Structure and construction method for reducing tangential frost heaving force of pile foundation in seasonal frozen soil region

Abstract

The invention discloses a structure for reducing tangential frost heaving force of a pile foundation in a seasonal frozen soil region and a construction method.The structure comprises a heat preservation and insulation layer, hot bars and a pile-soil isolation sleeve, the hot bars are arranged in the axial direction and annularly and evenly distributed and fixed to the inner side of a reinforcement cage of the pile foundation, and each hot bar is a closed metal pipe filled with a working medium; each hot rod comprises an evaporation section, a heat insulation section and a condensation section, the evaporation section is located in a deep non-freezing area, the condensation section is located in a seasonal frozen soil layer, the heat insulation section is located between the evaporation section and the condensation section and below the maximum freezing depth, and the evaporation section is filled with working medium liquid; in winter, the working medium liquid is evaporated and converted into working medium steam through the heat insulation section to enter the condensation section under the action of the up-down temperature difference, and in the condensation section, the working medium steam is condensed into a liquid phase to penetrate through the heat insulation section to fall back into the evaporation section. Tangential frost heaving force can be weakened, and pile periphery freezing depth and pile foundation freezing pulling development are restrained.

Description

Technical Field

[0001] The invention relates to the technical field of pile foundation construction engineering in cold regions, and in particular to a structure and a construction method for reducing the tangential frost heave force of a pile foundation in a seasonally frozen soil region. Background Art

[0002] In cold regions, the surface rock and soil that freezes in winter and completely melts in summer is called seasonal frozen soil. The area of ​​seasonal frozen soil in my country is about 5.137 million square kilometers, accounting for 53.5% of the country's land area. With the development of the economy and the demand for national energy allocation, construction activities such as transportation, electricity, and housing in seasonal frozen soil areas are becoming increasingly frequent. Pile foundations have been widely used in engineering construction in seasonal frozen soil areas in my country due to their high bearing capacity, excellent seismic performance, and strong adaptability. However, the safe operation of pile foundations in seasonal frozen soil areas faces huge challenges, especially the phenomenon of freeze pullout, which seriously affects the stability of pile foundations, and this problem has not yet been effectively solved.

[0003] Under the action of repeated freezing and thawing of seasonally frozen layers, the long-term operation safety of light or shallow pile foundations and their superstructures is seriously threatened. When the soil freezes, the volume expansion will produce frost heave force on the pile foundation. The frost heave force is mainly divided into horizontal frost heave force, normal frost heave force and tangential frost heave force. Among them, the tangential frost heave force is the main factor inducing pile foundation frost heave. In the early stage of winter freezing, the pile foundation is frozen together with the surrounding shallow soil. Under the action of tangential frost heave force, the pile foundation is lifted; when it melts in spring, the shallow soil falls back, but due to the friction resistance of the deep soil, the pile foundation fails to fall back completely, resulting in a certain amount of residual vertical displacement. With the continuous freeze-thaw cycle of seasonally frozen layers, the pile foundation frost heave accumulates year by year, eventually leading to pile foundation instability.

[0004] In seasonal permafrost areas with severe frost heave, surface water and groundwater are usually abundant. Traditional measures such as drainage, foundation soil improvement, applying isolation agents to the pile side, and changing the deep foundation section are difficult to effectively prevent and control frost heave and pile foundation frost pullout in this area due to limitations in durability, hydrological environment, geological conditions, and construction conditions.

[0005] Although there have been reports of heat rod structures applied to pile foundations (such as steel piles and bored piles) in permafrost areas, this method installs heat rods inside or around the pile foundation, cools the pile foundation in winter, stops working in summer, and achieves one-way heat conduction, thereby preventing pile foundation settlement. However, the application of heat rods in pile foundation freeze-up prevention and control in seasonally frozen areas has not been reported.

[0006] In view of the urgent need for pile foundation frost uplift disease prevention and control design in frozen soil areas during the severe frost heave season, it is very necessary to propose a pile foundation frost uplift disease prevention and control measure with simple structure, convenient construction and easy promotion. Summary of the invention

[0007] The purpose of the present invention is to provide a structure for reducing the tangential frost heaving force of pile foundations in seasonal frozen soil areas with strong frost heaving, in order to solve the problem that the frost heaving of pile foundations in seasonal frozen soil areas cannot be effectively prevented and controlled in the prior art.

