A method for supporting a foundation pit using a frozen soil wall

Abstract

The present application relates to the technical field of building engineering, and provides a method for foundation pit support using frozen soil wall, which is based on a plurality of holes arranged outside the foundation pit and freezing pipes or auxiliary pipes arranged in the holes; the auxiliary pipes are provided with water outlets; the depth of the holes is higher than the water level of underground water, and the holes include freezing holes and auxiliary holes; the freezing holes and the auxiliary holes are arranged in a grid pattern outside the foundation pit. The present application arranges a plurality of holes outside the foundation pit, firstly arranges freezing pipes or auxiliary pipes in the holes, secondly determines the water content of the soil layer, thirdly adjusts the water content of the soil layer through the auxiliary pipes until the freezing water content is reached, then freezes the soil layer around the foundation pit through the freezing pipes to form a frozen soil wall, and finally analyzes the freezing effect by real-time temperature measurement using the auxiliary pipes. Based on the method, the soil layer can be improved in the aspects of freezability and freezing speed, the freezing effect can be strengthened, and resource loss can be reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building engineering, in particular to a method for supporting a foundation pit by using a frozen soil wall. BACKGROUND

[0002] The design of foundation pit support forms is influenced by many factors. In engineering, the support form is determined according to the depth of the foundation pit, environmental conditions, soil type and groundwater conditions. As for the current deep foundation pit support method, it can be divided into pile row, double-row pile, underground continuous wall, soil nailing wall, gravity type cement soil wall, and slope.

[0003] CN201120212868.X discloses a shallow foundation pit enclosure structure, which comprises a freezing hole arranged around the foundation pit excavation position, and a freezing pipe arranged in the freezing hole. This scheme can ensure the safety of underground engineering construction in water-rich strata mainly composed of sandy silt and silt, effectively control the deformation of urban comprehensive pipelines outside the foundation pit, closely operated rail transit tracks and surrounding protective buildings, meet the construction requirements of various municipal comprehensive pipelines arranged near the foundation pit, provide effective and systematic technical support system for the design and construction of such foundation pits, and ensure the smooth implementation of the project. It is a traditional frozen soil wall foundation pit support method, which is only applicable to water-rich strata, i.e. the case where the water content rate is the saturated water content rate.

[0004] However, in the case where the groundwater level is relatively deep and the water content rate of the soil in the foundation pit excavation range is low, and other foundation pit support structures cannot meet the time limit requirements, the use of traditional frozen soil wall foundation pit support structures will result in the need for more coolant due to the low water content rate being lower than the saturated water content rate, or even the inability to freeze due to the extremely low water content rate.

[0005] Therefore, the technical problem to be solved by the present application is to provide a method for supporting a foundation pit by using a frozen soil wall in the case where the water content rate of the soil in the foundation pit excavation range is low, which can save costs and improve efficiency. SUMMARY

[0006] To solve the above technical problems, the present application sets a plurality of holes outside the foundation pit, first arranges a freezing pipe or an auxiliary pipe in the hole, secondly measures the water content rate of the soil layer, thirdly adjusts the water content rate of the soil layer through the auxiliary pipe until the freezing water content rate is reached, then freezes the soil layer around the foundation pit through the freezing pipe to form a frozen soil wall, and finally analyzes the freezing effect by using the auxiliary pipe to measure the temperature in real time. Based on this method, the freezability and freezing speed of the soil layer can be improved, the freezing effect can be enhanced, and resource consumption can be reduced.

[0007] The technical scheme of the present application is:

[0008] A method for foundation pit support using frozen soil wall, the method is based on several holes arranged outside the foundation pit, and freezing pipes or auxiliary pipes are arranged in the holes; the auxiliary pipes are provided with water outlets; the depth of the holes is higher than the water level of underground water, including freezing holes and auxiliary holes; the freezing holes and auxiliary holes are arranged in a grid pattern outside the foundation pit;

[0009] The method comprises the following steps:

[0010] Step (1): Sampling and measuring the initial moisture content of the soil layer at different positions and depths outside the foundation pit;

[0011] Step (2): According to the initial moisture content obtained in step (1), appropriate amount of water is input into the soil layer at different positions and depths outside the foundation pit through the auxiliary pipes, so as to humidify the soil layer to the freezing moisture content;

[0012] Step (3): Liquid nitrogen is input into the freezing pipe through the externally arranged liquid nitrogen storage tank, the liquid nitrogen is vaporized, absorbs the heat around the periphery of the freezing pipe, and thus the soil layer around the foundation pit is frozen.

