Introduction

Climatologists have predicted that the coming centurywill bring global warming of the Earths climate as aresult of the developing greenhouse effect. According tomany climatologists, an increase in the annual averageair temperature by 1¡C to 4¡C is likely. Such warmingwill inevitably lead to changes in the state of permafrostand its geotechnical properties, which in turn will affectthe reliability and durability of engineering structuresin the Far North. The first estimations of such variationwere made previously by the authors (Vyalov et al.,1993a). These estimations related only to specific loca-tions within the permafrost zone.

This paper shows the results of numerical simulationof the change in thermal regime and geotechnical prop-erties of permafrost in the entire permafrost region ofRussia caused by global warming of the Earths climate.The simulation was carried out assuming an increase inthe modern annual air average temperature Ta byÆTa=2¡C and 4¡C during the next 60 years.

Methods

A universal computer program was developed inclu-ding two blocks: the thermal block simulates variation

in thermal regime and the mechanical one simulatesvariation in the strength properties of frozen soils. Thethermal model provides the following: representationof the variable air temperature in the annual cycle assuccessive half-waves of the winter and summer sinu-soids; constant trend in the annual average air tempera-ture (0.033 and 0.067¡C per year); the difference of thewinter and summer air temperature amplitudes andtheir annual increments in the course of warming; heatflow which is constant in time at the lower boundary ofthe simulated body; the presence of vegetation andsnow covers on the ground surface with thermal resis-tance values changing during the year; variation in soilthermal properties in the temperature range due to achange in the unfrozen water content of the soil as tem-perature changes. The mechanical model simulatesvariation in time in long-term strength of the frozen soilcaused by both its creep and temperature variability, aswell as the variation in bearing capacity of buildingfoundations conditioned by this strength.

Taking into account the meridional and latitudinalvariations in permafrost temperature and thickness, theentire permafrost region is divided into four geother-mal zones based on the degree of sensitivity of frozensoils to thermal influences. This division is madedepending on the annual average temperature of frozen

Abstract

The paper examines potential changes in the thermal regime and geotechnical properties of permafrost in thepermafrost regions of Russia as a result of future climatic warming. The investigations were conducted bymathematical simulation of these processes using a computer program, with increases in annual average airtemperature of 2¡C and 4¡C by the middle of the next century. The entire permafrost region was divided intofour geothermal zones based on the degree of sensitivity of frozen soils to thermal actions. The calculationswere performed for 4 lines of longitude. The changes in average annual temperature, depth of thaw, long-termstrength of frozen soils and bearing capacity of foundations caused by warming were determined for each geot-hermal zone. As a result, the potential changes in the state and propagation of the permafrost were demonstrat-ed and their possible consequences for the durability of foundations were determined.

S.S. Vyalov, et al. 1097

INFLUENCE OF GLOBAL WARMING ON THE STATE AND GEOTECHNICALPROPERTIES OF PERMAFROST

S.S. Vyalov1, A.S. Gerasimov2, S.M. Fotiev3

1. Moscow State Civil Engineering University, Moscow, Russia

2. The North-Frost Laboratory, St. Petersburg, Russia 6-50, Chernyshevskogo ploschad, St. Petersburg, 196070, Russia

e-mail: tsan@comset.net

3. Cryosphere Institute, Moscow, Russia

soils Tz (taken in accordance with the Russian regula-tions at the depth of annual zero amplitude, equal to10 m): Zone I (0, -1¡C), Zone II (-1, -3¡C), Zone III (-3, -7¡C), Zone IV ( £-7¡C).

Zone I is characterized by permafrost, discontinuousin areal extent and depth, 0 to 50 m thick, and by thepresence of unfrozen areas and scattered permafrostbodies. The permafrost in this zone is very sensitive tohuman-induced and thermal change. Zone II has per-mafrost 100 to 200 m thick occurring as bodies eitherseparated by taliks or continuous. The permafrost inthis zone is moderately-sensitive to human-inducedand thermal change. The clayey permafrost soils ofZones I and II are in a plastic frozen state. Permafrostoccupies most of Zone III with a thickness 100 to 1000 m and more. The permafrost in this zone is of low-sensitivity to the aforementioned external influences.Zone IV is situated along the coast of the Arctic Ocean.This zone is underlain virtually everywhere by per-mafrost 30 to 1500 m thick that has a very low sensitivi-ty to external influences. The soils of zones III and IVare generally solidly frozen; saline soils may be anexception.

The calculations were performed for geographic local-ities characteristic of each of these zones as applied tothe four lines of longitude: 57.5¡, 75¡, 100¡ and 150¡E.

