A prestressed frozen soil composite support structure and construction method

Abstract

The invention discloses a prestressed frozen soil composite support structure and a construction method, which are suitable for use in underground engineering construction. A frozen wall is set in a soft water-bearing stratum around an excavation range, and the frozen wall is wrapped around the top plate and two sides of the excavation range, wherein the inner side of the frozen wall is the inner boundary of the frozen soil, and the outer side is the outer boundary of the frozen soil, and freezing pipes are respectively arranged at the outer boundary of the frozen soil and the inner boundary of the frozen soil, and the freezing pipes control the development range of the frozen wall and limit the frost heave effect of the frozen wall during the freezing process, so that the formed frozen wall is compacted to improve the strength, and the frost heave effect of the frozen wall also causes the freezing pipes at the outer boundary of the frozen soil and the inner boundary of the frozen soil to produce prestressed deformation, so that the freezing pipes and the compacted frozen wall together constitute a prestressed frozen soil composite support structure, and the prestressed frozen soil composite support structure provides support for the excavation construction process of the soil body in the internal space of the frozen wall, maintains the stability of the external soil body, and suppresses the impact of the freezing construction on the environment.

Description

Technical Field

[0001] The invention relates to a prestressed frozen soil composite support structure and a construction method, and is particularly suitable for the field of underground engineering construction in water-containing soft soil strata. Background Art

[0002] During the construction of urban underground projects, when excavation space is formed before structural construction, it is necessary to form a support structure around the excavation space to maintain the stability of the external soil layer. Especially when excavating in soft and water-rich strata, it is also necessary to isolate groundwater from entering the construction area, thereby creating a good construction environment. The artificial freezing method turns the soft soil stratum into frozen soil, thereby increasing the stratum strength and isolating groundwater, giving full play to the advantages of the freezing method. At present, in freezing construction, due to the characteristics of frozen soil expanding around along the freezing pipe, the freezing pipe is located in the middle position of the frozen wall, and the temperature and strength of the edge of the frozen wall are high, and the overall uniformity of the frozen wall is poor. As for the stress distribution characteristics of the cross-section after the frozen wall is loaded, the stress at the edge of the frozen wall is large, while the stress in the middle is small. Therefore, the frozen pipe in the middle position of the frozen wall cannot play the high-strength bearing role of steel, and the bearing role of the frozen pipe is not considered in the design. Moreover, due to the large stress at the edge of the frozen wall and the low strength of the frozen soil, a thicker frozen wall is generally required to provide support, so that the frozen soil development range far exceeds the design thickness range of the frozen wall. At the same time, the expansion of the volume of water after freezing during the freezing process will produce frost heave, which will also have a negative impact on the surrounding environment. The increased thickness of the frozen wall will produce additional frost heave, which will have an adverse effect on surrounding buildings and underground pipelines. Therefore, large-diameter steel pipes such as steel pipe sheds or pipe curtains are also used in underground engineering construction to carry the load, and cooperate with the water-sealing effect of the frozen wall to jointly provide maintenance for the excavation range. In these structures, the frozen wall can only provide a water-stopping effect. The bearing effect of frozen soil and steel pipes is not considered during design and construction, resulting in a large diameter of the steel pipe of the steel pipe shed, an uneven frozen wall, and the steel of the frozen pipe does not work. The steel pipe shed has no limiting effect on the frost heave of the frozen wall, so the frost heave generated during the freezing process will also have an adverse effect on the surrounding environment. Summary of the invention

[0003] In view of the shortcomings of the existing technology, a prestressed frozen soil composite support structure and working method are provided to give full play to the advantages of high tensile strength of frozen pipe steel, improve the uniformity of frozen soil formation, and give full play to the high bearing capacity advantages of the support structure. That is, the frozen pipe is limited to the inner and outer edge positions of the frozen wall, and the frost heave effect generated in the process of forming frozen soil can not only compact the frozen wall to improve the strength of the frozen soil, but also generate prestress in the frozen pipe, thereby forming a prestressed frozen soil composite support structure. The new support structure replaces the steel pipe shed with frozen pipes. When bearing external loads, the two circles of frozen pipes at the edge of the frozen wall can effectively give full play to the advantages of high strength of steel, and at the same time can also suppress the impact of frost heave on the surrounding environment. The uniform frozen wall and the bearing effect of high-strength steel frozen pipes can improve the bearing performance of the support structure and ensure the safety of excavation and structural construction.