[0013] In the method for foundation pit support using frozen soil wall, the freezing pipe is made of steel, the size is a pipe diameter of Φ133mm and a wall thickness of 8mm, and the freezing range is a diameter of 600-800mm.

[0014] In the method for foundation pit support using frozen soil wall, the auxiliary pipe is made of steel, and comprises an inner pipe cylinder and an outer pipe cylinder arranged on the same axis; the pipe wall of the outer pipe cylinder is provided with a plurality of water outlets, and the pipe wall of the inner pipe cylinder is sealed; the inner pipe cylinder is arranged with an externally arranged temperature sensor; the bottom end of the auxiliary pipe is sealed, and the top end is provided with a water inlet and a temperature measuring port.

[0015] In the method for foundation pit support using frozen soil wall, the freezing pipe comprises a non-freezing section and a freezing section arranged from top to bottom, a partition plate is arranged between the non-freezing section and the freezing section, a plurality of liquid supply pipes are arranged in the freezing pipe and extend from the port of the non-freezing section to different positions on the longitudinal direction from the bottom of the freezing section upwards, an exhaust pipe is arranged in the freezing pipe, a through hole section is arranged on the bottom of each liquid supply pipe and extends upwards, the through hole section is located in the freezing section, the bottom end of the liquid supply pipe is closed, and the through hole sections on the plurality of liquid supply pipes are not overlapped.

[0016] In the method for foundation pit support using frozen soil wall, the liquid supply pipe comprises a first liquid supply pipe, a second liquid supply pipe and a third liquid supply pipe, and the first liquid supply pipe, the second liquid supply pipe and the third liquid supply pipe are respectively provided with a first through hole section, a second through hole section and a third through hole section.

[0017] In the method for supporting a foundation pit using a frozen soil wall, the first liquid supply pipe extends from the port of the freezing pipe to 1 / 3 of the freezing section, the second liquid supply pipe extends from the port of the freezing pipe to 2 / 3 of the freezing section, and the third liquid supply pipe extends from the port of the freezing pipe to the bottom of the freezing section.

[0018] In the method for supporting a foundation pit using a frozen soil wall, the first through hole section is arranged at 0-1 / 3 of the freezing section where the first liquid supply pipe is located, the second through hole section is arranged at 1 / 3-2 / 3 of the freezing section where the second liquid supply pipe is located, and the third through hole section is arranged at 2 / 3 to the bottom of the freezing section where the third liquid supply pipe is located.

[0019] In the method for supporting a foundation pit using a frozen soil wall, the through holes on the first through hole section, the second through hole section and the third through hole section are arranged in an equal interval staggered and opposite opening manner.

[0020] In the method for supporting a foundation pit using a frozen soil wall, the freezing pipe is in a cylindrical structure, and the first liquid supply pipe, the second liquid supply pipe, the third liquid supply pipe and the exhaust pipe are in the freezing pipe, and the projections in the horizontal direction are plum blossom-shaped.

[0021] In the method for supporting a foundation pit using a frozen soil wall, the bottoms of the first liquid supply pipe, the second liquid supply pipe and the third liquid supply pipe are respectively provided with first, second and third cover plates for closing the bottom ends thereof.

[0022] One of the technical solutions in the above-mentioned technical solutions of the present application has at least one of the following advantages or beneficial effects:

[0023] Firstly, the present application sets a plurality of holes with a depth higher than the water level of underground water on the outside of the foundation pit, including freezing holes and auxiliary holes, then arranges freezing pipes in the freezing holes and auxiliary pipes in the auxiliary holes, when the water content is lower than the freezing water content, water is input into the soil layer through the auxiliary pipes to humidify the soil layer around the foundation pit, and then liquid nitrogen is input into the freezing pipes through the externally arranged liquid nitrogen storage tank, the liquid nitrogen is vaporized to absorb the heat around the freezing pipes, and the freezing work on the soil layer around the foundation pit is completed; the present application is not only suitable for projects with a tight construction period and foundation pit rescue, but also can enhance the tensile property of the wall body due to the reinforcing effect of the freezing pipes, the cross-sectional stress intensity of the wall body is greatly improved, the horizontal displacement and settlement of the top of the supporting structure are reduced, and the present application can be applied to supporting projects with a large excavation depth and high deformation requirement of the environment around the foundation pit.

