Tensile and compressible supporting system for foundation pit, prestressed node and construction method

Abstract

The invention discloses a supporting system capable of being pulled and pressed for a foundation pit, a prestress joint and a construction method, and belongs to the technical field of foundation pit supporting. The construction method comprises the following steps that the fender posts and the stand columns are constructed firstly, a foundation pit is excavated, the top beam steel bars are bound after the cushion layer is poured, and the embedded sleeves are inserted. Then the embedded steel bar is welded to the embedded plate, the center hole of the embedded plate and the embedded sleeve are aligned, the non-threaded section of the embedded steel bar and the top beam steel bar are fixed in a spot welding mode, and top beam concrete is poured. And then pre-stress joint installation, steel pipe support installation and steel strand installation are sequentially conducted, the steel pipe support is pressurized through the first center hole jack, and the steel strand is tensioned to a design value through the second center hole jack. Finally, internal force monitoring is conducted, steel strand tension and steel pipe support pressure are monitored, and the proportion of the two is adjusted according to the soil pressure direction. According to the drawable and compressible supporting system for the foundation pit, the prestress joint and the construction method, the drawable and compressible functions of the supporting system can be achieved, the structure is stable, support falling is prevented, and construction is convenient, fast and efficient.

Description

Technical Field

[0001] The invention belongs to the technical field of foundation pit support, and in particular relates to a tensile and compressible support system for a foundation pit, a prestressed node and a construction method. Background Art

[0002] In the field of foundation pit support technology, the internal support system is the core force transmission component of the enclosure structure, and its mechanical properties play a decisive role in the support safety. Traditional steel pipe support systems mostly use the flexible end structure to apply prestress to achieve connection, and can only transmit axial pressure in one direction. However, in some complex support scenarios, the support components need to withstand the tension and compression cyclic loads. The traditional structure has significant technical bottlenecks due to the lack of tension bearing mechanism: its force mechanism is single, and it only relies on the steel pipe to resist the soil pressure. When the side pressure direction of the soil body is reversed or unloading rebound occurs, the support system cannot balance the load through tension, resulting in insufficient structural resistance to deformation; under tension conditions, traditional supports are prone to stress relaxation and connection node failure, which in turn causes accidents such as "dropping support", especially in deep foundation pit projects in soft soil areas or adjacent to existing buildings. Because it cannot dynamically adapt to soil displacement, the risk of failure of the support system increases significantly; in addition, the traditional process requires the setting of concrete corbels on the crown beam to transmit the support reaction force, which has problems such as cumbersome procedures, large amount of wet work on site, and high demolition costs, making it difficult to meet the needs of green construction and efficient construction.

[0003] The unbalanced tensile and compressive performance defects of the supporting structure in the existing technology have become a key technical shortcoming restricting the improvement of the safety and efficiency of foundation pit projects. It is urgent to develop a new support system and construction method that is suitable for complex stress conditions. Summary of the invention

[0004] In view of the deficiencies existing in the related art, the purpose of the present invention is to provide a tensile and compressible support system for foundation pits, a prestressed node and a construction method to solve the problems raised in the above-mentioned background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions: A construction method of a tensile and compressible support system for a foundation pit, comprising the following steps: S1. Preparation steps: construct retaining piles and columns, excavate the foundation pit to the construction working surface, cast the cushion layer at the crown beam casting position and tie the crown beam steel bars, and insert the embedded sleeve into the crown beam steel bars; S2. Embedded parts installation steps: weld the embedded reinforcement to the embedded plate, align the center hole of the embedded plate with the embedded sleeve, then spot weld the non-threaded section of the embedded reinforcement to the crown beam steel bar, pour the crown beam concrete and cure it to the designed strength; S3, prestressed node installation steps: the fixing plate is bolted to the embedded plate through the threaded section of the embedded reinforcement, a clamp fixing part is welded on the fixing plate, and a first through-type jack is placed on the clamp fixing part; S4. Installation steps of steel pipe struts: Lift the steel pipe struts to the fixed part of the hoop clamp, then merge the adjustable part of the hoop clamp to the fixed part of the hoop clamp and lock it with bolts. Adjust the piston end of the first through-type jack to make the load nut fixed on the piston end contact the steel pipe strut; S5. Installation steps of steel strands: Pass the steel strands through the embedded sleeve, embedded plate, fixed plate, first through-type jack, load nut and steel pipe strut in sequence from the outside of the crown beam foundation pit. Insert pads, the first clamp, the second through-type jack and the second clamp into the steel strands outside the crown beam foundation pit in sequence; S6. Prestress application steps: The first through-type jack is lifted to pressurize the steel pipe strut to the designed compressive stress value, and then the second through-type jack is lifted to tension the steel strands to the designed tensile stress value; S7. Internal force monitoring steps: Monitor the tensile force of the steel strands and the pressure of the steel pipe struts, and adjust the ratio of the tensile force of the steel strands to the pressure of the steel pipe struts according to the direction of the soil pressure.

