Support unit element, foundation pit support structure and construction method thereof

Abstract

The application discloses a supporting unit element, which comprises an H-shaped steel, a reinforcing plate welded on the flange of the H-shaped steel, a groove opening of the H-shaped steel being closed, a containing cavity being formed between the H-shaped steel and the reinforcing plate, and concrete being cast in the containing cavity; one end of the flange of the H-shaped steel, which is away from the reinforcing plate, is formed into a connecting end, and a bolt hole is formed in the connecting end; end head plates are welded on both ends of the H-shaped steel, two groove openings of the H-shaped steel are closed towards the opening in the length direction of the H-shaped steel, and connecting holes are formed in the end head plates. The application further discloses a foundation pit supporting structure formed by the supporting unit element and a construction method of the foundation pit supporting structure. The supporting unit element has higher strength and rigidity of the structure, and can be used to conveniently manufacture combined crown beams, combined surrounding purlins, horizontal supports, supports and other foundation pit supporting components.

Description

Technical Field

[0001] This invention relates to a support unit, a foundation pit support structure using the support unit, and a construction method for the foundation pit support structure. Background Technology

[0002] To ensure safety during foundation pit construction, numerous support components are required within the pit. Most of these components are made of structural steel. However, due to the varying shapes and sizes of foundation pits and the diverse forms of the support components, significant differences exist between them. Although some support components have undergone standardized design, their proportion is low, resulting in many being single-use parts that can only be disassembled for other components or used as scrap steel after recycling. This not only wastes a large amount of steel but also increases construction costs.

[0003] As a primary support component of the foundation pit, horizontal supports often require prestressing during construction to resist the pressure of the external soil. During prestressing, two joints are installed between the horizontal support and the capping beam or waler. Jacks are used to widen the distance between the two joints, inducing prestress in the horizontal support. Steel wedges are then driven between the two joints. However, because the steel wedges are eccentrically stressed, the joints are unstable. During foundation pit construction, the steel wedges may sometimes move outwards or fall off, causing a significant reduction or loss of prestress in the horizontal support, affecting the safe construction of the foundation pit. Furthermore, due to the large rebound force when driving in the steel wedges, they may sometimes pop out, requiring re-application of prestress.

[0004] Therefore, in the existing technology, the steel wedges on the horizontal support are actually in an unstable state. When the axial force they are subjected to suddenly increases, they may pop out, causing the support to fail. In severe cases, it may lead to the collapse of the foundation pit slope. Summary of the Invention

[0005] To solve the above problems, this application first proposes a support unit, which includes an H-beam, with two opposite ends of a reinforcing plate welded to the two flanges of the H-beam facing the same end. The reinforcing plate closes the groove of a recess in the H-beam, forming a receiving cavity between the H-beam and the reinforcing plate, and concrete is poured into the receiving cavity.

[0006] The other groove of the H-beam is open. The two flanges of the H-beam are formed at the ends opposite to the reinforcing plate to form a connection end. Several bolt holes are provided at intervals along the length of the H-beam on each connection end. End plates are welded to both ends of the H-beam along its length. The end plates close the openings of the two grooves of the H-beam facing the length of the H-beam. Connection holes are provided on the end plates.

[0007] This support unit is actually a concrete reinforcement component. By utilizing the rigidity of concrete and the strength of H-beams and reinforcing plates, the strength and rigidity of the support unit are effectively improved, thereby enhancing its stability and the strength and rigidity of the structural components made from it.

[0008] This support unit can be used as a standard component. Single or multiple support units can form horizontal supports, walers, and capping beams, or serve as a replacement for H-beams. Using bolts and connecting holes on the end plates, several support units can be connected to form a longer structural member. After removing the bolts, the individual support units can be restored and reused.

[0009] By utilizing the bolt holes on the connecting ends, two parallel support units can be connected to form a structural component with higher strength. The distance between the two support units can be adjusted as needed to adapt to different working conditions. Because numerous bolt holes are pre-installed on the connecting ends, various external components can be detachably connected to the support units without the need for temporary additional drilling. Therefore, after removing the external components, the unit can be easily restored to its original state and used for other purposes without requiring further modifications to the support unit.

[0010] This support unit can be used to easily manufacture foundation pit support components such as combined cap beams, combined walers, horizontal supports, and brackets.

[0011] Secondly, this application also provides a foundation pit support structure, which includes support piles arranged along the edge of the foundation pit, and a composite capping beam arranged on the top of the support piles, the composite capping beam including an outer frame;

[0012] The outer frame is composed of several crown beam units connected in sequence. Each crown beam unit includes two crown beam unit members that extend parallel to each other in the horizontal direction and are spaced apart. The crown beam unit member is the support unit member. The reinforcing plates of the two crown beam unit members in the same crown beam unit are arranged opposite each other. The web of the crown beam unit member is arranged vertically. An upper connecting horizontal plate and a lower connecting horizontal plate are respectively installed on the upper and lower sides of the crown beam unit. The two ends of the upper connecting horizontal plate are detachably connected to the bolt holes of the upper connecting ends of the two crown beam unit members. The two ends of the lower connecting horizontal plate are detachably connected to the bolt holes of the lower connecting ends of the two crown beam unit members.

[0013] In each capping beam unit, the two capping beam components are referred to as the first component and the second component, respectively. The end plates of the first components of adjacent capping beam units are bolted together to form the first capping beam member, and the end plates of the second components of adjacent capping beam units are bolted together to form the second capping beam member. The space between the first and second capping beam members forms a casting cavity, through which the support pile passes downward. The casting cavity contains a filling block made of cast concrete, which wraps around the outer periphery of the support pile. An isolation membrane is provided between the filling block and the outer frame. The outer frame specifically includes the first capping beam member, the second capping beam member, an upper connecting horizontal plate, and a lower connecting horizontal plate.

[0014] Preferably, the two support units of the same crown beam unit have the same end face and are coplanar, which improves the convenience of assembling into an outer frame.

[0015] Preferably, no dividing elements are provided in the casting cavity, that is, the casting cavity is a through groove extending along the length direction of the composite crown beam to the end of the composite crown beam, without any dividing elements in the middle, so as to maintain the continuity of the filling block.

[0016] The isolation membrane can be made of materials such as geotextile or plastic film, or it can be formed by applying isolation paint to the surface of the cap beam component, the upper connecting plate and the lower connecting plate, and the paint film formed by the isolation paint.

[0017] The steel structural components in the existing composite capping beams all adopt a frame structure, specifically including an outer frame and dividing components such as cross braces or connecting plates set inside the outer frame. These dividing components divide the inner cavity of the outer frame into a large number of independent cavities, each cavity allowing 1-3 support piles to pass through. The dividing components can strengthen the outer frame. However, due to the different pile diameters used in different foundation pit constructions, when the recycled steel structural components are used in another composite capping beam, the dividing components need to be disassembled and reinstalled.

[0018] The outer frame is generally made of flat tubes, steel plates or shaped steel, etc. Holes need to be drilled in the outer frame along the width direction of the composite cap beam, and bolts are used to connect the segment to the outer frame. One end of the bolt will be located in the inner cavity of the outer frame. When pouring concrete, the end of the bolt located in the inner cavity of the outer frame will be poured into the concrete at the same time. When dismantling the composite cap beam, it is not easy to peel the bolt out of the concrete, which often leads to accidental damage to the outer frame, resulting in a low recycling rate of the outer frame.