[0004] In order to achieve the above technical objectives, the prestressed frozen soil composite support structure of the present invention is a frozen wall arranged in the soft water-bearing stratum around the excavation range, the frozen wall is wrapped around the top plate and two sides of the excavation range, wherein the inner side of the frozen wall is the inner boundary of the frozen soil, and the outer side is the outer boundary of the frozen soil, and a plurality of freezing pipes are respectively provided at the outer boundary of the frozen soil and the inner boundary of the frozen soil, the frozen wall and the plurality of freezing pipes constitute a prestressed frozen soil composite support structure, and the prestressed frozen soil composite support structure provides support for the soil excavation construction process within the excavation range inside the frozen wall.

[0005] Furthermore, the freezing wall in the soft water-bearing stratum is arranged along the edge of the excavation range, and the freezing range of the freezing wall is limited between the outer boundary and the inner boundary of the frozen soil and does not spread, so as to prevent the freezing wall from radiating cold to the outside of the soft water-bearing stratum and losing cold, and the freezing wall forming process produces frost heave effect and affects the surrounding environment; the freezing wall provides support force for the soil excavation construction process within the excavation range while blocking the water in the soft water-bearing stratum from penetrating into the excavation range, thus creating a good excavation construction environment inside the excavation range; the freezing pipes arranged at the outer boundary and the inner boundary of the frozen soil only release cold to the inside of the freezing wall in one direction, and limit the frost heave deformation generated during the formation of the freezing wall, and the freezing pipes and the freezing wall constitute a prestressed frozen soil composite support structure.

[0006] Furthermore, the prestressed frozen soil composite support structure includes a plurality of freezing pipes arranged along the direction of the excavation range. A plurality of freezing pipes are horizontally arranged at different height intervals at the inner boundary and the outer boundary of the frozen soil to form a frozen wall. While the freezing pipes provide cooling for the frozen wall, the plurality of freezing pipes arranged at the outer boundary and the inner boundary of the frozen soil effectively limit frost heave deformation during the formation of the frozen wall.

[0007] Furthermore, the freezing pipe is a one-way freezing device, and the side wall of the freezing pipe includes a cooling release surface and a non-cooling release surface, wherein the cooling release surface of the freezing pipe arranged at the outer boundary of the frozen soil points to the excavation range, and the cooling release surface of the freezing pipe arranged at the inner boundary of the frozen soil points to the soft water-bearing stratum outside the excavation range, and the cooling release surface of the freezing pipe arranged at the inner boundary of the frozen soil is arranged opposite to the cooling release surface of the freezing pipe arranged at the outer boundary of the frozen soil, thereby ensuring that the development range of the freezing wall is limited between the outer boundary and the inner boundary of the frozen soil, so that the freezing pipe is always at the edge of the frozen soil structure.

[0008] Furthermore, the freezing pipe is a low-carbon steel pipe. The freezing pipe has a non-cold-releasing surface formed by coating the outer side with thermal insulation paint, and the side not coated with the thermal insulation paint is the cold-releasing surface; or by using a divided-chamber circulating low-temperature refrigerant or vacuum insulation in the freezing pipe to concentrate the cold energy on the freezing wall side, limiting the expansion range of the frozen soil, so that the two circles of freezing pipes inside and outside the freezing wall are always located at the edge of the freezing wall.

