Engineering issues in Russian permafrost research

Olga I.Alekseeva

(Melnikov Permafrost Institute SB RAS，Yakutsk 677010，Russia.)

0 Introduction

Geocryology emerged as a distinct science in the 1920s at the cross-roads of geological，geographical，geophysical and engineering disciplines in response to the proposed development of the vast permafrost region of Siberia.Its foundations were laid by Mikhail Sumgin，whose 140thanniversary was celebrated by the internationalscientific community in 2013[1]. His student and follower，Pavel Melnikov established a Permafrost Institute in Yakutsk which now bears his name.Permafrost engineering studies as a subdiscipline within geocryology owes its inception to Nikolay Tsytovich，an internationally recognized expert in the fields of soil mechanics，foundation engineering and engineering geology[2-4].

Geocryologists utilize methods developed by allied disciplines，as well as approaches developed specifically for permafrost studies.Russian researchers have contributed to the development of cross-disciplinary areas in permafrost research，including thermal rheology of frozen soils[5-6]，cryolithology[7]，thermal physics of landscapes[8]，permafrost landscape studies[9-10]，groundwater geochemistry of permafrost areas[11]，frozen peats as a foundation material[12]，geothermics of the frozen zone of the lithosphere[13]，theory of cryogenesis of the lithosphere[14]，basic theory of engineering structure-frozen ground interaction[15]，engineering cryolithology[16-17]，fundamental concepts and principles of utilizing cryogenic building materials in frozen ground areas[18-19].

Based on the theories established，much attention has been given to the development of thermal design methods in permafrost geocryology as a whole，as well as calculation methods in frozen soil mechanics in particular.A few highlights will be mentioned here.Grechishchev[20]derived an equation relating strain rate and stress for time-variable creep processes and obtained numerical values for parameters characterizing tension，compression and shear creep behavior of frozen sands and silts.Kamensky[21]developed empirical expressions to determine the time for freezing systems to operate until frozen soil cylinders merge into a continuous frozen wall，considering the mutual effect of adjacent freeze pipes.Pavlov[22]proposed approximate methods for calculating soil freeze depth under snow cover and insulation covers，as well as mean annual soil temperatures.Studies by Goncharov[23]resulted in the development of an analytical design method for thin soil retaining walls，an aerodynamic analysis procedure for at-grade ventilated foundations，analytical equations for determining the air flow volumes and rates for heat transfer through the ventilated foundation，and a preliminary procedure for thermal design of thin-walled shell foundations. Gaydaenko[24]proposed a design model for bored，cast-in-situ piles based on bearing capacity tests.Guryanov[25]stated and solved a problem of mineshaft support buckling within a thaw zone，derived an equation for buckling of elements on elastic foundation，and presented design procedures for different conditions of static equilibrium and support deformation.Based on field experimentation to study the various relationships controlling heat transfer in thermosyphons，Makarov[26]developed design guidelines for thermosyphon foundations.Rastegaev et al[27].proposed an analysis method for selecting the construction principle in permafrost.A thermal analysis software package was developed by Kovalenko[28]for permafrost stabilization and ground freezing applications.The program takes into account phase change，groundwater flow，snow depth，effect of refrigeration systems，thermal effects from buildings and structures，and variations in soil type.

Many of the developments and procedures advanced by Russian permafrost researchers have been implemented into engineering practice，including:

-pile foundations incorporating an air space between the structure and ground surface[28-31];

-buried pipeline construction mode[32];

-thermal piles–reinforced concrete foundation piles with incorporated cooling devices[27];

-bored，cast-in-situ pile foundations[33];

-surface foundations(shell foundations，spatial foundations of structural type，and slab cellular foundation)[34];

-construction techniques for underground structures(cold accumulators and gas，fuel and food product storages)in permafrost[35-36];

-techniques for ensuring thermal and structural stability and seepage control in frozen core dams[37-38];

-engineering means to control thermal regime of frozen foundations[27，39-43].

More than thirty years of frozen ground engineering research in Murmansk，Norilsk，Krasnoyarsk，Igarka and Yakutsk allowed generalization and formulation to be made of the most significant scientific findings and practical guidelines.The foundation engineering philosophy in permafrost regions is to successively use the permafrost as an excavation material，then as a foundation material and，lastly，as an enclosing material，with the predominant approach being preservation of the natural，pre-construction condition，viz.，prevention of ground warming and thawing in frozen ground and prevention of freezing in thawed ground.

