Tunnel and socket type ballast bed member and construction method

Abstract

This invention provides a tunnel socket-type track bed component and construction method, relating to the field of tunnel prefabricated structure assembly. Addressing the current problem of insufficient longitudinal connection stability and safety in prefabricated track bed foundations, the invention sets up socket channels within prefabricated units. By inserting the two ends of a mandrel into the socket channels of adjacent prefabricated units, grouting is injected into the socket channels to connect the mandrel and the prefabricated unit, thereby establishing a stable connection between adjacent prefabricated units and mitigating the problems of loosening and failure in the connection between adjacent prefabricated units.

Description

Technical Field

[0001] This invention relates to the field of prefabricated tunnel structure assembly, specifically to a tunnel socket-type track bed component and its construction method. Background Technology

[0002] Precast reinforced concrete components have been widely used in above-ground civil engineering projects, and precast beam technology is also widely used in municipal bridge engineering. In underground structures, subway stations are already using prefabricated structures, shield tunnels are employing precast segment assembly technology, and precast track slabs have also been applied. Precast reinforced concrete components have the advantages of high quality, superior appearance, and high dimensional accuracy due to factory production. Furthermore, factory assembly line production methods offer advantages such as reduced resource consumption, reduced carbon emissions, and reduced environmental impact.

[0003] In shield tunnels, the tunnel segments and track slabs have been prefabricated, but the track bed structure between the segments and track slabs is still cast in place. The prefabricated slab track structure in Chinese patent (publication number: CN111877054A) uses pre-reserved holes that penetrate the thickness of the track slab. An elastic buffer layer is installed in the holes, and a filling layer is poured into the holes to form a flexible limit. The filling layer (track bed structure under the track slab) still uses unreinforced synthetic fiber concrete or steel fiber concrete, which does not meet the requirement of GB50157-2013 "Code for Design of Metro" that the track bed structure should be reinforced concrete. The filling layer construction still uses cast-in-place curing. The cast-in-place curing and strength gain of concrete require time, which limits the construction speed. The precast track bed foundation structure component unit proposed in Chinese patent (application number: 202210892403.6) is a solid body with reserved holes for easy installation and connection. The longitudinal connection adopts bolted connectors. As the tunnel is in operation, the track bed foundation structure at the bolted connector position is easily damaged by vibration, resulting in loosening and failure of the connection position, which affects the strength, operational stability and safety of the precast track bed foundation structure. Summary of the Invention

[0004] The purpose of this invention is to address the deficiencies of existing technologies by providing a tunnel socket-type track bed component and construction method. A socket channel is set within the precast unit, and a mandrel is inserted into the socket channels of adjacent precast units at both ends. Grouting is then performed within the socket channels to connect the mandrel and the precast unit, thereby establishing a stable connection between adjacent precast units and mitigating the problems of loosening and failure of connections between adjacent precast units.

[0005] The first objective of this invention is to provide a tunnel socket-type track bed component, which adopts the following solution:

[0006] It includes at least two precast units that are sequentially spliced ​​along the tunnel extension direction. Each precast unit has a socket channel for inserting a mandrel part along the tunnel extension direction. Adjacent precast units cooperate with at least one mandrel. Each precast unit has a grouting port that connects to the socket channel for grouting to fill the gap between the socket channel and the mandrel, and the gap between adjacent precast units.

[0007] Furthermore, along the tunnel extension direction, the socket channel penetrates through the precast unit, with one end of the mandrel inserted into the socket channel of the precast unit and the other end inserted into the socket channel of the adjacent precast unit.

[0008] Furthermore, the socket channels are distributed within the steel cage of the precast unit, and the mandrels inserted into the same socket channel are arranged at intervals; the mandrels are precast lightweight porous structures.

[0009] Furthermore, the socket channel is provided with a detachable protective sleeve, the outer wall of the protective sleeve is attached to the inner wall of the socket channel, and the mandrel is inserted into the protective sleeve.

[0010] Furthermore, the prefabricated unit is provided with multiple socket channels, and the socket channels on the same prefabricated unit are distributed in parallel along their axes.

[0011] Furthermore, the cross-section of the socket channel perpendicular to the axis is circular or polygonal, and the cross-sectional shape of the mandrel matches the inserted socket channel.

