An assembly type sinking well underground space underground excavation construction method based on PBA method

Abstract

The application discloses an assembly type sinking well underground space open cut construction method based on a PBA method, which comprises the following steps: S1: constructing a vertical shaft 1, a horizontal passage 2 and a small pilot tunnel 3; S2: constructing a support pile 4, a crown beam 5 and a station top longitudinal beam 6 in the small pilot tunnel 3; S3: constructing an initial support tied arch 7 between the small pilot tunnels 3; S4: constructing a station top arch 8, thereby forming a vertical and horizontal support system; S5: excavating soil bodies downwards in a sinking well mode, and constructing a main body structure in a prefabricated assembly mode; and S6: after a bottom plate is constructed to a predetermined position, finishing work is completed, temporary components in a construction process are removed, and an underground space forms a closed underground structure. Compared with a traditional PBA method, the application can avoid outsourcing waterproof construction, meanwhile, good waterproof effect is ensured, labor can be saved, a construction environment can be improved and a construction period can be shortened, temporary structures can be saved, the influence of underground water can be effectively reduced, and therefore, construction risks are reduced.

Description

Technical Field

[0001] This invention relates to the field of underground space excavation technology, and more specifically, to a prefabricated caisson underground space excavation construction method based on the PBA method. Background Technology

[0002] There are two main methods for constructing underground spaces: cut-and-cover and tunneling. Due to limitations in surface and underground conditions, tunneling is often used in busy urban areas when constructing underground spaces. The PBA (Plain Barrier Excavation) method is an important method for large-space tunneling. It utilizes small pilot tunnels to implement the support system, allowing for the excavation of large spaces under the protection of this system. The method is simple and widely applicable. Currently, the PBA method is widely used in subway construction and is continuously expanding into areas such as underground parking garages and underground driveways, with its application scope and depth constantly increasing.

[0003] However, with changes in national construction requirements and the need for deeper underground spaces, the application of the PBA method has been limited, and some new problems urgently need to be addressed: The PBA method faces significant challenges in water shut-off due to its deep burial depth and extensive penetration into groundwater. Furthermore, the limited construction space restricts the implementation of certain techniques. For instance, the application of commonly used open-cut foundation pit techniques such as interlocking piles, pile-jet grouting, and diaphragm wall construction to the PBA method has yielded less than ideal results in current trials and requires further improvement.

[0004] Therefore, in view of the above situation, the designers of this invention, through dedicated research and design, and by integrating years of experience and achievements in related industries, have researched and designed a prefabricated caisson underground space excavation construction method based on the PBA method, in order to overcome the problems mentioned above: (1) The problem of groundwater blockage during large-scale excavation; (2) Structural construction quality problems caused by limited space in underground excavation projects; (3) How to save manpower on site. Summary of the Invention

[0005] The summary section introduces a series of simplified concepts, which will be further explained in detail in the detailed description section. The summary section of this invention is not intended to limit the key features and essential technical features of the claimed technical solution, nor is it intended to determine the scope of protection of the claimed technical solution.

[0006] To at least partially solve the above problems, this invention provides a method for constructing prefabricated caissons in underground spaces using the PBA method, comprising the following steps: S1: Construction shaft, cross passage and pilot tunnel; S2: Construct support piles, capping beams, and longitudinal beams at the top of the station within the small pilot tunnel; S3: Enter the small pilot tunnel from the cross passage, excavate the space of the construction station's arch, and construct the initial support arch between the small pilot tunnels; S4: The roof arch of the construction station forms a vertical and horizontal support system; S5: The soil is excavated downwards using a caisson method to sink the bottom slab. The main structure is constructed using a prefabrication and assembly method. Prefabricated side walls and prefabricated floor slabs are assembled while sinking. The sinking speed and uniformity are controlled by the working machinery under the bottom slab and the jacks between the side walls and the station arch. The working machinery is connected to a sleeve, which passes through the holes reserved in the bottom slab to transport the waste soil from the shaft to the ground. S6: After the base slab is constructed to the predetermined position, the finishing work is completed, and the temporary components used in the construction process are removed, so that the underground space forms a closed underground structure.

[0007] Preferably, in step S1, the specific construction steps are as follows: S101: Construction of vertical shafts on the ground surface, with space reserved in the shafts to meet the requirements of later caisson construction and transportation of prefabricated components; S102: Construction cross passage, which is reserved with space to meet the requirements of later caisson construction and transportation of prefabricated components; S103: Construction of small pilot tunnel using PBA method.

