Environment-friendly arch protection structure suitable for shallow-buried tunnel crossing and construction method thereof

Abstract

The application relates to the technical field of tunnel engineering, and particularly discloses an environment-friendly arch protection structure suitable for shallow-buried tunnel crossing and a construction method thereof, which comprises a tunnel lining structure, the tunnel lining structure comprises secondary lining, a waterproof layer and a sprayed concrete layer arranged in sequence from inside to outside, the arch protection structure comprises an arch protection structure arranged at the top of the tunnel and support columns arranged at the two ends of the arch protection structure, the arch protection structure comprises a reinforced concrete arch protection structure and pipe roof arch protection structures arranged at the two ends of the reinforced concrete arch protection structure, the support columns are arranged on the pipe roof arch protection structures, and the support columns are integrally cast with the secondary lining; and the arch top backfill structure is formed by layer-by-layer backfilling of geotechnical material reinforced soil at the top end of the reinforced concrete arch protection structure, and bidirectional geogrids are arranged between the layers. The arch protection structure and the tunnel lining structure can solve the problems of shallow-buried section collapse, water and soil loss and waterproof failure in the prior art.

Description

Technical Field

[0001] This invention relates to the field of tunnel engineering technology, and in particular to an environmentally friendly arch support structure and its construction method suitable for shallow-buried tunnel crossings. Background Technology

[0002] With the acceleration of urbanization, underground transportation construction, represented by tunnels, has developed rapidly. The geological conditions of shallow-buried, water-rich sections pose great challenges to tunnel construction. Therefore, it is of great significance to study the comprehensive construction technology and effects of shallow-buried, water-rich tunnels.

[0003] Shallow-buried tunnel excavation technology is suitable for tunnel construction projects with low bearing capacity, poor geological conditions, and poor surrounding rock stability. Currently, many scholars have conducted research on the comprehensive construction technology of shallow-buried, water-rich sections of tunnels. They have concluded that using shallow-buried, cut-and-cover technology in water-rich sections of tunnels can effectively improve the overall stability of the tunnel.

[0004] However, shallow buried sections are prone to collapse during construction. When using conventional surface grouting methods during operation, there are problems such as unstable grouting effect, significant environmental damage, and long construction period. Shallow buried sections are susceptible to surface water infiltration and erosion during operation, which leads to a decrease in structural durability. Conventional support systems cannot effectively coordinate the deformation of the support structure and the surrounding rock, which poses a risk of collapse.

[0005] Based on this, the present invention proposes an environmentally friendly arch support structure and its construction method suitable for shallow-buried tunnel crossings, in order to solve the problems of shallow-buried section collapse, soil erosion and waterproofing failure in the existing technology. Summary of the Invention

[0006] The purpose of this invention is to provide an environmentally friendly arch support structure and its construction method suitable for shallow-buried tunnel crossings, so as to solve the problems existing in the prior art.

[0007] To achieve the above objectives, the present invention provides an environmentally friendly arch support structure suitable for shallow-buried tunnel crossings, comprising:

[0008] The tunnel lining structure includes a secondary lining, a waterproof layer, and a shotcrete layer arranged sequentially from the inside out.

[0009] The arch support structure includes an arch support set at the top of the tunnel and support columns set at both ends of the arch support; the arch support includes a reinforced concrete arch support and a pipe curtain arch support set at both ends of the reinforced concrete arch support, the support columns are set on the pipe curtain arch support, and the support columns are integrally cast with the secondary lining.

[0010] The arch backfill structure is constructed by backfilling the top of the reinforced concrete arch with reinforced soil in layers, with bidirectional geogrids laid between the layers.

[0011] Preferably, the concrete mix proportion of the sprayed concrete layer, by mass, is cement:fly ash:sand:aggregate:water-reducing agent:accelerator:water = 336:84:833:902:4.20:25.2:165.

[0012] Preferably, the secondary lining includes an inverted arch lining at the bottom of the tunnel, a lower step lining in the middle of the tunnel, and an upper step lining at the top of the tunnel; the reinforcing cages inside the inverted arch lining, the lower step lining, and the upper step lining are connected in sequence.

