Protective Structure and Construction Method for Connection Point Between Two Double-Layer Shield Tunnels

Abstract

This invention discloses a protective structure and construction method for the connection point between two double-layer shield tunnels. The protective structure includes upper protection, lower protection, and end protection. The upper protection includes a wall structure formed by steel shell shafts and steel box culverts on the main tunnel and ramp tunnel respectively, multiple transverse steel pipes between the two wall structures, and frozen structures placed around the two wall structures and each transverse steel pipe. The lower protection includes a curved pipe curtain extending along the main tunnel and ramp tunnel, and a frozen structure formed by freezing and water-stopping the curved pipe curtain. During construction, the protective structure is constructed first, then the segments of the main tunnel and ramp tunnel on opposite sides are removed sequentially from top to bottom, and the corresponding soil is excavated. Finally, the connection node is poured from bottom to top. The application of this invention enables trenchless connection between the main line and ramp of the shield tunnel, avoiding large-scale excavation and minimizing the impact on the surrounding environment.

Description

Technical Field

[0001] This invention relates to the field of shield tunnel construction technology, and in particular to the protective structure and construction method of the connection point between two double-layer shield tunnels. Background Technology

[0002] Existing technologies often employ the shield tunneling method to construct long or relatively long underground roads. This involves setting up open-cut ramps to connect the surface and underground roads, and setting up open-cut working shafts to connect the main shield tunneling line with the open-cut ramps, which also serve as the passage shafts for the main shield tunneling line.

[0003] However, existing technologies cannot avoid the following problems in practical applications:

[0004] 1. The open-cut method (ramp, working shaft) has a significant impact on the surrounding environment, a long construction period, and a high cost;

[0005] 2. To meet functional requirements, foundation pits are usually characterized by being extremely deep and large, requiring reliable support structures and foundation reinforcement measures. At the same time, the structure of deep and large working wells is subject to complex stresses and the treatment of confined water is difficult, resulting in significant implementation risks.

[0006] 3. It requires a large amount of ground construction space and takes 2-3 years, which is often difficult to meet in the core urban areas.

[0007] Therefore, how to minimize the impact on the surrounding environment and adopt trenchless methods to reduce the occupation of ground construction sites has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0008] In view of the above-mentioned deficiencies of the prior art, the present invention provides a protective structure and construction method for the connection point between two double-layer shield tunnels. The purpose is to achieve a non-excavation connection between the main line of the shield tunnel and the ramp, avoiding large-scale excavation and minimizing the impact on the surrounding environment.

[0009] To achieve the above objectives, the present invention discloses a protective structure for the connection point between two double-layer shield tunnels. During the construction of the connection node between the main tunnel and the ramp tunnel, the construction area surrounding the connection node includes upper protection, lower protection and end protection.

[0010] The upper protection is located above the construction area and includes multiple steel shell wells installed on the top of the main tunnel and the ramp tunnel;

[0011] A steel box culvert is provided between each two steel shell wells along the tunnel direction, forming a wall structure on the main tunnel and the ramp tunnel respectively;

[0012] Multiple parallel horizontal steel pipes that are connected sideways are provided between the two wall structures.

[0013] Each of the transverse steel pipes is connected to both ends of the two wall structures respectively;

[0014] Both wall structures, as well as the soil surrounding each of the transverse steel pipes, are reinforced with freezing water-stopping measures to form a frozen body.

[0015] The lower protection is located below the construction area and includes a curved pipe curtain extending along the main tunnel and the ramp tunnel, as well as a frozen body formed by freezing and water-stopping the curved pipe curtain.

[0016] The end protection is installed on the side where the boundary of the construction area intersects with the extension trajectory of the main tunnel or the ramp tunnel;

[0017] Each of the aforementioned end protections is a frozen body used to freeze and reinforce the soil at the corresponding location.

[0018] Preferably, each of the steel-shell wells extends from the top of the corresponding main tunnel or the corresponding ramp tunnel by vertically jacking it upwards within the corresponding main tunnel or the corresponding ramp tunnel.

[0019] Preferably, each pair of adjacent transverse steel pipes is connected by a male and female joint.

[0020] Preferably, each of the steel box culverts extends along a corresponding extension trajectory at a corresponding position in the corresponding main tunnel or the corresponding ramp tunnel.

