A method for expanding a multi-arch tunnel in situ

Abstract

The application relates to a construction method for in-situ expansion of a multi-arch tunnel, and belongs to the technical field of tunnel construction. The method comprises the following steps: according to the section contour of an existing multi-arch tunnel, a section contour of an in-situ expansion tunnel is designed; a part of the existing tunnel on one side exceeding the section contour of the in-situ expansion tunnel is treated by grouting backfilling and reinforcement; a part of rock mass on the other side of the arch top is excavated, and a part of the lining structure of the existing tunnel on the side is removed; a part of rock mass of the arch part is excavated, and a part of the lining structure of the existing tunnel on one side is removed to make the primary support closed into a ring; the secondary lining, the arch wall and other structures of the remaining part of the existing tunnel are removed; the surface and the inverted arch structure of the existing tunnel are removed by blasting operation, the inverted arch primary support is constructed, the secondary lining is constructed, and other auxiliary structures are constructed. The existing tunnel is utilized, and the excavation area of the expansion project is reduced; meanwhile, the spoil produced by excavation and the concrete, steel frame and other materials of the existing tunnel which are replaced are reused, and the construction concept of green construction is embodied.

Description

Technical Field

[0001] This invention belongs to the field of tunnel construction technology, and specifically relates to a method for in-situ expansion of a continuous arch tunnel. Background Technology

[0002] As a crucial component of highway engineering, highway tunnel construction has achieved remarkable results with the rapid pace of economic and social development and urbanization. As of 2021, there were 23,268 highway tunnels in operation nationwide, totaling 246.989 million meters in length. However, some major economic corridor tunnels were built earlier, and their capacity is no longer sufficient to meet the ever-increasing traffic demands. Therefore, upgrading and expanding existing highway tunnels to improve their capacity is imperative.

[0003] Arch tunnels, a common type of highway tunnel, are widely used in the construction of existing highway tunnels. Due to insufficient capacity of existing arch tunnels, reconstruction and expansion are often necessary. Under practical constraints, in-situ expansion of arch tunnels is sometimes required. However, current research on in-situ expansion of arch tunnels is insufficient to effectively guide construction. Therefore, a construction method for in-situ expansion of arch tunnels is urgently needed to ensure its safe and rapid implementation.

[0004] The double-sided-wall pilot tunnel method is a commonly used excavation method for large-section tunnel construction. By adopting a sectional excavation method, increasing temporary support structures, and shortening the excavation advance and bench length, the safety of large-section tunnel excavation is ensured. The existing chambers of a continuous arch tunnel can be treated as excavated and supported pilot tunnels, and the in-situ expansion construction of continuous arch tunnels can draw on the concept of the double-sided-wall pilot tunnel method. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for in-situ expansion of a continuous arch tunnel, which utilizes the existing tunnel, reduces the excavation area of ​​the expansion project, and ensures construction safety; at the same time, it reuses the excavated soil and the replaced existing tunnel concrete, steel frame and other materials, reflecting the construction concept of green construction.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for in-situ expansion of a multi-arch tunnel includes the following steps:

[0008] (1) Based on the existing cross-sectional profile of the continuous arch tunnel, design the cross-sectional profile of the in-situ expansion tunnel;

[0009] (2) Based on the designed cross-sectional profile of the in-situ expanded tunnel, the portion of the existing tunnel on one side that exceeds the designed cross-sectional profile of the in-situ expanded tunnel shall be reinforced by grouting and backfilling.

[0010] (3) According to the design of the in-situ expanded tunnel cross section outline, excavate part of the rock mass on the other side of the arch and remove part of the existing tunnel lining structure on that side, and construct initial support and temporary support on the side wall of the expanded tunnel.

[0011] (4) According to the design of the in-situ expanded tunnel cross section outline, excavate the arch rock mass and remove the existing tunnel lining structure on one side in step (2). Apply initial support to the side wall and arch of the expanded tunnel to close the initial support into a ring.

[0012] (5) Demolish the remaining secondary lining and arch wall structure of the existing tunnel;

[0013] (6) The existing tunnel pavement and invert structure were demolished by blasting, and the invert section of the tunnel expansion was excavated at the same time, and the initial support of the invert was constructed.

