Method for expanding excavation of urban portal tunnel

Abstract

The invention provides a city gate opening tunnel expanding excavation method, and relates to the technical field of tunnel construction, the city gate opening tunnel expanding excavation method comprises the following steps: grouting small guide pipes are respectively driven into arch feet on two sides of a built tunnel, and cement mortar is injected into the grouting small guide pipes; expanding excavation is conducted on one side of the rock mass below the built tunnel, and then expanding excavation is conducted on the other side of the rock mass below the built tunnel. The collapse risk during tunnel expanding excavation can be reduced.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel construction, and in particular to a method for expanding a city gate tunnel. Background Art

[0002] A city gate tunnel is a tunnel with a city gate-shaped cross-section. As traffic demand increases, the original city gate tunnel may not be able to meet the growing demand for transportation height and may need to be expanded.

[0003] In the related art, when expanding the Chengmendong tunnel, it is often necessary to remove part of the existing support structure. However, after the support structure is removed, the rock mass around the tunnel may become unstable, which may easily lead to collapse. Summary of the invention

[0004] The problem solved by the invention is: how to reduce the collapse risk during tunnel expansion.

[0005] In order to solve the above problems, the present invention provides a city gate tunnel expansion method.

[0006] The present invention provides a method for expanding a city gate tunnel, comprising the following steps:

[0007] Small grouting pipes are respectively driven into the arch feet on both sides of the built tunnel, and cement mortar is injected into the small grouting pipes;

[0008] One side of the rock mass below the built tunnel is expanded and excavated, and then the other side of the rock mass below the built tunnel is expanded and excavated.

[0009] Optionally, in the step of respectively driving small grouting tubes into the arch feet on both sides of the built tunnel and injecting cement mortar into the small grouting tubes, the small grouting tubes sequentially pass through the secondary lining of the built tunnel, the initial support of the built tunnel and the outer rock mass of the built tunnel.

[0010] Optionally, the small grouting conduit has a tail end located in the secondary lining of the built tunnel and a front end located in the outer rock mass of the built tunnel, and the small grouting conduit is inclined downward from the tail end to the front end.

[0011] Optionally, in the step of excavating one side of the rock mass below the built tunnel and then excavating the other side of the rock mass below the built tunnel, both excavations include:

[0012] Digging downward to form a downcut area;

[0013] spraying concrete on the side walls of the excavated area to form a primary sprayed concrete layer;

[0014] Arranging a new I-beam on the inner side of the primary shotcrete layer;

[0015] Spraying concrete on the inner side of the primary sprayed concrete layer and the new I-beam to form a secondary sprayed concrete layer;

[0016] Concrete is poured on the inner side of the composite shotcrete layer to form a lining concrete layer.

[0017] Optionally, a plurality of old I-beams are provided in the initial support of the built tunnel, and the plurality of old I-beams are sequentially spaced along the longitudinal direction of the built tunnel;

[0018] The step of arranging a new I-beam on the inner side of the primary sprayed concrete layer comprises:

[0019] Arranging a plurality of the new I-beams on the inner side of the primary sprayed concrete layer, and connecting the upper ends of the plurality of the new I-beams to the lower ends of the plurality of the old I-beams respectively;

[0020] The two adjacent new I-beams are connected by connecting steel bars.

[0021] Optionally, the step of connecting the upper ends of the plurality of new I-beams to the lower ends of the plurality of old I-beams respectively comprises:

[0022] Welding first end plates respectively at the lower ends of the plurality of old I-beams;

[0023] Welding second end plates to the upper ends of the plurality of new I-beams respectively, and welding third end plates to the lower ends of the plurality of new I-beams respectively;

[0024] The third end plate is supported at the bottom of the undercut area, and the second end plate is bolted to the first end plate.

[0025] Optionally, spraying concrete on the inner side of the primary sprayed concrete layer and the new I-beam to form a secondary sprayed concrete layer includes:

[0026] A mortar anchor rod is driven between every two I-beams, and the mortar anchor rod passes through the initial shotcrete layer and the outer rock mass of the excavation area in sequence;

[0027] A steel mesh is laid between the inner side of the primary sprayed concrete layer and the new I-beam, and then concrete is sprayed to form the secondary sprayed concrete layer.

