Deep foundation pit combined type steel frame pre-supporting device and construction method thereof

Abstract

The invention provides a deep foundation pit combined type steel frame pre-supporting device and a construction method thereof. The device comprises pre-supporting steel frame unit layers, servo pre-supporting mechanisms and vertical connecting pipes. Every two adjacent pre-supported steel frame unit layers are connected through a vertical connecting pipe, and the multiple pre-supported steel frame unit layers are arranged at intervals in the vertical direction to form a pre-supported steel frame body. Servo pre-supporting mechanisms are arranged at the two side ends of each pre-supporting steel frame unit layer, pre-supporting groove sections are constructed between the underground diaphragm walls located on the two sides of the foundation pit, the multiple pre-supporting groove sections are arranged at intervals in the wall length direction of the underground diaphragm walls, and a set of pre-supporting steel frame bodies below hoisting equipment can pass through each pre-supporting groove section. And the two side ends of the group of pre-supporting steel frame main bodies are supported on the inner walls of the underground diaphragm walls on the two sides of the foundation pit through servo pre-supporting mechanisms. The invention relates to the technical field of civil construction engineering construction, and can solve the problems of displacement, landslide and even sudden collapse of a foundation pit which is firstly excavated and then supported in traditional construction.

Description

Technical Field

[0001] This invention relates to the field of civil engineering construction technology, and in particular to a combined steel frame pre-support device for deep foundation pits and its construction method. Background Technology

[0002] With the advancement of urbanization, deep foundation pit construction has become particularly important in the construction engineering field. Deep foundation pit excavation involves changes in underground soil and rock strata, potentially causing geological shifts, including soil settlement, groundwater level fluctuations, and rock movement. This phenomenon is especially pronounced during subway deep foundation pit excavation, impacting not only underground structures and the geological environment but also leading to foundation settlement and building tilting in surrounding areas. Traditional foundation pit support typically follows a "excavate first, then support" construction logic; however, deep foundation pit construction is prone to risks of displacement, landslides, or even sudden collapse due to prolonged soil exposure.

[0003] Therefore, there is a need to provide a combined steel frame pre-support device for deep foundation pits and its construction method, which can solve the problems of displacement, landslides or even sudden collapse that are prone to occur in the traditional foundation pit construction of "excavation first, support later" in the existing technology. Summary of the Invention

[0004] The purpose of this invention is to provide a pre-supported steel frame device for deep foundation pits and its construction method, which can solve the problems of displacement, landslides or even sudden collapse that are common in the traditional foundation pit construction method of "excavation first, support later".

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A pre-supported steel frame structure for deep foundation pits includes: pre-supported steel frame unit layers, servo pre-supporting mechanisms, and vertical connecting pipes; adjacent pre-supported steel frame unit layers are connected by several vertical connecting pipes, making them parallel to each other; the pre-supported steel frame unit layers are arranged vertically at intervals to form the main body of the pre-supported steel frame; each pre-supported steel frame unit layer has a servo pre-supporting mechanism at both ends; pre-supporting trenches are formed between the underground continuous walls on both sides of the foundation pit; several pre-supporting trenches are arranged at intervals along the length of the underground continuous walls; each pre-supporting trench can be lowered into a pre-supported steel frame main body by hoisting equipment, and both ends of the pre-supported steel frame main body are supported on the inner walls of the underground continuous walls on both sides of the foundation pit by the servo pre-supporting mechanism.

[0007] Each pre-supported steel frame unit layer includes node connectors, a first standard section, and a second standard section; a pair of first standard sections and a pair of second standard sections are connected to form a rectangular frame structure by four node connectors. The node connectors at the four corners of the rectangular frame structure are connected to one end of the servo pre-support mechanism, so that when the rectangular frame structure is placed horizontally in the pre-support groove, the other end of the four servo pre-support mechanisms can support the inner wall of the underground continuous wall on both sides of the foundation pit; the vertical connecting pipe between two adjacent pre-supported steel frame unit layers is connected between two node connectors located on the same vertical line.

[0008] A short connecting pipe is connected between the node connector and one end of the servo pre-support mechanism.

[0009] The inner walls of the four node connectors of the first pre-supported steel frame unit layer are all connected with lifting ring plates. The upper part of the lifting ring plate extends upward to the top of the node connector and forms a lifting ring hole, so that the lifting ring plate can be connected to the sling of the hoisting equipment through the lifting ring hole.