[0008] Preferably, in step S3, the construction of the station's roof arch continues under the combined support of the initial support arch, the cap beam, and the support piles.

[0009] Preferably, in step S4, it is necessary to remove part of the side walls and bottom slab of the small guide tunnel and pour the construction station arch on site. After the station arch is completed, it can provide space for subsequent caisson construction and support the installation of mechanical equipment.

[0010] Preferably, in step S5, multiple caissons are constructed sequentially, and the specific steps for constructing each caisson are as follows: S501: Equipment for transporting caissons, precast components for the base slab, precast components for the side walls, and precast components for the floor slabs via vertical shafts and horizontal passageways; S502: Install the caisson equipment and assemble the prefabricated bottom slab components into a bottom slab; S503: While excavating the soil, the bottom slab is sunk. As it sinks, the precast components of the side walls and floor slabs are assembled into side walls and floor slabs until the bottom slab sinks to the predetermined elevation.

[0011] Preferably, in step S503, the initial soil surface excavated at the top of the station arch is used as the initial base elevation of the bottom slab. Then, the elevation of the bottom slab is adjusted by the working machinery and the jacks between the side walls and the top of the station arch, and the bottom slab is first lowered to the predetermined elevation. Then the prefabricated side wall components are assembled with the base slab; Continue excavating downwards to the predetermined elevation, assemble the corresponding precast components, until the precast components of the bottom slab, side walls and floor slab are assembled and sunk to the design elevation.

[0012] Preferably, in step S6, after the base slab is constructed to the predetermined position, plain concrete is poured from the reserved holes in the base slab into the over-excavated space below the base slab to serve as a joint and water-blocking agent. The side wall cast-in-place components are then poured on-site, and other reserved holes are sealed by post-pouring. Finally, the temporary components are removed to complete the main structure. Before removing the internal partition walls, the joints are grouted to prevent groundwater from entering.

[0013] Preferably, the caissons are constructed using mechanical methods, the precast components are dry-connected, and the caissons are connected to each other, and the precast components are connected to the cast-in-place station arch using wet connections.

[0014] Compared with the prior art, the present invention has at least the following beneficial effects: In step S1, the vertical shaft and cross passage mainly meet the needs of small pilot tunnel and arch construction, prefabricated components and deep soil transportation. The depth of the vertical shaft is only located near the top arch of the station, and it is not necessary to excavate to the bottom of the station. The cross passage is also only located on the upper level, which reduces the amount of engineering work of temporary structures such as vertical shaft and cross passage, reduces the impact of groundwater during the excavation process, saves costs and shortens the construction period.

[0015] In step S2, the support piles are used only as vertical load-bearing components. Compared with the support piles used as both vertical and horizontal load-bearing components in the traditional PBA tunneling construction, the number of support piles is less and the depth is shallower, which reduces the amount of temporary structure work and saves the construction period and cost of the temporary structure. The station top longitudinal beam is only used for load bearing in the arching stage and does not need to bear the vertical load in the excavation stage, thus the construction step of the central pile in the traditional PBA process can be omitted.

[0016] In step S4, the support piles, the station arch, and the truss system of the arch can be used as vertical load-bearing components, providing convenient large-space implementation conditions and a good station space effect for subsequent caisson construction.

[0017] In step S5, unlike the traditional PBA construction method, this invention employs a caisson method for large-scale underground excavation. Furthermore, the main secondary lining structure, including the side walls, utilizes a prefabricated structure. Compared to traditional cast-in-place methods, the construction quality of these components is superior, and the components themselves possess excellent waterproofing properties. Waterproofing measures, such as sealing gaskets at the joints, are only required, eliminating the need for external waterproofing of the cast-in-place structure and ensuring overall waterproofing. Simultaneously, the prefabricated assembly technology saves labor, avoiding the poor construction environment and labor shortages common in traditional methods, and also shortens the large-scale excavation period. Because the side wall construction proceeds simultaneously with the sinking, the caisson method inherently provides support and water-blocking effects compared to traditional large-scale excavation, preventing the impact of groundwater during excavation, conserving water resources, and proving more effective than other water-blocking methods. It is largely unaffected by groundwater. Prefabricated components can be directly processed in the factory, inspected for quality, and then transported for assembly, ensuring consistent structural construction quality.