[0028] Optionally, pouring concrete on the inner side of the shotcrete layer to form a lining concrete layer includes:

[0029] The bottom surface of the secondary lining of the built tunnel is roughened, and then steel bars are arranged, formwork is erected, and finally concrete is poured to form the lining concrete layer.

[0030] Optionally, after pouring concrete on the inner side of the shotcrete layer to form a lining concrete layer, the method further comprises:

[0031] A water-stop material is arranged between the joints of the secondary lining of the built tunnel and the lining concrete layer.

[0032] Optionally, in the step of spraying concrete on the side wall of the excavated area to form a primary sprayed concrete layer and the step of spraying concrete on the inner side of the primary sprayed concrete layer and the new I-beam to form a secondary sprayed concrete layer, the sprayed concrete is C25 concrete;

[0033] In the step of pouring concrete on the inner side of the sprayed concrete layer to form a lining concrete layer, the poured concrete is C30 concrete.

[0034] The beneficial effects of the city gate tunnel excavation method of the present invention are as follows: first, small grouting tubes are respectively driven into the arch feet on both sides of the built tunnel, and cement mortar is injected into the small grouting tubes, so that the built support structures on both sides of the built tunnel can be temporarily fixed, and the built support structures can be prevented from being suspended in the air and falling after subsequent downward excavation, thereby reducing the risk of collapse, and the injected cement mortar can diffuse outward through the grouting holes of the small grouting tubes to consolidate the surrounding rock mass, thereby sealing the rock mass fissure water, and further preventing the leakage of fissure water; then, one side of the rock mass below the built tunnel is excavated, and then the other side of the rock mass below the built tunnel is excavated, so that left-right staggered downward excavation can be achieved, and the downward excavation does not require the removal of the built support structure, which can reduce the risk of collapse, and the left-right staggered construction can prevent the built support structure from being suspended in the air at the same time, thereby further reducing the risk of collapse. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of step S1 of the city gate tunnel excavation method according to an embodiment of the present invention;

[0036] Figure 2 This is a schematic diagram of the structure of a small grouting conduit according to an embodiment of the present invention;

[0037] Figure 3 Schematic diagram of step S21 of the city gate tunnel excavation method according to an embodiment of the present invention;

[0038] Figure 4 Schematic diagram of step S22 of the city gate tunnel excavation method according to an embodiment of the present invention;

[0039] Figure 5 Schematic diagram of step S23 of the city gate tunnel excavation method according to an embodiment of the present invention;

[0040] Figure 6Schematic diagram of step S24 of the city gate tunnel excavation method according to an embodiment of the present invention;

[0041] Figure 7 Schematic diagram of step S25 of the city gate tunnel excavation method according to an embodiment of the present invention;

[0042] Figure 8 This is a schematic diagram of the connection of the new I-beam according to an embodiment of the present invention;

[0043] Fig. 9 This is a schematic diagram of the connection between the new I-beam and the old I-beam according to an embodiment of the present invention;

[0044] Fig.10 for Fig. 9 A magnified schematic diagram of the local A in the middle;

[0045] Fig.11 for Fig. 9 A magnified schematic diagram of the part B in the middle;

[0046] Fig.12 A detailed view of the excavation area after step S25 of the city gate tunnel excavation method according to an embodiment of the present invention;

[0047] Fig.13 This is a schematic diagram of the structure of a steel mesh according to an embodiment of the present invention;

[0048] Fig.14 It is a schematic diagram of the arrangement of the water-stop material according to an embodiment of the present invention.

[0049] Description of reference numerals:

[0050] 1. Existing tunnel; 11. Arch foot; 12. Secondary lining; 13. Initial support; 131. Old I-beam; 1311. First end plate; 2. Small grouting duct; 21. Grouting hole; 3. Part to be excavated; 31. Excavation area; 4. Initial sprayed concrete layer; 5. New I-beam; 51. Connecting steel bars; 52. Second end plate; 53. Third end plate; 54. Connecting bolts; 6. Re-sprayed concrete layer; 7. Lining concrete layer; 81. Mortar anchor rods; 82. Steel mesh; 9. Waterstop material. DETAILED DESCRIPTION

[0051] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. Although certain embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be interpreted as being limited to the embodiments described herein. On the contrary, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the drawings and embodiments of the present invention are only for exemplary purposes and are not intended to limit the scope of protection of the present invention.

