Cantilever type foundation pit supporting device capable of actively controlling side wall deformation and construction method

Abstract

The invention belongs to the technical field of foundation pit supporting, and particularly relates to a cantilever type foundation pit supporting device capable of actively controlling side wall deformation, which comprises a section steel supporting pile inserted in a preset cement soil pile; the prestressed reinforcement assembly comprises at least two prestressed reinforcements, the prestressed reinforcements are distributed on the tension side of the profile steel support pile and are symmetrically arranged with a web of the profile steel support pile as the symmetry axis, one end of each prestressed reinforcement is anchored to the profile steel support pile through a fixing component, and the other end of each prestressed reinforcement extends out of the top end of the profile steel support pile by a certain length. The structural steel supporting piles and the cement soil piles are cooperatively borne, and the symmetrically-arranged prestressed reinforcement assemblies, real-time strain monitoring and the design of the active tensioning system are combined, so that active control over deformation of the side wall of the foundation pit is achieved.

Description

Technical Field

[0001] This invention belongs to the field of foundation pit support technology, and particularly relates to a cantilever foundation pit support device for actively controlling sidewall deformation. Background Technology

[0002] Foundation pit engineering is a fundamental construction phase in fields such as building construction and municipal engineering. Its core requirement is to use support structures to resist the lateral earth pressure generated during foundation pit excavation, preventing excessive deformation or instability of the foundation pit sidewalls, thereby ensuring the safety of surrounding buildings, underground pipelines, and construction personnel. Among existing foundation pit support technologies, pile walls, diaphragm walls, and sheet piles are the most widely used support structure forms. The working principle of these structures relies on their own stiffness and strength to passively resist the action of earth pressure—the support force is only gradually generated after the retaining structure deforms under the action of earth pressure, which is a typical "passive force bearing" mode.

[0003] To control the deformation of the foundation pit sidewalls within allowable limits, existing technologies typically employ methods such as increasing the diameter of the support piles, thickening the wall, or increasing the number of internal supports and anchor bolts to enhance structural stiffness. However, this design approach has significant drawbacks: on the one hand, the stiffness design of the support structure needs to reserve sufficient redundancy for the most unfavorable working conditions during the foundation pit excavation process, leading to a substantial increase in the amount of engineering materials used and a significant rise in construction costs, resulting in a double waste of resources and economy; on the other hand, fixed structural stiffness cannot adapt to the dynamic changes in soil pressure distribution at different stages of foundation pit excavation (such as shallow excavation and deep excavation), making it difficult to achieve targeted deformation control, resulting in a contradiction between excessive stiffness in some areas and insufficient stiffness in key parts.

[0004] Meanwhile, deformation monitoring and stress control of existing foundation pit projects are separate and lack a linkage mechanism. Currently used deformation monitoring methods (such as inclinometers and total stations) require manual deployment of monitoring points and periodic data collection, resulting in significant lags in data analysis and feedback. When monitoring data shows excessive deformation of the foundation pit sidewalls, irreversible structural deformation or soil displacement has often already occurred. At this point, only passive remedial measures such as temporary support and grouting reinforcement can be taken. These remedial measures are not only difficult and costly to implement, but also have limited effectiveness in improving the stability of the foundation pit, failing to fundamentally curb deformation development and resulting in consistently high safety risks during foundation pit construction.

[0005] In addition, existing support technologies lack the ability to dynamically adjust the control of foundation pit deformation. Once the support structure is completed, its stress characteristics remain fixed and cannot be actively adjusted according to the deformation data monitored in real time. This makes it difficult to adapt to the deformation control requirements under complex geological conditions and variable construction conditions.

[0006] In summary, existing foundation pit support technologies suffer from prominent problems such as limited support stiffness, significant waste of materials and resources, disconnect between monitoring and control, and passive risk response. There is an urgent need for a foundation pit support device and construction method that can combine real-time monitoring and active control and flexibly adjust the support force to solve the above-mentioned technical bottlenecks. Summary of the Invention

[0007] The purpose of this invention is to address the aforementioned technical problems by providing a cantilevered foundation pit support device that actively controls sidewall deformation.

