Large-span deep foundation pit steel-concrete composite support structure and construction method thereof

Abstract

The present application relates to a kind of large-span deep foundation pit steel-mix combined support structure and its construction method, comprising: the profiled steel surround purlin of being located at foundation pit edge;Concrete edge truss structure is located at the opposite sides of foundation pit;Support is connected between the profiled steel support of oppositely arranged concrete edge truss structure;Oblique support is arranged in the multiple profiled steel corner brace of foundation pit corner, and the end of the profiled steel corner brace is connected with corresponding profiled steel surround purlin and concrete edge truss structure;Axial force servo system is connected on the profiled steel support and the profiled steel corner brace, for applying axial force to the profiled steel support and the profiled steel corner brace.The concrete edge truss structure used in the present application has good deformation control ability, as the prestressed profiled steel support and the force transmission buffer zone between enclosure structure compression roof beam, avoid concentrated axial force too large to cause foundation pit cracking, bending, tilting and other problems.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of foundation pit construction engineering, in particular to a large-span deep foundation pit steel-concrete combined support structure and a construction method thereof. BACKGROUND

[0002] With the rapid advancement of urbanization in China, the number of deep foundation pit projects has also increased dramatically, and the deformation control requirements of foundation pits are becoming more and more stringent. In order to ensure the safety of underground engineering construction, the selection of a reasonable and efficient foundation pit engineering support scheme is of the utmost importance. Among them, the water level outside the large-span deep foundation pit near the river is high, the support span is large, and the deformation control requirement is high, which makes the foundation pit support requirement higher than other types of deep foundation pits. The traditional reinforced concrete support has strong rigidity, is suitable for different foundation pits, but has poor flexibility and economy, the material cannot be reused, and safety and environmental problems are prone to occur during installation and removal. SUMMARY

[0003] The purpose of the present application is to overcome the defects of the prior art, provide a large-span deep foundation pit steel-concrete combined support structure and a construction method thereof, and solve the problems of poor flexibility and economy of the existing reinforced concrete support, non-reusable material, and safety and environmental problems prone to occur during installation and removal.

[0004] The technical scheme to achieve the above-mentioned purpose is:

[0005] The present application provides a large-span deep foundation pit steel-concrete combined support structure, comprising:

[0006] A steel enclosing purlin arranged at the edge of the foundation pit;

[0007] A concrete edge truss structure arranged at opposite sides of the foundation pit;

[0008] A steel support connected between the oppositely arranged concrete edge truss structures;

[0009] A plurality of steel corner braces arranged at the corner of the foundation pit, the end of the steel corner brace being connected with the corresponding steel enclosing purlin and concrete edge truss structure;

[0010] An axial force servo system connected to the steel support and the steel corner brace, for applying axial force to the steel support and the steel corner brace.

[0011] Further improvement of the large-span deep foundation pit steel-concrete combined support structure is that a plurality of pairs of support columns are driven into the foundation pit along the arrangement positions of the steel support and the steel corner brace, a support cross beam being connected between a pair of support columns, the support cross beam supporting the corresponding steel support and steel corner brace.

[0012] The further improvement of the large-span deep foundation pit steel-concrete combined support structure lies in that the concrete edge truss structure is provided with a concrete triangle structure corresponding to the steel support and the steel angle support, and one side surface of the concrete triangle structure is connected in butt joint with the end of the corresponding steel support and steel angle support.

[0013] The further improvement of the large-span deep foundation pit steel-concrete combined support structure lies in that the end of the steel support is provided with a pair of inclined braces close to the end of the concrete edge truss structure, and the pair of inclined braces are supported between the steel support and the concrete edge truss structure.

[0014] The further improvement of the large-span deep foundation pit steel-concrete combined support structure lies in that the steel enclosing purlin is provided with a steel triangle structure corresponding to the steel angle support, and one side surface of the steel triangle structure is connected in butt joint with the end of the steel angle support.

[0015] The application further provides a construction method of the large-span deep foundation pit steel-concrete combined support structure, which comprises the following steps:

[0016] The steel enclosing purlin is installed at the edge of the foundation pit;

[0017] The concrete edge truss structure is formed by pouring on the opposite sides of the foundation pit;

[0018] The steel support is provided, and the steel support is connected and supported between the oppositely arranged concrete edge truss structures;

[0019] The steel angle support is provided, and the steel angle support is arranged in an inclined manner at the corner of the foundation pit, and the end of the steel angle support is connected with the corresponding steel enclosing purlin and concrete edge truss structure;

[0020] The axial force servo system is provided, and the axial force servo system is connected on the steel support and the steel angle support, and the axial force servo system is used to apply axial force to the steel support and the steel angle support.

[0021] The further improvement of the construction method of the large-span deep foundation pit steel-concrete combined support structure lies in that before the steel support and the steel angle support are arranged, the support column is provided, and the support column is driven into the foundation pit along the arrangement position of the steel support and the steel angle support.