[0006] In some of the embodiments, in the internal force monitoring step, monitor the tensile force of the steel strands and the pressure of the steel pipe struts. When the pressure of the steel pipe strut is greater than the tensile force of the steel strand, it is determined that the direction of the soil pressure is towards the inside of the foundation pit. At this time, the pressure of the steel pipe strut and the soil pressure are initially balanced. When the first through-type jack is lifted to pressurize the steel pipe strut to the same pressure value as the soil pressure value F0, the second through-type jack synchronously tensions the steel strands to F1 to prevent the steel strands from loosening and failing. The first through-type jack continues to be lifted to pressurize the steel pipe strut to F2. At this time, the load balance formula is F0 + F1 = F2, F1 / F2 = n1, n1 ∈ (0, 0.25), that is, F0 = λ1F2, λ1 ∈ (0.75, 1), where n1 is the proportional coefficient of the tensile force of the steel strands to the pressure of the steel pipe strut, and λ1 is the proportional coefficient of the soil pressure to the pressure of the steel pipe strut.

[0007] In some of the embodiments, in the internal force monitoring step, monitor the tensile force of the steel strands and the pressure of the steel pipe struts. When the tensile force of the steel strand is greater than the pressure of the steel pipe strut, it is determined that the direction of the soil pressure is towards the outside of the foundation pit. At this time, the tensile force of the steel strand and the soil pressure are initially balanced. When the second through-type jack synchronously tensions the steel strands to the same tensile force value as the soil pressure value F0, the first through-type jack is lifted to pressurize the steel pipe strut to F2 to prevent the steel pipe strut from loosening and failing. The second through-type jack continues to synchronously tension the steel strands to F1. At this time, the load balance formula is F0 + F2 = F1, F2 / F1 = n2, n2 ∈ (0, 0.25), that is, F0 = λ2F1, λ2 ∈ (0.75, 1), where n2 is the proportional coefficient of the pressure of the steel pipe strut to the tensile force of the steel strand, and λ2 is the proportional coefficient of the soil pressure to the tensile force of the steel strand.

[0008] In some of the embodiments, in the installation step of the steel strands, determine the reserved length of the steel strands according to the predicted value of the foundation pit deformation, and reserve the steel strands outside the foundation pit for secondary tensioning.

[0009] A tensile and compressible support system for a foundation pit, comprising: The steel pipe support pressure system is located in the foundation pit and includes: Prestressed nodes, which include embedded plates, fixed plates and clamps; Steel pipe support, which is fixed between prestressed nodes by clamps; The first through-type jack is placed in the clamping clamp and is used to lift the steel pipe support to apply compressive stress; Steel strand tension system, the steel strand tension system includes: Steel strands, which are inserted into the prestressed nodes, the first through-type jacks and the steel pipe supports; The second through-type jack is arranged outside the foundation pit and is passed through the steel strand; Anchor assembly, the anchor assembly is arranged outside the foundation pit, the anchor assembly is passed through the steel strand, and the anchor assembly cooperates with the second through-type jack to tension the steel strand to apply tensile stress.

[0010] In some of the embodiments, the anchor assembly includes at least three stacked pads, a first clamp, an anchor plate, a clip and a second clamp; the first clamp is arranged between the at least three stacked pads and the anchor plate, the clip is arranged on the steel strand, and the second clamp is connected to the piston rod of the second through-type jack; the first clamp and the second clamp are both annular structures, and the inner walls are provided with tooth patterns matching the outer surface of the steel strand; at least three stacked pads are square plate-shaped pads, and the sizes decrease successively, and the smaller pads are stacked close to the anchor plate to disperse the local stress when the steel strand is tensioned. In some of the embodiments, a load nut is provided at the piston end of the first through-type jack, and the load nut is used to increase the load contact area between the first through-type jack and the steel pipe support.

[0011] In some of the embodiments, the tensile and compressive support system for foundation pits also includes two pressure sensors and a laser rangefinder. The two pressure sensors are respectively arranged on the steel pipe support and the steel strand to monitor internal forces, and the laser rangefinder is arranged on the crown beam to monitor displacement.