[0019] The composite capping beam in this application uses an upper connecting horizontal plate and a lower connecting horizontal plate to connect two parallel capping beam components to form an outer frame. The concrete inside the outer frame does not contact the bolts and will not affect the disassembly of the bolts. When recycling the outer frame, only the bolts need to be disassembled to recycle the upper connecting horizontal plate, the lower connecting horizontal plate and the capping beam components.

[0020] Furthermore, while the segmented components in existing composite capping beams effectively enhance the stability of the steel structure, they also divide the concrete into individual blocks. To facilitate dismantling, isolation layers are required between the steel structure and the concrete blocks. However, the connection between these blocks and the steel structure is weak, leading to outward bending deformation of the composite capping beam under horizontal support. Because the concrete blocks are spaced apart and have weak connections with the steel structure, they primarily act as force transfer elements. This means the steel structure bears the brunt of the force generated by the horizontal support, easily causing plastic deformation on the side of the steel structure away from the foundation pit. This reduces or eliminates the internal stress of the horizontal support, diminishing its protective effect on the foundation pit. This also limits the application of large axial prestress to the horizontal support, restricting the composite capping beam to shallow foundation pit protection (5-8 meters) or hard soil areas, and making it unsuitable for deep or soft soil foundation pits.

[0021] In this application, since the segmentation component is eliminated, the length of the filling block and the combined waler are equal. When subjected to the thrust of the horizontal support, the filling block and the capping beam component jointly resist the thrust, enabling the combined capping beam in this application to withstand a greater thrust of the horizontal support, thereby maintaining a greater axial prestress for the horizontal support. Therefore, the combined capping beam in this application can be applied to deep foundation pits of 15-22 meters and can be applied to foundation pit protection in soft soil areas.

[0022] Furthermore, a first horizontal support is detachably connected to the combined crown beam via a first joint assembly, the first horizontal support extending along a first axis; the first axis extending in a horizontal direction;

[0023] The first joint assembly includes a first prestressed seat and a first joint member spaced apart along a first axis. The first prestressed seat includes a first outer frame extending along the first axis and a first back plate and a first front plate fixedly installed at both ends of the first outer frame along the first axis. A first installation chamber is provided inside the first outer frame, and an inlet and outlet for entering and exiting the first installation chamber are provided on one side of the first outer frame. A first jack is detachably installed in the first installation chamber, and a first piston hole is provided on the first front plate. The first prestressed seat is detachably installed on the end of the first horizontal support facing the combined crown beam via the first back plate.

[0024] The first connector includes a first jacking plate, which is located on the side of the first front end plate facing the combined capping beam and is parallel to the first front end plate. A horizontal connecting plate is welded to the side of the first jacking plate away from the first front end plate. The first capping beam component is located inside the support pile, and the second capping beam component is located outside the support pile. The connecting plate is detachably installed on the connecting end of the support unit component in the first capping beam component facing the inside of the pit. The two ends of the first tension bolt are detachably connected to the first jacking plate and the first front end plate, respectively.

[0025] The first joint assembly is used to apply prestress to the first horizontal support. When the first joint assembly is used to apply prestress to the first horizontal support, the piston rod of the first jack extends out of the first mounting chamber through the first piston hole and pushes the first joint assembly to generate internal stress in the first horizontal support. After the push is completed, grout is poured into the gap between the first push plate and the first front end plate to form the first grout casting block. The first horizontal support is a brace or a corner brace.

[0026] The "inner side" refers to the side of the support pile facing inwards from the foundation pit, and the "outer side" refers to the side of the support pile facing outwards from the foundation pit. To reduce the adhesion between the grout and the first jacking plate and the first front end plate, thus facilitating the subsequent removal of the first joint assembly, a release agent is applied or a release film is pasted on the opposite sides of the first jacking plate and the first front end plate.

[0027] In this foundation pit support structure, a first joint assembly is used as the connecting component between the first horizontal support and the composite cap beam. A first grouting block replaces the existing steel wedges. The grouting material is essentially a fast-setting concrete. Because the first grouting block has high compressive strength, it can withstand the compressive force between the first horizontal support and the composite waler. A first tension bolt is used to restrain the first grouting block, further preventing it from separating from the gap between the first push plate and the first front end plate. The grouting material has a short setting time and rapid strength gain, ensuring construction efficiency. Utilizing the fluidity of the grouting material, it is not necessary for the first push plate and the first front end plate to be perfectly parallel; even if there is a small angle between them, no adjustment is required, thus improving construction efficiency.

[0028] Although the design requires the first jacking plate and the first front end plate to be parallel, achieving perfect parallelism is difficult in actual construction. This is a factor affecting the use of steel wedges in existing technologies. Even if there is an engineering-permissible angle between the first jacking plate and the first front end plate, this angle is still a disadvantage for the steel wedges, as it exerts a force that pushes the steel wedges outward. By using grouting, the grout can fill the entire space between the first jacking plate and the first front end plate and solidify, ensuring that the first horizontal support can extend along its original direction without deviation.

[0029] Because this application uses grout to fill the gap between the first jacking plate and the first front end plate, the included angle between the first jacking plate and the first front end plate is allowed to have a large construction or manufacturing error. Specifically, in this application, an included angle of ≤5° between the first jacking plate and the first front end plate is allowed. Although the included angle can be increased in actual construction, an excessively large included angle will cause the outer end face of the piston rod of the first jack to also form an included angle with the first jacking plate, causing the first jack to produce a radial component force when working, affecting the service life of the jack. It is recommended to make the first jacking plate and the first front end plate as parallel as possible.

[0030] The first connector in this application uses a horizontally arranged connecting plate, which is parallel to the flange of the H-beam in the support unit. The connecting plate can be fixed to the connecting end through the bolt holes on the connecting end using bolts, and it has the advantage of easy disassembly.

[0031] Furthermore, after the jacking is completed, the first tension bolt is first tensioned using a nut, and then grout is poured into the gap between the first jacking plate and the first front end plate to form the first grouting block; the first tension bolt passes through the first grouting block.

[0032] In this application, the first tension bolt is tensioned first, and then the grout is poured. The first grout pouring block is wrapped around the first tension bolt to form a prestressed concrete structural block, which further improves the stability of the first grout pouring block between the first push plate and the first front end plate.

[0033] Pre-tensioning the first tension bolt allows it to undergo elastic deformation beforehand. During construction, when the external pressure suddenly increases, the first tension bolt and the first grouting block can contract synchronously, avoiding the first grouting block being subjected to additional stress due to asynchronous contraction between the first grouting block and the first tension bolt, which would affect the structural stability of the first grouting block.

[0034] To prevent the grout from sticking to the first tension bolt, a section of plastic corrugated pipe can be fitted onto the first tension bolt, with the plastic corrugated pipe positioned between the first push plate and the first front end plate.

