A deep foundation pit pile-soil system top antifreeze structure and construction method thereof

Abstract

The present invention relates to a deep foundation pit pile-soil system top antifreeze structure and a construction method thereof, belonging to the field of building construction technology. It comprises a medium-coarse sand cushion layer, a grid-shaped steel-plastic geogrid, a foamed concrete insulation board, a 1:3 cement mortar protective layer, soil behind the pile, a supporting structure, backfill soil, and a drain pipe. The foamed concrete insulation board is placed vertically close to the soil behind the pile, and is composed of a foamed concrete surface layer and a thickened insulation polystyrene board, and the other side and the structural gap are filled with cement mortar; the medium-coarse sand cushion layer is filled in the foundation pit soil and the upper layer of the foamed concrete insulation board; the geogrid is composed of a plastic belt and an internal steel wire, which is laid on the upper layer of the medium-coarse sand cushion layer and fixed by a U-shaped fixed steel hook; the structure proposes multiple measures to work together, effectively overcoming the large-scale migration of water inside the soil, reducing the frost heave deformation damage of the local structure near the pile of the deep foundation pit pile-soil system in the cold winter, improving the anti-freeze performance of the structure, and extending the service life of the structure.

Description

Technical Field

[0001] The invention belongs to the technical field of building construction, and in particular relates to a top antifreeze structure of a deep foundation pit pile-soil system and a construction method thereof. Background Art

[0002] In cold-region projects, frost heave is particularly pronounced during winter due to the presence of unsaturated soil. Because of this, frost heave, which causes damage to the main structure and supporting structures, is difficult to avoid in many cold-region projects. For example, in urban underground space projects, cracks appear in the retaining structure's crown beams and roadbed and pavement, leading to reduced anti-seepage performance, mud bubbling at the top and bottom of the foundation pit, and reduced strength, stability, and excessive deformation of the retaining structure. With urban development, subways have gradually become a major means of transportation. The excavation of deep subway foundation pits differs from that of ordinary roadbeds and pavements. Stations can reach depths of 7-10 meters, while subway construction is at least 10 meters deep, resulting in deep foundation pits. Deep foundation pits, with their large engineering scale and long construction periods, inevitably experience a wintering period. Frost heave of the unsaturated soil within the pit can have immeasurable consequences. Furthermore, the unfrozen water content in the soil is the primary factor determining soil frost heave and has a significant impact on this. The effects of frost heave are further exacerbated by external water replenishment.

[0003] Most existing antifreeze methods involve replacing soil at the top of the foundation pit during underground construction, or laying straw mats or insulation boards on the outside of the support structure for simple antifreeze. Both of these measures can only temporarily provide insulation during construction. For existing underground projects in northern China, seasonal freezing occurs every year, and the deep foundation pit soil undergoes freeze-thaw cycles. Without antifreeze measures, coupled with the external influence of rainfall, the water content in the soil increases dramatically. During frost heave, the deformation of the upper soil is too large, which can easily cause structural damage. Once the underground project is completed, it is difficult to implement additional antifreeze measures. Therefore, a composite deep foundation pit pile-soil system antifreeze structure for underground projects is proposed. This structure can effectively overcome the problems of large-scale internal water migration, excessive deformation near the piles, and poor overall stability during construction and under external water replenishment conditions, achieving both year-round insulation and alleviating the exacerbation of frost heave, which has become an urgent problem to be solved. Summary of the Invention

