A permafrost region cast-in-place pile active cooling construction device and method

Abstract

The application discloses a permafrost area bored pile active cooling construction device and method, the device includes refrigeration cycle system, temperature monitoring module, temperature analysis module and refrigerant control module, the initial temperature field of the temperature monitoring module real-time monitoring permafrost area bored pile soil and the temperature field change in the process of drilling, pouring and maintenance; the temperature analysis module analyzes and processes the data measured by the temperature monitoring module, calculates the delivery and circulation rate required by the refrigerant control module, and estimates and evaluates the cooling effect of the cooling construction device and the running time required to achieve the target cooling effect; the refrigerant control module controls the delivery and circulation rate of the refrigerant in the refrigeration cycle system and the running time of the circulation duration, thus completing a complete cycle of temperature monitoring, temperature analysis and refrigerant control. The application can shorten the construction period and efficiency, improve the initial bearing capacity of the permafrost pile foundation, and is beneficial to promoting the subsequent construction engineering.

Description

Technical Field

[0001] This invention belongs to the field of cooling construction of bored cast-in-place piles, and relates to an active cooling construction device and method for bored cast-in-place piles in permafrost areas. Background Technology

[0002] Permafrost is a product of energy and hydrothermal exchange between the atmosphere and the Earth's lithosphere under specific climatic conditions. Based on the duration of its existence, soil or rock that has remained frozen for two years or more is called permafrost. During the transition from winter to summer, the thawing permafrost can only reach a certain depth. The distance from the thawed soil layer to the top of the permafrost is called the upper limit of permafrost, which is generally about 2 meters deep, but remains relatively stable throughout the year.

[0003] Drilled piles are a common support method for bridges, culverts, tunnels, and other structures in permafrost regions, renowned for their high bearing capacity, convenient construction, and readily available materials. However, in permafrost areas, ground disturbance during pile construction (such as excavation), concrete pouring, and hydration heat release all generate thermal disturbance, disrupting the original thermal balance between the surface and the atmosphere. The underlying permafrost becomes a non-equilibrium state dominated by heat absorption, significantly reducing the permafrost strength and pile bearing capacity. For every 0.1℃ increase in pile-soil interface temperature, the freezing strength of the frozen section around the pile decreases by 8 kPa. Over time, under the influence of the initial ground temperature and atmospheric environment, the process of the permafrost around the pile gradually refreezing to the natural permafrost temperature can take up to a year, severely impacting the construction period and project progress.

[0004] Currently, to address engineering problems caused by the disruption of the thermal balance of frozen soil, concrete incorporating mineral admixtures and antifreeze agents can be used to ensure concrete strength under low-temperature conditions. Additionally, the concrete's placement temperature can be controlled before pouring. While these methods can reduce the degree of thermal disturbance in frozen soil to some extent, they do not fundamentally solve the problem of heat transfer from the concrete hydration process to the frozen soil. Therefore, there is an urgent need for a cooling construction device suitable for bored piles in frozen soil in cold regions to effectively reduce the degree of thermal disturbance and ensure project progress. Summary of the Invention

[0005] The purpose of this invention is to provide an active cooling construction device and method for bored piles in permafrost regions, which mainly solves two key problems: First, the cooling construction device controls the appropriate pouring temperature of concrete under specific seasonal and site conditions, while simultaneously cooling and neutralizing the heat released by the hydration reaction during concrete pouring. The principle is to utilize the circulating flow of a heat-conducting working fluid to remove the heat released by concrete hydration. Second, it achieves dynamic self-regulation of cooling power, ensuring the design strength of the concrete pile while minimizing thermal disturbance to the permafrost around the pile caused by hydration heat, shortening the project cycle, and improving the reliability of the pile foundation bearing capacity.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] An active cooling construction device for bored piles in permafrost regions includes a refrigeration circulation system and a dynamic self-regulating system, wherein:

[0008] The refrigeration cycle system consists of an evaporator, a refrigeration compressor, a condenser, a throttling valve, and a circulating liquid refrigerant;

[0009] The evaporator, refrigeration compressor, condenser, and expansion valve are connected in sequence by a circulation pipeline to form a closed system.