[0012] Furthermore, the top surface of the precast unit is provided with mounting holes, and the precast unit is fixed to the segment through the mounting holes via connectors.

[0013] Furthermore, the top surface of the precast unit is provided with a pre-embedded groove, which is connected to the internal steel reinforcement cage of the precast unit through anchor rods.

[0014] A second objective of this invention is to provide a construction method for tunnel socket-type track bed components, comprising:

[0015] Transport the precast unit into the tunnel so that the core rod of the previous precast unit can be inserted into the socket channel of the precast unit;

[0016] After the precast unit is in place, it is fixed to the segment. A mandrel is inserted into the socket channel of the precast unit, and the next precast unit is transported to cooperate with the mandrel and dock with the precast unit.

[0017] Grouting is performed through the grouting port to fill the gaps between the socket channel and the mandrel, the gaps between adjacent precast units, and the gaps between the precast units and the mating segments, so that adjacent precast units, mandrels, and segments form a whole.

[0018] Furthermore, one end of the same mandrel is inserted into the socket channel of a precast unit, and the other end is inserted into the socket channel of another adjacent precast unit; during grouting, the gap between the mandrels in the same socket channel is filled.

[0019] Compared with the prior art, the advantages and positive effects of this invention are:

[0020] (1) To address the current problem of insufficient stability and safety of longitudinal connection of precast track bed foundation, a socket channel is set in the precast unit. The core rod is inserted into the socket channel in the adjacent precast unit at both ends, and grouting is injected into the socket channel to realize the connection between the core rod and the precast unit, thereby establishing a stable connection between adjacent precast units and mitigating the problem of loosening and failure of the connection between adjacent precast units.

[0021] (2) After opening the socket channel in the prefabricated unit, a core rod made of lightweight foamed concrete is placed inside. The core rod, together with the socket tunnel, realizes the rapid assembly and connection of the prefabricated track bed structure system. At the same time, the core rod body can use its material properties to achieve the effect of energy absorption and vibration reduction.

[0022] (3) After the precast individual components of the precast track bed are set with several cavities to form a socket channel, on the one hand, the weight of the precast individual components can be reduced by 10% to 20%, and on the other hand, the socket channel can be used to facilitate the use of existing transfer equipment, eliminating the need for precast individual components such as protruding lifting rings required for hoisting, thus facilitating construction, handling and assembly. Large-volume on-site pouring and curing are not required. After mechanized assembly, the work platform required for construction can be provided, greatly improving the efficiency of track bed construction.

[0023] (4) The core rod is inserted into the precast unit and grout is injected, replacing the traditional solid precast unit which is entirely made of concrete. The core rod made of foamed concrete replaces 10% to 20% of the concrete used in the precast unit. The comprehensive unit price of foamed concrete is about one-third cheaper than concrete, which can reduce the project cost. Replacing part of the concrete in the precast unit with foamed concrete can make full use of the properties of lightweight porous foamed concrete materials, so that the track bed structure has energy absorption and sound absorption functions, achieving the effect of sound insulation and noise reduction. Attached Figure Description

[0024] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0025] Figure 1 This is a schematic diagram of the structure of the prefabricated monomer in Embodiments 1 and 2 of the present invention.

[0026] Figure 2 This is a schematic diagram of the prefabricated unit connecting the track slab and the tube segment in Embodiments 1 and 2 of the present invention.

[0027] Figure 3 This is a schematic diagram showing the mandrel located in the socket channel in Embodiments 1 and 2 of the present invention.

[0028] Figure 4 This is a schematic diagram showing the sequential arrangement of multiple prefabricated units in Embodiments 1 and 2 of the present invention.

[0029] Figure 5 This is a schematic diagram of the distribution of the socket channels in Embodiments 1 and 2 of the present invention.

[0030] Figure 6 This is a schematic diagram of the prefabricated unit connecting the track slab and the tube segment in Embodiments 1 and 2 of the present invention.

[0031] Figure 7 This is a structural schematic diagram showing the distribution of the socket channels in Embodiments 1 and 2 of the present invention.

[0032] Figure 8 This is a schematic diagram of the prefabricated unit connecting the track slab and the tube segment in Embodiments 1 and 2 of the present invention.