[0008] Another object of the present invention is to provide a working method of the structure for reducing the tangential frost heave force of pile foundations in seasonally frozen soil areas.

[0009] Another object of the present invention is to provide a construction method for the structure for reducing the tangential frost heave force of pile foundations in seasonally frozen soil areas.

[0010] The technical solution adopted to achieve the purpose of the present invention is:

[0011] A structure for reducing the tangential frost heave force of a pile foundation in a seasonally frozen soil area, comprising a thermal insulation layer, a thermal rod and a pile-soil isolation sleeve, wherein:

[0012] The thermal insulation layer is arranged around the pile foundation and laid on the natural surface;

[0013] The pile-soil isolation sleeve is coaxially coated on the surface of the pile foundation, the top of the pile-soil isolation sleeve is flush with the ground surface, and the bottom is located at the maximum freezing depth;

[0014] The heat rods are axially arranged and evenly distributed in a ring shape and fixed on the inner side of the steel cage of the pile foundation. Each heat rod is a closed metal tube filled with a working fluid. Each heat rod includes an evaporation section, an insulation section and a condensation section. The evaporation section is located in a deep non-frozen area, the condensation section is located in a seasonally frozen soil layer, the insulation section is located between the evaporation section and the condensation section, and is located below the maximum freezing depth. The evaporation section is filled with working fluid liquid. In winter, the working fluid liquid evaporates under the action of the upper and lower temperature differences and turns into working fluid vapor, passes through the insulation section and enters the condensation section. In the condensation section, the working fluid vapor condenses into a liquid phase, passes through the insulation section and falls back into the evaporation section.

[0015] In the above technical solution, the thermal insulation layer is arranged in a ring shape around the pile foundation, the upper surface of the thermal insulation layer is flush with the natural surface, and the lower surface is embedded in the stratum. The thickness of the thermal insulation layer is 20-30 cm.

[0016] In the above technical solution, the steel cage is in the shape of a cylindrical barrel.

[0017] In the above technical solution, there are two heat rods, the diameter of the heat rods is 45-65 mm, and the tops of the heat rods are flush with the ground surface.

[0018] In the above technical solution, the tube wall material of the metal tube is aluminum, copper or stainless steel.

[0019] In the above technical solution, the filling rate of the working fluid is 20-30%.

[0020] In the above technical solution, the working fluid is liquid ammonia.

[0021] In the above technical solution, the outer wall of the evaporation section is fixed with evaporation section fins, the outer wall of the insulation section is coated with an insulation layer, the outer wall of the condensation section is fixed with condensation section fins, the evaporation section fins and the condensation section fins are made of aluminum or copper, the fin spacing between the evaporation section fins and the condensation section fins is 2-10mm, the fin thickness is 0.2-1mm, and the fin height is 5-30mm.

[0022] Another aspect of the present invention also includes a working method of the structure for reducing the tangential frost heave force of pile foundations in seasonal frozen soil areas, including the following steps: the evaporation section is located at the lower end of the heat rod and buried in the deep pile foundation. In winter, the low temperature of the seasonal frozen soil causes the working fluid vapor on the upper part of the heat rod to condense into liquid on the inner wall of the condensation section, thereby reducing the internal pressure of the heat rod, causing the liquid working fluid in the lower evaporation section to boil and evaporate. During the boiling and evaporation of the liquid working fluid, the evaporation section continuously absorbs deep heat. During the condensation of the working fluid vapor, the condensation section releases heat to the seasonal frozen soil layer. The liquid working fluid condensed in the condensation section flows back to the evaporation section under the action of gravity. Through this continuous convection process, the heat from the deep thawed soil can be used to warm the seasonal frozen soil layer, thereby reducing the maximum freezing depth.