[0004] In order to solve the above-mentioned technical problems, taking into full consideration the winter duration and external water replenishment conditions in the northern permafrost zone, a deep foundation pit pile-soil system top antifreeze structure and its construction method are proposed, which has good integrity, simple structure, long-term use and convenient construction. The present invention proposes to use a medium-coarse sand cushion layer with a small modulus and a low initial moisture content as an isolation layer of the antifreeze structure. Due to its good water absorption, the medium-coarse sand in the interlayer can absorb a large amount of surrounding unfrozen water when frost heave occurs in the deep foundation pit, reduce water migration, fix a large amount of free water in the sand body, effectively cut off the capillary water effect in the soil, and greatly reduce the formation of horizontal and vertical frost heave forces in the deep foundation pit pile-soil system. At the same time, the present invention also adds a vertical foamed concrete insulation board and a vertical cement mortar protective layer in the center of the structure to have a multi-layer insulation effect, and the free water in the soil behind the pile can be drained through the drainage hole. In addition, the present invention uses a steel-plastic geogrid to fixedly connect the coarse sand in the interlayer with the foundation pit soil of the structure through steel hooks, which can effectively reduce the problems of excessive vertical displacement of the foundation pit top and lateral horizontal displacement of the pile body, and improve the stability of the local structure near the pile.

[0005] The technical solution adopted in the present invention is as follows:

[0006] A deep foundation pit pile-soil system top antifreeze structure comprises a medium-coarse sand cushion layer, a gridded steel-plastic geogrid, a foamed concrete insulation board, a cement mortar protective layer, soil behind the piles, a top cap beam, concrete interlocking piles, a U-shaped connecting steel hook, and backfill soil. The deep foundation pit pile-soil system top antifreeze structure is based on a deep foundation pit project in which 1200@900 concrete interlocking piles and cap beams serve as supporting structures. The structure achieves thermal insulation and antifreeze effects primarily through the coordinated action of multiple measures, including the provision of vertical foamed concrete insulation boards, horizontal medium-coarse sand cushion layers, and the laying of gridded steel-plastic geogrids. The medium-coarse sand cushion layer is between the steel-plastic geogrid and the lower soil; the steel-plastic geogrid is laid between the medium-coarse sand and the backfill soil and is fixed to the medium-coarse sand by a U-shaped fixing steel hook to form a whole deformable shape; the foamed concrete insulation board includes two layers, a foamed concrete surface layer and a polystyrene board, which is vertically placed between the soil behind the pile and the post-cast 1:3 cement mortar protective layer; the 1:3 cement mortar protective layer is filled in the gap between the foamed concrete insulation board and the soil behind the pile and the top crown beam; the support structure is a combination of the top crown beam and the concrete bite pile.

[0007] Furthermore, the medium-coarse sand cushion layer has a fineness modulus of 2.5-3.5 and a density of 1600 kg / m 3, thermal conductivity of 1.2W / (m·°C), specific heat capacity of 0.9kJ / (kg·°C), saturated moisture content of 0.4, residual moisture content of 0.01, and saturated permeability of 1e-7. The medium-coarse sand cushion layer has a low initial and saturated moisture content. Furthermore, because the particles of medium-coarse sand are larger than those of the soil, they are more absorbent. These two factors allow the medium-coarse sand in the cushion layer to absorb a large amount of surrounding unfrozen water when frost heave occurs in deep foundation pits, reducing water migration and fixing a large amount of free water in the sand, effectively interrupting the capillary action of the soil.

[0008] Furthermore, the grid-like steel-plastic geogrid is formed by combining transversely built-in steel wires, longitudinally built-in steel wires, an upper thickening layer, an intermediate plastic belt, and a lower thickening layer through special processing. The upper thickening layer, the intermediate plastic belt, and the lower thickening layer are made of polyethylene (PE) or polypropylene (PP) through prefabricated templates and heated and pressed. The size of the intermediate plastic belt is a rectangular frame with an inner diameter of 150mm×150mm for the small unit, with a diameter of 40mm at the corners. The plastic belt connecting strip is 5mm wide and 5mm thick. The upper and lower thickening layers are added to the upper and lower sides of the intermediate plastic belt at the center connection point of each small unit. The thickened rectangular material has a side length of 30mm and a thickness of 5mm. The high-strength steel wires are divided into transversely built-in steel wires and longitudinally built-in steel wires. Both are prefabricated steel wires with a diameter of 3mm buried in the horizontal bidirectional intermediate plastic belt of the grid-like steel-plastic geogrid. The grid-like steel-plastic geogrid is laid in a single sheet, 960mm wide, with the specific laying length consistent with the side length of the deep foundation pit. It is fixed to the underlying medium-coarse sand cushion layer via U-shaped fixing steel hooks. The plastic belt in the steel-plastic geogrid is corrosion-resistant, aging-resistant, and high-temperature resistant, while the high-strength steel wire has low elongation at break and high strength. The synergistic effect of the two ensures good consolidation of medium-coarse sand and soil layers, reducing deformation.

