A support conversion method for realizing synchronous construction of adjacent deep foundation pits in open excavation

Abstract

The application discloses a support conversion method for realizing synchronous construction of deep foundation pits of adjacent sections of open excavation, and relates to the technical field of civil construction; the method comprises the following steps: installing a first layer of support conversion system under a first layer of inclined support system of a foundation pit, so that the first layer of support conversion system replaces the first layer of inclined support system; symmetrically excavating earthwork of adjacent foundation pits from the middle to both sides; firstly, unloading earthwork close to the middle of a plug wall; secondly, unloading earthwork close to the two sides of the enclosure pile; finally, unloading the remaining earthwork; removing the first layer of inclined support system of the foundation pit; repeating the operation until the n layer of inclined support system of the foundation pit is converted into the n layer of support conversion system; meanwhile, the plug wall is removed, the n time excavation of the adjacent foundation pit is completed, and the n layer of straight support system is installed; by replacing the inclined support system with the straight support system, and by adopting the method of unloading the earthwork after the plug wall is unloaded by means of partitioned and segmented support jumping, the load conversion is realized, the support conversion purpose is achieved, and the synchronous construction is realized on the basis of ensuring the safety of the foundation pit.

Description

Technical Field

[0001] This invention relates to the field of civil engineering construction technology, specifically to a support conversion method for realizing simultaneous construction of deep foundation pits with adjacent open-cut sections. Background Technology

[0002] For stations or sections constructed using the open-cut method, long foundation pits are typically divided into several sections for phased construction due to constraints such as land acquisition and demolition, traffic diversion, underground pipeline relocation, or technological limitations. A common approach is to install diagonal bracing on the endwall of foundation pit one. This bracing transfers the passive earth pressure at the endwall to the retaining structures on the left and right sides of the foundation pit, creating an internal equilibrium. Adjacent foundation pits two and three must be excavated only after the main structure of foundation pit one is completed and the steel diagonal bracing on the endwall is removed layer by layer. This inevitably increases costs, time constraints, safety concerns, schedule delays, and traffic congestion.

[0003] Current support replacement methods only apply to the same cross-section of the same foundation pit and structural construction section. Primarily used during the structural construction phase, these methods replace the horizontal internal supports that affect structural construction, such as retaining piles or diaphragm walls. By changing the height and position of the supports, they are placed on the already constructed inner lining wall, facilitating the construction of the middle or top slab at the support location. Generally, it's a replacement of one direct support with another. The direction of force on the supports remains unchanged, but the magnitude of the force on individual supports changes. Before and after the replacement, they remain independent force balance systems and cannot work together with the support systems of adjacent foundation pits. Thus, during the previous stage of foundation pit excavation, the lack of overall force balance between the support systems of adjacent foundation pits prevents simultaneous construction, resulting in wasted work space and increased costs, time constraints, safety concerns, schedule delays, and traffic congestion. Summary of the Invention

[0004] This invention addresses the technical problem that current support replacement methods only target the same foundation pit and fail to establish overall stress balance between adjacent foundation pits, thus preventing simultaneous construction of adjacent foundation pits. The aim is to provide a support conversion method for achieving simultaneous construction of adjacent deep foundation pits in open excavation. This method involves sequentially replacing the inclined bracing of the end wall of foundation pit one with straight bracing, and then excavating the adjacent foundation pit on the other side of the end wall using a planar partitioning approach, symmetrically from the center to both sides, skip-bracing, and gradual unloading. This gradually weakens the force transmitted from the end wall to the steel inclined bracing, allowing the steel straight bracing of foundation pit one to bear the active earth pressure on both sides. This achieves the goal of replacing the inclined bracing with straight bracing, establishing overall stress balance in the support system between adjacent foundation pits, and enabling simultaneous construction of adjacent foundation pits.

[0005] This invention is achieved through the following technical solution:

[0006] A method for support conversion to achieve simultaneous construction of adjacent open-cut deep foundation pits involves dividing the deep foundation pit into multiple pit areas for separate construction using end-cap walls. For a specific pit (pit 1) to be constructed first, retaining piles are installed, and a layered support system is constructed. The support system includes a vertical bracing system connected to the retaining piles and a diagonal bracing system connected to the end-cap walls. After pit 1 has been excavated to a certain stage, support conversion is performed, including the following steps:

[0007] S1. Install the first layer of replacement support system below the first layer of inclined support system in the foundation pit 1. The replacement support system includes steel replacement straight supports connected to the retaining piles.