[0021] Preferably, during the construction of the connecting node, both the main tunnel and the ramp tunnel are equipped with vertical and horizontal supports;

[0022] Each of the aforementioned vertical supports comprises two steel frames;

[0023] Each of the two steel frames for vertical support is arranged symmetrically about the axis of the main tunnel or the ramp tunnel in which it is located. The two steel frames can support the openings of the corresponding segments at the top and bottom of the main tunnel and the ramp tunnel near the opposite edge.

[0024] Each of the lateral supports is located at the axis of the corresponding main tunnel or the corresponding ramp tunnel.

[0025] More preferably, both the main tunnel and the ramp tunnel within the connection node range use steel or steel-concrete composite segments;

[0026] Each segment of the pipe that is in contact with the horizontal support and / or vertical frame during construction has the conditions for welding.

[0027] This invention also discloses a method for constructing a protective structure at the connection point between two double-layer shield tunnels, comprising the following steps:

[0028] Step 1: Complete the shield tunneling construction and the segment assembly of the main tunnel and the ramp tunnel;

[0029] Step 2: Construct the lower protection structure as described above;

[0030] Step 3: Construct the aforementioned upper protection structure;

[0031] Step 4: After the upper protection is completed, vertical and horizontal supports are installed in both the main tunnel and the ramp tunnel.

[0032] Each of the vertical supports and each of the horizontal supports is made of steel pipe, and the ends are welded to the corresponding pipe segments by steel plates;

[0033] Step 5: Freeze and reinforce the side where the boundary of the construction area intersects with the extension trajectory of the main tunnel or the ramp tunnel to form the end protection. At the same time, freeze and reinforce the lower protection and the upper protection again.

[0034] Step 6: Remove the segments and earthwork between the main tunnel or the ramp tunnel on the opposite side, and install horizontal steel supports in the main tunnel or the ramp tunnel to support the outer wall on the opposite side of the main tunnel or the ramp tunnel.

[0035] Step 7: Excavate the soil to the bottom plate construction elevation of the connection node; during the excavation process, the longitudinal slope is constructed with a slope ratio of no more than 1:2, and platforms with a width of no less than 2m are set in layers to ensure the longitudinal stability of the slope.

[0036] Step 8: Construct the base plate and the underlying pad layer;

[0037] Step 9: After the base plate meets the requirements, remove the transverse supports at the axis of the main tunnel and the ramp tunnel, and pour the side walls, middle walls and end walls below the middle plate of the connecting node, as well as the middle plate.

[0038] Step 10: After the middle plate meets the requirements, remove the lowest horizontal support and pour the remaining side wall, middle wall, end wall and top plate of the connection node;

[0039] Step 11: After the top plate meets the requirements, remove the uppermost horizontal steel support;

[0040] Step 12: Seal the holes left by each of the steel shell wells in the main tunnel and the ramp tunnel;

[0041] Step 13: After filling the gaps with lightweight concrete, the construction is complete.

[0042] Preferably, step 2 includes the following steps:

[0043] Step 2.1: Grouting is performed at the bottom of the ramp tunnel to form a pipe curtain reinforcement, and water-stopping reinforcement is performed below the construction area to form the frozen body of the lower protection.

[0044] Step 2.2: Cut the steel segments used to install the curved pipe curtain, carry out the construction of the curved pipe curtain, and receive it in the main tunnel to complete the construction of the lower protection curved pipe curtain.

[0045] Preferably, step 3 includes the following steps:

[0046] Step 3.1: Perform top grouting reinforcement on the top of the main tunnel and the ramp tunnel;

[0047] Step 3.2: In the main tunnel and the ramp tunnel, support brackets are erected at the locations corresponding to each steel shell well, and steel segments for setting the corresponding steel shell well are cut.

[0048] Step 3.3: Vertically lift each of the steel shell wells to form an upwardly convex steel shell well in the main tunnel or the ramp tunnel; during the lifting process, pay attention to the protection and stability of the surrounding soil to prevent soil and water from flowing into the main tunnel or the ramp tunnel;

[0049] Step 3.4: After the jacking is completed, seal the top slabs of the main tunnel and the ramp tunnel, and reliably connect each of the steel shell wells to the corresponding segment components;

[0050] Step 3.5: In each of the steel shell wells, construct a reinforced opening along the extension direction of the corresponding main tunnel or the corresponding ramp tunnel, cut the opening, and then construct the corresponding steel box culverts using the pipe jacking method to form two wall structures.