[0009] Furthermore, the foamed concrete insulation board between the foundation pit soil and the cement mortar protective layer consists of a foamed concrete surface layer, thickened insulating polystyrene panels, transverse internal grooves, longitudinal internal grooves, transverse internal steel wires, and longitudinal internal steel wires. The foamed concrete insulation board is a prefabricated component, primarily comprising a foamed concrete surface layer and thickened insulating polystyrene panels, and is a rectangular lightweight board with an overall thickness of 100-150 mm and a height of 1 m. Transverse internal grooves and longitudinal internal grooves are arranged on both sides of the thickened insulating polystyrene panels. Transverse internal steel wires and longitudinal internal steel wires are inserted on both sides at a thickness of 5 mm from the surface layer, with a spacing of 20-30 cm between the wires. A foamed concrete surface layer is added to one side of the thickened insulating polystyrene panels, forming a single unit with the internal steel wires and internal grooves. Another internal groove is reserved for later bonding with the other side after pouring 1:3 cement mortar. During the prefabrication process, the foamed concrete insulation board is manufactured by first securing the steel wires, then forming the insulating polystyrene panels, and then adding the foamed concrete surface layer. In actual projects, foamed concrete insulation panels are laid vertically and horizontally along the length of the foundation pit. During cold winter conditions, the thickened insulation panels provide excellent insulation, slowing the temperature drop in the soil behind, delaying the condensation and large-scale dynamic migration of unmoved water within the soil. Furthermore, their lightweight, earthquake-resistant construction, strong adhesion, ease of construction, and environmental and energy-saving characteristics offer a valuable reference for other engineering applications.

[0010] Furthermore, a 1:3 cement mortar protective layer is provided between the foamed concrete insulation board and the top crown beam. This layer bonds the foamed concrete insulation board to the top crown beam and concrete interlocking piles, forming a stable overall structure. The cement mortar layer, on one side, utilizes the transverse and longitudinal grooves, as well as the transverse and longitudinal steel wires, reserved for the insulation board, to ensure cross-bonding. Furthermore, the cement mortar protective layer serves to isolate the insulation board and provide some protection for the back insulation board.

[0011] Furthermore, the soil behind the pile is a natural soil layer of a deep foundation pit.

[0012] Furthermore, the top cap beam is a reinforced concrete structure, 1m high and 1m wide. The reinforced concrete interlocking piles are C30 rows with a spacing of 1200x900 mm. Based on the actual project design, the interlocking piles are arranged in rows for lateral support, providing stability and effectively saving on steel. The top is pre-installed with formwork, followed by drilling, then installing the rebar cage, and finally pouring the concrete together, effectively forming a single unit. This effectively avoids uneven bonding and the generation of additional stress at the interface of different pouring times.

[0013] Furthermore, the U-shaped fixed steel hook consists of a U-shaped hook body and a conical steel head, both of which are made of hot-rolled low-carbon wire rod and cold-drawn. The diameter of the U-shaped hook body is 2.5-6mm and the length is 8-15cm; the conical steel head is 1cm long and has a smooth surface.

[0014] Furthermore, the backfill soil is composed of slightly dense crushed stone, breccia soil, and clay soil, with a hard impurity content of more than 60%. The thickness of the backfill soil is between 150mm and 25mm, and is leveled with the crown beam.