[0010] The node connector has a cross-shaped structure in both its transverse and longitudinal sections, and several internally reinforced plates are spaced between the inner wall of the node connector and the lifting ring plate.

[0011] Fixed connecting rods are connected to the four node connectors of the first pre-supported steel frame unit layer, and the upper end of the fixed connecting rods is fixedly connected to the guide wall of the underground continuous wall.

[0012] The outer side of the pre-supported trench section is constructed with reinforcing piles. Several reinforcing piles are arranged between the underground continuous walls on both sides of the foundation pit along the length of the pre-supported trench section, and adjacent reinforcing piles are interlocked.

[0013] A construction method for the aforementioned deep foundation pit combined steel frame pre-bracing device includes the following steps:

[0014] Step 1: Construct the diaphragm wall and reinforce the trench walls of the diaphragm wall;

[0015] Step 2: Construct the guide wall and perform trenching for the pre-supported trench section;

[0016] Step 3: Assembly and hoisting of the pre-supported steel frame main body;

[0017] Step 4: The servo pre-support mechanism is loaded so that the two ends of the pre-supported steel frame can be supported on the inner walls of the underground continuous wall on both sides of the foundation pit through the servo pre-support mechanism.

[0018] Step 5: Connect the fixing rods between the top of the pre-supported steel frame and the guide wall, and backfill the pre-supported trench with solidified soil;

[0019] Step 6: Repeat steps 2 to 5 to complete the pre-support construction of the main body of the pre-supported steel frame in several pre-supported groove sections in sequence.

[0020] Step 3 includes the following sub-steps:

[0021] Step 31: Connect a pair of first standard sections and a pair of second standard sections with four node connectors to form a rectangular frame structure, forming a pre-supported steel frame unit layer. Splice several pre-supported steel frame unit layers in sequence according to the support height.

[0022] Step 32: Install the servo pre-support mechanism on the outside of the four node connectors of each pre-supported steel frame unit layer through short pipes;

[0023] Step 33: The connection nodes of two adjacent pre-supported steel frame unit layers are connected by vertical connecting pipes to form the main body of the pre-supported steel frame;

[0024] Step 34: Install lifting ring plate 13 on the connection node of the first pre-supported steel frame unit layer;

[0025] Step 35: The hoisting equipment's slings are connected to the lifting eye holes of the lifting eye plate. After the site is hardened, the pre-supported steel frame body is lowered into the pre-supported groove section using the hoisting equipment.

[0026] Step 36: Fill the space between the bottom of the lowest pre-supported steel frame unit layer and the bottom of the pre-supported groove 3 with micro-expansion self-compacting concrete.

[0027] In step 5, the solidified fluid soil is backfilled through a pre-embedded injection pipe. The pre-embedded injection pipe and the fixed connecting rod are lowered simultaneously, and the fixed connecting rod is tied to the connection node of the first pre-supported steel frame unit layer. After the main body of the pre-supported steel frame is lowered into place and the servo pre-supporting mechanism is loaded, the solidified fluid soil is pumped through the pre-embedded injection pipe to backfill the pre-supported trench section.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. This invention first constructs a pre-supported trench section and lowers the pre-supported steel frame main body for pre-support. After the servo pre-support mechanism is loaded and takes effect, the excavation of the foundation pit is carried out. A stable support system is established before the foundation pit is excavated, and the passive force of traditional support is transformed into active load resistance of pre-support. It has the advantage of being in a controlled state before the foundation pit is excavated, thereby effectively reducing the risk of soil deformation caused by the foundation pit being exposed for too long. It also breaks the time and space limitations of the process and can greatly shorten the construction cycle.

[0030] 2. In this invention, the trench section is pre-supported and constructed first, and then the foundation pit is excavated. The two processes are carried out in sequence, which avoids the high-altitude operation and foundation pit excavation that are carried out simultaneously during the traditional support installation, thereby reducing safety hazards such as mechanical collisions and falling objects. Attached Figure Description

[0031] The above and other objects, features and advantages of this disclosure will become more apparent from the accompanying drawings, in which like reference numerals generally denote like parts.