[0022] The support cross beam is provided, and the support cross beam is connected between a pair of support columns, and the support cross beam is used to support the corresponding steel support and steel angle support.

[0023] A further improvement to the construction method of the steel-concrete composite support structure for large-span deep foundation pits of the present invention lies in that, during the pouring and forming of the concrete side truss structure, reinforcing bars of a concrete triangular structure are set at corresponding positions on the side of the concrete side truss structure, and embedded parts that are connected to the ends of the corresponding steel supports and steel corner braces are set on the corresponding sides of the concrete triangular structure.

[0024] A further improvement of the construction method of the steel-concrete composite support structure for large-span deep foundation pits of the present invention is that, when setting up the steel support, a pair of diagonal braces are set between the steel support and the concrete side truss structure.

[0025] A further improvement of the construction method of the steel-concrete composite support structure for large-span deep foundation pits of the present invention is that, when installing the steel walers, a steel triangular structure is set on the steel walers at the position corresponding to the steel corner braces, and the steel triangular structure is used to connect the steel corner braces.

[0026] The beneficial effects of the steel-concrete composite support structure for large-span deep foundation pits and its construction method of the present invention are as follows:

[0027] The concrete side truss structure used in this invention has good deformation control capabilities. It serves as a force transmission buffer zone between the prestressed steel support and the capping beam of the retaining structure, avoiding problems such as cracking, bending, and tilting of the foundation pit caused by excessive concentrated axial force.

[0028] This invention sets up a concrete triangular structure on the side truss structure to connect with the steel support, thereby increasing the safety factor of the joint between the steel support and the scaffold. An axial force servo system is set on the steel support to accurately apply prestress, thereby realizing the functions of automatic low-pressure compensation and automatic high-pressure alarm.

[0029] The steel-concrete composite support structure for large-span deep foundation pits and its construction method of the present invention effectively improve work efficiency, shorten the construction period, save costs, and achieve the goal of safe and efficient construction. Attached Figure Description

[0030] Figure 1 This is a flowchart of the construction method for the steel-concrete composite support structure for large-span deep foundation pits according to the present invention.

[0031] Figure 2 This is a cross-sectional view of the connection between the steel support and the concrete side truss structure in the large-span deep foundation pit steel-concrete composite support structure of the present invention.

[0032] Figure 3 This is a top view of the steel-concrete composite support structure for large-span deep foundation pits according to the present invention.

[0033] Figure 4 This is a schematic diagram of the axial force servo system layout in the large-span deep foundation pit steel-concrete composite support structure of the present invention.

[0034] Figure 5This is a schematic diagram showing the connection between the corresponding parts of the concrete triangular structure and the side truss structure in the large-span deep foundation pit steel-concrete composite support structure of the present invention.

[0035] Figure 6 This is a schematic diagram of the reinforcement layout inside the concrete triangular structure in the large-span deep foundation pit steel-concrete composite support structure of the present invention.

[0036] Figure 7 This is a schematic diagram of the embedded parts installed at the concrete triangular structure in the large-span deep foundation pit steel-concrete composite support structure of the present invention.

[0037] Figure 8 This is a model diagram of the corbel support structure used in the construction method of the large-span deep foundation pit steel-concrete composite support structure of the present invention.

[0038] Figure 9 This is a model diagram of the installation of steel walers in the large-span deep foundation pit steel-concrete composite support structure and its construction method of the present invention.

[0039] Figure 10 This is a model diagram of the installation of support columns and beams in the large-span deep foundation pit steel-concrete composite support structure and its construction method of the present invention.

[0040] Figure 11 This is a cross-sectional view of the joint of the support columns in the large-span deep foundation pit steel-concrete composite support structure and its construction method of the present invention.

[0041] Figure 12 This is a model diagram of the formwork and reinforcement layout of the concrete side truss structure in the large-span deep foundation pit steel-concrete composite support structure and its construction method of the present invention.

[0042] Figure 13 This is a schematic diagram of the installation of steel angle braces in the large-span deep foundation pit steel-concrete composite support structure and its construction method of the present invention.

[0043] Figure 14 This is a schematic diagram of the installation of the axial force servo system in the large-span deep foundation pit steel-concrete composite support structure and its construction method of the present invention.

[0044] Figure 15 This is a model diagram of the steel-concrete composite support structure for large-span deep foundation pits according to the present invention.