[0015] Furthermore, the drainage pipe is composed of a PVC pipe, an outer geotextile, and a circular hole. The drainage pipe is buried in the concrete bite pile and the soil behind the pile at a downward slope of 5-10 degrees. The internal PVC pipe is made of polyvinyl chloride material, which is not only lightweight but also has good plasticity and corrosion resistance. The pipe diameter is 5-10cm and the pipe length is 2-4m. The outer geotextile is made of synthetic fiber with a thickness of 3-8mm, which can effectively prevent sand from entering the pipe. It can only allow the moisture inside the soil behind the pile to pass through the outer geotextile and the circular hole into the drainage hole for discharge. The circular hole is a hole with a diameter of 1-1.5cm opened on the pipe body. Two holes are opened opposite each other on the same horizontal line, and 3-5 holes are opened at intervals of 1m along the pipe body. It is used to collect moisture in the geotextile in the soil through the hole and drain into the pipe.

[0016] Beneficial effects of the present invention:

[0017] 1. The effects and advantages of the present invention are that the construction is convenient, the antifreeze and swelling reduction effects are obvious, and the invention can be used for a long time.

[0018] 2. The present invention selects low-cost medium-coarse sand as the core cushion layer of the anti-freeze structure, which can effectively overcome the large-scale migration of water in the soil and reduce the formation of horizontal and vertical frost heave forces in the pile-soil system in deep foundation pit projects and under external water replenishment conditions.

[0019] 3. Unlike existing underground engineering frost protection technologies, which rely on single measures, this invention incorporates an additional insulation panel at the center of the structure. Composed of a foamed concrete surface layer and insulating polystyrene panels, this panel provides secondary insulation. The other side is bonded to the rest of the structure via a protective layer of cement mortar. Furthermore, a drain pipe is incorporated to effectively drain the large amount of free water in the soil after freezing, reducing further frost heave.

[0020] 4. The present invention adds a layer of grid-like steel-plastic geogrid with built-in steel wires between the medium-coarse sand cushion layer and the upper backfill soil. The medium-coarse sand and the back soil are fixedly connected by the grid through U-shaped steel hooks to form an integral shape. The anti-freeze structure can be circulated for a long time, has good plasticity, is energy-saving and environmentally friendly, and can provide a reference for related projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1This is a schematic diagram of a top antifreeze structure of a deep foundation pit pile-soil system according to the present invention;

[0022] Figure 2 A three-dimensional schematic diagram of the top anti-freeze structure of a deep foundation pit pile-soil system;

[0023] Figure 3 This is a schematic plan view of a top anti-freeze structure for a deep foundation pit pile-soil system;

[0024] Figure 4 for Figure 3 Section 1-1 in;

[0025] Figure 5 This is a schematic diagram of the grid-shaped steel-plastic geogrid structure of the present invention;

[0026] Figure 6 This is a schematic diagram of the connection between the grid-shaped geogrid and the U-shaped fixed steel structure;

[0027] Figure 7 This is a schematic structural diagram of the foamed concrete insulation board in the present invention;

[0028] Figure 8 Schematic diagram of the support structure in the present invention;

[0029] Figure 9 This is a schematic diagram of the U-shaped fixed steel hook in the present invention;

[0030] Figure 10 Schematic diagram of the drain pipe in the present invention.

[0031] In the figure, 1 is a medium-coarse sand cushion layer; 2 is a grid-shaped steel-plastic geogrid; 2-1 is a transverse built-in steel wire; 2-2 is a first longitudinal built-in steel wire; 2-3 is an upper thickening layer; 2-4 is an intermediate plastic belt; 2-5 is a lower thickening layer; 3 is a foamed concrete insulation board; 3-1 is a foamed concrete surface layer; 3-2 is a thickened insulation polystyrene board; 3-3 is a transverse built-in groove; 3-4 is a longitudinal built-in groove; 3-5 is a transverse built-in steel wire; 3-6 is a second longitudinal built-in Steel wire; 4 is 1:3 cement mortar protective layer; 5 is soil behind the pile; 6 is top cap beam; 7 is concrete bite pile; 7-1 is concrete pile; 7-2-1 is vertical stress-bearing steel bar; 7-2-2 is spiral stirrup; 7-2 is concrete pile; 8 is U-shaped fixed steel hook; 8-1 is U-shaped hook body; 8-2 is tapered steel head; 9 is backfill soil; 10 is drain pipe; 10-1 is internal PVC pipe; 10-2 is outer geotextile; 10-3 is circular hole. DETAILED DESCRIPTION