[0023] Another aspect of the present invention also includes a construction method for reducing the tangential frost heave force of a pile foundation in a seasonally frozen soil region, comprising the following steps:

[0024] Step 1, determine the structural parameters of the pile foundation;

[0025] Step 2, determining the structural parameters of the heat rod;

[0026] Step 3, drilling the pile foundation;

[0027] Step 4, making a steel cage, arranging the hot rods axially and evenly annularly fixed on the inner side of the steel cage, the condensation section is located in the seasonal frozen soil layer, and the outer side of the steel cage within the seasonal frozen soil layer is covered with a pile-soil isolation sleeve;

[0028] Step 5, place the steel cage in the borehole, leave a concrete protective layer between the bottom of the steel cage and the bottom of the borehole, the main reinforcement of the top of the steel cage is exposed on the pile top, the top of the pile-soil isolation sleeve is flush with the ground surface, and the bottom is at the maximum freezing depth;

[0029] Step 6, injecting concrete into the drilled hole;

[0030] Step 7, after the pile foundation structure is constructed, a thermal insulation layer is horizontally laid around the pile foundation, with the lower portion of the thermal insulation layer embedded in the ground and the upper surface flush with the natural ground surface.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. The present invention introduces a heat rod for the first time for the prevention and control of pile foundation frost pullout in frozen soil areas during strong frost heave seasons, and combines two traditional measures, namely, a thermal insulation layer and a pile-soil isolation sleeve, to form a composite pile foundation frost pullout prevention and control structure, which can warm the seasonal frozen soil layer, weaken the tangential frost heave force, and inhibit the freezing depth around the pile and the development of pile foundation frost pullout.

[0033] 2. On the one hand, the present invention can realize passive starting by arranging a heat rod in the pile foundation, wherein the evaporation section of the heat rod is located in a deep non-frozen area, and the condensation section is located in the seasonal frozen depth. In winter, when the temperature around the condensation section of the heat rod is lower than that at the evaporation section, due to the effect of the pressure difference, the working fluid liquid begins to evaporate and forms working fluid vapor. The working fluid vapor rises to the condensation section, contacts the pipe wall, and condenses to release the latent heat of phase change. At the same time, the working fluid vapor is liquefied, and under the action of its own gravity, it flows back to the evaporation section along the pipe wall. This process is repeated to conduct the heat around the deep pile foundation to the seasonal frozen soil layer in the cold season. The deep geothermal energy and the latent heat of phase change of groundwater are used to warm the seasonal frozen soil layer and inhibit the development of the frozen depth around the pile. In addition, the thermal insulation effect of the thermal insulation layer effectively prevents the loss of heat from the shallow soil around the pile in winter. The combined effect reduces the maximum frozen depth around the pile and improves the frost heave of the seasonal frozen layer around the pile. On the other hand, fiberglass plates are wrapped on the surface of the pile foundation in the seasonally frozen layer to form a pile-soil isolation sleeve, which ensures the flatness of the pile foundation surface while isolating the pile-soil contact, effectively weakening the tangential frost heave force on the pile caused by soil frost heave.

[0034] From the above two aspects, the present invention can play the role of heat insulation, reducing freezing depth, and weakening freezing pullout force, effectively controlling the development of the cumulative freezing pullout of pile foundations in frozen soil areas during strong frost heaving seasons, and completely solving the problem of pile foundation instability caused by pulling out.

[0035] 3. In the present invention, a shallow heating system in seasonal frozen soil areas is formed by introducing heat rods and combining traditional heat insulation measures to reduce the heat loss of shallow soil in winter, and utilize deep geothermal energy and groundwater phase change latent heat in seasonal frozen soil areas with strong frost heave to warm the seasonal frozen soil layer and inhibit the freezing depth and frost heave development around the piles. Thus, the development of the accumulated frozen heave of pile foundations in seasonal frozen soil areas with strong frost heave can be simply and effectively controlled.

[0036] 4. The structure of the present invention is environmentally friendly, simple in structure, and convenient to construct, and is easy to promote and use on a large scale in frozen soil areas during strong frost heave seasons. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the structure of the present invention;

[0038] Figure 2 It is a top view of the structure of the present invention;

[0039] Figure 3 for Figure 1 Diagram of the structure of the middle heat rod;

[0040] Figure 4 This is the working principle diagram of the hot rod;

[0041] Figure 5 This is a schematic diagram of the winter working principle of the structure of the present invention;

[0042] Figure 6 It is a flow chart of the structural construction method of the present invention.