[0032] Figure 1 This is a partial top view of the construction of the pre-supporting groove section in the deep foundation pit combined steel frame pre-supporting device of the present invention;

[0033] Figure 2 This is a vertical sectional view of the main body of the pre-supported steel frame in the deep foundation pit combined steel frame pre-support device of the present invention;

[0034] Figure 3 This is a top view of the pre-supported steel frame unit layer in the deep foundation pit combined steel frame pre-support device of the present invention;

[0035] Figure 4 This is a construction schematic diagram of the deep foundation pit combined steel frame pre-support device of the present invention;

[0036] Figure 5 This is a cross-sectional schematic diagram of the node connectors and lifting ring plates in the deep foundation pit combined steel frame pre-support device of the present invention;

[0037] Figure 6 This is a vertical cross-sectional schematic diagram (perpendicular to the direction of the lifting ring plate) of the node connector and the lifting ring plate in the deep foundation pit combined steel frame pre-support device of the present invention.

[0038] Figure 7 This is a vertical cross-sectional schematic diagram (parallel to the direction of the lifting ring plate) of the node connector and the lifting ring plate in the deep foundation pit combined steel frame pre-support device of the present invention.

[0039] Figure 8 This is a side view of the installation of the lifting ring plate in the deep foundation pit combined steel frame pre-support device of the present invention;

[0040] Figure 9 This is a flowchart of the deep foundation pit combined steel frame pre-bracing method of the present invention.

[0041] In the figure, 1 is the reinforcing pile, 2 is the diaphragm wall, 3 is the pre-supported trench section, 5 is the guide wall, 6 is the fixed connecting rod, 8 is the node connector, 9 is the servo pre-support mechanism, 10 is the first standard section, 11 is the vertical connecting pipe, 12 is the short pipe, 13 is the lifting ring plate, 14 is the internal rib plate, 16 is the lifting ring hole, 17 is the foundation pit, and 18 is the second standard section. Detailed Implementation

[0042] The following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a further detailed explanation of the reinforced structure and construction method for the top water-resistant structure of an explosion-proof wall proposed in this invention. The advantages and features of this invention will become clearer from the following description and claims. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of this invention.

[0043] Please see the appendix Figure 1 and attached Figure 4 A pre-supported steel frame structure for deep foundation pits includes pre-supported steel frame unit layers, servo pre-supporting mechanisms 9, and vertical connecting pipes 11. Adjacent pre-supported steel frame unit layers are connected by several vertical connecting pipes 11, allowing them to be arranged parallel to each other. Several pre-supported steel frame unit layers are arranged vertically at intervals to form the main body of the pre-supported steel frame. Each pre-supported steel frame unit layer has a servo pre-supporting mechanism 9 at both ends. Pre-supporting grooves 3 are constructed between the underground continuous walls 2 on both sides of the foundation pit 17. Several pre-supporting grooves 3 are arranged at intervals along the length of the underground continuous walls 2. Each pre-supporting groove 3 can be lowered into a pre-supported steel frame main body using hoisting equipment, and both ends of this pre-supported steel frame main body are supported on the inner walls of the underground continuous walls 2 on both sides of the foundation pit 17 by the servo pre-supporting mechanism 9.

[0044] After the construction of the diaphragm wall 2 is completed, before the excavation of the foundation pit 17, a pre-supported trench section 3 is pre-constructed to lower several pre-supported steel frame unit layers and the pre-supported steel frame main body formed by connecting the vertical connecting pipes 11. In this way, the axial prestress is applied to the diaphragm wall 2 on both sides of the foundation pit 17 by the loading of the servo pre-support mechanism 9 at both ends of the pre-supported steel frame main body, thereby achieving the purpose of actively controlling the deformation of the diaphragm wall 2 in the foundation pit 17.

[0045] It should be noted that "17" in the figure represents the construction scope of the foundation pit. In this invention, the soil of foundation pit 17 has not yet been excavated.

[0046] Preferably, four pre-supported steel frame unit layers can be arranged vertically, with a spacing of 5m between two adjacent pre-supported steel frame unit layers. The number and spacing of the pre-supported steel frame unit layers can also be adjusted according to actual support requirements and support depth adaptability.

