Deep foundation pit supporting method and deep foundation pit

Abstract

The invention discloses a supporting method for a deep foundation pit and the deep foundation pit. The supporting method comprises the steps that a dewatering well (1) outside the deep foundation pit is constructed and used for reducing the pressure of water and soil outside the deep foundation pit; and the deep foundation pit inner supporting structure is constructed and used for providing acting force for the deep foundation pit supporting structure (2) so as to reduce the maximum bending moment and horizontal displacement of the deep foundation pit supporting structure (2). According to the supporting method for the deep and large foundation pit, on one hand, the water level outside the deep foundation pit is lowered, the water and soil pressure outside the deep foundation pit is lowered, and therefore deformation of a supporting structure of the deep foundation pit is reduced; and on the other hand, the supporting structure in the deep foundation pit is used for providing counter-acting force for the supporting structure, the acting force of the soil body outside the deep foundation pit on the supporting structure is resisted, and therefore the maximum bending moment and deformation of the deep foundation pit structure are reduced.

Description

Technical Field

[0001] The present application relates to the field of deep foundation pit support, and more specifically, to a deep foundation pit support method and a deep foundation pit. Background Art

[0002] In urban construction, deep and large foundation pits are usually used for the construction of large buildings, underground projects or transportation. Due to the large depth of the foundation pit, the geological and hydrological conditions will be more complicated, especially when developing soft soil areas in the south or coastal areas, the soil stability of deep and large foundation pits is poor, and support structures need to be set up to ensure the stability of the foundation pit.

[0003] At present, soil nail walls, pile rows or ground-connected walls, anchor cables, double-row piles, internal supports and other support methods are usually used for deep and large foundation pits. In soft soil areas, anchor cables are difficult to provide sufficient reaction force due to the engineering properties of the soil layer, and their applicability is poor. When the plane size of the foundation pit is too large, the internal support will reduce safety due to its large size, resulting in a long construction period and relatively high costs. The removal of the internal support and the disposal of construction waste in the later stage are also likely to cause environmental pollution. When the foundation pit is deep, double-row piles or counter-pressure soil cannot control the deformation of the foundation pit within the safety requirements and are limited.

[0004] Therefore, how to propose a deep foundation pit support method that can at least solve some of the above-mentioned technical problems becomes a technical problem that needs to be solved in this field. Summary of the invention

[0005] In view of this, the present application proposes a deep foundation pit support method and a deep foundation pit.

[0006] According to the first aspect of the present application, a deep foundation pit support method is proposed, which includes: constructing a dewatering well outside the deep foundation pit to reduce the water and soil pressure outside the deep foundation pit; constructing a support structure inside the deep foundation pit to provide force to the deep foundation pit support structure to reduce the maximum bending moment and horizontal displacement of the deep foundation pit support structure.

[0007] Preferably, the distance between the dewatering well and the deep foundation pit support structure is 1.5m-3m, the number of the dewatering wells is multiple, and the spacing between the dewatering wells is 7m-9m; Preferably, a water filter pipe is provided in the dewatering well to lower the water level in the soil layer around the deep foundation pit.

[0008] Preferably, the supporting structure in the construction of the deep foundation pit includes: a temporary construction structure and a permanent structure; the temporary construction structure includes: setting up counter-pressure soil, which is set up in the deep foundation pit and contacts with the deep foundation pit supporting structure; constructing an internal support, and the first end of the internal support is connected to the deep foundation pit supporting structure; the permanent construction structure includes: constructing a first permanent structure and a second permanent structure, and the first permanent structure is connected to the second end of the internal support; the second permanent structure is set at the position of the counter-pressure soil to replace the temporary structure.

[0009] Preferably, the counter-pressure soil is formed by excavating the soil above the deep foundation pit, and the counter-pressure soil is stepped toward the side inside the deep foundation pit, and the width of each step of the counter-pressure soil is not less than 5m and the height is 6m-8m.

[0010] Preferably, the setting of counter-pressure soil includes: setting counter-pressure soil piles, wherein the counter-pressure soil piles are set at the position where the counter-pressure soil is connected to the bottom of the deep foundation pit, so as to enhance the stability of the counter-pressure soil.