[0035] Furthermore, the foundation pit support structure also includes a combined waler installed on the inner side of the support piles, the combined waler including a waler frame and a grouting block;

[0036] The waler frame is composed of several sequentially connected waler units. Each waler unit includes two waler unit members that extend horizontally in parallel and are spaced apart vertically. These waler unit members are the support unit members. The reinforcing plates of the two waler unit members in the same waler unit are arranged opposite each other, and the web of the H-beam of the waler unit member is arranged horizontally. An inner connecting plate and an outer connecting plate are installed on the inner and outer sides of the waler unit, respectively. The two ends of the inner connecting plate are detachably connected to the bolt holes of the inner connecting ends of the two waler unit members, and the two ends of the outer connecting plate are detachably connected to the bolt holes of the outer connecting ends of the two waler unit members.

[0037] The end plates of the upward-facing waler units of adjacent waler units are bolted together to form a first waler component, and the end plates of the downward-facing waler units of adjacent waler units are bolted together to form a second waler component; the space between the first waler component and the second waler component forms a grouting cavity, and the grouting block is formed by concrete poured into the grouting cavity;

[0038] The second horizontal support is detachably connected to the combined waler via a second joint assembly, the second horizontal support extending along the first axis; the second joint assembly includes a second prestressed seat and a second joint member spaced apart along the first axis.

[0039] The second prestressed seat includes a second outer frame extending along the first axis and a second back plate and a second front plate fixedly installed at both ends of the second outer frame along the first axis. A second installation chamber is provided inside the second outer frame, and an inlet and outlet for entering and exiting the second installation chamber are provided on one side of the second outer frame. A second jack is detachably installed in the second installation chamber, and a second piston hole is provided on the second front plate. The second prestressed seat is detachably installed on one end of the second horizontal support facing the combined waler via the second back plate.

[0040] The second connector includes a second jacking plate, which is located on the side of the second front end plate facing the combined cap beam and is parallel to the second front end plate; the second jacking plate is detachably installed on the connecting end of the support unit in the waler member facing the inside of the pit; the two ends of the second tension bolt are detachably connected to the second jacking plate and the second front end plate respectively.

[0041] The second joint assembly is used to apply prestress to the second horizontal support. When the second joint assembly is used to apply prestress to the second horizontal support, the piston rod of the second jack extends out of the second installation chamber through the second piston hole and pushes the second joint assembly to generate internal stress in the second horizontal support. After the push is completed, grouting material is poured into the gap between the second push plate and the second front end plate to form the second grouting material pouring block.

[0042] Preferably, no dividing elements are provided within the injection cavity. That is, the injection cavity is a through groove extending along the length of the combined waler to the end of the combined waler, without any dividing elements in the middle, maintaining the continuity of the injection block. If the combined waler is a closed ring, the injection block is an endless ring.

[0043] The inner side of the waler unit refers to the side of the waler unit facing inwards from the foundation pit, while the outer side of the waler unit refers to the side of the waler unit facing outwards from the foundation pit.

[0044] To facilitate the recycling of steel structural components, it is preferable to install an isolation membrane between the waler frame and the grouting block. The isolation membrane can be made of materials such as geotextile or plastic film, or the surface of the waler components, inner connecting plates and outer connecting plates can be coated with isolation paint, and the paint film formed by the isolation paint forms the isolation membrane.

[0045] The combined waler and the combined cap beam have basically the same structure. The only difference is that there is no support pile involved. The combined waler is made of support unit components, which expands the application range of support unit components, reduces the types of components, improves the versatility of components, and reduces management costs.

[0046] Currently, walers are generally made of precast concrete or simply steel walers spliced ​​from H-beams. Recycled steel walers can be used in foundation pits with similar requirements. However, most foundation pits are different. Steel walers are made of two parallel H-beams welded together. When reusing them, they need to be disassembled, which is done by gas cutting. During welding and gas cutting, the steel is repeatedly heated, which reduces its strength and makes it unable to meet the usage requirements. It can only be used as scrap steel or cut into other small non-load-bearing components. As a result, the recycling rate of steel walers can only be maintained at 30-40%, resulting in a large waste of steel.

[0047] Using support unit components to fabricate composite walers can be applied to various types and requirements of foundation pits. Since the composite waler consists of two waler members spaced vertically apart, with concrete poured between the first and second waler members, the high compressive strength of concrete enhances the rigidity of the composite waler and reduces its deformation. Furthermore, the ease of concrete pouring allows for the adjustment of the distance between the two waler members to create composite walers of varying heights, increasing the contact area with the support piles and the inner wall of the foundation pit. Moreover, the necessary structural components can be embedded within the concrete, eliminating the need to weld them to the support unit components.

[0048] After the foundation pit construction is completed, the concrete in the composite waler is removed. As long as the structure of the support unit remains intact and is not damaged, it can be directly used in another foundation pit as a component of the composite waler. However, during the construction process, some composite walers will inevitably be damaged and cannot be recycled. Therefore, in this application, when using support unit to prepare composite walers, the recycling rate of the support unit can only be maintained at 92-96%, and it is impossible to recycle and reuse them all. However, compared with the existing steel walers spliced ​​by H-steels alone, its recycling rate is still greatly improved, and the construction cost is reduced.

[0049] Because the support unit can be used as a standard component to prepare composite cap beams and composite walers during the same foundation pit construction process, the management cost of structural components in foundation pit construction is greatly reduced. In fact, the support unit can also be used to make horizontal supports and other structural components such as supports for horizontal supports.

[0050] The structure of the second prestressing seat used to apply prestress to the second horizontal support is the same as that of the first prestressing seat, so it can be manufactured using the same standard to reduce manufacturing costs.

[0051] Furthermore, to reduce the adhesion of the grout to the piston rod, an anti-adhesion component is provided in the first prestressed seat. The anti-adhesion component includes a positioning ring and a stretching ring. The stretching ring is circular. The positioning ring is connected to the stretching ring via an elastic membrane or a stretching membrane. The positioning ring is fixed on the first front end plate or the cylinder of the first jack. When viewed along the first axis, the stretching ring is located inside the positioning ring and inside the first piston hole.

[0052] A stepped portion is provided at the outer end of the piston rod of the first jack. This stepped portion is formed by an axial concavity at the radially outer end of the outer end face of the piston rod, and has an annular stepped surface. The axial depth of this stepped portion is greater than or equal to the diameter of the stretching ring. When the piston rod extends outward, the stretching ring is fitted onto the stepped portion and presses against the stepped surface, stretching the elastic diaphragm or telescopic diaphragm so that the elastic diaphragm or telescopic diaphragm wraps around the piston rod. The elastic diaphragm can be made of butadiene rubber, natural rubber, styrene-butadiene rubber, or nitrile rubber, or other rubbers. The telescopic diaphragm is made of folded plastic film.

[0053] By utilizing the isolating effect of elastic or stretch membranes, the adhesion force of the grout to the piston rod will be reduced, thereby reducing the tensile force on the piston rod when it retracts.

[0054] Finally, this application also discloses a construction method for the aforementioned foundation pit support structure, which includes the following steps:

[0055] (1) Construct support piles at the edge of the foundation pit and arrange capping beam units, so that the first unit is located inside the support pile and the second unit is located outside the support pile. The end plates of the first unit of the adjacent capping beam units are detachably connected together to form the first capping beam component, and the end plates of the second unit of the adjacent capping beam units are detachably connected together to form the second capping beam component. Then, pour concrete into the pouring cavity between the first capping beam component and the second capping beam component to form a filling block, and complete the construction of the composite capping beam.

