CN115162412A

CN115162412A - Construction method of main span of long-distance multifunctional sea-crossing combined immersed tube tunnel

Info

Publication number: CN115162412A
Application number: CN202211020369.XA
Authority: CN
Inventors: 王新; 潘国庆; 姜弘; 张银屏
Original assignee: Shanghai Urban Construction Design Research Institute Group Co Ltd
Current assignee: Shanghai Urban Construction Design Research Institute Group Co Ltd
Priority date: 2022-08-24
Filing date: 2022-08-24
Publication date: 2022-10-11
Anticipated expiration: 2042-08-24
Also published as: CN115162412B

Abstract

The invention discloses a method for constructing a main span of a long-distance multifunctional sea-crossing combined immersed tube tunnel; the method comprises the following steps: 1. two artificial islands and anchor structures are built at the two ends of the cross-sea combined immersed tube tunnel to be built; 2. arranging a plurality of pin-horse piles on the seabed; 3. taking the two anchorage structures as bridge towers, and constructing a bridge structure positioned under water; 4. dragging each subsection of a main span of the sea-crossing combined immersed tube tunnel to the upper part of the grid type steel beam; 5. sinking each section of the main span underwater to be in place, fixing the section at a corresponding position of the grid type steel beam, and connecting the section with a pin stake at the corresponding position; 6. installing a grating type steel arch frame at the top of the cross-sea combined immersed tube tunnel underwater; 7. tightening a suspender, a suspension cable and a stay cable of the bridge structure; 8. and (5) performing through construction of the main span. The invention solves the construction problem of the long-distance multifunctional cross-sea tunnel by utilizing the construction technology of combining the bridge and the tunnel.

Description

Construction method of main span of long-distance multifunctional sea-crossing combined immersed tube tunnel

Technical Field

The invention relates to the technical field of construction of cross-sea immersed tube tunnels, in particular to a method for constructing a main span of a long-distance multifunctional cross-sea combined immersed tube tunnel.

Background

In the aspect of the existing long-distance sea crossing channel, such as 55km in the engineering length of the bridge and tunnel of mao bridge of mao hong Kong, no sea crossing channel engineering exceeding 100km exists.

Along with the improvement of economic development and capital construction technology, the construction of the cross-sea channel of the Bohai Bay is gradually proposed by various social circles, however, the length of the cross-sea channel of the Bohai Bay is about 130km, and the technical scheme is demonstrated for years and does not form unified understanding.

Therefore, how to solve the difficult problem of building the long-distance multifunctional cross-sea tunnel becomes a technical problem which needs to be solved urgently by the technical personnel in the field.

Disclosure of Invention

In view of the above defects in the prior art, the invention provides a method for constructing a main span of a long-distance multifunctional cross-sea combined immersed tunnel, which aims to solve the difficult problem of constructing a long-distance multifunctional cross-sea tunnel by using a technology of combining a bridge and a tunnel.

In order to achieve the purpose, the invention discloses a construction method of a main span of a long-distance multifunctional sea-crossing combined immersed tube tunnel; the method comprises the following steps:

step 1, building two artificial islands at two ends of a cross-sea combined immersed tube tunnel to be built; constructing an anchorage structure at the central position of each artificial island;

step 2, arranging a plurality of pin-horse piles in the length direction of the cross-sea combined immersed tube tunnel on the seabed;

step 3, taking the two anchorage structures as bridge towers to build a bridge structure under water;

the bridge frame structure is a cable-stayed suspension bridge comprising a grid type steel beam, a suspension rod, a suspension cable and a stay cable;

step 4, hauling each subsection of the main span of the sea-crossing combined immersed tube tunnel to the upper part of the grid type steel beam;

step 5, sinking each section of the main span into the water to be in place, fixing the section at the corresponding position of the grid type steel beam, and connecting the section with a stud pile at the corresponding position;

step 6, installing a grid type steel arch on the top of the cross-sea combined immersed tube tunnel underwater;

step 7, tightening the suspension rods, the suspension cables and the stay cables of the bridge structure;

and 8, performing through construction of the main span.