For comparability of the results, the calculations wereperformed for a single type of soil: non-saline suglinok(clayey silt) having a total moisture content wtot=0.25(the computations on PC carried out with the participa-tion of A.I. Zolotar).

Results

The results of the calculation of annual average tem-peratures and maximum thaw depths with the climatewarming are given in Table 1. As Table 1 shows, annualaverage soil temperature Tz increases as the climatewarms, and the absolute values of this increase (ÆTz2,ÆTz4) are greater in the North. Such variations occurthroughout the permafrost region and are illustrated byFigure 1 which shows the relationship between ÆTz2,ÆTz4 and Tz. As we can see, the form of the relationshipfor all the design meridians and geothermal zones islinear. It is satisfactorily described by: ÆTz2=0.47-0.12Tz and ÆTz4=0.95-0.21Tz. However, thislinearity is true only when |Tz|> ÆTa. Moreover, somedecrease in ÆTz2 and ÆTz4 values can be observed in thesouthern areas of the geothermal Zone I as Tz decreases.

The 7th International Permafrost Conference1098

Meridians Zones Localities Tz DTz2 DTz4 d Dd2 Dd4

57.5°� E I Pechora -0.3 0.3 1.5 217 995 1845

long II Adzva-Vom -1.2 0.3 0.4 123 101 412Varandey -3.1 0.8 1.2 78 32 107

I Surgut -0.2 0.4 2.2 222 completethawing

Numto -0.8 0.1 0.2 142 129 512II Urengoy -1.3 0.2 0.3 119 60 345

75°� E long Nyda -2.7 0.7 1.0 87 33 93

III Samburg -3.5 1.1 1.8 79 17 86Cape Kamenniy -6.2 1.4 2.4 57 18 38

IV Kharasavey -7.8 1.3 2.8 15 13 27Tambey -8.3 1.5 2.6 26 14 32

I Kerbo -1.0 0.2 0.3 150 90 366

100°� E long II Tembengi -3.0 0.6 1.0 100 27 73

III Yessey -6.9 1.2 2.3 71 14 71IV Taimyry -12.0 1.8 3.5 17 10 19I Palatka -0.8 0.2 0.3 146 132 528

150°� E long III Zyryanka -4.5 1.0 1.6 90 19 48

Ozhogino -6.6 1.4 2.3 61 16 35IV Chokurdakh -10.3 1.7 2.9 37 13 26

Table 1. Increase in the annual average temperature (¡C) and depth of thaw (cm) due to warming

Notes: Tz - annual average temperature of frozen soils at the beginning of warming; ÆTz2 and ÆTz4 - rise in annual average tem-perature Tz on warming by 2¡C and 4¡C; d - depth of thaw of frozen soils as of beginning of the warming; Æd2 and Æd4 - increasein the depth of thaw on warming by 2¡C and 4¡C.

The averaged ÆTz2 and ÆTz4 values at the northernboundaries of the geothermal zones are as follows: onwarming by 2¡C: 0.1, 0.8, 1.3 and 1.9¡C for Zones I, II,III and IV respectively; on warming by 4¡C: 0.2, 1.7, 2.4and 3.5¡C respectively.

An increase in the annual average temperature offrozen soils leads to an increase in the depth of thawand to a corresponding lowering of the permafrost table(Table 1). As this takes place, ÆTz2 (ÆTz4) valuesdecrease considerably from the south to the north andin the northern areas become quite small (cm). Thawingis very significant in Zone I and partially in Zone II(three meters and more), and complete thawing of per-mafrost is possible in the southern part of Zone I.

Variation in permafrost thermal regime results inchanging the boundaries of the geothermal zoneswhich are displaced northwards. Let us consider thisprocess by an example of the meridian 75¡E long(Western Siberia) (Vyalov et al., 1997). This example isillustrated by Figure 2 showing variation in the frozensoils� thermal regime according to the data from Table 1and the resulting shift of the geothermal zone boun-daries. The averaged values of the meridional width ofthese zones before and after warming, as well as theaveraged values of shifts of their southern and northernboundaries are shown in Table 2.

An increase in the temperature of permafrost soilswill naturally lead to a decrease in their long-termstrength. Let us consider the long-term shear strength tand the long-term strength of adfreezing frozen soilwith the pile surface taf corresponding to the designservice life of a structure as characteristics of soilstrength. The taf strength dependence on temperaturewas used in the numerical calculations based on thedata of the Russian regulations and the t/taf ratio wasfixed constant and equal to 1.35 according to the analy-sis of numerous experiments. The computations wereperformed with the extreme values of the intensity ofdecrease in the long-term strength in time; then thecomputed strength values were averaged (Gerasimov,1984).