[0012] A prestressed node structure of a tensile and compressible support system for a foundation pit, comprising: Embedded plate, embedded plate welded with embedded reinforcement, the embedded reinforcement including non-threaded section for fixing with crown beam and threaded section for connection; A fixing plate, which is connected to the embedded plate by bolts and threaded sections of embedded reinforcement, and a center hole for the steel strand to pass through is opened between the fixing plate and the embedded plate; The clamp comprises a clamp fixing part and an adjustable part, the clamp fixing part is welded with the fixing plate to form an integral body, and the adjustable part is locked with the clamp fixing part by bolts to fix the end of the steel pipe support.

[0013] In some of the embodiments, the fixing plate is provided with mounting holes corresponding one to one with the embedded reinforcement bars of the embedded plate.

[0014] Compared with the prior art, the present invention has the following beneficial effects: 1. The construction method of the tensile and compressible support system for foundation pits provided by the present invention has clear and systematic steps, and realizes accurate installation of various components through processes such as embedded parts installation and prestressed node installation. During construction, the internal force is monitored, and the ratio of the steel strand tension and the steel pipe support pressure can be dynamically adjusted according to the direction of soil pressure to ensure the stability of the support system, avoid the safety hazards caused by the support structure being able to only be compressed in traditional construction, and improve construction safety and efficiency.

[0015] 2. The tensile and compressive support system for foundation pits provided by the present invention integrates the steel pipe support compression system and the steel strand tension system, and can bear tensile and compressive loads at the same time, and adapt to the state of alternating tensile and compressive loads of the components in the foundation pit support. With the through-type jack and anchor assembly, it can effectively apply prestress, and monitor the internal force and displacement in real time through sensors and laser rangefinders, enhance structural stability, and reduce the occurrence of safety accidents such as support drop.

[0016] 3. The prestressed node structure of the tensile and compressible support system for foundation pits provided by the present invention is stably installed by means of embedded plates, fixed plates and clamps, and connected by anchor bars and bolts. The clamps can effectively restrain the ends of the steel pipe supports to prevent them from falling. The structure is simple, and installation and disassembly are convenient. There is no need to make concrete corbels. The piston rod of the through-type jack is extended to simplify the construction process, save construction time and cost, and facilitate the passage of steel strands to ensure the smoothness of prestressing. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings: Figure 1 A schematic diagram of the support system structure of an embodiment of a tensile and compressible support system, a prestressed node and a construction method for a foundation pit according to the present invention; Figure 2 It is a schematic structural diagram of a steel pipe support compression system of an embodiment of a tensile and compressive support system, a prestressed node and a construction method for a foundation pit of the present invention; Figure 3Schematic structural diagram of the steel strand tension system of an embodiment of the pullable and compressible support system, prestressed joint and construction method for foundation pits of the present invention; Figure 4 Exploded schematic structural diagram of the steel strand tension system of an embodiment of the pullable and compressible support system, prestressed joint and construction method for foundation pits of the present invention; Figure 5 Combined structural schematic diagram of the steel pipe strut compression system and the steel strand tension system of an embodiment of the pullable and compressible support system, prestressed joint and construction method for foundation pits of the present invention; Figure 6 Force analysis diagram of an embodiment of the pullable and compressible support system, prestressed joint and construction method for foundation pits of the present invention with the soil pressure direction towards the inside of the foundation pit; Figure 7 Force analysis diagram of an embodiment of the pullable and compressible support system, prestressed joint and construction method for foundation pits of the present invention with the soil pressure direction towards the outside of the foundation pit.

[0018] In the figure: 1. Steel pipe strut compression system; 11. Prestressed joint; 111. Embedded plate; 112. Fixed plate; 113. Hoop clamp; 1131. Hoop clamp fixing part; 1132. Hoop clamp adjustable part; 12. Steel pipe strut; 13. First through-type jack; 2. Steel strand tension system; 21. Steel strand; 22. Second through-type jack; 23. Anchor assembly; 231. Spacer block; 232. First clamp; 233. Anchor plate; 234. Wedge; 2341. First wedge; 2342. Second wedge; 235. Second clamp; 3. Load nut; 4. Post-inserted reinforcement; 41. Non-threaded section; 42. Threaded section; 5. Embedded sleeve; 6. Crown beam. Detailed implementation manners

[0019] The following will clearly and completely describe the technical solutions in the embodiments in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0020] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "transverse", "longitudinal", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention.

