A shield tunnel underwater docking structure and construction method thereof

Abstract

The present invention discloses an underwater docking structure for a shield tunnel and a construction method thereof. The structure comprises a lower caisson structure and an upper caisson structure, wherein the lower caisson structure and the upper caisson structure are connected by a connector. The lower caisson structure is a reinforced concrete structure, and the upper caisson structure is a detachable double-walled steel cofferdam structure. A caisson backfill body is provided within the lower caisson structure, and two shield machines are excavated in opposite directions within the caisson backfill body. The method of the present invention pre-installs the docking caisson structure, successively excavates two shield tunnels into the caisson structure, and after sealing and grouting the two ends of the shield tunnel, removes the shield machine and casts a secondary reinforced concrete lining structure, thereby achieving bidirectional docking of the shield tunnels and significantly shortening the construction period.

Description

Technical Field

[0001] The present invention relates to the technical field of shield tunnel engineering, and in particular to an underwater butt joint structure of a shield tunnel and a construction method thereof. Background Art

[0002] The fundamental approach to long-distance tunnel construction, known as "long tunnels with short, segmented excavation," is primarily used in mountain tunnels. The core principle is to increase the number of tunnel faces by adding vertical shafts, thereby shortening construction time. However, when using shield tunneling, it's necessary to consider the project's specific conditions and select a suitable vertical shaft location somewhere in the middle of the tunnel to create the conditions for the shield machine's launch and arrival, thereby increasing the number of tunnel faces the shield machine can excavate and shortening construction time.

[0003] When constructing long underwater tunnels, vertical shafts are required to create access for shield machines. This is often accomplished by constructing artificial islands. This method is suitable for shallow water sections with minimal impact on navigation channels, but it carries the disadvantages of high project investment, poor environmental impact, and long construction periods. When the middle of a tunnel lacks the conditions for a vertical shaft, underwater butting shield tunneling can be considered. This method requires consideration of the surrounding strata's characteristics and, if necessary, the implementation of various special water-stopping measures.

[0004] (1) The external stratum of the shield machine itself or after reinforcement meets the water-stopping requirements during docking

[0005] When the surrounding strength and water-stopping conditions of the stratum where the shield machine is docked are good, the docking can be directly carried out by disassembling the machine. This method has high requirements for the stratum. When the stratum where the shield machine is docked is permeable, the stratum around the cutterhead can be frozen to meet the requirements of disassembly. For example, "Shield Docking Semi-circular Ring Freezing Reinforcement Structure" CN205677624U and "Shield Docking Ground Bend Pipe Single-Side Freezing Method and Freezing Pipe Installation Device" CN102392653A require special design of the shield machine, especially when the shield machine diameter is small, it will not be possible to arrange additional components.

[0006] (2) The water-stopping requirements are met by replacing the external soil of the shield machine with other structures

[0007] For example, Chinese invention patent publication number CN115012974A, "A Shield-Sunk Tube Combined Construction Method for Subsea Tunnel Docking," pre-installs a section of immersed tube tunnel structure at the shield machine's intended docking location to facilitate docking joints. The immersed tube method is generally suitable for areas with shallow soil cover and requires excavation and backfilling of the existing riverbed or seabed. However, repeated disturbance of the soil at the docking demarcation point, after excavation and backfilling, can easily affect subsequent shield tunneling and stress. Furthermore, this method is difficult to implement when the shield tunnel is buried at a deep depth, resulting in certain limitations.

[0008] (3) Through special design of shield machine cutterhead, cutterhead docking water stop

[0009] Through special designs of shield machines, such as the Chinese invention patent with publication number CN112324447A, "A shield equipment and docking method capable of realizing underground docking", and the Chinese invention patent with publication number CN110242311A, "Shield underground docking structure and construction method", the shield equipment has a complex design, long-distance excavation and maintenance are difficult, and there are certain risks in underwater docking.

[0010] To sum up, how to solve the problem of long-distance underwater shield docking with complex geological conditions is an urgent problem that technical personnel in this field need to solve. Therefore, it is necessary to study a docking method based on the existing conventional shield machines and the current situation where there are certain allowable errors in shield construction, which is suitable for various complex strata. Summary of the Invention

[0011] The purpose of the present invention is to overcome the shortcomings of the above-mentioned background technology and provide an underwater docking structure of a shield tunnel and a construction method thereof. This method sets up a docking caisson structure in advance, and successively excavates two shield tunnels into the caisson structure. After the two ends of the shield tunnel are sealed and grouting is performed to stop water, the shield main machine is removed and the second lining reinforced concrete structure is cast, thereby realizing two-way docking of the shield tunnel and greatly shortening the construction period.