[0008] S2. Apply axial prestress to the first-layer support system in stages so that the first-layer support system can fully bear the axial load.

[0009] S3. Excavation of adjacent foundation pits: The excavation height extends to the area between the support system of this layer and the support system of the next layer. The excavation method is to excavate symmetrically from the middle to both sides. First, unload the soil near the middle of the end wall, then unload the soil near the retaining piles on both sides, and finally unload the remaining soil.

[0010] S4. Remove the first layer of the diagonal bracing system in foundation pit 1 and completely transfer the load of the diagonal bracing system to the first layer of the replacement bracing system;

[0011] S5. Repeat steps S1-S4 to convert the second layer of inclined bracing system of foundation pit 1 into the second layer of replacement bracing system. At the same time, remove the end wall to the excavation height of the adjacent foundation pit, retain the top cap beam of the end wall and the pile foundation inside the end wall as the first layer of direct bracing system of the adjacent foundation pit, and install the second layer of direct bracing system.

[0012] S6. Repeat step S5 until the first foundation pit completes the conversion of the nth layer of inclined bracing system, and the adjacent foundation pit completes the nth excavation and installs the nth layer of direct bracing system.

[0013] Furthermore, the replacement support system includes multiple steel replacement straight supports, connecting beam three, and replacement support steel lattice columns. The two ends of the steel replacement straight supports are fixed to the retaining piles by steel walers one. The replacement support steel lattice columns are vertically set in the foundation pit. Connecting beam three is installed on both sides of the replacement support steel lattice columns, and the steel replacement straight supports are fixed on the connecting beam three.

[0014] Furthermore, the end of the steel replacement straight support is hung on the top of the steel waler by an L-shaped steel plate, and the steel replacement straight support is connected to the capping beam of the foundation pit by a steel wire rope.

[0015] Furthermore, the steel straight brace is fixed to the connecting beam three by a U-shaped channel steel.

[0016] Furthermore, the end of the steel straight support is also equipped with an automatic axial force compensation device.

[0017] Furthermore, the support system of the first foundation pit is connected to the retaining piles via the second steel waler, and the support system of the adjacent foundation pits is connected to the retaining piles via the third steel waler.

[0018] Furthermore, the direct support system includes steel direct supports, direct support steel lattice columns, and connecting beam one. The two ends of the steel direct supports are fixed to the retaining piles by steel walers two. The direct support steel lattice columns are vertically set in the foundation pit. Connecting beam one is installed on both sides of the direct support steel lattice columns, and the steel direct supports are fixed on the connecting beam one.

[0019] Furthermore, the diagonal bracing system includes steel diagonal bracing, connecting beam two, and diagonal bracing steel lattice columns. One end of the steel diagonal bracing is fixed to the retaining pile through steel waler one, and the other end is connected to the end cap wall. The diagonal bracing steel lattice columns are vertically installed in the foundation pit. Connecting beam two is installed on both sides of the diagonal bracing steel lattice columns, and the steel diagonal bracing is fixed on the connecting beam two.

[0020] Furthermore, the axial prestressing of the first-layer support system is applied in three stages:

[0021] The first application is 40% of the design axial force, the second is 70% of the design axial force, and the third is 100% of the design axial force.

[0022] Furthermore, after removing the end wall to the excavation height of the adjacent foundation pit, the steel waler three of the adjacent foundation pit needs to be connected to the steel waler two of foundation pit one, and then the direct support system of the adjacent foundation pit is installed.

[0023] Furthermore, the steel walers corresponding to the second to nth layer of the support system are installed using a balanced counterweight method.

[0024] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0025] 1. This invention replaces the steel diagonal bracing of the same cross section with steel straight bracing in the height direction in the first foundation pit. The diagonal bracing of the end wall of the first foundation pit is replaced with straight bracing in sequence. On the other side of the end wall, the adjacent foundation pit is excavated in a planar partitioning manner, symmetrically from the middle to both sides, with skip bracing and step-by-step unloading. This makes the force transmitted from the end wall to the steel diagonal bracing gradually weaken. The steel straight bracing of the first foundation pit bears the active earth pressure on both sides, achieving the purpose of using straight bracing to replace diagonal bracing. This establishes the overall force balance of the support system between adjacent foundation pits, enabling the adjacent foundation pits to be constructed simultaneously.

