Tensile and compressive support system for foundation pit, prestressed node and construction method

Abstract

The present invention discloses a tensile and compressive support system, a prestressed node and a construction method for foundation pits, and belongs to the technical field of foundation pit support. The construction method is as follows: first construct the retaining piles and columns, excavate the foundation pit, cast the cushion layer, tie the crown beam steel bars, and insert the embedded sleeves. Then weld the embedded steel bars to the embedded plates, align the center holes of the embedded plates with the embedded sleeves, spot weld the non-threaded sections of the embedded steel bars to the crown beam steel bars, and cast the crown beam concrete. Then, install the prestressed nodes, install the steel pipe supports and install the steel strands in sequence, pressurize the steel pipe supports with the first through-type jack, and tension the steel strands to the design value with the second through-type jack. Finally, perform internal force monitoring, monitor the tension of the steel strands and the pressure of the steel pipe supports, and adjust the ratio of the two according to the direction of the soil pressure. The tensile and compressive support system, prestressed node and construction method for foundation pits provided by the present invention can realize the tensile and compressive functions of the support system, have a stable structure, prevent support from falling, and are convenient and efficient in construction.

Description

Technical Field

[0001] The present invention belongs to the technical field of foundation pit support, and in particular relates to a tensile and compressive 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 serves as the core force-transmitting component of the retaining structure, and its mechanical properties play a decisive role in support safety. Traditional steel pipe support systems often rely on prestressed connections through flexible end structures, which can only transmit axial pressure in one direction. However, in some complex support scenarios, support components must withstand cyclical tensile and compressive loads. Traditional structures, lacking a tensile load-bearing mechanism, face significant technical bottlenecks. Their single-load mechanism relies solely on the steel pipes to resist soil pressure. When the soil pressure reverses or rebound occurs, the support system is unable to balance the load through tension, resulting in insufficient structural resistance to deformation. Under tensile conditions, traditional supports are prone to stress relaxation and connection failure, leading to accidents such as "support drop." This is particularly true in deep foundation pits in soft soil areas or adjacent to existing buildings. The inability to dynamically adapt to soil displacement significantly increases the risk of support system failure. Furthermore, traditional processes require concrete corbels in the crown beam to transmit support reaction forces, which results in cumbersome processes, extensive on-site wet work, and high demolition costs, making them difficult to meet the requirements of green construction and efficient building.

[0003] The imbalance in the tensile and compressive performance of the supporting structure in the existing technology has become a key technical shortcoming that restricts the safety and efficiency improvement 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 shortcomings existing in the related art, the purpose of the present invention is to provide a tensile and compressive support system for foundation pits, a prestressed node and a construction method to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A construction method of a tensile and compressible support system for a foundation pit, comprising the following steps:

[0007] S1. Preparation steps: construct retaining piles and columns, excavate the foundation pit to the construction working surface, pour the cushion layer at the crown beam pouring position and tie the crown beam reinforcement, and insert the embedded sleeve into the crown beam reinforcement;

[0008] 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 reinforcement, pour the crown beam concrete and cure to the design strength;

[0009] S3, prestressed node installation steps: bolt the fixing plate to the embedded plate through the threaded section of the embedded reinforcement, weld a clamp fixing portion on the fixing plate, and place a first through-type jack on the clamp fixing portion;

[0010] S4. Steel pipe support installation steps: Hoist the steel pipe support to the fixed part of the clamp clamp, then merge the adjustable part of the clamp clamp into the fixed part of the clamp clamp and tighten it with bolts. 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;

[0011] 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. Insert the spacer, first clamp, second through-type jack and second clamp into the steel strand outside the crown beam foundation pit in sequence.

[0012] S6, prestressing step: the first through-type jack is lifted to pressurize the steel pipe support to the design compressive stress value, and then the second through-type jack is lifted to tension the steel strand to the design tensile stress value;

[0013] S7. Internal force monitoring steps: monitor the steel strand tension and steel pipe support pressure, and adjust the ratio of the steel strand tension and steel pipe support pressure according to the direction of soil pressure.

[0014] In some embodiments, 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 lifted and pressurized on the steel pipe support until the pressure value is the same as the soil pressure value F0. The second through-type jack is synchronously tensioned on the steel strand to F1 to prevent the steel strand from loosening and failing. The first through-type jack continues to lift and 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), where 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.