[0024] Secondly, the present application measures the initial water content of the soil layer at a plurality of positions and depths on the outside of the foundation pit, and then adjusts the water content of the soil layer by inputting appropriate water into the soil layer through the auxiliary pipes, so as to reduce the water consumption.

[0025] Thirdly, the freezing hole and the auxiliary hole are arranged in a grid pattern outside the foundation pit, and a freezing pipe is arranged in the freezing hole, so that the freezing pipe and the frozen soil form a safe and reliable frozen soil wall. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a working schematic diagram of a method for foundation pit support using a frozen soil wall according to Example 1;

[0027] Figure 2 is a M-M cross-sectional view of Figure 1 according to Example 1;

[0028] Figure 3 is a half cross-sectional schematic diagram of an auxiliary pipe and an N-N cross-sectional view thereof according to Example 1;

[0029] Figure 4 is a structural schematic diagram of a freezing pipe according to Example 1;

[0030] Figure 5 is a schematic diagram of a first through-hole section opening of a freezing pipe according to Example 1;

[0031] Figure 6 is an A-A cross-sectional view of a freezing pipe according to Example 1;

[0032] Figure 7 is a B-B cross-sectional view of a freezing pipe according to Example 1;

[0033] Figure 8 is a C-C cross-sectional view of a freezing pipe according to Example 1;

[0034] Figure 9 is a D-D cross-sectional view of a freezing pipe according to Example 1. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0036] Example 1

[0037] Please refer to Figures 1-9 , a method for foundation pit support using a frozen soil wall, the method is based on a plurality of holes arranged outside the foundation pit, and a freezing pipe 1 or an auxiliary pipe 2 is arranged in the hole; the auxiliary pipe 2 is provided with a water outlet 221; the depth of the hole is higher than the water level of the underground water, including a freezing hole and an auxiliary hole; the freezing hole and the auxiliary hole are arranged in a grid pattern outside the foundation pit, and the specific arrangement mode is referred to Figure 2 ;

[0038] In the embodiment, it is to be noted that the freezing water content range is the plastic limit water content-saturated water content;

[0039] Further, in order to more clearly illustrate the present scheme, in the embodiment, the soil layer simulation is set to silty clay, and the corresponding plastic limit water content is 17%; the freezing water content is considered as 17%, which has the advantage of reducing the water consumption, because when the water content is 17%, the freezing speed of the silty clay has reached 250 mm / d, and when the freezing diameter is 600 mm, only 2.40 d is needed to reach the freezing requirement, wherein d is the number of days.

[0040] However, it is to be further noted that the water content can be further increased in addition to the 17% water content in the embodiment. The water in the soil can be approximately regarded as capillary water, and the relationship between the freezing temperature and the water content can be simply analyzed by the Gibbs-Thomson equation, and it is not difficult to obtain that the smaller the equivalent capillary radius, the lower the freezing temperature. The equivalent capillary radius is related to the capillary action and the adsorption action on the surface of the soil particles, and the water content will affect the capillary action and the adsorption action. When the water content in the soil is smaller, the equivalent capillary radius is smaller, and the freezing temperature is lower; on the contrary, the higher the water content, the higher the freezing temperature, so under the same conditions, the higher the water content, the better the freezing efficiency, and the less the liquid nitrogen consumed for freezing, which is beneficial to further saving resources. For example, in the embodiment, when the water content reaches the saturated water content, the freezing speed is 280 mm / d, and when the freezing diameter is 600 mm, only 2.14 d is needed to reach the freezing requirement, and the amount of liquid nitrogen required is reduced by 11%.

