A double-hole tunnel expanded from a single-hole tunnel and a construction method thereof

Abstract

The application discloses a double-hole tunnel expanded from a single-hole tunnel and a construction method thereof. The double-hole tunnel expanded from the single-hole tunnel comprises an upper existing tunnel, a locking foot device and a lower newly-built tunnel. The upper existing tunnel comprises a first inverted arch, a maintenance passage, a hole wall arranged from inside to outside, a secondary lining structure and an initial support structure of the upper existing tunnel. The locking foot device comprises inclined piles, waist beams and temporary supports. The lower newly-built tunnel comprises lateral supports, side walls, a middle partition plate and a second inverted arch. The inclined piles are arranged in multiple rows in a vertical direction along one side of the upper existing tunnel. The angle of each row of the inclined piles along the one side of the upper existing tunnel is 30-60 degrees. The total width of the lower newly-built tunnel is smaller than that of the upper existing tunnel. The maintenance passage of the upper existing tunnel is adjusted to be a collision-preventing wall of the lower newly-built tunnel, so that the width of a vehicle lane of the lower newly-built tunnel is ensured, and the traffic capacity of the upper existing tunnel is increased by 0.6-1.0 times without increasing the land.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction technology, and in particular to a method for constructing a twin-tunnel expansion from a single-tunnel structure. Background Technology

[0002] With economic development, the demand for logistics and passenger flow is increasing, and the capacity of urban road infrastructure is struggling to keep up with the pace of this growth, leading to frequent traffic congestion. One effective way to alleviate traffic congestion is to widen roads. Generally, instead of directly widening tunnels, the approach is to add independent tunnels on one or both sides of existing tunnels. The advantage of this method is that it minimizes the impact on existing tunnels and ensures that traffic is not affected during construction. However, the disadvantage is that a reasonable distance must be maintained between the new and existing tunnels, which increases the land required for connecting roads. This additional land use may lead to extensive demolition and high economic costs. Summary of the Invention

[0003] The purpose of this invention is to at least solve one of the technical problems existing in the prior art, and to provide a double-bore tunnel for the expansion of a single-bore tunnel.

[0004] This invention also provides a construction method for expanding a single-tunnel tunnel into a double-tunnel structure.

[0005] According to a first aspect of the present invention, a twin-tunnel expansion of a single-tunnel is provided, comprising: an existing upper tunnel, a locking device, and a newly constructed lower tunnel. The existing upper tunnel includes a first invert, a maintenance passage, tunnel walls arranged from the inside out, a secondary lining structure, and an initial support structure. The first invert extends between the two side walls at the lower end of the existing upper tunnel. The maintenance passage is arranged along the length of the existing upper tunnel on both inner walls. The locking device includes inclined piles, waist beams, and temporary supports. The waist beams are arranged along the length of the existing upper tunnel on both inner walls, and the two waist beams are connected by temporary supports. Inclined piles are installed on both sides of the existing upper tunnel. The first invert can be removed after the locking device takes effect. The newly constructed lower tunnel includes lateral support, sidewalls, a central diaphragm, and a second invert. The lateral support is installed on both outer walls of the newly constructed lower tunnel. The central diaphragm separates the two tunnels. The second invert extends between the two side walls at the lower end of the newly constructed lower tunnel. The inclined piles are arranged in multiple rows along one side of the existing upper tunnel in a vertical direction. The inversion angle of each row of inclined piles along one side of the existing upper tunnel is 30-60°.

[0006] Beneficial effects: This single-tunnel expansion into a double-tunnel system includes the existing upper tunnel, a locking device, and a newly constructed lower tunnel. The existing upper tunnel includes a first invert arch, a maintenance passage, tunnel walls arranged from the inside out, a secondary lining structure, and an initial support structure. The first invert arch extends between the two side walls at the lower end of the existing upper tunnel. The maintenance passage is located on the inner side walls of the existing upper tunnel along its length. The locking device includes inclined piles, waist beams, and temporary supports. The waist beams are located on the inner side walls of the existing upper tunnel along its length, and are connected by temporary supports. The inclined piles are located on both sides of the existing upper tunnel. The first invert arch can be removed after the locking device takes effect. The newly constructed lower tunnel includes lateral supports, side walls, a central diaphragm, and a second invert arch. The lateral supports are located on the outer side walls of the newly constructed lower tunnel. The central diaphragm separates the two tunnels. The second invert arch extends between the two side walls at the lower end of the newly constructed lower tunnel. The inclined piles are arranged in multiple rows along one side of the existing upper tunnel in a vertical direction, with each row of inclined piles having an elevation angle of 30-60° along one side of the existing upper tunnel. Based on the existing upper tunnel, continue to excavate the lower tunnel to build a new one. Without increasing the land use, the number of lanes in the existing tunnel will be increased by 2, and the traffic capacity will be increased by 0.6 to 1.0 times.

