A construction method for a deep foundation pit with variable spacing supports held by a sliding pre-support

Abstract

The application provides a sliding pre-support holding movable deep foundation pit variable interval support construction method, which comprises the following steps: A, installing a foundation pit enclosure structure; B1, performing sliding pre-support construction; B2, performing permanent support layer construction; B3, performing temporary servo support layer construction; B4, performing permanent servo support layer construction; B5, moving and installing the temporary servo support layer; repeating the steps B4 and B5 until the distance between the last constructed permanent servo support layer and the bottom of the foundation pit is less than the set depth; B6, continuously digging the foundation pit earthwork in the space surrounded by the foundation pit enclosure structure to the bottom of the foundation pit, and constructing a foundation pit bottom plate; the distance between the adjacent permanent servo supports gradually decreases from top to bottom. The application has the advantages of avoiding support construction interference and being used for completing support variable interval installation, and can solve the problem of support equidistance installation waste.

Description

Technical Field

[0001] This application relates to the field of foundation pit construction technology, and in particular to a method for constructing a sliding pre-supported mobile deep foundation pit variable spacing support. Background Technology

[0002] Excavation of foundation pits is required during underground space development. The existing construction method for foundation pits is as follows: A retaining structure is built at the edge of the area containing the foundation pit. Then, the soil within the retaining structure is excavated to a predetermined depth (the depth to which the soil can be excavated in one go is called the predetermined depth; support must be provided during this excavation, otherwise the retaining structure will deform beyond its limits). A permanent support is then erected. This process is repeated until the foundation pit depth reaches the bottom elevation, at which point the bottom of the pit is poured. After the foundation pit construction is completed, the permanent support is removed (permanent support refers to support that is not removed before the foundation pit construction is completed). Existing foundation pit supports are installed at equal intervals to facilitate the excavation of the foundation pit soil. (Support is necessary before the foundation pit reaches the designated depth; otherwise, the deformation of the foundation pit retaining structure towards the inside of the pit will exceed the set range. Any inward or outward deformation of the retaining structure must be within the set range to meet requirements. The foundation pit retaining structure acts as an elastic body within the pit, and can produce localized arching when subjected to excessive pressure.) Traditional foundation pit construction typically uses reinforced concrete supports or (prestressed) steel supports. However, traditional supports often result in excessive deformation of the retaining structure and uneven development of axial forces among the supports. Therefore, a servo support system was designed. The servo support system can monitor and adjust the axial forces of each support in real time, actively controlling the deformation of the retaining structure. However, when the excavation depth is deep, the upper servo supports maintain a consistently high axial force, often causing negative deformation of the retaining structure towards the outside of the pit. To reduce this negative deformation, the axial force of the upper supports is often set at a lower threshold during subsequent construction, resulting in high servo support consumption. If the servo supports are installed with varying spacing from top to bottom, the consumption can be reduced. The location and axial force of each servo support can be preliminarily calculated when using variable spacing. During construction, only minor adjustments to the axial force are needed to correct for errors caused by actual geological conditions and geological data obtained from testing, ensuring the axial force meets actual requirements. However, when installing variable spacing servo supports, the spacing between supports will be greater than the set depth, making variable spacing servo support installation impossible. Summary of the Invention

[0003] This invention aims to provide a method for constructing mobile deep foundation pit variable-spacing supports using a sliding pre-support structure that avoids interference from the construction time of the supports, thereby solving the problem of wasted supports during equidistant installation.