[0014] (7) Construct secondary lining and other ancillary structures.

[0015] Optionally, in step (2), when grouting and backfilling the portion of the existing tunnel that extends beyond the designed in-situ expansion tunnel profile on one side, the grouting should be carried out along the following path: Figure 3 At the location of arc AB, boreholes are drilled in the existing tunnel lining structure and anchor bolts are installed. During anchor bolt installation, a portion of the bolt is driven into the surrounding rock, leaving a certain length for contact with the grouting backfill, thus anchoring the surrounding rock, existing structure, and grouting backfill into a single unit. The length of the anchor bolt driven into the surrounding rock is selected with reference to the design length of the existing tunnel anchor bolts, ensuring that the anchoring length is greater than the radius of the loosened ring. The anchor bolt spacing is selected with reference to the design spacing of the existing tunnel anchor bolts, and the installed anchor bolts are arranged alternately with the existing anchor bolt positions. When grouting backfills the portion of the existing tunnel that extends beyond the designed original tunnel cross-section, this should be done after the anchor bolt installation is completed. The formwork erection work was carried out. Three formwork panels were used for the erection. Formwork panel 1 was made of steel and had an arc AC that matched the profile of the expansion design section. Grouting holes and bolt holes were reserved. Panels 2 and 3 were made of wood and their shapes matched the fan-shaped area ABC that matched the portion of the existing tunnel on this side that extended beyond the design profile of the expansion tunnel section. Bolt holes matching those of formwork panel 1 were also reserved. When erecting the formwork, formwork panel 1 was erected first, followed by formwork panels 2 and 3. The bolt holes on formwork panels 2 and 3 were aligned with those on formwork panel 1. Finally, bolts were used to connect formwork panels 1, 2, and 3 into a whole.

[0016] Optionally, in step (2), when grouting backfills the portion of the existing tunnel that exceeds the designed in-situ expansion tunnel profile, after the formwork erection is completed, grout-soil mixture is injected into the mold through the grouting holes reserved on the formwork 1. The excavated soil from the arch rock mass in the subsequent working conditions is used as the material for backfilling the left tunnel. At the same time, when selecting the soil particle size distribution and grout parameters, the surrounding rock grade of the stratum where the tunnel is located is referenced. Through experimental debugging, the stratum resistance coefficient and elastic modulus parameters of the stratum backfilled by the grout-soil mixture are the same as those of the stratum where the tunnel is located.

[0017] Optionally, in step (3), before excavating the rock mass on the other side of the arch, a pre-grouting method is used to reinforce the surrounding rock mass to be excavated on that side of the arch. The reinforcement range is as follows: Figure 6 As shown in the polygon DEFGHIJ, the grouting reinforcement is mainly longitudinal grouting reinforcement, supplemented by radial grouting using the existing cavern on this side. The grouting parameters should be determined through numerical analysis and model experiments to ensure the construction safety of the DEF excavation of the rock mass on the right side of the arch.

[0018] When excavating the rock mass on the other side of the arch, the fan-shaped DEF section of rock mass is excavated by blasting. After the muck removal is completed, temporary support is installed at point D. The temporary support uses a steel arch frame, which is installed along DE. By adjusting the position of the steel arch frame, it can be supported between the surrounding rock of the excavation face and the existing tunnel lining. The muck generated by the blasting is collected and used for backfilling the existing tunnel.

[0019] When dismantling the existing tunnel lining on the right side, after the temporary support at DE is erected, non-blasting construction methods should be adopted to reduce the disturbance to the surrounding rock during construction. These methods include wire sawing, hydraulic fracturing, or static expansion agent crushing. The existing tunnel lining in the GFK section of the arc should be dismantled in one dismantling operation, with the dismantling distance of the existing lining in the longitudinal direction of the tunnel being consistent with the excavation advance of the arch. The dismantled existing tunnel lining should be collected for reuse.