[0011] Preferably, the construction of the first permanent structure in the deep foundation pit includes casting of a bottom plate structure in the deep foundation pit and construction of a main structure, and the main structure is arranged on the bottom plate structure in the deep foundation pit.

[0012] Preferably, the inner support is constructed from top to bottom, and the construction of the inner support includes: constructing a first inner support, which is arranged at the top of the deep foundation pit, one end of the first inner support is connected to the top of the deep foundation pit support structure, and the other end is arranged at the top of the main structure of the first permanent structure; after excavating the back pressure soil, sequentially constructing the second inner support and the third inner support, which are located inside the deep foundation pit and are connected to the deep foundation pit support structure and the first permanent structure; constructing a fourth inner support, both ends of which are connected to the second permanent structure respectively; wherein, the connection between the inner support and the first permanent structure and the second permanent structure is through a corbel structure.

[0013] Preferably, the construction of the second permanent structure is carried out from bottom to top, and the second permanent structure includes: a bottom plate, after the construction of the bottom plate, the third internal support is removed; a middle plate, after the construction of the middle plate, the second internal support is removed; and a top plate, after the construction of the top plate, the first internal support is removed.

[0014] According to a second aspect of the present application, a deep foundation pit is proposed, which is constructed by the above-mentioned deep foundation pit support method.

[0015] The support method for deep and large foundation pits proposed in this application, on the one hand, reduces the deformation of the deep foundation pit support structure by lowering the water level outside the deep foundation pit and reducing the water and soil pressure outside the deep foundation pit; on the other hand, it uses the support structure inside the deep foundation pit to provide a reaction force for the support structure to resist the force of the soil outside the deep foundation pit on the support structure, thereby reducing the maximum bending moment and deformation of the deep foundation pit structure.

[0016] Other features and advantages of the present application will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings constituting a part of the present application are used to provide a further understanding of the present application, and the schematic implementation modes and descriptions of the present application are used to explain the present application. In the accompanying drawings: Figure 1 It is a schematic diagram of the construction of back pressure soil and precipitation wells according to the preferred embodiment of the present application.

[0018] Figure 2 It is a schematic diagram of the construction of the first permanent structure according to the preferred embodiment of the present application.

[0019] Figure 3 This is a schematic diagram of the first internal support construction according to the preferred embodiment of the present application.

[0020] Figure 4 This is a schematic diagram of the second internal support construction according to the preferred embodiment of the present application.

[0021] Figure 5 It is a schematic diagram of the third and fourth internal support construction according to the preferred embodiment of the present application.

[0022] Figure 6 It is a schematic diagram of the middle plate construction of the second permanent structure according to the preferred embodiment of the present application.

[0023] Figure 7 It is a schematic diagram of the roof construction of the second permanent structure according to the preferred embodiment of the present application.

[0024] Figure 8 It is a schematic diagram after the deep foundation pit construction is completed according to the preferred embodiment of the present application. DETAILED DESCRIPTION

[0025] The technical solution of the present application will be described in detail below with reference to the accompanying drawings and in combination with the implementation modes.

[0026] In this application, deep and large foundation pits in coastal or southern soft soil areas are taken as examples.

[0027] According to the "Geotechnical Engineering Investigation Code", fine-grained soil with a natural porosity greater than or equal to 1.0 and a natural water content greater than the liquid limit should be judged as soft soil, including silt, silty soil, peat, peaty soil, etc.

[0028] For soft soil areas, the groundwater level in the soil layer is high or the water content of the soil layer is high. If precipitation treatment is not carried out before construction, it is easy to cause landslides, water gushing inside the foundation pit, and even the risk of soft soil liquefaction during deep foundation pit construction. The use effect of deep foundation pit support structure is closely related to the stability of the soil around the deep foundation pit. For example, the bearing capacity and stability of underground continuous walls or steel sheet piles will be reduced due to the buoyancy or compression of water in the surrounding soil.