[0004] To achieve the above-mentioned objectives, the present invention employs the following technology: a method for constructing a sliding pre-supported mobile deep foundation pit variable-spacing support, comprising: A) Installation of the foundation pit retaining structure: constructing the foundation pit retaining structure within the perimeter of the soil in the area where the foundation pit is located; B) Excavation of the foundation pit: excavating the foundation pit soil within the space enclosed by the foundation pit retaining structure and supporting the foundation pit retaining structure until the foundation pit is excavated to the bottom elevation; characterized in that the specific process of step B is as follows: B1) Construction of the sliding pre-support: excavating the foundation pit soil within the space enclosed by the foundation pit retaining structure to allow for the installation of the sliding pre-support and permanent support, and supporting the sliding pre-support within the foundation pit retaining structure; B2) Construction of the permanent support layer. A1. **Construction of Temporary Servo Support Layer:** The upper part of the foundation pit retaining structure is supported by several horizontally distributed permanent supports, located above the slip-down pre-supports. B2. **Construction of Temporary Servo Support Layer:** Within the space enclosed by the foundation pit retaining structure, the excavated foundation pit soil is further excavated to a set depth. The slip-down pre-supports are lowered to the lower end of the excavated foundation pit and pre-support the foundation pit retaining structure. At the depth of the slip-down pre-supports, several horizontally distributed temporary servo supports are used to support the foundation pit retaining structure. The axial force of the temporary servo supports is adjusted to meet the requirements. The temporary servo supports are located above the slip-down pre-supports. B3. **Construction of Permanent Servo Support Layer:** Within the space enclosed by the foundation pit retaining structure, the excavated foundation pit soil is further excavated to a depth above the foundation pit retaining structure. The location closest to the temporary servo support for installing the permanent servo support is exposed. The slip-down pre-support is lowered to the bottom of the excavated pit and pre-supports the pit retaining structure. At the depth of the slip-down pre-support, several horizontally distributed permanent servo supports are used to support the pit retaining structure at the location where the permanent servo support is installed. The axial force of the permanent servo support is adjusted to meet the requirements. The permanent servo support is located above the slip-down pre-support. B5. Temporary servo support layer relocation and installation: Within the space enclosed by the pit retaining structure, the excavated pit soil continues to be excavated to the set depth. The slip-down pre-support is lowered to the bottom of the excavated pit and pre-supports the pit retaining structure. The axial force of the temporary servo support is reduced to the temporary... The servo support can be removed, and the temporary servo support of the temporary servo support layer is moved to the depth position of the sliding pre-support. The axial force of the temporary servo support is adjusted to meet the requirements, and the temporary servo support is located above the sliding pre-support. Steps B4 and B5 are repeated until the distance between the last constructed permanent servo support layer and the bottom elevation of the foundation pit is less than the set depth. Step B6: Continue to excavate the foundation pit soil within the space enclosed by the foundation pit retaining structure to the bottom elevation of the foundation pit, and construct the foundation pit bottom slab. The distance between adjacent permanent servo support layers decreases sequentially from top to bottom, and the distance between the permanent support layer and the first permanent servo support layer is less than the distance between the two uppermost permanent servo support layers. This realizes the construction of variable-pitch servo support installation. By setting the sliding pre-support and servo support to perform pre-support before the actual support, the problem of the foundation pit support structure deformation not meeting expectations due to the servo support installation time exceeding the expectation can be avoided.

[0005] Preferably, the permanent support is a reinforced concrete structure, and the foundation pit retaining structure includes a diaphragm wall and a capping beam cast on top of the diaphragm wall, with the permanent support cast together with the capping beam. This ensures that the upper part of the foundation pit retaining structure remains in a fixed position.

[0006] Preferably, in step B5, during the process of reducing the axial force of the temporary servo support until it can be removed, the following inspection is performed: Check whether the deformation of the portion of the foundation pit retaining structure located between the two adjacent permanent servo support layers meets the requirements. If it does not meet the requirements, adjust the axial force of the permanent servo support located below the temporary servo support layer until the deformation of the portion of the foundation pit retaining structure located between the two adjacent permanent servo support layers meets the requirements. This ensures that the constructed foundation pit accurately meets the requirements.

[0007] Preferably, a dial indicator is installed at each end of the temporary servo support, with the tips of the two dial indicators extending in opposite directions. The temporary servo support is horizontal and perpendicular to the foundation pit retaining structure, providing support to the foundation pit retaining structure. When the axial force of the temporary servo support meets the requirements, the tips of both dial indicators are pressed against the foundation pit retaining structure, the readings of both dial indicators are non-zero, and the sum of the readings of the two dial indicators is n. When the absolute value of the difference between the sum of the readings of the two dial indicators and n is less than a set value, it indicates that the deformation of the foundation pit retaining structure meets the requirements. The axial force of the temporary servo support is then reduced. During the process of removing the temporary servo support, the readings of both dial gauges are maintained at a non-zero value. If the difference between the sum of the two dial gauge readings and n is greater than zero and greater than the set value, the axial force of the permanent servo support located below the temporary servo support is increased until the absolute value of the sum of the two dial gauge readings minus n is less than the set value. If the sum of the two dial gauge readings minus n is less than zero and the absolute value is greater than the set value, the axial force of the permanent servo support located below the temporary servo support is decreased until the absolute value of the sum of the two dial gauge readings minus n is less than the set value. This method allows for convenient detection of whether the deformation of the foundation pit retaining structure meets the requirements using the temporary servo support. The accuracy during detection is good. If the detection instrument is moved and repositioned during each detection, the resulting measurement error is large; this technical solution overcomes this problem.