[0020] Optionally, in step (3), when constructing initial and temporary support for the sidewall of the expanded tunnel, after the existing tunnel lining on the right side has been removed, the support is first constructed along the... Figure 7 The steel frame for the right sidewall of the tunnel expansion is erected along the arc GFE, and anchor bolts are installed. The temporary support steel arch at DE is adjusted, and the E end of the temporary support steel frame is welded to the steel frame of the right sidewall. Then, the D end of the temporary support steel frame is still attached to the existing lining structure. After the temporary support is completed, shotcrete is applied along the arc GFE. After the initial and temporary support of the right sidewall of the tunnel expansion is completed, the next cycle of excavation, removal of existing support, and application of initial and temporary support will begin.

[0021] Optionally, in step (4), before excavating the arch rock mass, in order to reduce the disturbance to the surrounding rock caused by construction, non-blasting construction methods are adopted, such as wire saw cutting, hydraulic fracturing, or static expansion agent crushing operations, to remove the rock. Figure 8 The existing tunnel lining structure of the arc AL section is shown. During the demolition of the lining structure, the steel arch frame erected in section AL will be retained, and only the existing concrete structure constructed in section AL will be demolished.

[0022] Optionally, in step (4), before excavating the arch rock mass, a pre-grouting method is used to reinforce the periphery of the arch rock mass to be excavated, and the reinforcement range is as follows: Figure 8 As shown in the quadrilateral INAM, grouting reinforcement is mainly longitudinal grouting reinforcement. Grouting parameters should be determined through numerical analysis, model experiments and other methods to ensure the construction safety of the AMEDOL arch rock mass excavation. After the pre-reinforcement is completed, according to the design cross-sectional outline of the expanded tunnel, the AMEDOL arch rock mass of the expanded tunnel will be excavated in one blasting operation. At the same time, the blasting debris generated in the arch will be collected for backfilling of the existing tunnel.

[0023] Optionally, in step (4), after the arch rock mass is blasted and excavated, the tunnel and the top tunnel along... Figure 9 In the middle arc section, CAE was used to lay out steel frames and apply shotcrete to quickly close the initial support of the tunnel sidewalls and arch into a ring; and the existing steel frames that were dismantled in the arc AL section were used as temporary support to ensure construction safety.

[0024] Optionally, in step (5), when dismantling the remaining lining, arch walls, and other structures of the existing tunnel, a wire saw cutting method is used for cutting and dismantling. Figure 10 The remaining steel frame of section AL, the remaining lining structure of section OK, the temporary support of section DE, and the intermediate arch wall structure.

[0025] Optionally, in step (6), the existing tunnel pavement structure, invert arch structure and the excavation part of the invert arch of the expanded tunnel are blasted and excavated in one go; vertical holes are drilled and explosives are loaded into the existing tunnel pavement structure to ensure that the existing tunnel pavement structure, invert arch structure and the excavation part of the invert arch of the expanded tunnel can be blasted and excavated smoothly; after the excavation and slag removal are completed, the initial support of the invert arch is promptly implemented.

[0026] The beneficial effects of this invention are as follows:

[0027] (1) An innovative construction method for in-situ expansion of a continuous arch tunnel is proposed, which fills the technical gap in in-situ expansion of continuous arch tunnels and can effectively ensure the smooth progress of the in-situ expansion project of continuous arch tunnels.

[0028] (2) Drawing on the construction concept of the double-sided wall pilot tunnel method, the existing tunnel after temporary support was constructed was used as the two pilot tunnels that had been completed, which reduced the excavation area during the expansion construction and ensured construction safety.

[0029] (3) When demolishing the existing tunnel lining structure, a non-blasting construction method was adopted, which reduced the construction disturbance;

[0030] (4) It makes full use of the excavated slag and the existing lining structure that was demolished, which reflects the concept of green construction.

[0031] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0032] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0033] Figure 1 Construction Flowchart of an In-situ Expansion Method for a Series-Arch Tunnel

[0034] Figure 2 Schematic diagram of the cross-sectional outline of the existing arch tunnel and the in-situ expanded tunnel

[0035] Figure 3 Schematic diagram of grouting and backfilling of the existing tunnel on the left

[0036] Figure 4 Template 1 Dimensional Construction Diagram

[0037] Figure 5 Template 2 and 3 Dimensional Construction Diagram

[0038] Figure 6 Schematic diagram of the excavation area on the right side of the arch and the removal area of ​​part of the secondary lining.