[0052] The Z axis in the drawings represents the vertical direction, that is, the up and down position, and the positive direction of the Z axis represents the top, and the reverse direction of the Z axis represents the bottom; the X axis in the drawings represents the horizontal direction, and is designated as the front and back position, and the positive direction of the X axis represents the front side, and the reverse direction of the X axis represents the back side; the Y axis in the drawings represents the left and right position, and the positive direction of the Y axis represents the left side, and the reverse direction of the Y axis represents the right side. It should also be noted that the aforementioned Z axis, Y axis, and X axis 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, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0053] The term "including" and its variations used in this document are open inclusions, that is, "including but not limited to"; the term "based on" means "based at least in part on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one other embodiment"; the term "some embodiments" means "at least some embodiments"; the term "optionally" means "optional embodiments". The relevant definitions of other terms will be given in the following description. It should be noted that the concepts of "first", "second", etc. mentioned in the present invention are only used to distinguish different devices, modules or units, and are not used to limit the order or interdependence of the functions performed by these devices, modules or units.

[0054] It should be noted that the modifications of "one" and "plurality" mentioned in the present invention are illustrative rather than restrictive, and those skilled in the art should understand that, unless otherwise clearly indicated in the context, it should be understood as "one or more".

[0055] In the related art, tunnel excavation is often carried out by excavating upwards, but the existing support structure on the arch must be removed before excavating upwards. The removal of the support structure will cause the rock mass near the arch to loosen, making it easy to collapse.

[0056] In order to solve the technical problems existing in the related art, the present invention provides a city gate tunnel excavation method to reduce the collapse risk during tunnel excavation.

[0057] like Figure 1 As shown, a city gate tunnel excavation method provided by an embodiment of the present invention comprises the following steps:

[0058] Step S1: driving small grouting pipes 2 into the arch feet 11 on both sides of the built tunnel 1, and injecting cement mortar into the small grouting pipes 2;

[0059] Step S2: excavating one side of the rock mass below the built tunnel 1, and then excavating the other side of the rock mass below the built tunnel 1.

[0060] The rock mass below the built tunnel 1 can be referred to Figure 1 The portion to be excavated 3 below the middle dotted line. It should be noted that the two sides of the built tunnel 1 refer to the left and right sides of the cross section of the built tunnel 1. In addition, a plurality of grouting holes 21 arranged in a staggered manner can be provided on the grouting small conduit 2 (the exemplary structure of the grouting small conduit 2 can refer to Figure 2 ), and it can be understood that after the cement mortar is injected into the grouting small conduit 2, the cement mortar can diffuse outward through the multiple grouting holes 21, and after consolidation, the surrounding structures can be reinforced. In addition, there is no restriction on the material of the cement mortar, for example, it can be M30 cement mortar. It should also be noted that one side and the other side of the lower rock mass of the built tunnel 1 refer to the left and right sides of the lower rock mass. In addition, in step S2, the left side of the lower rock mass can be excavated first, and then the right side of the lower rock mass can be excavated, or the right side of the lower rock mass can be excavated first, and then the left side of the lower rock mass can be excavated, and there is no restriction here.

[0061] In this embodiment, firstly, small grouting tubes 2 are respectively driven into the arch feet 11 on both sides of the built tunnel 1, and cement mortar is injected into the small grouting tubes 2, so that the built support structures on both sides of the built tunnel 1 can be temporarily fixed, so as to avoid the built support structures from being suspended in the air and falling after subsequent downward excavation, thereby reducing the risk of collapse, and the injected cement mortar can diffuse outward through the grouting holes 21 of the small grouting tubes 2 to consolidate the surrounding rock mass, thereby sealing the rock mass fissure water and further avoiding the leakage of fissure water; then, one side of the rock mass below the built tunnel 1 is excavated, and then the other side of the rock mass below the built tunnel 1 is excavated, so that left-right staggered downward excavation can be achieved, and the downward excavation does not require the dismantling of the built support structure, which can reduce the risk of collapse, and the left-right staggered construction can avoid the built support structure from being suspended in the air at the same time, thereby further reducing the risk of collapse.