[0047] Preferably, the servo pre-support mechanism 9 can be a servo jack. The servo pre-support mechanism 9 mainly consists of an end plate, channel steel, reinforcing plates, and jacks, and is part of the servo system. It can obtain the displacement data of the diaphragm wall 2 through the observation hole outside the diaphragm wall 2, thereby dynamically adjusting the pre-jacking force of the jacks. The servo jack is a commonly used axial prestressing loading device in this field, and its specific structure and usage will not be described in detail here.

[0048] Please see the appendix Figure 2 To be continued Figure 4 Each pre-supported steel frame unit layer includes node connectors 8, a first standard section 10, and a second standard section 18. A pair of first standard sections 10 and a pair of second standard sections 18 are connected by four node connectors 8 to form a rectangular frame structure. The node connectors 8 at the four corners of the rectangular frame structure are connected to one end of the servo pre-support mechanism 9, so that when the rectangular frame structure is placed horizontally in the pre-support groove 3, the other end of the four servo pre-support mechanisms 9 can support the inner wall of the underground continuous wall 2 on both sides of the foundation pit 17. The vertical connecting pipe 11 between two adjacent pre-supported steel frame unit layers is connected between two node connectors 8 located on the same vertical line.

[0049] Preferably, the node connector 8 can be made of steel pipe. The first standard section 10, the vertical connecting pipe 11 and the second standard section 18 are all made of φ800×20 steel pipe. The steel pipe specifications of the first standard section 10, the vertical connecting pipe 11 and the second standard section 18 are one size smaller than the steel pipe specifications of the ten-way connector, so as to facilitate the insertion and connection of the first standard section 10 and the second standard section 18 with the node connector 8, which ensures reliable connection and convenient assembly and disassembly.

[0050] The lengths of the first standard section 10, the vertical connecting pipe 11, and the second standard section 18 can be adjusted adaptively according to actual support requirements. The width of the pre-supported groove section 3 is slightly larger than the width of the rectangular frame structure. The length of the pre-supported groove section 3 is consistent with the spacing of the underground continuous walls 2 on both sides of the foundation pit 17, so as to ensure that the main body of the pre-supported steel frame can be lowered into the pre-supported groove section 3 and supported between the underground continuous walls 2 on both sides of the foundation pit 17.

[0051] The first standard section 10, the vertical connecting pipe 11, the second standard section 18, and the node connecting parts 8 can also be connected by existing methods such as end plates and flanges. These can be adapted to actual construction needs and will not be elaborated here.

[0052] Please see the appendix Figure 2 To be continued Figure 4 A short pipe 12 is connected between the node connector 8 and one end of the servo pre-support mechanism 9.

[0053] The short pipe 12 facilitates the connection between the node connector 8 and the servo pre-support mechanism 9, and can also better adapt to pre-support groove sections 3 of different lengths, enabling the pre-support steel frame body to be manufactured in a standardized manner. Preferably, the short pipe 12 can be made of steel pipe of the same specifications as the first standard section 10 and the second standard section 18, and the length of the short pipe 12 can be adjusted adaptively according to the length of the pre-support groove section 3.

[0054] Please see the appendix Figure 2 Appendix Figure 4 To be continued Figure 8The inner walls of the four node connectors 8 of the first pre-supported steel frame unit layer are all connected with lifting ring plates 13. The upper part of the lifting ring plate 13 extends upward to the top of the node connector 8 and forms a lifting ring hole 16, so that the lifting ring plate 13 can be connected to the sling of the hoisting equipment through the lifting ring hole 16.

[0055] Preferably, the lifting ring plate 13 can be made of steel plate, the height of the lifting ring plate 13 is greater than the height of the node connector 8, and the width of the lifting ring plate 13 is consistent with the inner diameter of the steel pipe of the node connector 8, so that the lifting ring plate 13 can be welded and fixed inside the steel pipe of the node connector 8.

[0056] Please see the appendix Figure 5 To be continued Figure 7 The node connector 8 has a cross-shaped structure in both its transverse and longitudinal sections, and several internally reinforced plates 14 are spaced between the inner wall of the node connector 8 and the lifting ring plate 13.

[0057] Preferably, the internal rib plate 14 can be made of steel plate. One end of the internal rib plate 14 is vertically welded to the lifting ring plate 13, and the other end of the internal rib plate 14 is welded to the inner wall of the steel pipe of the node connector 8. The number and arrangement of the internal rib plates 14 can be adaptively adjusted according to actual needs to improve the installation reliability of the lifting ring plate 13 in the node connector 8 and facilitate the hoisting of the entire pre-supported steel frame body through the lifting ring plate 13.