[0045] Figure 16 This is a flowchart illustrating the installation, use, and dismantling of the axial force servo system in the large-span deep foundation pit steel-concrete composite support structure and its construction method of the present invention. Detailed Implementation

[0046] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0047] See Figure 1This invention provides a steel-concrete composite support structure for large-span deep foundation pits and its construction method. Addressing the challenges of deep foundation pit construction near pipelines, high water levels, and large spans, traditional methods use reinforced concrete supports, but these methods are inflexible, uneconomical, and the materials cannot be reused. Furthermore, they can easily cause safety and environmental problems during installation and dismantling. Therefore, this invention employs a support system of steel profiles, corner braces, and concrete side trusses as the internal support for the foundation pit. The concrete side truss structure has good deformation control capabilities, serving as a force transmission buffer zone between the prestressed steel composite support and the capping beam of the retaining structure. This prevents excessive concentrated axial force from causing cracking, bending, and tilting problems in the foundation pit. The first vertical layer uses a single-piece steel support, while the second vertical layer uses a double-piece steel support, effectively addressing the issue of large deformation in the central area of ​​the retaining structure. The steel support is connected to the concrete side truss structure through force transmission components. Concrete triangular structures are set at the anchoring ends of the walers and force transmission components along the force direction to increase the safety factor at the junction of the steel support and the retaining structure. Simultaneously, the steel composite support is combined with an axial force servo system to precisely apply prestress. The second double-piece support is applied simultaneously from top to bottom, and the axial force servo system provides 24-hour real-time monitoring, enabling automatic low-pressure compensation and automatic high-pressure alarm functions. The construction method of steel-concrete composite support for large-span deep foundation pits effectively improves work efficiency, shortens the construction period, saves costs, and achieves the goal of safe and efficient construction. The following description, in conjunction with the accompanying drawings, illustrates the steel-concrete composite support structure and its construction method for large-span deep foundation pits of this invention.

[0048] See Figure 3 This image shows a top view of the steel-concrete composite support structure for large-span deep foundation pits according to the present invention. (Participants) Figure 4 This diagram shows the layout of the axial force servo system in the large-span deep foundation pit steel-concrete composite support structure of the present invention. (See also...) Figure 15 The diagram below shows a model of the steel-concrete composite support structure for large-span deep foundation pits according to the present invention. (See below for reference.) Figure 3 , Figure 4 and Figure 15 The present invention describes the steel-concrete composite support structure for large-span deep foundation pits.

[0049] like Figure 3 , Figure 4 and Figure 15As shown, the large-span deep foundation pit steel-concrete composite support structure of the present invention includes steel walers 21, concrete side truss structures 22, steel supports 23, steel corner braces 24, and an axial force servo system 25. The steel walers 21 are located at the edge of the foundation pit, with one side of the foundation pit having a steel waler 21. The concrete side truss structures 22 are located on opposite sides of the foundation pit, with the steel supports 23 located on both sides where they are needed. The steel supports 23 are connected between the oppositely arranged concrete side truss structures 22. Multiple steel corner braces 24 are obliquely positioned at the corners of the foundation pit, and their ends are connected to the corresponding steel walers 23 and concrete side truss structures 22. The axial force servo system 25 is connected to the steel supports 23 and steel corner braces 24 and is used to apply axial force to the steel supports 23 and steel corner braces 24.

[0050] like Figure 2 As shown, before excavating the foundation pit, a retaining structure 10 is first installed around the pit. This retaining structure 10 can be a diaphragm wall or a water-stop curtain, etc. A capping beam 11 is installed on top of the retaining structure 10. After the foundation pit is excavated to a certain depth, the first concrete side truss structure 22 can be constructed, which is connected to the capping beam 11. When the foundation pit is excavated to the height of the second support, a concrete waler 12 is installed on the inner side of the retaining structure 10, and the second concrete side truss structure 22 is connected to the concrete waler 12. Preferably, the steel reinforcement of the concrete side truss structure 22 can be embedded into the corresponding capping beam 11 and concrete waler 12 to achieve effective fixed connection.

[0051] In one specific embodiment of the present invention, such as Figure 8 and Figure 9 As shown, before installing the steel waler 21, a corbel bracket 212 is installed on the inner side of the capping beam 11. Then, the steel waler 21 is installed on the corbel bracket 212. A steel triangular structure 211 is set at the connection point of the steel waler 21 corresponding to the steel angle brace 24, combined with... Figure 13 As shown, one side of the steel triangular structure 211 is connected to the end of the steel angle brace 24.

[0052] In one specific embodiment of the present invention, such as Figure 12 and Figure 15 As shown, when constructing a concrete side truss structure, steel bars are tied at the corresponding positions and formwork is erected, and then concrete is poured to form the concrete side truss structure.

[0053] Furthermore, such as Figure 3 As shown, the concrete side truss structure 22 is provided with a concrete triangular structure 222 corresponding to the steel support 23 and the steel corner brace 24. One side of the concrete triangular structure 222 is connected to the end of the corresponding steel support 23 and the steel corner brace 24.

[0054] Combination Figure 5 and Figure 6 As shown, the concrete triangular structure 222 and the concrete side truss structure 22 are integrally cast. When setting the formwork and reinforcement of the concrete side truss structure 22, the formwork and reinforcement of the concrete triangular structure 222 are connected to the formwork and reinforcement of the concrete side truss structure 22. Specifically, the concrete triangular structure 222 includes multiple triangular bars 2223. The bending angle of the triangular bars 2223 is adapted to the angle of the concrete triangular structure 222. They are arranged at intervals along the thickness direction of the concrete triangular structure 222. The concrete triangular structure 222 also includes multiple U-shaped stirrups 2221. The U-shaped stirrups 2221 are fitted onto the triangular bars 2223 and partially extend into the concrete side truss structure 22. The concrete triangular structure 222 also includes multiple closed stirrups 2222. The closed stirrups 2222 are clamped onto the triangular bars 2223 and the U-shaped stirrups 2221. The setting direction of the closed stirrups 2222 is perpendicular to the setting direction of the U-shaped stirrups 2221.