[0062] Alternatively, if Figure 1 As shown, in the step of respectively driving small grouting tubes 2 into the arch feet 11 on both sides of the built tunnel 1 and injecting cement mortar into the small grouting tubes 2, the small grouting tubes 2 successively pass through the secondary lining 12 of the built tunnel 1, the initial support 13 of the built tunnel 1 and the outer rock mass of the built tunnel 1.

[0063] The outer rock mass of the built tunnel 1 is the left rock mass or the right rock mass of the built tunnel 1 .

[0064] In this optional embodiment, by allowing the small grouting tube 2 to pass through the secondary lining 12 of the existing tunnel 1, the initial support 13 of the existing tunnel 1 and the outer rock mass of the existing tunnel 1 in sequence, the secondary lining 12 and the initial support 13 can be fixed on the outer rock mass at the same time, preventing the secondary lining 12 and the initial support 13 from falling after the rock mass below is excavated; in addition, the small grouting tube 2 penetrates deep into the outer rock mass to ensure that the cement mortar is better diffused into the outer rock mass, thereby improving the sealing effect of the rock mass fissure water.

[0065] Alternatively, if Figure 1 As shown, the small grouting conduit 2 has a tail end located in the secondary lining 12 of the built tunnel 1 and a front end located in the outer rock mass of the built tunnel 1, and the small grouting conduit 2 is inclined downward from the tail end to the front end.

[0066] Specifically, the inclination angle of the grouting small duct 2 (the angle between the grouting small duct 2 and the horizontal plane) can be 25°. In addition, the expansion of the built tunnel 1 can be divided into multiple sections along the longitudinal direction of the built tunnel 1, and each section can be expanded in batches. In the expansion of each section, two grouting small ducts 2 can be set at the arch feet 11 on both sides of the section. The two grouting small ducts 2 are set at intervals along the longitudinal direction of the built tunnel 1, with a longitudinal interval of 0.6m. At the same time, the length of the grouting small duct 2 can be selected as 4.5m, and the diameter of the grouting small duct 2 can be selected as 42mm, so as to ensure the temporary fixing effect of the grouting small duct 2 on the secondary lining 12 and the initial support 13.

[0067] In this optional embodiment, by slanting the grouting duct 2 downward from the rear end to the front end, cement mortar can be injected downward to a certain depth, so that the side walls of the excavated area 31 formed by the downward expansion are more solid, and the fixing effect of the secondary lining 12 and the initial support 13 is improved.

[0068] Alternatively, if Figures 3 to 7 As shown, in the step of excavating one side of the rock mass below the built tunnel 1 and then excavating the other side of the rock mass below the built tunnel 1, both excavations include:

[0069] Step S21: digging downward to form a digging area 31;

[0070] Step S22: spraying concrete on the side wall of the excavated area 31 to form a primary sprayed concrete layer 4;

[0071] Step S23: placing a new I-beam 5 on the inner side of the primary sprayed concrete layer 4;

[0072] Step S24: spraying concrete on the inner side of the primary sprayed concrete layer 4 and the new I-beam 5 to form a secondary sprayed concrete layer 6;

[0073] Step S25: pouring concrete on the inner side of the re-sprayed concrete layer 6 to form a lining concrete layer 7.

[0074] It should be noted that the drilling and blasting method can be used for downward excavation. In addition, the "inside" or "inner surface" mentioned in steps S23 to S25 refers to the side of the structure facing the center line of the tunnel. In addition, the inner surface of the re-sprayed concrete layer 6 can be flush with the inner surface of the initial support 13 of the built tunnel 1, and the inner surface of the lining concrete layer 7 can be flush with the inner surface of the secondary lining 12 of the built tunnel 1. For example, if the thickness of the initial support 13 is 24 mm, and the thickness of the secondary lining 12 is 50 mm, then the thickness of the initial sprayed concrete layer 4 can be 4 mm, the thickness of the re-sprayed concrete layer 6 can be 20 mm, and the thickness of the lining concrete layer 7 can be 50 mm. Moreover, the above-mentioned two excavations are the excavation of the left side of the lower rock mass and the excavation of the right side of the lower rock mass. However, since the steps for the excavation on the left and right sides are the same, the following will be exemplified by the steps for excavating on the left side. Specifically, refer to Figures 3 to 7 , and excavate to the lower left side to form a lower excavation area 31; spray concrete on the left wall of the lower excavation area 31 to form a primary sprayed concrete layer 4; set a new I-beam 5 on the inner side of the primary sprayed concrete layer 4; spray concrete on the inner side of the primary sprayed concrete layer 4 and the new I-beam 5 to form a secondary sprayed concrete layer 6; pour concrete on the inner side of the secondary sprayed concrete layer 6 to form a lining concrete layer 7, and finally complete the excavation of the left side of the lower rock mass.

