [6-11]. To study the subsoil behavior there was modeled a thermal regime of the major facilities of the northern ports Sabetta and Tanalau. The goal of the simulation was to estimate temperature fields in the subsoil of the buildings. According to the project, the foundations of all the buildings are pile foundations. A ventilated underground area and vent pipes (channels) were used in the subsoil as the measures to preserve the frozen soil state. Strain-stress state of the freezing soil is to be described by a model. It could be the simplest, linear-elastic model. Moreover, it could be an elasto-plastic Coulomb-Mohr model or a model of soil hardening. At the first glance, the
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latter is supposed to be the most natural one, as strength and strain soil properties grow significantly when soil is freezing. The model describing the behavior of soils at thermal and strength loading, taking into account temperature hardening was proposed by I. I. Sakharov [12] in 1995. At first approximation mechanic soil properties were set according to the following linear dependency:
A(T )
A0 1 Ki T
(1)
where А0 is a mechanical characteristic for the thawed condition, Ki – a hardening index, Т – absolute values of negative temperatures of a finite element at the considered time moment. The conducted analysis of temperature fields distribution in the subsoil of the buildings (Fig. 1 a, b) allowed evaluating efficiency of various measures ensuring safe construction and subsequent safe operation of these buildings in accordance with principle I, i.e. preserving the frozen state of soils without allowing its thawing during exploitation.
а
b Fig. 1. The thawing through of the soil under the port technical building in 50 years after construction, the boundary temperature - 0°C: (a) calculation with unventilated channels; (b) calculation with ventilated channels.
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In order to design the port territory and access ways the calculations were done for selecting the required thermal insulation thickness to preserve the natural soils in the frozen state. The following thermal-technical soil properties were accepted in the calculations: x For crushed stone: the thermal conductivity is 63 072 kJ / (m × year × °C), the heat capacity – 1 700 kJ / (m3 × °C) in the thawed and frozen states. x For sand cushion (natural fine-grained sand): the thermal conductivity in the thawed state is 25 229 kJ / (m × year × °C), the thermal conductivity in the frozen state is 31 536 kJ / (m × year × °C), the heat capacity in the thawed state – 1 656 kJ / (m3 × °C), the heat capacity in the frozen state – 1 476 kJ / (m3 × °C). x For bituminous concrete: the thermal conductivity is 22 706 kJ / (m × year × °C), the heat capacity – 1 344 kJ / (m3 × °C).
Tight bituminous concrete
Porous bituminous concrete Crushed stone Insulation - PENOPLEX
Fine sand
Geotextile Subsoil
Typical designed structure of the road pavement and subgrade
All the calculations using the simulations allowed analyzing different frozen conditions taking into account possible climate warming by 2 ºС in 50 years. At the sand water content of 0.21 and the initial temperature -50 ºС the maximum depth of thawing is 90 cm. Let us consider a typical calculation of the subgrade structure without thermal insulation (Fig. 2): The maximum soil thawing depth below the crushed stone layer was 0.78 m (Fig. 3a), as from the ground surface - 0.78+0.06+0.04+0.4= 1.28 m. Then let us determine the thickness of the heat insulator sufficient to avoid thawing of the soil below the crushed stone. If the insulator thickness is 10 cm the depth of soil thawing under the heat insulator is 3 cm (Fig. 3b).
Fig. 2. Typical designed structure of the road pavement and subgrade.
3.2. Simulation results and discussion The analysis of the calculations resulted in drawing the following conclusions: x Construction of a 1.4-m-high ventilated underground area (for the office building) guarantees preservation of the subsoil in the frozen condition for the complete designed period of the building exploitation. The thawing depth under the building in summer does not exceed the seasonal values, that does not pose any risk for pile foundations. The technological regime of the underground area condition should be provided during the period of the building maintenance. This sort of construction is successfully used in the Northern cities provided the mode observation of their maintenance in the summer time [13].