[0007] According to one embodiment of the present invention, in the expansion of a single-tunnel into a twin-tunnel structure, the lower-level newly constructed tunnel also includes initial support and secondary lining. The initial support of the lower-level newly constructed tunnel consists of lateral anchors, steel supports, steel mesh, and shotcrete. The secondary lining of the lower-level newly constructed tunnel is a reinforced concrete sidewall with a wall thickness of 450-800 mm. A waterproof layer is provided at the arch and wall sections between the initial support and the secondary lining of the lower-level newly constructed tunnel. The waterproof layer includes a 350 g / m² non-woven fabric and a 1.2 mm thick waterproof board.

[0008] According to one embodiment of the present invention, in the expansion of a single-tunnel tunnel into a double-tunnel structure, the temporary support structure is in the form of a straight line or a star shape, the distance between the temporary supports is 4 to 8 meters, when a star-shaped support is used, the temporary supports are spaced at a large interval, and the temporary supports are made of reinforced concrete with a strength greater than or equal to C30.

[0009] According to one embodiment of the present invention, in the expansion of a single-tunnel into a double-tunnel structure, the width of the newly constructed lower tunnel is smaller than the width of the existing upper tunnel.

[0010] According to another embodiment of the present invention, a construction method is provided for expanding a single-tunnel into a double-tunnel as described in any one of the above embodiments:

[0011] Traffic from the existing upper tunnel will be diverted to surrounding roads. Traffic from the existing upper tunnel will be closed during construction. The ventilation system of the existing upper tunnel will be modified, and the top fans of the existing upper tunnel can continue to be used during construction to ensure air quality and the working environment of construction personnel during the downward expansion of the existing upper tunnel. The electromechanical system of the existing upper tunnel will be modified, and the maintenance tunnel or its pipelines will be relocated and suspended on the side wall of the existing upper tunnel to create conditions for the next stage of construction.

[0012] The existing upper tunnel shall be inspected, reinforced and monitored. Safety inspections shall be carried out on the existing upper tunnel. If water leakage or other defects are found, the defects shall be treated first. If the structural strength is insufficient, reinforcement and strengthening shall be carried out. Monitoring points shall be arranged on the sidewalls and arch of the existing upper tunnel. During the downward expansion construction, the sidewall settlement and arch settlement of the existing upper tunnel shall be monitored.

[0013] The inspection road is dismantled, and the locking device is installed below the existing upper tunnel. Without affecting the safety of the main structure of the existing upper tunnel, a hole with a diameter of 5-10cm is drilled, and three rows of inclined piles are constructed. The inclined piles are made of steel pipes with a diameter of 5-10cm, and three rows of steel pipes are installed on each side. Then the waist beam and the temporary support are constructed.

[0014] The upper step excavation is carried out. After the waist beam and the temporary support reach the design strength, the bottom plate of the existing upper tunnel and the first invert arch are removed. The lower layer of new tunnel earthwork is excavated in steps according to the geological conditions. When the upper step is excavated, the lateral anchor rods are constructed in time to provide initial lateral support for the tunnel.

[0015] After the upper step is excavated for 10-20m and the lateral shotcrete structure reaches the design strength, the lower step is excavated. The lower step and the upper step should always maintain a longitudinal distance of greater than or equal to 5m. Lateral anchors should also be installed in a timely manner during the excavation of the lower step to provide initial lateral support for the tunnel, restrain soil deformation, and ensure the safety of the existing tunnel above.

[0016] After the earthwork is excavated to the design elevation, the second invert arch concrete and the cushion layer of the lower-level new tunnel are poured. Before pouring the second invert arch concrete, a waterproof layer is set between the initial support of the lower-level new tunnel and the secondary lining of the lower-level new tunnel at the arch and wall parts.

[0017] After the construction of the side wall and the central diaphragm is completed, the steel bars of the side wall and the central diaphragm are tied, and the concrete of the side wall and the central diaphragm is poured. The central diaphragm is used as the bottom plate of the roadway.

[0018] When the concrete strength of the frame structure of the newly built lower tunnel meets the design requirements, the temporary support is removed, the stress system of the twin-tunnel is converted, and the concrete of the upper and lower tunnel surfaces is laid.

[0019] Improve the maintenance walkway, crash barriers, and tunnel drainage system; improve the traffic safety facilities, electromechanical and ventilation facilities of the upper and lower tunnels; and rebuild the maintenance walkway of the existing upper tunnel.