[0021] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0022] Embodiment 1: See Appendix Figures 1 to 7 , which gives a schematic embodiment of the construction method of the pullable and compressible support system for foundation pits proposed by the present invention. The construction method of the pullable and compressible support system for foundation pits includes the following steps: S1. Preparation step: Construct the retaining piles and columns, excavate the foundation pit to the construction working surface, pour the cushion layer at the pouring position of the capping beam 6 and bind the capping beam steel bars. Insert the embedded sleeve 5 into the capping beam steel bars, and weld and fix the embedded sleeve 5 to the capping beam steel bars; S2. Embedded part installation step: Weld the implanted bar 4 to the embedded plate 111, align the central hole of the embedded plate 111 with the embedded sleeve 5, then spot-weld the non-threaded section 41 of the implanted bar 4 to the capping beam steel bars, pour the capping beam concrete and cure it to the design strength; S3. Prestressed joint installation step: Bolt-connect the fixing plate 112 to the embedded plate 111 through the threaded section 42 of the implanted bar 4. A hoop fixture fixing part 1131 is welded on the fixing plate 112, and the first through-type jack 13 is placed on the hoop fixture fixing part 1131; S4. Steel pipe strut installation step: Hoist the steel pipe strut 12 to the hoop fixture fixing part 1131, then combine the adjustable part 1132 of the hoop fixture to the hoop fixture fixing part 1131 and lock it with bolts. Adjust the piston end of the first through-type jack 13 so that the load nut 3 fixed on the piston end contacts the steel pipe strut 12; S5. Steel strand installation step: Pass the steel strand 21 through the embedded sleeve 5, the embedded plate 111, the fixing plate 112, the first through-type jack 13, the load nut 3 and the steel pipe strut 12 in sequence from the outside of the capping beam foundation pit. The spacer 231, the first clamp 232, the second through-type jack 22 and the second clamp 235 are sequentially inserted into the steel strand 21 outside the capping beam foundation pit; S6. Prestress application step: The first through-type jack 13 is jacked up to pressurize the steel pipe strut 12 to the design compressive stress value, and then the second through-type jack 22 is jacked up to tension the steel strand 21 to the design tensile stress value; S7. Internal force monitoring step: Monitor the steel strand tension and the steel pipe strut pressure, and adjust the ratio of the steel strand tension to the steel pipe strut pressure according to the direction of the earth pressure.

[0023] In the internal force monitoring step, the tension of the steel strand and the pressure of the steel pipe strut are monitored. When the pressure of the steel pipe strut is greater than the tension of the steel strand, it is determined that the direction of the earth pressure is towards the inside of the foundation pit. At this time, the earth pressure is initially balanced by the pressure of the steel pipe strut. The uniformly distributed load of the earth pressure is simplified into a resultant force F0. When the first through-type jack 13 jacks up to pressurize the steel pipe strut 12 to the same pressure value as the earth pressure value F0, the second through-type jack 22 synchronously tensions the steel strand 21 to F1 to prevent the steel strand 21 from slackening and failing. The first through-type jack 13 continues to jack up to pressurize the steel pipe strut 12 to F2. At this time, the load balance formula is F0 + F1 = F2, F1 / F2 = n1, n1 ∈ (0, 0.25), that is, F0 = λ1F2, λ1 ∈ (0.75, 1), where n1 is the proportionality coefficient of the steel strand tension and the steel pipe strut pressure, and λ1 is the proportionality coefficient of the earth pressure and the steel pipe strut pressure.

[0024] In the internal force monitoring step, the tension of the steel strand and the pressure of the steel pipe strut are monitored. When the tension of the steel strand is greater than the pressure of the steel pipe strut, it is determined that the direction of the earth pressure is towards the outside of the foundation pit. At this time, the earth pressure is initially balanced by the tension of the steel strand. The uniformly distributed load of the earth pressure is simplified into a resultant force F0. When the second through-type jack 22 synchronously tensions the steel strand 21 to the same tension value as the earth pressure value F0, the first through-type jack 13 jacks up to pressurize the steel pipe strut 12 to F2 to prevent the steel pipe strut 12 from slackening and failing. The second through-type jack 22 continues to synchronously tension the steel strand 21 to F1. At this time, the load balance formula is F0 + F2 = F1, F2 / F1 = n2, n2 ∈ (0, 0.25), that is, F0 = λ2F1, λ2 ∈ (0.75, 1), where n2 is the proportionality coefficient of the steel pipe strut pressure and the steel strand tension, and λ2 is the proportionality coefficient of the earth pressure and the steel strand tension.