[0033] Figure 9 This is a schematic diagram of the distribution of the socket channels in Embodiments 1 and 2 of the present invention.

[0034] The components include: 1. Precast unit; 2. Protective sleeve; 3. Core rod; 4. Embedded part; 5. Grouting hole; 6. Mounting hole; 7. Socket channel; 8. Reinforcing cage; 9. Embedded groove; 10. Anchor rod; 11. Embedded channel; 12. Grouting pipe; 13.1. First connector; 13.2. Second connector; 14.1. First gasket; 14.2. Second gasket; 15.1. First fastener; 15.2. Second fastener; 16.1. First waterproof rubber gasket; 16.2. Second waterproof rubber gasket; 17. Grout; 18. Limiting device; 19. Connecting hole; 20. Precast track slab; 21. Rail and fastener; 22. Drainage ditch; 23. Segment; 24.1. First gap; 24.2. Second gap; 24.3. Third gap; 24.4. Fourth gap; 25. Reserved transverse channel; 26. Centerline. Detailed Implementation

[0035] Example 1

[0036] In a typical embodiment of the present invention, such as Figures 1-9 As shown, a tunnel socket-type track bed component is presented.

[0037] In shield tunnels, tunnel segments and track slabs have been prefabricated, but the track bed structure between the segments and track slabs is still cast in place. Chinese patent application number 202210892403.6 proposes prefabricated track bed foundation structure component units. These component units are solid bodies and are connected longitudinally using bolted connectors. After the connection is established, it will be damaged to some extent as the tunnel is in operation. The through holes of the bolted connectors at the component unit positions are prone to gradually loosening under vibration. The bolted connectors themselves have the potential for deformation and breakage, resulting in insufficient longitudinal connection stability of the component units, which affects the stability and safety of the tunnel during operation.

[0038] Based on this, this embodiment provides a tunnel socket-type track bed component to solve the problems of rapid assembly and connection of prefabricated track bed structure system and energy absorption, vibration reduction, sound insulation and noise reduction. While meeting the functional requirements and load-bearing capacity, it reduces the amount of concrete used in prefabricated track bed components and reduces the weight of the components themselves. While ensuring good connection performance between prefabricated units, it simplifies the assembly process and realizes rapid assembly and construction of prefabricated track bed assembly system.

[0039] The tunnel socket-type track bed component in this embodiment will now be described in detail with reference to the accompanying drawings.

[0040] See Figure 1 The tunnel socket-type track bed component is used for the construction of precast track bed foundation in shield tunnels. It mainly includes at least two precast units 1. The precast unit 1 is provided with a socket channel 7, and the socket channel 7 is equipped with a core rod 3. Depending on the requirements, a protective sleeve 2 is also provided in the socket channel 7 of the precast unit 1. The top surface of the socket unit is also provided with embedded parts 4, grouting holes 5 and reserved installation holes 6.

[0041] like Figure 4 As shown, multiple precast units 1 are spliced ​​sequentially along the tunnel extension direction during construction. Adjacent precast units 1 are connected by mandrels 3. To facilitate the installation of mandrels 3, a socket channel 7 is provided inside the precast unit 1 along the tunnel extension direction for inserting part of the mandrel 3. Part of the mandrel 3 is inserted into the socket channel 7 of one precast unit 1, and the other part passes through the gap between adjacent precast units 1 and is inserted into the socket channel 7 of the adjacent precast unit 1, thus establishing the connection relationship between adjacent precast units 1.

[0042] Each adjacent precast unit 1 works together with at least one core rod 3. The number of core rods 3 is configured according to requirements to ensure that the connection strength meets the requirements. The grouting port on the precast unit 1 is connected to the socket channel 7, which allows grout 17 to be injected into the socket channel 7. Since the socket channel 7 extends to the end face of the precast unit 1, the grout 17 in the socket channel 7 will flow to the outside of the precast unit 1 during grouting and reach the gap between the precast units 1. This allows the grout 17 to fill the gap between the socket channel 7 and the core rod 3, as well as the gap between adjacent precast units 1, thus completing the grouting and filling to establish a connection, making the precast unit 1 and the core rod 3 form an integrated structure.