[0018] The beneficial effects of the above technical solution are as follows: (1) We solved the problem of difficulty in blocking water when the underground space is buried at a great depth by using the prefabricated caisson method.

[0019] (2) We adopt the method of assembling prefabricated components on site, which replaces the traditional construction process of first tying steel bars and then casting through molds. Therefore, there is no need to consider the problem of external waterproofing. At the same time, since the prefabricated components are all processed in the factory, there is sufficient time, space and testing conditions to conduct quality testing on the prefabricated components before they are transported to the underground space. This solves the problems of inconsistent structural construction quality and poor waterproofing quality caused by the limited space in the underground excavation project.

[0020] (3) Precast components are processed in the factory, and mechanical excavation and tunnel transportation are carried out on site, saving on-site manpower and thus improving the tunnel construction environment; In summary, the cut-and-cover construction method of this invention inherits the advantages of the traditional PBA method. Compared with the traditional PBA method, it saves on temporary structures, effectively reduces the impact of groundwater, thereby reducing construction risks, eliminates the need for outsourced waterproofing while ensuring good waterproofing effect, saves labor, improves the construction environment, and shortens the construction period. It expands the application scope of the PBA method and promotes its development.

[0021] The prefabricated caisson underground space excavation construction method based on the PBA method described in this invention will have other advantages, objectives and features that will be partly apparent from the following description, and partly understood by those skilled in the art through research and practice of this invention. Attached Figure Description

[0022] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a construction diagram for step S1.

[0023] Figure 2 This is a construction diagram for step S2.

[0024] Figure 3 This is a construction diagram for step S3.

[0025] Figure 4 This is a construction diagram for step S4.

[0026] Figure 5 This is a construction diagram for step S5.

[0027] Figure 6 This is a construction diagram for step S6.

[0028] Figure 7 This is a top view of the structure after construction of the prefabricated caisson underground space excavation construction method based on the PBA method described in this invention.

[0029] In the diagram: 1. Vertical shaft; 2. Cross passage; 3. Small pilot tunnel; 4. Support pile; 5. Crown beam; 6. Station roof longitudinal beam; 7. Initial support arch; 8. Station roof arch; 9. Station side wall; 10. Station central column; 11. Station floor slab; 12. Station bottom longitudinal beam; 13. Middle slab beam; 14. Station floor slab; 15. Working machinery; 16. Jack device; 17. Excavation pipe for caisson construction; 18. Cast-in-place components of side wall; 19. Plain concrete; 20. Station end wall column. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments, so that those skilled in the art can implement it based on the description.

[0031] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0032] like Figures 1-7 As shown, this invention provides a method for constructing prefabricated caissons in underground spaces using the PBA method, comprising the following steps: S1: Construction shaft 1, horizontal passage 2, and small pilot tunnel 3; S2: Construct support piles 4, capping beam 5, and station top longitudinal beam 6 within the small pilot tunnel 3; S3: Enter the small guide tunnel 3 from the cross passage 2, excavate the space of the construction station arch 8, and construct the initial support arch 7 between the small guide tunnels 3; S4: The roof arch of the construction station 8 forms a vertical and horizontal support system; S5: Excavate the soil downwards using a caisson method, sink the bottom slab, and construct the main structure using a prefabrication and assembly method. As the caisson sinks, assemble the prefabricated side walls and prefabricated floor slabs. Control the sinking speed and uniformity by controlling the working machinery under the bottom slab and the jack device 16 between the side walls and the station arch 8. The working machinery is connected to a sleeve, which passes through the pre-reserved holes in the bottom slab to transport the waste soil from the shaft 1 to the ground. S6: After the base slab is constructed to the predetermined position, the finishing work is completed, and the temporary components used in the construction process are removed, so that the underground space forms a closed underground structure.

[0033] The working principle and beneficial effects of the above technical solution: The PBA method is a widely used method for constructing large underground spaces. Its main steps are: 1) Construct the main station tunnel using vertical shafts and cross passages; 2) Construct the main support piles, capping beam, central piles, central columns, and central longitudinal beams within the small pilot tunnel; 3) Initial support arch and secondary lining arch of the main body of the station during the construction of the transverse passage; 4) Under the protection of the support piles and arches, excavate the soil downwards and construct the corresponding main side walls and floor slabs until the closed structure is completed.