[0051] Step 3.6: Within the two wall structures, construct a transverse reinforcement hole along the opposite side of the main tunnel and the ramp tunnel, and cut the hole. Install all the transverse steel pipes along the tunnel transversely using the pipe jacking method. Connect each pair of transverse steel pipes with a male-female joint, and seal each transverse steel pipe with its own grouting pipe for water stop.

[0052] Preferably, step 6 includes the following steps:

[0053] Step 6.1: Symmetrically dismantle the segments near the top on the opposite sides of the main tunnel and the ramp tunnel, excavate the soil between the dismantled segments, and erect horizontal steel supports.

[0054] Step 6.2: Install another transverse support near the bottom of the main tunnel and the ramp tunnel, and remove the segments of the main tunnel and the ramp tunnel on the opposite sides and excavate the corresponding earthwork to near the axis height.

[0055] Step 6.3: Continue to remove the segments of the main tunnel and the ramp tunnel on the opposite sides and excavate the corresponding earthwork, and horizontally connect the two transverse supports located at the axial height in the main tunnel and the ramp tunnel;

[0056] Step 6.4: Continue to remove the segments of the main tunnel and the ramp tunnel on the opposite sides and excavate the corresponding earthwork, and horizontally connect the two transverse supports near the bottom of the main tunnel and the ramp tunnel.

[0057] The beneficial effects of this invention are:

[0058] The application of this invention enables trenchless connection between the main line of a shield tunnel and the ramps, avoiding large-scale excavation and minimizing the impact on the surrounding environment.

[0059] Furthermore, the construction method provided by this invention can enhance the applicability of the shield tunneling method and reduce the impact of land use conflicts and environmental disturbances caused by the construction of open-cut ramps.

[0060] The following will further explain the concept, specific structure, and technical effects of the present invention in conjunction with the accompanying drawings, so as to fully understand the purpose, features, and effects of the present invention. Attached Figure Description

[0061] Figure 1 A schematic diagram of a planar structure according to an embodiment of the present invention is shown.

[0062] Figure 2 A longitudinal cross-sectional structural schematic diagram of an embodiment of the present invention is shown.

[0063] Figure 3 This diagram shows a cross-sectional structure of a completed curved tube curtain according to an embodiment of the present invention.

[0064] Figure 4 This diagram shows a cross-sectional structure of the pipe curtain opening reinforcement in one embodiment of the present invention.

[0065] Figure 5 This diagram shows a cross-sectional structure of a steel-shell well according to one embodiment of the present invention.

[0066] Figure 6 This diagram shows a cross-sectional structure of the transverse steel pipe that completes the upper protection in one embodiment of the present invention.

[0067] Figure 7 This diagram illustrates a cross-sectional structure of the main tunnel and ramp tunnels, providing vertical support and lateral support at the axial height, according to an embodiment of the present invention.

[0068] Figure 8 This diagram illustrates a cross-sectional structure of a method for removing the segments near the top of the main tunnel and ramp tunnel on opposite sides and installing horizontal steel supports, according to one embodiment of the present invention.

[0069] Figure 9 This diagram illustrates the cross-sectional structure of the soil within the range from the top horizontal support to the axial support on the opposite side of the main tunnel and ramp tunnel, according to an embodiment of the present invention.

[0070] Figure 10 This diagram illustrates a cross-sectional structure of a solution in one embodiment of the present invention, showing the removal of segments from the opposing sides of the main tunnel and ramp tunnels near the axial height, and the completion of the lateral support connection at the axial height.

[0071] Figure 11 This diagram illustrates a cross-sectional structure of a present invention, showing the removal of tunnel segments near the bottom height on the opposing sides of the main tunnel and ramp tunnel, and the completion of a lateral support connection near the bottom height.

[0072] Figure 12 This diagram shows a cross-sectional structure of the completed base plate casting according to an embodiment of the present invention.

[0073] Figure 13 This diagram shows a cross-sectional structure of the completed middle plate casting according to an embodiment of the present invention.

[0074] Figure 14 This diagram shows a cross-sectional structure of the completed top slab pouring in one embodiment of the present invention.

[0075] Figure 15 This diagram shows a cross-sectional structure after all construction has been completed in one embodiment of the present invention. Detailed Implementation

[0076] Example: Figure 1 and Figure 2 As shown, the protective structure at the connection point between the two double-layer shield tunnels, during the construction of the connection node between the main tunnel 1 and the ramp tunnel 2, includes the construction area 3 surrounding the connection node, which includes upper protection, lower protection and end protection.