Preferably, in step 1, the process of building each artificial island is as follows:

step 1.1, constructing peripheral protection by adopting a plurality of steel pipe piles at the outer side of each artificial island to be built;

a steel sleeve box interface structure is arranged on the side wall of each peripheral protection surface facing or facing away from the main span;

step 1.2, filling an anti-seepage layer in an area between the plurality of steel pipe piles on the outermost side of the peripheral protection and the plurality of steel pipe piles on the innermost side;

step 1.3, filling a core layer in an area surrounded by a plurality of steel pipe piles at the innermost side of the peripheral protection;

in the process of filling the core layer, backfilling step by step, and extracting the seawater inside step by step;

step 1.4, after the core layer is filled to the height corresponding to the position of the bottom plate of the sea-crossing combined immersed tube tunnel, a pipe section corresponding to the part of the core layer in the artificial island is hauled into the artificial island through the steel casing box interface in an underwater dragging mode;

step 1.5, backfilling concrete in each steel pouring jacket interface structure to form a plug;

and step 1.6, constructing a pipe section of the artificial island corresponding to the core layer part, and backfilling until the designed elevation of the top of the artificial island is reached.

More preferably, every two adjacent steel pipe piles at the outermost side of each peripheral protection are connected through a lock catch.

In practical application, every two adjacent steel pipe piles at the outermost side are connected through the lock catches, so that filling materials can be prevented from being eroded by seawater.

More preferably, the anti-seepage layer is filled by adopting a geomembrane bag or plain concrete;

the core layer is formed by mixing and filling stone blocks, broken stones, sand and cement in a grading manner.

More preferably, in step 1.5, a filling body formed by backfilling concrete in each steel pouring jacket interface structure is isolated by arranging a plurality of underwater steel plates.

Preferably, each pin-horse pile is of a steel cylinder structure, the diameter of each pin-horse pile is 20-30 meters, the pin-horse pile is inserted into the seabed by a depth which is not less than 1 time of the diameter, and the top of each pin-horse pile is not higher than the structural top of the cross-sea combined immersed tube tunnel;

concrete or graded broken stones are poured into each steel cylinder structure.

Preferably, in the step 3, the grid-type steel beams are segmented according to the segments of the main span and are butted underwater segment by segment;

a plurality of positioning blocks are arranged on the upper surface of the grid type steel beam corresponding to the lower surface of each section of the main span;

each positioning block is welded on the grid-type steel beam and can be embedded under each section of the main span to limit the transverse displacement of each section of the main span on the grid-type steel beam;

the edge positions of the grid type steel beams are suspended on the suspension cables through the suspension rods or are directly connected with the artificial island through the stay cables.

Preferably, the prefabrication of each segment of the main span is completed before the step 4 is executed;

each section of the main span comprises a main body part of a steel shell concrete structure and an arc-shaped grid type steel arch frame;

the middle positions of two sides of each steel shell concrete structure are respectively provided with a protruding structure with a triangular cross section, so that the cross section of each section of the main span is in a shuttle shape, and the arc-shaped grid type steel arch is arranged on the main span;

both ends of each arc-shaped grid type steel arch are connected with the top steel shell edge of the corresponding steel shell concrete structure;

the prefabricating steps are as follows:

firstly, welding steel plates to form a steel shell of each steel shell concrete structure;

during welding, fixing the reinforcing bars of each steel shell concrete structure;

after the steel shell is formed into a closed structure, reserving a plurality of pouring holes and exhaust holes in the top of the steel shell;

after one outfitting is completed, installing end sealing doors, water stops and shear keys on the steel shell;

after the completion, drag into wharf harbor pond with the box hat, adopt self-compaction concrete to carry out concrete placement in wharf harbor pond.