[0056] (2) Erect the first horizontal support and detachably install the first prestressed seat on the end of the first horizontal support facing the combined crown beam via the first back plate, and detachably install the first joint on the connecting end of the first crown beam component via the connecting plate, with the first jacking plate and the first front end plate being set opposite to each other;

[0057] (3) Start the first jack in the first installation chamber. After the piston rod of the first jack extends out of the first installation chamber, it presses against the first connector and pushes the first connector until the first pre-pressure generated by the push reaches the set value.

[0058] When the piston rod extends outward into the first mounting chamber, the stretching ring is fitted onto the stepped part of the piston rod and presses against the stepped surface. The stretching ring stretches the elastic membrane or the stretching membrane, so that the elastic membrane or the stretching membrane wraps around the piston rod.

[0059] (4) Under the first set tension, connect the two ends of the first tension bolt to the first push plate and the first front end plate respectively, and then pour grout between the first front end plate and the first push plate. The grout is wrapped around the outer circumference of the piston rod through an elastic membrane or a telescopic membrane. When the grout reaches the first set strength, release the pressure of the first jack, retract the piston rod into the first installation chamber, and remove the first jack.

[0060] The first set tension is 20-30 MPa, and the first set strength is 20-30 MPa.

[0061] To reduce the adhesion between the grout and the first jacking plate and the first front end plate, thus facilitating the subsequent removal of the first joint assembly, a release agent or a release film is applied to the opposite sides of the first jacking plate and the first front end plate.

[0062] Because the internal stress of the first horizontal support will decrease slightly after the first jack is removed, the initial pre-pressure generated during jacking must exceed the set value of the internal stress of the first horizontal support. Generally, the set value of the initial pre-pressure is 5-10% higher than the set value of the internal stress of the first horizontal support. Before construction, the strength of the grouting material used needs to be tested to determine the pressure relief time of the first jack.

[0063] In this construction method, the capping beam unit is a prefabricated component, which reduces the installation time of the combined capping beam and improves work efficiency. During the prestressing process, after the jacking is completed, grout is poured between the first front end plate and the first jacking plate to form the first grouting block. This first grouting block replaces the steel wedges in the prior art. The first grouting block has a large compressive strength and can withstand the compressive force between the first front end plate and the first jacking plate. The first tension bolt is pre-tensioned, which allows it to undergo elastic deformation in the axial direction. During the construction of the foundation pit, when the first grouting block is subjected to a sudden increase in external pressure, the first tension bolt and the first grouting block can compress synchronously. This avoids the first grouting block being subjected to additional stress due to asynchronous contraction between the first tension bolt and the first grouting block, which would affect the structural stability of the first grouting block.

[0064] The first tension bolt ensures that the first grouting block is stably held in place by the first front end plate and the first push plate, and will not be pushed outward due to external vibration or compression.

[0065] Using this application, even if there is a small angle between the first front end plate and the first push plate due to poor parallelism, no adjustment is required. The first front end plate and the first push plate are allowed to have an angle of ≤5°. Although this angle can be increased in actual construction, an excessively large angle will cause the end face of the piston rod of the first jack to also form an angle with the first push plate, causing the first jack to produce a radial component force when working, which will affect the service life of the first jack.

[0066] Furthermore, the construction method also includes the following steps:

[0067] (5) After the installation of the first horizontal support is completed, the foundation pit is excavated until the installation elevation of the second horizontal support is reached. The excavation of the foundation pit is suspended. The combined waler is installed on the inner wall of the support pile and the second horizontal support is erected. The second prestressed seat is detachably installed on the end of the second horizontal support facing the combined waler via the second back plate. The second joint is installed on the connecting end of the combined waler via the second jacking plate. The second jacking plate is set opposite to the second front end plate.

[0068] (6) Start the second jack in the second installation chamber. After the piston rod of the second jack extends out of the second installation chamber, it presses against the second connector to push the second connector until the second pre-pressure generated by the push reaches the set value.

[0069] (7) Under the second set tension, connect the two ends of the second tension bolt to the second push plate and the second front plate respectively, and then pour grout between the second front plate and the second push plate. When the grout reaches the second set strength, release the pressure of the second jack, retract the piston rod into the second installation chamber, and remove the second jack.

[0070] To reduce the adhesion between the grout and the second jacking plate and the second front end plate, thus facilitating the subsequent removal of the second joint assembly, a release agent or release film is applied to the opposite sides of the second jacking plate and the second front end plate.

[0071] The second set tension is 20-30 MPa, and the second set strength is 20-30 MPa.

[0072] Because the internal stress of the second horizontal support will decrease slightly after the second jack is removed, the second preload generated during the jacking operation must exceed the set value of the internal stress of the second horizontal support. Generally, the set value of the second preload is 5-10% higher than the set value of the internal stress of the second horizontal support.

[0073] This construction method only describes the installation method of the second horizontal support. When a third, fourth, or more horizontal supports are required, the construction method of the second horizontal support can be used, and there is no need to use a different construction method.

[0074] Since the second horizontal support uses the same prestressing application technology as the first horizontal support, it can effectively improve the construction efficiency of the foundation pit support, thereby improving the overall efficiency of the foundation pit construction.

[0075] Specifically, when the first connector is not pushed, the gap between the first front end plate and the first push plate is 5-100mm. When the second connector is not pushed, the gap between the second front end plate and the second push plate is also set to 5-100mm.

[0076] If the first front end plate is tightly attached to the first jacking plate, during the installation of the first prestressed seat and the first connector, whether one is installed first and then the other, or the first prestressed seat and the first connector are first bolted together as a whole and then placed between the first horizontal support and the composite capping beam, a great deal of force is required to complete the installation of the first connector assembly. Furthermore, alignment is crucial during installation to prevent any deviation, which inevitably increases construction difficulty and reduces efficiency. However, by setting a small gap between the first front end plate and the first jacking plate, both the first prestressed seat and the first connector can be smoothly installed on the first horizontal support and the composite capping beam.

[0077] A similar gap is set between the second front end plate and the second push plate, also for the same reason. Attached Figure Description

[0078] Figure 1 This is a structural schematic diagram of the support unit.

[0079] Figure 2 yes Figure 1 A view from the center AA direction.

[0080] Figure 3 This is a schematic diagram of the foundation pit support structure.

[0081] Figure 4 yes Figure 3 Enlarged view of section B.

[0082] Figure 5 This is a schematic diagram of the composite crown beam structure.

[0083] Figure 6 yes Figure 5 A schematic diagram of the structure after the support piles have been removed.

[0084] Figure 7 yes Figure 5 Top view.

[0085] Figure 8 yes Figure 7 A schematic diagram of the structure after the infill blocks have been removed.

[0086] Figure 9 This is a structural schematic diagram of the cap beam unit.

[0087] Figure 10 This is a structural schematic diagram of the first connector assembly.

[0088] Figure 11 yes Figure 10 The exploded diagram.

[0089] Figure 12 This is a schematic diagram of the structure of the first prestressed seat.