[0043] like Figure 2 , Figure 3 As shown, along the tunnel extension direction, the socket channel 7 penetrates the precast unit 1, one end of the core rod 3 is inserted into the socket channel 7 of the precast unit 1, and the other end is inserted into the socket channel 7 of the adjacent precast unit 1.

[0044] A socket channel 7 for accommodating the mandrel 3 is pre-set inside the precast unit 1. The precast unit 1 is a reinforced concrete structure with an internal steel cage 8 as its framework and an external concrete layer. Figure 5 As shown, the socket channels 7 are distributed within the steel cage 8 of the precast unit 1. Multiple socket channels 7 are provided on the precast unit 1, with the socket channels 7 on the same precast unit 1 having parallel axes. Mandrels 3 inserted into the same socket channel 7 are arranged at intervals. Alternatively, the precast unit 1 can be configured as a symmetrical structure with its centerline 26 as the axis of symmetry.

[0045] After the mandrel 3 is inserted into the socket channel 7, it also enters the range of the steel cage 8. After grouting and filling, the bearing capacity of the mandrel 3 is improved.

[0046] The core rod 3 is a prefabricated lightweight porous structure, which can be made of foamed concrete. In other embodiments, the material is selected from plain concrete, reinforced concrete, or rubber concrete, etc., according to the size and functional requirements. In this embodiment, foamed concrete is used for manufacturing. On the one hand, the core rod 3 made of foamed concrete replaces the concrete of the prefabricated unit 1. The comprehensive unit price of foamed concrete is about one-third cheaper than that of concrete, which can reduce the project cost. On the other hand, replacing part of the concrete in the prefabricated unit 1 with foamed concrete can make full use of the material properties of lightweight porous foamed concrete, so that the track bed structure has energy absorption and sound absorption functions, achieving the effect of sound insulation and noise reduction. Furthermore, the core rod 3 body can achieve the effect of energy absorption and vibration reduction by utilizing its material properties.

[0047] like Figure 2 , Figure 3As shown, the socket channel 7 is equipped with a detachable protective sleeve 2. When transferring the precast unit 1, the transfer clamp can be positioned in the socket channel 7 with the protective sleeve 2 to reduce direct contact between the rigid transfer gap and the precast unit 1, thus protecting the precast unit 1. After the transfer is completed, the protective sleeve 2 can be pulled out from the socket channel 7, exposing the concrete structure of the inner wall of the socket tunnel, which facilitates the formation of a stable connection during grouting.

[0048] When the protective sleeve 2 is inserted into the socket channel 7, the outer wall of the protective sleeve 2 fits against the inner wall of the socket channel 7, and the mandrel 3 is inserted into the protective sleeve 2. When the protective sleeve 2 is not inserted into the socket channel 7, the protective sleeve 2 can be placed on the transfer clamp to protect the position where the transfer clamp contacts the socket tunnel.

[0049] Protective sleeve 2 is a finished product, and the material is plastic sleeve, steel pipe, etc., depending on the size and functional requirements.

[0050] The socket channel 7 can be configured in different shapes according to requirements. In this embodiment, the cross-section of the socket channel 7 perpendicular to the axis is circular or polygonal, and the cross-sectional shape of the mandrel 3 matches the inserted socket channel 7.

[0051] See Figure 5 , Figure 7 , Figure 9 The socket channel 7 is configured with a circular cross section and a rectangular cross section. The corresponding mandrel 3 can be configured as a cylindrical mandrel 3 and a cuboid mandrel 3. The cylindrical mandrel 3 is inserted into the socket channel 7 with a circular cross section, and the cuboid mandrel 3 is inserted into the socket channel 7 with a rectangular cross section.

[0052] like Figure 2 , Figure 6 and Figure 8 As shown, the top surface of the precast unit 1 is provided with mounting holes 6, which provide the necessary space for the installation of the connecting parts between the precast unit 1 and the segment 23. The mounting holes 6 fix the precast unit 1 to the segment 23 through the connecting parts. The top surface of the precast unit 1 is provided with embedded parts 4, which are a combination structure of embedded grooves 9 and anchor rods 10. The anchor rods 10 are welded to the embedded grooves 9 and embedded and fixed on the reinforcing cage 8, providing an anchoring end for the limiting device 18 on the precast track slab 20 that cooperates with the precast unit 1. At the same time, rails and fasteners 21 are also provided on the precast track slab.