[0041] Under the above design, the working process of the embodiment is as follows:

[0042] Step (1): Sampling and determining the initial water content of the silty clay soil layer at different positions and depths outside the foundation pit; when the water content of the silty clay soil layer at the position is lower than 17%, step (2) is performed.

[0043] Step (2): According to the initial water content obtained in step (1), an appropriate amount of water is input into the silty clay soil layer at the position of step (1) through the auxiliary pipe 2, so as to humidify the soil layer to 17%;

[0044] Step (3): Liquid nitrogen is input into the freezing pipe 1 through the externally provided liquid nitrogen storage tank, the liquid nitrogen is vaporized, absorbs the heat around the freezing pipe 1, and thus performs the frozen soil work on the silty clay soil layer around the foundation pit.

[0045] In order to make the plan easier to understand, the outside of the foundation pit - E, the inside of the foundation pit - F, the groundwater level - G, the site elevation - H, the elevation of the bottom of the foundation pit - I, the intercepting ditch - J, the drainage ditch - K, the safety guardrail - L, and the freezing range - Z are marked in the reference drawing.

[0046] In this embodiment, a number of holes with depths higher than the groundwater level are set on the outside of the foundation pit, including freezing holes and auxiliary holes. Then, freezing pipes 1 are arranged in the freezing holes, and auxiliary pipes 2 are arranged in the auxiliary holes. When the moisture content is lower than the freezing moisture content, water is input into the soil layer through the auxiliary pipes 2, thereby humidifying the soil layer around the foundation pit. Liquid nitrogen is then input into the freezing pipes 1 through an external liquid nitrogen storage tank. The liquid nitrogen vaporizes and absorbs the heat around the freezing pipes 1, thereby completing the freezing of the soil layer around the foundation pit. This embodiment is not only suitable for projects with tight construction schedules and foundation pit rescue operations, but also because the strengthening effect of the freezing pipes 1 can enhance the tensile properties of the wall, the cross-sectional stress strength of the wall will be greatly improved, and the horizontal displacement and settlement of the top of the support structure will also be reduced. It is suitable for support projects with large excavation depths and high deformation requirements for the surrounding environment of the foundation pit.

[0047] Furthermore, this embodiment measures the initial moisture content of the soil layer at multiple locations and depths outside the foundation pit, and then inputs an appropriate amount of water into the soil layer through the auxiliary pipe 2 to purposefully adjust the moisture content, thereby reducing water consumption.

[0048] In this embodiment, preferably, the freezing pipe 1 is a hot-rolled seamless steel pipe with a diameter of Φ133 mm and a wall thickness of 8 mm, and the freezing range Z is a diameter of 600-800 mm.

[0049] In this embodiment, it is more preferred that the freezing holes and auxiliary holes are arranged in a grid pattern outside the foundation pit. Specifically, in this embodiment, the freezing range Z of the freezing pipe 1 is 600 mm in diameter and the freezing ranges Z of four adjacent freezing pipes 1 intersect at one point, namely point P; the auxiliary holes are arranged at point P.

[0050] More preferably, a space is provided inside the freezing range Z outside the foundation pit.

[0051] Under the above design, the advantage is that the humidification range covers the freezing range Z more comprehensively, and the provision of space is for saving the cost of production and construction to a greater extent.

[0052] In this embodiment, it should be noted that in addition to the above-mentioned preferred arrangement scheme, different arrangement schemes can also be set according to different construction environments, soil layers and other factors.

[0053] Preferably, the auxiliary pipe 2 is a hot-rolled seamless steel pipe, comprising an inner pipe cylinder 21 and an outer pipe cylinder 22 arranged coaxially inside and outside; the outer pipe cylinder 22 is provided with a plurality of water outlets 221 on the pipe wall, and the inner pipe cylinder 21 is sealed; the inner pipe cylinder 21 is arranged with an externally arranged temperature sensor 3; the bottom end of the auxiliary pipe 2 is sealed, and the top end is provided with a water inlet 222 and a temperature measuring port 211.

[0054] In the embodiment, the outer pipe cylinder 22 of the auxiliary pipe 2 has a pipe diameter of Φ127 mm, and the inner pipe cylinder 21 has a pipe diameter of Φ89 mm, and the wall thickness of the outer pipe cylinder 22 and the inner pipe cylinder 21 is 6 mm.