[0015] In some of the embodiments, 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 steel pipe support pressure and steel strand tension, and λ2 is the proportional coefficient of soil pressure and steel strand tension.

[0016] In some embodiments, during the steel strand installation step, a reserved length of the steel strand is determined based on a predicted value of foundation pit deformation, and steel strands are reserved outside the foundation pit for secondary tensioning.

[0017] A tensile and compressible support system for a foundation pit, comprising:

[0018] The steel pipe support pressure system is located in the foundation pit and includes:

[0019] Prestressed nodes, which include embedded plates, fixed plates and clamps;

[0020] Steel pipe support, which is fixed between prestressed nodes by clamps;

[0021] The first through-type jack is placed in the clamp and is used to lift the steel pipe support to apply compressive stress;

[0022] Steel strand tension system, the steel strand tension system includes:

[0023] Steel strands, which are passed through the prestressed nodes, the first through-type jacks and the steel pipe supports;

[0024] The second through-type jack is installed outside the foundation pit and is passed through the steel strand;

[0025] 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 and apply tensile stress.

[0026] In some 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 wall is provided with a tooth pattern matching the outer surface of the steel strand; at least three stacked pads are square plate-shaped pads, and the size decreases successively, and the smaller pads are stacked close to the anchor plate to disperse the local stress when the steel strand is tensioned.

[0027] In some 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.

[0028] In some embodiments, the tensile and compressive support system for foundation pits further 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.

[0029] A prestressed node structure of a tensile and compressive support system for a foundation pit, comprising:

[0030] Embedded plate, embedded plate welded with embedded steel bars, the embedded steel bars including non-threaded sections for fixing with crown beams and threaded sections for connection;

[0031] The fixing plate is connected to the embedded plate through bolts and threaded sections of the embedded reinforcement. A central hole for the steel strand to pass through is opened between the fixing plate and the embedded plate;

[0032] The clamp includes a clamp fixing portion and an adjustable portion. The clamp fixing portion is welded to a fixed plate and is integrally formed. The adjustable portion is fastened to the clamp fixing portion by bolts to fix the end portion of the steel pipe support.

[0033] In some embodiments, the fixing plate is provided with mounting holes corresponding one to one with the embedded reinforcement bars of the embedded plate.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The present invention provides a method for constructing a tensile and compressive support system for foundation pits, with clear and systematic steps. Through processes such as embedded component installation and prestressed node installation, precise installation of each component is achieved. Internal forces are monitored during construction, and the ratio of steel strand tension to steel pipe support pressure can be dynamically adjusted based on the direction of soil pressure. This ensures the stability of the support system, avoids the safety hazards associated with traditional construction where the support structure can only withstand compression, and improves construction safety and efficiency.

[0036] 2. The present invention's tensile and compressive support system for foundation pits integrates a steel pipe support compression system with a steel strand tension system, capable of simultaneously bearing tensile and compressive loads and adapting to alternating tension and compression conditions within the foundation pit support components. Combined with through-hole jacks and anchor assemblies, it effectively applies prestress, and sensors and laser rangefinders monitor internal forces and displacements in real time, enhancing structural stability and reducing the risk of safety incidents such as support falls.

[0037] 3. The prestressed node structure of the tensile and compressive support system for foundation pits provided by the present invention utilizes embedded plates, fixed plates, and clamps, achieving secure installation through embedded rebar and bolt connections. The clamps effectively restrain the ends of the steel pipe supports to prevent them from falling. The structure is simple, allowing for easy installation and disassembly. Concrete corbels are not required, and instead are replaced by extended through-hole jack piston rods, simplifying the construction process, saving time and costs. It also facilitates the passage of steel strands, ensuring smooth application of prestressing force. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] 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:

[0039] Figure 1 A schematic diagram of the support system structure of an embodiment of a tensile and compressive support system, prestressed nodes, and construction method for a foundation pit according to the present invention;

[0040] Figure 2 This is a schematic structural diagram of a steel pipe support compression system according to one embodiment of a tensile and compressive support system, prestressed node, and construction method for a foundation pit according to the present invention;

[0041] Figure 3 This is a structural diagram of a steel strand tension system according to one embodiment of a tensile and compressive support system, prestressed nodes, and a construction method for a foundation pit according to the present invention;

[0042] Figure 4 This is an exploded schematic diagram of the steel strand tension system structure of one embodiment of the tensile and compressive support system, prestressed node, and construction method for foundation pits of the present invention;

