RU2786189C1 - Method for thermostabilization of soil around piles - Google Patents

Abstract

FIELD: soil thermal stabilization.

SUBSTANCE: invention relates to the field of thermal stabilization of the soil around the piles by the method for forced controlled supply of a coolant of a given temperature to the thermoelements from a refrigeration machine. The method for thermal stabilization of the soil around the piles includes freezing the array of permafrost soil with piles, thermoelements by the method for forced controlled supply of a coolant of a given temperature to them from an external cooling source. The cooled coolant from the outlet of the refrigeration machine is fed through a tube to the inlet of the cooled coolant collector, where it is distributed along the mains, then it enters sequentially into the hose, transport sections, inlet pipe and thermoelement, which is installed inside the pile at a depth that depends on the zone of soil thawing, and The inner space of the pile is filled with a non-freezing liquid, which improves the heat exchange between the pile body and the thermoelement. Passing through the thermoelement, the coolant heats up, and the temperature of the pile body and the soil adjacent to the pile decreases, after which the heated coolant sequentially enters the transport sections with the heated coolant, the hose, the line and the collector, at the inlet of the refrigeration machine.

EFFECT: increasing the efficiency of the soil thermal stabilization process.

2 cl, 2 dwg, 1 tbl

Description

The invention relates to the field of thermal stabilization of permafrost soils to ensure the stability of pile foundations.

A known method of soil thermal stabilization (Gorelik Ya.B., Khabitov A.Kh. On the effectiveness of the use of thermal stabilizers in construction on permafrost soils // Bulletin of the Tyumen State University. Physical and mathematical modeling. Oil, gas, energy, vol. 5, No. 3, 2019, pp. 25-46), which includes placing a heat stabilizer evaporator inside the hollow pile body and moving the finned condenser outside the pile body in the above-ground part.

The disadvantage of this method is the insufficient intensity of soil freezing, as well as a complete stop of the freezing process in the warm season.

There is a known method of soil freezing under the action of a thermal support (Okorokov N.S., Korkishko A.N., Korzhikova A.P. Experimental study of a forcedly ventilated pile / Vestnik MGSU, vol. 15, No. 5, 2020, p. 665-677), in which the thermal stabilization of the soil is provided by forced ventilation of the cold air of the refrigerating machine along the body of the pile immersed in the soil.

The disadvantage of the device is the use of air as a refrigerant, which has worse heat capacity compared to non-freezing liquids.

There is a known method of cooling the soil and a thermal pile for its cooling (patent RF 2256746, publ. 20.07.2005), including the condensation of the steam of the working fluid in the condenser cavity by cooling it with the environment above the soil surface, transportation of the condensed fluid under the action of gravity along the transport line to the evaporator cavity with its subsequent evaporation in it and the return transport of steam to the condenser cavity. Condensation of the steam of the working fluid is carried out in a volume larger than the volume in which the evaporation of the working fluid is carried out.

The disadvantage of this method is the insufficient intensity of soil freezing, as well as a complete stop of the freezing process in the warm season.

There is a known method for forced lowering of the temperature of permafrost soil in the foundations of piled foundations of supports of an operated bridge (RF patent 2731343, publ. 09/01/2020), according to which, if necessary, forced freezing with cold air from an air turborefrigeration machine, the shafts of seasonal cooling devices (SDU) are blown after complete evacuation of liquid coolant from them, which is again poured into the shafts of the SOU after the soils of the bases reach the calculated negative temperature values.

The disadvantage of this method is the complexity of the processes of pumping and pumping liquid coolant, as well as the risk of leaks of the coolant.

A known method of arranging a slab foundation on piles for a tank with a low-temperature product (RF patent 2552253, publ. 06/10/2015), adopted as a prototype, including additional freezing of an array of permafrost soil with piles using deep thermoelements by the method of forced controlled supply of refrigerant to them at a given temperature from an external source of its cooling through looped distribution lines. To freeze the soil base under the slab during storage of the product, its own negative temperature is used, while after a certain time, when the halo of freezing of the soil base from the impact of a low-temperature product in the tank reaches the design temperatures, additional forced freezing by deep thermoelements is partially or completely stopped. If it is necessary to strengthen individual sections of the pile foundation, coolant with a lower temperature is supplied to individual lines of individual sectors than in other sectors.