[0020] Beneficial effects: By continuing to excavate the new tunnel below based on the existing upper tunnel, the main structure of the existing tunnel can be fully utilized, which not only ensures safety during construction, but also saves tunnel construction investment and conserves resources.

[0021] According to another embodiment of the construction method of the present invention, the overall process can be carried out from one end to the other. While the construction of the new tunnel in the lower layer is being carried out at one end, the reinforcement of the existing tunnel in the upper layer, the construction of the inclined piles and the temporary supports can be carried out at the other end.

[0022] According to another embodiment of the construction method of the present invention, the maintenance passage is provided in the existing upper tunnel, and the newly constructed lower tunnel cannot completely excavate the earth and rock below the arch foot of the existing upper tunnel.

[0023] According to another embodiment of the construction method of the present invention, a 50cm wide crash barrier is provided in the lower-level newly built tunnel to ensure the clear width for vehicles in the lower-level newly built tunnel.

[0024] According to another embodiment of the construction method of the present invention, the vertical spacing of the steel pipes is 0.4-0.6m, the longitudinal spacing is 0.4-0.6m, the diameter of the steel pipes can be 5-10cm, the wall thickness is 3-6mm, and grouting holes with a diameter of 5-10mm are drilled around the pipe wall, and the grouting holes are arranged in a quincunx pattern.

[0025] According to another embodiment of the construction method of the present invention, the temporary support can be reinforced by steel pipe supports with a diameter of 600mm, the spacing between the steel pipe supports is 3 to 5m, and a pre-stressing force of 100 to 200kN is required when using steel pipe supports for reinforcement. Attached Figure Description

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments;

[0027] Figure 1 This is a schematic diagram of a double-tunnel expansion project for a single-tunnel structure according to the present invention. Figure 1 ;

[0028] Figure 2 This is a schematic diagram of a double-tunnel expansion project for a single-tunnel structure according to the present invention. Figure 2 ;

[0029] Figure 3 This is a schematic diagram of a double-tunnel expansion project for a single-tunnel structure according to the present invention. Figure 3 ;

[0030] Figure 4 This is a schematic diagram of a double-tunnel expansion project for a single-tunnel structure according to the present invention. Figure 4 ;

[0031] Figure 5 This is a schematic diagram of a double-tunnel expansion project for a single-tunnel structure according to the present invention. Figure 5 ;

[0032] Figure 6 This is a schematic diagram of a double-tunnel expansion project for a single-tunnel structure according to the present invention. Figure 6 ;

[0033] Figure 7 This is a schematic diagram of a double-tunnel expansion project for a single-tunnel structure according to the present invention. Figure 7 ;

[0034] Figure 8 This is a schematic diagram of a double-tunnel expansion project for a single-tunnel structure according to the present invention. Figure 8 ;

[0035] Figure 9 This is a top view of the linear support structure for the expansion of a single-tunnel tunnel into a double-tunnel structure according to the present invention.

[0036] Figure 10 This is a top view of the cross-shaped support structure for the expansion of a single-tunnel tunnel according to the present invention.

[0037] Figure 11 This is a cross-sectional view of the construction of a twin-tunnel expansion project for a single-tunnel structure according to the present invention. Detailed Implementation

[0038] This section will describe in detail specific embodiments of the present invention. Preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the drawings is to supplement the textual description with graphics, so that people can intuitively and vividly understand each technical feature and overall technical solution of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0039] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, top surface, bottom, inner side, outer side, etc., are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0040] In the description of this invention, "several" means one or more, "more than" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0041] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0042] With economic development, the demand for logistics and people exchange has increased, and the number of cars has grown rapidly. The capacity of urban road infrastructure is unable to keep up with the speed of demand growth, and traffic congestion often occurs in cities.

[0043] To alleviate traffic congestion, one effective method is to widen roads. However, for critical engineering projects, especially tunnel projects, due to constraints related to the stability of the surrounding rock and traffic management during construction, direct tunnel widening is generally not adopted. Instead, the option is to add independent tunnels on one or both sides of the existing tunnel. The advantage of this method of widening new tunnels is that it has minimal impact on the existing tunnel, ensuring that traffic is not affected during construction. The disadvantage is that a reasonable distance must be maintained between the new tunnel and the existing tunnel, which increases the land use for connecting roads. In land-scarce areas such as urban centers, the additional land use may lead to a large amount of demolition, making the construction of new tunnels on one or both sides of the existing tunnel costly.

[0044] Currently, some tunnels, when lacking the land conditions for adding a new tunnel on one side, are attempting to demolish the existing tunnel and expand the two-lane tunnel into a three-lane or four-lane tunnel in the original location. The advantage of this horizontal widening method is that it saves land compared to building a new independent tunnel, but traffic needs to be interrupted during construction, and it does not take into account the use of the existing tunnel at all, resulting in a large investment.