[0025] In the steel strand installation step, the reserved length of the steel strand 21 is determined according to the predicted value of the foundation pit deformation, and the steel strand 21 is reserved outside the foundation pit for secondary tensioning. Specifically, the steel strand 21 on one side of the capping beam 6 is cut short, and the other end is retained for secondary application of tensile stress.

[0026] In this embodiment, in the internal force monitoring step, in addition to monitoring the tension of the steel strand and the pressure of the steel pipe strut, the direction of the earth pressure can also be assisted in judgment by monitoring the displacement condition of the capping beam. Refer to the appendix Figure 1 , assuming that the initial distance between the capping beams is L0, if the value of L0 becomes smaller, it can be judged that the direction of the earth pressure is towards the inside of the foundation pit, and if the value of L0 becomes larger, it can be judged that the direction of the earth pressure is towards the outside of the foundation pit.

[0027] In the above-mentioned schematic embodiment, the construction method of the pullable and compressible support system for the foundation pit has clear and systematic steps. Through processes such as embedded part installation and prestressed node installation, precise installation of each component is achieved. During construction, the internal force is monitored, and the ratio of the steel strand tension to the steel pipe support pressure can be dynamically adjusted according to the direction of the soil pressure, ensuring the stability of the support system and avoiding potential safety hazards caused by the traditional support structure that can only be compressed, thereby improving the construction safety and efficiency.

[0028] Embodiment 2: See Appendix Figures 1 to 5 , which gives a schematic embodiment of the pullable and compressible support system for the foundation pit proposed by the present invention. The pullable and compressible support system for the foundation pit includes a steel pipe support compression system 1 and a steel strand tension system 2.

[0029] The steel pipe support compression system 1 is arranged in the foundation pit. The steel pipe support compression system 1 includes a prestressed node 11, a steel pipe support 12, and a first through-type jack 13. The prestressed node 11 includes an embedded plate 111, a fixing plate 112, and a hoop clamp 113. The steel pipe support 12 is fixed between the prestressed nodes 11 through the hoop clamp 113. The first through-type jack 13 is placed in the hoop clamp 113, and the first through-type jack 13 is used to lift the steel pipe support 12 to apply compressive stress. Specifically, the steel pipe support 12 is a Q355B steel circular pipe.

[0030] The steel strand tension system 2 includes a steel strand 21, a second through-type jack 22, and an anchor assembly 23. The steel strand 21 passes through the prestressed node 11, the first through-type jack 13, and the steel pipe support 12. The second through-type jack 22 is arranged outside the foundation pit, and the second through-type jack 22 passes through the steel strand 21. The anchor assembly 23 is arranged outside the foundation pit, the anchor assembly 23 passes through the steel strand 21, and the anchor assembly 23 cooperates with the second through-type jack 22 to tension the steel strand 21 to apply tensile stress.

[0031] The anchor assembly 23 includes at least three stacked pads 231, a first clamp 232, an anchor plate 233, wedge-shaped jaws 234, and a second clamp 235 in sequence; the first clamp 232 is arranged between at least three stacked pads 231 and the anchor plate 233, the wedge-shaped jaws 234 are arranged on the steel strand 21, and the second clamp 235 is connected to the piston rod of the second through-type jack 22; both the first clamp 232 and the second clamp 235 are annular structures, and the inner wall is provided with tooth patterns matching the outer surface of the steel strand 21; at least three stacked pads 231 are square plate-shaped pads 231, and the sizes decrease in sequence, and the pads 231 with smaller sizes are stacked in the direction close to the anchor plate 233 to disperse the local stress during the tension of the steel strand 21.

[0032] See Appendix Figure 4, in this embodiment, the wedge 234 includes a first wedge 2341 corresponding to the first fixture 232 and a second wedge 2342 corresponding to the second fixture 235. Among them, the first wedge 2341 is arranged between the first fixture 232 and the anchor plate 233, and the second wedge 2342 is arranged on the side of the second fixture 235 away from the second through-type jack 22.

[0033] When the piston rod of the first through-type jack 13 moves forward, the second fixture 235 and the second wedge 2342 are in a clamping state, jointly clamping the steel strand 21 and driving the steel strand 21 to be tensioned. After the appropriate tension is applied, the pressure is released, and the second fixture 235 and the second wedge 2342 become loose. At the same time, the first fixture 232 and the first wedge 2341 jointly clamp the steel strand 21 to achieve the prestress tensioning of the steel strand 21.

