Fabricated adjustable pre-camber steel pipe truss foundation pit supporting structure and construction installation method

Abstract

This invention relates to the field of construction technology, specifically to a prefabricated adjustable pre-camber steel pipe truss foundation pit support structure and its construction and installation method. It includes a ring-shaped diaphragm wall supported within the foundation pit, with horizontally arranged support beams installed within the ring cavity of the diaphragm wall. Each support beam comprises an extended section and standard members, with the extended sections and standard members connected sequentially along the extension / retraction direction of the extended sections. When the extended sections are in their extended state, both ends of the support beam are pressed against the cavity wall of the diaphragm wall, and an approximately equivalent stiffness is generated inside the support beam. This invention can accurately calculate the approximately equivalent stiffness of the support beam, thereby eliminating the potential for the support beam to fracture due to excessive stress and improving construction safety.

Description

Technical Field

[0001] This invention relates to the field of construction technology, specifically to a prefabricated adjustable pre-camber steel pipe truss foundation pit support structure and its construction and installation method. Background Technology

[0002] During the excavation of a foundation pit, the presence of surrounding roads, existing buildings, pipelines, and other structures can easily lead to collapse due to pressure. Therefore, to prevent collapse, support structures are typically used inside the foundation pit during excavation. This not only prevents pit collapse but also improves the safety of surrounding buildings.

[0003] In existing foundation pit support structures, the bottom of the wide plate is directly attached to the foundation pit, resulting in insufficient bottom support and easy inward movement, affecting the support effect. Furthermore, it can easily cause a slope to form at the bottom of the foundation pit, requiring readjustment of the support and increasing the difficulty of use. Therefore, to overcome the above technical problems, patent ZL202011329251.6 discloses a foundation pit support structure and component, including wide plates. Grooves are machined on the lower front of two wide plates, and connecting mechanisms are installed on the inner walls of both grooves. The connecting mechanisms include a short plate, a threaded rod, a handle, and a helical rod. The outer wall of the short plate is fixedly connected to the inner wall of the groove. By connecting the threaded rod to the soil through rotation and engagement of the helical rod, bottom stability is improved, preventing inward movement and ensuring support effectiveness. This enhances stability, prevents the formation of a slope at the bottom of the pit, eliminates the hassle of adjusting the support, and reduces the difficulty of use. The control mechanism's circular plate rotation, in conjunction with curved blocks, supports the bent plate, achieving a fixed block for the bent plate and allowing for the disassembly of the horizontal straight rods, reducing installation volume and facilitating installation and use. The support mechanism's inclined plate, in conjunction with a sleeve plate, supports the long rods, preventing bending caused by excessive internal pressure. While the above-mentioned existing technology provides effective support, in actual use, the support beams, supported inside the pit, bear significant pressure. The existing technology cannot accurately measure this pressure and therefore cannot compare it with the support beam's bearing capacity limit, ultimately leading to the safety hazard of the support beam breaking or bending due to excessive stress during support. To eliminate these safety hazards, the conventional approach is to increase the cross-sectional area of ​​the support beam or use more robust materials; while these methods can eliminate the safety hazards to some extent, they also increase construction costs, which is not a preferred solution for the entire construction team. Summary of the Invention

[0004] To avoid and overcome the technical problems existing in the prior art, this invention provides a prefabricated adjustable pre-camber steel pipe truss foundation pit support structure and its construction and installation method. This invention can accurately calculate the approximate equivalent stiffness of the support beam, thereby eliminating the hidden danger of the support beam breaking due to excessive stress and improving construction safety.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] The prefabricated adjustable pre-camber steel pipe truss foundation pit support structure includes a ring-shaped diaphragm wall supported within the foundation pit, with horizontally arranged support beams installed within the ring cavity of the diaphragm wall.

[0007] The support beam consists of extended sections and standard members. Each extended section and each standard member is connected sequentially along the extension and contraction direction of the extended section. Both ends of the support beam are pressed against the cavity wall of the diaphragm wall.

[0008] When the elongated section is in the elongated state, the approximate equivalent stiffness of the supporting beam is: , The calculation formula is as follows:

[0009]

[0010] in, This refers to the span of the supporting beams, i.e., the number of supporting beams. The elastic modulus of a standard bar; The cross-sectional area of ​​a standard rod; k The shear force required to generate a unit shear angle for the standard member (23); This refers to the elongation of the elongated segment; The thrust force for the elongated section; The moment of inertia of the cross section of the standard bar; This refers to the span of each section of the supporting beam, i.e., the length of the supporting beam. To support the mid-span deflection of each span of the beam; This refers to the weight per unit length of a standard rod.

[0011] As a further aspect of the present invention: when the extended section is in the locked state, the support beam is subjected to an axial force, and the formula for calculating the axial force is as follows:

[0012]

[0013] in, This refers to the remaining axial force in the support beam when the extended section is in the locked state. The elastic modulus of the elongated segment; This is the sum of the effective cross-sectional areas of the elongated sections; This is the length when the elongated section is locked.

[0014] As a further embodiment of the present invention: the diaphragm wall is rectangular, and the support beams are divided into transverse support beams and longitudinal support beams; the length direction of the transverse support beams is parallel to the width direction of the diaphragm wall, and each transverse support beam is arranged equidistantly along the length direction of the diaphragm wall; the length direction of the longitudinal support beams is parallel to the length direction of the diaphragm wall, and each longitudinal support beam is arranged equidistantly along the width direction of the diaphragm wall; each longitudinal support beam and each transverse support beam intersects and is fixed to each other at the intersection, forming a mesh frame support structure supported in the annular cavity of the diaphragm wall;

[0015] Both ends of the transverse support beam are support ends. Extended sections and standard members are arranged alternately from the support ends inward. In addition, pre-arched sections and standard members are arranged alternately from both sides towards the center of the beam in the middle of the transverse support beam, so that the transverse support beam forms an upward-curved bow-shaped rod structure.

[0016] Both ends of the longitudinal support beam are support ends, with extended sections and standard members alternately arranged inward from the support ends. In addition, connecting sections and standard members alternately arranged inward from both sides towards the center of the beam in the middle of the longitudinal support beam.

[0017] As a further embodiment of the present invention: the standard member includes three chords arranged in parallel to each other, and the three chords are fixed to each other by diagonal web members; two of the chords are located on the lower side and in the same horizontal plane, and the other chord is located on the upper side, so as to form a frame structure with an isosceles triangle cross-section.

[0018] As a further embodiment of the present invention: the elongated section includes three support screws, the front end of each support screw is threadedly connected to a support sleeve that is coaxially rotatably arranged at the tail end of each chord; a support sleeve is hinged to the tail end of each support screw, and each support sleeve is sleeved on the front end of the chord corresponding to the adjacent standard rod.

[0019] It also includes a tensioning screw with its tail end hinged to the adjacent ends of two adjacent standard rods. The front ends of the two tensioning screws are coaxially screwed into the tensioning sleeve from both ends of the same tensioning sleeve, and the axis of the tensioning sleeve intersects the axis of the support sleeve. Each hinge axis is parallel to each other and perpendicular to the axis of the support screw.