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x It is inadmissible to construct a compressor station, a technical building for ground support equipment, a boiling house, resting on 10-meter-long piles without additional measures for frozen soil preservation, because the depth of the soil thawing will exceed the length of piles during 50 years of the buildings maintenance. It may cause unexpected soil subsidence and general loss of stability of the subsoil of the buildings. x In order to preserve the frozen state of the soils in the subgrade of a compressor station, a technical building for ground support equipment, and a boiling house there was suggested and calculated the solution to lay pipes with forced air ventilation in winter. According to the calculations results, the area of thawing does not spread below the middle section of the cooling pipes that ensures the reliable operation of the pile foundations of the buildings. x In order to prevent settlements of floors a coarse-grained soil cushion should be filled up to the top of the pipes. Only the forced ventilation of air, which is supplied by means of fans in winter, can guarantee the efficiency of horizontal pipe operation in the subsoil. The proposal calculation methods upgrade to a new level the works associated with the prediction of development of possible deformations for a large range of transport facilities (railroads and highways, ports and airports) as well as stresses in soils during their freezing and thawing. The comparison of the results of the obtained calculations with the observation data and the failure states occurred in the latitudinal railway Salekhard-Igarka supports the state-of-theart methods of numerical modeling of difficult geotechnical situations.
Fig. 3a. The maximum soil thawing depth below the crushed stone layer without thermal insulation - 78 сm, Layers up to down: bituminous concrete – 10 cm, crushed stone – 40 cm, finite sand – 10 cm, subsoil
Fig. 3b. The maximum soil thawing depth under the10-cm-thick thermal insulator for the subgrade structure – 3 cm, Layers up to down: bituminous concrete – 10 cm, crushed stone – 40 cm, insulation – 30 cm, finite sand – 10 cm, subsoil
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3.3. The results of theoretical and experimental studies The abovementioned calculations of the transport infrastructure in the software complex “Termoground” have been tested through operation of anchor foundations. The test grounds with the experimental anchor foundations were located in East Siberia in the area of the cities of Angarsk and Usolie-Sibirskoe, the Irkutsk district. In situ investigations of anchor foundations have been carried out in different hydrogeological conditions in order to evaluate factors influencing stability of these foundations at development of shear forces of frost heave and normal pressures in time. The tested foundations have the form of reinforced concrete pillars of 0.25х0.25 m in the crosssection and the length of 3.9 m with special studs on the top to fix the loading deck. The field measurements of normal pressures have been made at the level of the upper surface of the anchor slab. For this purpose, the upper part of the anchor slab has been instrumented with acoustic pressure gauges which data have been systematically recorded and observed. The experiments have shown that pressure distribution depends on such factors as: the nature and magnitude of frost heave; contact links with the foundation; speeds of freezing; physical-mechanical properties of thawed and frozen soil. Distribution of normal pressures along the upper plane of the anchor foundation is demonstrated in fig. 4. Soil transition towards the thawed state leads to gradual reduction of pressures transferred to the anchor. The results of the numerical modeling have shown good agreement with the results of the large-scale field experiments.
Fig. 4. The graphs of distribution of normal pressures along the upper plane of the anchor foundation in time: 1 – the experiment; 2 – the calculation.