[0039] Figure 7 Schematic diagram of initial support and temporary support construction on the right side of the expanded tunnel

[0040] Figure 8 Schematic diagram of the arch excavation and the removal range of the secondary lining of the left tunnel.

[0041] Figure 9 Schematic diagram of initial support construction for tunnel expansion

[0042] Figure 10 Schematic diagram of the demolition of the arch wall and part of the lining structure

[0043] Figure 11 Schematic diagram of the bottom excavation of the expanded tunnel

[0044] Wherein: 1—Existing arch tunnel cross-sectional outline; 2—Designed cross-sectional outline of the in-situ expanded tunnel; 3—Existing left tunnel grout-soil backfill area; 4—Existing anchor bolts in the left tunnel; 5—Anchor bolts installed during backfilling of the left tunnel; 6—Curved edge of mold 1, for reference. Figure 3 The curvature design of the middle arc AC segment allows mold 1 to fit snugly against the arc AC segment when erected; 7—bolt holes pre-drilled on mold 1; 8—grouting holes pre-drilled on mold 1; 9—curved edges of molds 2 and 3, for reference. Figure 3 The curvature design of the AB segment of the central arc allows molds 2 and 3 to fit snugly against the AB segment during erection; 10—The curved edges of molds 2 and 3 are designed with reference to the curved edge 6 of mold 1, ensuring a good fit between molds 2 and 3 and mold 1, facilitating mold sealing operations; 11—The bolt holes pre-drilled on molds 2 and 3 are designed with reference to the bolt holes 7 pre-drilled on mold 1; 12—The grouting reinforcement design range around the rock mass to be excavated on the right side of the arch; 13—Temporary support to be installed after excavation of the rock mass on the right side of the arch; 14—Design of the rock mass to be excavated on the right side of the arch. Scope; 15—Existing right tunnel lining structure to be demolished; 16—Initial support for the right sidewall of the expanded tunnel; 17—Temporary support; 18—Existing left tunnel lining structure to be demolished; 19—Design scope of grouting reinforcement around the rock mass to be excavated in the arch; 20—Excavation scope of the arch of the expanded tunnel; 21—Initial support for the left sidewall and arch of the expanded tunnel; 22—Existing steel frame structure to be retained in the left tunnel; 23—Lining structure to be demolished in the right tunnel; 24—Arch wall structure to be demolished; 25—Excavation scope of the arch of the expanded tunnel. Detailed Implementation

[0045] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0046] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0047] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0048] Please see Figures 1 to 11 This is a method for in-situ expansion of a multi-arch tunnel, characterized by the following steps:

[0049] (1) Based on the existing cross-sectional profile of the continuous arch tunnel, design the cross-sectional profile of the in-situ expansion tunnel;

[0050] (2) Based on the cross-sectional profile of the tunnel after the in-situ expansion designed, the portion of the existing tunnel on the left side that exceeds the cross-sectional profile of the in-situ expansion designed shall be reinforced by grouting and backfilling.

[0051] (3) According to the design of the cross-section after the in-situ expansion, excavate part of the rock mass on the right side of the arch and remove part of the existing tunnel lining structure on the right side. Then, construct initial support and temporary support on the right sidewall of the expanded tunnel.

[0052] (4) According to the design of the cross-section after the in-situ expansion, excavate the arch rock mass and remove the existing tunnel lining structure on the left side. Apply initial support to the left sidewall and arch of the expanded tunnel so that the initial support is closed into a ring.

[0053] (5) Demolish the remaining secondary lining, arch walls and other structures of the existing tunnel;

[0054] (6) The existing tunnel pavement and invert structure were demolished by blasting, and the invert section of the tunnel expansion was excavated at the same time, and the initial support of the invert was constructed.

[0055] (7) Construct secondary lining and other ancillary structures.