[0008] Preferably, the temporary servo support includes a main body of the temporary servo support, with temporary servo support jacks at both ends; the permanent servo support includes a main body of the permanent servo support, with permanent servo support jacks at both ends; the sliding pre-support includes a frame extending circumferentially along the foundation pit retaining structure, several support rollers distributed circumferentially along the frame and supporting the inner surface of the foundation pit retaining structure, and several sliding pre-support jacks distributed circumferentially along the frame. The sliding pre-support jacks are used to press the frame tightly against the inner surface of the foundation pit retaining structure to support the foundation pit retaining structure. The sliding servo support has good maneuverability, reliable pre-support, and convenient sliding.

[0009] Preferably, the temporary servo support layer and the permanent servo support layer are horizontally staggered. The frame and the permanent support of the same permanent servo support layer enclose several openings, allowing the horizontal temporary servo support to pass through the openings directly below it. The main body of the temporary servo support has a cylindrical section, and the main body of the permanent servo support has a cylindrical section. A first connecting ring is fitted onto the cylindrical section of the temporary servo support. The first connecting ring is connected to one end of a telescopic structure via a rotating structure, and the other end of the telescopic structure is connected to a second connecting ring. The rotation includes a rotating axis, whose perpendicular axis intersects the centerline of the first connecting ring perpendicularly and is parallel to the telescopic direction of the telescopic structure. In the initial position, the temporary servo support is horizontal and perpendicular to the foundation pit retaining structure. The temporary servo support is in its initial state when it supports the foundation pit retaining structure. The second connecting ring is capable of... The opening and closing ring; the specific process of transferring the temporary servo support to the installation position at the pre-support depth in step B5 is as follows: The distance between the first and second connecting rings is adjusted using a telescopic structure until the second connecting ring can connect to the permanent servo support adjacent to the temporary servo support below it. The second connecting ring is then fitted onto the cylindrical section of the permanent servo support adjacent to the temporary servo support below it, detaching the temporary servo support from the pit retaining structure. The temporary servo support is rotated using a rotating structure until it can pass through the hole directly below it. The temporary servo support is then rotated about the cylindrical section of the permanent servo support until it is positioned below the permanent servo support connected to the second connecting ring. The temporary servo support is then driven back to its initial state using a rotating structure. The vertical position of the temporary servo support is adjusted using the telescopic structure until it aligns with the installation position of the temporary servo support on the pit retaining structure. The temporary servo support is then installed. Moving the temporary servo support is convenient, labor-saving, and safe.

[0010] Preferably, the telescopic structure is a hydraulic cylinder.

[0011] Preferably, the second connecting ring includes two half-rings, one end of which is hinged to a telescopic structure via a hinge pin; a locking bolt passing through the other end of each half-ring; and a locking nut threaded onto the locking bolt. In use, the locking nut and bolt are removed, the two half-rings are separated, and then moved radially along the permanent servo support to be mounted on the cylindrical section of the permanent servo support. The locking nut, in conjunction with the locking bolt, connects the two half-rings together, thus fitting them onto the cylindrical section of the permanent servo support. Connecting and removing the second connecting ring to the cylindrical section of the permanent servo support is convenient and provides reliable connection.

[0012] Preferably, a hanging ring is connected to the first connecting ring. The specific process of rotating the temporary servo support around the cylindrical section of the permanent servo support is as follows: the hoist is fixed to the permanent servo support or the permanent support located above the temporary servo support. The hook of the hoist's chain is hooked onto the hanging ring, causing the hoist to push against the temporary servo support, causing the temporary servo support to lose its balance. The rotation speed of the temporary servo support is controlled by controlling the extension speed of the hoist's chain. This improves the safety and convenience when moving the temporary servo support.

[0013] Preferably, the rotating structure includes a suspension cover connected to the rotating structure and a servo motor located within the suspension cover. One end of the rotating shaft is fixed to a first connecting ring, and the other end passes through the suspension cover and has a large-diameter section. The large-diameter section hooks the rotating shaft to the rotating cover. The servo motor is connected to a telescopic structure. This design allows for effortless rotation and precise control of the rotation angle. The built-in design provides good protection. The structure is compact.

[0014] Preferably, a first limiting block is provided on the large-diameter section, and a second limiting block is provided inside the suspension cover. When the rotating structure drives the telescopic structure to rotate until the second limiting block abuts against the first limiting block, the temporary servo support is in its initial state. This avoids the temporary servo support failing to reset properly, which would lead to poor accuracy when detecting deformation of the foundation pit retaining structure through the temporary servo support.