[0010] The evaporator is composed of a combined protective sleeve and a spiral finned tube. The combined protective sleeve is composed of an inner wall and an outer wall. The lower part of the inner wall is fitted with the outer wall to form a double-walled protective sleeve. The spiral finned tube is fixed in the interlayer between the inner wall and the outer wall and is wound around the outside of the inner wall. The two ends of the spiral finned tube are connected to the refrigerant inlet pipe and the refrigerant outlet pipe, respectively.

[0011] The dynamic self-regulation system includes a temperature monitoring module, a temperature analysis module, and a refrigerant control module;

[0012] The temperature monitoring module is used to monitor the initial temperature field of the soil around the bored pile and the temperature field changes during drilling, grouting and curing processes in real time.

[0013] The temperature analysis module is used to analyze and process the data measured by the temperature monitoring module. Based on the heat release of concrete hydration and its heat conduction formula, it calculates the required delivery and circulation rate of the refrigerant control module, and estimates and evaluates the cooling effect of the cooling construction device and the running time required to achieve the target cooling effect.

[0014] The refrigerant control module is used to control the refrigerant delivery and circulation rate and the duration of the cycle in the refrigeration cycle system, thus completing a complete cycle of temperature monitoring, temperature analysis and refrigerant control, thereby realizing the function of dynamic self-regulation.

[0015] A method for active cooling construction of bored piles in permafrost regions using the above-mentioned device includes the following steps:

[0016] Step 1: Install the evaporator using a vibratory hammer;

[0017] Step 2: Drill and clean the hole, hoist and place the steel cage, and install temperature sensors and refrigerant inlet and outlet pipes in the combined casing. The temperature sensors are connected to the dynamic self-regulation system, and the evaporator is connected to the refrigeration cycle system through the circulation pipe.

[0018] Step 3: While pouring concrete and curing the bored piles, start the cooling circulation system;

[0019] Step 4: The temperature analysis module calculates the heat capacity C and thermal conductivity λ of the frozen soil at the phase change interface according to formulas (1), (2), and (3), and then calculates the numerical solution of the temperature field of the frozen soil around the pile. According to the corresponding changes in the temperature field, combined with the pile diameter, pile spacing and initial ground temperature conditions of the drilled cast-in-place pile, the refrigerant control module is adjusted in real time. The temperature monitoring module feeds back the monitoring data to the temperature analysis module every once in a while.

[0020] Step 5: Repeat the analysis and adjustment control process of Step 4 to complete the dynamic self-regulation of the refrigeration cycle system.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. This invention can remove the heat released by hydration from the soil through a cooling circulation device before heat exchange and diffusion, effectively reducing the degree of thermal disturbance to the frozen soil during the grouting and hydration reaction process.

[0023] 2. This invention can dynamically control the cooling efficiency of the cooling construction device and intelligently regulate the refrigeration cycle system to achieve the cooling effect while ensuring the rate and extent of concrete hydration reaction.

[0024] 3. This invention controls the cooling process of the cooling construction device through basic and dynamic parameters, which can adapt to different drilling and grouting pile working conditions and different site environments.

[0025] 4. This invention can shorten the construction cycle and improve efficiency, and to a certain extent improve the initial bearing capacity of frozen soil pile foundations, which is conducive to promoting subsequent construction projects. Attached Figure Description

[0026] Figure 1 This is a general framework diagram of the cooling construction device for bored piles;

[0027] Figure 2 Diagram of the refrigeration cycle system;

[0028] Figure 3 A schematic diagram of the installation of double-layer sandwiched casing and spiral finned tube for bored cast-in-place piles;