[0009] A freezing method for a prestressed frozen soil composite support structure, the steps of which are as follows: in advance, freezing pipes are horizontally inserted into the soft water-bearing strata surrounding the two sides and the top plate of the excavation range to be constructed, at which time, the cooling release surface of the installed freezing pipes points to the soft water-bearing strata, the thickness of the freezing wall is preset according to needs, and a circle of freezing pipes is constructed to surround the excavation range after leaving enough space for the thickness of the freezing wall, and then the cooling release surface of the constructed freezing pipes points to the excavation range, so that the freezing wall is only formed between two circles of freezing pipes, the expansion range of the freezing wall is limited, and the two circles of freezing pipes are always located at the edge position of the formation of the freezing wall; during the formation of the freezing wall, the frost heave effect generated by the expansion of the frozen volume of water in the soft water-bearing stratum is constrained by the freezing pipes at the outer boundary and the inner boundary of the frozen soil, causing the deformation of the freezing pipes and the compaction of the freezing wall, thereby generating prestress in the freezing pipes and the freezing wall, forming a prestressed frozen soil composite support structure without causing deformation of the surrounding strata.

[0010] Furthermore, the prestressed frozen soil composite support structure is composed of a plurality of freezing pipes and freezing walls that are horizontally arranged and spaced apart. The spacing between the plurality of freezing pipes is adjusted as needed. The smaller the spacing, the stronger the bearing capacity that the prestressed frozen soil composite support structure can provide.

[0011] Further, the specific steps are as follows:

[0012] a. Arrange two circles of freezing pipes at the outer boundary of the excavation range and the outer boundary of the frozen wall of preset thickness. If the pre-designed thickness of the frozen wall is large, additional freezing pipes can be arranged between the two circles of freezing pipes;

[0013] b. Circulate low-temperature refrigerant inside the freezing pipe, and through the unidirectional freezing effect on the surface of the freezing wall, the frozen soil will only develop between the two circles of freezing pipes to form a freezing wall, while controlling the expansion range of the outer boundary and the inner boundary of the frozen soil, ensuring that the two circles of freezing pipes are located at the inner and outer edges of the freezing wall respectively, coordinating with the stress distribution characteristics on the cross section of the supporting structure, and giving full play to the advantages of the high tensile strength of the freezing pipe steel;

[0014] c. By reducing the spacing between the multiple freezing pipes forming the frozen wall, the adverse effects of frost heave during the freezing process on the surrounding environment of the frozen wall can be limited. Moreover, the frost heave constrained by the freezing pipes will compact the frozen wall, thereby increasing the strength of the frozen soil. The frost heave will also cause the frozen pipes to generate prestress, thereby increasing the bearing capacity of the frozen pipes, thereby forming a prestressed frozen soil composite support structure. At the same time, the frozen wall can also effectively prevent moisture from the soft water-bearing strata from invading the excavation range.

[0015] d. Under the bearing and water sealing function of the prestressed frozen soil composite support structure, excavation construction of the soil inside the excavation range is carried out to form the excavation range, and subsequent structural construction is carried out inside the excavation range;

[0016] e. After the structural construction is completed, stop the refrigerant circulation in the frozen pipes, cut off the frozen pipes, and complete the entire construction process after the ground thaws.

[0017] Beneficial effects: The freezing pipes in the prestressed frozen soil composite support structure limit the impact of frost heave on the surrounding environment, and transform the conventional negative effects of frost heave into positive effects. The prestress generated in the internal frozen soil and frozen pipes by frost heave is used to form a prestressed frozen soil composite support structure, which can improve the bearing capacity of the composite support structure. The freezing pipes arranged at the boundary of the frozen wall can give full play to the advantages of good tensile and high compressive strength of steel, and replace the steel pipes in the pipe shed or pipe curtain structure, which can not only ensure construction safety but also save construction costs.

[0018] This method improves the strength of prestressed frozen pipes and frozen soil, further improves the bearing capacity of the composite support structure, enhances the water sealing effect, and reduces the deformation of frozen soil during the bearing process. During construction, appropriate parameters such as freezing pipe spacing, size, and arrangement circle diameter interval can be selected according to the differences in bearing requirements, frost heave control standards, and construction requirements at different locations. The arrangement range of freezing pipes and frozen walls can also be adjusted as needed, so that the formed prestressed frozen soil composite support structure can not only give full play to the good bearing performance and water sealing effect, ensure construction safety, but also greatly reduce the volume of frozen soil, inhibit the impact of freezing construction on the environment, save construction costs, and reflect significant economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1It is a schematic diagram of a prestressed frozen soil composite support structure according to an embodiment of the present invention.