[0013] Preferably, the reinforcing cage inside the reinforced concrete arch is fixedly connected to the steel pipe inside the pipe curtain arch near one end of the reinforced concrete arch.

[0014] Preferably, the thickness of each layer of backfill in the arched structure is 100mm to 300mm, and the thickness of the first layer of backfill is not less than 300mm.

[0015] Preferably, the maximum particle size of the backfill material used in the arch backfill structure is no more than 60mm.

[0016] Preferably, the joints of the upper and lower layers of geogrid are staggered, and the staggered distance is not less than 500mm.

[0017] A construction method for an environmentally friendly arch support structure suitable for shallow-buried tunnel crossings includes the following steps:

[0018] Pipe jacking arch construction is carried out according to the thickness of the soil cover at the top of the tunnel;

[0019] The tunnel is constructed by open excavation with soil covering at the top and construction of reinforced concrete arch support. The open excavation is carried out until the pipe curtain arch is exposed at both ends. Reinforcing cages are tied between the pipe curtain arches at both ends and the two ends of the reinforcing cages are welded to the pipe curtain arches. After the formwork is supported, the reinforced concrete arch support is poured.

[0020] Excavation and shotcreting of the tunnel upper step area;

[0021] Excavation and shotcreting of the lower bench area of ​​the tunnel;

[0022] Excavation of the invert arch and shotcrete application;

[0023] Waterproofing layer construction;

[0024] Invert arch filling and grouting, with connecting bars for the support columns reserved during invert arch grouting;

[0025] Construction of the support columns and secondary lining: The steel cages of the support columns and secondary lining are tied simultaneously and welded to the pipe curtain arch; the support columns and secondary lining are poured after the formwork is in place.

[0026] For the arch backfilling construction, geotextile-reinforced soil is backfilled in layers on top of the reinforced concrete arch, with bidirectional geogrids laid between the layers.

[0027] Preferably, when the soil cover thickness at the top of the tunnel is greater than 8m, pipe jacking arch construction is carried out; when carrying out pipe jacking arch construction, it is carried out sequentially from both sides of the arch top towards the middle; if the soil cover thickness at the top of the tunnel is greater than 8m, then the open excavation of the soil cover and reinforced concrete arch construction at the top of the tunnel are not carried out.

[0028] Preferably, the end of the pipe-curtain arch away from the reinforced concrete arch is provided with a pipe-curtain arch foot, which extends to the inside of the tunnel.

[0029] Compared with the prior art, the present invention has the following advantages and technical effects:

[0030] The environmentally friendly arch support structure provided by this invention, suitable for shallow-buried tunnels, ensures the safety of the tunnel body during the excavation stage through the initial support of the shotcrete layer, and reduces problems such as collapse, soil erosion, and waterproofing failure caused by tunnel excavation. The waterproof layer further improves the waterproofing effect. Finally, the secondary lining further enhances the stability and waterproofing of the tunnel structure, thereby solving the problems of collapse, soil erosion, and waterproofing failure in shallow-buried sections existing in the prior art.

[0031] In addition, the installation of the arch support structure can ensure that the tunnel roof does not collapse during the main tunnel excavation stage. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the environmentally friendly arch support structure applicable to shallow-buried tunnels according to the present invention;

[0034] Figure 2 This is a graph showing the change of surface subsidence displacement and displacement rate above the monitoring section over monitoring time in Embodiment 3 of the present invention.

[0035] Figure 3 The curves showing the tunnel convergence deformation and rate of change in Embodiment 3 of the present invention are shown.

[0036] In the diagram: 1. Secondary lining; 2. Waterproof layer; 3. Shotcrete layer; 4. Reinforced concrete arch support; 5. Pipe curtain arch support; 6. Support column; 7. Arch top backfill structure; 8. Geogrid; 9. Invert arch lining; 10. Lower step lining; 11. Upper step lining; 12. Pipe curtain arch foot. Detailed Implementation

[0037] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other. The described embodiments are merely some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0038] Example 1

[0039] like Figure 1 As shown, the present invention provides an environmentally friendly arch support structure suitable for shallow-buried tunnel crossings, comprising:

[0040] The tunnel lining structure includes, from the inside out, a secondary lining 1, a waterproof layer 2, and a shotcrete layer 3.