[0075] In this optional embodiment, in the excavation step, the excavation is firstly performed downward to form a lower excavation area 31, and then concrete is sprayed on the side wall of the lower excavation area 31 to form a primary sprayed concrete layer 4. In this way, the rock surface after excavation can be leveled and temporarily sprayed, which helps to avoid rock blocks from falling off; then a new I-beam 5 is arranged on the inner side of the primary sprayed concrete layer 4, and then concrete is sprayed on the inner side surface of the primary sprayed concrete layer 4 and the new I-beam 5 to form a secondary sprayed concrete layer 6. In this way, the I-beam can be built into the secondary sprayed concrete layer 6, which is beneficial to improve the structural strength of the secondary sprayed concrete layer 6, so as to better support the existing supporting structure and surrounding rock of the built tunnel 1, thereby reducing the risk of collapse; finally, concrete is poured on the inner side surface of the secondary sprayed concrete layer 6 to form a lining concrete layer 7. In this way, the combination of the lining concrete layer 7 and the secondary sprayed concrete layer 6 can make the newly built structure more stable and further reduce the risk of collapse.

[0076] Alternatively, if Figure 5 and Figure 8As shown, a plurality of old I-beams 131 are provided in the initial support 13 of the built tunnel 1, and the plurality of old I-beams 131 are arranged in sequence and at intervals along the longitudinal direction of the built tunnel 1; the new I-beams 5 are arranged on the inner side of the initial sprayed concrete layer 4, including: arranging the plurality of new I-beams 5 on the inner side of the initial sprayed concrete layer 4, and connecting the upper ends of the plurality of new I-beams 5 with the lower ends of the plurality of old I-beams 131 respectively; and connecting two adjacent new I-beams 5 by connecting steel bars 51.

[0077] In this optional embodiment, by connecting the upper ends of multiple new I-beams 5 to the lower ends of multiple old I-beams 131 respectively, the supporting strength of the new I-beams 5 can be improved to further improve the structural strength of the re-sprayed concrete layer 6, thereby better preventing collapse. In addition, since two adjacent new I-beams 5 are connected by connecting steel bars 51, this can not only ensure the distance between two adjacent new I-beams 5 to reduce the displacement of the new I-beams 5, but also enable the multiple new I-beams 5 to form an integrated structure, thereby improving the structural strength of the re-sprayed concrete layer 6.

[0078] Alternatively, if Figures 9 to 11 As shown, the upper ends of the multiple new I-beams 5 are respectively connected to the lower ends of the multiple old I-beams 131, including: welding the first end plates 1311 to the lower ends of the multiple old I-beams 131; welding the second end plates 52 to the upper ends of the multiple new I-beams 5, and welding the third end plates 53 to the lower ends of the multiple new I-beams 5; supporting the third end plate 53 at the bottom of the excavated area 31, and bolting the second end plate 52 to the first end plate 1311.

[0079] Specifically, the second end plate 52 is bolted to the first end plate 1311, as shown in FIG. Fig.10 As shown, threaded holes can be opened on the second end plate 52 and the first end plate 1311 respectively, and the connecting bolts 54 can be passed through the threaded holes of the second end plate 52 and the threaded holes of the first end plate 1311 respectively, so as to realize the bolt connection between the second end plate 52 and the first end plate 1311.

[0080] In this optional embodiment, by bolting the second end plate 52 to the first end plate 1311, the effective connection between the new I-beam 5 and the old I-beam 131 can be ensured, so as to further improve the supporting strength of the new I-beam 5. In addition, since the third end plate 53 has a larger bottom area than the new I-beam 5, it has a better supporting effect at the bottom of the excavated area 31, thereby facilitating improving the supporting strength of the new I-beam 5.