4. Conclusions Having analyzed the failed experience of transport construction in the previous century, namely the construction of a part of the railway Salekhard-Igarka, there has emerged the necessity of applying modern numerical modeling at all stages (investigations, design, works implementation and subsequent monitoring) of creating the latitudinal Northern Route along the Arctic coast. It will provide safety of buildings and structures in the difficult climatic and soil conditions. Together with solving the basic transport problems one should take into account the related regional factors, which provide sustainable development of this important Russian territory: natural-geological, environmental, and socioeconomic [14, 15]. Our research allows solving issues of territorial planning at the level of the entities of the Russian Federation located along the Arctic coastline. For the long run they can be classified as follows: - enhancing living standards taking into account the specifics of the life of the indigenous peoples of the north; - minimizing emissions of harmful substances polluting the area due to active development of oil and gas fields associated with extraction of rare mineral resources and transportation of the related cargo; - drafting regulatory documents on environmental protection and preservation of permafrost bulks of soils, which can guarantee the stability of buildings and structures;
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- creating permanent automated geo-ecological monitoring based on the data of mathematical modeling taking into account a possible climate change. Therefore, the presented fragment of calculations using the software complex “Termoground” allows ensuring sustainability of the whole infrastructure of the largest northern ports (Sabetta, Tanalau etc.), including the buildings of considerable heat release, even at the stage of design. References [1] M. Minin, Prospects for development of the coastal infrastructure of the Northern Sea Route on the basis of design experience of the seaport in the Teriberskaya Bay and the seaport of Sabetta, J. “Hydrotechnics”, # 4 (2014), 101-106. [2] K. Wojtkowski, The USSR Academy of Sciences, The Siberian Branch. The Institute of Permafrost Studies: Strength and creeping of frozen soils, Moscow: The Publishing House of the USSR Academy of Sciences, 1963, 217 p. [3] S. Kudryavtsev, I. Sakharov, V. Paramonov, Freezing and thawing of the soil (practical examples and finite element calculations), St. Petersburg, The Group of Companies "Georeconstruction", 2014, 247 p. [4] V.N. Paramonov, I.I. Sakharov, Mathematical modeling of thermal and deformation processes in problems of freezing and thawing of soils. Proceedings 5-th Int. Geotechnical Symposium, Geotechnical Engineering for Disaster Prevention and Reduction. IGH5, 22-24 May 2013, Incheon South Korea, (2013) 122-127. [5] S.A. Kudryavtsev, V.N. Paramonov, V.M. Ulitskii, I.I. Sakharov, Bed – Structure System Analysis for Soil Freezing and Thawing Using the Termoground Program, Journal Soil Mechanics and Foundation Engineering 52 (5) (2015) 240–246. [6] O. Grindland, Frost protection of structures in the road network, Frost I Jorn. # 108 (2005) 41-43. [7] W.G. Spencer, A. Hermansson, Frost heave and water uptake relations in variably saturated aggregate base materials, Transportation Research Board 82nd Annual Meeting, Washington (2003) 126-142. [8] F. Işık1, S. Arasan, A. S. Zaimoğlu, R. K. Akbulut, Effect of moulding water content on freezing-thawing behavior of compacted two clayey soils, in: XV Danube - European Conference on Geotechnical Engineering (DECGE 2014) H. Brandl & D. Adam (eds.) 9-11 September 2014, Vienna, Austria (2014) 590-597. [9] M.M. Zhou, G. Meschke, A three phase thermos-hydromechanical finite element model for freezing soils. Int. J. Numer. Anal. Meth. Geomech. 37 (2013) 3173-3193. [10] Y. Yamamoto, S.M. Springman, Axial compression stress path tests on artificial frozen soil samples in a triaxial device at temperatures just below 0ºC. Canadian Geotechnical Journal 51 (10) (2014) 1178-1195. [11] Per Lindh, Nils Rydén, The effect of different binders on freeze durability of stabilized soil, Proceedings of the 17th International Conference on Soil Mechanics and Geotechnical Engineering (2009) 268-270. [12] I. Sakharov, Physical mechanics of the cryoprocesses in soils and its applications at evaluation of deformations of buildings and structures, Synopsis of ScD, Tech. Thesis, Perm. 1995. 44 p. [13] N. Tsytovich, General and applied permafrost soil mechanics: Textbook, 2nd ed., Moscow, Book House "LIBROKOM", 2010, 448 p. [14] Т. Titova, The Methodology of the complex evaluation of the influence of new technologies on geo-ecological situation, The Journal of the Research Institute of Rail Transport, #2 (2005), 98. [15] L.B. Svatovskaya, A.S. Sakharova, M.M. Baidarashvili et al., New geo-protection technologies at construction and reconstruction of railways, St. Petersburg State Transport University, St. Petersburg 2012, 81 p.