[0055] Under the above design, the auxiliary pipe 2 plays two roles, one of which is the humidification function as described above, and the other of which is that when step (3) is performed, the temperature inside the auxiliary pipe can be measured in real time by the externally arranged temperature sensor 3, so as to analyze the freezing effect and control the amount of liquid nitrogen used.

[0056] In the embodiment, more preferably, the water outlets 221 are arranged evenly and staggered on the pipe wall of the outer pipe cylinder 22.

[0057] Under the above design, the water is more evenly humidified in the soil layer.

[0058] In the embodiment, preferably, the freezing pipe 1 comprises a non-freezing section 112 and a freezing section 111 arranged from top to bottom, and a partition plate 15 is arranged between the non-freezing section 112 and the freezing section 111; the freezing pipe 1 is provided with a plurality of liquid supply pipes extending from the port of the non-freezing section 112 to different positions in the longitudinal direction from the bottom of the freezing section 111 upwards, and an exhaust pipe 11; each of the plurality of liquid supply pipes is provided with a through-hole section arranged extending upwards from the bottom thereof, and the through-hole section is located in the freezing section 111; the bottom end of the liquid supply pipe is closed; and the through-hole sections on the plurality of liquid supply pipes are not overlapped.

[0059] Under this design, because the other end of the liquid supply pipe extends to different positions in the longitudinal direction from the bottom of the freezing pipe 1 upwards in turn, and the through-hole sections on the plurality of liquid supply pipes are not overlapped, that is, the through-hole sections on each of the liquid supply pipes can be combined in turn to cover the entire freezing pipe 1; when liquid nitrogen reaches the freezing section during freezing, it begins to vaporize, and the gas is discharged in the through-hole section of each liquid supply pipe; at this time, the gas exchanges heat with the surrounding of the freezing pipe, absorbs heat from the surrounding of the freezing pipe, and then the gas transfers the heat to the liquid nitrogen in the plurality of liquid supply pipes, so as to vaporize the liquid nitrogen; due to the non-overlapping distribution of the through-hole sections, the entire freezing pipe 1 is in a heat exchange state, causing the surrounding temperature to drop rapidly, uniformly freezing the soil, improving the uniformity of the temperature distribution of the soil, and overcoming the phenomenon of uneven profile of the liquid nitrogen frozen soil.

[0060] In actual work, the non-freezing section 112 is placed on the ground, and the freezing section 111 is inserted into the soil layer.

[0061] In the above design, the soil below the ground is frozen.

[0062] In the present embodiment, the freezing pipe 1 comprises a freezing section 111 and a non-freezing section 112, and a partition 15 is arranged between the freezing section 111 and the non-freezing section 112 to prevent the low temperature of the freezing section 111 from spreading to the non-freezing section 112. The other ends of the plurality of liquid supply pipes extend to different positions in the longitudinal direction from the bottom of the freezing pipe 1, and the through hole sections of the liquid supply pipes are all located in the freezing section 111. Therefore, during freezing, the liquid nitrogen in the freezing section 111 is vaporized, and then the other end of the exhaust pipe 11 passes through the partition 15 to connect the freezing section 111 with the outside, and the gas is discharged through the exhaust pipe 11.

[0063] Preferably, the liquid supply pipes comprise a first liquid supply pipe 12, a second liquid supply pipe 13 and a third liquid supply pipe 14, and the first liquid supply pipe 12 is provided with a first through hole section 121, the second liquid supply pipe 13 is provided with a second through hole section 131, and the third liquid supply pipe 14 is provided with a third through hole section 141.

[0064] Preferably, the first liquid supply pipe 12, the second liquid supply pipe 13 and the third liquid supply pipe 14 do not have a specific length of extension, and one of them should extend to the bottom of the freezing pipe 1, and the first through hole section 121, the second through hole section 131 and the third through hole section 141 are arranged without overlapping.