[0056] Furthermore, a method for in-situ expansion of a continuous arch tunnel, the specific construction steps of which are as follows: Figure 1 As shown;

[0057] Furthermore, in step (1), the in-situ expansion tunnel cross-sectional outline design drawing is as follows: Figure 2 As shown;

[0058] Furthermore, in step (2), when grouting and backfilling the portion of the existing tunnel on the left side that exceeds the designed in-situ expansion tunnel cross-section outline, such as... Figure 3 As shown, holes are drilled and anchor bolts are installed along arc AB in the existing tunnel lining structure. During installation, a portion of the anchor bolt is driven into the surrounding rock, leaving a certain length for contact with the grouting backfill, thus anchoring the surrounding rock, existing structure, and grouting backfill into a single unit. The length of the anchor bolt driven into the surrounding rock is selected with reference to the design length of the existing tunnel anchor bolts, ensuring that the length driven into the surrounding rock is greater than the radius of the loosened zone. The anchor bolt spacing is selected with reference to the design spacing of the existing tunnel anchor bolts, and the installed anchor bolts are arranged alternately with the existing anchor bolt positions.

[0059] Furthermore, in step (2), when grouting and backfilling the portion of the existing tunnel on the left side that exceeds the designed in-situ expansion tunnel cross-section outline, the formwork erection work is carried out after the anchor bolts are installed. Three templates are used for formwork erection, of which template 1 is made of steel and has an arc that matches the design cross-section outline of the expansion (e.g., ...). Figure 3 The middle arc section (AC) has a certain thickness, and grouting holes and bolt holes are reserved, such as... Figure 4 As shown; templates 2 and 3 are made of wood, and their shapes match the cross-sectional outline of the existing tunnel on the left that extends beyond the designed original location (e.g., Figure 3 In the middle (the fan-shaped area enclosed by ABC), bolt holes matching template 1 are reserved, such as... Figure 5 As shown; when erecting the mold, first erect template 1, then erect templates 2 and 3, and make the bolt holes on templates 2 and 3 correspond to the positions of template 1. Finally, use bolts to connect templates 1, 2 and 3 into a whole.

[0060] Furthermore, in step (2), when grouting and backfilling the portion of the existing tunnel on the left side that exceeds the designed in-situ expansion tunnel profile, after the formwork erection is completed, grout-soil mixture is injected into the mold through the grouting holes reserved on the formwork 1. The excavated soil obtained from the arch rock mass excavation in subsequent working conditions can be used as the material for backfilling the left tunnel. At the same time, when selecting soil particle size distribution and grout parameters, the surrounding rock grade of the stratum where the tunnel is located should be referenced. Through experimental debugging, the stratum backfilled with grout-soil mixture is made to have basically the same stratum resistance coefficient, elastic modulus and other parameters as the stratum where the tunnel is located.

[0061] Furthermore, in step (2), when grouting and backfilling the portion of the existing tunnel on the left side that exceeds the cross-sectional outline of the designed in-situ expansion tunnel, the longitudinal length of each grouting and backfilling operation is 5m due to the limited bearing capacity of the mold and in order to ensure the quality of grouting and backfilling. The mold can be removed and the grouting and backfilling operation of the next section can only be carried out after the strength of the backfill soil has stabilized.

[0062] Furthermore, in step (3), as Figure 6As shown, before excavating the rock mass on the right side of the arch, the rock mass to be excavated on the right side of the arch is reinforced by advance grouting. The reinforcement range is shown as polygon DEFGHIJ. The grouting reinforcement is mainly longitudinal grouting reinforcement, supplemented by radial grouting using the existing cavern on the right side. The grouting parameters should be determined by numerical analysis, model experiments and other methods to ensure the construction safety of the excavation of the rock mass DEF on the right side of the arch.

[0063] Furthermore, in step (3), when excavating the rock mass on the right side of the arch, such as Figure 6 As shown, after excavating the fan-shaped DEF section of rock mass using blasting operations and completing the muck removal, temporary support was constructed at point D. The temporary support consisted of steel arch frames, which were installed along DE. The position of the steel arch frames was adjusted to ensure they supported the surrounding rock at the excavation face and the existing tunnel lining. To ensure construction safety, the excavation advance on the right side of the arch was designed to be 2 meters per pass. The blasting debris was collected and used for backfilling the existing left-side tunnel.