[0034] In this embodiment, the steel strand 21 is composed of multiple high-strength steel wires, and the first fixture 232, the wedge 234, and the second fixture 235 are made of high-strength alloy steel.

[0035] A load nut 3 is provided at the piston end of the first through-type jack 13, and the load nut 3 is used to increase the load contact area between the first through-type jack 13 and the steel pipe strut 12.

[0036] The pullable and compressible bracing system for the foundation pit further includes two pressure sensors and a laser rangefinder. The two pressure sensors are respectively arranged on the steel pipe strut 12 and the steel strand 21 to monitor the internal force, and the laser rangefinder is arranged on the capping beam 6 to monitor the displacement.

[0037] In this embodiment, the internal force monitoring of the steel pipe strut is achieved by symmetrically welding vibrating wire surface strain gauges along the axial direction on the surface of the steel pipe strut 12. By measuring the strain value of the steel pipe strut 12 and combining with the elastic modulus of the steel, it is converted into the axial force. The strain gauges are pasted with epoxy resin glue and welded with wires, and the wires are protected by a metal bellows jacket to prevent mechanical damage. The installation position of the strain gauges on the surface of the steel pipe strut 12 avoids the welds and joint areas, and the 1 / 3 span between two supports is selected as the monitoring section, where the stress distribution is uniform and it is easy to install.

[0038] In this embodiment, the tension monitoring of the steel strand is achieved by installing a through-type axial force gauge behind the anchor of the steel strand 21. The central hole of the axial force gauge matches the steel strand 21 and is connected to the anchor plate 233 by bolts to directly measure the axial tension of the steel strand 21 after tensioning. The axial force gauge on the steel strand 21 is integrally designed with the anchor assembly 23, and the outer diameter of the axial force gauge matches the size of the anchor plate 233, without affecting the tension construction process of the steel strand 21.

[0039] The strain gauges and the axial force gauges are connected to the distributed data collector on the edge of the foundation pit through shielded twisted pair wires, and the signal transmission is realized by using the RS485 communication protocol to ensure the anti-interference ability and the long-distance transmission stability.

[0040] In this embodiment, the laser rangefinder adopts a phase laser rangefinder, and the measurement accuracy can meet the needs of monitoring the horizontal displacement of the crown beam of the foundation pit. The laser rangefinder is fixed to the side of the crown beam 6 through an L-shaped bracket, and the bracket is welded to the main reinforcement of the crown beam 6 with expansion bolts to ensure a firm installation. The emission direction of the laser rangefinder is perpendicular to the axis of the crown beam 6 and is aimed at the reflective target on the opposite side of the foundation pit. The installation height of the reflective target is kept horizontal with the laser rangefinder, covering the full width of the foundation pit. In addition, a laser rangefinder is arranged at a set distance along the length direction of the crown beam 6 to form a linear monitoring network, covering the main deformation area of the foundation pit.

[0041] In the above exemplary embodiment, the tensile and compressive support system for the foundation pit integrates the steel pipe support compression system and the steel strand tension system, which can bear tensile and compressive loads at the same time and adapt to the state of alternating tensile and compressive loads of the components in the foundation pit support. With the through-type jack and anchor assembly, it can effectively apply prestress, and monitor the internal force and displacement in real time through sensors and laser rangefinders, enhance structural stability, and reduce the occurrence of safety accidents such as support drop.

[0042] Embodiment 3: See attached Figures 1 to 5 , a schematic embodiment of the prestressed node structure of the tensile and compressive support system for foundation pit proposed by the present invention is given, and the prestressed node structure of the tensile and compressive support system for foundation pit includes an embedded plate 111, a fixed plate 112 and a clamp 113.

[0043] The embedded plate 111 is welded with anchor bars 4, which include a non-threaded section 41 for fixing to the crown beam 6 and a threaded section 42 for connection. The non-threaded section 41 of the anchor bars 4 is tied or welded to the crown beam reinforcement. The fixed plate 112 is provided with mounting holes corresponding to the anchor bars 4 of the embedded plate 111. The fixed plate 112 is connected to the embedded plate 111 by bolts and the threaded section 42 of the anchor bars 4, and a center hole for the steel strand 21 to pass through is provided between the fixed plate 112 and the embedded plate 111; the clamp 113 includes a clamp fixing portion 1131 and a clamp adjustable portion 1132, the clamp fixing portion 1131 is welded to the fixed plate 112 as a whole, and the clamp adjustable portion 1132 is locked with the clamp fixing portion 1131 by bolts to fix the end of the steel pipe support 12 and restrict the end of the steel pipe support 12 from moving up, down, left and right.