[0045] To address the insufficient traffic capacity of existing tunnels, it is necessary to find a solution that utilizes existing tunnels, ensures safe construction, and saves land use for tunnels and connecting roads.

[0046] This invention primarily addresses the renovation of existing single-lane or three-lane tunnels with insufficient traffic capacity. It preserves the portion of the original tunnel above the arch foot, installs temporary supports at the arch foot location, removes the existing road surface and invert arch, and then excavates and supports the lower section of the existing tunnel in a stepped manner. This transforms the existing single-tube mountain tunnel into a double-layered tunnel. The lower tunnel features reinforced concrete sidewalls and a central diaphragm, which divides the tunnel into upper and lower layers. The diaphragm serves as both the floor of the upper tunnel's driveway and the roof of the lower tunnel, creating two enclosed double-layered tunnels. This invention is applicable to tunnel engineering on highways and municipal roads, and is particularly suitable for mountain tunnels requiring expansion and renovation due to insufficient existing tunnel capacity.

[0047] Reference Figures 1 to 11 A type of double-tunnel expansion of a single-tunnel, comprising an existing upper tunnel, a locking device, and a newly constructed lower tunnel.

[0048] As is easily understood, the upper-level existing tunnel includes a first invert arch 110, a maintenance passage 120, tunnel walls arranged from the inside out, a secondary lining structure 140 for the upper-level existing tunnel, and an initial support structure 150. The first invert arch 110 extends between the two side walls at the lower end of the upper-level existing tunnel. The first invert arch 110 can be removed. The maintenance passage 120 is arranged along the length of the upper-level existing tunnel on both inner walls of the upper-level existing tunnel.

[0049] As easily understood, the locking device includes inclined piles 210, wainscoting 220, and temporary supports 230. Wainscoting 220 is installed along the length of the existing upper tunnel on both sides of its inner wall, and the two wainscoting 220 are connected by temporary supports 230. The inclined piles 210 are installed on both sides of the existing upper tunnel. The locking device ensures the safety of the existing upper tunnel during the construction of the new lower tunnel and prevents settlement of the existing upper tunnel.

[0050] As is easily understood, the lower-level newly constructed tunnel includes initial support, sidewalls 320, a central diaphragm 330, and a second invert 340. The lateral support is installed on the outer walls of both sides of the lower-level newly constructed tunnel, the central diaphragm 330 separates the two tunnels, and the second invert 340 extends between the two sidewalls at the lower end of the lower-level newly constructed tunnel.

[0051] In one specific embodiment, the initial support for the newly constructed lower tunnel consists of lateral anchors, steel supports, reinforcing mesh, and shotcrete. The lateral anchors are hollow grouting anchors with a diameter of 25–28 mm, spaced 1.0 m vertically and 0.50–0.75 m along the tunnel length. The length of the hollow grouting anchors is 3.0–5.0 m. The steel supports are I22b I-beams, spaced 0.5–1.0 m apart. The upper part of the steel frame supports the existing tunnel. The steel frames are connected by steel bars with a diameter of 20-25mm. A steel mesh with a diameter of 8mm is attached to the steel frame. The mesh size is 200×200mm. C30 early-strength shotcrete is used, with a thickness of 250-280mm. The secondary lining of the newly built tunnel is a reinforced concrete sidewall with a wall thickness of 450-800mm.

[0052] It is easy to understand that the diaphragm is not only the load-bearing structure of the upper tunnel's driving lane, but also constrains the deformation in the middle of the tunnel, and serves as the structural roof of the lower tunnel, which is beneficial to the overall safety of the two-layer tunnel.

[0053] It is easy to understand that the side walls serve to constrain the deformation of the newly built tunnel below and support the central diaphragm.

[0054] In simple terms, the function of lateral support is to provide support for the existing tunnel above, prevent the existing tunnel above from settling and deforming, thereby affecting the safety of the existing tunnel above, and at the same time ensure the safety of the newly built tunnel below.

[0055] Reference Figure 2 The inclined piles 210 are arranged in three rows along one side of the existing upper tunnel in a vertical direction, and the elevation angle of each row of inclined piles 210 along one side of the existing upper tunnel is 30 to 60°.

[0056] It is easy to understand that the purpose of using a large angle of inclination of 30 to 60 degrees is to more effectively reinforce the slope toe, especially to provide greater vertical support after the removal of the existing tunnel invert arch in the upper layer.

[0057] In one specific embodiment, the elevation angles of each row of inclined piles 210 along one side of the existing upper tunnel from top to bottom are 30°, 45°, and 60°.

[0058] Reference Figure 9 and Figure 10 The temporary support 230 has a straight or star-shaped structure, and the distance between the temporary supports 230 is 4m.