[0064] Furthermore, in step (3), when removing the existing tunnel lining structure on the right side, such as Figure 6 As shown, after the temporary support at DE is erected, in order to reduce the disturbance to the surrounding rock during construction, non-blasting construction methods will be adopted, such as wire saw cutting, hydraulic fracturing or static expansion agent crushing, to remove the existing tunnel lining structure of the arc GFK section. In one demolition operation, the step distance of the existing lining in the longitudinal direction of the tunnel should be consistent with the excavation advance on the right side of the arch, i.e., 2m. The removed existing tunnel lining structure will be collected for secondary use.

[0065] Furthermore, in step (3), when constructing initial and temporary support on the right sidewall of the expanded tunnel, such as Figure 7 As shown, after the existing tunnel lining on the right side is removed, the steel frame for the right sidewall of the expanded tunnel is first erected along the arc GFE, and the anchor bolts are installed; the temporary support steel arch frame at DE is adjusted, and the E end of the temporary support steel frame is welded to the steel frame of the right sidewall. Then the D end of the temporary support steel frame is still attached to the existing lining structure; after the temporary support is completed, shotcrete is applied along the arc GFE.

[0066] Furthermore, in step (3), after the initial support and temporary support of the right sidewall of the expanded tunnel are completed, the next cycle of excavation-removal of existing support-construction of initial support and temporary support will be carried out.

[0067] Furthermore, in step (4), as Figure 8As shown, to minimize disturbance to the surrounding rock before excavating the arch section, non-blasting construction methods were employed, such as wire sawing, hydraulic fracturing, or static expansion agent breaking, to demolish the existing tunnel lining structure of the AL section. During the lining demolition, the steel arch frame erected in the AL section was retained, and only the existing concrete structure of the AL section was removed. In each demolition operation, the step distance for removing the existing lining in the longitudinal direction of the tunnel was 2m; the demolished existing tunnel lining structure was collected for reuse.

[0068] Furthermore, in step (4), as Figure 8 As shown, before excavating the arch rock mass, the surrounding rock mass to be excavated is reinforced by pre-grouting. The reinforcement range is shown in quadrilateral INAM. The grouting reinforcement is mainly longitudinal grouting reinforcement. The grouting parameters should be determined by numerical analysis, model experiments and other methods to ensure the construction safety of the AMEDOL arch rock mass excavation.

[0069] Furthermore, in step (4), as Figure 8 As shown, after the pre-reinforcement is completed, according to the design cross-sectional outline of the expanded tunnel, the arch rock mass of the expanded tunnel will be excavated by blasting in one go, with an excavation advance of 2m; at the same time, the blasting debris generated by the arch blasting will be collected for backfilling of the existing left-side tunnel.

[0070] Furthermore, in step (4), as Figure 9 As shown, after the blasting and excavation of the arch rock mass is completed, steel frames are laid out along the CAE of the left side chamber and the top chamber, and shotcrete is applied to quickly close the sidewalls and the initial support of the arch of the expanded tunnel into a ring; and the existing steel frame that was dismantled in the AL section of the arc is used as temporary support to ensure construction safety.

[0071] Furthermore, in step (5), as Figure 10 As shown, when dismantling the remaining lining, arch walls, and other structures of the existing tunnel, wire saw cutting should be used as much as possible to cut the remaining steel frame of section AL, the remaining lining structure of section OK, the temporary support of section DE, and the intermediate arch wall structure. This allows the structures to be dismantled completely and quickly, effectively improving construction efficiency and the utilization rate of the dismantled structures. To ensure construction safety, the remaining existing lining and arch walls within a 1m longitudinal range are removed in a single dismantling operation; the steel frame and concrete obtained from the dismantling are recycled.