[0043] Figure 5 This is a schematic diagram of the combined structure of a steel pipe support compression system and a steel strand tension system in one embodiment of a tensile and compressive support system, prestressed node, and construction method for a foundation pit according to the present invention;

[0044] Figure 6 A force analysis diagram showing the direction of soil pressure toward the inside of the foundation pit in one embodiment of the tensile and compressive support system, prestressed node, and construction method for a foundation pit according to the present invention;

[0045] Figure 7This is a force analysis diagram of an embodiment of the tensile and compressive support system, prestressed node and construction method for a foundation pit of the present invention, with the soil pressure direction toward the outside of the foundation pit.

[0046] In the picture:

[0047] 1. Steel pipe support compression system; 11. Prestressed node; 111. Embedded plate; 112. Fixed plate; 113. Clamp; 1131. Clamp fixing part; 1132. Clamp adjustable part; 12. Steel pipe support; 13. First through-type jack; 2. Steel strand tension system; 21. Steel strand; 22. Second through-type jack; 23. Anchor assembly; 231. Spacer; 232. First clamp; 233. Anchor plate; 234. Clip; 2341. First clip; 2342. Second clip; 235. Second clamp; 3. Load nut; 4. Anchor bar; 41. Non-threaded section; 42. Threaded section; 5. Embedded sleeve; 6. Crown beam. DETAILED DESCRIPTION

[0048] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0049] In the description of the present invention, it should be understood that the terms "center", "transverse", "longitudinal", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are 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 operate in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0050] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to direct connections, indirect connections through an intermediary, or internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0051] Example 1:

[0052] See attached Figures 1 to 7, provides an illustrative embodiment of the construction method of the tensile and compressive support system for foundation pits proposed by the present invention, and the construction method of the tensile and compressive support system for foundation pits includes the following steps:

[0053] S1. Preparation steps: construct retaining piles and columns, excavate the foundation pit to the construction working surface, cast a cushion layer at the casting position of the crown beam 6 and tie the crown beam reinforcement, insert the embedded sleeve 5 into the crown beam reinforcement, and weld the embedded sleeve 5 to the crown beam reinforcement;

[0054] S2, embedded parts installation steps: weld the anchor bar 4 to the embedded plate 111, align the center hole of the embedded plate 111 with the embedded sleeve 5, then spot weld the non-threaded section 41 of the anchor bar 4 to the crown beam steel bar, pour the crown beam concrete and cure it to the design strength;

[0055] S3, prestressed node installation step: bolt the fixing plate 112 to the embedded plate 111 through the threaded section 42 of the embedded rebar 4, weld a clamp fixing portion 1131 on the fixing plate 112, and place the first through-type jack 13 on the clamp fixing portion 1131;

[0056] S4. Installing the steel pipe support: Hoist the steel pipe support 12 to the clamp fixing portion 1131, then merge the clamp adjustable portion 1132 to the clamp fixing portion 1131 and tighten 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 support 12.

[0057] S5, steel strand installation step: From the outside of the crown beam foundation pit, the steel strand 21 is passed through the embedded casing 5, embedded plate 111, fixed plate 112, first through-type jack 13, load nut 3 and steel pipe support 12 in sequence; and the spacer 231, first clamp 232, second through-type jack 22 and second clamp 235 are passed through the steel strand 21 outside the crown beam foundation pit in sequence;

[0058] S6, prestressing step: the first through-type jack 13 is lifted to pressurize the steel pipe support 12 to the designed compressive stress value, and then the second through-type jack 22 is lifted to tension the steel strand 21 to the designed tensile stress value;

[0059] S7. Internal force monitoring steps: monitor the steel strand tension and steel pipe support pressure, and adjust the ratio of the steel strand tension and steel pipe support pressure according to the direction of soil pressure.

[0060] 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, and the soil pressure uniformly distributed load is simplified to the resultant force F0. The first through-type jack 13 is lifted and pressurized on the steel pipe support 12 until the pressure value is the same as the soil pressure value F0. The second through-type jack 22 synchronously tensions the steel strand 21 to F1 to prevent the steel strand 21 from loosening and failing. The first through-type jack 13 continues to lift and pressurize the steel pipe support 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 proportional coefficient of steel strand tension and steel pipe support pressure, and λ1 is the proportional coefficient of soil pressure and steel pipe support pressure.