1 Investigations and methods

Permafrost research emphasis in the late 20thand the early 21stcenturies has focused on the potential impacts of global climate warming on the strength and stability of frozen foundations.The recent period of warming has been observed from the 1970s and is predicted by some researchers[44-45]to continue up to 2015-2020.In Central Yakutia，permafrost temperatures in undisturbed areas exhibit no general warming trend in spite of the observed increase in mean annual air temperature by over 2℃.Theoretical and experimental investigations have been conducted in this respect.At monitoring sites with 30 or more years of record，both warming and cooling of permafrost temperatures are observed[46-48].Active-layer depths in different geographical zones respond differently to global climate change.This is because the process of seasonal soil thaw occurs over a short time period，while long-term climatic variations are determined by longer winter periods.

Climate warming significantly affects the rate of all geocryological processes.In general，permafrost has high thermal inertia，but long-term monitoring studies of the moisture and temperature regimes in different horizons of permafrost indicate significant detrimental effects of the processes occurring in its upper layer[49-50].report the rapid and widespread development of thaw subsidence，frost heaving，solifluction，and thermokarst in Yakutsk with attendant damage to pavements，utility lines，embankments and foundations.Inundation and water-logging by suprapermafrost water is one of the most serious problems for the stability of building foundations and support structures in Yakutsk.The soils are waterlogged both by fresh water and highly saline groundwater or cryopegs[51-53].

Modeling studies suggest that climate warming may lead to the development of residual thaw zones in the vertically continuous permafrost of Vorkuta，Novyy Urengoy and Yakutsk[54-55].Conventional methods of solving permafrost foundation problems，such as underpinning or greater embedment depths，will not work in this situation.Special engineering techniques will be required，such as improved foundation designs，or artificial control of the thermal regime of frozen foundation materials.New spatial foundation designs，such as shell foundations，spatial foundations of structural type，and slab cellular foundations，have been developed in Russia，which are constructed without ground disturbance and are adapted to ground warming and differential settlement[56].Unfortunately，their application to engineering practice is hindered by the absence of approved building standards.

Industrial techniques for radical cooling of foundation materials with thermal piles were successfully applied forty years ago in the city of Mirny.The use of thermal piles for a four-story residential building in Yakutsk，as well as for residential construction in Oganer，a satellite town of Norilsk，reduced the design ground temperatures by more than 1.5℃，thus improving the reliability of the pile foundations.It is known that decreasing the soil temperature from －0.3 to－1.5℃ will increase the bearing capacity of a pile foundation by 2.5 times，therefore artificial freezing is widely accepted as the most versatile and reliable means to improve soil strength.The efficiency of cooling devices is increased when they are used in combination with insulation materials embedded in the subgrade soil.

A foundation stabilization method was developed by the Permafrost Institute in the 1980s which integrated the at-grade foundation，high-performance insulation(plastic and polyurethane foams)and convection cooling concepts.This was an alternative to pile foundations with air spaces.Essentially，the foundation design consists of a fill pad and horizontal natural convection cooling pipes compatible with refrigeration units for increased reliability.The cooling system is a closed unit filled with easily liquefiable refrigerant(ammonia)operating as a two-phase thermosyphon.

Studies of the Laboratory of Permafrost Engineer-ing，Permafrost Institute，on combined cooling effects of thermosyphons and high-performance insulation materials demonstrated the efficiency and feasibility of such an integrated approach.Insulation materials in combination with cooling devices proved to completely prevent deep seasonal thaw，even in areas of accidental leaks from water and heating lines.

Roads and railroads are important subjects of research in permafrost geocryology.The stability of embankments remains an issue of major concern.The most common methods of preventing embankment deformation are to lower the mean annual temperature in the underlying ground and maintain it in a frozen condition through the use of snow removal，painting，snow sheds，vertical and horizontal thermosyphon systems，and geomembranes，or to replace ice-rich materials(ice lenses)with thaw-stable soils prior to construction[57-61].

Main oil and gas pipelines traverse wide regions with highly variable permafrost and geotechnical conditions.This requires different modes of construction depending on site specific conditions.It is optimal to construct pipelines in the buried mode to reduce the impacts from external factors.However，this does not eliminate the problems of thaw settlement and frost heave that may cause pipe rupture and leakage[62-63].The concept of terrain and infrastructure protection against adverse frost-related processes developed by the Melnikov Permafrost Institute is methodologically based on the systems approach that would provide tied decisions to mitigate or avoid the adverse impacts of the pipeline on the permafrost environment and the feedbacks from the altered environment[64-65].