[0008] In view of this, the present invention provides a cantilever foundation pit support device for actively controlling sidewall deformation, comprising: Steel support piles are inserted into pre-set cement-soil piles; A prestressed steel reinforcement assembly includes at least two prestressed steel bars, which are arranged on the tension side of the steel support pile and symmetrically arranged with the web of the steel support pile as the axis of symmetry. One end of the prestressed steel bar is anchored to the steel support pile through a fixing member, and the other end extends a certain length beyond the top of the steel support pile. An end plate is fixed to the top of the steel support pile. The end plate is perpendicular to the prestressed steel bar and has a pre-reserved opening for the prestressed steel bar to pass through. The strain monitoring component includes multiple strain sensors, which are arranged on the outer surface of the tension side flange of the steel support pile at intervals along the height direction of the steel support pile. The strain sensors are connected to the central controller for signal transmission. The active tensioning assembly includes an electromagnetic fixing clamp, a hydraulic tensioning jack, and a hydraulic oil pump. The electromagnetic fixing clamp and the hydraulic tensioning jack are installed on the prestressed steel bars extending from the top of the steel support pile. The hydraulic tensioning jack is connected to the hydraulic oil pump via an oil circuit. The hydraulic oil pump and the electromagnetic fixing clamp are respectively connected to the central controller via signals. The hydraulic tensioning jack is connected to the end plate via a reaction frame to provide tensioning reaction force.

[0009] Furthermore, the two prestressed steel bars are spaced 10-15cm apart and 5-10cm away from the wing plate of the steel support pile; the lower end of one prestressed steel bar is anchored at the depth of the steel support pile, and the lower end of the other prestressed steel bar is anchored at 1 / 2 of the excavation depth of the foundation pit, and the length of the prestressed steel bar extending beyond the top of the steel support pile is 0.8-1.2m.

[0010] Furthermore, the end plate is made of steel and is fixed to the steel support pile by welding or riveting.

[0011] Furthermore, a protective sleeve is provided at the location where the prestressed steel reinforcement passes through the capping beam of the steel support pile to avoid the steel support pile capping beam constraining the prestressed steel reinforcement.

[0012] Furthermore, the strain sensors are arranged at intervals of 0.3 to 0.5 meters from the top of the steel support pile, and communicate with the central controller via a wired connection.

[0013] Furthermore, the preset displacement control value in the central controller is 0.7 to 0.85 times the displacement alarm value of the pit sidewall.

[0014] A construction method for cantilever foundation pit support with active control of sidewall deformation, applied to a cantilever foundation pit support device with active control of sidewall deformation, includes the following steps: S1: A prestressed steel bar assembly and a strain monitoring assembly are installed on the steel profile. One end of the prestressed steel bar of the prestressed steel bar assembly is anchored to the steel profile, and the other end extends a certain length from the top of the steel profile. The strain sensors are installed at intervals along the height direction of the tension side of the steel profile. S2: Construct cement-soil piles in the designed foundation pit support area. Before the cement-soil pile material initially sets, insert the steel profiles processed in step S1 into the cement-soil piles and wait for the cement-soil piles to cure and solidify. S3: Install electromagnetic fixing clips and hydraulic tensioning jacks sequentially on the prestressed steel bars extending from the top of the steel profile. Connect the hydraulic tensioning jacks to the hydraulic oil pump through the oil circuit. Connect the hydraulic oil pump, electromagnetic fixing clips, and strain sensors to the central controller through signal lines. Debug the control system and set the displacement control value of the pit sidewall in the central controller. S4: Excavation of the foundation pit is carried out. The central controller collects the monitoring data of the strain sensor in real time and calculates the maximum displacement of the foundation pit sidewall through a preset algorithm. S5: When the calculated displacement of the foundation pit sidewall approaches the preset threshold, the central controller controls the hydraulic oil pump to start, driving the hydraulic tensioning jack to apply a predetermined tension to the prestressed steel bars. At the same time, it controls the electromagnetic fixing clamps to lock the prestressed steel bars, generating a bending moment inside the steel section in the opposite direction to the earth pressure, thus counteracting the earth pressure. S6: During the foundation pit construction, the tension of the prestressed steel bars is dynamically adjusted based on the real-time feedback data from the strain sensor until the foundation pit construction is completed. S7: After the construction is completed, the tension in the prestressed steel bars is removed, and then the steel sections are pulled out and recycled. In step S4, the signal transmission interval of the strain sensor is 10~30s.