ScienceDirect Procedia Engineering 189 (2017) 421 – 428
Transportation Geotechnics and Geoecology, TGG 2017, 17-19 May 2017, Saint Petersburg, Russia
The construction of transport infrastructure on permafrost soils Vladimir M. Ulitskya, Elena V. Gorodnovab * a
Sc.D, Tech. Professor, Head of Chair, Laurette of the State Prize of the Russian Federation, Emperor Alexander I St. Petersburg State Transport University, the Chair “Soils and Foundations”, 9 Moskovsky pr., Saint Petersburg, 190031, Russia b PhD, Tech. Docent, Emperor Alexander I St. Petersburg State Transport University, the Chair “Soils and Foundations”, 9 Moskovsky pr., Saint Petersburg, 190031, Russia
Abstract The issues associated with freezing and thawing of soils in the subsoil of a complex of port facilities including transport infrastructure have been considered. The solution of thermal-physical problems of freezing, frost heave and thawing of soils has been made in spatial domain; the results of calculations are compared with the practical values. Numerical simulation of the problem of stability of structures on permafrost soils allowed predicting a possible soil thawing depth in time and optimizing the use of modern thermal insulation materials. The proposed calculation methods will provide reducing cost of development of transport infrastructure and port facilities under construction in the important northern regions of Russia. © 2017 The Authors. Published by Elsevier Ltd. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the scientific committee of the International conference on Transportation Geotechnics and (http://creativecommons.org/licenses/by-nc-nd/4.0/). Geoecology. Peer-review under responsibility of the scientific committee of the International conference on Transportation Geotechnics and Geoecology Keywords: Railroad bed; soil freezing and thawing; permafrost soil; freezing boundary; transport infrastructure; numerical modeling
1. Introduction The prediction of possible thawing of permafrost soil bulks during exploitation of a large range of structures in the conditions of the Far North according to the regulatory documents is not in good agreement with observation results. The new methods of numerical modeling of the freezing-thawing processes are in good agreement with long-term observations of these processes. The account of the prediction of settlements during thawing of permafrost soils in the
* Corresponding author. Tel.: +7-921-339-8174; fax: +7-812-314-9013. E-mail address: [email protected]
1877-7058 © 2017 The Authors. 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.2017.05.067
422
Vladimir M. Ulitsky and Elena V. Gorodnova / Procedia Engineering 189 (2017) 421 – 428
subsoil of foundations of buildings and transport structures allows optimizing costs of their construction and subsequent operation. Moreover, application of numerical modeling helps to define reference values of stresses and strains in soils and superstructures. The obtained results of numerical calculations meet the requirements of the standards of the world geotechnical practice for design according to ultimate states. 2. The background information 2.1. The Northern Sea Route and adjacent coastal areas It is known that the Northern Sea Route is the main traffic artery in the Arctic that integrates European and Far Eastern seaports into a single transport network. The Russian legislation defines the Northern Sea Route as "the historically developed Russian national unified transport communications in the Arctic". One of the indicators of the level of development of the Arctic navigation is the volume of cargo traffic, which is defined by the following factors: the cargo base, the icebreaker support, the composition of the cargo fleet, existence of the transport and costal infrastructure sufficient for the support of navigation. The Arctic ports are currently a weak link of the Northern Sea Route. To solve this problem there is a goal of the state Arctic policy to provide navigation safety in the sea ports and their approaches as well as to construct the sea ports infrastructure [1]. The most important prospect to promote the Northern Sea Route is to develop the Arctic shelf deposits and create significant port infrastructure, which is required for intake, storage and loading of hydrocarbons for shipping to Russia and abroad. The Yamal Peninsula is one of the most important strategic regions of Russia. Commercial development of the Yamal gas fields and adjacent water areas is essential for substantial growth of the Russian gas production after 2010. "Yamal LNG" Project envisages the construction of an LNG plant using the reserves of the South Tambey field. However, Yamal is characterized by rather poorly developed transport infrastructure, and the industrial development of the region is impossible without adequate development of railway traffic. Nowadays a significant amount of cargo is delivered to the Yamal Peninsula by sea during the summer season navigation. To provide all-year-round cargopassenger traffic and shipping a new railway "Obskaya – Bovanenkovo" is being built to the Yamal Peninsula. During the design of railways perennial natural processes are taken into account, therefore, designers need to know what processes