[0026] 2. Traditional sequential construction of adjacent foundation pits results in a limited number of working faces per pit. Each trade can only proceed sequentially according to its designated steps, leading to idle time for trades outside the time frame of their assigned tasks, thus increasing costs. However, with the method of this invention, adjacent foundation pits can be excavated while the previous stage of excavation is still underway, creating new working faces. This allows for continuous construction by different trades, reducing idle time, improving the efficiency of construction resource utilization, lowering construction costs, accelerating progress, and minimizing municipal traffic pressure and investment waste caused by phased traffic diversion.

[0027] 3. In this invention, the prestressing of the steel-to-straight brace is applied in stages according to the design axial force value of 0→40%→70%→100%. By installing an automatic axial force compensation device at the movable end of the steel-to-straight brace, the axial force is automatically compensated and dynamically corrected during the unloading of earthwork in the adjacent foundation pit, thus ensuring the design prestress value of the steel-to-straight brace and ensuring the safety of the foundation pit.

[0028] 4. This invention achieves the gradual unloading of the active earth pressure on the end wall by using segmented and phased jump bracing to unload the earthwork after the end wall is completed. This gradually weakens the force transmitted from the steel waler to the steel diagonal bracing, and re-establishes a stable and balanced force system at the ends of the foundation pit. After the earthwork is unloaded in stages, the steel waler is no longer subjected to active earth pressure, and the diagonal bracing can be easily removed, achieving load transfer and the purpose of replacing the bracing.

[0029] 5. In this invention, when excavating and cutting the end wall layer by layer, a pile foundation is left in the middle of the top cap beam at the top of the end wall to ensure the compressive stability of the top cap beam when it is transformed into the first layer of steel straight support.

[0030] 6. After the end wall is cut into layers, the steel walers between adjacent foundation pits are immediately connected to form a whole. If the distance is greater than the designed steel straight brace spacing, an additional steel straight brace needs to be added near the end wall to form an effective unified support and ensure the stability of the overall structure. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0032] Figure 1 This is a plan view of foundation pit 1 and adjacent foundation pits;

[0033] Figure 2 This is a plan layout diagram of the installation and replacement support system for the foundation pit;

[0034] Figure 3A cross-sectional view of the first layer of the replacement support system installed in the foundation pit;

[0035] Figure 4 This is a schematic diagram of the connection structure between the retaining piles and the replacement support system.

[0036] Figure 5 A schematic diagram of the connection structure between the steel straight brace and the connecting beam 3;

[0037] Figure 6 This is a zoning diagram for unloading earthwork from adjacent foundation pits;

[0038] Figure 7 This is a longitudinal section view of the first foundation pit after the completion of the first layer of support replacement and the adjacent foundation pit;

[0039] Figure 8 This is a cross-sectional view of the foundation pit after the first layer of support replacement is completed.

[0040] Figure 9 A cross-sectional view of the installation of the second-layer replacement support system in the foundation pit;

[0041] Figure 10 This is a longitudinal section view of the first foundation pit after the completion of the second layer of support replacement and the adjacent foundation pit;

[0042] Figure 11 A cross-sectional view of the completed second-layer support system for the foundation pit;

[0043] Figure 12 This is a cross-sectional view of the second excavation of the foundation pit;

[0044] Figure 13 This is a longitudinal section view of the first foundation pit after the nth layer of support replacement is completed, and the adjacent foundation pit.

[0045] Figure 14 This is a cross-sectional view of the nth layer of the foundation pit support system after completion.

[0046] Figure 15 This is a cross-sectional view of the second foundation pit after the nth excavation.