More preferably, the step 4 comprises the following steps:

4.1, after pouring is finished in the wharf harbor basin and the design strength is reached, performing secondary outfitting on each steel shell concrete structure, and installing steel corbels, manholes and a positioning tower;

4.2, hauling all the steel shell concrete structures to a position, corresponding to the main span, on the bridge structure by a tugboat;

from the two artificial islands to the middle of the main span, butting and sinking each steel-shell concrete structure with the island side pipe joints of the artificial islands one by one;

4.3, after sinking, realizing the compaction of every two adjacent steel shell concrete structures through an external prestress pulling device which is arranged on the steel shell of each steel shell concrete structure along the circumference of the section;

4.4, after each section is compressed, fixing two sides of each steel shell concrete structure close to the two end positions with the pin-stud-pile at the corresponding position through at least 3 steel trusses; and simultaneously, the triangular protruding structures on two sides of each steel shell concrete structure are tensioned and fixed on the corresponding subsections of the grid type steel beams by prestressed steel cables.

More preferably, in step 8, the penetrating construction of the main span includes the steps of:

removing end sealing doors after the water stop belts are sufficiently extruded between the pipe section structures of every two adjacent immersed tube tunnels except for the joint of the last two steel shell concrete structures corresponding to the midspan position of the main span, so as to realize the communication of the immersed tube tunnels;

the construction method of pushing the pipe section inwards is adopted at the joint of the last two steel shell concrete structures corresponding to the midspan position of the main span, specifically, the section size is enlarged at the joint of the last two steel shell concrete structures, and a section of inner sleeve pipe section which can move along the length direction and is inserted into the other steel shell concrete structure is sleeved in one steel shell concrete structure;

during construction, the inner casing pipe section is pushed out to the other steel shell concrete structure through a jack to realize through connection.

The invention has the beneficial effects that:

the invention utilizes the construction technology of combining the bridge and the tunnel, the immersed tube tunnel has certain buoyancy to offset a part of vertical load, and the stress of the bridge cable structure is reduced.

The bridge cables of the floating bridge structure are symmetrically arranged on the bridge tower to form self-anchoring, so that the stress of the bridge pier is reduced.

According to the invention, vertical support is provided for each section of the main span of the sea-crossing combined immersed tube tunnel through the bridge cable structure of the floating transportation and bridge structure, and the buoyancy of each section of the main span reduces vertical load for the bridge cable structure, so that the vertical support and the vertical support bring out the best in each other.

The main body of each section of the main span is of a steel shell concrete structure, so that large-area dry dock is avoided, and investment is saved.

The steel shell concrete structure has large section and complete functions, and enhances the communication of passengers and goods.

The invention can be used for carrying out tunnel construction on multiple working faces, and the total construction period is saved.

The conception, the specific structure and the technical effects of the present invention will be further described with reference to the accompanying drawings to fully understand the objects, the features and the effects of the present invention.

Drawings

Fig. 1 is a schematic view showing a construction state according to an embodiment of the present invention.

Fig. 2 is a schematic cross-sectional view of a cross-sea combination immersed tunnel according to an embodiment of the present invention.

Fig. 3 is a schematic top view of an artificial island according to an embodiment of the present invention.

FIG. 4 shows a schematic block diagram of a top view of a segment spanning primarily one of the top directions in an embodiment of the present invention.

Detailed Description

Examples

As shown in fig. 1 to 4, a method for constructing a main span of a long-distance multifunctional sea-crossing combined immersed tube tunnel; the method comprises the following steps:

step 1, building two artificial islands 1 at two ends of a cross-sea combined immersed tube tunnel to be built; constructing an anchorage structure 2 at the central position of each artificial island 1;

step 2, arranging a plurality of pin-horse piles 3 in the length direction of the cross-sea combined immersed tunnel on the seabed

Step 3, constructing a bridge structure under water by taking the two anchorage structures 2 as bridge towers;

the bridge frame structure is a cable-stayed suspension bridge comprising a grid type steel beam 4, a suspender 6, a suspension cable 7 and a stay cable 8;

step 4, dragging and transporting each subsection of a main span 5 of the sea-crossing combined immersed tube tunnel to the upper part of a grid type steel beam 4;

step 5, sinking each section of the main span 5 into water to be in place, fixing the section at a corresponding position of the grid type steel beam 4, and connecting the section with the pin-stud piles 3 at the corresponding position;

step 6, installing a grating type steel arch frame 9 at the top of the cross-sea combined immersed tube tunnel underwater;

step 7, tightening a suspender 6 of the bridge structure, a suspension cable 7 and a stay cable 8;

and 8, performing through construction of the main span 5.