[0059] Since the existing upper tunnel is a closed structure, its structural stress is in equilibrium. To construct a new double-layer tunnel, it is necessary to remove the invert arch of the existing upper tunnel, changing its structure from a closed to an open structure, thus altering its stress state. Therefore, it is required to install a locking device before removing the invert arch to ensure that the stress balance and deformation stability of the existing tunnel are not altered during construction.

[0060] Using straight or cross-shaped supports, the amount of masonry required is small. It not only supports the stability of the existing tunnel arch foot above, but also ensures the stress balance of the existing tunnel above.

[0061] Furthermore, the use of straight and cross-shaped support structures opens up the space between the upper and lower levels, allowing the use of the existing ventilation system of the upper tunnel during construction, resulting in better air quality during construction.

[0062] When reinforced concrete slabs are used for support, a large amount of masonry is required, and the existing tunnel above and the newly built tunnel below are isolated. The construction of the newly built tunnel below also requires the construction of a new ventilation system, resulting in poor air quality during the construction process.

[0063] In one specific embodiment, the width of the newly built tunnel at the lower level is smaller than the width of the existing tunnel at the upper level.

[0064] While constructing a new tunnel with the same width as the existing tunnel above may facilitate lane arrangement within the tunnel, it is detrimental to the protection of the existing tunnel above. Under the influence of gravity, the existing tunnel above may move downwards. Even a small displacement can lead to cracking of the existing tunnel structure and relative displacement between the existing tunnel above and the original surrounding rock support structure, thereby damaging the waterproof structure of the existing tunnel above and affecting its safety.

[0065] When the width of the newly built tunnel in the lower layer is slightly smaller than the width of the existing tunnel in the upper layer, the soil below the arch foot of the existing tunnel in the upper layer is retained. This serves two purposes: first, it effectively prevents the relative downward displacement of the existing tunnel in the upper layer, ensuring its safety; second, the newly built tunnel in the lower layer and the existing tunnel in the upper layer are not structurally rigidly connected, and there is no bending moment transfer in the stress structure, making the stress distribution clear.

[0066] In one specific embodiment, the width of the carriageway of the newly built tunnel is ensured by adjusting the maintenance lane of the existing tunnel on the upper level to serve as the crash barrier for the newly built tunnel on the lower level.

[0067] This invention still ensures the width of the carriageway. It eliminates the need for a tunnel maintenance walkway and installs a 50cm wide crash barrier in the newly constructed lower tunnel to guarantee the clear width for vehicles and ensure tunnel structural safety. Furthermore, it addresses tunnel maintenance issues by deploying intelligent monitoring facilities. The lower tunnel primarily utilizes intelligent facilities for routine monitoring and employs intelligent inspection vehicles for patrols, reducing the workload of manual inspections.

[0068] This invention provides a construction method for constructing a double-bore tunnel expansion project from a single-bore tunnel as described above:

[0069] Traffic from the existing upper tunnel will be diverted to surrounding roads. Traffic from the existing upper tunnel will be closed during construction. The ventilation system of the existing upper tunnel will be modified so that the top fans of the existing upper tunnel can continue to be used during construction, ensuring air quality and the working environment of construction personnel during the downward expansion of the existing upper tunnel. The electromechanical system of the existing upper tunnel will be modified, and the maintenance tunnel or its pipelines will be relocated and suspended on the side wall of the existing upper tunnel to create conditions for the next stage of construction.

[0070] The existing tunnel above the upper level will be inspected, reinforced, and monitored. Safety inspections will be conducted on the existing tunnel above the upper level. If defects such as water leakage are found, the defects should be treated first. If the structural strength is insufficient, reinforcement and strengthening treatment should be carried out. Monitoring points will be set up on the sidewalls and arches of the existing tunnel above the upper level. During the downward expansion construction, the sidewall settlement and arch settlement of the existing tunnel above the upper level will be monitored.

[0071] Remove the maintenance roadway 120, install a locking device below the existing tunnel on the upper level, and without affecting the safety of the main structure of the existing tunnel on the upper level, drill holes with a diameter of 5-10cm, construct three rows of inclined piles 210, the inclined piles 210 use steel pipes with a diameter of 5-10cm, and set three rows of steel pipes on each side, and then construct the waist beam 220 and temporary support 230.

[0072] After the upper bench excavation is completed and the waist beam 220 and temporary support 230 reach the design strength, the bottom slab of the existing upper tunnel and the first invert arch 110 are removed. The earthwork of the new tunnel in the lower layer is excavated in stages according to the geological conditions. When the upper bench is excavated, the lateral anchor bolts 410 are constructed in time to provide initial support for the tunnel side. The upper bench can be excavated in full section or in sections according to the geological conditions.