[0029] In the diagram, 1. Refrigeration cycle system; 2. Refrigerant; 3. Evaporator; 4. Refrigeration compressor; 5. Condenser; 6. Circulation pipeline; 7. Throttling valve; 8. Spiral finned tube; 9. Solenoid valve; 10. Thermostat; 11. Dual-pressure controller; 12. Oil separator; 13. Liquid receiver; 14. Inner wall of casing; 15. Refrigerant inlet pipe; 16. Outer wall of casing; 17. Refrigerant outlet pipe; 18. Heat transfer oil; 19. Dynamic self-regulation system; 20. Temperature monitoring module; 21. Temperature analysis module; 22. Refrigerant control module; 23. Construction application method; 24. Embedding the combined casing; 25. Drilling; 26. Lifting and placing the reinforcing cage; 27. Laying out the circulation pipeline; 28. Laying out temperature sensors; 29. ​​Pouring concrete; 30. Curing piles; 31. Recovering refrigeration equipment. Detailed Implementation

[0030] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0031] This invention provides an active cooling construction device for bored piles in permafrost regions, such as... Figure 1-3 As shown, the cooling construction device consists of a refrigeration cycle system 1 and a dynamic self-regulating system 19, wherein:

[0032] The refrigeration cycle system 1 consists of an evaporator 3, a refrigeration compressor 4, a condenser 5, a throttle valve 7, and a circulating refrigerant 2. The evaporator 3, the refrigeration compressor 4, the condenser 5, and the throttle valve 7 are connected in sequence by a circulation pipe 6 to form a closed system.

[0033] The evaporator 3 is composed of a combined protective casing and a spiral finned tube 8. The combined protective casing consists of an inner wall 14 and an outer wall 16. The upper part of the combined protective casing is defined as the inner wall 14, and the lower part of the inner wall 14 is fitted with the outer wall 16 to form a double-walled casing. The bottom of the inner wall 14 is provided with a cutting edge. The top surface of the outer wall 16 is 0.5m above the upper limit of the frost line, and the bottom surface is 0.5m below the lower limit of the frost line. The distance between the inner wall 14 and the outer wall 16 is 2cm. The outer wall 16 has a wall thickness of 10mm. The diameter of the 16 is 20cm larger than that of the drilled pile. The combined casing is arranged from the ground to 2m below the lower limit of the frost line as follows: the inner wall 14 of the casing has a length H1 (0.5m above the original ground to 1m above the upper limit of the frost line) with a wall thickness of 20mm + the outer wall of the casing has a length H2 (1m above the upper limit of the frost line to 1m below the lower limit of the frost line) with a wall thickness of 10mm + the cutting edge (1m) with a wall thickness of 20mm. The interlayer between the inner wall 14 and the outer wall 16 of the casing is filled with heat transfer oil 18 with a high specific heat capacity to enhance the heat exchange efficiency of the spiral finned tube 8 during the refrigeration cycle.

[0034] The spiral finned tube 8 is fixed in the interlayer between the inner wall 14 and the outer wall 16 of the protective cylinder. The spiral finned tube 8 is connected to the refrigeration cycle system 1 via inlet and outlet pipes. The lower end of the spiral finned tube 8 is connected to the refrigerant inlet pipe 15, and the upper end is connected to the refrigerant outlet pipe 17. For the spiral specification of the vertical pipe, the height of the spiral finned tube 8 is equal to the height of the outer wall 16 of the protective cylinder. To improve heat exchange efficiency, fins are added to the surface of the spiral finned tube 8 to increase the outer (or inner) surface area of ​​the heat exchange tube, thereby improving heat exchange efficiency. The pitch and rotation speed of the spiral finned tube 8, as well as the fin type, are calculated using heat transfer formulas.

[0035] The condenser 5 uses a filled U-shaped condensing pipe. After the steam enters from the side pipe, it comes into contact with the cold water sprayed down from above. The condenser 5 is filled with ceramic ring packing. After the packing is wetted by water, the contact area between the cold water and the steam is increased. After the steam condenses into water, it flows out along the lower pipe. The condensed gas is extracted by the vacuum pump along the upper pipe to ensure a certain degree of vacuum in the condenser.