[0020] It also includes jacks that are positioned between two adjacent standard members and provide a jacking force to push the two adjacent standard members apart, with the axis of the jacks being parallel to the axis of the support screw.

[0021] As a further embodiment of the present invention: the pre-arch section includes two parallel hinge rods, each hinge rod being formed by two connecting rods hinged together; the two ends of the two hinge rods are respectively coaxially fixed to the ends of the two lower chords in the adjacent standard rods, and the hinge axes of the two sets of hinge rods coincide with each other and are perpendicular to the chord axis.

[0022] It also includes pre-arched threaded sleeves, both ends of which are coaxially threaded with pre-arched screws, and the tail ends of the two pre-arched screws are hinged with pre-arched sleeves. The two pre-arched sleeves are coaxially fixed to the upper chord of the adjacent standard members.

[0023] It also includes a tensioning screw with its tail end hinged to the adjacent ends of two adjacent standard rods. The front ends of the two tensioning screws are coaxially screwed into the tensioning sleeve from both ends of the same tensioning sleeve, and the axis of the tensioning sleeve intersects with the axis of the support sleeve.

[0024] As a further embodiment of the present invention: the front end of the support end and the extension section cooperate with each other, and the structure of the front end of the support end is the same as the structure of the end of the standard rod and the extension section that cooperates with each other.

[0025] The three chords in the support end gradually contract toward the tail end of the support end and are fixed to the support plate, which is pressed against the cavity wall of the diaphragm wall.

[0026] The cavity wall of the diaphragm wall is provided with an annular sill, and an end support is provided on the sill. The support end is pressed tightly against the end support from top to bottom, and the support plate is pressed against the plate surface of the sill.

[0027] The connecting section includes three parallel hinge rods, the two ends of which are coaxially fixed to the ends of the chord members in the adjacent standard rods. The hinge axes of the three sets of hinge rods coincide with each other and are perpendicular to the axis of the chord members. It also includes a fastening screw rod with its tail end hinged to the adjacent ends of two adjacent standard rods. The front ends of the two fastening screw rods are coaxially screwed into the fastening screw sleeve from both ends of the same fastening screw sleeve, and the axis of the fastening screw sleeve intersects with the axis of the support screw sleeve.

[0028] As a further embodiment of the present invention: each span of the transverse support beam includes continuously arranged... n -1 pre-arched section, the distance from the first pre-arched section of each span to the end support or column is denoted as... The distances between the remaining adjacent pre-arch sections are respectively denoted as... , … The distance from the last pre-arch section to the end support or column is denoted as... The formula for calculating the pre-camber of the pre-cambered section is as follows:

[0029]

[0030] in, This is the calculated value of the pre-camber of the pre-cambered section; Deflection caused by its own weight; This refers to the deflection caused by longitudinal support pressure. The lateral deformation is caused by the thrust of the elongated section. This refers to the lateral deformation caused by soil pressure during the construction phase. This is the long-term increase factor for deflection;

[0031] The formulas for calculating the pre-arch angle of each pre-arch segment are as follows:

[0032]

[0033]

[0034]

[0035]

[0036]

[0037]

[0038] in, The angle between the axis of the standard member connecting the first pre-arched section and the horizontal line is positive counterclockwise and negative clockwise. ( Take 1, 2, ..., n-1) as the supplementary angle between the standard members at both ends of each pre-arch section in each span, with counterclockwise being positive and clockwise being negative; ( Take 1, 2, ..., n-1) as the pre-camber calculation value for each pre-camber segment.

[0039] As a further embodiment of the present invention, it also includes a column, on which a slide rail extending in a vertical direction is arranged, and a support rod is slidably arranged on the slide rail, the support rod supporting the bottom of two chords located on the lower side of the transverse support beam from bottom to top;

[0040] The sliding end of the support rod is provided with a vertically extending groove in the direction of the groove length, and the groove is a tapering groove structure that gradually narrows from the groove cavity to the groove opening, and the groove slides and engages on the guide rail.

[0041] The slide has a tapered groove on its wall, the length of which is parallel to the length of the slide, and the cavity of the tapered groove gradually narrows along the length of the groove. A tapered wedge is inserted into the tapered groove along the length of the groove to lock the guide rail in the slide.

[0042] The conical wedge includes two conical clips that can be mated to form a shape that matches a conical groove. The two conical clips are mated to form bolt holes for the front end of a bolt to pass through. The front end of the bolt passes through the conical groove and connects to a nut to wed the two conical clips tightly in the conical groove.

[0043] As a further embodiment of the present invention, the following installation steps are included:

[0044] Step 1: Construction layout and excavation of the foundation pit;

[0045] Step 2: Arrange the diaphragm walls and install fencing on them;

[0046] Step 3: Install the columns in the foundation pit according to the construction standards;

[0047] Step 4: Assemble the first layer of transverse support beams. Place the transverse support beams in the foundation pit and press the support ends of the transverse support beams against the corresponding end supports. At the same time, support the columns at the bottom of the transverse support beams. Adjust the length of the extended sections and the pre-camber of each pre-camber section of the transverse support beams to make the transverse support beams reach the predetermined elevation.

[0048] Step 5: Assemble the longitudinal support beams. Place the longitudinal support beams in the foundation pit and press the support ends of the longitudinal support beams firmly onto the corresponding end supports. Fix the longitudinal support beams and transverse support beams together to form the first layer of the mesh support structure.

[0049] Step 6: Following steps 1 to 5, construct the remaining support structures in sequence.

[0050] Compared with the prior art, the beneficial effects of the present invention are:

[0051] 1. This invention can accurately calculate the equivalent stiffness of the support beam during the support process, and then compare it with the beam's own bearing limit to determine whether there is a risk of fracture due to excessive stress. If not, construction can continue smoothly; if so, adjustments can be made to eliminate the safety hazard, improving construction safety and support reliability. Simultaneously, this invention can also adjust the jacking force of the elongated section based on the equivalent stiffness, ensuring that the thrust of the support beam on the foundation pit during support reaches the set requirements, thereby effectively preventing foundation pit collapse and improving support safety.

[0052] 2. The present invention can accurately calculate the axial force in the support beam when the extension section is locked, thereby ensuring that the thrust of the support beam on the foundation pit reaches the set requirements and improving the safety of the support.

[0053] 3. This invention can incorporate a pre-camber to reduce the structural geometric nonlinearity caused by the vertical deflection of the transverse support beam; simultaneously, it weakens the P-Δ effect of the transverse support beam under soil pressure, increases the axial stiffness of the transverse support beam, and reduces soil displacement. This invention incorporates a pre-camber section in the transverse support beam. By adjusting the angles of the standard members at both ends of this section, the axial elevation of the transverse support beam can be varied, which to some extent offsets the long-term deflection of the transverse support beam under its own weight, creep, and other effects. This reduces the geometric nonlinearity of the transverse support beam under axial loads, increases the overall axial stiffness of the transverse support beam, and improves the safety of the foundation pit support.

[0054] 4. This invention is applicable to foundation pit support with different excavation widths, increasing the turnover rate of foundation pit support, reducing usage costs, and promoting the circular and sustainable development of the construction industry. This invention incorporates an extension section in the support beam, enabling continuous spatial variation of the support beam, meeting the support requirements for different foundation pit excavation widths and depths, solving the problem of support distance variations caused by uneven surfaces of underground structures such as diaphragm walls, and achieving sustainable economic and resource development.