[0015] Furthermore, in step S5, the bending moment generated by the initial tension force is 0.5 times the maximum bending moment inside the steel section under earth pressure. The initial tension force is determined based on the elastic modulus of the steel section, the maximum strain value measured by the strain sensor, the moment of inertia of the steel section, and the prestressed steel reinforcement placement parameters.

[0016] Furthermore, in step S6, if the displacement of the pit sidewall does not recover below the control value after initial tensioning, the tension force is gradually increased by 10% to 15% until the displacement meets the requirements.

[0017] Furthermore, in step S6, when the excavation depth of the foundation pit is less than 1 / 2 of the designed excavation depth, only the prestressed steel bars anchored at 1 / 2 of the excavation depth at the lower end are tensioned; when the excavation depth of the foundation pit is greater than 1 / 2 of the designed excavation depth, only the prestressed steel bars anchored at the lower end at the excavation depth of the foundation pit are tensioned, or both prestressed steel bars are tensioned simultaneously.

[0018] The beneficial effects of this invention are: This application utilizes the synergistic bearing capacity of steel-supported piles and cement-soil piles, combined with symmetrically arranged prestressed steel reinforcement components, real-time strain monitoring, and an active tensioning system to achieve active control of the deformation of the foundation pit sidewalls. Specifically: Prestressed steel bars are symmetrically arranged on the tension side of the steel section. They can generate a reverse bending moment through active tensioning, accurately offset the earth pressure, significantly suppress the lateral deformation of the steel support piles, and improve the stability and bearing capacity of the foundation pit support structure. Strain sensors are spaced along the height of the steel profile and work with the central controller to collect stress data in real time, providing accurate data for active tensioning, realizing dynamic feedback control of deformation, and avoiding excessive deformation or failure of the support structure. The combination design of electromagnetic fixing clamps and hydraulic tensioning jacks can quickly respond to control commands, making tensioning operation convenient and highly controllable. The cooperation between the reaction frame and the end plate ensures stable transmission of tension reaction force, further improving the reliability of the support effect. The overall structure is highly integrated, and the components work together. It retains the advantages of convenient construction of cantilever support, while making up for the shortcomings of traditional cantilever support in passively bearing loads and weak deformation control. It is suitable for a variety of foundation pit excavation scenarios. Attached Figure Description

[0019] Figure 1 This is a first-view structural schematic diagram of a cantilever foundation pit support device for actively controlling sidewall deformation proposed in this invention. Figure 2 This is a second-view structural schematic diagram of a cantilever foundation pit support device for actively controlling sidewall deformation proposed in this invention. Figure 3 This is a schematic diagram of the signal connection of the central controller of a cantilever foundation pit support device for actively controlling sidewall deformation proposed in this invention.

[0020] The markings in the diagram are as follows: 1. Steel support piles; 2. Prestressed steel bars; 4. Strain sensors; 5. Anchor ends; 6. End plates; 7. Electromagnetic fixing clips; 8. Hydraulic tensioning jacks; 9. Reaction frames; 10. Hydraulic oil pumps; 11. Central controllers. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0022] In the description of this application, it should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. For ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following drawings denote similar items; therefore, once an item is defined in one drawing, it need not be further discussed in subsequent drawings.