[0029] Therefore, according to the first aspect of the present application, a deep foundation pit support method is proposed, which includes: constructing a dewatering well 1 outside the deep foundation pit to reduce the water and soil pressure outside the deep foundation pit; constructing a support structure inside the deep foundation pit to provide a force to the deep foundation pit support structure 2 to reduce the maximum bending moment and horizontal displacement of the deep foundation pit support structure 2.

[0030] The above-mentioned dewatering well 1 outside the deep foundation pit is mainly used to lower the groundwater level outside the deep foundation pit. By lowering the water level around the deep foundation pit, the impact of water on the foundation pit is reduced to ensure the stability of the foundation pit. The depth of the above-mentioned dewatering well 1 is determined according to the dewatering calculation (refer to "Technical Code for Building Foundation Pit Support" JGJ 120-2012). In order to ensure that the water level in the deep foundation pit is within a safe range during the construction of the deep foundation pit, a drainage well can also be set up inside the deep foundation pit. The setting of the above-mentioned drainage well is determined according to the water level inside the foundation pit. If the water level in the foundation pit is high, it needs to be set up. If the water level is at least 0.5m lower than the excavation surface, it does not need to be set up. The specific structural setting inside the above-mentioned drainage well is the same as that inside the dewatering well.

[0031] The above-mentioned dewatering well 1 outside the deep foundation pit can reduce the pressure of water on the foundation pit, prevent the displacement and softening of the soil around the foundation pit, and help to improve the stability and bearing capacity of the supporting structure 2.

[0032] The above-mentioned support structure in the deep foundation pit is mainly used to further enhance the stability of the deep foundation pit and prevent the support structure 2 from becoming unstable due to external force or soil deformation during the excavation of the foundation pit. The support structure can provide a reaction force with the surrounding soil, effectively control the deformation of the support structure 2 caused by the pressure of the surrounding soil, ensure the verticality of the foundation pit and the stability of the support structure 2, and prevent the displacement of the support structure 2 due to horizontal pressure, thereby reducing the instability of the soil or the settlement of surrounding buildings caused by displacement.

[0033] The above-mentioned support structure in the deep foundation pit can provide temporary support during construction, and can also provide permanent support after the deep foundation pit construction is completed, so as to improve the long-term stability of the deep foundation pit and the surrounding environment.

[0034] In summary, the deep foundation pit support method proposed in this application utilizes a dewatering well outside the pit to reduce the pressure of the soil layer around the deep foundation pit, and a support structure is arranged inside the pit to provide a strong reaction force to the support structure to resist the horizontal pressure of the soil layer outside the deep foundation pit and the pressure of deformation of the support structure, thereby ensuring the stability of the deep foundation pit during and after the construction of the deep foundation pit.

[0035] According to a preferred embodiment of the present application, in order to ensure the effect of precipitation outside the deep foundation pit, as Figure 1 As shown, the distance between the above-mentioned precipitation well 1 and the above-mentioned deep foundation pit support structure 2 needs to be based on the water level in the soil layer, the excavation depth of the foundation pit, the type of soil layer, the strength of the support structure 2, the surrounding buildings and facilities, and the economy. In this application, it can be 1.5m-3m, which is specifically determined according to the situation of the construction site. In this application, it is preferably 1.5m. The number of the above-mentioned precipitation wells 1 can be multiple, and the spacing of the above-mentioned precipitation wells 1 can be considered comprehensively based on the construction situation and construction cost, generally 7m-9m. The above-mentioned precipitation well 1 is drilled by a drilling rig. In order to discharge the water in the soil layer in time, a filter pipe can be set in the above-mentioned precipitation well 1. The above-mentioned filter pipe can be a bridge filter pipe or a sandless concrete filter pipe, preferably a bridge filter pipe. The bridge filter pipe has the advantages of drainage performance, anti-blocking ability, strong adaptability, simple construction and maintenance, durability and corrosion resistance. Especially in soft soil areas, facing complex hydrogeological conditions, the bridge filter pipe can effectively lower the groundwater level and ensure the stability and safety of foundation pit construction. In order to further prevent the filter pipe from being blocked during use, the filter pipe is wrapped with 2 layers of 100-mesh nylon cloth, and medium-coarse sand filter material is backfilled between the filter pipe and the inner wall of the precipitation well within the well depth range. The particle size of the above coarse sand can be larger than the aperture of the filter pipe, so that groundwater in the surrounding soil layer can enter through the pores of the filter pipe wall and be pumped out by a water pump. In order to ensure that the water level in the deep foundation pit is not less than 0.5m below the excavation surface, a drainage well can be set in the deep foundation pit according to the water level in the deep foundation pit.