happen in the roadbed and track superstructure in the long term for several decades. This is especially important in the permafrost soil zone, where more than 5,000 km of Russian railway lines are laid. 2.2. The Problems of development of territories with seasonally frozen and permafrost soils In geological-engineering terms, the northern regions of Russia are territories with seasonally frozen and permafrost soils. Permafrost soils spread over the most of Siberia and throughout the Arctic coast. The area is about 11 million square km. These specific soil conditions for the world construction practice impose a number of requirements to be taken into account in investigations, design, and workflow management as well as in subsequent maintenance of building structures including the constant post-construction monitoring. In permafrost soil areas there are various permafrost and frozen-soil conditions [2]. One of the authors of this paper has been working in the permafrost soil regions for a long time, as well as in the areas of deep seasonal freezing and the presence of permafrost lenses. In general, as regards deformation nature frozen soils can be divided into the following categories: x Frozen dispersed soils, well cemented by ice with evenly distributed small ice inclusions of sands, sandy clays, loams, clayey rocks. Ice cemented pebbles and other alluvial sediments can be also attributed to the group. x The same soils but with large inclusions of ice in the form of separate layers, wedges and bulks. x Frozen dispersed ice-saturated soils with rock inclusions. x Fractured bedrocks with cracks filled with ice. The characteristic features of the geological-engineering stratum of frozen soils include frost-geomorphological sediments, frost friction, solifluction, the presence of areas with underground ice and massive ice deposits. The areas
Vladimir M. Ulitsky and Elena V. Gorodnova / Procedia Engineering 189 (2017) 421 – 428
where reliable rocks have large slopes increasing a thickness of permafrost dispersive soil bulk, that leads to development of differential settlements of buildings and structures, may be considered risky as well. In the practice of construction on permafrost soils there are some cases of considerable deformations of structures built in very coarse, fractured or eroded rocks due to their thawing. These deformations are typical for very coarse soils with substantial content of ice crusts which envelop large fragments. Considerable settlements may occur in fractured rocks due to thawing. Significant deformations due to thawing are also typical for soft rocks (siltstone, argillite, marl etc.) In frozen state these soils have high strength. However, due to thawing these soils may disintegrate and considerable settlements occur. According to structural and technological features of buildings and structures, geotechnical conditions and the ability to change subsoil properties as required, one of the following principles to use permafrost soils as a subsoil for buildings and structures, generally accepted in Russia, is applied: Principle 1 – permafrost soils are used in the frozen condition which is preserved during the process of construction and the whole specified period of building or structure maintenance; Principle 2 – permafrost soils are used in the thawed condition (thawing of soil is admitted during building or structure maintenance or before construction of a building or structure down to a designed depth). The choice of one or another principle of using a subsoil may also depend on the priority of construction of a structure. For example, while railroads are constructed bridges and conduits may become the barrier objects, which construction completion as well as the start of transportation through them define a completion of the whole road section construction. Quite often principle 2 is applied to the construction of such barrier objects regardless permafrost soil conditions, even if the construction cost in this case is higher in comparison with the application of principle 1. This solution is explained by the fact that while preserving the subsoil in the frozen condition almost always there is a need to provide a technological break between the foundation construction completion and the start of its constructional and operational loading. The duration of this period is determined by the time of adfreezing of the soil and foundation or foundation elements, it ranges from several days to a month or even a longer period (depending on a soil temperature and construction practice). Obviously, such a break is unacceptable according the construction requirements to the whole road section. As a rule, the infrastructure of the Northern ports is to be constructed according to principle I (preservation of the frozen state of soil). In order to substantiate the accepted solutions on implementation of subsoils and foundations for buildings and structures as well as to construct and provide reliable operation of the port area the numerical modeling of this problem was carried out. This modeling is a basic requirement of Federal Law # 384 RF “Technical Regulations for Provision of Safety of Buildings and Structures” enacted in 2010. 