The principle of the invention is as follows:

the invention utilizes the construction technology of combining the bridge and the tunnel, and the main span 5 of the sea-crossing combined immersed tube tunnel is positioned and constructed through a bridge structure built under the water surface;

each section of the main span 5 can be transported by utilizing the buoyancy of the water body, a part of vertical load can be offset, and meanwhile, the stress of a bridge cable of the bridge structure is reduced.

The bridge cables are symmetrically arranged on the bridge tower to form self-anchoring, so that the stress of the bridge pier can be reduced.

The bridge cable provides vertical support for the main span 5 of the sea-crossing combined immersed tube tunnel, and the buoyancy of each section of the main span 5 reduces vertical load for the bridge cable structure, so that the vertical load is brought out in a complementary manner.

In some embodiments, in step 1, the process of building each artificial island 1 is as follows:

step 1.1, constructing peripheral protection by adopting a plurality of steel pipe piles 10 on the outer side of each artificial island 1 to be built;

the side wall of each peripheral protective surface facing or facing away from the main span 5 is provided with a steel jacket box interface structure 11;

step 1.2, filling an anti-seepage layer in a region between a plurality of steel pipe piles 10 on the outermost side and a plurality of steel pipe piles 10 on the innermost side of the periphery protection;

step 1.3, filling a core layer in an area surrounded by a plurality of steel pipe piles 10 at the innermost side of the peripheral protection;

in the process of filling the core layer, the core layer is gradually backfilled, and the seawater inside the core layer is gradually pumped;

step 1.4, after filling the core layer to the height corresponding to the position of the bottom plate of the sea-crossing combined immersed tube tunnel, dragging a pipe section of the corresponding core layer part in the artificial island 1 to enter through a steel casing box interface in an underwater dragging mode;

step 1.5, backfilling concrete in each steel pouring jacket interface structure 11 to form a plug;

and step 1.6, constructing a pipe section of the artificial island 1 corresponding to the core layer part, and backfilling until the designed elevation of the top of the artificial island 1 is reached.

In some embodiments, each two adjacent steel pipe piles 10 at the outermost side of each peripheral protection are connected by using a lock catch.

In practical application, the lock catch connection between every two adjacent steel pipe piles 10 at the outermost side can prevent the filling material from being eroded by seawater.

In certain embodiments, the impervious layer is filled with geomembrane bags or plain concrete;

the core layer adopts stone blocks, rubbles, sand and cement to mix and fill through gradation.

In certain embodiments, in step 1.5, the backfill formed by the backfilled concrete in each steel casing box interface structure 11 is isolated by providing a plurality of underwater steel plates.

In some embodiments, each pin-horse pile 3 is of a steel cylinder structure, the diameter of each pin-horse pile is 20-30 meters, the pin-horse pile is inserted into the seabed by a depth of not less than 1 time of the diameter, and the top of each pin-horse pile is not higher than the structural top of the cross-sea combined immersed tube tunnel;

concrete or graded broken stones are poured into each steel cylinder structure.

In some embodiments, in step 3, the grid-type steel beams 4 are segmented according to the segmentation of the main span 5 and butted underwater section by section;

a plurality of positioning blocks 12 are arranged on the upper surface of the grid type steel beam 4 corresponding to the lower surface of each section of the main span 5;

each positioning block 12 is welded on the grid type steel beam 4 and can be embedded below each section of the main span 5 to limit the transverse displacement of each section of the main span 5 on the grid type steel beam 4;

the edge positions of the grid type steel beams 4 are all suspended on suspension cables 7 through suspension rods 6 or are directly connected with the artificial island 1 through stay cables 8.