[0043] In the figure: 1-pile foundation, 2-thermal insulation layer, 3-thermal rod, 4-pile-soil isolation sleeve, 5-reinforcement cage;

[0044] 31-evaporation section, 32-adiabatic section, 33-condensation section;

[0045] 311-working fluid, 312-evaporation section fins, 331-condensation section fins. DETAILED DESCRIPTION

[0046] The present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0047] A structure for reducing the tangential frost heave force of a pile foundation in a seasonally frozen soil region, comprising a thermal insulation layer 2, a thermal rod 3 and a pile-soil isolation sleeve 4, wherein:

[0048] The thermal insulation layer 2 is arranged in a ring shape around the pile foundation 1 and laid on the natural surface. Preferably, the upper surface of the thermal insulation layer 2 is flush with the natural surface, and the lower surface is embedded in the stratum. The thickness of the thermal insulation layer 2 is 20-30 cm.

[0049] The pile-soil isolation sleeve 4 is coated on the surface of the pile foundation 1, the top of the pile-soil isolation sleeve 4 is flush with the ground surface, and the bottom is located at the maximum frost depth. Preferably, the material of the pile-soil isolation sleeve 4 is glass fiber reinforced plastic;

[0050] The heat rods 3 are axially arranged and evenly distributed in a ring shape and fixed on the inner side of the steel cage 5 of the pile foundation 1. Preferably, the steel cage 5 is in a cylindrical barrel shape. There are two heat rods 3. The diameter of the heat rods 3 is 45-65 mm. The top of the heat rods 3 is level with the ground surface. Each heat rod 3 is a closed metal tube filled with a working fluid. Each heat rod 3 includes an evaporation section 31, an insulation section 32 and a condensation section 33. The evaporation section 31 is located in a deep non-frozen area, the condensation section 33 is located in a seasonally frozen soil layer, and the insulation section 32 is located between the evaporation section 31 and the condensation section 33. The evaporation section 31 is below the maximum freezing depth. The evaporation section 31 is filled with a working fluid liquid 311, which has the characteristics of low boiling point and high vapor pressure. The filling rate of the working fluid liquid 311 is 20-30%. In winter, the shallow soil freezes, the working fluid vapor in the condensation section 33 condenses and reduces the pressure in the metal pipe. The working fluid liquid 311 in the evaporation section 31 is evaporated by the pressure reduction and transformed into working fluid vapor, passes through the adiabatic section 32 and enters the condensation section 33. In the condensation section 33, the working fluid vapor condenses into a liquid phase, passes through the adiabatic section 32 and falls back into the evaporation section 31. The working fluid liquid is liquid ammonia.

[0051] The evaporation section 31 is located at the lower end of the heat rod 3 and buried in the deep pile foundation to absorb the heat of the thawed soil in winter. The working fluid liquid 311 in the metal tube absorbs the surrounding heat through evaporation phase change; the insulation section 32 is usually located below the maximum seasonal freezing depth and does not directly participate in the heat exchange process. In this section, the vaporized working fluid vapor rises through its own pressure difference and is transmitted to the condensation section 33; the condensation section 33 is usually located at the upper end of the heat rod 3 and is arranged in the seasonal frozen soil layer (cold source). After the working fluid vapor reaches the condensation section 33, it exchanges heat with the external cold source through heat dissipation, cools and condenses into liquid, and releases heat into the seasonal frozen soil, thereby reducing the maximum freezing depth.

[0052] The heat rod 3 comprises a metal tube filled with a working medium. The tube wall of the metal tube is made of metal material with good thermal conductivity, such as aluminum, copper or stainless steel, to ensure that external heat can be quickly transferred to the inside of the metal tube, thereby achieving efficient heat transfer through the phase change of the working medium.