[0034] However, the above construction methods require effective rainwater management, and the PBA (Precipitation Barrier) water-blocking technology is currently not mature enough. Given the application scenarios mentioned in the background section of this invention, which cannot meet rainwater management requirements and whose water-blocking technology is still immature, we have improved upon the PBA method to address the application scenarios described in the background section and overcome its corresponding problems.

[0035] In step S1, the vertical shaft 1 and the horizontal passage 2 are mainly used to meet the construction of the small guide tunnel 3 and the arch, as well as the transportation of prefabricated components and deep soil. The depth of the vertical shaft 1 is only located near the top arch 8 of the station, and it is not necessary to excavate to the bottom of the station. The horizontal passage 2 is also only located on the upper level, which reduces the amount of engineering work of temporary structures such as the vertical shaft 1 and the horizontal passage 2, reduces the impact of groundwater during the excavation process, saves costs, and shortens the construction period.

[0036] In step S2, the support piles 4 serve only as vertical load-bearing components. Compared with the traditional PBA tunneling construction where the support piles 4 serve as both vertical and horizontal load-bearing components, the number of support piles 4 is smaller and the depth is shallower, which reduces the amount of temporary structure work and saves the construction period and cost of the temporary structure. The station top longitudinal beam 6 is only used for load bearing in the arch-fastening stage and does not need to bear the vertical load in the excavation stage, thus the construction step of the central pile in the traditional PBA process can be omitted.

[0037] In step S4, the support piles 4, the station arch 8, and the truss system of the arch can be used as vertical load-bearing components, providing convenient large-space implementation conditions and good station space effect for subsequent caisson construction.

[0038] In step S5, unlike the traditional PBA construction method, this invention employs a caisson method for large-scale underground excavation. Furthermore, the main secondary lining structure, including the side walls, utilizes a prefabricated structure. Compared to traditional cast-in-place methods, the construction quality of these components is superior, and the components themselves possess excellent waterproofing properties. Waterproofing measures, such as sealing gaskets at the joints, are only required, eliminating the need for external waterproofing of the cast-in-place structure and ensuring overall waterproofing. Simultaneously, the prefabricated assembly technology saves labor, avoiding the poor construction environment and labor shortages common in traditional methods, and also shortens the large-scale excavation period. Because the side wall construction proceeds simultaneously with the sinking, the caisson method inherently provides support and water-blocking effects compared to traditional large-scale excavation, preventing the impact of groundwater during excavation, conserving water resources, and proving more effective than other water-blocking methods. It is largely unaffected by groundwater. Prefabricated components can be directly processed in the factory, inspected for quality, and then transported for assembly, ensuring consistent structural construction quality.

[0039] The beneficial effects of the above technical solution are as follows: (1) We solved the problem of difficulty in blocking water when the underground space is buried at a great depth by using the prefabricated caisson method.

[0040] (2) We adopt the method of assembling prefabricated components on site, which replaces the traditional construction process of first tying steel bars and then casting through molds. Therefore, there is no need to consider the problem of external waterproofing. At the same time, since the prefabricated components are all processed in the factory, there is sufficient time, space and testing conditions to conduct quality testing on the prefabricated components before they are transported to the underground space. This solves the problems of inconsistent structural construction quality and poor waterproofing quality caused by the limited space in the underground excavation project.

[0041] (3) Precast components are processed in the factory, and mechanical excavation and tunnel transportation are carried out on site, saving on-site manpower and thus improving the tunnel construction environment; In summary, the cut-and-cover construction method of this invention inherits the advantages of the traditional PBA method. Compared with the traditional PBA method, it saves on temporary structures, effectively reduces the impact of groundwater, thereby reducing construction risks, eliminates the need for outsourced waterproofing while ensuring good waterproofing effect, saves labor, improves the construction environment, and shortens the construction period. It expands the application scope of the PBA method and promotes its development.

[0042] In one embodiment, we further refine the cut-and-cover method, including the following steps: S101: Construct shaft 1 on the ground surface. Shaft 1 can be constructed using the inverted shaft wall method or the open excavation method. Shaft 1 is reserved with space to meet the requirements of later caisson construction and the transportation of prefabricated components. S102: Construction of cross passage 2. Cross passage 2 can be constructed by step-by-step excavation method. Cross passage 2 is reserved with space to meet the requirements of later caisson construction and transportation of prefabricated components. S103: Construction of small pilot tunnel 3 using PBA method.