[0032] In the present invention, unless otherwise expressly specified or limited, terms such as "mounted," "connected," "connect," and "fixed" should be understood broadly. For example, they may refer to fixed connection, detachable connection, or integration; they may refer to direct connection or indirect connection through an intermediate medium; they may refer to internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0033] The technical solutions of the embodiments of the present invention are explained and illustrated below in conjunction with the accompanying drawings of the present invention. However, the following embodiments are only preferred embodiments of the present invention and are not exhaustive.

[0034] like Figure 4 As shown, the supporting structure of the deep foundation pit pile-soil system is completed first. First, the location of the deep foundation pit supporting structure is determined by checking the drawings and measuring and setting out. Then, the soil of the height and thickness of the crown beam is excavated to lay out the crown beam formwork. Then, a fixed pile driver is used to drive a pile hole of a certain diameter and depth according to the design pile body instructions. According to the design instructions, the already tied steel cage is lowered into the hole of the concrete pile 7-2 in the concrete interlocking pile 7, and the designed steel bars are tied into the crown beam formwork. Furthermore, the C30 concrete that has been mixed in advance is poured into the interior of the plain piles and the concrete piles and the crown beam formwork. After the concrete is cured, the top crown beam formwork is removed.

[0035] Furthermore, if Figure 7 As shown, a hole is drilled in the concrete pile 7-1 at an angle of 5-10 degrees upwards, and a drainage pipe 10 consisting of a PVC pipe 10-1 and an outer geotextile 10-2 is inserted into the hole. If it is unstable, only a slight grouting is required in the gap.

[0036] Furthermore, if Figure 2 As shown, the soil behind the pile is excavated to a certain depth. A shallow rectangular trench is then excavated near the pile, approximately the combined thickness and depth of the foamed concrete insulation board 3 and the 1:3 cement mortar protective layer 4. The prefabricated foamed concrete insulation board 3 is then lowered vertically into the soil, aligned horizontally and vertically.

[0037] Furthermore, a medium-coarse sand cushion layer (1) with a fineness modulus of 2.5-3.5 is placed over the exposed excavated soil and the upper portion of the installed insulation panels. This is then turned evenly and manually compacted. The medium-coarse sand's inherent low deformation and high plasticity are utilized to alleviate stress concentration within the structure and reduce overall strain.

[0038] Furthermore, a prefabricated grid-like steel-plastic geogrid 2 is laid on the upper part of the medium-coarse sand cushion layer 1 along the side length direction of the deep foundation pit, and Figure 7The U-shaped steel hooks 8 shown are fixedly connected to the medium-coarse sand cushion layer 1 at equal intervals and on both sides of the geogrid. Because the U-shaped steel hooks 8 have tapered steel heads 8-2, the hooks can be fixed by simply aligning the middle plastic strip 2-4 of the geogrid 2 with the hook and pressing the two sides firmly into the medium-coarse sand cushion layer 1.

[0039] Furthermore, there is a certain gap between the foamed concrete insulation board and the top crown beam 6 and the concrete bite pile 7. The gap is filled with a cement mortar with a pre-mixed ratio of 1:3 to form a cement mortar protective layer, which has a certain protective effect on the internal foamed concrete insulation board 3 and at the same time makes the foamed concrete insulation board 3, the medium-coarse sand cushion layer 1, the grid-shaped steel-plastic geogrid 2, and the support structure form a whole, and the stability is enhanced.