[0047] The attached diagram shows the markings and corresponding component names:

[0048] 1-Retaining piles, 2-Straight bracing system, 21-Steel straight bracing, 22-Straight bracing steel lattice column, 23-Connecting beam one, 3-Diagonal bracing system, 31-Steel diagonal bracing, 32-Connecting beam two, 33-Diagonal bracing steel lattice column, 4-Replacement bracing system, 41-Steel replacement straight bracing, 42-Connecting beam three, 43-Replacement bracing steel lattice column, 44-L-shaped steel plate, 45-U-shaped channel steel, 5-End wall, 501-Top cap beam, 6-Automatic axial force compensation device, 7-Steel waler one, 8-Steel waler two, 9-First cap beam of foundation pit, 10-Steel wire rope, 11-Steel waler three, 12-Pile foundation. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0050] Example 1

[0051] For the first foundation pit of the subway open-cut foundation pit, which is currently under earthwork excavation, this embodiment adopts steel straight bracing 21 to replace the reinforced concrete diagonal bracing or steel diagonal bracing 31 in each layer in the depth direction of the foundation pit. In conjunction with the adjacent foundation pit to be excavated simultaneously, a method of symmetrical, skip-bracing, and step-by-step unloading of earthwork is adopted on the other side of the end wall 5, from the middle to both sides, to achieve the purpose of replacing the diagonal bracing with straight bracing and excavating the adjacent foundation pit simultaneously.

[0052] The specific implementation process will be described in detail below with reference to the accompanying drawings.

[0053] Example 1

[0054] This embodiment 1 describes the structure of the support system and the replacement support system 4 involved in the present invention, such as... Figure 1-5 As shown.

[0055] The deep foundation pit is divided into multiple foundation pits by the end wall 5 to facilitate construction in different areas. The top of the end wall 5 has a top cap beam 501, and a pile foundation 12 is left inside. One of the foundation pits that is excavated first is designated as foundation pit one. The support system of foundation pit one and the adjacent foundation pits are the same. The support system of foundation pit one is connected to the retaining pile 1 through steel waler two 8. The support system of the adjacent foundation pits is connected to the retaining pile 1 through steel waler three 11.

[0056] The straight support system 2 includes steel straight supports 21, straight support steel lattice columns 22, and connecting beams 23. The two ends of the steel straight supports 21 are fixed to the retaining piles 1 by steel walers 8. The straight support steel lattice columns 22 are vertically set in the foundation pit. Connecting beams 23 are installed on both sides of the straight support steel lattice columns 22. The steel straight supports 21 are fixed on the connecting beams 23. The connecting beams 23 connect multiple steel straight supports 21 into one unit and are connected to the steel straight supports 21 at 90°.

[0057] The diagonal bracing system 3 includes steel diagonal braces 31, connecting beams 32, and diagonal bracing steel lattice columns 33. One end of the steel diagonal brace 31 is fixed to the retaining pile 1 through a steel waler 7, and the other end is connected to the end wall 5. The diagonal bracing steel lattice columns 33 are vertically installed in the foundation pit. Connecting beams 32 are installed on both sides of the diagonal bracing steel lattice columns 33. The steel diagonal braces 31 are fixed on the connecting beams 32. The connecting beams 32 connect multiple steel diagonal braces 31 into one unit and are connected to the steel diagonal braces 31 at a 90° angle.

[0058] The replacement support system 4 includes multiple steel replacement straight supports 41, connecting beam 3 42, and replacement support steel lattice columns 43.

[0059] The two ends of the steel replacement straight brace 41 are fixed to the retaining pile 1 through the steel waler 1 7. The steel waler 1 7 is installed below the steel waler 2 8 of the first layer of inclined bracing system 3, so that the prestress of the steel replacement straight brace 41 is transferred to the retaining pile 1 or diaphragm wall on both sides through the steel waler to achieve force balance.

[0060] Multiple steel straight braces 41 need to be installed to directly bear the active earth pressure on both sides during the bracing replacement process. Installed under the steel diagonal braces 31, they reduce the stress on the diagonal braces to zero during the staged application of prestress, thus achieving the purpose of replacing the diagonal braces. In the limited space near the end wall 5, the number of steel straight braces 41 plus the number of replacement braces is usually equal to the number of steel diagonal braces 31.

[0061] The end flange of the steel transformer straight support 41 is welded with an L-shaped steel plate 44 and hung on the top of the steel waler 7. The anti-fall measure is to use a φ16 steel wire rope 10 to be tightened with a pre-embedded steel ring of the foundation pit crown beam 9. The end of the steel transformer straight support 41 is also equipped with an automatic axial force compensation device 6, which can automatically replenish the prestress loss to the design value at any time.

[0062] The steel lattice column 43 is vertically installed in the foundation pit and pre-anchored with bored piles to transfer the vertical weight of the connecting beam 3 42 and the steel straight support 41 to the foundation.