[0072] Furthermore, in step (6), as Figure 11As shown, in order to improve construction efficiency, the existing tunnel pavement structure, invert arch structure, and the excavation part of the invert arch of the expanded tunnel will be blasted and excavated in one go. In order to improve blasting efficiency, vertical holes will be drilled and explosives will be loaded into the existing tunnel pavement structure, and the amount of explosives will be appropriately increased to ensure that the existing tunnel pavement structure, invert arch structure, and the excavation part of the invert arch of the expanded tunnel can be blasted and excavated smoothly. After the excavation and muck removal are completed, the initial support of the invert arch will be constructed in a timely manner.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for in-situ expansion of a twin-arch tunnel, characterized in that, Includes the following steps: (1) Based on the existing cross-sectional profile of the continuous arch tunnel, design the cross-sectional profile of the in-situ expansion tunnel; (2) Based on the designed cross-sectional profile of the in-situ expanded tunnel, the portion of the existing tunnel on one side that exceeds the designed cross-sectional profile of the in-situ expanded tunnel shall be reinforced by grouting and backfilling. (3) According to the design of the in-situ expanded tunnel cross section outline, excavate part of the rock mass on the other side of the arch and remove part of the existing tunnel lining structure on that side, and construct initial support and temporary support on the side wall of the expanded tunnel. (4) According to the design of the in-situ expanded tunnel cross section outline, excavate the arch rock mass and remove the existing tunnel lining structure on one side in step (2). Apply initial support to the side wall and arch of the expanded tunnel to close the initial support into a ring. (5) Demolish the remaining secondary lining and arch wall structure of the existing tunnel; (6) The existing tunnel pavement and invert structure were demolished by blasting, and the invert section of the tunnel expansion was excavated at the same time, and the initial support of the invert was constructed. (7) Construct secondary lining and other ancillary structures.

2. The in-situ expansion construction method for a series-arch tunnel according to claim 1, characterized in that: In step (2), when grouting and backfilling the portion of the existing tunnel that extends beyond the designed in-situ tunnel section on one side, holes are drilled and anchor bolts are installed on the existing tunnel lining structure along the arc AB position shown in Figure 3. When installing the anchor bolts, a portion of the bolts is driven into the surrounding rock, leaving a certain length for contact with the grouting backfill, thus anchoring the surrounding rock, existing structure, and grouting backfill into a single unit. The length of the anchor bolt driven into the surrounding rock is selected with reference to the design length of the existing tunnel anchor bolts, ensuring that the length driven into the surrounding rock is greater than the radius of the loosening zone. The anchor bolt spacing is selected with reference to the design anchor bolt spacing of the existing tunnel, and the anchor bolt installation is arranged alternately with the existing anchor bolt positions. When the portion of the existing tunnel that extends beyond the designed in-situ tunnel section on this side is grouting and backfilling, holes are drilled and anchor bolts are installed along the arc AB position shown in Figure 3. When grouting and backfilling the contour section, the formwork erection work is carried out after the anchor bolts are installed. Three templates are used for the formwork erection. Template 1 is made of steel and has an arc AC that matches the contour of the expansion design section. Grouting holes and bolt holes are reserved. Templates 2 and 3 are made of wood and their shape matches the fan-shaped area ABC that matches the part of the existing tunnel on this side that extends beyond the design in-situ expansion tunnel section. Bolt holes that match those of Template 1 are reserved. When erecting the formwork, Template 1 is erected first, followed by Templates 2 and 3. The bolt holes on Templates 2 and 3 are aligned with those on Template 1. Finally, templates 1, 2, and 3 are connected into a whole using bolts.

3. The in-situ expansion construction method for a series-arch tunnel according to claim 2, characterized in that: In step (2), when grouting backfills the portion of the existing tunnel that exceeds the cross-sectional outline of the tunnel expansion project on the same side, after the formwork erection is completed, grout-soil mixture is injected into the mold through the grouting hole reserved on the formwork. The excavated soil from the arch rock mass in the subsequent working conditions is used as the material for backfilling the left tunnel. At the same time, the soil particle size distribution and grout parameters are selected with reference to the surrounding rock grade of the stratum where the tunnel is located. Through experimental debugging, the stratum resistance coefficient and elastic modulus parameters of the stratum backfilled by the grout-soil mixture are the same as those of the stratum where the tunnel is located.