The results of the numerical calculations of thedecrease in strength for all the design localities areshown in a generalized form in Figure 3, where all thedata are represented for all four meridians. The long-term strength of soils before (t0) and after warming (t2,t4) are shown. The calculations were carried out for

S.S. Vyalov, et al. 1099

Figure 1. Rise in the modern annual average temperature of permafrost Tzon warming by 2¡C and 4¡C (ÆTz2 and ÆTz4).

Zone # I II III IV

at Ta 490 220 380 360*

Zone width, km at Ta+2°�C 390 270 470 140*

at Ta+4°�C 280 280 540* KSWA

at Ta+2°�Csouthern 80 130 220 KSWA

Shift of zoneboundaries,

northern 180 80 130 220**

kmat Ta+4°�C

southern 140 200 360** KSWA

northern 350 140 200 360**

Table 2. Variation in the width of the geothermal zones and shift of their boundaries as the modern annual average air tem-perature Ta rises by 2¡C and 4¡C

Notes: * zone width within the dry land; ** zone boundary shift within the dry land; KSWA - Kara Sea Water Area.

various depths, however, Figure 3 shows the results ofcalculations for the depth equal to 3.5 m below the sur-face, since such a depth is characteristic of the depth forlaying foundations in permafrost. The values of t0, t2,t4 are calculated taking into account temperature varia-tion during the design period tu=60 years (Vyalov et al.,1993a; Gerasimov, 1984).

The calculations show that with consideration for thevariation of temperature in the process of warming,including its periodic changes in annual cycles, the ne-gative influence of climate warming upon frozen soils'strength is quite substantial. Considering the variationof strength with depth, we can see from the calculationsthat the intensity of the strength lowering decreases asthe depth increases. All the predictions are for non-

saline suglinok (clayey silt), whereas other types of soilscan be affected by warming differently. In particular,the calculations show that the decrease in strength onthe warming would be more significant for saline soils.

The strength calculation data can be used to evaluatevariations in bearing capacity of building foundationsfollowing warming. For example, Figure 4 illustratesthe results of the numerical calculations of the pilefoundation bearing capacity. The bearing capacity wasdetermined by the formula

where w is a pile perimeter; h¦ - length of a pile with-in permafrost; z - depth; a - coefficient; A - pile lowerend area.

The 7th International Permafrost Conference1100

Figure 2. Variation in the annual average temperature of permafrost Tz and boundaries of the thermal zones along the 75¡E line of longitude on warming by 2¡Cand 4¡C.

A - profiles of latitudinal variations in annual average permafrost temperature (Curve 1), on warming by 2¡C (Curve 2), and 4¡C (Curve 3); B - thickness andprevalence of permafrost layer; C - shift of the geothermal boundaries of Zones I-IV (made by S.M. Fotiev)

F = +òW Z dZ AafO

h f

t a t( )

The calculations were carried out for all the designgeographic localities, however, as is seen on Figure 4,the data obtained for all four meridians are representedby generalized curves.

Discussion and Conclusions

The analysis of the variation in thermal and mechani-cal properties of permafrost resulting from future cli-mate warming allows an evaluation of the change inthe state of permafrost which is critical for the durabili-ty of the structure foundations.

The increase in annual average air temperature by themiddle of the next century by 2¡C and 4¡C will lead to asignificant rise in the annual average temperature ofpermafrost and depths of thaw within the entire per-mafrost region of Russia, with a corresponding shift ofthe geothermal zones� boundaries to the north. This risein temperature decreases, as a rule, from the north tothe south, while the depth of thaw increases in the samedirection according to the degree of sensitivity of per-mafrost soils to external influences.

In the southern Zones I and II where permafrost isvery sensitive to thermal change, even a slight air tem-perature rise will cause an increase in the areas occu-pied by discontinuous permafrost and permafrostislands will develop. With warming of 2¡C and 4¡C,permafrost with an annual average temperature of -0.5¡C to -0.6¡C will thaw everywhere, to a depth of atleast 10 m. The area occupied by Zone I will decreasesignificantly. In other words, such warming will resultin permafrost degradation in the southern regions, andthe southern boundary of the permafrost region willshift hundreds of kilometers to the north.

The northern Zones III and IV will not face progres-sive permafrost thawing, but an increase in design tem-peratures will take place, without altering the solidlyfrozen state of soils in any substantial part of the territo-ry. Saline soils, which can be in plastic frozen state in awide range of negative temperatures, are an exception.