[0012] To achieve the above-mentioned purpose, the present invention designs an underwater docking structure of a shield tunnel, which includes a lower caisson structure and an upper caisson structure, and the lower caisson structure and the upper caisson structure are connected by connecting parts; the lower caisson structure is a reinforced concrete structure, and the upper caisson structure is a detachable double-wall steel cofferdam structure; a caisson backfill body is arranged in the lower caisson structure, and two shield machines are excavating towards each other in the caisson backfill body.

[0013] In the above technical solution, the lower caisson structure is prefabricated and assembled, and is divided into several prefabricated structures in the height direction. The reinforced concrete structure pipe sections are connected by bolts, and the joints are sealed with rubber expansion waterstops.

[0014] In the above technical solution, the upper caisson structure is prefabricated and assembled, and is divided into several prefabricated structures in the height direction. The steel cofferdam structure pipe sections are connected by bolts, and the joints are sealed with rubber expansion waterstops.

[0015] In the above technical solution, the structural strength of the caisson backfill is C10-C15, and the permeability coefficient is not less than 1×10 -7 cm / s.

[0016] In the above technical solution, the shield machine includes a shield main unit, a shield blade is provided at the front end of the shield main unit, a shield segment is provided at the rear end of the shield main unit, and the gap between the shield segment and the caisson backfill body is covered with a secondary grouting layer.

[0017] The present invention also provides a construction method for an underwater butt joint structure of a shield tunnel, comprising the following steps:

[0018] S1: Setting up the working platform

[0019] Set up an operating platform on the water, which is assembled with steel pipe piles and longitudinal and transverse connecting beams. The steel pipe piles are driven in by ships or floating cranes, and transverse connections are added to connect them into a whole. Vertical and transverse connecting beams are set on the top to form the operating platform.

[0020] S2: Combined caisson sinking

[0021] On-site positioning is performed to determine the central pile position and the longitudinal and transverse axis control pile positions of the caisson. Excavation within the caisson adopts undrained sinking construction. The caisson structure is divided into a lower caisson structure and an upper caisson structure. The lower caisson structure that enters below the stratum is a reinforced concrete structure, while the upper caisson structure above the stratum to the water level line adopts a double-walled steel cofferdam. The two are connected by bolts, and rubber expansion waterstops are used at the joints.

[0022] S3: Caisson Backfill and Demolition

[0023] After the caisson is sunk to the designated position, a plain concrete structure is poured underwater to fill the cavity excavated from the entire lower caisson with a dense plain concrete structure to form the caisson backfill. After the concrete structure reaches the designed strength, the upper caisson structure is removed.

[0024] S4: Shield Tunneling

[0025] The two shield machines moving in opposite directions enter the caisson backfill body one after another and stop excavating when the distance between the two shield cutter heads is 0.2 to 0.5 meters;

[0026] S5: Shield dismantling machine

[0027] The various structures inside the shield machine are dismantled and transported outside the tunnel. Finally, the shield cutterhead is cut into pieces and transported out.

[0028] S6: Casting lining structure

[0029] After the shield machine is dismantled, steel bars are tied and concrete structures are poured inside the shield main casing within the caisson backfill to form an inner lining structure, thus achieving two-way docking and penetration of the shield tunnel.

[0030] In the above technical solution, in step S2, the caisson structure adopts prefabricated pipe segment assembly technology, and the pipe segments are connected by bolts.

[0031] In the above technical solution, in step S4, the propulsion parameters of the shield machine are set according to the stratum and caisson structure that the shield machine passes through.

[0032] In the above technical solution, in step S4, synchronous grouting is performed during the shield advancement process to timely fill the gap between the lining and the backfill body and perform secondary grouting; wherein, the synchronous grouting material is a mixture of one or more materials selected from cement, sand, bentonite, fly ash, and water reducer; and pure cement slurry is used for the secondary grouting.

[0033] In the above technical solution, in step S5, the shield tail is densely grouted for the second time before the shield machine is dismantled, the longitudinal leakage channels of the shield main body and shield segments are filled densely, and longitudinal tensioning measures are adopted for the existing shield segments to ensure that the joints of the existing shield segments are watertight.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] Firstly, the present invention is applicable to the docking of two shield tunnels under construction in opposite directions at a certain middle position in an area of water. By setting a docking caisson structure in advance at a certain position in the middle of the water, the caisson structure is excavated to a designated position, and then the caisson is backfilled with underwater low-grade concrete. The two shield tunnels are successively excavated into the plain concrete backfill body of the caisson structure. After the shield segments at both ends of the shield tunnel are reinforced with secondary grouting, the longitudinal seepage channel is closed, the shield main machine is dismantled, and the second lining reinforced concrete structure is cast, thereby realizing two-way docking of the tunnels and greatly shortening the construction period.