3. A thermal regime of a northern port. Simulations of major facilities 3.1. “Thermoground” numerical modeling For complex studying of the problem the numerical modeling was carried out using the software module “Thermoground”, developed by experts of Saint Petersburg State Transport University and Saint Petersburg State University of Architecture and Civil Engineering for solving thermal-physical problems. The numerical modeling [3-5] was based on the software package “FEM models”, widely implemented in the design practice by the Group of Companies "Georeconstruction" for diverse soil conditions of different Russian regions. The issues under consideration have been analyzed in the works of the foreign scholars [6-11]. To study the subsoil behavior there was modeled a thermal regime of the major facilities of the northern ports Sabetta and Tanalau. The goal of the simulation was to estimate temperature fields in the subsoil of the buildings. According to the project, the foundations of all the buildings are pile foundations. A ventilated underground area and vent pipes (channels) were used in the subsoil as the measures to preserve the frozen soil state. Strain-stress state of the freezing soil is to be described by a model. It could be the simplest, linear-elastic model. Moreover, it could be an elasto-plastic Coulomb-Mohr model or a model of soil hardening. At the first glance, the
423
424
Vladimir M. Ulitsky and Elena V. Gorodnova / Procedia Engineering 189 (2017) 421 – 428
latter is supposed to be the most natural one, as strength and strain soil properties grow significantly when soil is freezing. The model describing the behavior of soils at thermal and strength loading, taking into account temperature hardening was proposed by I. I. Sakharov [12] in 1995. At first approximation mechanic soil properties were set according to the following linear dependency:
A(T )
A0 1 Ki T
(1)
where А0 is a mechanical characteristic for the thawed condition, Ki – a hardening index, Т – absolute values of negative temperatures of a finite element at the considered time moment. The conducted analysis of temperature fields distribution in the subsoil of the buildings (Fig. 1 a, b) allowed evaluating efficiency of various measures ensuring safe construction and subsequent safe operation of these buildings in accordance with principle I, i.e. preserving the frozen state of soils without allowing its thawing during exploitation.
а
b Fig. 1. The thawing through of the soil under the port technical building in 50 years after construction, the boundary temperature - 0°C: (a) calculation with unventilated channels; (b) calculation with ventilated channels.
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In order to design the port territory and access ways the calculations were done for selecting the required thermal insulation thickness to preserve the natural soils in the frozen state. The following thermal-technical soil properties were accepted in the calculations: x For crushed stone: the thermal conductivity is 63 072 kJ / (m × year × °C), the heat capacity – 1 700 kJ / (m3 × °C) in the thawed and frozen states. x For sand cushion (natural fine-grained sand): the thermal conductivity in the thawed state is 25 229 kJ / (m × year × °C), the thermal conductivity in the frozen state is 31 536 kJ / (m × year × °C), the heat capacity in the thawed state – 1 656 kJ / (m3 × °C), the heat capacity in the frozen state – 1 476 kJ / (m3 × °C). x For bituminous concrete: the thermal conductivity is 22 706 kJ / (m × year × °C), the heat capacity – 1 344 kJ / (m3 × °C).
Tight bituminous concrete
Porous bituminous concrete Crushed stone Insulation - PENOPLEX
Fine sand
Geotextile Subsoil
Typical designed structure of the road pavement and subgrade
All the calculations using the simulations allowed analyzing different frozen conditions taking into account possible climate warming by 2 ºС in 50 years. At the sand water content of 0.21 and the initial temperature -50 ºС the maximum depth of thawing is 90 cm. Let us consider a typical calculation of the subgrade structure without thermal insulation (Fig. 2): The maximum soil thawing depth below the crushed stone layer was 0.78 m (Fig. 3a), as from the ground surface - 0.78+0.06+0.04+0.4= 1.28 m. Then let us determine the thickness of the heat insulator sufficient to avoid thawing of the soil below the crushed stone. If the insulator thickness is 10 cm the depth of soil thawing under the heat insulator is 3 cm (Fig. 3b).
Fig. 2. Typical designed structure of the road pavement and subgrade.
3.2. Simulation results and discussion The analysis of the calculations resulted in drawing the following conclusions: x Construction of a 1.4-m-high ventilated underground area (for the office building) guarantees preservation of the subsoil in the frozen condition for the complete designed period of the building exploitation. The thawing depth under the building in summer does not exceed the seasonal values, that does not pose any risk for pile foundations. The technological regime of the underground area condition should be provided during the period of the building maintenance. This sort of construction is successfully used in the Northern cities provided the mode observation of their maintenance in the summer time [13].
