Year-round cooling and thermal stabilization of water-saturated soils under engineering structures

Vladimir Moiseev,Nicolai Vasiliev,Tatyana Komarova,Olga Komarova

1.Department ofMathematics,EmperorAlexanderI St.PetersburgStateTransport University,MoskovskiyAve.,9,St.Petersburg190031,Russia

2.Static Research of Soils Laboratory,B.E.Vedeneev VNIIG,JSC,Gzhatskaya 21,St.Petersburg 195220,Russia

3.DISIST Scientific Center,Novocherkasky Ave,40,St.Petersburg 195112,Russia

4.DISIST Scientific Center,Novocherkasky Ave,40,St.Petersburg 195112,Russia

Year-round cooling and thermal stabilization of water-saturated soils under engineering structures

Vladimir Moiseev1,Nicolai Vasiliev2*,Tatyana Komarova3,Olga Komarova4

1.Department ofMathematics,EmperorAlexanderI St.PetersburgStateTransport University,MoskovskiyAve.,9,St.Petersburg190031,Russia

2.Static Research of Soils Laboratory,B.E.Vedeneev VNIIG,JSC,Gzhatskaya 21,St.Petersburg 195220,Russia

3.DISIST Scientific Center,Novocherkasky Ave,40,St.Petersburg 195112,Russia

4.DISIST Scientific Center,Novocherkasky Ave,40,St.Petersburg 195112,Russia

We consider the problem of year-round cooling of water-saturated soil to freezing temperatures in order to convert it into a state of permafrost.Anew soil-cooling apparatus is proposed.The apparatus is to be made in modular form and connected to passive?active thermal piles(thermosyphons).The estimated capacity of one apparatus allows simultaneous use of up to 1,000 thermal piles for ground freezing.The apparatus is based on natural sources of energy:solar radiation and wind;and it can be used for soil freezing.This approach can prevent thawing of soft soils under railways and roads,as well as under buildings or structures,in an area of more than tens of hectares.The apparatus has no mechanical moving parts and can operate for a long time in stand-alone mode without staff involvement.

thermopiles;frozen soil;preventing of thawing;the apparatus for cooling

1 Introduction

At present,dynamic development of the northern territories of Russia connected with the building of roads,sea and river ports,buildings and engineering structures,etc.,is taking place.First of all,this activity is determined by the development of new oil and gas deposits.For these northern territories,the most efficient approach,consisting of preserving the soil in the frozen condition,has gained widespread interest. Soils in the frozen condition possess high strength parameters.All attempts connected with construction management of roads,bridges,buildings,and other structures are based on using devices created in the foundations of structures,railways,and motorways for thermal stabilization of soils(thermopiles)(Gurevich,1992).Thermal piles usually consist of pipes plugged at the bottom and filled with fluid coolant,e.g.,kerosene.The operation of thermal stabilization devices involves transferring of the natural cold to the foundation bottom to maintain constant negative temperatures in the permafrost,so that the heat coming from the structures or from natural processes is balanced.The devices require no power cost and automatically start working due to the difference of temperature between the soil and outside air.The applicable scope of thermal stabilization devices is wide:(1) linear structures;(2)engineering structures;(3)buildings,including civil engineering applications;and(4) hydraulic engineering structures.

Over the spring and summer period,however, when permafrost soils weaken,thermopiles do notwork.The fluid in the pipes congeals into a stable, laminated condition;and its circulation stops.

The other types of seasonal cooling devices—thermosyphons or heat-transfer tubes—are labour-intensive and require considerable capital commitment. With the low-boiling-point and aggressive fluids used in thermal piles,failure may cause environmental damage.Finally,almost all of them have the same negative attribute:they cannot cool soils in the summer because of the mode of their operation.

The summer melting of frozen soils creates difficulties in the building and operating of structures.For this reason,a lot of problems arise,requiring support for building and transportation on weak,saturated soils in the climate conditions described.

Also,a degradation of the long-term frost occurs: elevation of the temperatures of the frozen soils in the negative range and their melting at the boundary surface.These conditions lead to the development of strains in buildings and engineering structures,and also to difficulties in greenfield development,connected with the necessity of preliminary freezing(cooling)of the soils and maintaining of the project temperature conditions during the life of the constructions.

2 The task of creating the device

Therefore,the task of creating a device ensuring year-round soil cooling in large areas(no less than 2,000?3,000 m2)was set to prevent thawing of the soil under railways,motorways,buildings,and other constructions for a period not less than 4 months.The device should be easily transported to scarcely populated regions and be operational in a self-inclusive state without permanent working staff,and also be environmentally clean and of low price.