[0055] An embedded part 2224 is provided on one side of the steel angle brace 24 connecting the concrete triangular structure 222. This embedded part 2224 is connected to the triangular reinforcement 2223, U-shaped stirrup 2221, and closed stirrup 2222 within the concrete triangular structure 222 via connecting bars 2225. Figure 7 As shown, the side plate of the embedded part 2224 is connected to the bolt 2227, and the end of the bolt 2227 is connected to the rebar connector 2226. The rebar connector 2226 is connected to the embedded rebar 2225, so that the embedded rebar 2225 extends into the interior of the concrete triangular structure 222.

[0056] After the formwork and reinforcing bars of the concrete triangular structure are set up, concrete is poured to form the concrete side truss structure 22 and the concrete triangular structure 222.

[0057] Furthermore, to improve the structural stability of the concrete side truss structure 22, vertical lattice columns 221 are also provided in the foundation pit. There are multiple vertical lattice columns 221, which are supported on the beams corresponding to the concrete side truss structure 22.

[0058] In one specific embodiment of the present invention, such as Figure 10 and Figure 15As shown, before installing the steel supports 23 and steel corner braces 24, several pairs of support columns 261 are driven into the foundation pit along the installation positions of the steel supports 23 and steel corner braces 24. The support columns 261 are positioned on both sides of the corresponding steel supports 23 and steel corner braces 24 to be installed. A support beam 262 is connected between a pair of support columns 261. The support beam 262 is used to support the corresponding steel supports 23 and steel corner braces 24. That is, when installing the steel supports 23 and steel corner braces 24, they are placed on the corresponding support beam 262.

[0059] Combination Figure 11 As shown, when driving in the support column 261, the driving depth of the support column 261 needs to reach a certain distance below the bottom of the foundation pit. Therefore, the support column 261 is formed by butt welding of multiple steel columns. During welding, corresponding connecting plates are set at the joints to meet the welding quality requirements. The support column 261 is formed by connecting multiple steel columns. When driving in the support column 261, it should be ensured that no welded joints appear above the bottom elevation of the foundation pit.

[0060] In one specific embodiment of the present invention, such as Figure 3 , Figure 4 and Figure 15 As shown, a pair of diagonal braces 231 are provided at the end of the steel support 23 near the end of the concrete side truss structure 22. The pair of diagonal braces 231 provide inclined support between the steel support 23 and the concrete side truss structure 22. The ends of the diagonal braces 231 are fixedly connected to the embedded parts on the corresponding concrete triangular structure 222.

[0061] When the steel support 23 is installed, its end is perpendicularly connected to the beam corresponding to the concrete side truss structure 22. The diagonal bracing 231 is installed in the same direction as the diagonal chord on the concrete side truss structure 22 to ensure consistent force transmission.

[0062] In one specific embodiment of the present invention, such as Figure 14 and Figure 15 As shown, the axial force servo system 25 includes a monitoring station, an operator station, a field control station, a hydraulic servo pump station system, a bus system, a power distribution system, a communication system, a mobile diagnostic system, a compensation section (servo combination booster jack), a wireless distributed CNC hydraulic station junction box device, and a software system (operating platform). Depending on the number of servo hydraulic jacks, the axial force servo system can be divided into several wireless distributed CNC pump stations, each of which is independently controlled and does not affect each other.

[0063] Each CNC pump station has four independent hydraulic circuit channels, enabling independent control of four sets of supports. One channel can control six servo hydraulic jacks. Each servo hydraulic jack's CNC pump has built-in hydraulic pressure and displacement sensors to achieve dual control of hydraulic pressure and stroke, thereby regulating axial force.

[0064] The foundation pit of this invention is supported by two layers of prestressed steel composite supports: a first layer of single-unit supports and a second layer of double-unit supports. The first layer of prestressed steel composite supports, employing a servo system, consists of two sets, and the second layer consists of four sets. Each set of prestressed steel composite supports using a servo system employs six jacks. During construction, the pre-applied axial force of each support set is determined based on design values ​​and experience. Furthermore, during the foundation pit excavation process, the axial force of the supports is adjusted according to axial force and deformation monitoring data.

[0065] This invention also provides a construction method for a steel-concrete composite support structure for large-span deep foundation pits, which will be described below.