[0073] After the upper step is excavated for 10-20m and the lateral shotcrete structure reaches the design strength, the lower step is excavated. The lower step and the upper step should always maintain a longitudinal distance of greater than or equal to 5m. Lateral anchor bolts 410 should also be installed in a timely manner during the excavation of the lower step to provide initial lateral support for the tunnel, restrain soil deformation, and ensure the safety of the existing tunnel above. The step excavation is mainly to ensure the safety of the existing tunnel and avoid excavating to the bottom of the tunnel at one time, which may cause instability of the existing tunnel. The thickness of each step is greater than 3.0m to ensure the convenience of construction workers.

[0074] After the earthwork excavation reaches the design elevation, the second invert arch concrete and the foundation layer of the lower-level new tunnel are poured. Before pouring the second invert arch concrete, a waterproof layer is installed between the initial support of the lower-level new tunnel and the secondary lining of the lower-level new tunnel, at the arch and wall sections. This layer uses 350g / m2 non-woven fabric + 1.2mm thick EVA waterproof board. For the waterproof layer materials, reliable waterproofing performance and good mechanical strength properties are used in the selection of waterproof membrane and non-woven fabric materials.

[0075] After the second invert arch and the foundation layer are completed, the steel bars of the side walls and the central diaphragm are tied, and the concrete of the side walls and the central diaphragm is poured. The central diaphragm is used as the bottom plate of the driveway.

[0076] When the concrete strength of the frame structure of the newly built tunnel in the lower layer meets the design requirements, the temporary supports are removed, the stress system of the twin tunnels is converted, and the concrete of the upper and lower road surfaces of the tunnel is laid.

[0077] Improve the maintenance walkway, crash barriers, and tunnel drainage system; improve traffic safety facilities, electromechanical and ventilation facilities in the upper and lower tunnels; and rebuild the maintenance walkway in the existing upper tunnel.

[0078] In one specific embodiment, the tunnel ancillary works also include drainage ditches, sump pits, ventilation facilities, fire protection facilities, smart monitoring facilities, lighting facilities, etc.

[0079] In one specific embodiment, a preferred method is to adopt a construction process from one end to the other. While the construction of the new lower-level tunnel is being carried out at one end, the reinforcement, inclined piles, and temporary supports of the existing upper-level tunnel can be constructed at the other end. This allows for better organization of the continuous construction process.

[0080] In one specific embodiment, construction can also be carried out from both ends of the tunnel toward the middle, with two working faces for the construction of the new tunnel in the lower layer. However, because access to the existing tunnel in the upper layer is inconvenient, construction can only be carried out at both ends simultaneously after the reinforcement, inclined piles and temporary supports of the existing tunnel in the upper layer are completed.

[0081] It is easy to understand that the construction should take into full account the convenience of earthwork removal and minimize the impact on the subsequent construction of side walls and invert arches.

[0082] It is easy to understand that the existing tunnel in the upper layer has a maintenance passage, and the newly built tunnel in the lower layer cannot fully excavate the earth and rock below the arch foot of the existing tunnel in the upper layer due to construction safety considerations.

[0083] The earthwork at this location needs to support the existing tunnel above, and lateral anchor bolts 410 need to be installed in a timely manner to provide initial lateral support for the tunnel and constrain soil deformation.

[0084] By preserving the earthwork directly beneath the existing upper tunnel and laterally restraining it, good support can be provided for the existing upper tunnel, ensuring its safety.

[0085] In one specific embodiment, the vertical spacing of the steel perforated pipes is 0.4–0.6 m, the longitudinal spacing is 0.4–0.6 m, the diameter of the steel perforated pipes can be 5–10 cm, the wall thickness of the steel perforated pipes is 3–6 mm, and grouting holes with a diameter of 5–10 mm are drilled around the perimeter of the pipe walls, arranged in a staggered pattern. The grouting pressure is 0.2–1.0 MPa.

[0086] Cement grout is injected using a high-pressure pump, with the pressure controlled between 0.5 and 2.0 MPa. A field grouting test is conducted before grouting, and the grouting parameters are adjusted according to the actual situation. The grout is then injected into the hole using a grouting pump, and the stratum is reinforced through the grouting holes in the steel pipe wall.

[0087] Grouting pressure is controlled using a graded pressure increase method, with dual control of final pressure and grouting volume. Generally, the designed grouting volume for a single pipe is used as the standard. Grouting can be terminated if the grouting volume still falls short of the design standard after the grouting pressure reaches the designed final pressure for at least 20 minutes. After the steel perforated pipe grouting is completed, drilling is performed. The quality of the grouting is judged by whether the drill cuttings contain cement slurry.