[0090] Figure 13 yes Figure 12 A view directed towards the center (CC).

[0091] Figure 14 yes Figure 13 Enlarged view of section D.

[0092] Figure 15 yes Figure 14 A diagram showing the state of the piston rod of the first jack when it extends outward.

[0093] Figure 16 This is a structural diagram of the anti-stick component.

[0094] Figure 17 yes Figure 16 Enlarged view of section E in the middle.

[0095] Figure 18 This is a structural schematic diagram of the first connector.

[0096] Figure 19 This is a structural diagram of the combined walers.

[0097] Figure 20 yes Figure 19 A schematic diagram of the FF direction.

[0098] Figure 21 yes Figure 19 A magnified view of section G in the middle.

[0099] Figure 22 This is a schematic diagram of the second connector. Detailed Implementation

[0100] The following is a description of the support unit 100:

[0101] Please see Figure 1 and Figure 2 The support unit 100 includes an H-beam 11. Along the thickness direction of the web 12 of the H-beam 11, the two flanges 13 of the H-beam have one end facing the same direction as a closed end 138, and the other end with the two flanges facing the same direction as a connecting end 139. A reinforcing plate 15 extends along the length direction of the H-beam 11. The two ends of the reinforcing plate 15 in the width direction are welded to the two closed ends 138, respectively, closing the opening of one groove in the H-beam. A receiving cavity is formed between the H-beam and the reinforcing plate 15, and first concrete 16 is poured into this cavity. The opening of the other groove in the H-beam is open; that is, the opening of the groove on the side of the H-beam opposite to the reinforcing plate is open.

[0102] Each connecting end 139 is provided with a plurality of bolt holes 14 spaced apart along the length of the H-beam. In this embodiment, the H-beam 11 is of type H700×300, the inner diameter of the bolt holes is 18, and the center distance between adjacent bolt holes is 250mm.

[0103] End plates 17 are welded to both ends of the H-beam along its length. The end plates close the two slots of the H-beam facing the openings along its length. Connecting holes 171 with an inner diameter of 18mm are provided on the end plates. Using the connecting holes, two support unit components can be connected together to extend their length.

[0104] The following describes the foundation pit support structure:

[0105] Please see Figures 3-22 In the attached diagram, the first axis X extends horizontally, and the second axis Z extends vertically. The foundation pit support structure includes support piles 20 installed along the edge of the foundation pit, and a composite capping beam 120 is installed on top of the support piles.

[0106] The outer frame is composed of several crown beam units 200 connected in sequence. Each crown beam unit 200 includes two crown beam unit members that extend horizontally in parallel and are spaced apart. These crown beam unit members are the aforementioned support unit members 100. The reinforcing plates 15 of the two crown beam unit members in the same crown beam unit are arranged opposite each other. The web of the crown beam unit member is vertically arranged. An upper connecting horizontal plate 21 and a lower connecting horizontal plate 22 are respectively installed on the upper and lower sides of the crown beam unit. The two ends of the upper connecting horizontal plate are detachably connected to the bolt holes of the upward-facing connection ends of the two crown beam unit members by first bolts 23. The two ends of the lower connecting horizontal plate are detachably connected to the bolt holes of the downward-facing connection ends of the two crown beam unit members by second bolts 24.

[0107] The two crown beam unit members in each crown beam unit are referred to as the first unit member and the second unit member, respectively. The end plates of the first unit members of adjacent crown beam units are fixed together by bolts to form the first crown beam member 128. The end plates of the second unit members of adjacent crown beam units are fixed together by bolts to form the second crown beam member 129. The space between the first crown beam member and the second crown beam member forms a casting cavity. The support pile passes downward through the casting cavity and has a filling block 25 made of concrete in the casting cavity. The filling block wraps around the outer circumference of the support pile 20. Figure 9 An example of a support pile 20 is shown in the figure.

[0108] An isolation membrane is provided between the filling block and the outer frame. In this embodiment, the isolation membrane is made of geotextile. It can be understood that in other embodiments, plastic film is also used as the isolation membrane, or an isolation paint is applied to the inner surfaces of the first crown beam member, the second crown beam member, the upper connecting horizontal plate, and the lower connecting horizontal plate, and the paint film formed by the isolation paint serves as the isolation membrane.

[0109] The first capping beam component 128 is located inside the support pile 20, and the second capping beam component 129 is located outside the support pile 20; the inside refers to the side of the support pile facing the inside of the pit, and the outside refers to the side of the support pile facing the outside of the pit.

[0110] No dividing elements are set in the casting cavity. That is, the casting cavity is a through groove extending along the length of the composite crown beam to the end of the composite crown beam, without any dividing elements in the middle, so as to maintain the continuity of the filling block.

[0111] In this embodiment, the support pile 20 is formed by mixing piles 26 and H-steel piles 27 inserted into the mixing piles. The top surface of the H-steel piles extends upward beyond the top surface of the mixing piles, and adjacent mixing piles overlap each other radially. The lower connecting horizontal plate is supported on the top surface of the mixing piles, and the top surface of the H-steel piles 27 extends upward beyond the upper connecting horizontal plate.

[0112] A first horizontal support 410 is detachably connected to the combined crown beam 120 via a first joint assembly 300, and the first horizontal support 410 extends along a first axis. In this embodiment, the first horizontal support is a counterbracing. It can be understood that in another embodiment, the first horizontal support may also be a corner brace.

[0113] The first joint assembly 300 includes a first prestressed seat 310 and a first joint member 320 spaced apart along the first axis. The first prestressed seat 310 includes a first outer frame 103 extending along the first axis and a first back plate 101 and a first front plate 102 fixedly installed at both ends of the first outer frame 103 along the first axis.

[0114] In this embodiment, the first outer frame 103 is formed by splicing two H-beams 131 extending along the first axis. The webs A132 of the two H-beams extend vertically and are parallel to each other. The upper flanges A133 of the two H-beams are welded together, and the lower flanges A134 are welded together, forming a rectangular cavity between the two H-beams. This rectangular cavity forms the first mounting chamber 105. A piece is cut off from each of the opposite sides of the upper flanges A of the two H-beams to form a rectangular inlet / outlet 104. This inlet / outlet is used for entering and exiting the first mounting chamber, i.e., the inlet / outlet is located on the upper side of the first outer frame.

[0115] A support plate 135 is horizontally welded to the lower side of the first installation chamber. The first jack 106 is located inside the first installation chamber 105 and is detachably mounted on the support plate 135. The piston rod 161 of the first jack can extend towards the first front end plate.

[0116] A first piston hole 126 and a tension hole 127 are provided on the first front end plate 102. The first piston hole 126 is square and is directly opposite the piston rod 161. The tension hole is arranged on the periphery of the first front end plate 102.

[0117] First bolt holes A116 are provided on the periphery of the first back plate 101. Bolts are used to install the first back plate onto the end of the first horizontal support facing the composite crown beam through the first bolt holes A116, so that the first prestressed seat can be detachably installed on the first horizontal support.

[0118] The first connector 320 includes a first push plate 201, which is located on the side of the first front end plate facing the combined crown beam and is parallel to the first front end plate. A horizontal connecting plate 202 is welded to the side of the first push plate away from the first front end plate. Two connecting plates 202 are spaced apart in the vertical direction, and a reinforcing plate 203 is provided between the two connecting plates. A push plate hole 211 for connecting the first tension bolt 330 is provided on the first push plate.