[0053] Preferably, the outer wall of the evaporation section 31 is fixed with an evaporation section fin 312, the outer wall of the insulation section 32 is coated with an insulation layer, and the outer wall of the condensation section 33 is fixed with a condensation section fin 331. The evaporation section fin 312 and the condensation section fin 331 are usually made of aluminum and copper. The fin spacing is usually designed to be between 2-10 mm, the fin thickness is usually designed to be between 0.2-1 mm, and the fin height is usually between 5-30 mm.

[0054] Example 2

[0055] The working method of the structure for reducing the tangential frost heave force of pile foundation in seasonal frozen soil area as described in Example 1 is as follows:

[0056] The heat rod 3 is a gravity-assisted cooling device, the evaporation section 31 of the heat rod 3 is embedded in the thawed soil (deep non-frozen area) with a relatively high temperature, while the condensation section 33 is buried in the seasonally frozen soil layer with a low temperature.

[0057] When winter comes, cold air cools and freezes the shallow soil, causing the working fluid vapor to condense and reduce the pressure in the pipe. Then the working fluid liquid begins to boil and evaporate, taking away the heat from the deeper, warmer thawed soil. The working fluid vapor rises and condenses on the inner surface of the condensation section 33, releasing heat to the seasonal frozen soil layer. At the same time, it condenses on the inner wall of the condensation section 33 into liquid, which flows back to the evaporation section 31 under the action of gravity. Through this continuous convection process, the heat from the deep thawed soil can be used to warm the seasonal frozen soil layer, thereby reducing the freezing depth and weakening the effects of frost heave and frost pull. In the warm season, the heat rod stops working and transfers very little heat.

[0058] The thermal insulation layer 2 effectively isolates the seasonal frozen soil layer around the pile from the heat exchange with the cold air, changes the original heat balance conditions, and slows down the development of frozen depth. In addition, under the effect of the lateral heat exchange of the seasonal frozen soil layer (heat exchange between the heat rod 3 and the seasonal frozen soil layer), the migration direction of the freezing front is changed (such as Figure 5 As shown in the figure, the development direction of the condensed ice is no longer vertical, which changes the original direction of the frost heave force and weakens the frost pull effect.

[0059] Example 3

[0060] The construction method of the structure for reducing the tangential frost heave force of pile foundations in seasonal frozen soil areas as described in Example 1 comprises the following steps:

[0061] Step 1, through field tests and reference materials, determine the design parameters, the parameters include side resistance, end resistance, seasonal maximum freezing depth and unit tangential frost heave force. Through stability verification, determine the pile foundation structure and structural parameters, the parameters include pile length, pile diameter, reinforcement and concrete grade. The above parameter determination methods are all prior art and will not be repeated here. In this embodiment, the pile diameter is 1.2m, the cross-section reinforcement ratio is 0.65%, and the concrete grade is C30.

[0062] At the same time, the following construction preparations are carried out:

[0063] (1) Site preparation: Clean the construction site and level it to ensure normal operating space for machinery and equipment.

[0064] (2) Measurement and layout: According to the design drawings, positioning and layout are carried out to determine the specific location of the pile foundation.

[0065] (3) Mechanical equipment preparation: Check drilling equipment, concrete equipment and other machinery to ensure that the equipment is operating normally and the materials are ready

[0066] Step 2, according to the principle of conservation of energy, combined with the pile foundation structure, air temperature and hydrological conditions, deep ground temperature, seasonal freezing depth and shallow soil characteristics, determine the structural parameters of the heat rod, the parameters include the overall length and diameter of the heat rod, as well as the length of the condensation section, insulation section, evaporation section, type of working fluid and filling rate. The above parameter determination methods are all prior art and will not be repeated here. In this embodiment, the diameter of the heat rod is not less than 45mm, and the working fluid filling rate is not less than 20%.

[0067] Step 3: Select a specific drilling process for pile foundation drilling based on hydrogeology, engineering geology, load type, construction environment and regulatory requirements.

[0068] The drilling steps are as follows:

[0069] (1) Positioning drilling: Drill holes using a drilling rig according to the measured pile positions. Ensure that the drilling positions are consistent with the design requirements.