[0055] 5. The standard rod of the present invention uses a split steel pipe composite section for the extended section, support end and pre-arched section. It uses less material, is lightweight and has a very large bending moment of inertia, thus greatly increasing the overall stability of the support and improving the support efficiency.

[0056] 6. This invention, by pre-installing jacks and other lifting hydraulic devices in the extended section of the support beam, can apply the required supporting force to the soil through the extension and retraction of the hydraulic devices, actively overcome the active earth pressure of the soil, control the amount of soil deformation, and increase the stability of the soil around the foundation pit.

[0057] 7. This invention incorporates bolts and sleeves in the extended section of the support beam. When a large jacking force is required from the support beam, it can be extended first using jacks, and then the corresponding sleeves can be tightened. The entire construction process requires only 1-2 jacks to complete all the foundation pit support work, reducing the cost of foundation pit support, improving economic efficiency, and enhancing the quality of construction.

[0058] 8. A cross brace column connection is installed at the intersection of the transverse support beam and the column. This connection mainly consists of guide rails and support rods. It not only reduces the span of the transverse support but also accommodates variations in the vertical spacing of multiple transverse support beams, making construction more convenient and faster. The guide rails allow the support rods to slide up and down, adapting to different foundation pits or variations in the vertical spacing of multiple transverse support beams within the same pit. Conical clamps prevent slippage of the support rods at any target elevation.

[0059] 9. This invention mainly uses positioning pins and sleeves for connection, which makes disassembly and assembly convenient. In addition, the use of positioning pins overcomes the problem of bolts being difficult to remove due to corrosion. Attached Figure Description

[0060] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0061] Figure 2 This is a schematic diagram of the transverse support beam in this invention.

[0062] Figure 3 This is a schematic diagram of the longitudinal support beam in this invention.

[0063] Figure 4 This is a schematic diagram of the structure of the standard rod in this invention.

[0064] Figure 5 This is a schematic diagram of the structure of the column in this invention.

[0065] Figure 6 This is a schematic diagram of the structure of the support terminal in this invention.

[0066] Figure 7 This is a schematic diagram of the elongated section in this invention.

[0067] Figure 8 This is a schematic diagram of the pre-arched section in this invention.

[0068] Figure 9 This is a schematic diagram of the elongated section in this invention.

[0069] Figure 10 This is a schematic diagram of the assembly structure of the supporting end and the end support in this invention.

[0070] Figure 11 This is a schematic diagram of the structure at the intersection of the transverse support beam and the longitudinal support beam in this invention.

[0071] Figure 12 This is a schematic diagram of the assembly structure of the transverse support beam and the column in this invention.

[0072] Figure 13 This is a schematic diagram of the structure of the column guide rail in this invention.

[0073] Figure 14 This is a schematic diagram of the split structure at the guide rail in this invention.

[0074] Figure 15 This is a schematic diagram of the conical chuck in this invention.

[0075] In the picture:

[0076] 10. Diaphragm wall; 11. Corridor; 12. End support; 20. Support beam; 201. Transverse support beam; 202. Longitudinal support beam; 21. Support end; 211. Support beam; 203. Tightening bolt; 204. Tightening bolt sleeve; 205. Locating pin; 206. Anti-slip pin; 22. Extension section; 221. Support bolt; 2211. Anti-slip groove; 222. Support bolt sleeve; 223. Support sleeve 224. Pipe; 23. Jack; 23. Standard rod; 231. Chord; 232. Diagonal web member; 24. Pre-arched section; 241. Hinge rod; 2411. Connecting rod; 242. Pre-arched threaded sleeve; 243. Pre-arched threaded rod; 244. Pre-arched sleeve; 25. Connecting section; 30. Column; 31. Guide rail; 32. Support rod; 321. Slide groove; 322. Conical groove; 323. Conical wedge; 3231. Conical clamp. Detailed Implementation

[0077] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0078] Please see Figures 1-15 In this embodiment of the invention, the prefabricated adjustable pre-camber steel pipe truss foundation pit support structure includes an annular diaphragm wall 10 supported in the foundation pit to prevent its collapse. The diaphragm wall 10 is selected according to the shape of the foundation pit. Common shapes of diaphragm walls 10 are mostly circular or rectangular. This invention is based on the research of a rectangular diaphragm wall 10.

[0079] A mesh frame support structure is constructed within the annular cavity of the diaphragm wall 10, supporting the cavity wall. The mesh frame support structure is mainly composed of sequentially intersecting support beams 20. The support beams 20 include transverse support beams 201 and longitudinal support beams 202. The transverse support beams 201 extend along the width of the rectangular diaphragm wall 10, and each transverse support beam 201 is arranged equidistantly along the length of the diaphragm wall 10. The longitudinal support beams 202 extend along the length of the rectangular diaphragm wall 10, and each longitudinal support beam 202 is arranged equidistantly along the width of the diaphragm wall 10.

[0080] Multiple columns 30 are arranged at equal intervals along the length of the transverse support beam 201. The columns 30 are fixed to the transverse support beam 201. The bottom of the columns 30 is supported on the ground of the foundation pit, thus providing multiple support points for the transverse support beam 201 and preventing the transverse support beam 201 from collapsing downward.

[0081] Both ends of the transverse support beam 201 are support ends 21. Extended sections 22 and standard members 23 are arranged alternately from the support ends 21 inwards. In addition, pre-arched sections 24 and standard members 23 are arranged alternately from both sides towards the center of the beam in the middle of the transverse support beam 201, so that the transverse support beam 201 forms an upward-curved bow-shaped beam structure.

[0082] Both ends of the longitudinal support beam 202 are support ends 21. Extended sections 22 and standard members 23 are arranged alternately from the support ends 21 inwards. Connecting sections 25 and standard members 23 are arranged alternately from both sides towards the center of the beam in the middle of the longitudinal support beam 202.

[0083] The assembly process of a commonly used transverse support beam 201 is as follows:

[0084] The transverse support beam 201 comprises two support ends 21, two extended sections 22, three pre-arched sections 24, and four standard members 23, arranged in a symmetrical structure. The arrangement order along the length of the transverse support beam 201 is as follows: support ends 21, extended sections 22, standard members 23, pre-arched sections 24, standard members 23, pre-arched sections 24, standard members 23, extended sections 22, and support ends 21.