[0065] However, in order to ensure the uniformity of the temperature distribution in the freezing pipe 1, the extension lengths of the first liquid supply pipe 12, the second liquid supply pipe 13 and the third liquid supply pipe 14 are preferably as follows: the first liquid supply pipe 12 extends from the port of the freezing pipe 1 to 1 / 3 of the freezing section 111, the second liquid supply pipe 13 extends from the port of the freezing pipe 1 to 2 / 3 of the freezing section 111, and the third liquid supply pipe 14 extends from the port of the freezing pipe 1 to the bottom of the freezing section 111, so that the freezing section 111 of the freezing pipe 1 is evenly divided into three equal parts.

[0066] As a further optimization of the present embodiment, the first through hole section 121 is arranged at 0-1 / 3 of the freezing section 111 where the first liquid supply pipe 12 is located, the second through hole section 131 is arranged at 1 / 3-2 / 3 of the freezing section 111 where the second liquid supply pipe 13 is located, and the third through hole section 141 is arranged at 2 / 3 to the bottom of the freezing section 111 where the third liquid supply pipe 14 is located. Therefore, the first through hole section 121, the second through hole section 131 and the third through hole section 141 are arranged to cover the entire freezing pipe 1, and if only one liquid supply pipe is used, the temperature distribution of the lower part and the upper part of the freezing pipe 1 will be very uneven.

[0067] Preferably, in order to make the through hole processing more convenient, the through holes 1211 on the first through hole section 121, the second through hole section 131 and the third through hole section 141 are arranged in the staggered and opposite opening mode with equal intervals, and the arrangement of the through holes 1211 on the first through hole section 121 is taken as an example. Figure 5 In the embodiment, the arrangement of the through holes 1211 on the second through hole section 131 and the third through hole section 141 is the same as that of the first through hole section 121, and thus the through holes 1211 on the second through hole section 131 and the third through hole section 141 are not described in detail in the embodiment.

[0068] Preferably, the diameter of the through hole 1211 is 5 mm, and the interval of the through hole 1211 in the vertical direction is 500 mm.

[0069] It should be noted that the arrangement of the through hole 1211 is not specified, but the increase or decrease of the through hole 1211, the change of the diameter and the interval of the through hole 1211 are within the protection scope of the application.

[0070] Preferably, the freezing pipe 1 adopts a cylindrical structure, and the first liquid supply pipe 12, the second liquid supply pipe 13, the third liquid supply pipe 14 and the exhaust pipe 11 are arranged in the freezing pipe 1, and the projection in the horizontal direction is in the plum blossom shape, which can ensure that the distance from the first liquid supply pipe 12, the second liquid supply pipe 13 and the third liquid supply pipe 14 to the pipe wall of the freezing pipe 1 is uniform.

[0071] As a further optimization of the embodiment, in order to ensure that the first liquid supply pipe 12, the second liquid supply pipe 13 and the third liquid supply pipe 14 maintain the plum blossom structure unchanged when extending from the non-freezing section 112 to different positions in the freezing section 111, a plurality of fixed plates 16 are arranged at equal intervals in the embodiment, and a plurality of air holes 161 for gas flow are arranged on the fixed plates 16. After the fixed plate 16 is added, the first liquid supply pipe 12, the second liquid supply pipe 13 and the third liquid supply pipe 14 located in the freezing section 111 are fixed in position, so that the first liquid supply pipe 12, the second liquid supply pipe 13 and the third liquid supply pipe 14 maintain the plum blossom structure.

[0072] In the embodiment, the bottom of the first liquid supply pipe 12, the second liquid supply pipe 13 and the third liquid supply pipe 14 is respectively provided with a first cover plate 1212, a second cover plate (not shown in the figure) and a third cover plate (not shown in the figure) for closing the bottom end. Figure 5 Because the structure and connection mode of the second cover plate and the third cover plate on the second liquid supply pipe 13 and the third liquid supply pipe 14 are the same as those of the first cover plate 1212 on the first liquid supply pipe 12, the second cover plate and the third cover plate on the second liquid supply pipe 13 and the third liquid supply pipe 14 are not described in detail in the embodiment.

[0073] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the claims and their equivalents.