[0053] A through-hole grouting hole 5 is pre-drilled at the top of the precast unit 1, and a grouting pipe 12 is inserted into it. The grouting pipe 12 has multiple holes in its wall, and the grouting hole 5 communicates with the cavity. After the precast unit 1 and the core rod 3 are assembled, grout 17 is injected through the grouting hole 5 to ensure effective bonding between the precast components and to ensure the integrity and stability of the precast track bed structure system. The grouting pipe 12 is installed inside the grouting hole 5, and the grouting pipe 12 is made of rigid materials such as plastic pipe, steel pipe, or composite pipe.

[0054] The grout 17 fills the first gap 24.1 formed between the precast mandrels 3, the second gap 24.2 formed between the precast mandrels 3 and the inner wall of the inner socket channel 7 of the precast unit 1, the third gap 24.3 formed between the end faces of adjacent precast units 1, and the fourth gap 24.4 formed between the precast unit 1 and the segment 23, thereby achieving the overall effect of the precast assembled track bed structure and improving the stability of the precast assembled track bed structure.

[0055] A reserved transverse passage 25 can be provided according to the requirements of the track-crossing pipeline, facilitating the crossing and installation of the pipeline. The size of the reserved transverse passage 25 is adjusted and determined according to the pipeline size. A drainage ditch 22 is also provided on the pre-installed unit, such as... Figure 2 As shown; drainage ditch 22 can also be formed by combining prefabricated unit 1 with pipe segment 23, such as Figure 6 , Figure 8 As shown; alternatively, a non-filled socket channel 7 can be reserved as a drainage ditch 22; similarly, the size of the drainage ditch 22 can be adjusted and determined according to requirements.

[0056] Example 2

[0057] In another typical embodiment of the present invention, such as Figures 1-9 As shown, a construction method for tunnel socket-type track bed components is presented.

[0058] Combination Figures 1-9 The construction method includes:

[0059] Transport the precast unit 1 into the tunnel so that the core rod 3 inside the previous precast unit 1 is inserted into the socket channel 7 of the precast unit 1.

[0060] After the precast unit 1 is in place, it is fixed to the segment 23. The core rod 3 is inserted into the socket channel 7 of the precast unit 1. The next precast unit 1 is transported to cooperate with the core rod 3 and dock with the precast unit 1.

[0061] One end of the same core rod 3 is inserted into the socket channel 7 of a precast unit 1, and the other end is inserted into the socket channel 7 of another adjacent precast unit 1.

[0062] Grouting is performed through the grouting port to fill the gaps between the socket channel 7 and the core rod 3, the gaps between adjacent precast units 1, the gaps between the precast unit 1 and the mating segment 23, and the gaps between adjacent core rods 3 within the same socket channel 7, so that adjacent socket channels 7, core rods 3, and segments 23 form a whole.

[0063] Specifically, the above construction method will be described in detail with reference to the accompanying drawings and Example 1.

[0064] The prefabricated unit 1 with temporary protective sleeve 2 is transported to the tunnel where the segment 23 has been assembled and cleaned using construction assembly equipment. After aligning the reserved installation hole 6 in the prefabricated unit 1 with the embedded channel 11 in the segment 23, the first connector 13.1 (T-bolt) is inserted through the reserved installation hole 6 into the embedded channel 11 in the segment 23 and rotated 90 degrees. The first washer 14.1 (first rubber pad) and the first fastener 15.1 (first nut) are installed in sequence at the end of the first connector 13.1 (T-bolt). The first waterproof rubber sealing gasket 16.1 is pressed into the reserved installation hole 6.

[0065] Insert the grouting pipe 12 into the grouting hole 5 that runs vertically through the top center of the precast unit 1 and through the socket channel 7 to the bottom of the precast unit 1 to the segment 23. Insert half the length of the precast core rod 3 into the socket channel 7 until it touches the grouting pipe 12. Install the next precast unit 1 with the grouting pipe 12 already installed. Insert the other half of the length of the precast core rod 3 from the previous step through the reserved internal socket channel 7 along the longitudinal direction of the tunnel. Repeat the same steps in sequence.