[0023] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and are not limited in number; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0024] It should be noted that in the description of this application, the directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this application. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0025] It should be noted that, in this application, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0026] Reference Figures 1 to 3 A cantilever foundation pit support device for actively controlling sidewall deformation, comprising: Steel support pile 1 is inserted into a pre-set cement-soil pile, wherein the cement-soil pile is a cement-soil mixing pile, an underground cement-soil continuous wall, or a fluidized solidified soil grouting pile. The prestressed steel bar 2 assembly includes at least two prestressed steel bars 2. The prestressed steel bars 2 are arranged on the tension side of the steel support pile 1 and are symmetrically arranged with the web of the steel support pile 1 as the axis of symmetry. One end of the prestressed steel bar 2 is anchored to the steel support pile 1 through a fixing member to form an anchor end 5, and the other end extends out of the top of the steel support pile 1 by a certain length. End plate 6 is fixed to the top of steel support pile 1. The end plate 6 is perpendicular to the prestressed steel bar 2 and has a reserved opening for the prestressed steel bar 2 to pass through. The strain monitoring component includes multiple strain sensors 4, which are arranged on the outer surface of the tension side flange of the steel support pile 1 and spaced apart along the height direction of the steel support pile 1. The strain sensors 4 are connected to the central controller 11 via signal. The active tensioning assembly includes an electromagnetic fixing clamp 7, a hydraulic tensioning jack 8, and a hydraulic oil pump 10. The electromagnetic fixing clamp 7 and the hydraulic tensioning jack 8 are installed on the prestressed steel bars 2 at the top of the protruding steel support pile 1. The hydraulic tensioning jack 8 is connected to the hydraulic oil pump 10 through an oil circuit. The hydraulic oil pump 10 and the electromagnetic fixing clamp 7 are respectively connected to the central controller 11 via signals. The hydraulic tensioning jack 8 is connected to the end plate 6 through a reaction frame 9 to provide tensioning reaction force.

[0027] This application utilizes the collaborative bearing capacity of steel support piles 1 and cement-soil piles, combined with the design of symmetrically arranged prestressed steel reinforcement 2 components, real-time strain monitoring, and an active tensioning system to achieve active control of the deformation of the foundation pit sidewalls, wherein: The prestressed steel bars 2 are symmetrically arranged on the tension side of the steel section. They can generate a reverse bending moment through active tensioning, accurately offset the earth pressure, significantly suppress the lateral deformation of the steel support piles 1, and improve the stability and bearing capacity of the foundation pit support structure. Strain sensors 4 are spaced along the height of the steel section and work with the central controller 11 to collect stress data in real time, providing accurate basis for active tensioning, realizing dynamic feedback control of deformation, and avoiding excessive deformation or failure of the support structure. The combination design of electromagnetic fixing clamp 7 and hydraulic tensioning jack 8 can quickly respond to control commands, making tensioning operation convenient and highly controllable. The cooperation between reaction frame 9 and end plate 6 ensures stable transmission of tensioning reaction force, further improving the reliability of support effect. The overall structure is highly integrated, and the components work together. It retains the advantages of convenient construction of cantilever support, while making up for the shortcomings of traditional cantilever support in passively bearing loads and weak deformation control. It is suitable for a variety of foundation pit excavation scenarios.

[0028] In the example of this application, the two prestressed steel bars 2 are spaced 10-15cm apart and 5-10cm away from the wing plate of the steel support pile 1; the lower end of one prestressed steel bar 2 is anchored at the depth of the steel support pile 1, and the lower end of the other prestressed steel bar 2 is anchored at 1 / 2 of the excavation depth of the foundation pit, and the length of the prestressed steel bar 2 extending out of the top of the steel support pile 1 is 0.8-1.2m.

[0029] As a preferred example of the present invention, the spacing of 10~15cm and the wing plate distance of 5~10cm are designed to ensure that the prestressed steel bars 2 are subjected to balanced forces, avoid local stress concentration, and improve the rationality of the stress on the tension side of the steel support pile 1. Two prestressed steel bars 2 are anchored at the depth of the steel section and at 1 / 2 of the excavation depth of the foundation pit, respectively, forming a graded bearing system. This system can accurately exert the tensioning effect according to the soil pressure distribution characteristics at different stages of foundation pit excavation, thereby enhancing the flexibility of deformation control. The extension length design of 0.8~1.2m not only meets the installation and operation space requirements of the hydraulic tensioning jack 8, but also avoids material waste or unstable force caused by excessive extension, thus balancing construction convenience and structural economy.

[0030] In the example of this application, the end plate 6 is made of steel and is fixed to the steel support pile 1 by welding or riveting.

[0031] As a preferred example of the present invention, the steel end plate 6 has high strength and high rigidity, which can effectively withstand the tensioning reaction force of the hydraulic tensioning jack 8, avoid deformation or damage of the end plate 6, and ensure the stability and reliability of the tensioning process. Welding or riveting provides a strong and well-sealed connection that can withstand long-term loads without loosening, thus improving the structural durability and service life of the support device. The fixed connection between the end plate 6 and the steel support pile 1 enables the tension reaction force to be evenly transmitted to the main body of the steel section, avoiding damage to the steel section caused by excessive local stress and ensuring the effective realization of the active tensioning function.