[0036] Secondly, the present invention is applicable to long-distance underwater shield construction, eliminating the need for modification of existing shield machines or special design of new shield machines. It is also suitable for tunnel structures of all cross-sectional dimensions, regardless of tunnel depth or geological conditions, and has a wide range of applications. Caisson operations have a short impact on navigation in existing waters and a limited scope.

[0037] Thirdly, when the present invention adopts the shield connection scheme, the tunnel construction period can be shortened by half, which is beneficial to improving the construction progress and achieving the benefits of early production.

[0038] Fourthly, the present invention can be applied to the shield machine inspection or cutterhead repair working conditions corresponding to long-distance underwater shield construction. For example, a caisson backfilled with plain concrete can be set in advance at a certain mileage position where the shield machine is expected to inspect or repair the cutterhead. When the shield machine excavates to the caisson, secondary grouting is performed, and maintenance workers can safely inspect or repair the cutterhead. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1This is a schematic diagram of the cross-section structure before the shield machine enters the caisson backfill;

[0040] Figure 2 This is a schematic diagram of the planar structure before the first shield machine enters the caisson backfill;

[0041] Figure 3 This is a schematic diagram of the planar structure after the first shield machine enters the caisson backfill;

[0042] Figure 4 This is a schematic diagram of the plan view of the second shield machine after it enters the caisson backfill;

[0043] In the figure, 1-lower caisson structure, 2-upper caisson structure, 3-caisson backfill body, 4-shield machine, 4.1-shield main machine, 4.2-shield blade, 4.3-shield segment, 4.4-secondary grouting layer, 5-working platform, 6-steel pipe pile. DETAILED DESCRIPTION

[0044] The following describes the implementation of the present invention in detail with reference to the examples, but they do not limit the present invention and are merely examples. At the same time, the advantages of the present invention will become clearer and easier to understand.

[0045] like Figure 1 As shown, an underwater docking structure for a shield tunnel according to the present invention includes a lower caisson structure 1 and an upper caisson structure 2, which are connected by a connector. The lower caisson structure 1 is a reinforced concrete structure, and the upper caisson structure 2 is a removable double-walled steel cofferdam structure. A caisson backfill body 3 is disposed within the lower caisson structure 1, and two shield machines 4 are excavating toward each other within the caisson backfill body 3. The shield machine 4 includes a shield main unit 4.1, a shield blade 4.2 is disposed at the front end of the shield main unit 4.1, and a shield segment 4.3 is disposed at the rear end of the shield main unit 4.1. The gap between the shield segment 4.3 and the caisson backfill body 3 is covered with a secondary grouting layer 4.4.

[0046] The lower caisson structure 1 has a circular, thin-walled plan. A circular plan reduces stress and is adaptable to various tunnel depths. For shallow tunnel depths, the caisson can also adopt a rectangular plan, which reduces the excavation area. However, this requires increasing the wall thickness. A uniform vertical thickness is employed, resulting in a thin-walled cylindrical structure. To facilitate subsequent caisson sinking, backfilling, and shield cutting, the structure is constructed of reinforced concrete. Fiberglass reinforcement replaces steel bars within the shield cutting area, and the exterior facade of the caisson is partially cast flat, originally curved, to facilitate shield cutting into the caisson. Considering the limited surface area for water operations and to speed up construction, the lower caisson structure is prefabricated and assembled, divided vertically into several prefabricated structures. The reinforced concrete pipe sections are connected with bolts, and rubber expansion waterstops are used at the joints.

[0047] The upper caisson structure 2 is a thin-walled circular structure in plan, with a uniform thickness vertically, resulting in an overall thin-walled cylindrical shape, consistent with the lower caisson structure. To facilitate later dismantling, a double-walled steel cofferdam is used. Given the limited surface area available for water operations and to expedite construction, the upper caisson structure is prefabricated and assembled, divided vertically into several prefabricated sections. Bolts connect the steel pipe sections, and rubber expansion waterstops are used at the joints.

[0048] After the caisson sinks to the designated position, low-grade plain concrete is backfilled into the lower caisson structure on the working platform, thereby replacing the original highly permeable underwater stratum with a concrete structure with certain strength and anti-permeability. To ensure that the shield can cut the backfill smoothly and have certain strength and anti-permeability when dismantling the machine, the caisson backfill body 3 is made of low-grade plain concrete, with a structural strength of C10-C15 and a permeability coefficient of not less than 1×10 -7 cm / s.