[0070] (2) Drilling process control: During the drilling process, monitor the verticality, hole diameter and depth of the borehole to prevent deviation or hole collapse.

[0071] (3) Mud wall protection: In order to prevent hole collapse, mud wall protection is usually required to maintain the stability of the hole wall.

[0072] (4) Hole cleaning: After drilling, clean the bottom of the hole to ensure that there is no silt or debris at the bottom of the hole to ensure the bearing capacity of the pile foundation and the quality of the grouting. Use methods such as slurry replacement or clean water circulation to clean the hole to ensure that the hole is clean.

[0073] Step 4, make a cylindrical barrel-shaped steel cage 5, set the hot rod 3 axially and evenly annularly fixed on the inner side of the steel cage 5, ensure that the upper condensation section 33 is located in the seasonal frozen soil layer, the condensation section 33 is greater than 50 cm from the top of the steel cage 5 to avoid the pile head processing section, and the outer side of the steel cage within the seasonal frozen soil layer is covered with a pile-soil isolation sleeve 4 (made of fiberglass).

[0074] Specifically, the preparation steps of the steel cage 5 are as follows:

[0075] (1) Material preparation: Be familiar with the design requirements of the pile foundation, including pile type, diameter, length and reinforcement method. Prepare the required steel bars, tying wires and other materials according to the design requirements.

[0076] (2) Steel bar processing: Cut the steel bars according to the dimensions of the design drawings to ensure that the length of each steel bar meets the requirements. For steel bars that need to be bent, bend them according to the design requirements, using special equipment to ensure the accuracy of the bending angle and radius.

[0077] (3) Make steel cage: Make steel cage according to design drawings and ensure that the steel bars meet the specifications and quality requirements.

[0078] The installation steps of Hot Rod 3 are as follows:

[0079] (1) Positioning: Place the hot rod on the steel cage and position it according to the position indicated on the design drawing. Ensure that there is an appropriate distance between the hot rod and the main reinforcement so that it can be fully wrapped during subsequent concrete pouring.

[0080] (2) Installation: Starting from one end, pass the binding wire around the hot rod and the main reinforcement, then tighten and tie a knot. Pay attention to the strength when binding, and do not tie it too loose or too tight to avoid damaging the reinforcement or affecting the overall structure.

[0081] (3) Inspection: After the binding is completed, check the position and fixation of each heat rod to ensure that it meets the design requirements. If any problems are found, adjust the position or re-bind in time.

[0082] Step 5, placing the steel cage 5 in the drilled hole, leaving a 10 cm thick concrete protective layer between the bottom of the steel cage 5 and the bottom of the drilled hole, preferably, the thickness of the concrete protective layer is 5 to 6 cm, the top main reinforcement of the steel cage 5 is exposed 30 cm from the top of the pile, the top of the pile-soil isolation sleeve 4 is flush with the ground surface, and the bottom is located at the maximum freezing depth.

[0083] The installation steps of the steel cage 5 are as follows:

[0084] (1) Preparation for hoisting: Ensure that the hoisting equipment (such as tower cranes, cranes, etc.) is in good condition and has passed the inspection. Confirm that the steel cage has been completed and has undergone necessary anti-rust treatment.

[0085] (2) On-site layout: According to the construction drawings and on-site conditions, the hoisting position of the steel cage should be reasonably planned. A cordon should be set up around the hoisting area to ensure that no personnel or obstacles enter.

[0086] (3) Hoisting the steel cage: Hoist the prepared steel cage into the hole to ensure that the center position of the steel cage is correct and not deformed.

[0087] The installation steps of the pile-soil isolation sleeve 4 are as follows:

[0088] (1) Hoisting of the pile-soil isolation sleeve 4: According to the design drawings, the installation position and direction of the pile-soil isolation sleeve 4 are clearly defined. The pile-soil isolation sleeve 4 is slowly placed into the pile hole, ensuring that it is vertical and aligned with the center line. A level can be used for calibration.

[0089] (2) Fixing of the pile-soil isolation sleeve 4: Confirm that the gap between the bottom of the pile-soil isolation sleeve 4 and the pile foundation 1 meets the design requirements. If necessary, the pile-soil isolation sleeve 4 can be fixed by a support frame or other means to prevent movement during subsequent construction.