[0063] The steel lattice column 43 is welded with connecting beams 3 42 on both sides. The steel straight brace 41 is fixed to the connecting beams 3 42 by U-shaped channel steel 45. The U-shaped channel steel 45 constrains the steel straight brace 41, which can reduce the span of the steel straight brace 41 and maintain compressive stability, while transferring the weight of the steel straight brace to the steel lattice column 43.

[0064] It should be noted that, for ease of distinction and explanation, in this invention, the connecting beam of the steel straight brace 21 is uniformly referred to as connecting beam one 23, the connecting beam of the steel diagonal brace 31 is uniformly referred to as connecting beam two 32, and the connecting beam of the steel straight brace 41 is uniformly referred to as connecting beam three 42; the steel waler of the cross bracing system 4 in the foundation pit one is uniformly referred to as steel waler one 7, the steel waler of the support system is uniformly referred to as steel waler two 8, and the steel walers of adjacent foundation pits are uniformly referred to as steel waler three 11.

[0065] Example 2

[0066] A method for support conversion to enable simultaneous construction of adjacent open-cut deep foundation pit sections, such as... Figure 6-15 As shown, the deep foundation pit is divided into multiple foundation pit areas for construction by the end wall 5. For a certain foundation pit that is constructed first, retaining piles 1 (or diaphragm wall) are set up and a support system is set up in layers. The support system includes a straight support system 2 connected to the retaining piles 1 and an inclined support system 3 connected to the end wall 5.

[0067] With the excavation of foundation pit 1 having reached a certain stage and external factors restricting construction of adjacent foundation pits ceasing, the retaining piles 1 and the first layer of support system can be constructed in the adjacent foundation pits. At this point, in order to achieve synchronous excavation of the foundation pits, the following method is adopted for support conversion, specifically including the following steps:

[0068] S1. Install the first layer of replacement support system 4 below the first layer of inclined support system 3 in foundation pit 1, such as... Figure 3 As shown.

[0069] S11. After the first layer of concrete support for adjacent foundation pits is completed, install the first layer of steel waler 7 and angle steel brackets under the capping beam of foundation pit 1. Install φ16 steel wire rope 10 and turnbuckles for fall prevention between the first layer of steel waler 7 and the capping beam and tighten them. Use C25 quick-setting fine stone concrete to compact the steel waler 7 and the retaining pile 1 (or diaphragm wall). The angle steel brackets (L125×12mm) are arranged at 2m intervals along the mileage direction and are fixed to the interlocking piles or diaphragm wall with steel expansion bolts M20L=285.

[0070] S12. On both sides of the replacement steel lattice column 43 and below the first layer of steel replacement straight support 41, install and fix the connecting beam 3 42 (2[40C channel steel) of the steel replacement straight support 41, and weld the connecting beam 3 42 to both sides of the replacement steel lattice column 43.

[0071] S2. Replace the first layer of the inclined support system 3 of the foundation pit with the first layer of the replacement support system 4, and unload the soil in the adjacent foundation pit.

[0072] S21. Install the first layer of steel-coupling straight bracing 41 under the first layer of inclined bracing system 3 in the foundation pit, and apply axial prestress to the first layer of steel-coupling straight bracing 41 in stages, from 0 to 40% to 70% to 100% to the most unfavorable working condition value, so that the steel-coupling straight bracing 41 can fully bear the Y-direction load.

[0073] S22. Excavation of adjacent foundation pits: The excavation height extends from the original ground level to the midpoint between the first and second support systems. The excavation method is symmetrical excavation from the center outwards, using a skip-bracing technique. Figure 6 As shown, the earthwork in zone ① is unloaded first, then the earthwork in zone ② is unloaded, and finally the earthwork in zone ③ is unloaded. When unloading the load in the X direction, the axial force automatic compensation device 6 installed at the shaft end of the first layer of steel straight support 41 can automatically replenish the prestress loss to the design value at any time.

[0074] S23. Remove the first layer of steel diagonal bracing 31, connecting beam 2 32, and steel waler 2 8 from foundation pit 1, completely transferring the load from steel diagonal bracing 31 to the second layer of steel direct bracing 41. Then, cut off the diagonal bracing steel lattice column 33 from the bottom of the first layer of steel diagonal bracing 31 to the top of the second layer of steel diagonal bracing 31, thus achieving the purpose of replacing the diagonal bracing with direct bracing. The structure of foundation pit 1 after the first layer of bracing replacement is shown in the figure. Figure 7and Figure 8 As shown.