[0049] A construction method of an underwater butt joint structure of a shield tunnel according to the present invention comprises the following steps:

[0050] S1: Setting up the working platform

[0051] like Figure 1 As shown, the work platform 5 is assembled using steel pipe piles 6 and longitudinal and transverse connecting beams. The steel pipe piles are driven using equipment such as ships or floating cranes, and are connected by additional transverse ties. The longitudinal and transverse connecting beams are installed on top of the piles to form the work platform. The steel pipe pile construction platform has a high load-bearing capacity and excellent stability, effectively resisting the impact of high-velocity water pressure and ensuring construction accuracy.

[0052] S2: Combined caisson sinking

[0053] On-site positioning is carried out to determine the center pile position of the caisson and the control pile positions of the longitudinal and transverse axes. The caisson excavation adopts undrained sinking construction. To facilitate on-site operations, the caisson structure adopts prefabricated pipe segment assembly technology, and the various pipe segments are connected by bolts. During the sinking process of the caisson, excessive tilt should be avoided as much as possible. However, if a large tilt occurs due to reasons such as stratum changes, a technical correction plan should be prepared in advance. When the caisson sinks to a design elevation of more than 1m, it should be basically corrected, the sinking speed should be slowed down, and anti-sinking measures should be taken; if the caisson has difficulty sinking, measures such as pressurization or external flushing can be used to assist the sinking of the caisson.

[0054] S3: Caisson Backfill and Demolition

[0055] After the caisson is lowered to the designated location, a plain concrete structure is poured underwater, filling the entire cavity created by the excavation of the lower caisson with a dense, plain concrete structure. Once the concrete structure reaches its designed strength, the upper caisson structure is removed, thus ensuring that existing water navigation is not affected.

[0056] S4: Shield Tunneling

[0057] like Figures 2 to 4 As shown, two shield machines traveling in opposite directions successively enter the caisson backfill and stop excavating when the distance between the two shield cutterheads is 0.2 to 0.5 meters. During shield excavation, it is important to control the shield excavation parameters and grouting parameters in the process of cutting the caisson structure and backfill, optimize the cutterhead configuration in advance, and reduce ground disturbance and ground loss. The specific measures are as follows:

[0058] 1) Shield tunneling parameters

[0059] Shield propulsion parameters should be set and strictly controlled based on the strata and caisson structure the shield machine is traversing. These primarily include cutterhead and soil bin pressure, excavation volume and advance speed, screw speed, and total jack thrust. This ensures the stability of the excavation face and minimizes ground disturbance and ground loss during excavation. The ground loss rate due to excavation volume should be controlled within 3%. During the shield machine's caisson drilling process, advance speed and cutterhead torque should be reduced to optimize cutterhead configuration.

[0060] 2) Synchronous grouting of shield tail and secondary grouting in the hole

[0061] During the shield advancement process, timely synchronous grouting is carried out and the grouting volume is appropriately increased. The gaps between the lining and backfill are filled in time, and secondary grouting is carried out to make up for the shortcomings of synchronous grouting. Repeat the secondary grouting when necessary; the synchronous grouting materials are mixed materials such as cement, sand, bentonite, fly ash, and water reducer. The relevant proportions are determined based on experiments and combined with geological conditions to ensure the effect of synchronous grouting. Pure cement slurry is used for secondary grouting.

[0062] S5: Shield dismantling machine

[0063] Before dismantling the shield, ensure that the shield tail is fully densely packed with secondary grouting, fill the longitudinal leakage channels of the shield machine and shield segments, and use longitudinal tie-down measures to ensure watertight joints between the existing shield segments. During dismantling, the various mechanical structures within the shield machine are disassembled and removed, transported outside the tunnel, and the cutterhead is cut into pieces and transported out.

[0064] S6: Casting lining structure

[0065] After the two shield machines were removed from the caisson, the 0.2-0.5m thick plain concrete partition wall between the shield machines was manually broken down, allowing the two tunnels to be connected. To ensure safety during shield operation, steel bars were tied and high-strength concrete was poured inside the shield machine shell within the caisson backfill, achieving bidirectional connection and connection between the shield tunnels.

[0066] The above is only a specific embodiment of the present invention. It should be pointed out that any changes or substitutions that can be easily thought of by any technician familiar with the field within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. The rest not described in detail belong to the prior art.