[0036] like Figure 2-Figure 8As shown, in order to provide sufficient support force for the deep foundation pit support structure 2, preferably, the construction of the support structure in the deep foundation pit may include: construction of a temporary structure and a permanent structure; the construction of the temporary structure includes: setting up a back pressure soil 3, which is set up in the deep foundation pit and contacts the deep foundation pit support structure 2; construction of an internal support, the first end of the internal support is connected to the deep foundation pit support structure 2; the construction of the permanent structure includes: construction of a first permanent structure 4 and a second permanent structure 5, the first permanent structure 4 is connected to the second end of the internal support; the second permanent structure 5 is set at the position of the back pressure soil 3 to replace the temporary structure. When constructing in the deep foundation pit, the back pressure soil 3 in the temporary structure is first used to provide support for the support structure 2 of the deep foundation pit, the first permanent structure 4 next to the back pressure soil 3 is constructed, and then the first permanent structure 4 is used to construct the internal support to replace the back pressure soil 3, and then the second permanent structure 5 is constructed from the position of the back pressure soil 3 to gradually replace the internal support. During the construction process, it can ensure that the support structure 2 has sufficient supporting force at each stage of the construction to avoid settlement or deformation of the foundation pit due to support failure; avoid unnecessary risks caused by construction of deep foundation pits without support; and save construction time.

[0037] According to a preferred embodiment of the present application, Figure 1 As shown, the above-mentioned counter-pressure soil 3 can be set after the deep foundation pit is excavated. In this application, it is preferably formed by excavating the soil above the deep foundation pit. When the deep foundation pit is excavated, a portion of the counter-pressure soil 3 is reserved, which can save construction costs, save construction time, and improve the stability of the foundation pit. In order to gradually increase the force of the counter-pressure soil 3 on the supporting structure 2 in layers during the excavation of the foundation pit, the counter-pressure soil 3 is stepped toward one side of the deep foundation pit. The width and height of the above-mentioned counter-pressure soil must ensure the stability of the counter-pressure soil and provide sufficient resistance to the supporting structure 2. Generally, the width of each step of the counter-pressure soil 3 is not less than 5m and the height is 6m-8m. The stepped counter-pressure soil 3 can avoid excessive pressure shocks on the supporting structure 2 during the excavation of the foundation pit, thereby ensuring the stability of the supporting structure 2. The stepped design can optimize the stability of the soil, reduce settlement and disturbance, improve the bearing capacity of the supporting structure 2, and make the construction process more flexible and controllable. The number of layers of the counter-pressure soil 3 is determined according to the depth of the deep foundation pit. The slope of the counter-pressure soil 3 varies according to the properties of the soil layers around the deep foundation pit, and is generally 1:1-1:1.25.

[0038] Before excavating a deep foundation pit, it is necessary to construct column piles 11 in advance, and insert columns 12 on top. When the length of the inner support is large, the columns 12 are set to reduce the calculated length of the inner support and improve the resistance of the inner support.

[0039] In order to enhance the stability of the counter-pressure soil 3, anchor rods 32 perpendicular to the slope are arranged on the slope of each layer of the counter-pressure soil 3 excavated. The vertical spacing of the anchor rods 32 is 1.5m and the length is 6m-9m.