[0058] Please see the appendix Figure 3 The four node connectors 8 of the first pre-supported steel frame unit layer are all connected with fixed connecting rods 6, and the upper end of the fixed connecting rods 6 is fixedly connected to the guide wall 5 of the underground continuous wall 2.

[0059] Preferably, the fixed connecting rod 6 can be made of steel profiles to improve the installation and pre-support stability of the pre-supported steel frame body. The specifications and models of the fixed connecting rod 6 can be selected according to the actual support conditions.

[0060] Please see the appendix Figure 1 The pre-supported trench section 3 is constructed with reinforcing piles 1 on the outside. Several reinforcing piles 1 are arranged between the underground continuous walls 2 on both sides of the foundation pit 17 along the length direction of the pre-supported trench section 3, and two adjacent reinforcing piles 1 are interlocked.

[0061] Preferably, the reinforcing pile 1 can be a triaxial mixing pile, used to reinforce the trench wall of the pre-supported trench section 3, thereby ensuring the safety and reliability of the lowering, installation, and pre-support loading of the pre-supported steel frame main body. The reinforcing pile 1 can be of the same specification as the reinforcing piles of the diaphragm wall 2 and constructed simultaneously.

[0062] Please see the appendix Figure 1 To be continued Figure 9 A construction method for a pre-supported composite steel frame device for deep foundation pits includes the following steps:

[0063] Step 1: Construct diaphragm wall 2 and reinforce the trench walls of diaphragm wall 2.

[0064] Before constructing the trench wall of diaphragm wall 2, the flatness of the existing diaphragm wall sidewalls should be assessed to ensure that the trench wall meets the settlement conditions of the pre-supported steel frame. The slurry mix ratio for trench wall protection should be determined through testing.

[0065] The trench walls of diaphragm wall 2 can be reinforced with triaxial mixing piles. The reinforcement of diaphragm wall 2 and its trench walls is a routine procedure in foundation pit construction, and will not be elaborated here.

[0066] Step 2: Construct guide wall 5 and perform trenching construction for pre-supported trench section 3.

[0067] The guide wall 5 is a standard procedure in foundation pit construction and will not be described in detail here. After the guide wall 5 is cured, the pre-supported trench section 3 is constructed using the underground continuous wall 2 construction equipment. Specialized equipment should be used during the trenching process, and the verticality should be monitored in real time on-site to ensure it meets design requirements. By optimizing the mud slurry mix ratio, increasing the mud slurry's specific gravity and various properties, the wall stability is improved, and the risk of collapse is controlled.

[0068] During the trenching process of pre-supported section 3, effective measures should be taken to prevent trench wall collapse and narrowing of the trench width. Latex should be removed from the connection points between the pre-supported section 3 and the diaphragm wall 2 at both ends to ensure a smooth and flat surface at this location. Pre-supported section 3 should be inspected according to specifications and design requirements to ensure trenching quality and avoid affecting the settlement of the pre-supported steel frame structure. After the trench walls have stabilized, the construction of the guide wall 5 should begin, followed by curing.

[0069] Step 3: Assembly and hoisting of the pre-supported steel frame main body.

[0070] Step 3 includes the following sub-steps:

[0071] Step 31: Connect a pair of first standard sections 10 and a pair of second standard sections 18 through four node connectors 8 to form a rectangular frame structure, forming a pre-supported steel frame unit layer. Then, splice several pre-supported steel frame unit layers in sequence according to the support height.

[0072] Step 32: The servo pre-support mechanism 9 is installed on the outside of the four node connectors 8 of each pre-supported steel frame unit layer through the short pipe 12.

[0073] Step 33: The connection nodes 8 of two adjacent pre-supported steel frame unit layers are connected by vertical connecting pipes 11 to form the main body of the pre-supported steel frame.

[0074] Step 34: Install the lifting ring plate 13 on the connection node 8 of the first pre-supported steel frame unit layer.

[0075] Step 35: The hoisting equipment is connected to the lifting eye hole 16 of the lifting eye plate 13. After the site is hardened, the main body of the pre-supported steel frame is lowered into the pre-supported groove section 3 by the hoisting equipment.