[0066] like Figure 15 As shown, the construction method of the present invention includes the following steps:

[0067] Install steel walers at the edge of the foundation pit;

[0068] Concrete side truss structures were formed by pouring concrete on both sides of the foundation pit;

[0069] Provide steel supports to support and connect the steel supports between the oppositely arranged concrete side truss structures;

[0070] Provide steel corner bracing, which is diagonally supported at the corner of the foundation pit, and connects the ends of the steel corner bracing to the corresponding steel waler and concrete side truss structure;

[0071] An axial force servo system is provided, which is connected to the steel profile support and steel angle brace to apply axial force to the steel profile support and steel angle brace.

[0072] The large-span deep foundation pit steel-concrete composite support structure of this invention is applied to a construction project at the confluence of the Qiantang River and the Beijing-Hangzhou Grand Canal. On the side of the construction project near the Qiantang River, there are three sewage trunk lines outside the pit, which carry nearly 50% of Hangzhou's daily sewage volume. The sewage pipes are less than 6m away from the edge of the foundation pit excavation. To ensure stable settlement, dewatering is prohibited outside the pit. The water pressure outside the pit is high, and the foundation pit deformation requirements are high. The foundation pit of the project is relatively regular, with a span of 134.5m and an average excavation depth of 14.95m. Some pits within the pit are up to 6m deep, indicating a large span and deep excavation depth.

[0073] like Figure 1As shown, the construction method of this invention includes construction preparation, carefully reviewing the design drawings, organizing professional subcontractors to conduct drawing review and obtain handover minutes; based on the verified support drawings and drawing handover minutes, the professional subcontractors carry out detailed design of the steel support; before the detailed design of the steel support, the deviation of the constructed vertical retaining structure is checked in conjunction with the construction status of the vertical retaining structure, and the actual deviation is taken into account in the detailed design of the steel support to ensure accurate dimensions and reduce the difficulty of closure during support installation.

[0074] If engineering piles can be used, lattice columns can be used; if no engineering piles can be used, steel columns can be installed on site.

[0075] Next, the bracket set and support columns can be installed simultaneously.

[0076] Installation of Support Columns: Support columns are made of structural steel, such as I-beams. For columns requiring butt welding, ensure no weld joints appear above the bottom elevation of the base plate. The structural steel is directly inserted using a robotic arm. During construction, strictly control the insertion depth, angle, and verticality of the steel to facilitate subsequent connection of the support and crossbeams. After the pile is in place, use two theodolites intersecting at 90° to check the verticality of the pile. The vertical deviation of the pile inserted into the soil must not exceed 1% of the pile length. Use an S3 level during pile driving, and pre-mark the driving rod to control the pile top elevation (pile top elevation error controlled within approximately +2cm). Over-driving and subsequent pulling are strictly prohibited. If the steel column pile is not aligned with the pile position during insertion, it should be pulled out and re-inserted. If it deviates from the pile position due to underground obstacles, immediately pull out the column pile, remove the underground obstacles, backfill the hole, and then re-lay out and re-drive the pile. If the steel section can be easily driven to the design pile bottom elevation (especially for projects with silty soil layers), the supervision unit should be notified immediately. The supervision unit should then contact the support design unit and take measures to lengthen the column to ensure that the bottom of the steel section column enters a better soil layer (in order to reduce the settlement of the steel section column).

[0077] Installation of corbel supports: The position and elevation of the corbel supports installed around the perimeter of the foundation pit should be determined according to the design drawings. The surface elevation of the corbel supports (elevation deviation not exceeding ±2mm) should ensure that the steel walers (centerline) above them are on the same horizontal plane and are straight and aesthetically pleasing. Before welding the corbel supports, the connection areas (such as embedded parts, H-beams, etc.) within an area of ​​not less than 200mm×200mm must be thoroughly cleaned of rust, oil stains, concrete residue, and other debris. The welded corbel supports must ensure that the connection parts are firm and reliable, with sufficient stability, and without any twisting or incomplete welding. The elevation of the upper surface of the corbel supports should be controlled within 2mm, and its elevation angle should be controlled ≥90 degrees and should not exceed 95 degrees. When welding the steel corbel supports, an excavator must be used to hoist, position, and weld them. Hoisting can only be stopped after the lower or upper support points are fully welded to ensure operational safety.

[0078] Steel waler installation: Benchmark point setting and string line positioning. Before installing the walers, the axis benchmark points must be determined. Using a total station or theodolite, the benchmark points on the inner sides of the two adjacent corners of the foundation pit are calculated and set. The walers are then positioned using a string line method based on these benchmark points. The actual installation axis deviation must not exceed ±10mm. The string line used for stringing is generally a chord or cotton thread, with a diameter of 0.8–1.0mm, depending on the distance of the string line on site. A plumb bob is used to determine the center; its specifications are not fixed, but a diameter of 25–50mm is usually suitable. The tip of the plumb bob must be accurate to align with the center point. Securely install the waler frame at a location other than the benchmark center point, hang the chord or cotton thread, and tighten it (the tension should be 40%–60% of the breaking strength of the thread). After positioning, mark the bracket for controlling the waler installation position. The basic requirement is that the positioning lines of the inner waler of the foundation pit must be in a straight line. This is to ensure that the outer retaining structure is evenly stressed after prestressing is applied. The waler installation should follow the principle of "longer walers first, shorter walers later, reducing the number of joints, and staggering joints," prioritizing the use of longer walers to reduce the number of joints. The walers are hoisted section by section in sequence with the support erection. Manual labor is used in conjunction with the crane to place the steel walers onto the corbel supports. After the walers are in place, the steel corbels should be checked for loosening due to impact; if any loosening is found, they should be immediately welded and reinforced.