Extensive research has been carried out at the Melnikov Permafrost Institute to solve an economically crucial problem of improving the reliability of low-head dams on permafrost.Research findings have been used in the design，construction and operation of many small dams in the Russian permafrost regions，as well as in the development of relevant standards and guidelines[43，66].

In applied research，Russian geocryologists seek to develop new technologies aimed at ensuring safety of infrastructure under changing climate conditions and increasing human activities.The important developments include the system of geophysical monitoring methods，instruments and technology for large dam and mining projects，implemented at the Vilyui River hydro schemes and the Mir，International and Udachnaya diamond mines[67-68];and the establishment of geocryological monitoring programs in support of megaprojects，such as the Amur-Yakutsk Railroad，the Lena，Vilyui and Amur Roads，and the East Siberia– Pacific Oil Pipeline，as well as several mining projects[69-70].

Significant developments have been made by the Melnikov Permafrost Institute in the field of energy-saving technologies[71].The first phase of a seed repository completed recently in Yakutsk implements the patented technology of using the natural cold resources for low-cost，safe long-term storage of seeds in permafrost at stable temperatures and moisture contents.The Yakutsk seed repository in permafrost is the first of its kind in Russia.A Russian patent has also been granted to the Institute for a method of long-term seed conservation.

Developing design，construction and operation guidelines for various types of infrastructure is an important outcome of permafrost engineering research.Zhang et al.[72]have formulated fundamental principles and requirements related to small dams on permafrost and developed design and construction guidelines applicable for new construction，as well as for restoration of existing water supply and reclamation dams.Vlasov[73]have established guidelines for the design and construction of pile foundations in thawing and thawed ground in the Magadan Oblast.They are applicable when the active approach is adopted in an area of sporadic，discontinuous or continuous permafrost.Goncharov and Popovich[74]have prepared design guidelines for at-grade spatial ventilated foundations intended to maintain the permafrost in a frozen state.The guidelines address static and thermal analyses，structural design，and installation procedures.

Adequate prediction of the stability of existing and new infrastructure and its interaction with the environment requires engineering-geological mapping at differ-ent scales and database development.The Melnikov Permafrost Institute has completed a 1∶2500000-scale engineering-geocryological map covering the Republic of Sakha(Yakutia)and Magadan Oblast，as well as the adjoining areas of Krasnoyarsk Krai，Irkutsk Oblast and Khabarovsk Krai[75].A long-term cooperative mapping program undertaken by the Melnikov Permafrost Institute，the Diamond and Precious Metal Geology Institute and the Republic of Sakha(Yakutia)Committee for Geology and Mineral Resources Development has resulted in a 1∶1500000-scale engineering-geological map of the Republic of Sakha/Yakutia.The map compiled in ArcGis version 10 provides recent data on soil/rock type，cryolithology，suprapermafrost water chemistry and properties，as well as permafrost-related landforms and surficial processes.The Yakutia Geocryological Database has been developed to provide data and information that can be used in modeling changes in stability of engineering structures and bearing capacity of soils，as well as in developing environmental protection and engineering management strategies for permafrost areas[76].A database developed by Alexeev and Kamensky[77]contains information on fundamental Russian-language publications on engineering cryology.

2 Summary

Today，permafrost engineering research in Russia is driven by the prospects of expanded and accelerated development of the country's northern and eastern areas.Extensive，but sensitive infrastructure already exists in the permafrost regions，including oil and gas production wells，main pipelines thousands of kilometers in length，surface and underground mines，hydropower stations，large and small communities，roads and railroads，airfields，and ports.New hydropower，mineral and petroleum resource development projects and related transportation infrastructure have been proposed or underway.

As in the early years of its history，engineering geocryology is challenged today，in the 21stcentury，to adequately respond to the needs of practice.The current level of permafrost engineering research is quite high in most areas.This suggests that further studies will likely be directed to interpretation of existing knowledge，analysis of results，monitoring of permafrost conditions，as well as development and implementation of design and construction standards and guidelines，integrating considerations of current and future permafrost conditions.Permafrost engineering is intimately linked to mechanics，physics and physical chemistry of frozen，thawing and thawed ground.Russian research in these areas was limited in the last quarter of the twentieth century.The first decade of this century has witnessed a regained interest in these topics，as demonstrated by the contributions to the Ninth International Symposium on Permafrost Engineering held in September 2011 in Mirny，Russia[53].Expanding research on the thermophysical state of permafrost remains a high priority for research to facilitate global assessments and predictions，as well as to develop international standards for permafrost monitoring.

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