[0066] After the pre-embedded units in a certain area are installed and debugged, the filling material grout 17 is injected through the grouting pipe 12 to fill the first gap 24.1 between the precast core rods 3, the second gap 24.2 between the precast core rods 3 and the socket channel 7 of the precast unit 1, the third gap 24.3 between the end faces of adjacent units, and the fourth gap 24.4 between the precast unit 1 and the segment 23, thereby forming the precast track bed components into an integral structure.

[0067] After the second connector 13.2 (T-bolt) for the limiting device 18 is passed through the connecting hole 19 of the limiting device 18, it is inserted into the pre-embedded groove 9 of the upper pre-embedded part 4 of the prefabricated unit 1 and rotated 90 degrees. The second washer 14.2 (second rubber pad) and the second fastener 15.2 (second nut) are installed in sequence at the end of the second connector 13.2 (T-bolt). The second waterproof rubber sealing gasket 16.2 is pressed into the connecting hole 19. Finally, the upper prefabricated track plate 20, rail and fastener 21 are installed in sequence.

[0068] After the precast unit 1 of the precast track bed is equipped with a cavity to form a socket channel 7, the weight of the component itself can be reduced by 10% to 20%. On the other hand, the cavity is fully utilized to facilitate construction, handling and assembly. There is no need for large-volume on-site pouring and curing. After mechanized assembly, it can provide the working platform required for construction, which greatly improves the construction efficiency of the track bed. Foamed concrete can replace 10% to 20% of the concrete used in the precast component unit. The comprehensive unit price of foamed concrete is about one-third cheaper than that of concrete, which can reduce the project cost.

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A tunnel and bell type ballast bed member characterized by, It includes at least two precast units that are sequentially spliced ​​along the tunnel extension direction. Each precast unit has a socket channel for inserting a mandrel part along the tunnel extension direction. Adjacent precast units cooperate with at least one mandrel. Each precast unit has a grouting port that connects to the socket channel for grouting to fill the gap between the socket channel and the mandrel, and the gap between adjacent precast units. The mandrel is a precast lightweight porous structure. Along the tunnel extension direction, the socket channel runs through the precast unit, with one end of the mandrel inserted into the socket channel of the precast unit and the other end inserted into the socket channel of the adjacent precast unit; this establishes a stable connection between adjacent precast units and mitigates the problem of loosening and failure of the connection between adjacent precast units.

2. The tunnel and bell bed module of claim 1, wherein, The socket channels are distributed within the steel cage of the precast unit, and the mandrels inserted into the same socket channel are arranged at intervals.

3. The tunnel and bell bed module of claim 1, wherein, The socket channel is equipped with a detachable protective sleeve, the outer wall of which is fitted against the inner wall of the socket channel, and the mandrel is inserted into the protective sleeve.

4. The tunnel and bell bed module of claim 1, wherein, The precast unit is provided with multiple socket channels, and the socket channels on the same precast unit are distributed in parallel along their axes.

5. The tunnel and bell bed module of claim 4, wherein, The cross-section of the socket channel perpendicular to the axis is circular or polygonal, and the cross-sectional shape of the mandrel matches the inserted socket channel.

6. The tunnel and bell bed module of claim 1, wherein, The precast unit has mounting holes on its top surface, and the mounting holes are used to fix the precast unit to the segment through connectors.

7. The tunnel socket-type track bed component as described in claim 1, characterized in that, The top surface of the precast unit is provided with a pre-embedded groove, which is connected to the internal steel cage of the precast unit through anchor rods.

8. A method of constructing a tunnel socket bed member according to any one of claims 1 to 7, characterised in that, include: Transport the precast unit into the tunnel so that the core rod of the previous precast unit can be inserted into the socket channel of the precast unit; After the precast unit is in place, it is fixed to the segment. A mandrel is inserted into the socket channel of the precast unit, and the next precast unit is transported to cooperate with the mandrel and dock with the precast unit. Grouting is performed through the grouting port to fill the gaps between the socket channel and the mandrel, the gaps between adjacent precast units, and the gaps between the precast units and the mating segments, so that adjacent precast units, mandrels, and segments form a whole.

9. The construction method according to claim 8, wherein One end of the same mandrel is inserted into the socket channel of a precast unit, and the other end is inserted into the socket channel of another adjacent precast unit; during grouting, the gap between the mandrels in the same socket channel is filled.

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