[0079] Installation of brackets and crossbeams: The horizontal elevation of the brackets must be strictly controlled during installation. The top surface horizontal elevation is determined by inversely calculating the elevation of the brackets using the positioning elevations of the corner braces, counterbraces, and H-beams. The bracket surface elevation = center elevation of the supporting structure - (half the height of the supporting component + height of the crossbeam). The deviation of the bracket surface elevation (no greater than ±2mm) should ensure that the corresponding crossbeam surfaces are on the same plane. The brackets and steel columns are secured with no fewer than 6 high-strength bolts (Note: the installation direction of the bolts connecting the column and bracket must be consistent). The verticality of the bracket installation must be strictly controlled. Even if the steel column is misaligned, the bracket must be made vertical by adding shims. If the elevation of the steel column deviates, a channel steel can be used as a temporary adjustment to connect it to the support beam. When drilling holes on-site using oxy-acetylene torches on the support beam and the original support, care must be taken to control the hole diameter to prevent bolt slippage under stress. The installed support must be securely fastened to the steel column pile, and the torque of the friction-type high-strength bolts must meet the specified requirements. The elevation deviation of the support surface of each steel column must not exceed 5mm. After the support is installed and the surface elevation is checked, the crossbeam can be installed. The crossbeam specifications should meet the requirements of the design drawings and there should be no butt joints (materials should be inspected and accepted one by one upon arrival). When adjusting the positioning of the steel column (avoiding structural beams, walls, columns, etc.), the span of the crossbeam must not be increased without authorization.

[0080] Construction of the concrete side truss structure: The capping beam (waler), concrete triangular beams, and steel supports shall be constructed according to the detailed connection node drawings. Pouring can commence after the reinforcement binding is completed, the embedded reinforcement parts are installed, and have passed inspection.

[0081] Installation of steel supports and angle braces: Before installing each steel composite support beam, if site conditions permit, pre-assembly should be carried out on the ground, and the straightness of the pre-assembled support should be checked. The eccentricity of the center line of both ends of the spliced ​​support (including jacks and TO components) should be controlled within 2cm. After passing the inspection, the entire support should be hoisted into place according to its location. For projects where pre-assembly is not feasible on site, a total station (theodolite) should be used for positioning, and control lines for the support beam should be marked on the crossbeam. Then, pre-assembly should be carried out from one end (or from both ends for projects exceeding 100 meters) along the control lines, ensuring that the steel composite support beam is straight in the plane. During pre-assembly, the WA components, special jacks, TO components, etc., should be securely connected with high-strength bolts. The cross lock of the special jack must be set in the center, leaving a margin of three threads at the front and back to facilitate the removal of prestress during dismantling. During the assembly of the steel composite support beam, if there is excess space in the placement gap of the SC, steel plates of corresponding thickness must be used to tightly shim it to prevent the overall support system from becoming eccentric under stress. Before assembling and pressurizing the steel composite support beam, clamps should be used to temporarily connect it to the crossbeam. The joint bolts can only be tightened after the inspection is qualified.

[0082] Installation of the axial force servo system: Installation, usage, and removal procedures are as follows Figure 16 As shown, equipment debugging: After the system is powered on, test the system pressure, pressure holding, solenoid valve switching, manual loading, automatic loading, communication distance, etc., to ensure that the pump station equipment is normal.

[0083] Jack hoisting and installation: For steel supports involving axial force servo systems, the assembly should be carried out in accordance with the node construction requirements of the servo component during the installation of this support. After meeting the following requirements, the jack should be positioned at the center of the pressure-applying component:

[0084] ① A crossbeam (usually achieved using a grid-like crossbeam) is provided below the support component of the servo node to ensure that the support node does not sink under its own weight;

[0085] ② The pressure component at the servo node should be in natural contact with the power supply box or the gap should not exceed 5mm (the width of the power supply box is 400mm and the size of the servo hydraulic jack is Φ455×359mm). The power supply box and the pressure component should be connected by bolts with a length of not less than 200mm (all bolts should not be tightened and should maintain the same and large expansion space).

[0086] ③ Except for the servo node, other support splices should be tightly joined (if there are gaps, wedges should be inserted before pressurization) to avoid uneven stress on the support components caused by gaps during pressurization.

[0087] ④ The horizontal support components and the crossbeam are connected by clamps (to avoid lateral displacement of the crossbeam when pressure is applied). All other support components (including channel steel and cover plate) are bolted and fastened in place.