[0032] In the example of this application, a protective sleeve is provided at the location where the prestressed steel bar 2 passes through the capping beam of the steel support pile 1, in order to avoid the constraint of the capping beam of the steel support pile 1 on the prestressed steel bar 2.

[0033] As a preferred example of the present invention, the casing can isolate the cap beam and the prestressed steel bar 2, avoid the lateral constraint on the steel bar after the cap beam concrete hardens, ensure that the prestressed steel bar 2 can deform freely when tensioned, ensure that the tension force is accurately transmitted to the steel support pile 1, and give full play to the effect of active deformation control. To prevent damage to the reinforcing bars due to friction or compression between the capping beam and the reinforcing bars, improve the service life and stress safety of the prestressed reinforcing bars 2, and at the same time avoid cracks in the capping beam due to deformation of the reinforcing bars, thus ensuring the overall stability of the support structure.

[0034] In the example of this application, the strain sensor 4 is arranged at intervals of 0.3~0.5m starting from the top of the steel support pile 1, and communicates with the central controller 11 by wired connection.

[0035] As a preferred example of the present invention, the 0.3~0.5m interval layout design can fully cover the key stress area on the tension side of the steel support pile 1, collect strain data at different height positions in real time, ensure the comprehensiveness and accuracy of the monitoring results, and provide complete force feedback for the central controller 11. Wired connection provides stable signal transmission and strong anti-interference capabilities, avoiding signal delays or loss issues that may occur with wireless transmission. It ensures real-time and reliable transmission of strain data, providing a guarantee for timely response to active tensioning and improving the accuracy of deformation control.

[0036] In the example of this application, the preset displacement control value in the central controller 11 is 0.7 to 0.85 times the displacement alarm value of the pit sidewall.

[0037] As a preferred example of the present invention, the central controller 11 presets the displacement control value to be 0.7 to 0.85 times the alarm value, which can trigger the active tensioning operation in advance, avoid the displacement of the foundation pit sidewall approaching or reaching the alarm value, realize early intervention from warning to control, effectively prevent excessive deformation of the support structure, reduce the risk of foundation pit collapse, and improve construction safety. The reasonable range design of the control value takes into account both the safety reserve and economy of the support structure, avoids over-tensioning (waste of energy) due to excessively high control values ​​or control failure due to excessively low control values, and achieves the optimal balance of deformation control. A construction method for cantilever foundation pit support with active control of sidewall deformation, applied to a cantilever foundation pit support device with active control of sidewall deformation, includes the following steps: S1: A prestressed steel bar 2 assembly and a strain monitoring assembly are installed on the steel profile. One end of the prestressed steel bar 2 assembly is anchored to the steel profile, and the other end extends a certain length from the top of the steel profile. The strain sensors 4 are installed at intervals along the height direction of the tension side of the steel profile. S2: Construct cement-soil piles in the designed foundation pit support area. Before the cement-soil pile material initially sets, insert the steel profiles processed in step S1 into the cement-soil piles and wait for the cement-soil piles to cure and solidify. S3: Install electromagnetic fixing clips 7 and hydraulic tensioning jacks 8 sequentially on the prestressed steel bars 2 extending from the top of the steel profile. Connect the hydraulic tensioning jacks 8 to the hydraulic oil pump 10 through an oil circuit. Connect the hydraulic oil pump 10, electromagnetic fixing clips 7 and strain sensors 4 to the central controller 11 through signal lines. Debug the control system and set the pit sidewall displacement control value in the central controller 11. S4: Excavation of the foundation pit is carried out. The central controller 11 collects the monitoring data of the strain sensor 4 in real time and calculates the maximum displacement of the foundation pit sidewall through a preset algorithm. S5: When the calculated displacement of the foundation pit sidewall approaches the preset threshold, the central controller 11 controls the hydraulic oil pump 10 to start, driving the hydraulic tensioning jack 8 to apply a predetermined tension to the prestressed steel bar 2, and simultaneously controls the electromagnetic fixing clamp 7 to lock the prestressed steel bar 2, generating a bending moment inside the steel bar in the opposite direction to the earth pressure, thus counteracting the earth pressure effect; S6: During the foundation pit construction process, the tension of the prestressed steel bar 2 is dynamically adjusted according to the real-time feedback data of the strain sensor 4 until the foundation pit construction is completed; S7: After the construction is completed, the tension in the prestressed steel bar 2 is released, and then the steel section is pulled out and recycled. In step S4, the signal transmission interval of the strain sensor 4 is 10~30s.