[0040] Finally, after the 1:3 cement mortar protective layer 4 in the gap is poured and cured, backfill soil 9 is backfilled on the medium-coarse sand cushion layer 1 and the 1:3 cement mortar protective layer 4. The backfill soil is composed of miscellaneous and plain backfill soil composed of crushed stone, angular gravel, etc., which is turned evenly and compacted.

[0041] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A deep foundation pit pile-soil system top antifreeze structure, characterized by: The invention comprises a medium-coarse sand cushion layer (1), a grid-shaped steel-plastic geogrid (2), a foamed concrete insulation board (3), a 1:3 cement mortar protective layer (4), soil behind the pile (5), a top crown beam (6), a concrete bite pile (7), a U-shaped fixed steel hook (8), backfill soil (9) and a drain pipe (10); the medium-coarse sand cushion layer (1) is filled between the grid-shaped steel-plastic geogrid (2) and the lower soil and the foamed concrete insulation board (3); the grid-shaped steel-plastic geogrid (2) is composed of a transverse built-in steel wire (2-1), a first longitudinal built-in steel wire (2-2), an upper thickening layer (2-3), an intermediate plastic belt (2-4) and a lower thickening layer (2-5); the size of the intermediate plastic belt (2-4) is a small unit with an inner diameter of 1 A rectangular frame of 50mm×150mm, with a 40mm diameter fillet at the corner, a plastic strip connecting strip of 5mm width and 5mm thickness, and an upper thickening layer (2-3) and a lower thickening layer (2-5) are added to the upper and lower sides of the plastic strip in the center connection part of each small unit to connect the center point. The thickening layer is made of the same rectangular material with a side length of 30mm and a thickness of 5mm; the high-strength steel wire is divided into a transverse built-in steel wire (2-1) and a first longitudinal built-in steel wire (2-2), both of which are prefabricated steel wires with a diameter of 3mm buried in the horizontal bidirectional middle plastic strip (2-4) of the grid-shaped steel-plastic geogrid; the grid-shaped steel-plastic geogrid (2) is laid between the medium-coarse sand cushion layer (1) and the backfill soil (9) and is connected to the medium-coarse sand by a U-shaped fixed steel hook (8). The sand cushion layer (1) is fixed, and the foamed concrete insulation board (3) is composed of a foamed concrete surface layer (3-1), a thickened thermal insulation benzene board (3-2), a transverse built-in groove (3-3), a longitudinal built-in groove (3-4), a transverse built-in steel wire (3-5), and a second longitudinal built-in steel wire (3-6). The transverse built-in groove (3-3) and the longitudinal built-in groove (3-4) are arranged on both sides of the thickened thermal insulation benzene board (3-2). At the same time, the transverse built-in steel wire (3-5) and the second longitudinal built-in steel wire (3-6) are inserted at a thickness of 5 mm from the surface layer on both sides, and the distance between the steel wires is 20-30 cm. A foamed concrete surface layer (3-1) is added on one side of the thickened thermal insulation benzene board (3-2), and the two form a foamed concrete surface layer through the built-in steel wire and the built-in groove. The invention relates to a structure comprising a foamed concrete insulation board (3-2) and a thickened heat-insulating polystyrene board (3-2). The other side of the thickened heat-insulating polystyrene board (3-2) is provided with a built-in groove for later connection with a post-cast 1:3 cement mortar protective layer (4); the foamed concrete heat-insulating board (3) is vertically placed between the soil behind the pile and the post-cast 1:3 cement mortar protective layer (4); the 1:3 cement mortar protective layer (4) is filled in the gap between the foamed concrete heat-insulating board (3), the soil behind the pile (5) and the top crown beam (6); the combination of the top crown beam (6) and the concrete bite pile (7) serves as a supporting structure; the drain pipe (10) is composed of a PVC pipe (10-1), an outer geotextile (10-2) and a circular hole (10-3), and is buried in the concrete bite pile (7) and the soil behind the pile (5) at a downward inclination of 5-10 degrees.