[0081] Alternatively, if Fig.12As shown, the process of spraying concrete on the inner side of the primary sprayed concrete layer 4 and the new I-beam 5 to form the secondary sprayed concrete layer 6 includes: driving a mortar anchor rod 81 between every two of the I-beams, and the mortar anchor rod 81 sequentially passes through the primary sprayed concrete layer 4 and the outer rock mass of the excavation area 31; laying a steel mesh 82 between the inner side of the primary sprayed concrete layer 4 and the new I-beam 5, and then spraying concrete to form the secondary sprayed concrete layer 6.

[0082] Specifically, multiple mortar anchor rods 81 are provided, and multiple mortar anchor rods 81 are arranged in an array. More specifically, the mortar anchor rods 81 are 4.5 meters long, with an annular spacing (the distance between two adjacent mortar anchor rods 81 along the annular direction of the tunnel) of 1.5 meters, a longitudinal spacing (the distance between two adjacent mortar anchor rods 81 along the longitudinal direction of the tunnel) of 0.6 meters, and a diameter of 25 mm, so as to ensure the fixing effect of the mortar anchor rods 81 with the primary sprayed concrete layer 4 and the outer rock mass. In addition, referring to Fig.13 The steel mesh 82 can be a φ8 steel mesh @25×25cm to ensure the structural strength of the sprayed concrete layer 6.

[0083] In this optional embodiment, by pre-setting mortar anchor rods 81 and steel mesh 82 and then spraying concrete, the structural strength of the sprayed concrete layer 6 formed after spraying can be improved, thereby further reducing the risk of collapse.

[0084] Alternatively, if Fig.14 As shown, pouring concrete on the inner side of the re-sprayed concrete layer 6 to form a lining concrete layer 7 includes: roughening the bottom surface of the secondary lining 12 of the built tunnel 1, then laying steel bars, erecting formwork, and finally pouring concrete to form the lining concrete layer 7.

[0085] In this optional embodiment, the roughening process can ensure the effective connection between the lining concrete layer 7 and the secondary lining 12 of the existing tunnel 1, which is beneficial to reduce the joint between the two and improve the waterproof effect.

[0086] Alternatively, if Fig.14 As shown, after pouring concrete on the inner side of the re-sprayed concrete layer 6 to form a lining concrete layer 7, it also includes: setting a water stop material 9 between the joint of the secondary lining 12 of the built tunnel 1 and the lining concrete layer 7.

[0087] Specifically, the water-stop material 9 can be a P-201 super water-stop material to ensure a waterproof effect.

[0088] In this optional embodiment, a water-stopping material 9 is provided between the joints of the secondary lining 12 and the lining concrete layer 7 of the built tunnel 1 to prevent water leakage from the joints and improve the waterproof effect of the tunnel.

[0089] Optionally, in the step of spraying concrete on the side wall of the excavated area 31 to form a primary sprayed concrete layer 4 and in the step of spraying concrete on the inner side of the primary sprayed concrete layer 4 and the new I-beam 5 to form a secondary sprayed concrete layer 6, the sprayed concrete is C25 concrete; and in the step of pouring concrete on the inner side of the secondary sprayed concrete layer 6 to form a lining concrete layer 7, the poured concrete is C30 concrete.

[0090] In this optional embodiment, C25 concrete has a lower cost than C30 concrete. Using it as the material for the primary sprayed concrete layer 4 and the secondary sprayed concrete layer 6 can reduce costs while ensuring supporting strength. C30 concrete has better compressive resistance and waterproof ability than C25 concrete, thereby improving the durability of the tunnel.

[0091] Although the present invention is disclosed as above, the protection scope of the present invention is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A method for expanding a city gate tunnel, characterized in that: The following steps are involved: Small grouting conduits (2) are respectively driven into the arch feet (11) on both sides of the built tunnel (1), and cement mortar is injected into the small grouting conduits (2); One side of the rock mass below the built tunnel (1) is excavated, and then the other side of the rock mass below the built tunnel (1) is excavated.

2. The method for expanding a city gate tunnel according to claim 1, characterized in that: In the step of respectively driving small grouting conduits (2) into the arch feet (11) on both sides of the built tunnel (1) and injecting cement mortar into the small grouting conduits (2), the small grouting conduits (2) sequentially pass through the secondary lining (12) of the built tunnel (1), the initial support (13) of the built tunnel (1) and the outer rock mass of the built tunnel (1).