[0077] The upper protection is set above the construction area 3, including multiple steel shell wells 4 set on the top of the main tunnel 1 and the ramp tunnel 2;

[0078] A steel box culvert 5 is provided between every two steel shell wells 4 along the tunnel direction, forming a wall structure on the main tunnel 1 and the ramp tunnel 2 respectively;

[0079] Multiple parallel horizontal steel pipes 6 are installed between the two wall structures and are connected on the sides.

[0080] Both ends of each horizontal steel pipe 6 are connected to the two wall structures respectively;

[0081] The two wall structures, as well as the soil around each horizontal steel pipe 6, are reinforced with freezing water to form a frozen body 7.

[0082] The lower protection is set below the construction area 3, including the curved pipe curtain 11 extending along the main tunnel 1 and the ramp tunnel 2, and the frozen body 7 formed by freezing and water-stopping the curved pipe curtain 11.

[0083] End protection 8 is installed on the side where the boundary of construction area 3 intersects with the extension trajectory of main tunnel 1 or ramp tunnel 2;

[0084] Each end protection 8 is a frozen body 7 that freezes and reinforces the soil at the corresponding location to stop water seepage.

[0085] This invention utilizes vertical jacking construction to build a steel shell well 4. A robust upper protection is formed by a pipe curtain structure consisting of multiple parallel and side-connected transverse steel pipes 6. A lower protection with good water-stopping effect is formed by using curved pipe curtain 11 and corresponding freezing bodies 7.

[0086] In some embodiments, each steel-shell well 4 extends from the top of the corresponding main tunnel 1 or the corresponding ramp tunnel 2 by vertically jacking it upwards within the corresponding main tunnel 1 or the corresponding ramp tunnel 2.

[0087] In some embodiments, each pair of adjacent transverse steel pipes 6 is connected by a male and female joint.

[0088] In some embodiments, each steel box culvert 5 extends along an extension trajectory at a corresponding position in the corresponding main tunnel 1 or the corresponding ramp tunnel 2.

[0089] In some embodiments, during the construction of the connecting nodes, vertical supports 9 and horizontal supports 10 are installed in both the main tunnel 1 and the ramp tunnel 2.

[0090] Each vertical support 9 includes two steel frames;

[0091] Each vertical support 9 has two steel frames arranged symmetrically with respect to the axis of the main tunnel 1 or the ramp tunnel 2 in which they are located. The two steel frames can support the openings of the corresponding segments at the top and bottom of the main tunnel 1 and the ramp tunnel 2 near the opposite edge.

[0092] Each lateral support 10 is installed at the axis of the corresponding main tunnel 1 or the corresponding ramp tunnel 2.

[0093] In some embodiments, both the main tunnel 1 and the ramp tunnel 2 use steel or steel-concrete composite segments within the connection node range;

[0094] Each segment in which horizontal supports and / or vertical frames are installed during construction has welding capabilities at the contact points with the horizontal supports or vertical frames.

[0095] like Figures 2 to 15 As shown, the present invention also discloses a method for constructing a protective structure at the connection point between two double-layer shield tunnels, comprising the following steps:

[0096] Step 1: Complete the shield tunneling construction and the segment assembly of the main tunnel 1 and the ramp tunnel 2;

[0097] Step 2: Construct lower protection;

[0098] Step 3: Construct upper protection;

[0099] Step 4: After the upper protection is completed, vertical supports 9 and horizontal supports 10 are installed in both the main tunnel 1 and the ramp tunnel 2.

[0100] Each vertical support 9 and each horizontal support 10 is made of steel pipe, and the ends are welded to the corresponding pipe segments by steel plates.

[0101] Step 5: On the side where the boundary of construction area 3 intersects with the extension trajectory of main tunnel 1 or ramp tunnel 2, freeze and reinforce to form end protection 8. At the same time, freeze and reinforce the lower and upper protection again.

[0102] Step 6: Remove the segments and earthwork 14 between the main tunnel 1 or ramp tunnel 2 on the opposite side, and install horizontal steel supports 15 inside the main tunnel 1 or ramp tunnel 2 to support the outer wall of the opposite side of the main tunnel 1 or ramp tunnel 2.

[0103] Step 7: Excavate the soil to the construction elevation of the bottom plate 16 of the connection node; during the excavation process, the longitudinal slope is constructed with a slope ratio of no more than 1:2, and platforms 12 with a width of no less than 2m are set in layers to ensure the longitudinal stability of the slope.