[0020] In the figure: 1- ground surface; 2- soft water-bearing stratum; 3- outer boundary of frozen soil; 4- frozen pipe; 5- frozen wall; 6- excavation range; 7- inner boundary of frozen soil. DETAILED DESCRIPTION

[0021] The embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

[0022] like Figure 1 As shown, a prestressed frozen soil composite support structure of the present invention is characterized by: a freezing wall 5 arranged in the soft water-bearing stratum 2 around the excavation range 6, the freezing wall 5 is wrapped around the top plate and the two sides of the excavation range 6, wherein the top plate is a flat top plate or an arched top plate to provide support performance as needed, and the freezing wall 5 can be set in the soft water-bearing stratum 2 at the bottom plate for waterproofing according to the surrounding environment, or it can be not set; wherein the inner side of the freezing wall 5 is the frozen soil inner boundary 7, and the outer side is the frozen soil outer boundary 3, and the frozen soil outer boundary 3 and the frozen soil inner boundary 7 are respectively provided with freezing pipes 4. The freezing wall 5 in the soft water-bearing stratum 2 is arranged along the edge of the excavation range 6, and the freezing range of the freezing wall 5 is limited to between the outer boundary 3 of the frozen soil and the inner boundary 7 of the frozen soil and does not spread, so as to prevent the freezing wall 5 from radiating cold and losing cold to the soft water-bearing stratum 2, and the process of forming the freezing wall affects the surrounding environment; the freezing wall 5 provides support force for the excavation range 6 while blocking the water in the soft water-bearing stratum 2 from penetrating into the excavation range 6, and the freezing pipes arranged on the freezing wall 5 at the outer boundary 3 and the inner boundary 7 of the frozen soil only release cold in one direction toward the freezing wall 5, thereby forming a freezing bearing structure at the outer boundary 3 and the inner boundary 7 of the frozen soil, and the freezing pipes and the freezing wall together constitute a prestressed frozen soil composite support structure. The prestressed frozen soil composite support structure includes multiple freezing pipes 4 and freezing walls 5 arranged along the direction of the excavation range. Multiple freezing pipes 4 are horizontally arranged at different height intervals at the inner boundary 7 of the frozen soil and the outer boundary 3 of the frozen soil. While the freezing pipes 4 provide cold air for the freezing wall 5, the multiple freezing pipes 4 at the outer boundary 3 of the frozen soil and the inner boundary 7 of the frozen soil limit the frost heave deformation during the formation of the freezing wall.

[0023] The freezing pipe 4 is a one-way freezing device, and the side wall of the freezing pipe 4 includes a cooling surface and a non-cooling surface, wherein the cooling surface of the freezing pipe 4 arranged at the outer boundary 3 of the frozen soil points to the excavation range 6, and the cooling surface of the freezing pipe 4 arranged at the inner boundary 7 of the frozen soil points to the soft water-bearing stratum 2 outside the excavation range 6, and the cooling surface of the freezing pipe 4 arranged at the inner boundary 7 of the frozen soil is arranged opposite to the cooling surface of the freezing pipe 4 arranged at the outer boundary 3 of the frozen soil, so as to ensure that the frozen wall 5 is limited between the outer boundary 3 of the frozen soil and the inner boundary 7 of the frozen soil, so that the freezing pipe 4 is always at the edge of the frozen wall 5. The freezing pipe 4 is a low-carbon steel pipe, and the freezing pipe 4 is formed by brushing heat-insulating paint on the outer side to form a non-cooling surface, and the side not brushed with heat-insulating paint is the cooling surface; or by using a divided cavity to circulate low-temperature refrigerant in the freezing pipe 4 or using vacuum insulation to concentrate the cold on the frozen wall 5, the expansion range of the frozen soil is limited, so that the inner and outer circles of freezing pipes of the frozen wall 5 are always located at the edge of the frozen wall.