[0061] 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, and the soil pressure uniformly distributed load is simplified to the resultant force F0. The second through-type jack 22 synchronously tensions the steel strand 21 until the tension value is the same as the soil pressure value F0. The first through-type jack 13 lifts and pressurizes the steel pipe support 12 to F2 to prevent the steel pipe support 12 from loosening 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 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.

[0062] During the strand installation step, the reserved length of the strand 21 is determined based on the predicted pit deformation value, and the strand 21 is reserved outside the pit for secondary tensioning. Specifically, the strand 21 on one side of the crown beam 6 is shortened, and the other end is retained for secondary tensile stress application.

[0063] In this embodiment, in the internal force monitoring step, in addition to monitoring the steel strand tension and steel pipe support pressure, the displacement of the crown beam can also be monitored to assist in determining the direction of the soil pressure. Figure 1 , assuming that the initial state crown beam spacing is L0, if the L0 value becomes smaller, it can be judged that the direction of soil pressure is toward the inside of the foundation pit, if the L0 value becomes larger, it can be judged that the direction of soil pressure is toward the outside of the foundation pit.

[0064] In the above-described exemplary embodiment, the construction method for a tensile and compressive support system for foundation pits features clear and systematic steps. Through processes such as embedded component installation and prestressed joint installation, precise assembly of all components is achieved. Internal forces are monitored during construction, and the ratio of steel strand tension to steel pipe support pressure can be dynamically adjusted based on the direction of soil pressure. This ensures the stability of the support system, avoids the safety hazards associated with traditional construction where the support structure can only withstand compression, and improves construction safety and efficiency.

[0065] Example 2:

[0066] See attached Figures 1 to 5 , gives a schematic embodiment of the tensile and compressive support system for foundation pits proposed in the present invention, which includes a steel pipe support compression system 1 and a steel strand tension system 2.

[0067] The steel pipe support compression system 1 is installed in the foundation pit and 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 fixed plate 112, and a clamp 113. The steel pipe support 12 is fixed between the prestressed nodes 11 via the clamp 113. The first through-type jack 13 is placed in the clamp 113 and is used to lift the steel pipe support 12 to apply compressive stress. Specifically, the steel pipe support 12 is a Q355B steel round tube.

[0068] The steel strand tensioning system 2 includes a steel strand 21, a second through-type jack 22, and an anchor assembly 23. The steel strand 21 is threaded through the prestressed node 11, the first through-type jack 13, and the steel pipe support 12. The second through-type jack 22 is located outside the foundation pit and threaded through the steel strand 21. The anchor assembly 23 is also located outside the foundation pit and threaded through the steel strand 21. The anchor assembly 23 and the second through-type jack 22 cooperate to tension the steel strand 21 and apply tensile stress.

[0069] The anchor assembly 23 includes at least three stacked pads 231, a first clamp 232, an anchor plate 233, a clip 234 and a second clamp 235; the first clamp 232 is arranged between the at least three stacked pads 231 and the anchor plate 233, the clip 234 is arranged on the steel strand 21, and the second clamp 235 is connected to the piston rod of the second through-type jack 22; the first clamp 232 and the second clamp 235 are both annular structures, and the inner wall is provided with a tooth pattern matching the outer surface of the steel strand 21; at least three stacked pads 231 are square plate-shaped pads 231, and the size decreases successively. The smaller pads 231 are stacked close to the anchor plate 233 to disperse the local stress when the steel strand 21 is tensioned.

[0070] See attached Figure 4In this embodiment, the clip 234 includes a first clip 2341 corresponding to the first clamp 232 and a second clip 2342 corresponding to the second clamp 235. The first clip 2341 is disposed between the first clamp 232 and the anchor plate 233, and the second clip 2342 is disposed on a side of the second clamp 235 away from the second through-type jack 22.

[0071] When the piston rod of the first through-type jack 13 moves forward, the second clamp 235 and the second clamp 2342 are in a clamping state, which cooperate to clamp the steel strand 21 and drive the steel strand 21 to be tensioned. After the appropriate tension is applied, the pressure is released, and the second clamp 235 and the second clamp 2342 are relaxed. At the same time, the first clamp 232 and the first clamp 2341 cooperate to clamp the steel strand 21 to achieve prestressed tensioning of the steel strand 21.

[0072] In this embodiment, the steel strand 21 is composed of multiple strands of high-strength steel wire ropes, and the first clamp 232, the clamping piece 234 and the second clamp 235 are made of high-strength alloy steel.