[0036] The throttling valve 7 is a thermostatic expansion valve that adjusts the valve orifice opening by utilizing changes in the superheat of the refrigerant vapor at the evaporator outlet. It is a throttling device that regulates the liquid supply to the evaporator 3 using a thermistor. The thermistor is connected in series with a heater on the expansion valve diaphragm, and the electric heat flux of the heater varies with the thermistor value. When the superheat of the refrigerant vapor at the evaporator 3 outlet increases, the thermistor temperature rises, the resistance value decreases, the current of the electric heater increases, the liquid in the diaphragm chamber is heated, and the temperature and pressure increase, pushing the diaphragm and valve stem downwards, causing the valve orifice to open or widen. When the load on the evaporator 3 decreases, the superheat of the evaporator outlet vapor decreases, or it becomes wet vapor, the thermistor is cooled, and the valve orifice closes or shuts off. In this way, the thermostatic expansion valve can control the liquid supply to the evaporator to adapt to the heat load.

[0037] The refrigeration compressor 4 is a vapor compression refrigeration machine based on hydraulic evaporative refrigeration. The refrigerant undergoes a periodic gas-liquid phase change, and the liquid refrigerant serves as the working fluid for completing the thermodynamic cycle in the refrigeration machine. Pressurized liquefied tetrafluoroethane (R-134a type) is used as the liquid refrigerant in this invention. After absorbing heat from the object being cooled in the evaporator 3, the liquid refrigerant vaporizes into low-temperature, low-pressure vapor, which is then drawn into the refrigeration compressor 4, compressed into high-pressure, high-temperature vapor, and discharged into the condenser 5. In the condenser 5, it releases heat to the cooling medium (water or air), condenses into a high-pressure liquid, is throttled by the expansion valve 7 into a low-pressure, low-temperature refrigerant, and re-enters the evaporator 3 to absorb heat and vaporize, achieving the purpose of cyclic refrigeration. Thus, the refrigerant 2 completes one refrigeration cycle in the system through four basic processes: compression, condensation, throttling, and evaporation.

[0038] The dynamic self-regulation system 19 includes a temperature monitoring module 20, a temperature analysis module 22, and a refrigerant control module 21, which can adjust the cooling power in real time based on the temperature changes of the soil around the pile.

[0039] The temperature monitoring module 20 consists of a temperature sensor and a digital display screen. The temperature sensor is fixed on the outside of the bored pile sleeve to monitor the initial temperature field of the soil around the pile and the temperature field changes during drilling, grouting and curing.

[0040] The temperature analysis module 21 can input basic parameters and dynamic parameters. The basic parameters include parameters of the bored pile such as pile diameter, length, and pile spacing, as well as engineering experience parameters such as the time required for the frozen soil to refreeze under natural site conditions. The dynamic parameters are the data measured by the temperature monitoring module and implemented feedback. Based on the heat conduction formula of the heat released by concrete hydration, the refrigerant delivery and circulation rate are adjusted to reduce the thermal disturbance to the soil around the pile during construction, while maintaining a certain hydration reaction rate of the poured concrete.

[0041] The refrigerant control module 22 controls the refrigerant 2's delivery and circulation rate and the duration of the circulation in the refrigeration cycle system 1. This completes a full cycle of the temperature monitoring module 20, temperature analysis module 21, and refrigerant control module 22, thus realizing the function of the dynamic self-regulating system 2. Through the above module configuration, the dynamic self-regulating system can determine the cooling efficiency of the cooling construction device and the time required for cyclic cooling.

[0042] Figure 1 The specific construction steps are given, mainly including the following steps:

[0043] (1) A vibratory hammer is used to install a combined casing. The combined casing consists of two sections, including an inner wall 14 and an outer wall 16. The space between the inner wall 14 and the outer wall 16 is filled with heat transfer oil 18 to increase the heat transfer efficiency. A spiral finned tube 8 is fixed between the inner wall 14 and the outer wall 16. The height of the spiral finned tube 8 is equal to the height of the outer wall 16. The lower end of the spiral finned tube 8 is connected to the refrigerant inlet pipe 15, and the upper end is connected to the refrigerant outlet pipe 17.

[0044] (2) In accordance with the design specifications, after the combined casing is installed, the hole is drilled and cleaned, the steel cage is hoisted and placed, temperature sensors and refrigerant inlet and outlet pipes are installed, and the combined casing and its internal spiral finned tubes are connected to the refrigeration cycle system as evaporators.