[0085] First, connect the two support ends 21 and the two extension sections 22 together. Then, fit the three support sleeves 223 in the extension section 22 onto the three chord members 231 at the front end of the support end 21. Through holes are made at the ends of the chord members 231 and the overlapping sections of the support sleeves 223, and locating pins 205 are inserted into these through holes to secure the support sleeves 223 together. Next, secure the tail of the standard part to the extension section 22 already installed on the support end 21. Rotate the support threaded sleeve 222 coaxially to the end of the hollow chord member 231. Then, screw the front end of the support screw 221 into the support threaded sleeve 222 by rotating it. In this way, the connection of the three support screws 221 and the support threaded sleeve 222 is completed. Then, a tensioning screw 203 is hinged to the end of the support end 21 and the end of the standard rod 23, respectively. Next, a tensioning sleeve 204 is used to connect the two tensioning screws 203 together, and the tensioning sleeve 204 intersects with the three support screws 221. This allows them to cooperate with each support screw 221 within the space formed by the three support screws 221, forming a stable triangular structure and improving stability. A locking pin is also arranged on each sleeve to lock the sleeve when it stops rotating, further improving the stability of the support. When adjusting the extension length of the extension section 22, the lengths of each support screw 221 and tensioning screw 203 are adjusted by rotating the support sleeve 222 and tensioning sleeve 204 respectively, thus achieving a balance. During the extension of the extension section 22, if the resistance is not significant, the sleeves can be manually rotated for adjustment. However, when the resistance is large, a jack 224 can be temporarily installed between the support end 21 and the adjacent standard rod 23 through the mounting base to provide a jacking force for the extension section 22, and the screw sleeve can be rotated with the assistance of the jack 224.

[0086] Assemble the pre-arched section 24 and standard rods 23 together using a similar assembly method as before. The free ends of the two connecting rods 2411 of the hinge rod 241 have the same structure as the sleeve end of the support sleeve 223. The two ends of the hinge rod 241 are then sleeved onto the ends of the corresponding chord rods 231 and fixed with locating pins 205. First, connect the two pre-arched screws 243 and pre-arched sleeves 242 to each other using threads. Then, while installing the hinge rods 241, sleeve the two pre-arched sleeves 244 onto the ends of the corresponding chord rods 231 and fix them with locating pins 205. Simultaneously with the installation of the pre-arched screws 243, the fastening screws 203 and fastening sleeves 204 also need to be installed between the two standard rods 23. The installation method and the final structure are the same as those at the elongated section 22. When the pre-camber section 24 needs angle adjustment, the pre-camber sleeve 242 and the fastening sleeve 204 at the pre-camber section 24 are rotated simultaneously. The two standard rods 23 are rotated around the hinge point of the hinge rod 241 until a suitable angle is reached. The angle during the rotation process can be measured using a level or a professional angle measuring instrument. At this point, the transverse support beam 201 is assembled. The assembly method of the longitudinal support beam 202 is the same as that of the transverse connecting rod, but the longitudinal support beam 202 is assembled step by step only after all the transverse support beams 201 in the same layer have been installed. Fastening screws 203 and fastening sleeves 204 are arranged in all extension sections 22, pre-camber sections 24, and connecting sections 25. This increases the stability of the support beam 20 and provides pre-camber force, thereby adjusting the angle of the pre-camber section 24. In the transverse support beam 201 and the longitudinal support beam 202, the axes of all hinge shafts are arranged horizontally and perpendicular to the length direction of the corresponding support beam 20.

[0087] The elongated section 22 is located at both ends of the transverse support beam 201 and the longitudinal support beam 202. Two sections are arranged on each transverse support beam 201 and longitudinal support beam 202, respectively located at the connection between the standard member 23 and the support end 21. It consists of three support screws 221, three support sleeves, three support tubes 223, two tightening screws 203, and one tightening sleeve 204. The maximum elongation distance of each elongated section 22 is 0.5m, allowing for continuous variation in top position from 0 to 0.5m. The support screws 221 and tightening sleeve 204 are used to realize the expansion and contraction of the transverse support beam 201 and to withstand the earth pressure of the supporting soil. The tightening screws 203 and tightening sleeve 204 together form the diagonal web member 232, which, while cooperating with the expansion and contraction of the transverse support beam 201, resists the large shear force near the support end. The installation direction of the tensioning bolt 203 and tensioning sleeve 204 should be carefully considered to ensure they remain under pressure under the weight of the transverse support beam 201 or soil pressure. The anti-slip pin serves to fix the bolt and sleeve, preventing the sleeve from loosening due to vibration or other external factors during subsequent construction. When the required force for supporting the soil is small, workers can manually tighten the sleeve to achieve the desired force. When the required jacking force is large, workers can initially tighten the sleeve before using jack 224 to achieve the required jacking force. Then, the sleeve is tightened again, jack 224 is removed, and an anti-slip pin is inserted. The anti-slip pin passes through the support sleeve 222 and is inserted into the anti-slip groove 3212211 on the support bolt 221 along its axial direction to prevent the support sleeve 222 from loosening.

[0088] The pre-arched section 24 is located in the middle of the transverse support beam 201. Each transverse support beam 201 has a varying number of pre-arched sections 24 depending on the width of the excavated pit. The pre-arched section 24, 0.5m long, is located at the connection point of any two standard members 23 and is used to adjust the angle of the connected standard members 23 to achieve the pre-arching degree of the transverse support beam 201. It consists of two hinge rods 241, two pre-arched sleeves 244, eighteen positioning pins 205, two pre-arched bolts 243, one pre-arched threaded sleeve 242, two fastening bolts 203, one fastening threaded sleeve 204, and four anti-slip pins. By rotating the pre-arched threaded sleeve 242, the angle between the standard members 23 connected to the pre-arched section 24 is changed, thereby achieving the pre-arching degree. By rotating the tight-fitting sleeve 204, the angle is changed, and the gap between the member holes is eliminated; at the same time, it acts as a diagonal web member 232 to resist the shear force that may occur here, and increases the number of constraints on the pre-arched section 24 to improve the safety reserve of this section.

[0089] The connecting section 25 is located in the middle of the longitudinal support beam 202. The number of connecting sections 25 varies depending on the width of the excavated pit. Each connecting section 25, 0.2m long, is located at the connection point between any two standard members 23, connecting the two standard members 23 to form a unified structure capable of bearing the earth pressure of the supporting soil. The connecting section 25 consists of three hinge rods 241, seventeen positioning pins 205, two fastening bolts 203, one fastening sleeve 204, and two anti-slip pins. The two fastening bolts 203 and the fastening sleeve 204 work together to form a diagonal web member 232, increasing the overall integrity of the connection.

[0090] Meanwhile, the connecting fasteners can also eliminate errors caused by manufacturing, installation, deformation, etc. of the 20 supporting beams, making installation easier.

[0091] Jack 224 is placed at the temporary location of the extended section 22 to provide a larger jacking force. When the required force for supporting the soil is relatively small, the temporary jack 224 is not required, and the force can be applied manually by the construction workers by turning the bolt sleeve. After the jacking force is applied and the bolt sleeve is tightened, the jack 224 can be removed.

[0092] The longitudinal and transverse connecting keys are welded to the lower sides of both ends of the lower chord 231 of the standard rod 23. They are provided with four screw holes for connecting the longitudinal and transverse supports together with the screws and connecting fasteners.

[0093] The thicker end of the support sleeve 222 has no internal thread and is used to insert into the end of the chord 231 of the standard rod 23; the other end is relatively thinner and has internal threads, used to connect with the support sleeve 222 to allow the rod to extend and shorten. The through hole on the side of the support sleeve 222 is used to insert an anti-slip pin to inhibit its rotation.

[0094] The pre-arched threaded sleeve 242 and the tight-fitting threaded sleeve 204 are both double-ended threaded sleeves with opposite threads at both ends, which are rotated to achieve relative extension and retraction of the screws connected to their ends. The holes on the side of the double-ended threaded sleeve are used to insert anti-slip pins to inhibit their rotation.