[0073] 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 support 12 .

[0074] 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 12 and the steel strand 21 to monitor internal forces, and the laser rangefinder is arranged on the crown beam 6 to monitor displacement.

[0075] In this embodiment, the internal force of the steel pipe support is monitored by symmetrically welding vibrating wire surface strain gauges along the axial direction of the steel pipe support 12. The strain values ​​of the steel pipe support 12 are measured and converted into axial force based on the elastic modulus of the steel. The strain gauges are attached with epoxy resin and the wires are welded. The wires are protected by metal bellows to prevent mechanical damage. The strain gauges on the steel pipe support 12 are installed away from welds and joints. The monitoring section is located at 1 / 3 of the span between the two supports, where stress distribution is uniform and installation is easy.

[0076] In this embodiment, the strand tension is monitored by installing a through-hole axial force gauge behind the anchor of strand 21. The gauge's center hole matches the strand 21 and is bolted to the anchor plate 233, directly measuring the axial tension of the stretched strand 21. The axial force gauge on strand 21 is integrated with the anchor assembly 23, and the outer diameter of the axial force gauge matches the size of the anchor plate 233, ensuring no disruption to the strand 21 tensioning process.

[0077] The strain gauges and axial force gauges are connected to the distributed data acquisition instrument at the edge of the foundation pit through shielded twisted pair cables, and the RS485 communication protocol is used for signal transmission to ensure anti-interference and long-distance transmission stability.

[0078] In this embodiment, the laser rangefinder uses a phase-type laser rangefinder, and its measurement accuracy can meet the needs of monitoring the horizontal displacement of the foundation pit crown beam. The laser rangefinder is fixed to the side of the crown beam 6 by an L-shaped bracket. 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 set intervals along the length of the crown beam 6 to form a linear monitoring network that covers the main deformation area of ​​the foundation pit.

[0079] In the exemplary embodiment described above, the excavation support system integrates a steel pipe support compression system and a steel strand tension system, capable of simultaneously bearing tensile and compressive loads and adapting to the alternating tension and compression conditions of the excavation support components. Combined with through-hole jacks and anchor assemblies, it effectively applies prestress, and sensors and laser rangefinders monitor internal forces and displacements in real time, enhancing structural stability and reducing the risk of safety incidents such as support falls.

[0080] Example 3:

[0081] See attached Figures 1 to 5 , gives a schematic embodiment of the prestressed node structure of the tensile and compressive support system for foundation pits proposed in the present invention, and the prestressed node structure of the tensile and compressive support system for foundation pits includes an embedded plate 111, a fixed plate 112 and a clamp 113.

[0082] 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 bar 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 bar 4. A central 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 and the fixed plate 112 are welded together into one piece, 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 constrain the end of the steel pipe support 12 to move up, down, left and right.

[0083] In this embodiment, the prestressed node structure also includes an elastic locking device, which is provided at the bolt connection between the fixed portion and the adjustable portion of the clamp. This device prevents the bolts from loosening due to foundation pit vibration or stress cycling, further reducing the risk of the steel pipe support 12 falling off. Specifically, the elastic locking device can be a spring washer, a lock nut, or a wedge-shaped block, which can achieve self-tightening fixation and improve the stability of the support system under complex working conditions.

[0084] In this embodiment, the non-threaded section 41 of the anchor bar 4 can be anchored with a ribbed barb structure or chemical anchor bolts 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, replacing traditional flat welding to improve the pullout resistance of the joint.

[0085] Technical effect: In soft soil or high water level foundation pits, the pull-out resistance of the nodes is enhanced, the displacement of the embedded plates due to excessive lateral pressure of the soil is avoided, and the overall stability of the support system is ensured.

[0086] In the above-described exemplary embodiment, the prestressed node structure of the tensile and compressive support system for foundation pits utilizes embedded plates, fixed plates, and clamps, securely installed through embedded rebar and bolt connections. The clamps effectively restrain the ends of the steel pipe supports, preventing them from falling. This simple structure allows for easy installation and disassembly. Concrete corbels are eliminated, replaced by extended piston rods of through-hole jacks, simplifying the construction process, saving time and costs. It also facilitates the passage of steel strands and ensures smooth prestressing.

[0087] 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.