[0015] Preferably, in step B5, during the process of reducing the axial force of the temporary servo support until it can be removed, the following detection operation is performed: The deformation of the portion of the foundation pit retaining structure located between two adjacent permanent servo support layers is checked to ensure it meets the requirements. If it does not meet the requirements, the axial force of the permanent servo support located below the temporary servo support layer is adjusted until the deformation of the portion of the foundation pit retaining structure located between the two adjacent permanent servo support layers meets the requirements. A dial indicator is installed at each end of the temporary servo support, with the tops of the two dial indicators extending in opposite directions. The temporary servo support is horizontal and supports the foundation pit retaining structure perpendicular to it. When the axial force of the temporary servo support meets the requirements, the tops of both dial indicators are pressed against the foundation pit retaining structure, the readings of both dial indicators are non-zero, and the sum of the readings of the two dial indicators is n. When the absolute value of the difference between the sum of the readings of the two dial indicators and n is less than a set value, it indicates that the deformation of the foundation pit retaining structure meets the requirements. During the reduction... During the process of removing the temporary servo support from the axial force of the low temporary servo support, the readings of the two dial gauges are always kept non-zero. If the difference between the sum of the two dial gauge readings and n is greater than zero and greater than the set value, the axial force of the permanent servo support below the temporary servo support is increased until the absolute value of the sum of the two dial gauge readings minus n is less than the set value. If the sum of the two dial gauge readings minus n is less than zero and the absolute value is greater than the set value, the axial force of the permanent servo support below the temporary servo support is decreased until the absolute value of the sum of the two dial gauge readings minus n is less than the set value. The dial gauge is hinged to one end of the connecting seat via a hinge shaft perpendicular to the main body of the temporary servo support. The other end of the connecting seat is fixed to the main body of the temporary servo support. The frame can pass through between the dial gauge and the main body of the temporary servo support. The connecting seat is provided with a limiting step on the side of the dial gauge facing the main body of the temporary servo support. A reset torsion spring that drives the dial gauge to approach the limiting step is sleeved on the hinge shaft. This technical solution enables the dial indicator to avoid collision with the sliding pre-support when the temporary servo support is moved after the test.

[0016] The present invention has the following advantages: the variable pitch setting of the support can reduce the number of supports and make full use of the load capacity of the supports; the accuracy of detecting the deformation of the foundation pit retaining structure is good and convenient; the servo support is safe and convenient to move; and it can avoid the excessive deformation of the foundation pit retaining structure caused by the installation time of the servo support exceeding the expectation. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the pre-supported sliding section during foundation pit construction;

[0018] Figure 2This is a schematic diagram of the permanent support and slippage pre-support during the construction of the foundation pit;

[0019] Figure 3 This is a schematic diagram of the temporary servo support after the foundation pit construction is completed;

[0020] Figure 4 yes Figure 3 A magnified view of a portion of point B;

[0021] Figure 5 yes Figure 6 This is a schematic diagram of the first permanent servo support after the foundation pit construction is completed;

[0022] Figure 6 yes Figure 5 Top view diagram

[0023] Figure 7 This is a diagram showing the temporary support being moved below the first permanent servo support.

[0024] Figure 8 This is a schematic diagram showing the second permanent servo support after the foundation pit construction is completed;

[0025] Figure 9 This is a diagram showing the temporary support being moved below the second permanent servo support.

[0026] Figure 10 This is a diagram showing the completion of all permanent servo support installations;

[0027] Figure 11 This is a cross-sectional schematic diagram of the connection between the temporary servo support and the permanent servo support connected to the temporary servo support.

[0028] Figure 12 yes Figure 11 A-A sectional view.

[0029] In the diagram: 1. Excavation pit retaining structure; 2. Soil in the area where the excavation pit is located; 3. Diaphragm wall; 4. Crown beam; 5. Slip-down pre-support; 6. Permanent support; 7. Temporary servo support; 8. Permanent servo support; 9. Excavation pit bottom slab; 10. Main body of temporary servo support; 11. Jack of temporary servo support; 12. Dial indicator; 13. Top of dial indicator; 14. Hinge shaft; 15. Connecting seat; 16. Limiting step; 17. First connecting ring; 18. Rotating structure; 19. Telescopic structure; 20. Second connecting ring; 21. Hinge shaft; 22. Half ring; 23. Locking bolt; 24. Locking nut; 25. Hanging ring; 26. Suspension cover; 27. Servo motor; 28. Rotating shaft; 29. ​​Large diameter section; 30. First limiting block; 31. Second limiting block; 32. Main body of permanent servo support; 33. Jack of permanent servo support; 34. Frame; 35. Support roller; 36. Jack of slip-down pre-support; 37. Hole. Detailed Implementation

[0030] The present invention will now be described in conjunction with the accompanying drawings and specific embodiments, wherein the anchor rod is inclined with one end higher than the other end, which is connected to the inner retaining wall, and the lower end of the anchor rod is lower than the bottom of the inner pit.