[0095] The support screw 221, pre-arched screw 243, and tightening screw 203 are all rods with externally protruding coarse threads. They come in four different specifications depending on their location and function. All support screws 221, pre-arched screws 243, and tightening screws 203 have through-hole anti-slip grooves 3212211 on their sides to facilitate the insertion of anti-slip pins.

[0096] In the standard member 23, the chord member 231 located on the lower side is called the lower chord member, and the chord member 231 located on the upper side is called the upper chord member.

[0097] During construction, the foundation pit is first excavated according to the construction standards. Then, diaphragm walls 10 are installed in the foundation pit, and the surface of the diaphragm walls 10 is cleaned to provide a cleaner installation base for the subsequent installation of the screen wall 11, thereby improving the installation accuracy.

[0098] The retaining wall 11 is mainly composed of two parallel I-beams joined together. The retaining wall 11 is arranged along the cavity wall of the diaphragm wall 10 and installed on the diaphragm wall 10 by welding or fixing with expansion bolts, forming a ring structure. Multiple end supports 12 are welded to the retaining wall 11 at equal intervals according to the expected construction standards. The end supports 12 are U-shaped plate structures. During welding, a portion of the U-shaped plate is pressed tightly against the retaining wall 11, and then welding is performed only at the joints using a welding gun. This ensures that after welding, the length of the U-shaped groove on the upper part of the U-shaped plate is perpendicular to the wall surface of the diaphragm wall 10, and the groove opening is vertically upward. According to requirements, after all the necessary end supports 12 are welded, one layer of retaining wall 11 is considered completely completed. Subsequently, according to construction requirements, multiple layers of retaining wall 11 are arranged within the ring cavity of the diaphragm wall 10 along the depth direction of the foundation pit to meet usage needs.

[0099] After all the retaining walls 11 are installed according to the set requirements, the next step is to install the uprights 30. According to the construction requirements, the corresponding installation points are set on the ground of the foundation pit. Then, the rectangular uprights 30, welded from angle steel, are vertically fixed at the installation points. Along the height of the uprights 30, two rows of screw holes are sequentially opened on each of the four sides of the uprights 30, and guide rails 31 are fixed through these screw holes.

[0100] Column 30 is a hollow lattice column, welded from four equal-leg angle steels and steel plates. Bolt holes are provided at the welded joints of the angle steels and steel plates to facilitate the installation of guide rail 31, thereby reducing the span of the transverse support beam 201 and enhancing its overall integrity. Column 30 is installed using a pile driver before soil excavation.

[0101] When constructing column 30, first select four equal-leg angle steels as the four sides of column 30. Then, select small steel plates and weld them at equal intervals from top to bottom along the length of the equal-leg angle steels until all four sides are welded. After welding, drill screw holes in each steel plate for later use.

[0102] After the columns 30 are installed, the guide rails 31 are fixed to the corresponding sides of the columns 30 according to the height of the girder 11. At the corresponding position of each column 30, two guide rails 31 extending vertically are arranged on the same side, forming a set of guide rails 31. Then, according to the number of layers of the girder 11, a corresponding number of sets of guide rails 31 are installed on each column 30. The cross-section of the installed guide rails 31 is an isosceles trapezoid, with the top edge of the isosceles trapezoid close to the side of the column 30. Support rods 32 are slidably arranged on the guide rails, and the tail end of the support rods 32 has a groove 321 whose shape matches the guide rail 31. The support rods 32 slide with the guide rails 31 through the grooves 321, and the length direction of the support rods 32 is perpendicular to the length direction of the guide rails 31. A conical groove 322 is also formed in the cavity of the groove 321, and a conical wedge 323 is inserted into the conical groove 322. The conical wedge 323 includes two conical clamping pieces 3231 that can be mated to form a shape that matches the conical groove 322. The two conical clamping pieces 3231 are mated to form bolt holes for the front end of the bolt to pass through. The front end of the bolt passes through the conical groove 322 and is connected to the nut, so as to wed the two conical clamping pieces 3231 tightly in the conical groove 322, thereby locking the support rod 32 on the guide rail 31, so as to play the role of supporting the transverse support beam 201 from bottom to top.

[0103] Once the columns 30 are in place and the bottom support rods 32 are adjusted, the assembled transverse support beams 201 can be sequentially placed on the support rods 32. The length of the extended section 22 in the transverse support beam 201 is initially adjusted so that the transverse support beam 201 is slightly shorter than the width of the diaphragm wall 10 to facilitate hoisting. The support ends 21 at both ends of the transverse support beam 201 are pressed tightly into the grooves of the end supports 12 from top to bottom. The long-term deflection of the transverse support beam 201 is calculated. Based on the calculated value and engineering experience, the pre-camber sleeves 244 at the pre-camber section 24 are initially adjusted to adjust the included angle between the standard rods 23 connected to both ends of the pre-camber section 24 in the transverse support beam 201, thus initially setting the pre-camber of the transverse support beam 201. Simultaneously, the extension length of the extended section 22 is adjusted so that the support plate 211 of the support end 21 is pressed against the inner side of the cladding 11. A jack 224 is installed at one of the extended sections 22 of the transverse support beam 201 to apply a jacking force to the standard members 23 at both ends of the extended section 22. Simultaneously, the support sleeve 222 and the tightening sleeve 204 are adjusted. After the jacking force is applied, the support sleeve 222 and the tightening sleeve 204 are locked, and the jack 224 is removed. The same method of using the jack 224 is used when extending the longitudinal support beam 202.

[0104] Based on the vertical displacement of each standard member 23 in the transverse support beam 201, the height of the corresponding support rod 32 is adjusted and locked by the conical wedge 323, thereby supporting the bottom of the standard member 23 and preventing deformation of the transverse support beam 201 after it is shaped. After the support rod 32 is locked, the support rod 32 and the chord member 231 it supports are fixed to each other using common construction site fasteners.

[0105] After all the transverse support beams 201 in the first floor are installed, the longitudinal support beams 202 are then installed step by step. First, the support end 21, the extension section 22, and the standard member 23 at one end of the longitudinal support beam 202 are assembled together, and the support end 21 is overlapped on the corresponding end support 12. At this time, the end of the assembled standard member 23 overlaps with the standard member 23 of the first transverse support beam 201. Then, the second standard member 23 of the longitudinal support beam 202 is overlapped between the second transverse support beam 201 and the longitudinal support beam 202. The two standard members 23 are connected together via connecting section 25. The remaining standard members 23 are connected one by one in this manner. When the standard members 23 in the longitudinal support beam 202 overlap the standard members 23 in the transverse support beam 201, the two lower chord members 231 of the former standard member 23 are pressed down onto the two lower chord members 231 of the latter. The hinge rod 241 of connecting section 25 passes through the standard members 23 in the transverse support beam 201, thus connecting two adjacent standard members 23. After all the longitudinal support beams 202 are installed, the length of the extension section 22 is adjusted so that both ends of the longitudinal support beam 202 are pressed against the retaining wall 11. The overlapping chord members 231 are fixed together using fasteners commonly used on construction sites. At this point, the first layer of support beams 20 is installed. The installation continues in the same manner until the requirements are met.