In some embodiments, the prefabrication of each segment of the main span 5 is completed before step 4 is performed;

each section of the main span 5 comprises a main body part of a steel shell concrete structure 13 and an arc-shaped grid type steel arch 9;

the middle positions of two sides of each steel shell concrete structure 13 are respectively provided with a convex structure with a triangular cross section, so that the cross section of each section of the main span 5 is in a shuttle shape, and an arc-shaped grid type steel arch frame 9 is arranged on the main span;

both ends of each arc-shaped grid type steel arch 9 are connected with the top steel shell edge of the corresponding steel shell concrete structure 13;

the prefabricating steps are as follows:

firstly, welding steel plates to form a steel shell of each steel shell concrete structure 13;

during welding, the reinforcing bars of each steel shell concrete structure 13 are fixed;

after one outfitting is finished, installing an end sealing door, a water stop and a shear key on the steel shell;

after the completion, drag the box hat into pier harbor pond, adopt self-compaction concrete to carry out concrete placement in pier harbor pond.

In certain embodiments, step 4 comprises the steps of:

4.1, after pouring is finished in the wharf harbor basin and the design strength is reached, performing secondary outfitting on each steel shell concrete structure 13, and installing steel corbels, manholes and positioning towers;

step 4.2, dragging all the steel shell concrete structures 13 to the positions, corresponding to the main span 5, on the bridge structure through a tugboat;

from the two artificial islands 1 to the middle of the main span 5, each steel-shell concrete structure 13 is butted and sunk with an island side pipe joint of the artificial island 1 one by one;

4.3, after sinking, realizing the compaction of every two adjacent steel shell concrete structures 13 through an external prestress pulling device which is arranged on the steel shell of each steel shell concrete structure 13 along the circumference of the section;

4.4, after each section is compressed, fixing two sides of each steel shell concrete structure 13 close to two end positions with the stud piles 3 at corresponding positions through at least 3 steel trusses; meanwhile, prestressed steel cables 14 are adopted to tighten and fix the triangular protruding structures on both sides of each steel shell concrete structure 13 on the corresponding sections of the grid-type steel beams 4.

In practical application, the pin-horse piles 3 are symmetrically arranged on two sides of each steel shell concrete structure 13 and are arranged according to the length of the pipe section structure of the immersed tube tunnel, so that the lateral force of seawater ocean current is resisted, and the structural stability of the immersed tube tunnel at the joint is ensured.

The external prestress pulling-in device arranged along the circumference of the section of the steel shell of each steel shell concrete structure 13 comprises a stay cable and an anchorage.

Each of the pin-horse piles 3 is connected with the pipe section structure of the immersed tunnel through 3 steel trusses 15, and the trusses are respectively welded on the steel shell surface of the pipe section structure and the side surface of the pin-horse pile 3.

In step 4.2, hauling the steel shell concrete structure 13 comprises the following steps:

pulling the steel shell concrete structure 13 to any artificial island 1 by using a tugboat along the longitudinal direction, and then sinking the steel shell concrete structure 13 to the corresponding island side pipe section structure of the artificial island 1 for butt joint;

or, the steel-shell concrete structure 13 is firstly sunk onto the bridge structure, and the steel-shell concrete structure 13 slides to the artificial island 1 on the bridge structure along the longitudinal direction through a traction device on the bridge to realize butt joint.

In some embodiments, in step 8, the penetrating construction of the main span 5 comprises the following steps:

removing the end sealing door after the water stop belts are sufficiently extruded between the pipe section structures of every two adjacent immersed tube tunnels except for the joint of the last two steel shell concrete structures 13 corresponding to the midspan position of the main span 5, so as to realize the communication of the immersed tube tunnels;

the construction method of pushing the pipe section inwards is adopted at the joint of the last two steel shell concrete structures 13 corresponding to the midspan position of the main span 5, specifically, the section size is enlarged at the joint of the last two steel shell concrete structures 13, and a section of inner casing pipe section which can move along the length direction and is inserted into the other steel shell concrete structure 13 is sleeved in one steel shell concrete structure 13;

during construction, the inner casing pipe section is pushed out to the other steel shell concrete structure 13 through the jack to realize through connection.