2. The deep foundation pit pile-soil system top antifreeze structure according to claim 1, characterized in that: The medium-coarse sand cushion layer (1) has a fineness modulus of 2.5-3.5 and a density of 1600 kg / m 3 , thermal conductivity is 1.2W / (m·℃), specific heat capacity is 0.9kJ / (kg·℃), saturated moisture content is 0.4, residual moisture content is 0.01, and saturated permeability coefficient is 1e-7.

3. The antifreeze structure at the top of a deep foundation pit pile-soil system according to claim 1, characterized in that: The upper thickening layer (2-3), the middle plastic strip (2-4), and the lower thickening layer (2-5) are formed from polyethylene or polypropylene through a prefabricated template and heated and pressed. The grid-shaped steel-plastic geogrid is laid in a whole piece with a width of 960 mm. The specific laying length is consistent with the side length of the deep foundation pit, and is fixedly connected to the lower medium-coarse sand cushion layer (1) through a U-shaped fixing steel hook (8).

4. The deep foundation pit pile-soil system top antifreeze structure according to claim 1, characterized in that: The foamed concrete insulation board (3) is a prefabricated component, a rectangular lightweight board with an overall thickness of 100-150 mm and a height of 1 m, wherein the foamed concrete surface layer (3-1) has a thickness of 10-20 cm.

5. The antifreeze structure at the top of a deep foundation pit pile-soil system according to claim 1, characterized in that: A cement mortar protective layer (4) is provided between the foamed concrete insulation board (3) and the top crown beam (6), and the cement mortar protective layer (4) is a post-cast 1:3 cement mortar protective layer; the cement mortar protective layer is used to bond the foamed concrete insulation board (3), the top crown beam (6) and the concrete bite pile (7) to form an overall stable structure, and one side of the cement mortar protective layer is cross-bonded by a transverse built-in groove (3-3), a longitudinal built-in groove (3-4) reserved by the thickened insulation styrene board (3-2), a transverse built-in steel wire (3-5), and a second longitudinal built-in steel wire (3-6).

6. The deep foundation pit pile-soil system top antifreeze structure according to claim 1, characterized in that: The soil behind the pile (5) is a natural soil layer of a deep foundation pit; the top cap beam (6) is a reinforced concrete with a height of 1m and a width of 1m; the reinforced concrete interlocking piles are 1200@900 C30 pile rows, consisting of plain piles and concrete piles, and vertical stress-bearing steel bars (7-2-1) and spiral stirrups (7-2-2) are arranged inside the concrete piles.

7. The deep foundation pit pile-soil system top antifreeze structure according to claim 1, characterized in that: The U-shaped fixed steel hook (8) consists of a U-shaped hook body (8-1) and a tapered steel head (8-2), both of which are made of hot-rolled low-carbon wire rods and cold-drawn. The U-shaped hook body (8-1) has a diameter of 2.5-6 mm and a length of 8-15 cm; the tapered steel head (8-2) has a length of 1 cm and a smooth surface.

8. The antifreeze structure at the top of a deep foundation pit pile-soil system according to claim 1, characterized in that: The backfill soil (9) is composed of slightly dense crushed stone, breccia soil and clay soil, with a hard impurity content of more than 60%. The backfill soil thickness is between 150mm and 25mm, and is leveled with the top crown beam (6).

9. The deep foundation pit pile-soil system top antifreeze structure according to claim 1, characterized in that: The inner PVC pipe (10-1) is made of polyvinyl chloride, with a diameter of 5-10 cm and a length of 2-4 m; the outer geotextile (10-2) is made of synthetic fiber and has a thickness of 3-8 mm; the circular holes (10-3) are holes with a diameter of 1-1.5 cm opened on the pipe body, two of which are opened opposite each other on the same horizontal line, and 3-5 holes are opened along the pipe body at intervals of 1 m, for collecting moisture in the soil in the geotextile through the holes and discharging it into the pipe.

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