[0043] In step S1, the vertical shaft 1 and the horizontal passage 2 serve as construction and transportation channels. Generally, multiple shafts can be set up according to the length of the underground space and the conditions of the ground site, which serves as a prerequisite for the subsequent construction of multiple shafts.

[0044] S2: Construct support piles 4, capping beams 5, and station roof longitudinal beams 6 within the small pilot tunnel 3; support piles 4 are mainly used as vertical load-bearing components during arch construction and caisson construction, and only need to meet the vertical bearing capacity requirements. The small pilot tunnel 3 is only used for the initial support arch 7 and station roof arch 8 construction, and the main earthwork is carried out by the station roof arch 8 during the excavation stage.

[0045] S3: Enter the small guide tunnel 3 from the cross passage 2, excavate the space for the construction of the station's top arch 8, and construct the initial support arch 7 between the small guide tunnels 3. Then, under the joint support of the initial support arch 7, the cap beam 5, and the support piles 4, continue the construction of the station's top arch 8.

[0046] S4: Remove part of the side walls and bottom slab of the small guide tunnel 3, and pour the construction of the station arch 8 on site to form a vertical and horizontal support system; after the station arch 8 is completed, it can provide space for subsequent caisson construction and support the installation of mechanical equipment.

[0047] S5: The soil is excavated downwards using multiple caissons constructed sequentially. It is important to note that the hoisting and jacking equipment is installed on the already constructed station arch 8 for hoisting and assembling prefabricated components. The jacking equipment provides both downward pressure to aid in the structural sinking and upward tension to prevent excessive sinking or tilting.

[0048] S501: Transport caisson equipment, precast base slab components, precast side wall components, and precast floor slab components from vertical shaft 1 and horizontal passageway 2; S502: Install the caisson equipment and assemble the prefabricated bottom slab components into a bottom slab; S503: The initial soil surface excavated from the station arch (8) is used as the initial base elevation of the bottom slab. Then, the elevation of the bottom slab is adjusted by the working machinery and the jacks (16) between the side walls and the station arch (8). The bottom slab is first lowered to the predetermined elevation. The width of each sinking of the caisson is the width of the station, and the length is about 80m. The caisson adopts a combination of air pressure sealing and mechanical excavation to achieve groundwater sealing and earthwork excavation. The elevation of the bottom slab is adjusted by the jacks (16) set on the station arch 8. The bottom slab is first lowered to the predetermined elevation. Then the prefabricated side wall components are assembled with the base slab; Continue excavating downwards to the predetermined elevation, assemble the corresponding precast components, until the precast components of the bottom slab, side walls and floor slab are assembled and sunk to the design elevation.

[0049] S6: After the base slab is constructed to the predetermined position, plain concrete is poured into the over-excavated space beneath the base slab through the reserved holes to serve as joints and water-blocking. Side wall cast-in-place components are then poured on-site, and other reserved holes are sealed with post-cast concrete. Finally, temporary components used during construction are removed to complete the main structure, creating a closed underground structure. Before removing the internal partition walls, grouting is applied to the joints to prevent groundwater intrusion. Specifically, the caissons are connected and waterproofed using a combination of external grouting and internal cast-in-place construction. The caissons are constructed using mechanical methods. Precast components are dry-connected using mortise and tenon joints. The longitudinal width of the precast components is 2m, and vertically, according to the structural stress, the connection points are set at 1 / 3 of the span, with the maximum vertical segment length less than 4m. Mortise and tenon joints and bolts are used between segments and sections, while wet connections are used between caissons and between precast components and the cast-in-place station arch 8. The caisson sinking is controlled by a triple approach of excavation, air pressure, and jacks. The overall construction process basically does not consider rainwater or large-scale water blocking; only the holes or joints in the base slab are blocked by air pressure, combined with the pouring of concrete.