[0088] The purpose of using steel pipe grouting is to reinforce the soil and rock mass below the slope toe of the existing tunnel above, improve the strength of the soil and rock mass, and utilize the strength of the steel pipe itself to share the vertical bearing capacity of the existing tunnel above with the soil and rock mass.

[0089] In one specific embodiment, the lintel is a reinforced concrete structure attached to the sidewall of the existing tunnel above, with a concrete strength of not less than C30. The lintel has a cross-sectional width of approximately 60–80 cm and a height of approximately 80–120 cm.

[0090] In one specific embodiment, temporary supports are preferably made of reinforced concrete with a concrete strength greater than or equal to C30. Temporary supports can also be reinforced using 600mm diameter steel pipe supports spaced 3-5m apart. When using steel supports for reinforcement, a pre-stressing force of approximately 100-200kN must be applied. This ensures the transfer of stress after the removal of the existing tunnel invert arch, providing support for the safety of subsequent construction.

[0091] Reference Figure 11 The following are marked as upper step 420, lower step 430, existing upper tunnel without modification 440, tunnel under modification 450, and double-bore tunnel after modification 460.

[0092] It's easy to understand why building a new double-deck tunnel is relatively easy:

[0093] For newly constructed double-layer tunnels, considering only the stability of the surrounding rock, a top-down layered support and step-by-step excavation approach can be adopted.

[0094] Widening an existing tunnel in situ requires not only consideration of the stability of the surrounding rock, but also ensuring the safety of the existing tunnel, which is a technically demanding process compared to building a new tunnel in the lower level.

[0095] The beneficial effects of this technical solution are: under the premise of ensuring the safety of the existing tunnel, by continuing to excavate earth and rock below the existing single-tube tunnel above and using the cut-and-cover method to construct a new single-layer tunnel structure, the following objectives are achieved:

[0096] 1. By making full use of the existing main structure of the upper tunnel, safety during construction is ensured, tunnel construction investment is saved, and resources are conserved;

[0097] 2. Without acquiring new land, the number of lanes in the existing upper tunnel will be increased by 2, and the traffic capacity will be increased by 0.6 to 1.0 times;

[0098] 3. By combining with the road network, rapid passage can be achieved on the lower level, while the upper level can solve the service traffic around the tunnel;

[0099] 4. This structure is also suitable for adjusting the upper and lower tunnels to accommodate traffic flows in different directions.

[0100] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for expanding a single-bore tunnel into a double-bore tunnel, characterized in that, The single-bore tunnel, as the upper existing tunnel of the double-bore tunnel, includes a first invert arch, a maintenance passage, tunnel walls arranged from the inside to the outside, a secondary lining structure of the upper existing tunnel, and an initial support structure. The first invert arch extends between the two side walls at the lower end of the upper existing tunnel, and the maintenance passage is arranged along the length of the upper existing tunnel on both inner walls of the upper existing tunnel. The method for expanding a single-bore tunnel into a double-bore tunnel includes the following steps: The maintenance walkway of the existing upper tunnel is removed, and a locking device is installed below the existing upper tunnel. The locking device includes inclined piles, waist beams, and temporary supports. The waist beams are installed along the length of the existing upper tunnel on both sides of the inner wall of the existing upper tunnel, and the waist beams on both sides are connected by temporary supports. The inclined piles are installed on both sides of the existing upper tunnel. The first invert arch can be removed after the locking device takes effect. The temporary supports have a straight or star-shaped structure, and the distance between the temporary supports is 4-8m. When using star-shaped supports, the temporary supports are spaced at a large distance. The temporary supports are made of reinforced concrete with a strength greater than or equal to C30. The upper step excavation is carried out. After the waist beam and the temporary support reach the design strength, the bottom plate of the existing upper tunnel and the first invert arch are removed. The lower layer of new tunnel earthwork is excavated in steps according to the geological conditions. When the upper step is excavated, the lateral anchor rods are constructed in time to provide initial lateral support for the tunnel. After the upper step is excavated for 10-20m and the lateral shotcrete structure reaches the design strength, the lower step is excavated. The lower step and the upper step should always maintain a longitudinal distance of greater than or equal to 5m. Lateral anchors should also be installed in a timely manner during the excavation of the lower step to provide initial lateral support for the tunnel, restrain soil deformation, and ensure the safety of the existing tunnel above. After the earthwork is excavated to the design elevation, the second invert concrete and the cushion layer of the lower-level new tunnel are poured. Before pouring the second invert concrete, a waterproof layer is set between the initial support of the lower-level new tunnel and the secondary lining of the lower-level new tunnel at the arch and wall parts. After the second invert arch and the foundation layer are completed, the steel bars of the side walls and the diaphragm are tied, and the concrete of the side walls and the diaphragm is poured. The diaphragm is used as the bottom slab of the upper tunnel's driving lane. When the concrete strength of the frame structure of the newly built tunnel in the lower layer meets the design requirements, the temporary support is removed, the stress system of the twin tunnel is converted, and the concrete of the upper and lower road surfaces of the tunnel is laid. Improve the maintenance walkway, crash barriers, and tunnel drainage system; improve the traffic safety facilities, electromechanical and ventilation facilities of the upper and lower tunnels; and rebuild the maintenance walkway of the existing upper tunnel. The newly constructed lower tunnel is located below the existing upper tunnel and includes lateral supports, sidewalls, a central partition, and a second invert. The lateral supports are installed on the outer walls of both sides of the newly constructed lower tunnel. The central partition separates the two tunnels. The second invert extends between the two sidewalls at the lower end of the newly constructed lower tunnel. The width of the newly constructed lower tunnel is smaller than the width of the existing upper tunnel. The newly constructed lower tunnel has a rectangular structure and is equipped with a 50cm wide crash barrier to ensure the clear width for vehicles. The inclined piles are arranged in multiple rows along one side of the existing upper tunnel, with each row of inclined piles having an elevation angle of 30-60° along one side of the existing upper tunnel.