[0104] Step 8: Construct the base plate 16 and the underlying pad; the thickness of the pad is usually 200mm.

[0105] Step 9: After the bottom plate 16 meets the requirements, remove the transverse supports 10 at the axis of the main tunnel 1 and the ramp tunnel 2, and pour the side walls, middle walls and end walls below the middle plate 17 of the connection node, as well as the middle plate 17.

[0106] Step 10: After the middle plate 17 meets the requirements, remove the lowest horizontal support 10 and pour the remaining side walls, middle walls, end walls and top plate 18 of the connection node.

[0107] Step 11: After the top plate 18 meets the requirements, remove the uppermost horizontal steel support 15;

[0108] Step 12: Seal the holes left by each steel shell well 4 in the main tunnel 1 and the ramp tunnel 2;

[0109] Step 13: After filling the gaps with lightweight concrete, the construction is complete.

[0110] like Figure 4 and Figure 5 As shown, in some embodiments, step 2 includes the following steps:

[0111] Step 2.1: Grouting is performed at the bottom of the ramp tunnel 2 to form a pipe curtain reinforcement, and water-stopping reinforcement is performed below the construction area 3 to form a frozen body 7 for lower protection;

[0112] Step 2.2: Cut the steel segments used to install the curved pipe curtain 11, carry out the construction of the curved pipe curtain 11, and receive it in the main tunnel 1 to complete the construction of the lower protection curved pipe curtain 11.

[0113] like Figures 5 to 7 As shown, in some embodiments, step 3 includes the following steps:

[0114] Step 3.1: Perform top grouting reinforcement on the top of the main tunnel 1 and the ramp tunnel 2;

[0115] Step 3.2: In the main tunnel 1 and ramp tunnel 2, support brackets 13 are erected at the positions corresponding to each steel shell well 4, and steel segments for setting the corresponding steel shell well 4 are cut.

[0116] Step 3.3: Vertically lift each steel shell well 4 to form an upwardly convex steel shell well 4 in the main tunnel 1 or ramp tunnel 2; during the lifting process, pay attention to the protection and stability of the surrounding soil to prevent soil and water from flowing into the main tunnel 1 or ramp tunnel 2.

[0117] Step 3.4 After the jacking is completed, the top slab 18 of the main tunnel 1 and the ramp tunnel 2 is sealed, and each steel shell well 4 is reliably connected to the corresponding segment component.

[0118] Step 3.5: In each steel shell well 4, construct a reinforced opening along the extension direction of the corresponding main tunnel 1 or the corresponding ramp tunnel 2, and cut the opening. Then, construct the corresponding steel box culverts 5 using the pipe jacking method to form a two-wall structure.

[0119] Step 3.6: Within the two wall structures, construct the reinforcing hole in the transverse direction of the main tunnel 1 and the ramp tunnel 2 on the opposite side, and cut the hole. Implement all transverse steel pipes 6 in the transverse direction of the tunnel using the pipe jacking method. Connect each pair of transverse steel pipes 6 with male and female joints, and seal each transverse steel pipe 6 with its own grouting pipe for water stop.

[0120] like Figures 8 to 11 In some embodiments, step 6 includes the following steps:

[0121] Step 6.1: Symmetrically demolish the segments near the top on the opposite sides of the main tunnel 1 and the ramp tunnel 2, excavate the soil 14 between the demolished segments, and erect horizontal steel supports 15.

[0122] Step 6.2: Install another transverse support 10 near the bottom of the main tunnel 1 and the ramp tunnel 2, and remove the segments of the main tunnel 1 and the ramp tunnel 2 on the opposite side and excavate the corresponding earthwork 14 to the height close to the axis.

[0123] Step 6.3: Continue to remove the segments on the opposite sides of the main tunnel 1 and the ramp tunnel 2 and excavate the corresponding earthwork 14, and horizontally connect the two transverse supports 10 located at the axis height in the main tunnel 1 and the ramp tunnel 2.

[0124] Step 6.4: Continue to remove the segments on the opposite sides of the main tunnel 1 and the ramp tunnel 2 and excavate the corresponding earthwork 14, and horizontally connect the two transverse supports 10 near the bottom of the main tunnel 1 and the ramp tunnel 2.