[0040] In order to further enhance the stability of the counter-pressure soil 3, preferably, the setting of the counter-pressure soil 3 may include: setting a counter-pressure soil pile 31, which is set at the position where the counter-pressure soil 3 is connected to the bottom of the deep foundation pit, for enhancing the stability of the counter-pressure soil 3. The insertion depth of the above-mentioned counter-pressure soil pile 31 at the bottom of the deep foundation pit is related to the geological conditions and the cantilever height, and the height is generally 6m-9m. The above-mentioned counter-pressure soil pile 31 can provide additional support force to prevent the counter-pressure soil 3 from settling, moving or displacing, and can limit the horizontal displacement of the counter-pressure soil 3, thereby reducing the deformation of the support structure 2, and can also share the horizontal pressure of the counter-pressure soil 3, reduce the burden of the support structure 2, and ensure the stability of the deep foundation pit during excavation and subsequent construction.

[0041] According to a preferred embodiment of the present application, Figure 2 As shown, the construction of the first permanent structure 4 in the deep foundation pit may include casting of the bottom plate structure 41 in the deep foundation pit and construction of the main structure, wherein the main structure is arranged on the bottom plate structure in the deep foundation pit. The casting of the bottom plate structure and the construction of the main structure adopt reinforced concrete structure.

[0042] In order to gradually remove the back pressure soil 3, preferably, as Figure 2-Figure 5 As shown, the inner support is constructed from top to bottom, and the construction of the inner support may include: constructing the first inner support 6, which can be set at the top of the deep foundation pit, one end of the first inner support 6 is connected to the top of the deep foundation pit support structure 2, and the other end is set at the top of the main structure; the first support provides support for the top position of the support structure 2 to replace the supporting force of the top counter-pressure soil 3. Subsequently, after excavating the counter-pressure soil 3, the inner supports below are gradually constructed, and the number of the above inner supports is set according to the soil pressure and depth around the deep foundation pit. In this application, there are three inner supports below as an example; after excavating the counter-pressure soil 3, the second inner support 7 and the third inner support 8 are sequentially constructed, and the second inner support 7 and the third inner support 8 are located inside the deep foundation pit and are connected to the deep foundation pit support structure 2 and the first permanent structure 4; constructing the fourth inner support 9, and the two ends of the fourth inner support 9 are respectively connected to the second permanent structure 5; wherein, the connection between the inner support and the first permanent structure 4 and the second permanent structure 5 is connected through the bracket structure 10.

[0043] The above-mentioned corbel structure 10 is a reinforced concrete structure and can be cast simultaneously with the construction of the main structure.

[0044] The second to fourth inner supports are constructed after excavating the back pressure soil 3, rather than being constructed sequentially after completely removing the back pressure soil 3. The first permanent structure 4 and the inner supports are used to provide force for the support structure 2 to reduce its deformation range.

[0045] The first inner support 6 and the second inner support 7 are respectively arranged parallel to the ground, and are used to provide a horizontal reaction force to the support structure 2. One end of the third inner support 8 is in contact with the bottom plate structure of the first permanent structure 4, and the other end is higher than the bottom plate structure of the first permanent structure 4 in the horizontal direction, connected to the support structure 2, and arranged at an angle with the ground. The angle does not exceed 45°, and the specific angle is determined according to the structural conditions and manual calculations; the fourth inner support 9 is arranged in the angle space formed by the third inner support 8 and the ground, and the fourth inner support 9 is connected to the support structure 2 through a support transfer belt. The support transfer belt is generally plain concrete, cast on site, and can also be made of reinforced concrete beams or steel sections. A vertical wall 54 of the second permanent structure is also arranged between the support transfer belt and the fourth inner support 9.

[0046] The inner support and the supporting structure 2 are connected via the embedded bars on the supporting structure 2. The embedded bars are steel bars.