The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.

Claims

1. A method for constructing a main span of a long-distance multifunctional sea-crossing combined immersed tunnel; the method is characterized by comprising the following steps:

step 1, building two artificial islands (1) at two ends of a cross-sea combined immersed tube tunnel to be built; constructing an anchorage structure (2) at the central position of each artificial island (1);

step 2, arranging a plurality of pin-horse piles (3) in the seabed in the length direction of the cross-sea combined immersed tube tunnel;

step 3, constructing a bridge structure under water by taking the two anchorage structures (2) as a bridge tower;

the bridge frame structure is a cable-stayed suspension bridge comprising a grid type steel beam (4), a suspender (6), a suspension cable (7) and a stay cable (8);

step 4, hauling each subsection of a main span (5) of the sea-crossing combined immersed tube tunnel to the upper part of the grid type steel beam (4);

step 5, sinking each section of the main span (5) into water to be in place, fixing the section at the corresponding position of the grid type steel beam (4), and connecting the section with the pin-stud piles (3) at the corresponding position;

step 6, installing a grid type steel arch frame (9) at the top of the cross-sea combined immersed tube tunnel underwater;

step 7, tightening the suspension rods (6), the suspension cables (7) and the stay cables (8) of the bridge structure;

and 8, performing through construction on the main span (5).

2. The construction method of the main span of the long-distance multifunctional cross-sea combined immersed tunnel according to claim 1, wherein in the step 1, the process of constructing each artificial island (1) is as follows:

step 1.1, constructing peripheral protection by adopting a plurality of steel pipe piles (10) at the outer side of each artificial island (1) to be built;

a steel jacket box interface structure (11) is arranged on the side wall of each peripheral protective surface facing or facing away from the main span (5);

step 1.2, filling an anti-seepage layer in a region between the plurality of steel pipe piles (10) on the outermost side of the peripheral protection and the plurality of steel pipe piles (10) on the innermost side;

step 1.3, filling a core layer in an area surrounded by a plurality of steel pipe piles (10) at the innermost side of the peripheral protection;

step 1.4, after the core layer is filled to the height corresponding to the position of a bottom plate of the cross-sea combined immersed tube tunnel, a pipe section corresponding to the core layer part in the artificial island (1) is hauled into the artificial island through the steel sleeve box interface in an underwater dragging mode;

step 1.5, backfilling concrete in each steel pouring jacket interface structure (11) to form a plug;

and step 1.6, constructing a pipe section of the artificial island (1) corresponding to the core layer part, and backfilling until the designed elevation of the top of the artificial island (1) is reached.

3. The construction method of the main span of the long-distance multifunctional sea-crossing combined immersed tube tunnel according to claim 2, wherein every two adjacent steel pipe piles (10) at the outermost side of each peripheral protection are connected by adopting a lock catch.

In practical application, the lock catch connection is adopted between every two adjacent steel pipe piles (10) at the outermost side, so that the filling materials can be prevented from being eroded by seawater.

4. The construction method of the main span of the long-distance multifunctional cross-sea combined immersed tunnel according to claim 2, wherein the anti-seepage layer is filled with geomembrane bags or plain concrete;

5. The method for constructing the main span of the long-distance multifunctional sea-crossing combined immersed tunnel according to claim 2, wherein in step 1.5, a filling body formed by backfilling concrete in each steel casing box interface structure (11) is isolated by arranging a plurality of underwater steel plates.