The disadvantage of this method is the need to drill wells for deep thermoelements. Another disadvantage is that in order to freeze individual sections of the pile foundation with different intensity, it is necessary to obtain a refrigerant of different temperatures.

The technical result of the method is to increase the efficiency of the soil thermal stabilization process.

The technical result is achieved by the fact that the cooled coolant from the outlet of the refrigeration machine is fed through a tube to the inlet of the cooled coolant collector, where it is distributed along the lines, then sequentially enters the hose, transport sections, the inlet pipe and the thermoelement, which is installed inside the pile at a depth that depends from the zone of soil thawing, and the internal space of the pile is filled with a non-freezing liquid, while the heat exchange between the pile body and the thermoelement improves, passing through the thermoelement, the heat carrier heats up, and the temperature of the pile body and the soil adjacent to the pile decreases, after which the heated coolant sequentially enters the transport areas with heated coolant, hose, line and manifold, to the inlet of the refrigeration machine. With an increase in the depth of lowering of the thermoelements, additional transport sections are sequentially installed.

The method of thermal stabilization of the soil around the pile is illustrated by the following figure:

fig. 1 - layout of equipment for freezing soil on a slab and in piles;

fig. 2 – simulation results, where:

1 - pile;

2 - plate;

3 – thermoelement;

4 - transport section with a cooled coolant;

5 - transport section with a heated coolant;

6 – hose with cooled coolant;

7 – hose with heated coolant;

8 - refrigerator;

9 - cooled coolant collector;

10 - collector of heated coolant;

11 – tube with cooled coolant;

12 - tube with heated coolant;

13 - line with cooled coolant;

14 - line with heated coolant;

15 - input tube;

16 - suspension device.

The method is implemented as follows. On piles 1, buried in the ground and forming a pile field, a plate 2 is fixed, on which an external cooling source is installed, which is used as a refrigerator 8. As a refrigerator 8, an absorption refrigerator can be used, operating due to excess thermal energy from equipment placed on stove 2, or a compressor chiller. The cooled coolant from the outlet of the refrigerating machine 8 enters through a tube with a cooled coolant 11 to the inlet of the cooled coolant collector 9, in which it is distributed along the lines with a cooled coolant 13. After that, the cooled coolant enters sequentially into a hose with a cooled coolant 6, transport sections with a cooled coolant 4 and inlet pipe 15. Then the cooled coolant enters the inlet of thermoelement 3, which is installed inside pile 1 at a depth depending on the zone of soil thawing. If necessary, several thermoelements 3 installed in series can be used inside each pile 1, with several input pipes 15 being installed in series. To improve heat exchange between the body of the pile 1 and the thermoelement 3, the interior of the pile 1 is filled with a non-freezing liquid, for example, kerosene. Passing through the thermoelement 3, the coolant heats up, and the temperature of the body of the pile 1 in the area of the thermoelement 3 and the temperature of the soil adjacent to the pile 1 decreases. The heated coolant from the outlet of the thermoelement 3 flows sequentially to the transport sections with the heated coolant 5, the hose with the heated coolant 7 and the line with the heated coolant 14. the inlet of the refrigeration machine 8. In the refrigeration machine 8, the coolant is cooled and fed to the tube with the cooled coolant 11. Then the cycle of circulation of the coolant in a closed circuit is repeated.

With an increase in the depth of lowering of thermoelements 3, additional transport sections with a cooled coolant 4 are installed in series, and additional transport sections with a heated coolant 5 are installed in a similar manner. with heated coolant 5. Fixation in the suspension device 16 can be carried out by clamping with screws.

The method is illustrated by the following example. A pile foundation model was built in the COMSOL Multiphysics software package. The pile foundation includes a steel plate 8 m long, 5 m wide and 0.2 m high. The slab is fixed on three steel hollow piles located in the same plane with a diameter of 0.4 m, a length of 10 m, with a wall thickness of 10 mm, and is located at a height 2 m above the ground. An object with a thermal radiation power of 10 kW is installed on the stove. Inside the piles, thermoelements are installed, made of a thin-walled copper tube with an outer diameter of 15 mm, and the distance between the thermoelements and the inner wall of the pile is 20 mm. The thermoelements are spirals with 20 turns, the interturn distance is 0.1 m. The inner space of the piles is filled with kerosene to the ground level, the upper part of the inner space of the piles is occupied by air. The transport sections are made of copper. Freon R20 is supplied to the transport sections, cooled to a temperature of -3 °C. Transport sections with a cooled coolant are thermally insulated with a polyurethane pipe with a wall thickness of 50 mm, tightly adjacent to the transport section with a cooled coolant.