[0024] A freezing method for a prestressed frozen soil composite support structure comprises the following steps: inserting a freezing pipe 4 horizontally into a soft water-bearing stratum 2 in advance around an excavation range 6 waiting for construction, wherein the cooling surface of the installed freezing pipe 4 points to the soft water-bearing stratum 2, presetting the thickness of a freezing wall 5 according to needs, and then constructing a circle of freezing pipes 4 around the excavation range 6 after leaving enough space for the thickness of the freezing wall 5, and then constructing the cooling surface of the freezing pipes 4 pointing to the excavation range 6, so that the freezing wall 5 is only formed between two circles of freezing pipes 4, limiting the expansion range of the freezing wall 5, and making the two circles of freezing pipes 4 always located at the edge position of forming the freezing wall 5; during the formation of the freezing wall 5, the frost heave effect generated by the expansion of the frozen volume of water in the soft water-bearing stratum 2 is constrained by the freezing pipes 4 at the outer boundary 3 and the inner boundary 7 of the frozen soil, which will cause the deformation of the freezing pipes 4 and the compaction of the freezing wall 5, and generate prestress in the freezing pipes 4 and the freezing wall 5, thereby jointly forming a prestressed frozen soil composite support structure without causing deformation of the surrounding strata.

[0025] Not only is the uniformity of the frozen wall formation greatly improved, but the frozen pipe is located at the edge of the frozen wall where the tensile and compressive stresses are the greatest, which can give full play to the advantages of the high tensile and compressive strength of the steel pipe. The frozen pipe can replace the steel pipes separately set up in the construction of the pipe shed or pipe curtain, thereby saving construction time and costs. The characteristics of high temperature and low strength in the middle of the frozen wall are also coordinated with the characteristics of the minimum stress in the neutral layer of the cross section, giving full play to the strength characteristics of the support structure cross section.

[0026] During construction, appropriate parameters such as freezing pipe spacing, size, and arrangement circle diameter interval can be selected according to the differences in bearing requirements, frost heave control standards, and construction requirements at different locations. This ensures that the prestressed frozen soil composite support structure can fully exert its good bearing performance and water sealing effect to ensure construction safety, while greatly reducing the volume of frozen soil, inhibiting the impact of freezing construction on the environment, saving construction costs, and reflecting significant economic and social benefits.

[0027] The specific steps are as follows:

[0028] a. In the excavation range 6 below the ground surface 1, the outer boundary of the excavation range 6 and the outer boundary of the frozen wall 5 of the preset thickness are arranged with two circles of freezing pipes 4, respectively. If the thickness of the pre-designed frozen wall 5 is large, it is also possible to increase the layout of the freezing pipe 4 between the two circles;

[0029] b. Circulate low-temperature refrigerant inside the freezing pipe 4, and through the unidirectional freezing effect on the surface of the freezing wall 4, the frozen soil only develops between the two circles of freezing pipes 4 to form a freezing wall 5, while controlling the expansion of the outer boundary 3 and the inner boundary 7 of the frozen soil to ensure that the two circles of freezing pipes 4 are respectively located at the inner and outer edge positions of the freezing wall 5, coordinating with the stress distribution characteristics on the cross-section of the composite support structure, and giving full play to the advantage of the high tensile strength of the steel material of the freezing pipe 4; the prestressed frozen soil composite support structure is a plurality of freezing pipes 4 arranged horizontally and spaced apart, and the spacing between the plurality of freezing pipes 4 is adjusted as needed, and the smaller the spacing, the stronger the bearing capacity that the pipe curtain freezing can provide.

[0030] c. By reducing the spacing between the multiple freezing pipes 4 forming the freezing wall 5, the adverse effects of frost heave during the freezing process on the surrounding environment of the freezing wall 5 can be limited. Moreover, the frost heave constrained by the freezing pipes 4 will compact the freezing wall 5, thereby increasing the strength of the frozen soil. The frost heave will also cause the freezing pipes 4 to generate prestress, thereby increasing the bearing capacity of the freezing pipes 4, thereby forming a prestressed frozen soil composite support structure. At the same time, the freezing wall 5 can also effectively prevent the water in the soft water-bearing stratum 2 from invading the excavation range 6.