[0031] See Figures 1 to 11A method for constructing a sliding pre-supported mobile deep foundation pit variable-spacing support includes: A) Installation of the foundation pit retaining structure: constructing the foundation pit retaining structure 1 within the perimeter of the soil 2 in the area where the foundation pit is located; the foundation pit retaining structure includes a diaphragm wall 3 and a capping beam 4 cast on top of the diaphragm wall. B) Excavation of the foundation pit: excavating the foundation pit soil within the space enclosed by the foundation pit retaining structure and erecting horizontal supports until the foundation pit is excavated to the bottom elevation; the specific process of step B is as follows: B1) Construction of sliding pre-support: excavating the foundation pit soil within the space enclosed by the foundation pit retaining structure to the point where sliding pre-supports 5 and permanent supports 6 can be installed, and supporting the sliding pre-supports within the foundation pit retaining structure; B2) Construction of the permanent support layer: supporting the upper end of the foundation pit retaining structure with several horizontally distributed permanent supports, the permanent supports being located above the sliding pre-supports; B3) Construction of the temporary servo support layer: on the foundation pit retaining structure... Continue excavating the foundation pit to a set depth within the space enclosed by the structure. Lower the slip-down pre-support 5 to the lower end of the excavated foundation pit and pre-support the foundation pit retaining structure. At the depth of the slip-down pre-support, use several horizontally distributed temporary servo supports 7 to support the foundation pit retaining structure. Adjust the axial force of the temporary servo supports to meet the requirements. The temporary servo supports are located above the slip-down pre-support. B4. Construction of the permanent servo support layer: Continue excavating the foundation pit within the space enclosed by the foundation pit retaining structure until the location of the foundation pit retaining structure closest to the temporary servo supports for installing the permanent servo supports is exposed. The pre-support is lowered to the bottom of the excavated pit and pre-supports the pit retaining structure. At the depth of the pre-support, several horizontally distributed permanent servo supports are used to support the pit retaining structure at the location where the permanent servo supports are installed. The axial force of the permanent servo supports is adjusted to meet the requirements. The permanent servo supports are located above the pre-support. B5. Temporary servo support layer relocation and installation: The excavated pit soil is further removed to a set depth within the space enclosed by the pit retaining structure. The pre-support is lowered to the bottom of the excavated pit and pre-supports the pit retaining structure. The axial force of the temporary servo supports is reduced. Once the temporary servo support can be removed, move the temporary servo support layer to the depth position of the slip-down pre-support, adjust the axial force of the temporary servo support to meet the requirements, and position the temporary servo support above the slip-down pre-support; repeat steps B4 and B5 until the distance between the last constructed permanent servo support layer and the bottom elevation of the foundation pit is less than the set depth; B6, continue excavating the foundation pit soil within the space enclosed by the foundation pit retaining structure to the bottom elevation of the foundation pit, remove the slip-down pre-support, construct the foundation pit bottom slab 9, and remove it; the distance between adjacent permanent servo supports decreases sequentially from top to bottom. The permanent support is a reinforced concrete structure, and the permanent support is cast together with the capping beam.