[0044] In this embodiment, the prestressed node structure also includes an elastic locking device, which is provided at the bolt connection between the fixed part of the clamp and the adjustable part of the clamp to prevent the bolt from loosening due to foundation pit vibration or stress cycle, and further reduce the risk of falling off of the steel pipe support 12. Specifically, the elastic locking device can be selected from spring washers, anti-loosening nuts or wedge-shaped blocks, which can achieve self-tightening fixation and improve the stability of the support system under complex working conditions.

[0045] In this embodiment, the non-threaded section 41 of the embedded bar 4 can be compositely anchored with a ribbed barb structure or a chemical anchor bolt to increase the bite force with the concrete of the crown beam 6. The contact surface between the embedded plate 111 and the crown beam 6 is provided with a rough tooth pattern to replace the traditional plane welding and improve the pull-out resistance of the node.

[0046] Technical effect: In soft soil or high water level foundation pits, the pull-out resistance of the nodes is enhanced to avoid displacement of the embedded plates due to excessive lateral pressure of the soil, thus ensuring the overall stability of the support system.

[0047] In the above exemplary embodiment, the prestressed node structure of the tensile and compressive support system for foundation pits is stably installed by means of embedded plates, fixed plates and clamps, and connected by anchor bars and bolts. The clamps can effectively restrain the ends of the steel pipe supports to prevent them from falling. The structure is simple, easy to install and disassemble, and there is no need to make concrete corbels. Instead, the piston rod of the through-type jack is extended to simplify the construction process, save construction time and cost, and facilitate the passage of steel strands to ensure the smoothness of prestressing.

[0048] Finally, it should be noted that: the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0049] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or some technical features can be replaced by equivalents without departing from the spirit of the technical solution of the present invention, which should be included in the scope of the technical solution for protection of the present invention.

Claims

1. A construction method of a pullable and compressible support system for foundation pits, characterized in that, The steps include: S1. Preparation steps: construct retaining piles and columns, excavate the foundation pit to the construction working surface, cast the cushion layer at the crown beam casting position and tie the crown beam steel bars, and insert the embedded sleeve into the crown beam steel bars; S2. Embedded parts installation steps: weld the embedded reinforcement to the embedded plate, align the center hole of the embedded plate with the embedded sleeve, then spot weld the non-threaded section of the embedded reinforcement to the crown beam steel bar, pour the crown beam concrete and cure it to the designed strength; S3, prestressed node installation steps: the fixing plate is bolted to the embedded plate through the threaded section of the embedded reinforcement, a clamp fixing part is welded on the fixing plate, and a first through-type jack is placed on the clamp fixing part; S4, steel pipe support installation steps: hoist the steel pipe support to the fixing part of the clamp clamp, then merge the adjustable part of the clamp clamp into the fixing part of the clamp clamp, and tighten it with bolts, and adjust the piston end of the first through-type jack so that the load nut fixed on the piston end contacts the steel pipe support; S5, steel strand installation steps: pass the steel strand from the outside of the crown beam foundation pit through the embedded casing, embedded plate, fixed plate, first through-type jack, load nut and steel pipe support in sequence, and insert the cushion block, first clamp, second through-type jack and second clamp into the steel strand outside the crown beam foundation pit in sequence; S6, prestressing step: the first through-type jack is lifted to pressurize the steel pipe support to the designed compressive stress value, and then the second through-type jack is lifted to tension the steel strand to the designed tensile stress value; S7. Internal force monitoring steps: monitor the tension of the steel strands and the pressure of the steel pipe support, and adjust the ratio of the tension of the steel strands to the pressure of the steel pipe support according to the direction of the soil pressure.

2. The construction method of the pullable and compressible support system for foundation pits according to claim 1, characterized in that, In the internal force monitoring step, the steel strand tension and the steel pipe support pressure are monitored. When the steel pipe support pressure is greater than the steel strand tension, it is determined that the soil pressure is directed toward the foundation pit. At this time, the steel pipe support pressure and the soil pressure are initially balanced. The first through-type jack is used to pressurize the steel pipe support until the pressure value is the same as the soil pressure value F0. The second through-type jack is used to simultaneously tension the steel strand to F1 to prevent the steel strand from loosening and failing. The first through-type jack continues to pressurize the steel pipe support to F2. At this time, the load balance formula is F0+F1=F2, F1 / F2=n1, n1∈(0,0.25), that is, F0=λ1F2, λ1∈(0.75,1), wherein n1 is the proportional coefficient between the steel strand tension and the steel pipe support pressure, and λ1 is the proportional coefficient between the soil pressure and the steel pipe support pressure.