[0031] d. Under the bearing and water sealing maintenance of the prestressed frozen soil composite support structure, excavation construction is carried out to form excavation range 6, and subsequent structural construction is carried out within the excavation range 6;

[0032] e. After the structural construction is completed, the refrigerant circulation in the freezing pipe 4 is stopped, and the freezing pipe 4 is cut off, and the entire construction process can be completed after the ground thaws.

Claims

1. A prestressed frozen soil composite support structure, characterized in that: A frozen wall (5) is arranged in a soft water-bearing stratum (2) around an excavation range (6), wherein the frozen wall (5) is wrapped around the top plate and two sides of the excavation range (6), wherein the inner side of the frozen wall (5) is a frozen soil inner boundary (7), and the outer side is a frozen soil outer boundary (3), and a plurality of frozen pipes (4) are respectively arranged on the frozen soil outer boundary (3) and the frozen soil inner boundary (7), and the frozen wall (5) and the plurality of frozen pipes (4) constitute a prestressed frozen soil composite support structure, and the prestressed frozen soil composite support structure provides support for the soil excavation construction process within the excavation range (6) inside the frozen wall (5); The prestressed frozen soil composite support structure comprises a plurality of freezing pipes (4) arranged along the direction of the excavation range, and a plurality of freezing pipes (4) are horizontally arranged at different height intervals at the inner boundary (7) of the frozen soil and the outer boundary (3) of the frozen soil to form a frozen wall (5). While the freezing pipes (4) provide cold energy for the frozen wall (5), the plurality of freezing pipes (4) arranged at the outer boundary (3) of the frozen soil and the inner boundary (7) of the frozen soil effectively limit the frost heave deformation during the formation process of the frozen wall (5); The freezing pipe (4) is a one-way freezing device. The side wall of the freezing pipe (4) includes a cooling surface and a non-cooling surface. The cooling surface of the freezing pipe (4) arranged at the outer boundary (3) of the frozen soil points to the excavation range (6), and the cooling surface of the freezing pipe (4) arranged at the inner boundary (7) of the frozen soil points to the soft water-bearing stratum (2) outside the excavation range (6). The cooling surface of the freezing pipe (4) arranged at the inner boundary (7) of the frozen soil is arranged opposite to the cooling surface of the freezing pipe (4) arranged at the outer boundary (3) of the frozen soil, thereby ensuring that the development range of the frozen wall (5) is limited between the outer boundary (3) of the frozen soil and the inner boundary (7) of the frozen soil, so that the freezing pipe (4) is always at the edge of the frozen wall (5).

2. The prestressed frozen soil composite support structure according to claim 1 is characterized in that: The freezing wall (5) in the soft water-bearing stratum (2) is arranged along the edge of the excavation range (6). The freezing range of the freezing wall (5) is limited to the frozen soil outer boundary (3) and the frozen soil inner boundary (7) and does not spread, so as to prevent the freezing wall (5) from radiating cold to the outside of the soft water-bearing stratum (2) and causing a frost heave effect during the formation of the freezing wall (5) and affecting the surrounding environment. The freezing wall (5) provides support force for the soil excavation construction process in the excavation range (6) while blocking the water in the soft water-bearing stratum (2) from penetrating into the excavation range (6), thereby creating a good excavation construction environment inside the excavation range (6). The freezing pipe (4) arranged at the frozen soil outer boundary (3) and the frozen soil inner boundary (7) only releases cold to the frozen wall (5) in one direction, and limits the frost heave deformation generated during the formation of the frozen wall. The freezing pipe (4) and the freezing wall (5) constitute a prestressed frozen soil composite support structure.