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x It is inadmissible to construct a compressor station, a technical building for ground support equipment, a boiling house, resting on 10-meter-long piles without additional measures for frozen soil preservation, because the depth of the soil thawing will exceed the length of piles during 50 years of the buildings maintenance. It may cause unexpected soil subsidence and general loss of stability of the subsoil of the buildings. x In order to preserve the frozen state of the soils in the subgrade of a compressor station, a technical building for ground support equipment, and a boiling house there was suggested and calculated the solution to lay pipes with forced air ventilation in winter. According to the calculations results, the area of thawing does not spread below the middle section of the cooling pipes that ensures the reliable operation of the pile foundations of the buildings. x In order to prevent settlements of floors a coarse-grained soil cushion should be filled up to the top of the pipes. Only the forced ventilation of air, which is supplied by means of fans in winter, can guarantee the efficiency of horizontal pipe operation in the subsoil. The proposal calculation methods upgrade to a new level the works associated with the prediction of development of possible deformations for a large range of transport facilities (railroads and highways, ports and airports) as well as stresses in soils during their freezing and thawing. The comparison of the results of the obtained calculations with the observation data and the failure states occurred in the latitudinal railway Salekhard-Igarka supports the state-of-theart methods of numerical modeling of difficult geotechnical situations.
Fig. 3a. The maximum soil thawing depth below the crushed stone layer without thermal insulation - 78 сm, Layers up to down: bituminous concrete – 10 cm, crushed stone – 40 cm, finite sand – 10 cm, subsoil
Fig. 3b. The maximum soil thawing depth under the10-cm-thick thermal insulator for the subgrade structure – 3 cm, Layers up to down: bituminous concrete – 10 cm, crushed stone – 40 cm, insulation – 30 cm, finite sand – 10 cm, subsoil
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3.3. The results of theoretical and experimental studies The abovementioned calculations of the transport infrastructure in the software complex “Termoground” have been tested through operation of anchor foundations. The test grounds with the experimental anchor foundations were located in East Siberia in the area of the cities of Angarsk and Usolie-Sibirskoe, the Irkutsk district. In situ investigations of anchor foundations have been carried out in different hydrogeological conditions in order to evaluate factors influencing stability of these foundations at development of shear forces of frost heave and normal pressures in time. The tested foundations have the form of reinforced concrete pillars of 0.25х0.25 m in the crosssection and the length of 3.9 m with special studs on the top to fix the loading deck. The field measurements of normal pressures have been made at the level of the upper surface of the anchor slab. For this purpose, the upper part of the anchor slab has been instrumented with acoustic pressure gauges which data have been systematically recorded and observed. The experiments have shown that pressure distribution depends on such factors as: the nature and magnitude of frost heave; contact links with the foundation; speeds of freezing; physical-mechanical properties of thawed and frozen soil. Distribution of normal pressures along the upper plane of the anchor foundation is demonstrated in fig. 4. Soil transition towards the thawed state leads to gradual reduction of pressures transferred to the anchor. The results of the numerical modeling have shown good agreement with the results of the large-scale field experiments.
Fig. 4. The graphs of distribution of normal pressures along the upper plane of the anchor foundation in time: 1 – the experiment; 2 – the calculation.