Claims

1. A method for supporting a foundation pit using a frozen soil wall, characterized in that: The method is based on setting a plurality of holes outside the foundation pit, and arranging freezing pipes or auxiliary pipes in the holes; the auxiliary pipes are provided with water outlets; the holes are deeper than the groundwater level and include freezing holes and auxiliary holes; the freezing holes and auxiliary holes are arranged in a grid pattern outside the foundation pit; wherein the freezing ranges of adjacent freezing pipes intersect at a point, namely, point P; the auxiliary holes are arranged at point P; The process includes the following steps: Step (1): Sampling and measuring the initial moisture content of soil layers at different locations and depths outside the foundation pit; Step (2): According to the initial moisture content obtained in step (1), appropriate amounts of water are respectively inputted into the soil layers at different positions and depths outside the foundation pit through auxiliary pipes, thereby humidifying the soil layers to the freezing moisture content; Step (3): Liquid nitrogen is input into the freezing pipe through an external liquid nitrogen storage tank, and the liquid nitrogen vaporizes and absorbs the heat around the freezing pipe, thereby freezing the soil layer around the foundation pit; In which, the freezing pipe includes a non-freezing section and a freezing section arranged from top to bottom, a partition is provided between the non-freezing section and the freezing section, and the freezing pipe is provided with multiple liquid supply pipes and exhaust pipes extending from the non-freezing section port to different positions in the longitudinal direction from the bottom of the freezing section upward. The multiple liquid supply pipes are all provided with a through hole section extending from the bottom upward, the through hole section is located in the freezing section, the bottom end of the liquid supply pipe is closed, and the through hole sections on the multiple liquid supply pipes do not overlap.

2. The method for supporting a foundation pit using a frozen soil wall according to claim 1, wherein: The freezing pipe is made of steel, has a diameter of Φ133mm, a wall thickness of 8mm, and a freezing range of 600-800mm in diameter.

3. The method for supporting a foundation pit using a frozen soil wall according to claim 1, characterized in that The auxiliary tube is made of steel and includes an inner tube and an outer tube arranged coaxially inside and outside; the wall of the outer tube is provided with several water outlets, and the wall of the inner tube is sealed; an external temperature sensor is arranged in the inner tube; the bottom end of the auxiliary tube is sealed, and the top end is provided with a water inlet and a temperature measuring port.

4. The method for supporting a foundation pit using a frozen soil wall according to claim 1, wherein: The liquid supply pipe includes a first liquid supply pipe, a second liquid supply pipe, and a third liquid supply pipe. The first liquid supply pipe, the second liquid supply pipe, and the third liquid supply pipe are respectively provided with a first through hole section, a second through hole section, and a third through hole section.

5. The method for supporting a foundation pit using a frozen soil wall according to claim 4, wherein: The first liquid supply pipe extends from the port of the freezing pipe to 1 / 3 of the freezing section, the second liquid supply pipe extends from the port of the freezing pipe to 2 / 3 of the freezing section, and the third liquid supply pipe extends from the port of the freezing pipe to the bottom of the freezing section.

6. The method for supporting a foundation pit using a frozen soil wall according to claim 5, characterized in that: The first through hole section is set at 0-1 / 3 of the freezing section where the first liquid supply pipe is located, the second through hole section is set at 1 / 3-2 / 3 of the freezing section where the second liquid supply pipe is located, and the third through hole section is set at 2 / 3 to the bottom of the freezing section where the third liquid supply pipe is located.

7. The method for supporting a foundation pit using a frozen soil wall according to claim 4, wherein: The through holes on the first through hole section, the second through hole section and the third through hole section are all arranged in a staggered manner with equal spacing.

8. The method for supporting a foundation pit using a frozen soil wall according to any one of claims 4 to 7, characterized in that: The freezing pipe is a cylindrical structure. The first liquid supply pipe, the second liquid supply pipe, the third liquid supply pipe and the exhaust pipe are inside the freezing pipe, and their horizontal projection is a plum blossom shape.

9. The method for supporting a foundation pit using a frozen soil wall according to claim 4, wherein: The bottoms of the first liquid supply pipe, the second liquid supply pipe and the third liquid supply pipe are respectively provided with a first cover plate, a second cover plate and a third cover plate for sealing the bottom ends thereof.

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