[0038] Based on the sensor signals, the maximum displacement of the pit sidewall was calculated using the following method: In the formula: s max denoted as , where is the maximum displacement of steel support pile 1 (mm); E is the elastic modulus of steel support pile 1 (Pa). I is the strain value measured by the i-th strain sensor 4 from the top of the steel support pile 1 downwards; I is the moment of inertia (mm) of the cross-section of the steel support pile 1 about the neutral axis. 4 ); d is the height of the web of the steel section (mm); hi is the distance (m) from the top of the i-th strain sensor 4 downward from the top of the steel support pile 1; α is the empirical value of displacement correction, which takes the value of 0.95~1.1; When the displacement of the pit sidewall exceeds the preset value, the central controller 11 sends a signal to the hydraulic oil pump 10, which tensions the steel bars through the hydraulic tensioning jack 8, generating a bending moment inside the steel support pile 1, causing the steel support pile 1 to deform away from the excavation side of the pit, thus offsetting the deformation caused by the earth pressure and reducing the displacement of the pit sidewall.

[0039] The bending moment generated by the initial tension force is 0.5 times the maximum bending moment within the steel retaining pile 1 under earth pressure, and is determined as follows: Where: T is the initial tension force, and E is the elastic modulus (Pa) of the steel support pile 1. I represents the maximum strain value measured by strain sensor 4; I is the moment of inertia (mm) of the steel section about the neutral axis. 4 ); d is the web height of steel retaining pile 1 (mm); d s The distance (mm) from the center of the reinforcing bar to the flange of the steel section. The foundation pit support construction method in this application has a clear overall construction process. The components are laid out first and then the steel is inserted. The equipment installation and commissioning are carried out simultaneously, which shortens the construction cycle and improves construction efficiency. During the excavation of the foundation pit, strain data is monitored in real time, and the maximum displacement is calculated through algorithms to realize dynamic monitoring of deformation and active tension linkage, so as to timely counteract the earth pressure, effectively control the deformation of the sidewall, and ensure the safety of the foundation pit and the surrounding environment. After tensioning is completed, the tension force is dynamically adjusted based on real-time feedback to adapt to the stress changes at different stages of foundation pit excavation, thereby improving the adaptability and reliability of the support effect. The recyclable steel sections after the project is completed enable resource reuse, reduce construction costs, and reduce construction waste, which is in line with the concept of green construction. The 10-30s signal transmission interval design ensures real-time updates of monitoring data, providing timely basis for tension adjustment and avoiding deformation accumulation. In the example of this application, in step S5, the bending moment generated by the initial tension force is 0.5 times the maximum bending moment inside the steel section under earth pressure. The initial tension force is determined based on the elastic modulus of the steel section, the maximum strain value measured by the strain sensor 4, the moment of inertia of the steel section, and the layout parameters of the prestressed steel bars 2.

[0040] As a preferred example of the present invention, the bending moment generated by the initial tension force is 0.5 times the maximum bending moment of the earth pressure, which can effectively offset the effect of the initial earth pressure, avoid excessive initial deformation of the support structure, and lay the foundation for subsequent dynamic adjustment. The initial tension force is determined based on parameters such as the elastic modulus of the steel section, the maximum strain value, the moment of inertia of the section, and the location of the reinforcing bars. This ensures accurate tension force calculation, avoids insufficient tension (inability to effectively control deformation) or excessive tension (leading to damage to the steel section under pressure), and improves the scientificity and reliability of active control.

[0041] In the example of this application, in step S6, when the displacement of the pit sidewall after initial tensioning does not recover to below the control value, the tensioning force is gradually increased by 10% to 15% until the displacement meets the requirements.