[0090] Step 6, inject concrete into the borehole. According to the geological conditions (in this embodiment, the groundwater depth is shallow), hydrological conditions, construction equipment and specification requirements, the grouting process is selected. The pile foundation concrete is poured underwater using a conduit to ensure sufficient vibration during the grouting process. The hot rod 3 should be avoided during vibration.

[0091] The concrete pouring steps are as follows:

[0092] (1) Placement of the conduit: Install the concrete conduit and ensure that the bottom of the conduit is at an appropriate distance from the bottom of the hole to avoid blockage or concrete segregation.

[0093] (2) Concrete pouring: Concrete is poured through the conduit using continuous pouring to ensure that the concrete evenly fills the entire pile hole.

[0094] (3) Vibration and compaction: Vibration and compaction are used to ensure that the concrete is dense and avoid the formation of voids and honeycomb structures.

[0095] (4) As the concrete pouring is gradually completed, the guide tube is slowly pulled out to ensure that the concrete is densely filled in the hole. After the pile is completed, the surface treatment is carried out to ensure that the pile top elevation meets the design requirements.

[0096] Step 7: After the construction of pile foundation 1 is completed, maintenance and quality inspection are carried out.

[0097] (1) Maintenance: After completing the pile foundation construction, necessary maintenance should be carried out on the pile top to keep it moist to promote the growth of concrete strength.

[0098] (2) Quality inspection: The bearing capacity and construction quality of the pile foundation are inspected through low-strain testing, static load testing and other methods.

[0099] Step 8, shallow excavation, laying a thermal insulation layer 2 around the pile foundation 1, the lower part of the thermal insulation layer 2 is embedded in the stratum, and the upper surface is flush with the natural surface. In this embodiment, the thickness of the thermal insulation layer is 25 cm, and the layout range is 20 square meters according to the maximum freezing depth and pile foundation diameter in this area.

[0100] The steps of shallow excavation are as follows:

[0101] (1) Scope Determination: According to the design drawings, clearly define the scope of earthwork to be excavated and mark it.

[0102] (2) Excavation: Excavate in layers according to the designed depth and range to ensure that it does not exceed the design requirements.

[0103] The thermal insulation layer 2 is formed by splicing thermal insulation boards. The laying steps of the thermal insulation boards are as follows:

[0104] (1) Laying of thermal insulation layer 2: According to the design requirements, the thermal insulation boards are laid one by one around the pile foundation 1, ensuring that there are no gaps between each thermal insulation board and the joints should be staggered to improve the overall insulation effect. If necessary, special glue or adhesive can be used to fix the thermal insulation boards.

[0105] (2) Inspection and adjustment: After laying, the entire thermal insulation layer 2 is inspected to ensure that it is flat and has uniform thickness and meets the design requirements. If any problems are found, they should be adjusted in a timely manner.

[0106] After the construction is completed, the construction records and inspection reports are submitted for project acceptance. After the acceptance is qualified, the pile foundation construction task is completed.

[0107] The above is only a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A structure for reducing the tangential frost heave force of pile foundations in seasonal frozen soil areas, characterized in that: It includes thermal insulation layer, thermal rod and pile-soil isolation sleeve, among which: The thermal insulation layer is arranged around the pile foundation and laid on the natural surface; The pile-soil isolation sleeve is coaxially coated on the surface of the pile foundation, the top of the pile-soil isolation sleeve is flush with the ground surface, and the bottom is located at the maximum freezing depth; The heat rods are axially arranged and evenly distributed in a ring shape and fixed on the inner side of the steel cage of the pile foundation. Each heat rod is a closed metal tube filled with a working fluid. Each heat rod includes an evaporation section, an insulation section and a condensation section. The evaporation section is located in a deep non-frozen area, the condensation section is located in a seasonally frozen soil layer, the insulation section is located between the evaporation section and the condensation section, and is located below the maximum freezing depth. The evaporation section is filled with working fluid liquid. In winter, the working fluid liquid evaporates under the action of the upper and lower temperature differences and turns into working fluid vapor, passes through the insulation section and enters the condensation section. In the condensation section, the working fluid vapor condenses into a liquid phase, passes through the insulation section and falls back into the evaporation section.