[0106] During the installation process, after the first layer of support beam 20 at the bottom is installed, the elevation of the transverse support beam 201 is checked with a level. If there is a large difference from the target elevation, the pre-arch section 24 and the column 30 can be adjusted to adjust the elevation of the transverse support beam 201 to meet the expected target.

[0107] Lateral support pre-supply setting:

[0108] The formula for calculating the camber of pre-camber segment 24 is as follows:

[0109]

[0110] in, This is the calculated value of the pre-camber of pre-camber section 24; Deflection caused by its own weight; This refers to the deflection caused by longitudinal support pressure. The lateral deformation caused by the thrust of the elongated section 22; This refers to the lateral deformation caused by soil pressure during the construction phase. This is the long-term deflection increase factor, which is determined based on engineering experience or specifications.

[0111] Calculation of the pre-arch angle:

[0112] The transverse support beam 201 includes continuously arranged sections in each span. n -1 Pre-arch section 24, the distance from the first pre-arch section 24 of each span to the end support 12 or column 30 is denoted as The distances between the remaining adjacent pre-arch sections 24 are respectively denoted as , ... The distance from the last pre-arch section 24 to the end support 12 or column 30 is denoted as... ,Depend on:

[0113]

[0114]

[0115]

[0116]

[0117]

[0118]

[0119] Find:

[0120]

[0121]

[0122]

[0123]

[0124]

[0125]

[0126] in, The angle between the axis of the standard member 23 connected to the first pre-arched section 24 and the horizontal line is positive counterclockwise and negative clockwise. ( Take 1, 2, ..., n-1) as the supplementary angle between the standard members 23 at both ends of each pre-arch section 24 in each span, with counterclockwise being positive and clockwise being negative; ( Take 1, 2, ..., n-1) as the precamber value for each precamber segment 24. From this, the supplementary angle between the standard members 23 at both ends of each precamber segment 24 in each span can be calculated, thus facilitating the setting of the precamber of the transverse support for each span.

[0127] Taking a span with two pre-arched sections of 24 as an example, the calculation results are shown in Table 1:

[0128]

[0129] Top thrust setting:

[0130] After the jack 224 was used for pressurization and jacking, the mid-span deflection of each span of the transverse support structure was: It can be directly measured by a level instrument, and the span of each span is... Considering that the spans of each span are not significantly different, it is approximated that the deformation curve of the supporting structure in each span is the same and is a sine curve: ,in , These represent the lateral displacement of the supporting structure and the distance from each section to the support end or column 30, respectively.

[0131] From the functional relationship, we can approximate the following:

[0132]

[0133] Furthermore, we can obtain:

[0134]

[0135] in: This represents the span of the lateral support; The elastic modulus of standard rod 23; This refers to the cross-sectional area of ​​standard member 23. and These are the piston extension and thrust of jack 224, respectively, which can be directly measured or read. The bending moment of inertia of the cross section of standard member 23; To provide lateral support for the span of each span; To provide lateral support for the mid-span deflection of each span; The weight is 23 units per unit length for a standard rod. This is the approximate equivalent stiffness of the lateral support after the overall axial stiffness is reduced due to geometric nonlinearity.

[0136] Requirements: The jacking force during the jacking process of jack 224:

[0137] in: This is the active earth pressure reduction factor, which is determined based on engineering experience or specifications. To support the overall stability and load-bearing capacity of the 20 supporting beams; : is the minimum value function.

[0138] Based on the jacking force during the jacking process of jack 224 and the corresponding piston elongation Both can be directly measured or read during the jacking process of temporary jack 224. The remaining axial force in the lateral support after the temporary jack 224 is removed can then be calculated using the following formula, thus guiding the setting of the jacking force within the foundation pit support:

[0139]

[0140] in: To remove the remaining axial force in the lateral support after the temporary jack 224 is removed; The elastic modulus of the axial coarse screw in the elongated section 22; This is the sum of the effective cross-sectional areas of the axially thickened screw section 22; : Length of the extended section 22 screw.

[0141] Specific steps for construction and installation:

[0142] S1. Construction layout and excavation of foundation pit.

[0143] S2. Clean the diaphragm wall 10, lay out the positioning and install the double-I-beam fence 11, install the end support 12, and drive the pile driver to drive the column 30 into the designated position in the soil.

[0144] S3. Based on the excavation width of the foundation pit, select a standard member 23 of appropriate length and assemble the extension section 22 and the pre-arched section 24.

[0145] During the assembly of the elongated section 22: First, connect the support sleeve and insert the locating pin 205 to fix it to the chord 231; then, hinge the support screw 221 onto the support sleeve. Next, screw the support sleeve 222 into the support screw 221. Then, insert the support screw 221 with the support sleeve 222 into the chord 231 of the standard member 23. Next, install the tensioning screw 203 and the tensioning sleeve 204. Finally, fully tighten the tensioning sleeve 204 and the support sleeve 222 and secure them with anti-slip pins.

[0146] During the installation of the pre-arched section 24: First, install the end hinge rod 241, then install the pre-arched sleeve 244, followed by the pre-arched screw rod 243 and the pre-arched sleeve 242; next, install the tensioning screw rod 203 and the tensioning sleeve 204. Finally, fully tighten the tensioning sleeve 204 and the pre-arched sleeve 242 until all gaps between the rods and the gaps are completely eliminated, and secure them with anti-slip pins.

[0147] S4. Initially adjust the length of the extended section 22 in the transverse support beam 201 so that the transverse support beam 201 is slightly shorter than the excavation width of the foundation pit, in order to facilitate hoisting.

[0148] S5. Install the first layer of support rods 32 for supporting the transverse support beam 201.

[0149] During the installation of the support rod 32: First, clean the soil off the column 30, then fasten the guide rail 31, which has been welded with connecting fasteners, to the column 30 using fixing nuts. Next, insert the tapered clamp 3231 into the pre-drilled tapered hole at the end of the support rod 32, and insert the bolt through the pre-drilled hole on the tapered clamp 3231, then tighten the bolt. Note that the bolt should not be tightened too much to allow the support rod 32 to slide on the guide rail 31. Then, using a level, gently tap the end of the support rod 32 near the guide rail 31 with a small hammer to adjust the elevation of the support rod 32 until the target elevation is reached; finally, tighten the bolt to fully compress the tapered clamp 3231, ensuring sufficient resistance to vertical loads between the guide rail 31 and the support rod 32.

[0150] S6. Calculate the long-term deflection of the transverse support beam 201. Based on the calculated value and engineering experience, pre-cambered threaded sleeves 242 at the pre-cambered section 24 are initially adjusted to adjust the included angle between the standard members 23 connected to both ends of the pre-cambered section 24 of the transverse support beam 201, so as to initially set the pre-camber of the transverse support beam 201.

[0151] S8. Hoist the transverse support beam 201 onto the designated joint support and support rod 32, and initially tighten the bolts at the conical clamp 3231.

[0152] S9. The construction personnel manually make preliminary adjustments to the support sleeve 222 at the extension section 22, and simultaneously adjust the tight support sleeve 204 until the support plate 211 is pressed against the screen wall 11 to apply a preliminary pushing force to prevent beam falling accidents, and fully tighten the bolts at the conical clamp 3231.