[0088] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the same. Although the present invention has been described in detail with reference to preferred embodiments, persons skilled in the art should understand that the specific implementation methods of the present invention may still be modified or some technical features may be replaced by equivalents without departing from the spirit of the technical solutions of the present invention, and all of these should fall within the scope of the technical solutions claimed for protection by the present invention.

Claims

1. A tensile and compressible support system for foundation pit, characterized in that: include: The steel pipe support pressure system is arranged in the foundation pit and includes: A prestressed node structure, comprising an embedded plate, a fixed plate and a clamp; A steel pipe support, wherein the steel pipe support is fixed between the prestressed node structures by the clamp; A first through-type jack is placed in the clamping clamp and is used to lift the steel pipe support to apply compressive stress; A steel strand tensioning system, comprising: Steel strands, the steel strands being passed through the prestressed node structure, the first through-type jack and the steel pipe support; a second through-type jack, wherein the second through-type jack is arranged outside the foundation pit and is passed through the steel strand; An 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 and apply tensile stress; In which, the anchor assembly includes at least three pads stacked in sequence, a first clamp, an anchor plate, a clip and a second clamp; the first clamp is arranged between the at least three pads stacked in sequence 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 wall is provided with a tooth pattern matching the outer surface of the steel strand; the at least three pads stacked in sequence are square plate-shaped pads, and the size decreases in sequence, and the smaller pads are stacked close to the anchor plate to disperse the local stress when the steel strand is tensioned.

2. The tensile and compressible support system for foundation pit according to claim 1, characterized in that: In the prestressed node structure: the embedded plate is welded with embedded steel bars, and the embedded steel bars include a non-threaded section for fixing to the crown beam and a threaded section for connection; the fixed plate is connected to the embedded plate by bolts and the threaded section of the embedded steel bars, and a center hole for the steel strand to pass through is opened between the fixed plate and the embedded plate; the hoop clamp includes a hoop clamp fixing part and a hoop clamp adjustable part, the hoop clamp fixing part is welded to the fixed plate as one piece, and the hoop clamp adjustable part is locked with the hoop clamp fixing part by bolts to fix the end of the steel pipe support.

3. The tensile and compressible support system for foundation pit according to claim 2, characterized in that: 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.

4. The tensile and compressible support system for foundation pit according to claim 2, characterized in that: The fixing plate is provided with mounting holes corresponding to the embedded reinforcement bars of the embedded plate.

5. The tensile and compressible support system for foundation pit according to claim 1, characterized in that: It 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.

6. A construction method of a tensile and compressible support system for a foundation pit, using the tensile and compressible support system for a foundation pit according to claim 3, characterized in that: The construction method comprises the following steps: S1. Preparation steps: construct retaining piles and columns, excavate the foundation pit to the construction working surface, pour the cushion layer at the crown beam pouring position and tie the crown beam reinforcement, and insert the embedded sleeve into the crown beam reinforcement; 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 reinforcement, pour the crown beam concrete and cure to the design strength; S3, prestressed node structure installation steps: bolt the fixing plate to the embedded plate through the threaded section of the embedded reinforcement, weld a clamp fixing portion on the fixing plate, and place a first through-type jack on the clamp fixing portion; S4. Steel pipe support installation steps: Hoist the steel pipe support to the fixed part of the clamp clamp, then merge the adjustable part of the clamp clamp into the fixed part of the clamp clamp and tighten it with bolts. 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. Insert the spacer, 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 design compressive stress value, and then the second through-type jack is lifted to tension the steel strand to the design tensile stress value; S7. Internal force monitoring steps: monitor the steel strand tension and steel pipe support pressure, and adjust the ratio of the steel strand tension and steel pipe support pressure according to the direction of soil pressure.

7. The construction method of the tensile and compressible support system for foundation pit according to claim 6, 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 lifted 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 synchronously tensioned to F1 to prevent the steel strand from loosening and failing. The first through-type jack continues to lift and 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), where n1 is the proportional coefficient of steel strand tension and steel pipe support pressure, and λ1 is the proportional coefficient of soil pressure and steel pipe support pressure.

8. The construction method of the tensile and compressible support system for foundation pit according to claim 7, 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.

9. The construction method of the tensile and compressible support system for foundation pit according to claim 6, characterized in that: During the steel strand installation step, the reserved length of the steel strand is determined based on the predicted value of foundation pit deformation, and steel strands are reserved outside the foundation pit for secondary tensioning.

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