2. The structure for reducing the tangential frost heaving force of pile foundations in seasonal frozen soil areas according to claim 1, characterized in that: The thermal insulation layer is arranged in a ring shape around the pile foundation, the upper surface of the thermal insulation layer is flush with the natural ground surface, and the lower surface is embedded in the ground. The thickness of the thermal insulation layer is 20-30 cm.

3. The structure for reducing the tangential frost heaving force of pile foundations in seasonal frozen soil areas according to claim 1, characterized in that: The steel cage is in the shape of a cylindrical barrel.

4. The structure for reducing the tangential frost heaving force of pile foundations in seasonal frozen soil areas according to claim 1, characterized in that: There are two heat rods, each with a diameter of 45-65 mm, and the top of the heat rod is flush with the ground surface.

5. The structure for reducing the tangential frost heaving force of pile foundations in seasonal frozen soil areas according to claim 1, characterized in that: The tube wall material of the metal tube is aluminum, copper or stainless steel.

6. The structure for reducing the tangential frost heaving force of pile foundations in seasonal frozen soil areas according to claim 1, characterized in that: The filling rate of the working fluid is 20-30%.

7. The structure for reducing the tangential frost heaving force of pile foundations in seasonally frozen soil areas according to claim 1, characterized in that: The working fluid is liquid ammonia.

8. The structure for reducing the tangential frost heaving force of pile foundations in seasonally frozen soil areas according to claim 1, characterized in that: The outer wall of the evaporation section is fixed with evaporation section fins, the outer wall of the insulation section is coated with an insulation layer, the outer wall of the condensation section is fixed with condensation section fins, the evaporation section fins and the condensation section fins are made of aluminum or copper, the fin spacing between the evaporation section and the condensation section is 2-10mm, the fin thickness is 0.2-1mm, and the fin height is 5-30mm.

9. The working method of the structure for reducing the tangential frost heave force of pile foundation in seasonal frozen soil area according to any one of claims 1 to 8, characterized in that: The following steps are involved: The evaporation section is located at the lower end of the heat rod and buried in the deep pile foundation. In winter, the low temperature of seasonal frozen soil causes the working fluid vapor on the upper part of the heat rod to condense into liquid on the inner wall of the condensation section, reducing the internal pressure of the heat rod, causing the liquid working fluid in the lower evaporation section to boil and evaporate. During the boiling and evaporation of the liquid working fluid, the evaporation section continuously absorbs deep heat. During the condensation of the working fluid vapor, the condensation section releases heat to the seasonal frozen soil layer. The liquid working fluid condensed in the condensation section flows back to the evaporation section under the action of gravity. Through this continuous convection process, the heat from the deep thawed soil can be used to warm the seasonal frozen soil layer, thereby reducing the maximum freezing depth.

10. The construction method of a structure for reducing tangential frost heaving force of pile foundation in seasonal frozen soil areas according to any one of claims 1 to 8, characterized in that: The following steps are involved: Step 1, determine the structural parameters of the pile foundation; Step 2, determining the structural parameters of the heat rod; Step 3, drilling the pile foundation; Step 4, making a steel cage, arranging the hot rods axially and evenly annularly fixed on the inner side of the steel cage, the condensation section is located in the seasonal frozen soil layer, and the outer side of the steel cage within the seasonal frozen soil layer is covered with a pile-soil isolation sleeve; Step 5, place the steel cage in the borehole, leave a concrete protective layer between the bottom of the steel cage and the bottom of the borehole, the main reinforcement of the top of the steel cage is exposed on the pile top, the top of the pile-soil isolation sleeve is flush with the ground surface, and the bottom is at the maximum freezing depth; Step 6, injecting concrete into the drilled hole; Step 7, after the pile foundation structure is constructed, a thermal insulation layer is horizontally laid around the pile foundation, with the lower portion of the thermal insulation layer embedded in the ground and the upper surface flush with the natural ground surface.

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