[0153] S10. Repeat steps S3-S9 to install the remaining transverse support beams 201.

[0154] S11. Based on the excavation length of the foundation pit, select a standard member 23 of appropriate length, and first assemble the support ends 21, extension sections 22 and standard members 23 at both ends of the longitudinal support beam 202.

[0155] During the assembly of the elongated section 22: First, connect the support sleeve and insert the locating pin 205 to fix it to the chord 231; then, hinge the support screw 221 onto the support sleeve. Next, screw the support sleeve 222 into the support screw 221. Then, insert the support screw 221 with the support sleeve 222 into the chord 231 of the standard member 23. Next, install the tensioning screw 203 and the tensioning sleeve 204. Finally, fully tighten the tensioning sleeve 204 and the support sleeve 222 and secure them with anti-slip pins.

[0156] S12. Hoist the assembled support end 21, extension section 22 and standard rod 23 to the installation location, and place the support end 21 on the end support 12, so that the other end of the standard rod 23 overlaps with the standard rod 23 in the first span transverse support beam 201, and fix the overlapping chords 231 together by connecting fasteners.

[0157] S13. Install the standard members 23 in the longitudinal support beam 202 step by step from both ends to the middle, and fix them to the transverse support beam 201 with connecting fasteners.

[0158] S14. Manually adjust the support sleeve 222 and the tightening sleeve 204 at the elongated section 22 of the longitudinal support beam 202 until they are fully tightened to initially apply some jacking force.

[0159] S15. Repeat S11-S14 to install other longitudinal support beams 202.

[0160] S16. Check the elevation of the transverse support beam 201 using a level. If the difference from the target elevation is large, adjust the elevation of the transverse support beam 201 at the pre-arch section 24 to meet the expected target.

[0161] S17. Install a jack 224 at one of the extended sections 22 of the transverse support beam 201, apply a jacking force, and simultaneously adjust the support sleeve 222 and the tight support sleeve 204; after the jacking force is applied, use the anti-slip pin 206 to lock the sleeve.

[0162] S18. Check the elevation of the transverse support beam 201 using a level. If the elevation differs significantly from the target elevation, the elevation of the transverse support beam 201 can be adjusted by adjusting the pre-arch section 24 to meet the target.

[0163] S19, Remove jack 224.

[0164] S20. For other transverse support beams 201, repeat steps S16-S19.

[0165] S21. Install a jack 224 at one of the extended sections 22 of the longitudinal support beam 202, apply a jacking force, and simultaneously adjust the support sleeve 222 and the tight support sleeve 204; after the jacking force is applied, use the anti-slip pin 206 to lock the sleeve.

[0166] S22. Check the elevation of the transverse support beam 201 using a level. If the elevation differs significantly from the target elevation, the elevation of the transverse support beam 201 can be adjusted by adjusting the pre-arch section 24 to meet the target.

[0167] S23. At this point, all the transverse support beams 201 and longitudinal support beams 202 of the first layer have been installed. That is, after the first support structure is completed, continue to excavate the remaining soil of the first layer to the designated elevation.

[0168] S24. Repeat S2-S23 to construct the second support structure.

[0169] The steps for dismantling the supporting structure are as follows:

[0170] A1. Install jack 224, apply thrust, remove anti-slip pin, and appropriately loosen the support sleeve 222 and the tight support sleeve 204 of the extension section 22.

[0171] A2. Remove longitudinal support beam 202.

[0172] A3. Remove the transverse support beam 201.

[0173] A4. Repeat steps A1-A3 to remove other supporting structures.

[0174] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A prefabricated adjustable pre-camber steel pipe truss foundation pit support structure, characterized in that, It includes a ring-shaped diaphragm wall (10) that is arranged in the foundation pit, and a horizontally arranged support beam (20) is installed in the ring cavity of the diaphragm wall (10). The support beam (20) includes an elongated section (22) and a standard member (23). Each elongated section (22) and each standard member (23) are connected in sequence along the extension and contraction direction of the elongated section (22). When the elongated section (22) is in the extended state, both ends of the support beam (20) are pressed against the cavity wall of the diaphragm wall (10), and the support beam (20) generates approximately equivalent stiffness inside. Approximate equivalent stiffness The calculation formula is as follows: in, The span of the supporting beam (20) is the number of supporting beams (20); The elastic modulus of the standard rod (23); The cross-sectional area of ​​the standard rod (23); k The shear force required to generate a unit shear angle for the standard member (23); The elongation of the elongated segment (22); The thrust force for the elongated section (22); The bending moment of inertia of the cross section of the standard bar (23); The span of each span of the supporting beam (20) is the length of the supporting beam (20); To support the mid-span deflection of each span of the beam (20); The weight per unit length of the standard rod (23) is 1.

2. The prefabricated adjustable pre-camber steel pipe truss foundation pit support structure according to claim 1, characterized in that, When the elongated section (22) is in the locked state, the support beam (20) is subjected to axial force, and the formula for calculating the axial force is as follows: in, The remaining axial force in the support beam (20) when the elongated section (22) is in the locked state; The elastic modulus of the elongated segment (22); This is the sum of the effective cross-sectional areas of the elongated segment (22); The length of the elongated segment (22) when locked.

3. The prefabricated adjustable pre-camber steel pipe truss foundation pit support structure according to claim 1 or 2, characterized in that, The diaphragm wall (10) is rectangular, and the support beams (20) are divided into transverse support beams (201) and longitudinal support beams (202). The length direction of the transverse support beams (201) is parallel to the width direction of the diaphragm wall (10), and each transverse support beam (201) is arranged equidistantly along the length direction of the diaphragm wall (10). The length direction of the longitudinal support beams (202) is parallel to the length direction of the diaphragm wall (10), and each longitudinal support beam (202) is arranged equidistantly along the width direction of the diaphragm wall (10). Each longitudinal support beam (202) and each transverse support beam (201) intersects and is fixed to each other at the intersection, forming a mesh frame support structure supported in the annular cavity of the diaphragm wall (10). Both ends of the transverse support beam (201) are support ends (21), and extension sections (22) and standard members (23) are alternately arranged inward from the support ends (21). In addition, pre-arched sections (24) and standard members (23) are alternately arranged in the middle of the transverse support beam (201) from both sides toward the center of the rod, so that the transverse support beam (201) forms an upward-curved bow-shaped rod structure. Both ends of the longitudinal support beam (202) are support ends (21), and extension sections (22) and standard members (23) are arranged alternately from the support ends (21) inward. In addition, the middle part of the longitudinal support beam (202) is arranged alternately from both sides towards the center of the rod with connecting sections (25) and standard members (23).

4. The prefabricated adjustable pre-camber steel pipe truss foundation pit support structure according to claim 3, characterized in that, The standard member (23) includes three chords (231) arranged in parallel to each other, and the three chords (231) are fixed to each other by diagonal web members (232); two of the chords (231) are located on the lower side and in the same horizontal plane, and the other chord (231) is located on the upper side, so as to form a frame structure with an isosceles triangle cross section.