[0032] The temporary servo support includes a main body 10, with temporary servo support jacks 11 at both ends. A cylindrical section of the temporary servo support is also provided on the main body (in this embodiment, the entire main body is cylindrical, thus having a cylindrical section). A dial indicator 12 is provided at each end of the temporary servo support, with the tips 13 of the two dial indicators extending in opposite directions. When the axial force of the temporary servo support meets the requirements, the tips of both dial indicators are pressed against the foundation pit retaining structure, and the readings of both dial indicators are non-zero. The sum of the readings of the two dial indicators is n. When the absolute value of the sum of the readings of the two dial indicators minus n is less than the set value, it indicates that the deformation of the foundation pit retaining structure meets the requirements. The dial indicator is specifically connected as follows: the dial indicator is hinged to one end of the connecting seat 15 via a hinge shaft 14 perpendicular to the main body of the temporary servo support. The other end of the connecting seat is fixed to the main body of the temporary servo support. The frame 34 can pass through between the dial indicator and the main body of the temporary servo support. The connecting seat is provided with a limiting step 16 on the side of the dial indicator facing the main body of the temporary servo support. A reset torsion spring that drives the dial indicator to approach the limiting step is sleeved on the hinge shaft. A first connecting ring 17 is sleeved on the cylindrical section of the temporary servo support. The first connecting ring is connected to one end of the telescopic structure 19 via a rotating structure 18. The other end of the telescopic structure is connected to a second connecting ring 20. The second connecting ring is an openable and closable ring. The telescopic structure is a hydraulic cylinder. The second connecting ring includes two half-rings 22, one end of which is hinged to the telescopic structure via a hinge shaft 21, a locking bolt 23 passing through the other end of the two half-rings, and a locking nut 24 threaded onto the locking bolt. A hanging ring 25 is connected to the first connecting ring. The rotating structure includes a suspension cover 26 connected to the telescopic rotating structure, a servo motor 27 located inside the suspension cover, and a rotating shaft 28 connected at one end to the first connecting ring. The other end of the rotating shaft passes through the suspension cover and has a large-diameter section 29, which hooks the rotating shaft to the rotating cover. The servo motor is fixed to the telescopic structure. The axis of the rotating shaft is perpendicular to the center line of the first connecting ring. A first limiting block 30 is provided on the large-diameter section, and a second limiting block 31 is provided inside the suspension cover. When the rotating structure drives the telescopic structure to rotate until the second limiting block abuts against the first limiting block, the temporary servo support is in its initial state. In its initial state, the temporary support is horizontal and perpendicular to the pit retaining structure. The temporary servo support is in its initial state when supporting the pit retaining structure. The permanent servo support includes a permanent servo support body 32, and permanent servo support jacks 33 are provided at both ends of the permanent servo support body.The slip-down pre-support includes a frame 34 extending circumferentially along the foundation pit retaining structure, several support rollers 35 distributed circumferentially along the frame on the inner surface of the foundation pit retaining structure, and several slip-down pre-support jacks 36 distributed circumferentially along the frame. The slip-down pre-support jacks are used to press the frame tightly against the inner surface of the foundation pit retaining structure to support it. In step B5, during the process of reducing the axial force of the temporary servo support until it can be removed, the following inspection is performed: The deformation of the portion of the foundation pit retaining structure located between two adjacent permanent servo support layers meets the requirements. If it does not meet the requirements, the axial force of the permanent servo support located below the temporary servo support layer is adjusted until the deformation of the portion of the foundation pit retaining structure located between two adjacent permanent servo support layers meets the requirements. During the process of reducing the axial force of the temporary servo support until it can be removed, the readings of both dial gauges are always kept non-zero. If the difference between the sum of the two dial gauge readings and n is greater than zero and greater than the set value, the axial force of the permanent servo support located below the temporary servo support is increased until the absolute value of the sum of the two dial gauge readings minus n is less than the set value. If the sum of the two dial gauge readings minus n is less than zero and the absolute value is greater than the set value, the axial force of the permanent servo support located below the temporary servo support is reduced until the absolute value of the sum of the two dial gauge readings minus n is less than the set value. Between adjacent temporary servo support layers and permanent servo support layers, the temporary and permanent servo supports are horizontally offset. The frame and the permanent support of the same permanent servo support layer enclose several openings 37, allowing the temporary servo support in a horizontal state to pass through the openings located directly below it. The specific process of transferring the temporary servo support to the installation position at the pre-support depth in step B5 is as follows: The distance between the first and second connecting rings is adjusted using a telescopic structure until the second connecting ring can connect to the permanent servo support adjacent to the temporary servo support below it. The second connecting ring is then fitted onto the cylindrical section of the permanent servo support adjacent to the temporary servo support below it, thus detaching the temporary servo support from the pit retaining structure. The temporary servo support is then rotated using a rotating structure until it can pass through the hole directly below it. The temporary servo support is then rotated about the cylindrical section of the permanent servo support until it is positioned below the permanent servo support connected to the second connecting ring. The temporary servo support is then driven back to its initial state using a rotating structure. Finally, the vertical position of the temporary servo support is adjusted using the telescopic structure until it aligns with the installation position of the temporary servo support on the pit retaining structure. The temporary servo support is then installed.The specific process of rotating the temporary servo support around the cylindrical section of the permanent servo support is as follows: the hoist is fixed on the permanent servo support or the permanent support located above the temporary servo support, the hook of the hoist chain is hooked on the hanging ring, so that the hoist pushes the temporary servo support, causing the temporary servo support to lose balance, and the rotation speed of the temporary servo support is controlled by controlling the extension speed of the hoist chain.