[0119] In this embodiment, the first front end plate is perpendicular to the first axis, and the push plate hole 211 corresponds one-to-one with the tension hole 127. The push plate hole is located between two adjacent reinforcing plates or between the connecting plate and an adjacent reinforcing plate, so that the space between two adjacent reinforcing plates and between the connecting plate and an adjacent reinforcing plate forms an operating space 213 for tightening the nut.

[0120] A second bolt hole A221 is provided on the connecting plate. The bolts pass through the second bolt hole A221 and the bolt hole on the connecting end to detachably install the connecting plate on the connecting end of the support unit in the first cap beam component facing the inside of the pit.

[0121] The first tension bolt 330 passes through the tension hole 127 and the push plate hole 211 and is connected to the first push plate and the first front end plate. Both ends of the first tension bolt are detachably connected to the second push plate and the second front end plate, respectively.

[0122] The connecting plate is detachably installed on the connecting end of the support unit in the first cap beam member facing the inside of the pit; the two ends of the first tension bolt are detachably connected to the first push plate and the first front end plate, respectively.

[0123] The piston rod 161 of the first jack 106 can extend along the first axis towards the first connector, and after extending outward through the piston hole into the force application chamber, press against the first connector to push the first connector.

[0124] An anti-adhesion component 108 is provided within the first prestressed seat. This anti-adhesion component 108 includes a positioning ring 181 and a stretching ring 183. Both the positioning ring and the stretching ring are annular, with the outer diameter of the stretching ring being smaller than the inner diameter of the positioning ring. The positioning ring 181 is connected to the stretching ring 183 via an elastic membrane 182. The positioning ring is fixedly bonded to the edge of the first piston hole facing the first back plate. Viewed along the first axis, the stretching ring is located inside the positioning ring and within the first piston hole.

[0125] The elastic membrane is a ring-shaped rubber sheet. The outer circumferential end of the rubber sheet is bonded to a positioning ring, and the edge of the central hole of the rubber ring is bonded to a drawing ring. In this embodiment, for ease of processing, the first piston hole is square; however, in another embodiment, the piston hole can also be circular.

[0126] A stepped portion 163 is provided at the outer end of the piston rod 161 of the first jack 106. The stepped portion 163 is formed by the radially outer end of the outer end face 162 of the piston rod being recessed axially. The stepped portion 163 has an annular stepped surface 164. The axial depth K of the stepped portion 163 is 2 mm larger than the diameter of the ring body of the stretching ring 183. This ensures that when the stretching ring presses against the stepped surface 164, the side of the stretching ring away from the first back plate does not extend beyond the outer end face 162 of the piston rod, thus preventing the stretching ring from directly pressing against the first joint during the jacking process and affecting the smooth application of prestress.

[0127] When the piston rod extends outward, the stretching ring is fitted onto the step portion and presses against the step surface. The stretching ring stretches the elastic membrane, causing the elastic membrane to wrap around the piston rod. In this embodiment, the elastic membrane is made of butadiene rubber. It is understood that in other embodiments, the elastic membrane can also be made of natural rubber, styrene-butadiene rubber, or nitrile rubber, or of course, other rubber materials.

[0128] The first joint assembly is used to apply prestress to the first horizontal support. When the first joint assembly is used to apply prestress to the first horizontal support, the piston rod of the first jack extends out of the first mounting chamber through the first piston hole and pushes the first joint assembly to generate internal stress in the first horizontal support. After the push is completed, the nut on the tension bolt is tightened to tension the first tension bolt. After the tension bolt is tensioned, grout is poured into the gap between the first push plate and the first front end plate to form the first grout casting block 340. The first tension bolt passes through the first grout casting block.

[0129] A combined waler 400 is installed on the inner side of the support pile 20, and a corbel is installed on the inner wall of the support pile. The combined waler is supported on the corbel.

[0130] The combined waler includes a waler frame and grouting blocks 43. The waler frame is composed of several sequentially connected waler units 460. Figure 19 The waler unit 460 is connected together by bolts. Each waler unit includes two waler unit members that extend horizontally in parallel and are spaced apart vertically. These waler unit members are the support unit members 100. The reinforcing plates of the two waler unit members in the same waler unit are arranged opposite each other, and the web of the H-beam of the waler unit is arranged horizontally. An inner connecting plate 42 and an outer connecting plate 41 are installed on the inner and outer sides of the waler unit, respectively. The two ends of the inner connecting plate 42 are detachably connected to the bolt holes of the inner connecting ends of the two waler unit members, and the two ends of the outer connecting plate 41 are detachably connected to the bolt holes of the outer connecting ends of the two waler unit members.

[0131] The end plates of the upward-facing waler units of adjacent waler units are bolted together to form a first waler component 401, and the end plates of the downward-facing waler units of adjacent waler units are bolted together to form a second waler component 402; the space between the first waler component and the second waler component forms a grouting cavity, and the grouting block 43 is formed by concrete poured into the grouting cavity.

[0132] The second horizontal support 420 is detachably connected to the combined waler 400 via the second joint assembly 440, the second horizontal support extending along the first axis direction; the second joint assembly includes a second prestressed seat and a second joint member 450 spaced apart along the first axis direction.

[0133] The second prestressing seat has the same structure as the first prestressing seat, which is briefly described below:

[0134] The second prestressed seat includes a second outer frame extending along the first axis and a second back plate and a second front plate fixedly installed at both ends of the second outer frame along the first axis. A second installation chamber is provided inside the second outer frame, and an inlet and outlet for entering and exiting the second installation chamber are provided on one side of the second outer frame. A second jack is detachably installed in the second installation chamber, and a second piston hole is provided on the second front plate. The second prestressed seat is detachably installed on one end of the second horizontal support facing the combined waler via the second back plate.

[0135] Please see Figure 22 The second connector 450 includes only one second push plate 451, which is vertically arranged. Push plate holes A452 are provided at both ends of the second push plate in the horizontal direction, and fixing holes 453 are provided at both ends of the second push plate in the vertical direction.

[0136] The second jacking plate is located on the side of the second front end plate facing the combined cap beam and is parallel to the second front end plate. Using bolts, the second jacking plate is detachably installed on the connecting end of the support unit in the waler member facing the inside of the pit through fixing holes and bolt holes; the two ends of the second tension bolt are respectively inserted through the jacking plate hole A452 of the second jacking plate and the tension hole of the second front end plate.

[0137] The second joint assembly is used to apply prestress to the second horizontal support. When the second joint assembly is used to apply prestress to the second horizontal support, the piston rod of the second jack extends out of the second installation chamber through the second piston hole and pushes the second joint assembly to generate internal stress in the second horizontal support. After the push is completed, grouting material is poured into the gap between the second push plate and the second front end plate to form the second grouting material pouring block.