The degradation of permafrost will sharply affect itsecological condition and the reliability of buildings.Common paludification of thawing territories, develop-ment of thermokarst lakes, intensive solifluction of soilson slopes, subsidences of territory surface and buildingfoundations, etc. will take place. In turn, the develop-ment of subsidence phenomena will cause loss of stabil-ity of engineering structures, particularly those asso-ciated with transportation.

The rise in the design temperatures of soils caused bythe warming will lead to a decrease in the strength ofsoils and bearing capacity of building foundations. The

S.S. Vyalov, et al. 1101

Figure 3. Decrease in frozen soilsÕ strength at the depth of 3. 5 m on thewarming.t0 - long-term strength of soil at the depth 3.5 m below the surface at thebeginning of warming; t2 and t4- strength of the same soil with Ta rising by2¡C and 4¡C.

Figure 4. Decrease in bearing capacity of a pile (cross-section - 0.3 x 0.3 m,length in soil - 7 m) on warming: F0, F2 and F4 - bearing capacity before andafter warming by 2¡C and 4¡C.

degree of warming effect will increase from the north tothe south following the variation in sensitivity of thegeothermal zones to external influences. Nearly com-plete loss of bearing capacity of foundations as a resultof permafrost degradation will occur in the southernpart of the permafrost region where the annual averagetemperature of soils ranges from 0¡C to -0.6¡C. The restof the permafrost region will have bearing capacitydecreased. In particular, for soils 3.5 m deep, thedecrease in strength for the northern boundaries of thegeothermal Zones I-IV will on the average be as fol-lows: on warming by 2¡C: I - 40%, II - 20%, III - 10%, IV- 5%; on warming by 4¡C: I - 100%, II - 40%, III - 20%, IV- 10%. Since the design soil strength characteristicstaken as of the beginning of the warming are based onthe design service life of a building equal to 50 to 100years, then a decrease in strength as a result of thewarming will lead to a shortening of this life, i.e. to adecrease in durability of buildings erected where per-mafrost is to be preserved around the foundation.

The negative consequences of climate warming uponthe state of permafrost can be partially and in somecases completely neutralized by special engineering-technical measures. Such measures can be aimed toincrease bearing capacity of foundations: on one hand,with the help of the construction methods worked outbased on the lowered strength values of frozen soils,and on the other hand - increasing this strength by cooling building foundations

The construction methods can include variation ofsizes and design of foundations, as well as adaptationof the system above-ground structures - foundation -

base to raised deformations. Cooling of the foundationscan be carried out by supplying natural cold in one wayor another into the base soils, since annual average tem-perature of the outside air is lower than that of per-mafrost; for example, seasonally operated coolingdevices can be used (Vyalov et al., 1993b). Applicationof the above methods is most expedient in geothermalZones II-IV.

In Zone I and partially in Zone II, where permafrostdegradation can take place, it may prove expedient toconstruct buildings using permafrost soils in thawingstate. In this case it is necessary to carry out subgrading(by means of preliminary permafrost thawing, etc.) andconstructive adaptation of buildings to the raised settle-ments of a base.

The above-mentioned measures are designed forapplication in new construction, where the influence ofclimate global warming should be taken into account.As for existing buildings erected without considerationfor the global warming, neutralization of its negativeconsequences can mostly be carried out by cooling per-mafrost soils. In all cases, it is expedient to monitor thethermal regime of permafrost, particularly in existinglocalities, for important buildings and during largescale construction, in order to organize necessary pre-ventive measures in time.

The 7th International Permafrost Conference1102

References

Gerasimov A.S. (1984). Foundations of light buildings on per-mafrost. Stroiisdat, Leningrad (153 pp) [in Russian]

Vyalov S.S., Fotiev S.M., Gerasimov A.S., Zolotar A.I.(1993b). Ensuring the permafrost ground bearing capacityin the course of the climate warming. Bases, foundationsand soil mechanics, 6, 2-6 [in Russian].

Vyalov S.S., Fotiev S.M., Gerasimov A.S., Zolotar A.I.(1997). Variation of boundaries of the geothermal zones inthe Western Siberia on the global warming of the climate.Hydrotechnical construction, 11, 9-13 [in Russian].

Vyalov S.S., Gerasimov A.S., Zolotar A.I., Fotiev S.M.(1993a). Ensuring structural stability and durability inpermafrost ground areas at global warming of the Earth�sclimate. In Proceeding 6th International Conference onPermafrost, Beijing, China, pp. 955-960.