Claims

1. A method for constructing an underwater butt joint structure of a shield tunnel, characterized by: The shield tunnel underwater docking structure comprises a lower caisson structure (1) and an upper caisson structure (2), wherein the lower caisson structure (1) and the upper caisson structure (2) are connected by a connecting piece; the lower caisson structure (1) is a reinforced concrete structure, and the upper caisson structure (2) is a detachable double-walled steel cofferdam structure; a caisson backfill body (3) is provided in the lower caisson structure (1), and two shield machines (4) are excavated in opposite directions in the caisson backfill body (3); the construction method of the shield tunnel underwater docking structure comprises the following steps: S1: Setting up the working platform An operating platform is built on the water. The operating platform is assembled with steel pipe piles and longitudinal and transverse connecting beams. The steel pipe piles are driven into the water by ships and are connected into a whole by adding transverse connections. The longitudinal and transverse connecting beams are set on the top to form the operating platform. S2: Combined caisson sinking On-site positioning is performed to determine the central pile position and the longitudinal and transverse axis control pile positions of the caisson. Excavation within the caisson adopts undrained sinking construction. The caisson structure is divided into a lower caisson structure and an upper caisson structure. The lower caisson structure that enters below the stratum is a reinforced concrete structure, while the upper caisson structure above the stratum to the water level line adopts a double-walled steel cofferdam. Bolts are used to connect the pipe sections of the reinforced concrete structure, and bolts are used to connect the pipe sections of the steel cofferdam structure. Rubber expansion waterstops are used at the joints. S3: Caisson Backfill and Demolition After the caisson is sunk to the designated position, a plain concrete structure is poured underwater to fill the cavity excavated from the entire lower caisson with a dense plain concrete structure to form the caisson backfill. After the concrete structure reaches the designed strength, the upper caisson structure is removed. S4: Shield Tunneling The two shield machines moving in opposite directions enter the caisson backfill body one after another and stop excavating when the distance between the two shield cutter heads is 0.2 to 0.5 meters; S5: Shield dismantling machine The various structures inside the shield machine are dismantled and transported outside the tunnel. Finally, the shield cutterhead is cut into pieces and transported out. S6: Casting lining structure After the shield machine is dismantled, steel bars are tied and concrete structures are poured inside the shield main casing within the caisson backfill to form an inner lining structure, thus achieving two-way docking and penetration of the shield tunnel.

2. The construction method of the underwater docking structure of a shield tunnel according to claim 1, characterized in that: The lower caisson structure (1) is prefabricated and assembled, and is divided into several prefabricated structures in the height direction. The reinforced concrete structure pipe sections are connected by bolts, and the joints are sealed with rubber expansion water stop strips.

3. The construction method of the underwater docking structure of a shield tunnel according to claim 1, characterized in that: The upper caisson structure (2) is prefabricated and assembled, and is divided into several prefabricated structures in the height direction. The steel cofferdam structure pipe sections are connected by bolts, and the joints are sealed with rubber expansion water stop strips.

4. The construction method of the underwater docking structure of a shield tunnel according to claim 1, characterized in that: The structural strength of the caisson backfill (3) is C10-C15, and the permeability coefficient is not less than 1×10 -7 cm / s.

5. The construction method of the underwater butt joint structure of a shield tunnel according to claim 1, characterized in that: The shield machine (4) comprises a shield main unit (4.1), a shield blade (4.2) is provided at the front end of the shield main unit (4.1), a shield segment (4.3) is provided at the rear end of the shield main unit (4.1), and a secondary grouting layer (4.4) is covered in the gap between the shield segment (4.3) and the caisson backfill body (3).

6. The construction method of the underwater butt joint structure of a shield tunnel according to claim 1, characterized in that: In step S2, the caisson structure adopts the prefabricated pipe segment assembly technology, and the pipe segments are connected by bolts.

7. The construction method of the underwater docking structure of a shield tunnel according to claim 1, characterized in that: In step S4, the propulsion parameters of the shield machine are set according to the stratum and caisson structure that the shield machine passes through.

8. The construction method of the underwater docking structure of a shield tunnel according to claim 1, characterized in that: In step S4, synchronous grouting is performed during the shield advancement process to timely fill the gap between the lining and the backfill body, and secondary grouting is performed; wherein, the synchronous grouting material is a mixture of one or more materials selected from cement, sand, bentonite, fly ash, and water reducer; and pure cement slurry is used for the secondary grouting.

9. The construction method of the underwater butt joint structure of a shield tunnel according to claim 1, characterized in that: In step S5, before the shield machine is dismantled, the shield tail is densely grouted for the second time, the longitudinal leakage channels of the shield main body and shield segments are filled densely, and longitudinal tensioning measures are taken on the existing shield segments to ensure that the joints of the existing shield segments are watertight.

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