[0076] Step 36: Fill the space between the bottom of the lowest pre-supported steel frame unit layer and the bottom of the pre-supported groove 3 with micro-expansion self-compacting concrete.

[0077] Step 4: The servo pre-support mechanism 9 is loaded so that the two ends of the pre-supported steel frame body can be supported on the inner walls of the underground continuous wall 2 on both sides of the foundation pit 17 through the servo pre-support mechanism 9.

[0078] Specifically, the servo pre-support mechanism 9 is loaded in multiple stages. When the main body of the pre-supported steel frame is lowered to the corresponding design vertical depth, all the servo pre-support mechanisms 9 on the main body of the pre-supported steel frame are loaded at the same time. The load size should be determined according to the design working conditions, and the axial force should be observed regularly in the later stage.

[0079] Step 5: Connect the fixed connecting rod 6 between the top of the pre-supported steel frame body (connection node 8 of the first pre-supported steel frame unit layer) and the guide wall 5, and backfill the pre-supported trench section 3 with solidified soil.

[0080] Specifically, the solidified fluidized soil is recharged through a pre-embedded injection pipe. The pre-embedded injection pipe and the fixed connecting rod 6 are lowered simultaneously, and the fixed connecting rod 6 is tied to the connection node 8 of the first pre-supported steel frame unit layer with lead wire. After the main body of the pre-supported steel frame is lowered into place and the servo pre-support mechanism 9 is loaded, the solidified fluidized soil is pumped through the pre-embedded recharge pipe to backfill the pre-supported trench section 3.

[0081] The 7-day compressive strength of the reinjected premixed fluidized solidified soil should not be less than 0.5 MPa, and the 28-day compressive strength should not be less than 1.0 MPa. The solidifying agent used to prepare the fluidized solidified soil should preferably be a cement-based or mineral-based composite cementitious material. The selected solidifying agent should be free of heavy metal contamination, and its quality inspection should meet the relevant provisions of the current industry standard "Soft Soil Stabilizer" CJ / T526 and the Shanghai Municipal Engineering Construction Standard "Technical Standard for Application of Soil Hardener" DG / TJO8-2082.

[0082] Step 6: Repeat steps 2 to 5 to complete the pre-support construction of the main body of the pre-supported steel frame in several pre-supported groove sections 3.

[0083] Once the pre-support construction of all the pre-supported steel frame main bodies is completed, the excavation of the foundation pit 17 can be carried out.

[0084] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the protection scope of the claims.

Claims

1. A pre-supported composite steel frame device for deep foundation pits, characterized in that, include: The pre-supported steel frame unit layer, the servo pre-support mechanism (9) and the vertical connecting pipe (11) are connected by several vertical connecting pipes (11) between two adjacent pre-supported steel frame unit layers, so that the two adjacent pre-supported steel frame unit layers are set parallel to each other. Several pre-supported steel frame unit layers are arranged vertically at intervals to form the main body of the pre-supported steel frame. Each pre-supported steel frame unit layer is provided with a servo pre-support mechanism (9) on both sides. A pre-supported groove section (3) is formed between the underground continuous walls (2) on both sides of the foundation pit (17). Several pre-supported groove sections (3) are arranged at intervals along the wall length direction of the underground continuous wall (2). A set of pre-supported steel frame main bodies can be lowered in each pre-supported groove section (3) by hoisting equipment. Both sides of the set of pre-supported steel frame main bodies are supported on the inner wall of the underground continuous wall (2) on both sides of the foundation pit (17) by the servo pre-support mechanism (9).

2. The deep foundation pit combined steel frame pre-support device as described in claim 1, characterized in that, Each pre-supported steel frame unit layer includes node connectors (8), a first standard section (10), and a second standard section (18); a pair of first standard sections (10) and a pair of second standard sections (18) are connected to form a rectangular frame structure by four node connectors (8). The node connectors (8) at the four corners of the rectangular frame structure are connected to one end of the servo pre-support mechanism (9), so that when the rectangular frame structure is placed horizontally in the pre-support groove (3), the other end of the four servo pre-support mechanisms (9) can support the inner wall of the underground continuous wall (2) on both sides of the foundation pit (17); the vertical connecting pipe (11) between two adjacent pre-supported steel frame unit layers is connected between two node connectors (8) located on the same vertical line.