6. The construction method of the main span of the long-distance multifunctional cross-sea combined immersed tunnel according to claim 1, wherein each of the pin-horse piles (3) is of a steel cylinder structure, has a diameter of 20-30 m, is inserted into the sea bottom to a depth of not less than 1 time of the diameter, and has no top higher than the structural top of the cross-sea combined immersed tunnel;

concrete or graded broken stones are poured into each steel cylinder structure.

7. The construction method of the main span of the long-distance multifunctional sea-crossing combined immersed tunnel according to claim 1, wherein in the step 3, the grid-type steel beams (4) are segmented according to the segmentation of the main span (5) and are butted underwater section by section;

a plurality of positioning blocks (12) are arranged on the upper surface of the grid type steel beam (4) corresponding to the lower surface of each section of the main span (5);

each positioning block (12) is welded on the grid type steel beam (4) and can be embedded under each section of the main span (5) to limit the transverse displacement of each section of the main span (5) on the grid type steel beam (4);

the edge positions of the grid type steel beams (4) are all suspended on suspension cables (7) through suspension rods (6) or are directly connected with the artificial island (1) through stay cables (8).

8. The construction method of a main span of a long-distance multifunctional sea-crossing combined immersed tube tunnel according to claim 1, wherein prefabrication of each segment of the main span (5) is completed before step 4 is performed;

each section of the main span (5) comprises a main body part of a steel shell concrete structure (13) and an arc-shaped grid type steel arch (9);

the middle positions of two sides of each steel shell concrete structure (13) are respectively provided with a protruding structure with a triangular cross section, so that the cross section of each section of the main span (5) is in a shuttle shape, and the arc-shaped grid type steel arch frame (9) is arranged on the main span;

both ends of each arc-shaped grid type steel arch frame (9) are connected with the top steel shell edge of the corresponding steel shell concrete structure (13);

the prefabricating steps are as follows:

firstly, welding steel plates to form a steel shell of each steel shell concrete structure (13);

during welding, firstly fixing the reinforcing bars of each steel shell concrete structure (13);

9. The method for constructing the main span of the long-distance multifunctional cross-sea combined immersed tunnel according to claim 8, wherein the step 4 comprises the steps of:

4.1, after pouring is finished in the wharf harbor basin and the design strength is reached, performing secondary outfitting on each steel shell concrete structure (13), and installing steel corbels, manholes and positioning towers;

step 4.2, hauling all the steel shell concrete structures (13) to the positions, corresponding to the main span (5), on the bridge structure through a tugboat;

from the two artificial islands (1) to the middle of the main span (5), butting and sinking each steel shell concrete structure (13) and an island side pipe joint of the artificial island (1) one by one;

4.3, after sinking, realizing the compaction of every two adjacent steel shell concrete structures (13) through an external prestress pulling device which is arranged on the steel shell of each steel shell concrete structure (13) along the circumference of the section;

4.4, after each section is compressed, fixing two sides of each steel shell concrete structure (13) close to two end positions with the pin stud piles (3) at corresponding positions through at least 3 steel trusses; and simultaneously, the triangular protruding structures on two sides of each steel shell concrete structure (13) are tensioned and fixed on the corresponding sections of the grid type steel beams (4) by prestressed steel cables (14).

10. The construction method of the main span of the long-distance multifunctional sea-crossing combined immersed tunnel according to claim 6, wherein in step 8, the penetration construction of the main span (5) comprises the following steps:

removing end sealing doors after the water stop belts are sufficiently extruded between the pipe section structures of every two adjacent immersed tube tunnels except for the joint of the last two steel shell concrete structures (13) corresponding to the midspan position of the main span (5), so as to realize the communication of the immersed tube tunnels;

the construction method of pipe section pushing inwards is adopted at the joint of the last two steel shell concrete structures (13) corresponding to the midspan position of the main span (5), the section size is enlarged at the joint of the last two steel shell concrete structures (13), and an inner sleeve pipe section which can move along the length direction and is inserted into the other steel shell concrete structure (13) is sleeved inside one steel shell concrete structure (13);

during construction, the inner casing pipe section is pushed out to the other steel shell concrete structure (13) through a jack to realize through connection.