3. The method for expanding a city gate tunnel according to claim 2, characterized in that: The small grouting conduit (2) has a rear end located in the secondary lining (12) of the built tunnel (1) and a front end located in the outer rock mass of the built tunnel (1), and the small grouting conduit (2) is arranged to be inclined downward from the rear end to the front end.

4. The method for expanding a city gate tunnel according to any one of claims 1 to 3, characterized in that: In the step of excavating one side of the rock mass below the built tunnel (1), and then excavating the other side of the rock mass below the built tunnel (1), both excavations include: Digging downward to form a down-dig area (31); spraying concrete on the side wall of the excavated area (31) to form a primary sprayed concrete layer (4); A new I-beam (5) is arranged on the inner side of the primary sprayed concrete layer (4); spraying concrete on the inner side of the primary sprayed concrete layer (4) and on the new I-beam (5) to form a secondary sprayed concrete layer (6); Concrete is poured on the inner side of the sprayed concrete layer (6) to form a lining concrete layer (7).

5. The method for expanding a city gate tunnel according to claim 4, characterized in that: A plurality of old I-beams (131) are provided in the initial support (13) of the built tunnel (1), and the plurality of old I-beams (131) are sequentially spaced apart along the longitudinal direction of the built tunnel (1); The method of arranging a new I-beam (5) on the inner side of the primary sprayed concrete layer (4) comprises: Arranging a plurality of the new I-beams (5) on the inner side of the primary sprayed concrete layer (4), and connecting the upper ends of the plurality of the new I-beams (5) to the lower ends of the plurality of the old I-beams (131) respectively; Two adjacent new I-beams (5) are connected via a connecting steel bar (51).

6. The method for expanding a city gate tunnel according to claim 5, characterized in that: The step of connecting the upper ends of the plurality of new I-beams (5) to the lower ends of the plurality of old I-beams (131) comprises: Welding first end plates (1311) at the lower ends of the plurality of old I-beams (131) respectively; A second end plate (52) is welded to the upper ends of the plurality of new I-beams (5), and a third end plate (53) is welded to the lower ends of the plurality of new I-beams (5); The third end plate (53) is supported at the bottom of the excavated area (31), and the second end plate (52) is bolted to the first end plate (1311).

7. The method for expanding a city gate tunnel according to claim 4, characterized in that: The method of spraying concrete on the inner side of the primary sprayed concrete layer (4) and on the new I-beam (5) to form a secondary sprayed concrete layer (6) comprises: A mortar anchor rod (81) is driven between every two of the I-beams, and the mortar anchor rod (81) passes through the primary shotcrete layer (4) and the outer rock mass of the excavation area (31) in sequence; A steel mesh (82) is laid between the inner side of the primary sprayed concrete layer (4) and the new I-beam (5), and then concrete is sprayed to form the secondary sprayed concrete layer (6).

8. The method for expanding a city gate tunnel according to claim 4, characterized in that: The step of pouring concrete on the inner side of the sprayed concrete layer (6) to form a lining concrete layer (7) comprises: The bottom surface of the secondary lining (12) of the built tunnel (1) is roughened, and then steel bars are laid, formwork is erected, and finally concrete is poured to form the lining concrete layer (7).

9. The method for expanding a city gate tunnel according to claim 8, characterized in that: After pouring concrete on the inner side of the sprayed concrete layer (6) to form a lining concrete layer (7), the method further comprises: A water-stopping material (9) is arranged between the joints of the secondary lining (12) of the built tunnel (1) and the lining concrete layer (7).

10. The method for expanding a city gate tunnel according to claim 4, characterized in that: In the step of spraying concrete on the side wall of the excavated area (31) to form a primary sprayed concrete layer (4) and in the step of spraying concrete on the inner side of the primary sprayed concrete layer (4) and on the new I-beam (5) to form a secondary sprayed concrete layer (6), the sprayed concrete is C25 concrete; In the step of pouring concrete on the inner side of the sprayed concrete layer (6) to form a lining concrete layer (7), the poured concrete is C30 concrete.

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