Claims

1. A method for constructing a sliding pre-supported movable deep foundation pit variable-spacing support, comprising: A) installation of the foundation pit retaining structure: constructing the foundation pit retaining structure to the perimeter of the soil in the area where the foundation pit is located; B) excavation of the foundation pit: excavating the foundation pit soil within the space enclosed by the foundation pit retaining structure and supporting the foundation pit retaining structure until the foundation pit is excavated to the bottom elevation; characterized in that... Step B's specific process is as follows: B1. Construction of the slip-down pre-support: Excavate the foundation pit within the space enclosed by the foundation pit retaining structure until the slip-down pre-support and permanent support can be installed. The slip-down pre-support is then placed within the foundation pit retaining structure. B2. Construction of the permanent support layer: Support the upper part of the foundation pit retaining structure with several horizontally distributed permanent supports, positioned above the slip-down pre-support. B3. Construction of the temporary servo support layer: Continue excavating the foundation pit to a set depth within the space enclosed by the foundation pit retaining structure. Lower the slip-down pre-support to the lower end of the excavated foundation pit and pre-support the foundation pit retaining structure. At the slip-down pre-support depth, support the foundation pit retaining structure with several horizontally distributed temporary servo supports. Adjust the axial force of the temporary servo supports to meet the requirements. The temporary servo supports are positioned above the slip-down pre-support. B4. Construction of the permanent servo support layer: Continue excavating the foundation pit within the space enclosed by the foundation pit retaining structure until the location of the foundation pit retaining structure closest to the temporary servo supports for installing the permanent servo supports is exposed. B4. Descending the slip-down pre-support to the lower end of the excavated pit and pre-supporting the pit retaining structure, then using several horizontally distributed permanent servo supports at the depth of the slip-down pre-support to support the pit retaining structure at the installation location of the permanent servo supports, adjusting the axial force of the permanent servo supports to meet the requirements, with the permanent servo supports positioned above the slip-down pre-support; B5. Temporary servo support layer relocation and installation: Continue excavating the pit soil to the set depth within the space enclosed by the pit retaining structure, lowering the slip-down pre-support to the lower end of the excavated pit and pre-supporting the pit retaining structure, reducing the axial force of the temporary servo supports until they can be removed, transferring the temporary servo supports of the temporary servo support layer to the depth of the slip-down pre-support, adjusting the axial force of the temporary servo supports to meet the requirements, with the temporary servo supports positioned above the slip-down pre-support; repeat steps B4 and B5 until the distance between the last constructed permanent servo support layer and the bottom elevation of the pit is less than the set depth; B6. Continue to excavate the excavated soil within the space enclosed by the foundation pit retaining structure until the bottom elevation of the foundation pit is reached, and construct the foundation pit bottom slab; the distance between adjacent permanent servo support layers decreases sequentially from top to bottom, and the distance between the permanent support layer and the first permanent servo support layer is less than the distance between the two uppermost permanent servo support layers.

2. The method for constructing a sliding pre-supported movable deep foundation pit variable-spacing support according to claim 1, characterized in that, The permanent support is a reinforced concrete structure, and the foundation pit retaining structure includes a diaphragm wall and a capping beam cast on top of the diaphragm wall. The permanent support is cast together with the capping beam.

3. A method for constructing a sliding pre-supported movable deep foundation pit variable-spacing support according to claim 1 or 2, characterized in that, In step B5, during the process of reducing the axial force of the temporary servo support until the temporary servo support can be removed, the following inspection work is performed: The deformation of the portion of the foundation pit retaining structure located between the two adjacent permanent servo support layers meets the requirements. If it does not meet the requirements, the axial force of the permanent servo support located below the temporary servo support layer is adjusted until the deformation of the portion of the foundation pit retaining structure located between the two adjacent permanent servo support layers meets the requirements. A dial indicator is installed at each end of the temporary servo support, and the extension directions of the tops of the two dial indicators are set in opposite directions. The temporary servo support is in a horizontal state and supports the foundation pit retaining structure in a state perpendicular to the foundation pit retaining structure.

4. A method for constructing a sliding pre-supported movable deep foundation pit variable-spacing support according to claim 1 or 2, characterized in that, The temporary servo support includes a temporary servo support body, with temporary servo support jacks at both ends of the temporary servo support body; the permanent servo support includes a permanent servo support body, with permanent servo support jacks at both ends of the permanent servo support body; the sliding pre-support includes a frame extending circumferentially along the foundation pit retaining structure, a plurality of support rollers distributed circumferentially along the frame and supporting the inner surface of the foundation pit retaining structure, and a plurality of sliding pre-support jacks distributed circumferentially along the frame, wherein the sliding pre-support jacks are used to press the frame tightly against the inner surface of the foundation pit retaining structure to support the foundation pit retaining structure.