[0125] During construction, this invention provides pre-support for the segment structure in both horizontal and vertical directions, with symmetrical support and excavation, which further ensures the stability of the connection nodes, making the invention safer and enabling trenchless construction of the main tunnel 1 and ramp tunnel 2, reducing land use conflicts and environmental impact.

[0126] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A protective structure for the connection point between two double-layer shield tunnels, wherein during the construction of the connection node between the main tunnel (1) and the ramp tunnel (2), the construction area (3) surrounding the connection node is characterized in that, Includes upper protection, lower protection, and end protection; The upper protection is set above the construction area (3) and includes multiple steel shell wells (4) set on the top of the main tunnel (1) and the ramp tunnel (2). A steel box culvert (5) is provided between each two steel shell wells (4) along the tunnel direction, forming a wall structure on the main tunnel (1) and the ramp tunnel (2); Multiple parallel horizontal steel pipes (6) are provided between the two wall structures and are connected side by side. Both ends of each of the transverse steel pipes (6) are respectively connected to the two wall structures; The two wall structures and the soil around each of the transverse steel pipes (6) are reinforced with freezing water to form a frozen body (7). The lower protection is located below the construction area (3) and includes a curved pipe curtain (11) extending along the main tunnel (1) and the ramp tunnel (2), and a frozen body (7) formed by freezing and water-stopping the curved pipe curtain (11). The end protection (8) is set on the side where the boundary of the construction area (3) intersects with the extension trajectory of the main tunnel (1) or the ramp tunnel (2); Each of the aforementioned end protections (8) is a frozen body (7) used to freeze and reinforce the soil at the corresponding location.

2. The protective structure at the connection point between two double-layer shield tunnels as described in claim 1, characterized in that, Each of the steel shell wells (4) extends from the top of the corresponding main tunnel (1) or the corresponding ramp tunnel (2) by vertically jacking it upward within the corresponding main tunnel (1) or the corresponding ramp tunnel (2).

3. The protective structure at the connection point between two double-layer shield tunnels as described in claim 1, characterized in that, Each pair of adjacent transverse steel pipes (6) are connected by a male and female joint.

4. The protective structure at the connection point between two double-layer shield tunnels as described in claim 1, characterized in that, Each of the steel box culverts (5) extends along the corresponding extension trajectory at the corresponding position in the corresponding main tunnel (1) or the corresponding ramp tunnel (2).

5. The protective structure at the connection point between two double-layer shield tunnels as described in claim 1, characterized in that, During the construction of the connection node, vertical supports (9) and horizontal supports (10) are installed in both the main tunnel (1) and the ramp tunnel (2). Each of the vertical supports (9) comprises two steel frames; Each of the two steel frames of the vertical support (9) is arranged symmetrically about the axis of the main tunnel (1) or the ramp tunnel (2) in which it is located. The two steel frames can support the openings of the corresponding segments at the top and bottom of the main tunnel (1) and the ramp tunnel (2) near the opposite edge. Each of the lateral supports (10) is located at the axis of the corresponding main tunnel (1) or the corresponding ramp tunnel (2).

6. The protective structure at the connection point between two double-layer shield tunnels as described in claim 5, characterized in that, Both the main tunnel (1) and the ramp tunnel (2) within the connection node area use steel or steel-concrete composite segments; Each segment of the pipe that is in contact with the horizontal support and / or vertical frame during construction has the conditions for welding.