2. The method for expanding a single-bore tunnel into a double-bore tunnel according to claim 1, characterized in that: The newly constructed lower tunnel also includes initial support and secondary lining. The initial support of the newly constructed lower tunnel consists of lateral anchors, steel supports, steel mesh, and shotcrete. The secondary lining of the newly constructed lower tunnel is a reinforced concrete sidewall with a wall thickness of 450-800mm. A waterproof layer is provided at the arch and wall sections between the initial support and the secondary lining of the newly constructed lower tunnel. The waterproof layer consists of 350g / m2 non-woven fabric and a 1.2mm thick waterproof board.

3. The method for expanding a single-bore tunnel into a double-bore tunnel according to claim 1, characterized in that: Before dismantling the maintenance access road, the following are also included: Traffic from the existing upper tunnel will be diverted to surrounding roads. Traffic from the existing upper tunnel will be closed during construction. The ventilation system of the existing upper tunnel will be modified, and the top fans of the existing upper tunnel can continue to be used during construction to ensure air quality and the working environment of construction personnel during the downward expansion of the existing upper tunnel. The electromechanical system of the existing upper tunnel will be modified, and the maintenance tunnel or its pipelines will be relocated and suspended on the side wall of the existing upper tunnel to create conditions for the next stage of construction. The existing upper tunnel shall be inspected, reinforced and monitored. Safety inspections shall be carried out on the existing upper tunnel. If water leakage or other defects are found, the defects shall be treated first. If the structural strength is insufficient, reinforcement and strengthening shall be carried out. Monitoring points shall be set up on the sidewalls and arch of the existing upper tunnel. During the downward expansion construction, the sidewall settlement and arch settlement of the existing upper tunnel shall be monitored. The locking device is installed below the existing upper tunnel, including: drilling a hole with a diameter of 5-10cm, constructing three rows of inclined piles without affecting the safety of the main structure of the existing upper tunnel, the inclined piles being made of steel pipes with a diameter of 5-10cm, with 3 rows of steel pipes on each side, and then constructing the waist beam and the temporary support.

4. The method for expanding a single-bore tunnel into a double-bore tunnel according to claim 1, characterized in that: The overall construction process can be carried out from one end to the other. While the construction of the new tunnel at the lower level is being carried out at one end, the reinforcement of the existing tunnel at the upper level, the construction of the inclined piles and the temporary supports can be carried out at the other end.

5. The method for expanding a single-bore tunnel into a double-bore tunnel according to claim 1, characterized in that: The maintenance tunnel is provided in the existing upper tunnel, and the newly built lower tunnel cannot completely excavate the earth and rock below the arch foot of the existing upper tunnel.

6. The method for expanding a single-bore tunnel into a double-bore tunnel according to claim 3, characterized in that: The vertical spacing of the steel pipes is 0.4~0.6m, and the longitudinal spacing is 0.4~0.6m. The diameter of the steel pipes can be 5~10cm, the wall thickness is 3~6mm, and grouting holes with a diameter of 5~10mm are drilled around the pipe wall. The grouting holes are arranged in a quincunx pattern.

7. The method for expanding a single-bore tunnel into a double-bore tunnel according to claim 1, characterized in that: The temporary support can be reinforced using steel pipe supports with a diameter of 600mm. The spacing between the steel pipe supports is 3 to 5m. When using steel pipe supports for reinforcement, a pre-stressing force of 100 to 200kN needs to be applied.

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