5. The method for constructing a sliding pre-supported movable deep foundation pit variable-spacing support according to claim 4, characterized in that, Between adjacent temporary servo support layers and permanent servo support layers, the temporary servo supports and permanent servo supports are staggered in the horizontal direction. The frame and the permanent support of the same permanent servo support layer enclose several holes, and the temporary servo supports in the horizontal state can pass through the holes located directly below the temporary servo supports. The main body of the temporary servo support part is provided with a cylindrical section of the temporary servo support part, and the main body of the permanent servo support part is provided with a cylindrical section of the permanent servo support part. A first connecting ring is sleeved on the cylindrical section of the temporary servo support part. The first connecting ring is connected to one end of the telescopic structure through a rotating structure, and the other end of the telescopic structure is connected to a second connecting ring. The rotation includes a rotating axis, and the axis perpendicular to the rotating axis intersects the center line of the first connecting ring perpendicularly and is parallel to the telescopic direction of the telescopic structure. In the initial position, the temporary servo support is in a horizontal state and perpendicular to the foundation pit retaining structure. When the temporary servo support supports the foundation pit retaining structure, it is in the initial state. The second connecting ring is a ring that can be opened and closed. The specific process of transferring the temporary servo support to the installation position at the pre-support depth in step B5 is as follows: The distance between the first and second connecting rings is adjusted using a telescopic structure until the second connecting ring can connect to the permanent servo support adjacent to the temporary servo support below it. The second connecting ring is then fitted onto the cylindrical section of the permanent servo support adjacent to the temporary servo support below it, thus detaching the temporary servo support from the pit retaining structure. The temporary servo support is then rotated using a rotating structure until it can pass through the hole directly below it. The temporary servo support is then rotated about the cylindrical section of the permanent servo support until it is positioned below the permanent servo support connected to the second connecting ring. The temporary servo support is then driven back to its initial state using a rotating structure. Finally, the vertical position of the temporary servo support is adjusted using the telescopic structure until it aligns with the installation position of the temporary servo support on the pit retaining structure. The temporary servo support is then installed.

6. The method for constructing a sliding pre-supported movable deep foundation pit variable-spacing support according to claim 5, characterized in that, The second connecting ring includes two half-rings, one end of which is hinged to the telescopic structure via a hinge shaft, a locking bolt passing through the other end of the two half-rings, and a locking nut threaded onto the locking bolt.

7. The method for constructing a sliding pre-supported movable deep foundation pit variable-spacing support according to claim 5, characterized in that, The first connecting ring is connected to a hanging ring. The specific process of rotating the temporary servo support around the cylindrical section of the permanent servo support is as follows: the hoist is fixed on the permanent servo support or the permanent support located above the temporary servo support. The hook of the hoist chain is hooked on the hanging ring, so that the hoist pushes the temporary servo support, causing the temporary servo support to lose balance. The rotation speed of the temporary servo support is controlled by controlling the extension speed of the hoist chain.

8. The method for constructing a sliding pre-supported movable deep foundation pit variable-spacing support according to claim 5, characterized in that, The rotating structure includes a suspension cover connected to the telescopic structure and a servo motor located inside the suspension cover. One end of the rotating shaft is fixed to the first connecting ring, and the other end passes through the suspension cover and has a large diameter section. The large diameter section hooks the rotating shaft to the rotating cover. The servo motor is connected to the telescopic structure.

9. The method for constructing a sliding pre-supported movable deep foundation pit variable-spacing support according to claim 8, characterized in that, The large-diameter section is provided with a first limiting block, and the suspension cover is provided with a second limiting block. When the rotating structure drives the telescopic structure to rotate until the second limiting block abuts against the first limiting block, the temporary servo support is in its initial state.

10. The method for constructing a sliding pre-supported movable deep foundation pit variable-spacing support according to claim 5, characterized in that, In step B5, during the process of reducing the axial force of the temporary servo support until it can be removed, the following inspection is performed: The deformation of the portion of the foundation pit retaining structure located between two adjacent permanent servo support layers meets the requirements. If it does not meet the requirements, the axial force of the permanent servo support located below the temporary servo support layer is adjusted until the deformation of the portion of the foundation pit retaining structure located between two adjacent permanent servo support layers meets the requirements. A dial indicator is installed at each end of the temporary servo support, with the tops of the two dial indicators extending in opposite directions. The temporary servo support is in a horizontal state and supports the foundation pit retaining structure perpendicular to it. The dial indicator is hinged to one end of the connecting seat via a hinge shaft perpendicular to the main body of the temporary servo support. The other end of the connecting seat is fixed to the main body of the temporary servo support. The frame can pass through between the dial indicator and the main body of the temporary servo support. The connecting seat has a limiting step on the side of the dial indicator facing the main body of the temporary servo support. A reset torsion spring is sleeved on the hinge shaft to drive the dial indicator to approach the limiting step.

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