[0047] In order to gradually replace the internal support and maintain the stability of the support structure 2 during the construction of the second permanent structure 5, preferably, Figure 5-Figure 7 As shown, the construction of the second permanent structure 5 can be carried out from bottom to top, and the second permanent structure 5 can include: a bottom plate 51, after the construction of the bottom plate 51, the third internal support 8 is removed; a middle plate 52, after the construction of the middle plate 52, the second internal support 7 is removed; and a top plate 53, after the construction of the top plate 53, the first internal support 6 is removed. Under the action of the fourth internal support 9, the force provided by the third internal support 8 is replaced by the fourth internal support 9, and then the middle plate 52 structure is implemented, the third internal support 8 is removed, and the construction is carried out upwards in sequence until the first internal support 6 is replaced. The second permanent structure 5 is constructed from bottom to top, which can always ensure the force of the bottom of the deep foundation pit on the supporting structure 2, avoid instability or deformation of the bottom of the supporting structure 2, and the upper supporting structure 2 is subjected to a smaller horizontal force, and the construction is relatively easy. A supporting force transmission belt is arranged between the bottom plate 51 and the supporting structure; a supporting force transmission belt and a vertical wall of the second permanent structure are arranged between the middle plate 52 and the top plate 53 and the supporting structure, and a fertilizer trough is used to backfill between the supporting force transmission belts, for example, the earthwork or fluidized soil in the site can be used for backfilling. The supporting force transmission belt is in the same horizontal direction as the bottom plate 51, the middle plate 52 and the top plate 53, so as to provide support for the supporting structure with the help of the second permanent structure.

[0048] When the second permanent structure replaces the internal support, along with the construction of the second permanent structure, the corresponding support-replacement force-transfer belts, vertical walls and fertilizer trough backfill are gradually constructed.

[0049] According to a second aspect of the present application, a deep foundation pit is proposed, which is constructed by the above-mentioned deep foundation pit support method.

[0050] The construction steps of the deep foundation pit support method proposed in this application are as follows: (1) Construction of drainage well 1 and support structure 2 on the ground. The diameter of drainage well 1 is generally 500-700mm, with a built-in bridge filter pipe with a diameter of 273mm. The surrounding area is filled with medium-coarse sand filter material. Support structure 2 can be piled, ground-connected wall, etc. The specific selection is determined according to the on-site construction. According to the water level in the foundation pit, a drainage well is set in the foundation pit and pumped in real time according to the progress of earthwork excavation. Generally, the water level in the foundation pit is guaranteed to be no less than 0.5m below the excavation surface.

[0051] (2) Construct column piles 11 and insert column 12. Excavate the earthwork in layers and blocks, and reserve counterpressure soil 3. Pump water from the dewatering well 1 outside the pit to reduce the groundwater outside the pit to the calculated specified height. Anchor rods 32 are implemented during the earthwork excavation process. Construct counterpressure soil piles 31 as foot guards to enhance the stability of the counterpressure soil 3.

[0052] (3) Construct the bottom plate structure of the first permanent structure 4; when the earthwork is excavated to the bottom of the foundation pit, cast the bottom plate structure. Construct the main structure of the first permanent structure 4, construct the corbel structure on the top of the main structure, connect the support structure 2 and the first permanent structure 4 through the first internal support 6, and provide the reaction force of the first internal support 6 through the first permanent structure 4.

[0053] (4) Excavate the counter-pressure soil 3 to the second inner support position, implement the corbel structure, construct the second inner support 7, and provide the reaction force of the second inner support through the second permanent structure 5.

[0054] (5) Excavate the counter-pressure soil 3, remove the counter-pressure soil piles 31, implement the corbel structure, construct the third inner support 8, and provide the reaction force of the third inner support through the second permanent structure 5.

[0055] (6) Excavate the remaining counter-pressure soil 3, implement the bottom plate 51 of the second permanent structure 5, implement the first support force transfer belt 13, construct a vertical wall on the bottom plate 51, implement the second support force transfer belt 14, implement the corbel structure 10 on the bottom plate 51, implement the fourth internal support 9, and remove the third internal support 8 and the corbel structure through the reaction force provided by the bottom plate 51 of the second permanent structure 5.

[0056] (7) Install the middle plate 52 of the second permanent structure 5, replace the third support force transmission belt 15, remove the fourth inner support 9 and the corbel structure 10 on the bottom plate 51; remove the second inner support 7 and the corbel structure 10.

[0057] (8) Install the top plate 53 of the second permanent structure 5, replace the force transmission belt 4 17, remove the first inner support 6, remove the bracket structure on the top plate, remove the columns, and complete the construction (such as Figure 8 as shown).

[0058] The preferred embodiments of the present application are described in detail above; however, the present application is not limited to the specific details in the above embodiments. Within the technical concept of the present application, a variety of simple modifications can be made to the technical solution of the present application, and these simple modifications all fall within the protection scope of the present application.