[0088] Oil pipe and data cable connection: Connect the oil pipe and data cable from the corresponding oil line and data interface on the pump station, and run them along the side of the vertical retaining structure and the support side to the jack position. Install the ultrasonic sensor, ensuring its end face is flush with the mounting end face, then connect the displacement line and observe whether the indicator light on the ultrasonic sensor is normal. Next, connect the oil pipe; the inlet pipe connects to the lower chamber of the jack, and the return pipe connects to the upper chamber of the jack, adding gaskets. Then, use cable ties to secure the displacement line and oil pipe to the support head, ensuring that the joint is not under stress.

[0089] Applying axial force: After the jack is in place and before applying axial force, the two sides of the jack should be firmly attached to the pressure-applying component in the "0" stroke state (the gap should not be greater than 5mm. If the gap is too large, it is easy to cause insufficient pressure even at the maximum stroke). Adjust the oil pressure so that the jack piston presses against the pressure-applying component to generate axial force. At this time, if the piston stroke is large, it should be adjusted by using a wedge.

[0090] Setting Axial Force Control Values: After pressurizing to the design pre-pressurized value, set the axial force design value and upper and lower limit design alarm values ​​for each design working condition in the central monitoring system according to design requirements. If there are design requirements, set the upper and lower limit values ​​according to the design requirements. If there are no design requirements, set the upper limit alarm value to 1.05-1.1 times the support pre-pressurized value (1.3-1.5 times for silty soil layers), and set the lower limit alarm value to 0.85-0.95 times the support pre-pressurized value (1.0 times for silty soil layers).

[0091] On-site monitoring and control: The system monitoring and control adopts closed-loop continuous monitoring and control. Any changes to the monitoring and control method must be reported to and approved by the design unit. Simultaneously with system monitoring and control, manual monitoring is conducted in the monitoring room and through manual inspections. The monitoring room is staffed 24 hours a day (or remotely online), and any data anomalies are responded to immediately.

[0092] Decompression and Exit: Decompression can begin after receiving the support removal order. To avoid excessive release of pre-stress that could lead to local deformation and cracking of the structure, a step-by-step unloading method is adopted. Unloading is divided into three stages. When the pressure is reduced to 0, the jack piston is retracted.

[0093] Support for demolition, demolition principles:

[0094] (1) The side truss is dismantled in accordance with the principle of "replacing the support first and then dismantling the support". Once the strength of the replacement support structure reaches 100%, the support can be dismantled.

[0095] (2) In accordance with the principle of “first the corner bracing, then the parallel bracing, and first the longer corner bracing, then the shorter one”, the overall dismantling of each support adopts the principle of “symmetrical dismantling, first the secondary components, then the main components”, and proceeds gradually backward, from small to large, and from the middle to both ends.

[0096] (3) On the side adjacent to the subway tunnel and sewage trunk line, in order to ensure the safety of the foundation pit and reduce the disturbance to the surrounding environment, the demolition was carried out by static cutting method.

[0097] Support pressure relief:

[0098] (1) The pressure relief should be carried out slowly and in stages (first depressurize 50%, stabilize for 1 hour, and then depressurize to zero). Rapid pressure relief is strictly prohibited.

[0099] (2) If any abnormalities such as cracking of the floor slab load-transmitting belt or the top beam are found during depressurization, depressurization should be suspended; if the monitoring data is abnormal, pressurization should be temporarily resumed.

[0100] In one specific embodiment of the present invention, before setting the steel supports and steel corner braces, support columns are provided first, and the support columns are driven into the foundation pit in pairs along the setting positions of the steel supports and steel corner braces;

[0101] Provide a support beam to connect a pair of support columns, and use the support beam to support the corresponding steel supports and steel corner braces.

[0102] In one specific embodiment of the present invention, when the concrete side truss structure is cast, reinforcing bars of a concrete triangular structure are set at corresponding positions on the side of the concrete side truss structure, and embedded parts that are connected to the ends of the corresponding steel supports and steel corner braces are set on the corresponding sides of the concrete triangular structure.

[0103] In one specific embodiment of the present invention, when setting up the steel support, a pair of diagonal braces are set between the steel support and the concrete side truss structure.

[0104] In one specific embodiment of the present invention, when installing the steel waler, a steel triangular structure is set on the steel waler at the position corresponding to the steel corner brace, and the steel corner brace is connected by the set steel triangular structure.

[0105] The present invention has been described in detail above with reference to the accompanying drawings and embodiments. Those skilled in the art can make various modifications to the present invention based on the above description. Therefore, certain details in the embodiments should not be construed as limiting the present invention, and the scope of protection of the present invention shall be defined by the appended claims.