For completing the task,the following suggestions are contributed.

For cooling the soil,screw thermopiles are proposed,the blades of which ensure lowering the piles into the weakened soil and at the same time function as heat-exchangedevices.Thisconstructionhelpstofreeze much wider zones surrounding the axes of the piles.

As primary sources of energy for the device,it is proposed to use natural solar radiation or wind energy.

The cooling of thermopiles is supposed to be realized with help of a coolant(kerosene)having negative temperature,moving naturally without pumps, and being cooled with the natural sources named.

The system of thermopile cooling is proposed to be made in a block-modular way,using one module for cooling several hundreds of thermopiles.

3 Description of the device

The proposed device is covered by a patent (Vasilievet al.,2016),and the scheme of the device is presented in Figure 1.

The device consists of the thermal piles(1)connected by pipes(3)to the thermal battery(4)and the heat-exchange unit(5).The thermal battery is filled with thermal-energy storage material.The heat-exchange unit is filled with coolant and connected to the cooling elements(10).The cooling elements are the parts of an absorption lithium bromide refrigerating machine.Also,the device has a solar radiation collector with mirror(11);and the collector may be changed to the wind electro-generator.

The fluid circulates via the closed-loop contour pipes"a-b-c-d-e-f-g-h"through the thermal battery (4)and the heat-exchange unit(5)and the blocks of the thermal piles(1)in the frozen soil(2).

When springtime comes,the primary heating of the thermal-energy storage material(charging of the thermal battery)needs to be done.The heating is carried out with help of the heater(12)from the source (13).At the same time,the thermal-energy storage material is heated with an additional heater with help of the solar radiation collector with mirror(11).

After heating the thermal-energy storage material until it reaches the aggregative transition,there is no need for the heater,which serves to start the process of the heat exchange in the proposed device.The heat capacity of the thermal-energy storage material should be high enough to keep it in the melted condition, maintaining a high temperature for three or four days, in case of inadequate solar radiation.

While the thermal-energy storage material in the thermal battery is melted and at a high enough temperature,all the cooling elements generate the cold,maintaining the negative temperature of the coolant in the heat-exchange unit(5)continuously.At the same time,the natural convection of the liquid coolant starts in the circulation contour"a-b-c-d-e-f-g-h,"including the thermal piles(1).

The liquid coolant in the pipes(3),after going through the heat-exchange unit(5)with the coolant at the line"d-e"of the circulation contour,reaches the negative temperature itself.Having gone through the entry collector(6),it separates through the entry adapter sleeves(7)among the piped interlocking pipes, maintaining the negative temperature of the frozen soil (2)by means of heat exchange.

After going through the piped interlocking thermal piles(1),the liquid coolant comes back through the exit adapter sleeves(8)to the outlet collector(9) to the thermal battery(4);and the cycle of its moving along the contour"a-b-c-d-e-f-g-h"repeats.

At present,the proposed device has not been used yet;but a computer model of it has been developed. For creating the model,the computational fluid dynamics(CFD)software from ANSYS was used to simu-late the operation of the device.Also,all the necessary calculations of the cooling system of the thermal piles block correspond to the standard hydraulic calculations of the simple pipeline.Our calculations show the high level of effectiveness of the proposed device for cooling of soil,especially at intensive solar radiation.The working conditions are best when the temperature of the thermal battery is about 130°C.In this case,the temperature of the liquid coolant is about?7°C;and its flow velocity is rather high.These parameters maintain the frozen state of the soil during the entire summer period.

Figure 1 The scheme of the proposed device

4 Conclusions

Therefore a primary engineering elaboration of the device for the year-round stabilization of weak,saturated soils is completed,which shows the possibility of its practical realization.The device does not require energy to be supplied from the external power lines and works independently without staff.The high reliability of the device is determined by its lack of moving pieces.

:Moiseev V,Vasiliev N,Komarova T,et al.,2017.Year-round cooling and thermal stabilization of water-saturated soils under engineering structures.Sciences in Cold and Arid Regions,9(3):0258-0260.

10.3724/SP.J.1226.2017.00258.

November 14,2016Accepted:December 14,2016

*Correspondence to:Nicolai Vasiliev,Ph.D.,head of static research of soils laboratory,B.E.Vedeneev VNIIG,JSC. Gzhatskaya 21,St.Petersburg 195220,Russia.E-mail:nicolaivasiliev@hotmail.com

Gurevich VB,1992.The port hydrotechnik objects.In:Transport. Moscow,pp.692.(in Russian)

Vasiliev NK,Moiseev VI,Komarova TA,et al.,2016.Patent of Russian Federation N163882.