[0045] (3) While pouring concrete and curing the bored piles, the refrigeration cycle system is started. The specific heat transfer path is as follows: During the concrete pouring and curing, heat Q1 is released. First, refrigerant 2 passes through the refrigerant inlet pipe 15, the spiral finned tube 8 and the refrigerant outlet pipe 17 in sequence. In the evaporator 3, it absorbs heat Q2 through the heat transfer oil 18 in the interlayer between the inner wall 14 and the outer wall 16 of the casing and vaporizes into low-temperature and low-pressure steam to achieve the purpose of controlling the temperature of the formwork and neutralizing the heat released by the hydration of the concrete. Second, the low temperature and low pressure of refrigerant 2 Steam is drawn into the refrigeration compressor 4 and compressed into high-pressure, high-temperature steam before being discharged into the condenser 5. In the condenser 5, it releases heat to the cooling medium (water or air) and condenses into a high-pressure liquid. The high-pressure liquid is then throttled by the expansion valve 7 into low-pressure, low-temperature refrigerant 2, which re-enters the evaporator 3 to absorb heat and vaporize, thus achieving the purpose of cyclic refrigeration. Finally, the refrigerant 2 completes one refrigeration cycle through four basic processes: compression, condensation, throttling, and evaporation in the refrigeration cycle system. This process removes the heat released by the hydration of the bored pile, effectively reducing the degree of thermal disturbance to the frozen soil site during the grouting and curing construction process.

[0046] (4) The dynamic self-regulation system 19 mainly includes a temperature monitoring module 20, a temperature analysis module 21, and a refrigerant control module 22. The temperature monitoring module 20 is connected to the temperature sensor 28 installed in the combined casing. The temperature analysis module 21 can calculate the heat capacity C and thermal conductivity λ of the frozen soil at the phase change interface according to formulas (1), (2), and (3), and then calculate the numerical solution of the temperature field of the frozen soil around the pile. According to the corresponding changes in the temperature field, combined with the pile diameter, pile spacing and initial ground temperature conditions of the drilled cast-in-place pile, the refrigerant control module 22 is adjusted in real time. The temperature monitoring module 20 feeds back the monitoring data to the temperature analysis module 21 every once in a while, repeating the above analysis process and adjustment and control process to complete the dynamic self-regulation of the refrigeration cycle system.

[0047]

[0048]

[0049]

[0050] In the formula: C is the heat capacity of frozen soil; C f C is the heat capacity of permafrost under frozen conditions. u L is the heat capacity of permafrost under thawing conditions; T is the latent heat of phase change of water-bearing soil and rock; m To apply the sensible heat capacity method, assume the temperature at which the phase transition occurs; ΔT is the temperature change; λ is the thermal conductivity; λ f λ is the thermal conductivity of frozen soil in its frozen state. u y is the thermal conductivity of the frozen soil under thawing conditions; x, y, z are the spatial coordinates; t is the time elapsed.

[0051] The aforementioned cooling construction device and application method work together to effectively reduce the thermal disturbance of the frozen soil sidewalls caused by bored pile construction, shorten the frozen soil refreezing time, shorten the project construction cycle, and improve the applicability of bored pile technology in frozen soil areas.