[0138] The construction method for the aforementioned foundation pit support structure is described below, and the method includes the following steps:

[0139] (1) Construct support piles 20 at the edge of the foundation pit, and arrange capping beam units such that the first unit is located inside the support piles and the second unit is located outside the support piles. Use bolts to detachably connect the end plates of the first unit of adjacent capping beam units to form the first capping beam component 128. Use bolts to detachably connect the end plates of the second unit of adjacent capping beam units to form the second capping beam component 129. Then pour concrete into the casting cavity between the first capping beam component and the second capping beam component to form a filling block 25, thus completing the construction of the combined capping beam 120.

[0140] (2) A first horizontal support 410 is erected on the bracket. The first prestressed seat 310 is detachably installed on the end of the first horizontal support 410 facing the combined crown beam 120 via the first back plate 101 using bolts. The first connector 320 is detachably installed on the connecting end of the first crown beam component via the connecting plate 202 using bolts. The first push plate and the first front end plate are arranged opposite each other, and the gap between the first front end plate and the first push plate is 8mm. The bracket is not shown in the attached drawings; the bracket can be set up according to existing technology.

[0141] The first tension bolt 330 is passed through the push plate hole 211 and tension hole 127, and is kept in a free state. A release varnish is applied to the opposite sides of the first front end plate and the first push plate.

[0142] (3) Activate the first jack 106 in the first installation chamber 105. The piston rod 161 of the first jack 106 extends outward from the first installation chamber and presses against the first push plate 201 of the first connector 320 to push the first connector until the first pre-pressure generated by the push reaches the set value. In this embodiment, the set value of the first pre-pressure generated during the push is 7% higher than the set value of the internal stress of the first horizontal support.

[0143] When the piston rod extends outward from the first mounting chamber, the stretching ring 183 is fitted onto the step portion 163 of the piston rod, and the stretching ring presses against the step surface 164. The stretching ring 183 stretches the elastic membrane 182, so that the elastic membrane wraps around the piston rod.

[0144] (4) Tighten the nut on the first tension bolt until the tension generated by the first tension bolt reaches the first set tension of 25 MPa, so that the first tension bolt connects the first push plate and the first front end plate. Pour grout between the first front end plate and the first push plate, and the grout is wrapped around the outer circumference of the piston rod through an elastic membrane or a telescopic membrane. When the grout reaches the first set strength of 25 MPa, it forms the first grout pouring block 340, the pressure of the first jack is released, the piston rod is retracted into the first installation chamber, and the first jack is removed.

[0145] (5) After the installation of the first horizontal support 410 is completed, the foundation pit is excavated until the installation elevation of the second horizontal support 420 is reached. The excavation of the foundation pit is then suspended. Corbels are installed on the inner wall of the support piles 20, and combined walers 400 are erected on the corbels. Then, the second horizontal support 420 is erected on the support. The erection of the second horizontal support on the support can be carried out in accordance with existing technology.

[0146] Using bolts, the second prestressed seat is detachably installed on the end of the second horizontal support facing the combined waler via the second back plate. The second connector is installed on the connecting end of the combined waler via the second push plate. The installation method of the second prestressed seat and the second horizontal support is the same as that of the first prestressed seat and the first horizontal support.

[0147] Using bolts, the second jacking plate is detachably installed on the connecting end of the support unit facing the inside of the pit in the waler component, through fixing holes and bolt holes; the second jacking plate is positioned opposite to the second front end plate and is parallel to each other. The gap between the second jacking plate and the second front end plate is 20mm.

[0148] The second tension bolt is passed sequentially through the push plate hole A452 of the second push plate and the tension hole of the second front end plate, and the second tension bolt is kept in a free state.

[0149] (6) Start the second jack in the second installation chamber. After the piston rod of the second jack extends out of the second installation chamber, it presses against the second connector to push the second connector until the second pre-pressure generated by the push reaches the set value.

[0150] In this embodiment, the set value of the second pre-pressure generated during the jacking is 7% higher than the set value of the internal stress of the second horizontal support.

[0151] (7) Tighten the nut on the second tension bolt until the tension of the second tension bolt reaches the second set tension of 25MPa, so that the two ends of the second tension bolt are connected to the second push plate and the second front end plate respectively. The sides of the second front end plate and the second push plate are coated with isolation paint. Then, pour grout between the second front end plate and the second push plate. When the grout reaches the second set strength of 25MPa, release the pressure of the second jack, retract the piston rod into the second installation chamber, and remove the second jack.

Claims

1. A foundation pit support structure, characterized in that, It includes support piles installed along the edge of the foundation pit, and a composite capping beam installed on top of the support piles, the composite capping beam including an outer frame; The outer frame is composed of several crown beam units connected in sequence. Each crown beam unit includes two crown beam unit members that extend parallel to each other in the horizontal direction and are spaced apart. Each crown beam unit member is a support unit member. Each support unit member includes an H-beam with end plates welded to both ends of the H-beam along its length. The end plates close the two slots of the H-beam facing the openings along the length of the H-beam. Connection holes are provided on the end plates. The opposite ends of the reinforcing plates are respectively welded to the two flanges of the H-beam facing the same end. The ends of the two flanges of the H-beam facing away from the reinforcing plates form the connection ends. The reinforcing plates of the two crown beam unit members in the same crown beam unit are arranged opposite each other. The two crown beam unit members in each crown beam unit are referred to as the first unit member and the second unit member, respectively. The end plates of the first unit members of adjacent crown beam units are fixed together by bolts to form the first crown beam component. The end plates of the second unit members of adjacent crown beam units are fixed together by bolts to form the second crown beam component. A first horizontal support is detachably connected to the combined crown beam via a first joint assembly, the first horizontal support extending along a first axis; the first axis extends in a horizontal direction; The first joint assembly includes a first prestressed seat and a first joint member spaced apart along a first axis. The first prestressed seat includes a first outer frame extending along the first axis and a first back plate and a first front plate fixedly installed at both ends of the first outer frame along the first axis. A first installation chamber is provided inside the first outer frame, and an inlet and outlet for entering and exiting the first installation chamber are provided on one side of the first outer frame. A first jack is detachably installed in the first installation chamber, and a first piston hole is provided on the first front plate. The first prestressed seat is detachably installed on the end of the first horizontal support facing the combined crown beam via the first back plate. The first connector includes a first jacking plate, which is located on the side of the first front end plate facing the combined capping beam and is parallel to the first front end plate. A horizontal connecting plate is welded to the side of the first jacking plate away from the first front end plate. The first capping beam component is located inside the support pile, and the second capping beam component is located outside the support pile. The connecting plate is detachably installed on the connecting end of the support unit component in the first capping beam component facing the inside of the pit. The two ends of the first tension bolt are detachably connected to the first jacking plate and the first front end plate, respectively. The first joint assembly is used to apply prestress to the first horizontal support. When the first joint assembly is used to apply prestress to the first horizontal support, the piston rod of the first jack extends out of the first installation chamber through the first piston hole and pushes the first joint assembly to generate internal stress in the first horizontal support. After the push is completed, grout is poured into the gap between the first push plate and the first front end plate to form the first grout casting block.