[0075] S3. Replace the second layer of inclined bracing system 3 of foundation pit 1 with the second layer of replacement bracing system 4, continue to unload the soil of the adjacent foundation pit, connect foundation pit 1 and the adjacent foundation pit and install the second layer of straight bracing system 2.

[0076] S31. Install the second-layer support system according to steps S1-S21. Figure 9 As shown, the second layer of the diagonal bracing system 3 in foundation pit 1 is then replaced;

[0077] S32. Excavation of adjacent foundation pits, with the excavation height from the first excavation height to the middle of the second and third support systems, using the same excavation method as step S22.

[0078] S33. Remove the second layer of steel diagonal bracing 31, connecting beam 2 32, and steel waler 2 8 from foundation pit one, completely transferring the load of steel diagonal bracing 31 to the second layer of steel direct bracing 41. Then, cut off the diagonal bracing steel lattice column 33 from the bottom of the second layer of steel diagonal bracing 31 to the top of the third layer of steel diagonal bracing 31. The structure of foundation pit one after the completion of the second layer of bracing replacement is as follows. Figure 10-11 As shown.

[0079] S34. Use a wire saw to cut and remove the end cap wall 5. The cutting height is from the bottom of the top cap beam 501 of the end cap wall 5 to the second excavation height of the adjacent foundation pit. Figure 12 As shown, the top crown beam 501 of the retaining wall 5 and the pile foundation 12 are retained as the first layer of direct support at this location. The second layer of steel waler 3 11 of the adjacent foundation pit is connected to the second layer of steel waler 7 of the foundation pit to form a whole. If the distance between the steel replacement direct support 41 and the steel direct support 21 between adjacent foundation pits is greater than the design distance, an additional steel replacement direct support 41 needs to be added near the retaining wall 5 to form an effective unified support whole and ensure the stability of the overall structure.

[0080] S35. Install a second layer of direct support system 2 on adjacent foundation pits.

[0081] S4. Repeat the second layer of support replacement operation until the nth layer of the foundation pit is completed, replacing the inclined structure with a straight one. For adjacent foundation pits, complete the nth earthwork unloading and install the nth layer of straight support system 2. Figure 13-15 As stated above.

[0082] It should be noted that the excavation height of adjacent foundation pits is between the current support system and the next layer of support system. For example, if the nth excavation is carried out, the excavation height is between the heights of the nth and n+1th layer support systems.

[0083] Among them, the steel walers 7 corresponding to the second to nth layer replacement support system 4 are installed using the balance weight method.

[0084] Finally, it should be noted that the above specific embodiments are only used to describe the purpose, technical solution, and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation of the present invention and is not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the foregoing specific embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions or improvements can be made to some or all of the technical features. These modifications, equivalent substitutions, and improvements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A support conversion method for realizing synchronous construction of deep foundation pits with adjacent sections in open excavation, wherein the deep foundation pit is divided into multiple foundation pit areas for construction by means of a headwall (5), and retaining piles (1) are set for a certain foundation pit to be constructed first and a support system is set in layers, the support system including a straight support system (2) connected to the retaining piles (1) and an inclined support system (3) connected to the headwall (5), characterized in that, After the foundation pit has been excavated to a certain stage, the support conversion is carried out, including the following steps: S1. Install the first layer of replacement support system (4) below the first layer of inclined support system (3) in the foundation pit. The replacement support system (4) includes steel replacement straight support (41) connected to the retaining pile (1). S2. Apply axial prestress to the first layer of the replacement support system (4) in stages so that the first layer of the replacement support system (4) can fully bear the axial load. S3. Excavation of adjacent foundation pits, the excavation height is between the support system of this layer and the support system of the next layer. The excavation method is to excavate symmetrically from the middle to both sides. First, unload the soil near the middle of the end wall (5), then unload the soil near the retaining piles (1) on both sides, and finally unload the remaining soil. S4. Remove the first layer of the diagonal bracing system (3) of the foundation pit and completely transfer the load of the diagonal bracing system (3) to the first layer of the replacement bracing system (4); S5. Repeat steps S1-S4 to convert the second layer of inclined bracing system (3) of foundation pit 1 into the second layer of replacement bracing system (4). At the same time, remove the end wall (5) to the excavation height of the adjacent foundation pit, retain the top crown beam (501) of the end wall (5) and the pile foundation (12) inside the end wall (5) as the first layer of direct bracing system (2) of the adjacent foundation pit, and install the second layer of direct bracing system (2). S6. Repeat step S5 until the first foundation pit completes the conversion of the nth layer of inclined bracing system (3), and the adjacent foundation pit completes the nth excavation and installs the nth layer of direct bracing system (2).