[0042] As a preferred example of the present invention, the tension force is gradually increased by 10% to 15%, which can avoid the sudden change in the stress of the support structure caused by a one-time increase in the tension force, prevent the steel support pile 1 or the prestressed steel bar 2 from being damaged due to excessive instantaneous load, and improve the structural stress safety. The gradual adjustment method can adapt to the deformation situation in real time according to the displacement feedback, ensuring that the displacement is stably restored to below the control value, avoiding displacement rebound, improving the stability and accuracy of deformation control, and making the operation flexible and highly controllable. In the example of this application, in step S6, when the excavation depth of the foundation pit is less than 1 / 2 of the designed excavation depth, only the prestressed steel bars 2 anchored at 1 / 2 of the excavation depth of the foundation pit are tensioned; when the excavation depth of the foundation pit is greater than 1 / 2 of the designed excavation depth, only the prestressed steel bars 2 anchored at 1 / 2 of the excavation depth of the foundation pit are tensioned, or both prestressed steel bars 2 are tensioned at the same time.

[0043] As a preferred example of the present invention, the prestressed steel bars 2 are selected for tensioning according to the excavation depth of the foundation pit, realizing graded tensioning control. When the excavation depth is less than 1 / 2, only the lower anchored steel bars are tensioned. When it is greater than 1 / 2, single or double steel bars are selectively tensioned. Tensioning force is applied as needed to avoid unnecessary tensioning operations and save energy consumption and construction costs. The force is precisely applied according to the soil pressure distribution characteristics of different excavation depths to ensure that the tensioning effect is highly targeted, effectively counteracting the soil pressure at the corresponding depth, avoiding excessive local deformation, and improving the stress rationality and deformation control efficiency of the support structure.

[0044] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A cantilever foundation pit support device for actively controlling sidewall deformation, characterized in that, include: Steel support piles (1) are inserted into pre-set cement-soil piles; The prestressed steel bar (2) assembly includes at least two prestressed steel bars (2), which are arranged on the tension side of the steel support pile (1) and symmetrically arranged with the web of the steel support pile (1) as the axis of symmetry. One end of the prestressed steel bar (2) is anchored to the steel support pile (1) through a fixing member, and the other end extends a certain length beyond the top of the steel support pile (1). End plate (6) is fixed to the top of the steel support pile (1). The end plate (6) is perpendicular to the prestressed steel bar (2) and has a reserved opening for the prestressed steel bar (2) to pass through. The strain monitoring component includes multiple strain sensors (4), which are arranged on the outer surface of the tension side flange of the steel support pile (1) and spaced apart along the height direction of the steel support pile (1). The strain sensors (4) are connected to the central controller (11) via signal. The active tensioning assembly includes an electromagnetic fixing clamp (7), a hydraulic tensioning jack (8), and a hydraulic oil pump (10). The electromagnetic fixing clamp (7) and the hydraulic tensioning jack (8) are installed on the prestressed steel bars (2) at the top of the protruding steel support pile (1). The hydraulic tensioning jack (8) is connected to the hydraulic oil pump (10) through an oil circuit. The hydraulic oil pump (10) and the electromagnetic fixing clamp (7) are respectively connected to the central controller (11) via signals. The hydraulic tensioning jack (8) is connected to the end plate (6) through a reaction frame (9) to provide tensioning reaction force.

2. The cantilever foundation pit support device for actively controlling sidewall deformation according to claim 1, characterized in that, The two prestressed steel bars (2) are spaced 10-15cm apart and 5-10cm away from the wing plate of the steel support pile (1); the lower end of one prestressed steel bar (2) is anchored at the depth of the steel support pile (1), and the lower end of the other prestressed steel bar (2) is anchored at 1 / 2 of the excavation depth of the foundation pit. The length of the prestressed steel bar (2) extending out of the top of the steel support pile (1) is 0.8-1.2m.

3. The cantilever foundation pit support device for actively controlling sidewall deformation according to claim 1, characterized in that, The end plate (6) is made of steel and is fixed to the steel support pile (1) by welding or riveting.