3. The deep foundation pit combined steel frame pre-support device as described in claim 2, characterized in that, A short pipe (12) is connected between the node connector (8) and one end of the servo pre-support mechanism (9).

4. The deep foundation pit combined steel frame pre-support device as described in claim 2 or 3, characterized in that, The inner walls of the four node connectors (8) of the first pre-supported steel frame unit layer are all connected with lifting ring plates (13). The upper part of the lifting ring plate (13) extends upward to the top of the node connector (8) and forms a lifting ring hole (16), so that the lifting ring plate (13) can be connected to the sling of the hoisting equipment through the lifting ring hole (16).

5. The deep foundation pit combined steel frame pre-support device as described in claim 4, characterized in that, The node connector (8) has a cross-shaped structure in both its transverse and longitudinal sections, and several internal ribbed plates (14) are connected between the inner wall of the node connector (8) and the lifting ring plate (13) at intervals.

6. The deep foundation pit combined steel frame pre-bracing device as described in claim 2, characterized in that, Fixed connecting rods (6) are connected to the four node connectors (8) of the first pre-supported steel frame unit layer. The upper end of the fixed connecting rods (6) is fixedly connected to the guide wall (5) of the underground continuous wall (2).

7. The deep foundation pit combined steel frame pre-bracing device as described in claim 1 or 2, characterized in that, The pre-supported trench section (3) is constructed with reinforcing piles (1) on the outside. Several reinforcing piles (1) are arranged along the length of the pre-supported trench section (3) between the underground continuous walls (2) on both sides of the foundation pit (17), and two adjacent reinforcing piles (1) are interlocked.

8. A construction method for the deep foundation pit combined steel frame pre-bracing device as described in claim 2, characterized in that, Includes the following steps: Step 1: Construct the diaphragm wall (2) and reinforce the trench walls of the diaphragm wall (2); Step 2: Construction of guide wall (5) and trenching of pre-supported trench section (3); Step 3: Assembly and hoisting of the pre-supported steel frame main body; Step 4: The servo pre-support mechanism (9) is loaded so that the two ends of the pre-supported steel frame body can be supported on the inner wall of the underground continuous wall (2) on both sides of the foundation pit (17) through the servo pre-support mechanism (9); Step 5: Connect the fixed connecting rod (6) between the top of the pre-supported steel frame body and the guide wall (5), and backfill the pre-supported groove section (3) with solidified soil; Step 6: Repeat steps 2 to 5 to complete the pre-support construction of the main body of the pre-support steel frame in several pre-supported grooves (3) in sequence.

9. The construction method as described in claim 8, characterized in that, Step 3 includes the following sub-steps: Step 31: Connect a pair of first standard sections (10) and a pair of second standard sections (18) into a rectangular frame structure through four node connectors (8) to form a pre-supported steel frame unit layer. Then, splice several pre-supported steel frame unit layers in sequence according to the support height. Step 32: The servo pre-support mechanism (9) is installed on the outside of the four node connectors (8) of each pre-supported steel frame unit layer through the short pipe (12); Step 33: The connection nodes (8) of two adjacent pre-supported steel frame unit layers are connected by vertical connecting pipes (11) to form the main body of the pre-supported steel frame; Step 34: Install the lifting ring plate (13) on the connection node (8) of the first pre-supported steel frame unit layer; Step 35: The hoisting equipment is connected to the lifting eye hole (16) of the lifting eye plate (13). After the site is hardened, the main body of the pre-supported steel frame is lowered into the pre-supported groove section (3) by the hoisting equipment. Step 36: Fill the space between the bottom of the lowest pre-supported steel frame unit layer and the bottom of the pre-supported groove (3) with micro-expansion self-compacting concrete.

10. The construction method as described in claim 8, characterized in that, In step 5, the solidified fluid soil is backfilled through the pre-embedded injection pipe. The pre-embedded injection pipe and the fixed connecting rod (6) are lowered simultaneously, and the fixed connecting rod (6) is tied to the connection node (8) of the first pre-supported steel frame unit layer. After the main body of the pre-supported steel frame is lowered into place and the servo pre-supporting mechanism (9) is loaded, the solidified fluid soil is pumped through the pre-embedded injection pipe to backfill the pre-supported trench section (3).

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