4. The in-situ expansion construction method for a series-arch tunnel according to claim 1, characterized in that: In step (3), before excavating the rock mass on the other side of the arch, the rock mass to be excavated on the arch side is reinforced by advance grouting. The reinforcement range is shown as polygon DEFGHIJ in Figure 6. The grouting reinforcement is mainly longitudinal grouting reinforcement, supplemented by radial grouting using the existing cavern on the side. The grouting parameters should be determined by numerical analysis and model experiment to ensure the construction safety of the excavation of the rock mass DEF on the right side of the arch. When excavating the rock mass on the other side of the arch, the fan-shaped DEF section of rock mass is excavated by blasting. After the muck removal is completed, temporary support is installed at point D. The temporary support uses a steel arch frame, which is installed along DE. By adjusting the position of the steel arch frame, it can be supported between the surrounding rock of the excavation face and the existing tunnel lining. The muck generated by the blasting is collected and used for backfilling the existing tunnel. When dismantling the existing tunnel lining on the right side, after the temporary support at DE is erected, a non-blasting construction method is adopted to reduce the disturbance to the surrounding rock during construction. The existing tunnel lining of the arc GFK section is dismantled. In one dismantling operation, the step distance of the existing lining in the longitudinal direction of the tunnel should be consistent with the excavation advance of the arch. The dismantled existing tunnel lining is collected for secondary use.

5. The in-situ expansion construction method for a twin-arch tunnel according to claim 4, characterized in that: In step (3), when the initial and temporary support of the sidewall of the expanded tunnel is being constructed, after the existing tunnel lining on the right side is removed, the steel frame of the right sidewall of the expanded tunnel is first erected along the arc GFE shown in Figure 7, and the locking anchor rods are installed; the temporary support steel arch frame at DE is adjusted, and the E end of the temporary support steel frame is welded to the steel frame of the right sidewall, and then the D end of the temporary support steel frame is still attached to the existing lining structure; after the temporary support is completed, sprayed concrete is applied along the arc GFE; after the initial and temporary support of the right sidewall of the expanded tunnel is completed, the next cycle of excavation-removal of existing support-construction of initial and temporary support is carried out.

6. The in-situ expansion construction method for a twin-arch tunnel according to claim 1, characterized in that: In step (4), before excavating the arch rock mass, in order to reduce the disturbance of the surrounding rock to the construction, a non-blasting construction method is adopted to demolish the existing tunnel lining structure of the arc AL section as shown in Figure 8; during the lining structure demolition operation, the steel arch frame erected in the AL section is retained, and only the existing concrete structure constructed in the AL section is demolished.

7. The in-situ expansion construction method for a series-arch tunnel according to claim 6, characterized in that: In step (4), before excavating the arch rock mass, the arch rock mass to be excavated is reinforced by pre-grouting. The reinforcement range is shown as quadrilateral INAM in Figure 8. The grouting reinforcement is mainly longitudinal grouting reinforcement. The grouting parameters should be determined by numerical analysis and model experiment to ensure the construction safety of the arch rock mass AMEDOL excavation. After the pre-reinforcement is completed, the arch rock mass AMEDOL of the expanded tunnel is excavated by blasting in one go according to the design cross-section outline of the expanded tunnel. At the same time, the slag generated by the arch blasting construction is collected for backfilling of the existing tunnel.

8. The in-situ expansion construction method for a twin-arch tunnel according to claim 1, characterized in that: In step (4), after the blasting and excavation of the arch rock mass is completed, steel frames are laid out along the arc CAE in Figure 9 for the cavern and the top cavern, and shotcrete is applied to quickly close the sidewalls and the initial support of the arch of the expanded tunnel into a ring; and the existing steel frames that have not been removed in the arc AL section are used as temporary support to ensure construction safety.

9. The in-situ expansion construction method for a twin-arch tunnel according to claim 1, characterized in that: In step (5), when dismantling the remaining lining and arch wall structure of the existing tunnel, the remaining steel frame of section AL, the remaining lining structure of section OK, the temporary support of section DE and the intermediate arch wall structure in Figure 10 are cut and dismantled by wire saw cutting method.

10. The in-situ expansion construction method for a twin-arch tunnel according to claim 1, characterized in that: In step (6), the existing tunnel pavement structure, invert arch structure and the excavation part of the invert arch of the expanded tunnel are blasted and excavated in one go; vertical holes are drilled and explosives are loaded into the existing tunnel pavement structure to ensure that the existing tunnel pavement structure, invert arch structure and the excavation part of the invert arch of the expanded tunnel can be blasted and excavated smoothly; after the excavation and slag removal are completed, the initial support of the invert arch is promptly implemented.

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