[0059] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this application will not further describe various possible combinations.

[0060] In addition, the various implementation modes of the present application may be arbitrarily combined, and as long as they do not violate the concept of the present application, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A deep foundation pit support method, characterized in that: The support method includes: Constructing a dewatering well (1) outside the deep foundation pit to reduce the water and soil pressure outside the deep foundation pit; A support structure is constructed in a deep foundation pit to provide a force to the deep foundation pit support structure (2) so as to reduce the maximum bending moment and horizontal displacement of the deep foundation pit support structure (2).

2. The deep foundation pit support method according to claim 1, characterized in that: The distance between the dewatering well (1) and the deep foundation pit support structure (2) is 1.5m-3m, the number of the dewatering wells (1) is multiple, and the spacing between the dewatering wells (1) is 7m-9m.

3. The deep foundation pit support method according to claim 2, characterized in that: A water filter pipe is arranged in the dewatering well (1) to lower the water level in the soil layer around the deep foundation pit.

4. The deep foundation pit support method according to claim 1, characterized in that: The supporting structure in the deep foundation pit includes: temporary construction structure and permanent structure; The temporary construction structure comprises: a counter-pressure soil (3) is arranged in the deep foundation pit and is in contact with the deep foundation pit support structure (2); Constructing an inner support, wherein a first end of the inner support is connected to a deep foundation pit support structure (2); The permanent structure of the construction includes: A first permanent structure (4) and a second permanent structure (5) are constructed, wherein the first permanent structure (4) is connected to the second end of the inner support; and the second permanent structure (5) is arranged at the position of the counterpressure soil (3) to replace the temporary structure.

5. The deep foundation pit support method according to claim 4, characterized in that: The counter-pressure soil (3) is formed by excavating the soil above the deep foundation pit. The counter-pressure soil (3) is stepped on one side facing the deep foundation pit. The width of each step of the counter-pressure soil (3) is not less than 5m and the height is 6m-8m.

6. The deep foundation pit support method according to claim 4, characterized in that: The provision of the counter-pressure soil (3) comprises: provision of a counter-pressure soil pile (31), wherein the counter-pressure soil pile (31) is provided at a position where the counter-pressure soil (3) is connected to the bottom of the deep foundation pit, and is used to enhance the stability of the counter-pressure soil (3).

7. The deep foundation pit support method according to claim 4, characterized in that: The construction of the first permanent structure (4) in the deep foundation pit comprises casting of a bottom plate structure (41) in the deep foundation pit and construction of a main structure (42), wherein the main structure (42) is arranged on the bottom plate structure (41) in the deep foundation pit.

8. The deep foundation pit support method according to claim 4, characterized in that: The inner support is constructed from top to bottom, and the construction of the inner support includes: Constructing a first internal support (6), the first internal support (6) being arranged at the top of the deep foundation pit, one end of the first internal support (6) being connected to the top of the deep foundation pit support structure (2), and the other end being arranged at the top of the main structure (42) of the first permanent structure (4); After excavating the counterpressure soil (3), a second inner support (7) and a third inner support (8) are sequentially constructed. The second inner support (7) and the third inner support (8) are located inside the deep foundation pit and are connected to the deep foundation pit support structure (2) and the first permanent structure (4); A fourth internal support (9) is constructed, with both ends of the fourth internal support (9) respectively connected to the second permanent structure (5); wherein the internal support is connected to the first permanent structure (4) and the second permanent structure (5) via a corbel structure (10).

9. The deep foundation pit support method according to claim 8, characterized in that: The second permanent structure (5) is constructed from bottom to top, and the second permanent structure (5) comprises: A bottom plate (51), after the bottom plate (51) is constructed, the third inner support (8) is removed; A middle plate (52), after the middle plate (52) is constructed, the second inner support (7) is removed; A top plate (53), after the top plate (53) is constructed, the first inner support (6) is removed.

10. Deep foundation pit, characterized in that: The deep foundation pit is constructed by the deep foundation pit support method described in any one of claims 1-9.

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