3. The prestressed frozen soil composite support structure according to claim 2 is characterized in that: The freezing pipe (4) is a low-carbon steel pipe. The freezing pipe (4) is coated with a heat-insulating coating on the outside to form a non-cold-releasing surface, and the side not coated with the heat-insulating coating is a cold-releasing surface; or by using a divided-chamber circulating low-temperature refrigerant or vacuum insulation in the freezing pipe (4) to release the cold energy toward the freezing wall (5), the expansion range of the frozen soil is limited, so that the two circles of freezing pipes inside and outside the freezing wall (5) are always located at the edge of the frozen wall (5).

4. A freezing method using the prestressed frozen soil composite support structure according to any one of the above claims, characterized in that: In advance, freezing pipes (4) are inserted horizontally into the soft water-bearing stratum (2) surrounding the excavation range (6) on both sides and the top plate. At this time, the freezing pipes (4) are installed with the cooling surface pointing to the soft water-bearing stratum (2). The thickness of the freezing wall (5) is preset according to the needs. After leaving enough space for the thickness of the freezing wall (5), a circle of freezing pipes is constructed around the excavation range (6). The cooling surface of the freezing pipes is then directed to the excavation range (6), so that the freezing wall (5) is formed only between the two circles of freezing pipes, thereby limiting the freezing. The expansion range of the wall (5) ensures that the two circles of freezing pipes are always located at the edge of the frozen wall (5); during the formation of the frozen wall (5), the frost heave effect caused by the expansion of the frozen volume of water in the soft water-bearing stratum (2) is constrained by the freezing pipe (4) at the position of the outer boundary (3) and the inner boundary (7) of the frozen soil, causing the deformation of the freezing pipe (4) and the compaction of the frozen wall (5), thereby generating prestress in the freezing pipe (4) and the frozen wall (5), forming a prestressed frozen soil composite support structure without causing deformation of the surrounding strata.

5. The freezing method according to claim 4, characterized in that: The prestressed frozen soil composite support structure is composed of a plurality of freezing pipes (4) and freezing walls (5) which are horizontally arranged and spaced apart. The spacing between the plurality of freezing pipes (4) is adjusted as required. The smaller the spacing, the greater the bearing capacity that the prestressed frozen soil composite support structure can provide.

6. The freezing method according to claim 4, characterized in that The specific steps are as follows: a. Arrange two circles of freezing pipes (4) at the outer boundary of the excavation range (6) and the outer boundary of the frozen wall (5) of preset thickness. If the thickness of the pre-designed frozen wall (5) is large, additional freezing pipes (4) are arranged between the two circles of freezing pipes (4); b. A low-temperature refrigerant is circulated inside the freezing pipe (4), and through the unidirectional freezing effect on the surface of the freezing pipe (4), the frozen soil is only developed between the two circles of freezing pipes (4), forming a frozen wall (5), while the expansion range of the outer boundary (3) and the inner boundary (7) of the frozen soil is controlled to ensure that the two circles of freezing pipes (4) are respectively located at the inner and outer edge positions of the frozen wall (5), and the stress distribution characteristics on the cross section of the support structure are coordinated to give full play to the advantage of the high tensile strength of the steel material of the freezing pipe (4); c. By reducing the arrangement spacing between the plurality of freezing pipes (4) forming the freezing wall (5), the adverse effect of frost heave during the freezing process on the surrounding environment of the freezing wall (5) can be limited. Furthermore, the frost heave constrained by the freezing pipes (4) will compact the freezing wall (5) and thus improve the strength of the frozen soil. The frost heave will also cause the freezing pipes (4) to generate prestress, thereby improving the bearing capacity of the freezing pipes (4), thereby forming a prestressed frozen soil composite support structure. At the same time, the freezing wall (5) can also effectively prevent the water in the soft water-bearing stratum (2) from invading the excavation range (6); d. Under the bearing and water sealing function of the prestressed frozen soil composite support structure, excavation construction is performed inside the excavation range (6) to form the excavation range (6), and subsequent structural construction is performed inside the excavation range (6); e. After the structural construction is completed, the circulation of the refrigerant in the freezing pipe (4) is stopped, and the freezing pipe (4) is cut off. The entire construction process can be completed after the ground thaws.

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