In the model, the heat transfer rate in the air part of the computational domain is set to 0.2 m/s. The air temperature at the boundaries of the computational domain, except for the boundary towards which the heat transfer is directed due to the wind, is set equal to +8 °С. The initial conditions are above the ground surface +8 °С. Initial conditions below the ground are -2 °C, except for transport sections with polyurethane thermal insulation and thermocouples, for which the initial temperature is set to -3 °C.

Simulation of the stationary process of thermal stabilization of the soil around the piles was carried out. During the simulation, the depth of lowering the thermoelements inside the pile changed, while the length of the transport sections with polyurethane insulation increased by the required value. The results of modeling the temperature field of the soil adjacent to the piles for some options for placing thermoelements inside the piles are shown in Table 1.

Table 1. Options for placing coils inside piles and the results of modeling the temperature field of the soil adjacent to the piles

No. Lowering depth of the upper part of the thermoelement relative to the ground level, m Average pile surface temperature below ground level, °С Average soil temperature in the calculation area, °C Pile 1 Pile 2 Pile 3 Pile 1 Pile 2 Pile 3 in section in volume one No thermocouples 1.01 0.79 0.54 -0.46 -0.81 2 one -0.87 -1.05 -1.12 -0.58 -0.84 3 1.5 -0.90 -1.06 -1.13 -0.64 -0.82 4 2 -0.81 -1.00 -1.08 -0.62 -0.88 five 3 -0.84 -0.97 -1.02 -0.61 -0.85 6 1.5 one one -0.88 -1.10 -1.19 -0.68 -0.90 7 2 one one -0.85 -1.13 -1.22 -0.68 -0.92 eight 3 one one -1.02 -1.24 -1.31 -0.72 -0.91 nine 4 one one -0.68 -1.09 -1.14 -0.62 -0.86

An analysis of the simulation results showed that under given conditions, different depths of thermoelement insertion inside three piles lead to lower soil temperatures than at the same insertion depth of thermoelements. In FIG. Figure 2 shows the simulation results, the isotherms are given for option No. 8 of Table 1. The controllability of the soil freezing process is ensured both by regulating the coolant supply by the refrigeration machine 8 and by regulating the depth of lowering of the thermoelement 3 inside the pile 1.

An increase in the efficiency of the soil thermal stabilization process is achieved due to the location of thermoelements for freezing the soil inside the piles, as well as due to the possibility of regulating the depth of lowering of the thermoelements. With an increase in the depth of lowering of the thermoelements, additional transport sections with a cooled coolant are sequentially installed, and additional transport sections with a cooled coolant are sequentially installed. To improve heat transfer between the pile body and the thermoelement, the internal space of the piles is filled with an antifreeze liquid.

Claims (2)

1. A method for thermal stabilization of soil around piles, including freezing a mass of permafrost soil with piles, thermoelements by the method of forced controlled supply of a coolant of a given temperature to them from an external cooling source, characterized in that the cooled coolant from the outlet of the refrigeration machine is fed through a tube to the inlet of the cooled coolant collector, where it is distributed along the highways, then sequentially enters the hose, transport sections, the inlet tube and the thermoelement, which is installed inside the pile at a depth that depends on the soil thawing zone, and the interior of the pile is filled with a non-freezing liquid, while improving heat transfer between the pile body and a thermoelement, passing through the thermoelement, the heat carrier is heated, and the temperature of the pile body and the soil adjacent to the pile decreases, after which the heated heat carrier sequentially enters the transport sections with the heated coolant, the hose, the mains trawl and collector, at the inlet of the refrigeration machine. 2. The method according to p. 1, characterized in that with an increase in the depth of lowering of the thermoelements, additional transport sections are sequentially installed.

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