Claims

1. A steel-concrete composite support structure for large-span deep foundation pits, characterized in that, include: Steel walers installed at the edge of the foundation pit; Concrete side truss structures located on opposite sides of the foundation pit; Steel supports are used to connect the opposing concrete side truss structures. Multiple steel corner braces are installed at the corners of the foundation pit, and the ends of the steel corner braces are connected to the corresponding steel walers and concrete side truss structures. An axial force servo system connected to the steel profile support and the steel profile angle brace is used to apply axial force to the steel profile support and the steel profile angle brace; It also includes several pairs of support columns driven into the foundation pit along the setting positions of the steel supports and the steel corner braces, with a support beam connecting a pair of support columns, and the support beam supporting the corresponding steel supports and steel corner braces; The concrete side truss structure is provided with a concrete triangular structure corresponding to the steel support and the steel corner brace. One side of the concrete triangular structure is connected to the end of the corresponding steel support and the steel corner brace. The concrete triangular structure and the concrete side truss structure are cast integrally. When setting the formwork and reinforcement of the concrete side truss structure, the formwork and reinforcement of the concrete triangular structure are connected to the formwork and reinforcement of the concrete side truss structure. The concrete triangular structure includes multiple triangular bars, the bending angle of which matches the angle of the concrete triangular structure. They are arranged at intervals along the thickness direction of the concrete triangular structure. The concrete triangular structure also includes multiple U-shaped stirrups, which are fitted onto the triangular bars and partially extend into the concrete side truss structure. The concrete triangular structure also includes multiple closed stirrups, which are clamped onto the triangular bars and U-shaped stirrups. The setting direction of the closed stirrups is perpendicular to the setting direction of the U-shaped stirrups. One side of the steel angle brace connecting the concrete triangular structure is provided with an embedded part. The embedded part is connected to the triangular bars, U-shaped stirrups and closed stirrups in the concrete triangular structure through connecting bars. The side plate of the embedded part is connected with bolts, and the end of the bolts is connected to the steel bar connector. The steel bar connector is connected to the embedded bar, so that the embedded bar extends into the interior of the concrete triangular structure.

2. The steel-concrete composite support structure for large-span deep foundation pits as described in claim 1, characterized in that, The end of the steel support is provided with a pair of diagonal braces near the end of the concrete side truss structure, and the pair of diagonal braces are inclined between the steel support and the concrete side truss structure.

3. The steel-concrete composite support structure for large-span deep foundation pits as described in claim 1, characterized in that, The steel waler is provided with a steel triangle structure corresponding to the steel corner brace, and one side of the steel triangle structure is connected to the end of the steel corner brace.

4. A construction method for a steel-concrete composite support structure for large-span deep foundation pits, characterized in that, Includes the following steps: Install steel walers at the edge of the foundation pit; Concrete side truss structures were formed by pouring concrete on both sides of the foundation pit; Provide steel supports to support and connect the steel supports between oppositely arranged concrete side truss structures; Provide steel angle bracing, which is obliquely supported at the corner of the foundation pit, and connects the end of the steel angle bracing to the corresponding steel waler and concrete side truss structure; An axial force servo system is provided, which is connected to the steel profile support and the steel profile angle brace, and the axial force servo system is used to apply axial force to the steel profile support and the steel profile angle brace; Before installing the steel supports and steel corner braces, provide support columns and drive the support columns in pairs into the foundation pit along the installation positions of the steel supports and steel corner braces; Provide a support beam, connect the support beam between a pair of support columns, and use the support beam to support the corresponding steel support and steel corner brace; When the concrete side truss structure is poured, the steel bars of the concrete triangular structure are set at the corresponding position on the side of the concrete side truss structure, and the embedded parts that are connected to the end of the corresponding steel support and steel corner brace are set on the corresponding side of the concrete triangular structure. The concrete triangular structure and the concrete side truss structure are cast integrally. When setting the formwork and reinforcement of the concrete side truss structure, the formwork and reinforcement of the concrete triangular structure are connected to the formwork and reinforcement of the concrete side truss structure. The concrete triangular structure includes multiple triangular bars, the bending angle of which matches the angle of the concrete triangular structure. They are arranged at intervals along the thickness direction of the concrete triangular structure. The concrete triangular structure also includes multiple U-shaped stirrups, which are fitted onto the triangular bars and partially extend into the concrete side truss structure. The concrete triangular structure also includes multiple closed stirrups, which are clamped onto the triangular bars and U-shaped stirrups. The setting direction of the closed stirrups is perpendicular to the setting direction of the U-shaped stirrups. One side of the steel angle brace connecting the concrete triangular structure is provided with an embedded part. The embedded part is connected to the triangular bars, U-shaped stirrups and closed stirrups in the concrete triangular structure through connecting bars. The side plate of the embedded part is connected with bolts, and the end of the bolts is connected to the steel bar connector. The steel bar connector is connected to the embedded bar, so that the embedded bar extends into the interior of the concrete triangular structure.

5. The construction method of the steel-concrete composite support structure for large-span deep foundation pits as described in claim 4, characterized in that, When setting up steel supports, a pair of diagonal braces are installed between the steel supports and the concrete side truss structure.

6. The construction method of the steel-concrete composite support structure for large-span deep foundation pits as described in claim 4, characterized in that, When installing the steel waler, a steel triangle structure is set on the steel waler at the position corresponding to the steel corner brace, and the steel triangle structure is used to connect the steel corner brace.

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