Claims

1. An active cooling construction device for bored piles in permafrost regions, characterized in that... The device includes a refrigeration cycle system and a dynamic self-regulating system, wherein: The refrigeration cycle system consists of an evaporator, a refrigeration compressor, a condenser, a throttling valve, and a circulating liquid refrigerant; The evaporator, refrigeration compressor, condenser, and expansion valve are connected in sequence by a circulation pipeline to form a closed system. The evaporator is composed of a combined protective sleeve and a spiral finned tube. The combined protective sleeve is composed of an inner wall and an outer wall. The lower part of the inner wall is fitted with the outer wall to form a double-walled protective sleeve. The spiral finned tube is fixed in the interlayer between the inner wall and the outer wall and is wound around the outside of the inner wall. The two ends of the spiral finned tube are connected to the refrigerant inlet pipe and the refrigerant outlet pipe, respectively. The dynamic self-regulation system includes a temperature monitoring module, a temperature analysis module, and a refrigerant control module; The temperature monitoring module is used to monitor the initial temperature field of the soil around the bored pile and the temperature field changes during drilling, grouting and curing processes in real time. The temperature analysis module is used to analyze and process the data measured by the temperature monitoring module. Based on the heat release of concrete hydration and its heat conduction formula, it calculates the required delivery and circulation rate of the refrigerant control module, and estimates and evaluates the cooling effect of the cooling construction device and the running time required to achieve the target cooling effect. The refrigerant control module is used to control the refrigerant delivery and circulation rate and the duration of the cycle in the refrigeration cycle system, thus completing a complete cycle of temperature monitoring, temperature analysis and refrigerant control, thereby realizing the function of dynamic self-regulation.

2. The active cooling construction device for bored piles in permafrost regions according to claim 1, characterized in that... The bottom of the inner wall of the casing is equipped with a cutting edge. The top surface of the outer wall of the casing is 0.5m above the upper limit of the frozen soil and the bottom surface is 0.5m below the lower limit of the frozen soil. The distance between the inner wall and the outer wall of the casing is 2cm. The thickness of the outer wall of the casing is 10mm. The diameter of the outer wall of the casing is 20cm larger than the diameter of the drilled pile.

3. The active cooling construction device for bored piles in permafrost regions according to claim 1, characterized in that... Heat-conducting oil is injected into the interlayer between the inner and outer walls of the casing.

4. The active cooling construction device for bored piles in permafrost regions according to claim 1, characterized in that... The condenser uses a packed U-shaped condensation pipe, and the condenser is filled with ceramic ring packing.

5. The active cooling construction device for bored piles in permafrost regions according to claim 1, characterized in that... The throttle valve is a thermostatic expansion valve.

6. The active cooling construction device for bored piles in permafrost regions according to claim 1, characterized in that... The refrigeration compressor is a vapor compression refrigeration unit.

7. The active cooling construction device for bored piles in permafrost regions according to claim 1, characterized in that... The height of the spiral finned tube is equal to the height of the outer wall of the casing.

8. A method for active cooling construction of bored piles in permafrost regions using the device described in any one of claims 1-7, characterized in that... The method includes the following steps: Step 1: Install the evaporator using a vibratory hammer; Step 2: Drill and clean the hole, hoist and place the steel cage, and install temperature sensors and refrigerant inlet and outlet pipes in the combined casing. The temperature sensors are connected to the dynamic self-regulation system, and the evaporator is connected to the refrigeration cycle system through the circulation pipe. Step 3: While pouring concrete and curing the bored piles, start the cooling circulation system; Step 4: The temperature analysis module calculates the heat capacity of the frozen soil at the phase change interface. and thermal conductivity Then, the numerical solution of the temperature field of the frozen soil around the pile is calculated; based on the corresponding changes in the temperature field, combined with the pile diameter, pile spacing and initial ground temperature conditions of the drilled cast-in-place pile, the refrigerant control module is adjusted in real time, and the temperature monitoring module feeds back the monitoring data to the temperature analysis module every once in a while. Step 5: Repeat the analysis and adjustment control process of Step 4 to complete the dynamic self-regulation of the refrigeration cycle system.

9. The method for active cooling construction of bored piles in permafrost areas according to claim 8, characterized in that... The heat capacity of frozen soil and thermal conductivity The calculation formula is as follows: （1） （2） （3） In the formula: For the heat capacity of permafrost; The heat capacity of permafrost under frozen conditions; The heat capacity of permafrost under thawing conditions; The latent heat of phase transition in water-bearing rocks and soils; To assume the temperature at which the phase transition occurs when applying the sensible heat capacity method; This refers to the change in temperature. Thermal conductivity; The thermal conductivity of permafrost in its frozen state; The thermal conductivity of the frozen soil under thawing conditions; , , Spatial location coordinates; The time elapsed.

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