3. The construction method of the pullable and compressible support system for foundation pits according to claim 2, characterized in that, In the internal force monitoring step, the steel strand tension and the steel pipe support pressure are monitored. When the steel strand tension is greater than the steel pipe support pressure, it is determined that the soil pressure is directed toward the outside of the foundation pit. At this time, the steel strand tension and the soil pressure are initially balanced. The second through-type jack synchronously tensions the steel strand until the tension value is the same as the soil pressure value F0. The first through-type jack lifts and pressurizes the steel pipe support to F2 to prevent the steel pipe support from loosening and failing. The second through-type jack continues to synchronously tension the steel strand to F1. At this time, the load balance formula is F0+F2=F1, F2 / F1=n2, n2∈(0,0.25), that is, F0=λ2F1, λ2∈(0.75,1), where n2 is the proportional coefficient of the steel pipe support pressure and the steel strand tension, and λ2 is the proportional coefficient of the soil pressure and the steel strand tension.

4. The construction method of the pullable and compressible support system for foundation pits according to claim 1, characterized in that, In the installation step of the steel strand, the reserved length of the steel strand is determined according to the predicted value of the foundation pit deformation, and the steel strand is reserved outside the foundation pit for secondary tensioning.

5. A pullable and compressible support system for foundation pits, characterized in that, Including: The steel pipe strut compression system is arranged inside the foundation pit, and the steel pipe strut compression system includes: The prestressed node includes an embedded plate, a fixing plate and a hoop fixture; The steel pipe strut is fixed between the prestressed nodes by the hoop fixture; The first through-type jack is placed inside the hoop fixture, and the first through-type jack is used to lift the steel pipe strut to apply compressive stress; The steel strand tension system includes: The steel strand is threaded through the prestressed node, the first through-type jack and the steel pipe strut; The second through-type jack is arranged outside the foundation pit, and the second through-type jack is threaded through the steel strand; The anchor assembly is arranged outside the foundation pit, the anchor assembly is threaded through the steel strand, and the anchor assembly cooperates with the second through-type jack to tension the steel strand to apply tensile stress.

6. The pullable and compressible support system for foundation pits according to claim 5, wherein, The anchor assembly includes at least three stacked pads, a first fixture, an anchor plate, clamping pieces and a second fixture; the first fixture is arranged between the at least three stacked pads and the anchor plate, the clamping pieces are arranged on the steel strand, and the second fixture is connected to the piston rod of the second through-type jack; both the first fixture and the second fixture are of a ring structure, and the inner wall is provided with tooth patterns matching the outer surface of the steel strand; the at least three stacked pads are square plate-shaped pads, and the sizes decrease in sequence, and the pads with smaller sizes are stacked in the direction close to the anchor plate to disperse the local stress during the tensioning of the steel strand.

7. The pullable and compressible support system for foundation pits according to claim 5, characterized in that A load nut is arranged at the piston end of the first through-type jack, and the load nut is used to increase the load contact area between the first through-type jack and the steel pipe strut.

8. The pullable and compressible support system for foundation pits according to claim 5, wherein It also includes two pressure sensors and a laser rangefinder. The two pressure sensors are respectively arranged on the steel pipe strut and the steel strand to monitor the internal force, and the laser rangefinder is arranged on the crown beam to monitor the displacement.

9. The prestressed joint structure of a pullable and compressible support system for a foundation pit, characterized in that, Including: The embedded plate is welded with planted bars. The planted bars include a non-threaded section for fixing with the crown beam and a threaded section for connection; The fixing plate is connected to the embedded plate through bolts and the threaded section of the planted bar. A central hole for the steel strand to pass through is opened between the fixing plate and the embedded plate; The hoop fixture includes a hoop fixture fixing part and a hoop fixture adjustable part. The hoop fixture fixing part is integrally formed by welding with the fixing plate, and the hoop fixture adjustable part is locked with the hoop fixture fixing part through bolts to fix the end of the steel pipe strut.

10. The prestressed joint structure of the pullable and compressible support system for foundation pits according to claim 9, characterized in that, The fixing plate is provided with installation holes corresponding to the planted bars of the embedded plate one by one.

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