5. The prefabricated adjustable pre-camber steel pipe truss foundation pit support structure according to claim 4, characterized in that, The elongated section (22) includes three support screws (221), the front end of each support screw (221) is threadedly connected to the support sleeve (222) that is coaxially rotatably arranged at the tail end of each chord (231); each support screw (221) is hinged to a support sleeve (223), and each support sleeve (223) is sleeved on the front end of the corresponding chord (231) of the adjacent standard rod (23); It also includes a tensioning screw (203) with its tail end hinged to the adjacent ends of two adjacent standard rods (23). The front ends of the two tensioning screws (203) are coaxially screwed into the tensioning sleeve (204) from both ends of the same tensioning sleeve (204). The axis of the tensioning sleeve (204) intersects the axis of the support sleeve (222). Each hinge axis is parallel to each other and perpendicular to the axis of the support screw (221). It also includes a jack (224) that is positioned between two adjacent standard members (23) and provides a pushing force to push the two adjacent standard members (23) apart from each other, the axis of the jack (224) being parallel to the axis of the support screw (221).

6. The prefabricated adjustable pre-camber steel pipe truss foundation pit support structure according to claim 5, characterized in that, The pre-arch section (24) includes two parallel hinge rods (241), each hinge rod (241) being formed by two connecting rods (2411) hinged together; the two ends of the two hinge rods (241) are respectively coaxially fixed to the ends of the two lower chord members (231) in the adjacent standard members (23), and the hinge axes of the two sets of hinge rods coincide with each other and are perpendicular to the axis of the chord members (231); It also includes a pre-arched screw sleeve (242), both ends of which are coaxially threaded with pre-arched screws (243), and the tail ends of the two pre-arched screws (243) are hinged with pre-arched sleeves (244). The two pre-arched sleeves (244) are coaxially fixed to the upper chord (231) of the adjacent standard rod (23); It also includes a tensioning screw (203) with its tail end hinged to the adjacent ends of two adjacent standard rods (23). The front ends of the two tensioning screws (203) are coaxially screwed into the tensioning sleeve (204) from both ends of the same tensioning sleeve (204), and the axis of the tensioning sleeve (204) intersects with the axis of the support sleeve (222).

7. The prefabricated adjustable pre-camber steel pipe truss foundation pit support structure according to claim 6, characterized in that, The front end of the support end (21) and the extension section (22) cooperate with each other, and the structure of the front end of the support end (21) is the same as the structure of the end of the standard rod (23) and the extension section (22) that cooperate; The three chords (231) in the support end (21) gradually contract toward the tail end of the support end (21) and are fixed to the support plate (211), and the support plate (211) abuts against the cavity wall of the diaphragm wall (10); The cavity wall of the diaphragm wall (10) is provided with an annular gate (11), and an end support (12) is provided on the gate (11). The supporting end (21) is pressed from top to bottom onto the end support (12), and the supporting plate (211) is pressed against the plate surface of the gate (11). The connecting section (25) includes three parallel hinge rods (241), the two ends of which are coaxially fixed to the ends of the chord rods (231) in the adjacent standard rods (23), and the hinge axes of the three sets of hinge rods coincide with each other and are perpendicular to the axis of the chord rods (231); it also includes a fastening screw (203) with its tail end hinged to the adjacent ends of the two adjacent standard rods (23), the front ends of the two fastening screws (203) are coaxially screwed into the fastening sleeve (204) from both ends of the same fastening sleeve (204), and the axis of the fastening sleeve (204) intersects with the axis of the support sleeve (222).

8. The prefabricated adjustable pre-camber steel pipe truss foundation pit support structure according to claim 7, characterized in that, The transverse support beam (201) includes continuously arranged sections in each span. n -1 pre-arch section (24), the distance from the first pre-arch section (24) of each span to the end support (12) or column (30) is denoted as The distances between the remaining adjacent pre-arch sections (24) are respectively denoted as , … The distance from the last pre-arch section (24) to the end support (12) or column (30) is denoted as The formula for calculating the pre-camber of the pre-camber section (24) is as follows: in, The pre-camber is the calculated value of the pre-camber of the pre-camber section (24); Deflection caused by its own weight; This refers to the deflection caused by longitudinal support pressure. The lateral deformation caused by the thrust of the elongated section (22); This refers to the lateral deformation caused by soil pressure during the construction phase. This is the long-term increase factor for deflection; The formulas for calculating the pre-arch angle of each pre-arch segment (24) are as follows: in, The angle between the axis of the standard member (23) connected to the first pre-arched section (24) and the horizontal line is positive when counterclockwise and negative when clockwise. ( Take 1, 2, ... n-1) as the supplementary angle between the standard members (23) at both ends of each pre-arch section (24) in each span, with counterclockwise being positive and clockwise being negative; ( Take 1, 2, ..., n-1) as the pre-camber calculation value for each pre-camber segment (24).

9. The prefabricated adjustable pre-camber steel pipe truss foundation pit support structure according to claim 8, characterized in that, It also includes a column (30), on which a slide rail extending in the vertical direction is arranged, and a support rod (32) is slidably arranged on the slide rail. The support rod (32) is supported from bottom to top on the bottom of two chords (231) located on the lower side of the transverse support beam (201). The sliding end of the support rod (32) is provided with a vertically extending groove (321) in the direction of groove length, and the groove (321) is a groove structure that gradually narrows from the groove cavity to the groove opening. The groove (321) is slidably engaged on the guide rail (31). A conical groove (322) is provided on the groove wall of the slide (321). The length direction of the conical groove (322) is parallel to the length direction of the slide (321), and the cavity of the conical groove (322) gradually narrows along the length direction. A conical wedge (323) is inserted into the conical groove (322) along the length direction to lock the guide rail (31) in the slide (321). The conical wedge (323) includes two conical clips (3231) that can be joined together to form a shape that matches the conical groove (322). The two conical clips (3231) are joined together to form bolt holes for the front end of the bolt to pass through. The front end of the bolt passes through the conical groove (322) and is connected to the nut to wed the two conical clips (3231) tightly in the conical groove (322).

10. A construction and installation method, wherein the construction and installation method applies the prefabricated adjustable pre-camber steel pipe truss foundation pit support structure as described in claim 9, characterized in that, The installation process includes the following steps: Step 1: Construction layout and excavation of the foundation pit; Step 2: Arrange the diaphragm wall (10) and install the gate (11) on the diaphragm wall (10); Step 3: Install the column (30) in the foundation pit according to the construction standards; Step 4: Assemble the first layer of transverse support beams (201), place the transverse support beams (201) in the foundation pit, and press the support ends (21) of the transverse support beams (201) onto the corresponding end supports (12), while supporting the columns (30) at the bottom of the transverse support beams (201); adjust the length of the elongated section (22) and the pre-camber of each pre-cambered section (24) of the transverse support beams (201) so that the transverse support beams (201) reach the predetermined elevation; Step 5: Assemble the longitudinal support beam (202), place the longitudinal support beam (202) in the foundation pit, and press the support end (21) of the longitudinal support beam (202) onto the corresponding end support (12); fix the longitudinal support beam (202) and the transverse support beam (201) to each other to form the first support structure of the mesh. Step 6: Following steps 1 to 5, construct the remaining support structures in sequence.

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