2. The support conversion method for realizing synchronous construction of open-cut adjacent deep foundation pits according to claim 1, characterized in that, The replacement support system (4) includes multiple steel replacement straight supports (41), connecting beam three (42) and replacement support steel lattice column (43). The two ends of the steel replacement straight supports (41) are fixed to the retaining piles (1) through steel walers one (7). The replacement support steel lattice column (43) is vertically set in the foundation pit. Connecting beam three (42) is installed on both sides of the replacement support steel lattice column (43). The steel replacement straight supports (41) are fixed on the connecting beam three (42).

3. The support conversion method for realizing synchronous construction of open-cut adjacent deep foundation pits according to claim 2, characterized in that, The end of the steel replacement straight support (41) is hung on the top of the steel waler (7) by an L-shaped steel plate (44), and the steel replacement straight support (41) is connected to the foundation pit cap beam (9) by a steel wire rope (10).

4. The support conversion method for realizing synchronous construction of open-cut adjacent deep foundation pits according to claim 2, characterized in that, The steel straight brace (41) is fixed to the connecting beam three (42) by U-shaped channel steel (45).

5. The support conversion method for realizing synchronous construction of open-cut adjacent deep foundation pits according to claim 2, characterized in that, The end of the steel straight support (41) is also equipped with an automatic axial force compensation device (6).

6. The support conversion method for realizing synchronous construction of open-cut adjacent deep foundation pits according to claim 1, characterized in that, The support system of the first foundation pit is connected to the retaining pile (1) through the second steel waler (8), and the support system of the adjacent foundation pit is connected to the retaining pile (1) through the third steel waler (11).

7. The support conversion method for realizing synchronous construction of open-cut adjacent deep foundation pits according to claim 1, characterized in that, The straight support system (2) includes a steel straight support (21), a straight support steel lattice column (22), and a connecting beam (23). The two ends of the steel straight support (21) are fixed to the retaining piles (1) by steel walers (8). The straight support steel lattice column (22) is vertically set in the foundation pit. The connecting beam (23) is installed on both sides of the straight support steel lattice column (22). The steel straight support (21) is fixed on the connecting beam (23).

8. The support conversion method for realizing synchronous construction of open-cut adjacent deep foundation pits according to claim 1, characterized in that, The diagonal bracing system (3) includes steel diagonal bracing (31), connecting beam two (32), and diagonal bracing steel lattice column (33). One end of the steel diagonal bracing (31) is fixed to the retaining pile (1) through steel waler one (7), and the other end is connected to the end wall (5). The diagonal bracing steel lattice column (33) is vertically set in the foundation pit. Connecting beam two (32) is installed on both sides of the diagonal bracing steel lattice column (33), and the steel diagonal bracing (31) is fixed on the connecting beam two (32).

9. The support conversion method for realizing synchronous construction of open-cut adjacent deep foundation pits according to claim 1, characterized in that, The axial prestressing of the first-layer support system (4) is applied in three stages: The first application is 40% of the design axial force, the second is 70% of the design axial force, and the third is 100% of the design axial force.

10. The support conversion method for realizing synchronous construction of open-cut adjacent deep foundation pits according to claim 1, characterized in that, After removing the end wall (5) to the excavation height of the adjacent foundation pit, the steel waler three (11) of the adjacent foundation pit needs to be connected to the steel waler two (8) of the foundation pit one, and then the direct support system (2) of the adjacent foundation pit is installed.

11. The support conversion method for realizing synchronous construction of open-cut adjacent deep foundation pits according to claim 1, characterized in that, The steel walers (7) corresponding to the second to nth layer replacement support system (4) are installed using the balance weight method.

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