7. The method for constructing the protective structure at the connection point between two double-layer shield tunnels as described in claim 1, characterized in that, Includes the following steps: Step 1: Complete the shield tunneling construction and the segment assembly of the main tunnel (1) and the ramp tunnel (2); Step 2: Construct the lower protection structure as described above; Step 3: Construct the aforementioned upper protection structure; Step 4: After the upper protection is completed, vertical supports (9) and horizontal supports (10) are installed in both the main tunnel (1) and the ramp tunnel (2). Each of the vertical supports (9) and each of the horizontal supports (10) are made of steel pipes, and their ends are welded to the corresponding pipe segments by steel plates. Step 5: Freeze and reinforce the side of the boundary of the construction area (3) where it intersects with the extension trajectory of the main tunnel (1) or the ramp tunnel (2) to form the end protection (8), and at the same time freeze and reinforce the lower protection and the upper protection again. Step 6: Remove the segments and earthwork (14) between the main tunnel (1) or the ramp tunnel (2) on the opposite side, and install horizontal steel supports (15) in the main tunnel (1) or the ramp tunnel (2) to support the outer wall of the opposite side of the main tunnel (1) or the ramp tunnel (2). Step 6.1: Symmetrically dismantle the segments of the main tunnel (1) and the ramp tunnel (2) on the opposite side near the top, excavate the soil (14) between the dismantled segments, and erect horizontal steel supports (15). Step 6.2: Install another transverse support (10) near the bottom of the main tunnel (1) and the ramp tunnel (2), and remove the segments of the main tunnel (1) and the ramp tunnel (2) on the opposite side and excavate the corresponding earthwork (14) to near the axis height. Step 6.3: Continue to remove the segments of the main tunnel (1) and the ramp tunnel (2) on the opposite side and excavate the corresponding earthwork (14), and connect the two transverse supports (10) located at the axial height in the main tunnel (1) and the ramp tunnel (2) horizontally. Step 6.4: Continue to remove the segments of the main tunnel (1) and the ramp tunnel (2) on the opposite side and excavate the corresponding earthwork (14), and connect the two transverse supports (10) near the bottom of the main tunnel (1) and the ramp tunnel (2) horizontally. Step 7: Excavate the soil to the construction elevation of the bottom plate (16) of the connection node; during the excavation process, the longitudinal slope is constructed with a slope ratio of no more than 1:2, and platforms (12) with a width of no less than 2m are set in layers to ensure the longitudinal stability of the slope. Step 8: Construct the base plate (16) and the underlying cushion layer; Step 9: After the base plate (16) meets the requirements, remove the transverse supports (10) at the axis of the main tunnel (1) and the ramp tunnel (2), and pour the side walls, middle walls and end walls below the middle plate (17) of the connecting node, as well as the middle plate (17). Step 10: After the middle plate (17) meets the requirements, remove the lowest horizontal support (10) and pour the remaining side wall, middle wall, end wall and top plate (18) of the connection node. Step 11: After the top plate (18) meets the requirements, remove the uppermost horizontal steel support (15). Step 12: Seal the holes left by each of the steel shell wells (4) in the main tunnel (1) and the ramp tunnel (2); Step 13: After filling the gaps with lightweight concrete, the construction is complete.

8. The method for constructing the protective structure at the connection point between two double-layer shield tunnels as described in claim 7, characterized in that, Step 2 includes the following steps: Step 2.1: Grouting is performed at the bottom of the ramp tunnel (2) to form a pipe curtain reinforcement, and water-stopping reinforcement is performed below the construction area (3) to form the lower protective frozen body (7). Step 2.2: Cut the steel pipe segments used to set the curved pipe curtain (11), carry out the construction of the curved pipe curtain (11), and receive it in the main tunnel (1) to complete the construction of the lower protection curved pipe curtain (11).

9. The method for constructing the protective structure at the connection point between two double-layer shield tunnels as described in claim 7, characterized in that, Step 3 includes the following steps: Step 3.1: Perform top grouting reinforcement on the top of the main tunnel (1) and the ramp tunnel (2); Step 3.2: In the main tunnel (1) and the ramp tunnel (2), a support (13) is erected at the position corresponding to each of the steel shell wells (4), and the steel segments for setting the corresponding steel shell wells (4) are cut. Step 3.3: Each of the steel shell wells (4) is vertically jacked up to form an upwardly protruding steel shell well (4) in the main tunnel (1) or the ramp tunnel (2); during the jacking process, attention is paid to the protection and stability of the surrounding soil to prevent soil and water from flowing into the main tunnel (1) or the ramp tunnel (2). Step 3.4 After the jacking is completed, the top plate (18) of the main tunnel (1) and the ramp tunnel (2) is sealed, and each of the steel shell wells (4) is reliably connected to the corresponding segment; Step 3.5: In each of the steel shell wells (4), a hole reinforcement body is constructed along the extension direction of the corresponding main tunnel (1) or the corresponding ramp tunnel (2), and the hole is cut. Then, the corresponding steel box culvert (5) is constructed by pipe jacking method to form two wall structures. Step 3.6: In the two wall structures, a hole is drilled horizontally along the direction of the main tunnel (1) and the ramp tunnel (2) facing each other, and the hole is cut. All the horizontal steel pipes (6) are installed horizontally along the tunnel using the pipe jacking method. Each pair of horizontal steel pipes (6) is connected by a male and female joint, and each horizontal steel pipe (6) is sealed with water by its own grouting pipe.

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