2. The foundation pit support structure according to claim 1, characterized in that, The reinforcing plate closes the opening of one groove of the H-beam, forming a receiving cavity between the H-beam and the reinforcing plate, and concrete is poured into the receiving cavity; the opening of the other groove of the H-beam is open, and several bolt holes are provided at intervals along the length of the H-beam at each connection end. The web of the crown beam unit is vertically arranged. An upper connecting plate and a lower connecting plate are installed on the upper and lower sides of the crown beam unit, respectively. The two ends of the upper connecting plate are detachably connected to the bolt holes of the upward connecting ends of the two crown beam units, and the two ends of the lower connecting plate are detachably connected to the bolt holes of the downward connecting ends of the two crown beam units. The space between the first capping beam member and the second capping beam member is formed as a casting cavity. The support pile passes downward through the casting cavity and has a filling block made of concrete inside the casting cavity. The filling block wraps around the outer periphery of the support pile. An isolation membrane is provided between the filling block and the outer frame.

3. The foundation pit support structure according to claim 2, characterized in that, No dividing parts are installed inside the casting cavity.

4. The foundation pit support structure according to claim 1, characterized in that, After the jacking is completed, the first tension bolt is tensioned by the nut, and then grout is poured into the gap between the first jacking plate and the first front end plate to form the first grouting block; the first tension bolt passes through the first grouting block.

5. The foundation pit support structure according to claim 1, characterized in that, It also includes a combined waler installed on the inner side of the support pile, the combined waler comprising a waler frame and a grouting block; The waler frame is composed of several sequentially connected waler units. Each waler unit includes two waler unit members that extend horizontally in parallel and are spaced apart vertically. The waler unit members are the support unit members as described in claim 1. The reinforcing plates of the two waler unit members in the same waler unit are arranged opposite each other, and the web of the H-beam of the waler unit member is arranged horizontally. An inner connecting plate and an outer connecting plate are respectively installed on the inner and outer sides of the waler unit. The two ends of the inner connecting plate are detachably connected to the bolt holes of the inner connecting ends of the two waler unit members. The two ends of the outer connecting plate are detachably connected to the bolt holes of the outer connecting ends of the two waler unit members. The end plates of the upward-facing waler units of adjacent waler units are bolted together to form a first waler component, and the end plates of the downward-facing waler units of adjacent waler units are bolted together to form a second waler component; the space between the first waler component and the second waler component forms a grouting cavity, and the grouting block is formed by concrete poured into the grouting cavity; The second horizontal support is detachably connected to the combined waler via a second joint assembly, the second horizontal support extending along the first axis; the second joint assembly includes a second prestressed seat and a second joint member spaced apart along the first axis. The second prestressed seat includes a second outer frame extending along the first axis and a second back plate and a second front plate fixedly installed at both ends of the second outer frame along the first axis. A second installation chamber is provided inside the second outer frame, and an inlet and outlet for entering and exiting the second installation chamber are provided on one side of the second outer frame. A second jack is detachably installed in the second installation chamber, and a second piston hole is provided on the second front plate. The second prestressed seat is detachably installed on one end of the second horizontal support facing the combined waler via the second back plate. The second connector includes a second jacking plate, which is located on the side of the second front end plate facing the combined cap beam and is parallel to the second front end plate; the second jacking plate is detachably installed on the connecting end of the support unit in the waler member facing the inside of the pit; the two ends of the second tension bolt are detachably connected to the second jacking plate and the second front end plate respectively. The second joint assembly is used to apply prestress to the second horizontal support. When the second joint assembly is used to apply prestress to the second horizontal support, the piston rod of the second jack extends out of the second installation chamber through the second piston hole and pushes the second joint assembly to generate internal stress in the second horizontal support. After the push is completed, grouting material is poured into the gap between the second push plate and the second front end plate to form the second grouting material pouring block.

6. The foundation pit support structure according to claim 1 or 5, characterized in that, An anti-adhesion component is provided in the first prestressed seat. The anti-adhesion component includes a positioning ring and a stretching ring. The stretching ring is circular. The positioning ring is connected to the stretching ring via an elastic membrane or a stretching membrane. The positioning ring is fixed on the first front end plate or the cylinder of the first jack. When viewed along the first axis, the stretching ring is located inside the positioning ring and inside the first piston hole. A stepped portion is provided at the outer end of the piston rod of the first jack. The stepped portion is formed by the radial outer end of the outer end face of the piston rod being recessed axially. The stepped portion has an annular stepped surface. The axial depth of the stepped portion is greater than or equal to the diameter of the stretching ring. When the piston rod extends outward, the stretching ring is sleeved on the stepped portion and presses against the stepped surface. The stretching ring stretches the elastic membrane or the stretching membrane, so that the elastic membrane or the stretching membrane wraps around the piston rod.

7. The construction method of the foundation pit support structure according to claim 6, characterized in that, Includes the following steps: (1) Construct support piles at the edge of the foundation pit and arrange capping beam units, so that the first unit is located inside the support pile and the second unit is located outside the support pile. The end plates of the first unit of the adjacent capping beam units are detachably connected together to form the first capping beam component, and the end plates of the second unit of the adjacent capping beam units are detachably connected together to form the second capping beam component. Then, pour concrete into the pouring cavity between the first capping beam component and the second capping beam component to form a filling block, and complete the construction of the composite capping beam. (2) Erect the first horizontal support and detachably install the first prestressed seat on the end of the first horizontal support facing the combined crown beam via the first back plate, and detachably install the first joint on the connecting end of the first crown beam component via the connecting plate, with the first jacking plate and the first front end plate being set opposite to each other; (3) Start the first jack in the first installation chamber. After the piston rod of the first jack extends out of the first installation chamber, it presses against the first connector and pushes the first connector until the first pre-pressure generated by the push reaches the set value. When the piston rod extends outward into the first mounting chamber, the stretching ring is fitted onto the stepped part of the piston rod and presses against the stepped surface. The stretching ring stretches the elastic membrane or the stretching membrane, so that the elastic membrane or the stretching membrane wraps around the piston rod. (4) Under the first set tension, connect the two ends of the first tension bolt to the first push plate and the first front end plate respectively, and then pour grout between the first front end plate and the first push plate. The grout is wrapped around the outer circumference of the piston rod through an elastic membrane or a telescopic membrane. When the grout reaches the first set strength, release the pressure of the first jack, retract the piston rod into the first installation chamber, and remove the first jack.

8. The construction method according to claim 7, characterized in that, It also includes the following steps: (5) After the installation of the first horizontal support is completed, the foundation pit is excavated until the installation elevation of the second horizontal support is reached. The excavation of the foundation pit is suspended. The combined waler is installed on the inner wall of the support pile and the second horizontal support is erected. The second prestressed seat is detachably installed on the end of the second horizontal support facing the combined waler via the second back plate. The second joint is installed on the connecting end of the combined waler via the second jacking plate. The second jacking plate is set opposite to the second front end plate. (6) Start the second jack in the second installation chamber. After the piston rod of the second jack extends out of the second installation chamber, it presses against the second connector to push the second connector until the second pre-pressure generated by the push reaches the set value. (7) Under the second set tension, connect the two ends of the second tension bolt to the second push plate and the second front plate respectively, and then pour grout between the second front plate and the second push plate. When the grout reaches the second set strength, release the pressure of the second jack, retract the piston rod into the second installation chamber, and remove the second jack.

9. The construction method according to claim 7, characterized in that, When the first connector is not pushed, the gap between the first front end plate and the first push plate is 5-100mm.

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