4. The cantilever foundation pit support device for actively controlling sidewall deformation according to claim 1, characterized in that, A protective sleeve is provided at the location where the prestressed steel bar (2) passes through the cap beam of the steel support pile (1) to avoid the constraint of the cap beam of the steel support pile (1) on the prestressed steel bar (2).

5. The cantilever foundation pit support device for actively controlling sidewall deformation according to claim 1, characterized in that, The strain sensors (4) are installed at intervals of 0.3 to 0.5 m from the top of the steel support pile (1) and communicate with the central controller (11) via wired connection.

6. The cantilever foundation pit support device for actively controlling sidewall deformation according to claim 1, characterized in that, The preset displacement control value in the central controller (11) is 0.7 to 0.85 times the displacement alarm value of the pit sidewall.

7. A construction method for cantilever foundation pit support with active control of sidewall deformation, applied to the cantilever foundation pit support device with active control of sidewall deformation as described in any one of claims 1, characterized in that, Includes the following steps: S1: A prestressed steel bar (2) assembly and a strain monitoring assembly are installed on the steel profile. One end of the prestressed steel bar (2) assembly is anchored to the steel profile, and the other end extends a certain length from the top of the steel profile. The strain sensors (4) are installed at intervals along the height direction of the tension side of the steel profile. S2: Construct cement-soil piles in the designed foundation pit support area. Before the cement-soil pile material initially sets, insert the steel profiles processed in step S1 into the cement-soil piles and wait for the cement-soil piles to cure and solidify. S3: Install electromagnetic fixing clips (7) and hydraulic tensioning jacks (8) sequentially on the prestressed steel bars (2) extending from the top of the steel profile. Connect the hydraulic tensioning jacks (8) to the hydraulic oil pump (10) through the oil circuit. Connect the hydraulic oil pump (10), electromagnetic fixing clips (7) and strain sensors (4) to the central controller (11) through signal lines. Debug the control system and set the displacement control value of the pit sidewall in the central controller (11). S4: Excavation of the foundation pit is carried out. The central controller (11) collects the monitoring data of the strain sensor (4) in real time and calculates the maximum displacement of the foundation pit sidewall through the preset algorithm. S5: When the calculated displacement of the pit sidewall is close to the preset threshold, the central controller (11) controls the hydraulic oil pump (10) to start, drives the hydraulic tensioning jack (8) to apply a predetermined tension to the prestressed steel bar (2), and controls the electromagnetic fixing clamp (7) to lock the prestressed steel bar (2), generating a bending moment inside the steel bar that is opposite to the direction of the earth pressure, thus counteracting the earth pressure. S6: During the construction of the foundation pit, the tension of the prestressed steel bars (2) is dynamically adjusted according to the real-time feedback data of the strain sensor (4) until the foundation pit construction is completed; S7: After the construction is completed, the tension in the prestressed steel bars (2) is removed, and the steel is pulled out and recycled. In step S4, the signal transmission interval of the strain sensor (4) is 10~30s.

8. The cantilever foundation pit support construction method for actively controlling sidewall deformation according to claim 7, characterized in that, In step S5, the bending moment generated by the initial tension force is 0.5 times the maximum bending moment inside the steel section under the action of earth pressure. The initial tension force is determined based on the elastic modulus of the steel section, the maximum strain value measured by the strain sensor (4), the moment of inertia of the steel section and the layout parameters of the prestressed steel bars (2).

9. The cantilever foundation pit support construction method for actively controlling sidewall deformation according to claim 7, characterized in that, In step S6, if the displacement of the pit sidewall does not recover below the control value after initial tensioning, the tension force is gradually increased by 10% to 15% until the displacement meets the requirements.

10. The cantilever foundation pit support construction method for actively controlling sidewall deformation according to claim 7, characterized in that, In step S6, when the excavation depth of the foundation pit is less than 1 / 2 of the designed excavation depth, only the prestressed steel bars (2) anchored at 1 / 2 of the excavation depth of the foundation pit are tensioned; when the excavation depth of the foundation pit is greater than 1 / 2 of the designed excavation depth, only the prestressed steel bars (2) anchored at 1 / 2 of the excavation depth of the foundation pit are tensioned, or both prestressed steel bars (2) are tensioned at the same time.

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