[0050] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0051] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0052] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. Other modifications can be easily made by those skilled in the art. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for constructing prefabricated caissons in underground spaces using the PBA method, characterized in that, The steps include the following: S1: Construction shaft (1), cross passage (2) and small guide tunnel (3), the depth of which is located near the top arch (8) of the station, without excavation to the bottom of the station; S2: Construct support piles (4), cap beams (5) and station top longitudinal beams (6) inside the small guide tunnel (3). The support piles (4) serve only as vertical bearing components. S3: Enter the small guide tunnel (3) from the cross passage (2), excavate the space of the construction station top arch (8), and construct the initial support arch (7) between the small guide tunnels (3). S4: Construction station arch (8), forming a vertical and horizontal support system; S5: The soil is excavated downwards by means of a caisson, the bottom slab is sunk, and the main structure is constructed by prefabrication and assembly. Prefabricated side walls and prefabricated floor slabs are assembled while sinking. The sinking speed and uniformity are controlled by controlling the working machinery under the bottom slab and the jack device (16) between the side wall and the station arch (8). The working machinery is connected to a sleeve, which passes through the hole reserved in the bottom slab to transport the waste soil from the vertical shaft (1) to the ground. The caisson adopts the method of air pressure sealing combined with mechanical excavation to realize groundwater sealing and earthwork excavation. S6: After the base slab is constructed to the predetermined position, the finishing work is completed and the temporary components used in the construction process are removed, so that the underground space forms a closed underground structure; the overall construction does not adopt dewatering or large-scale water blocking measures, only the holes or joints of the base slab are blocked by air pressure combined with grouting concrete.

2. The method for constructing prefabricated caissons underground spaces using the PBA method according to claim 1, characterized in that, In step S1, the specific construction steps are as follows: S101: Construct a vertical shaft (1) on the ground surface. The vertical shaft (1) is reserved with space that meets the requirements of the later caisson construction and the transportation of prefabricated components. S102: Construction cross passage (2), the cross passage (2) is reserved with space to meet the requirements of later caisson construction and transportation of prefabricated components; S103: Construction of small pilot tunnel using PBA method (3).

3. The method for constructing prefabricated caissons underground spaces using the PBA method according to claim 1, characterized in that, In step S3, the station arch (8) continues to be constructed under the joint support of the initial support arch (7), the cap beam (5), and the support piles (4).

4. The method for constructing prefabricated caissons underground spaces using the PBA method according to claim 1, characterized in that, In step S4, it is necessary to remove part of the side wall and bottom plate of the small guide tunnel (3) and pour the construction station arch (8) on site. After the station arch (8) is completed, it can provide space for subsequent caisson construction and support the installation of mechanical equipment.

5. The method for constructing prefabricated caissons underground spaces using the PBA method according to claim 4, characterized in that, In step S5, multiple caissons are constructed successively. The specific steps for the construction of each caisson are as follows: S501: Transport caisson equipment, precast bottom slab components, precast side wall components and precast floor slab components from the vertical shaft (1) and horizontal passage (2); S502: Install the caisson equipment and assemble the prefabricated bottom slab components into a bottom slab; S503: While excavating the soil, the bottom slab is sunk. As it sinks, the precast components of the side walls and floor slabs are assembled into side walls and floor slabs until the bottom slab sinks to the predetermined elevation.

6. The method for constructing prefabricated caissons in underground space using the PBA method according to claim 5, characterized in that, In step S503, the initial soil surface excavated at the station arch (8) is used as the initial base elevation of the bottom plate. Then, the elevation position of the bottom plate is adjusted by the working machinery and the jack device (16) between the side wall and the station arch (8). The bottom plate is first lowered to the predetermined elevation. Then the prefabricated side wall components are assembled with the base slab; Continue excavating downwards to the predetermined elevation, assemble the corresponding precast components, until the precast components of the bottom slab, side walls and floor slab are assembled and sunk to the design elevation.

7. The method for constructing prefabricated caissons in underground space using the PBA method according to claim 1, characterized in that, In step S6, after the base slab is constructed to the predetermined position, plain concrete is poured from the reserved holes in the base slab into the over-excavated space below the base slab to serve as a joint and water-blocking agent. The side wall cast-in-place components are then poured on-site, and other reserved holes are sealed by post-pouring. Finally, the temporary components are removed to complete the main structure. Before removing the internal partition walls, the joints are grouted to prevent groundwater from flowing in.

8. The method for constructing prefabricated caissons underground spaces using the PBA method according to claim 7, characterized in that, The caissons are constructed using mechanical methods, the precast components are dry-connected, and the caissons are wet-connected with each other and with the precast components and the cast-in-place station arch (8).

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