4. Conclusions Having analyzed the failed experience of transport construction in the previous century, namely the construction of a part of the railway Salekhard-Igarka, there has emerged the necessity of applying modern numerical modeling at all stages (investigations, design, works implementation and subsequent monitoring) of creating the latitudinal Northern Route along the Arctic coast. It will provide safety of buildings and structures in the difficult climatic and soil conditions. Together with solving the basic transport problems one should take into account the related regional factors, which provide sustainable development of this important Russian territory: natural-geological, environmental, and socioeconomic [14, 15]. Our research allows solving issues of territorial planning at the level of the entities of the Russian Federation located along the Arctic coastline. For the long run they can be classified as follows: - enhancing living standards taking into account the specifics of the life of the indigenous peoples of the north; - minimizing emissions of harmful substances polluting the area due to active development of oil and gas fields associated with extraction of rare mineral resources and transportation of the related cargo; - drafting regulatory documents on environmental protection and preservation of permafrost bulks of soils, which can guarantee the stability of buildings and structures;
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- creating permanent automated geo-ecological monitoring based on the data of mathematical modeling taking into account a possible climate change. Therefore, the presented fragment of calculations using the software complex “Termoground” allows ensuring sustainability of the whole infrastructure of the largest northern ports (Sabetta, Tanalau etc.), including the buildings of considerable heat release, even at the stage of design. References [1] M. Minin, Prospects for development of the coastal infrastructure of the Northern Sea Route on the basis of design experience of the seaport in the Teriberskaya Bay and the seaport of Sabetta, J. “Hydrotechnics”, # 4 (2014), 101-106. [2] K. Wojtkowski, The USSR Academy of Sciences, The Siberian Branch. The Institute of Permafrost Studies: Strength and creeping of frozen soils, Moscow: The Publishing House of the USSR Academy of Sciences, 1963, 217 p. [3] S. Kudryavtsev, I. Sakharov, V. Paramonov, Freezing and thawing of the soil (practical examples and finite element calculations), St. Petersburg, The Group of Companies "Georeconstruction", 2014, 247 p. [4] V.N. Paramonov, I.I. Sakharov, Mathematical modeling of thermal and deformation processes in problems of freezing and thawing of soils. Proceedings 5-th Int. Geotechnical Symposium, Geotechnical Engineering for Disaster Prevention and Reduction. IGH5, 22-24 May 2013, Incheon South Korea, (2013) 122-127. [5] S.A. Kudryavtsev, V.N. Paramonov, V.M. Ulitskii, I.I. Sakharov, Bed – Structure System Analysis for Soil Freezing and Thawing Using the Termoground Program, Journal Soil Mechanics and Foundation Engineering 52 (5) (2015) 240–246. [6] O. Grindland, Frost protection of structures in the road network, Frost I Jorn. # 108 (2005) 41-43. [7] W.G. Spencer, A. Hermansson, Frost heave and water uptake relations in variably saturated aggregate base materials, Transportation Research Board 82nd Annual Meeting, Washington (2003) 126-142. [8] F. Işık1, S. Arasan, A. S. Zaimoğlu, R. K. Akbulut, Effect of moulding water content on freezing-thawing behavior of compacted two clayey soils, in: XV Danube - European Conference on Geotechnical Engineering (DECGE 2014) H. Brandl & D. Adam (eds.) 9-11 September 2014, Vienna, Austria (2014) 590-597. [9] M.M. Zhou, G. Meschke, A three phase thermos-hydromechanical finite element model for freezing soils. Int. J. Numer. Anal. Meth. Geomech. 37 (2013) 3173-3193. [10] Y. Yamamoto, S.M. Springman, Axial compression stress path tests on artificial frozen soil samples in a triaxial device at temperatures just below 0ºC. Canadian Geotechnical Journal 51 (10) (2014) 1178-1195. [11] Per Lindh, Nils Rydén, The effect of different binders on freeze durability of stabilized soil, Proceedings of the 17th International Conference on Soil Mechanics and Geotechnical Engineering (2009) 268-270. [12] I. Sakharov, Physical mechanics of the cryoprocesses in soils and its applications at evaluation of deformations of buildings and structures, Synopsis of ScD, Tech. Thesis, Perm. 1995. 44 p. [13] N. Tsytovich, General and applied permafrost soil mechanics: Textbook, 2nd ed., Moscow, Book House "LIBROKOM", 2010, 448 p. [14] Т. Titova, The Methodology of the complex evaluation of the influence of new technologies on geo-ecological situation, The Journal of the Research Institute of Rail Transport, #2 (2005), 98. [15] L.B. Svatovskaya, A.S. Sakharova, M.M. Baidarashvili et al., New geo-protection technologies at construction and reconstruction of railways, St. Petersburg State Transport University, St. Petersburg 2012, 81 p.