[0041] The arch support structure includes an arch support set at the top of the tunnel and support columns 6 set at both ends of the arch support; the arch support includes a reinforced concrete arch support 4 and a pipe curtain arch support 5 set at both ends of the reinforced concrete arch support 4, and the support columns 6 are set on the pipe curtain arch support 5. The support columns 6 are integrally cast with the secondary lining 1.

[0042] The arch backfill structure 7 is constructed by backfilling the top of the reinforced concrete arch 4 with reinforced soil in layers, and laying bidirectional geogrid 8 between the layers.

[0043] Further optimization of the scheme: the concrete mix proportion of sprayed concrete layer 3 by mass is cement: fly ash: sand: gravel: water-reducing agent: quick-setting agent: water = 336: 84: 833: 902: 4.20: 25.2: 165.

[0044] Further optimization of the scheme: the secondary lining 1 includes an inverted arch lining 9 set at the bottom of the tunnel, a lower step lining 10 set in the middle of the tunnel, and an upper step lining 11 set at the top of the tunnel; the steel cages inside the inverted arch lining 9, the lower step lining 10, and the upper step lining 11 are connected in sequence.

[0045] To further optimize the design, the steel cage inside the reinforced concrete arch 4 is fixedly connected to the steel pipe inside the pipe curtain arch 5 near one end of the reinforced concrete arch 4.

[0046] Further optimize the scheme, the thickness of each layer of backfill in the arched structure 7 is 100mm to 300mm, and the thickness of the first layer of backfill is not less than 300mm.

[0047] Further optimization of the scheme: the maximum particle size of the backfill material used in the arch backfill structure 7 is no more than 60mm.

[0048] The scheme was further optimized so that the joints of the upper and lower geogrids 8 are staggered alternately, and the staggered distance is not less than 500mm.

[0049] Example 2

[0050] A construction method for an environmentally friendly arch support structure suitable for shallow-buried tunnel crossings includes the following steps:

[0051] The construction of the pipe curtain arch protection 5 is carried out according to the thickness of the soil cover at the top of the tunnel.

[0052] The tunnel is constructed by open excavation with soil covering at the top and construction of reinforced concrete arch 4. The open excavation is carried out until the pipe curtain arch 5 is exposed at both ends. Reinforcing cages are tied between the pipe curtain arch 5 at both ends and the two ends of the reinforcing cages are welded to the pipe curtain arch 5. After the formwork is supported, the reinforced concrete arch 4 is poured. During the open excavation stage, the slope is supported by shotcrete.

[0053] Excavation and shotcreting of the tunnel upper step area;

[0054] Excavation and shotcreting of the lower bench area of ​​the tunnel;

[0055] Excavation of the invert arch and shotcrete application;

[0056] Waterproofing layer 2 construction;

[0057] The invert arch is filled and grouted, and the connecting bars of the support column 6 are reserved during the invert arch grouting.

[0058] Construction of support column 6 and secondary lining 1: The steel cages of support column 6 and secondary lining 1 are tied simultaneously and welded to the pipe curtain arch 5; after the support formwork is installed, the pouring of support column 6 and secondary lining 1 is completed.

[0059] For the arch backfilling construction, geotextile reinforced soil is used to backfill the top of the reinforced concrete arch 4 in layers, with bidirectional geogrid 8 laid between the layers; before backfilling, the slope support of the open excavation stage is removed.

[0060] Further optimize the plan: when the soil cover thickness at the top of the tunnel is greater than 8m, construct the pipe jacking arch 5; when constructing the pipe jacking arch 5, proceed sequentially from both sides of the arch top towards the middle; if the soil cover thickness at the top of the tunnel is greater than 8m, then do not carry out the open excavation of the soil cover at the top of the tunnel and the construction of the reinforced concrete arch 4.

[0061] The scheme was further optimized by setting a pipe curtain arch foot 12 at the end of the pipe curtain arch 5 away from the reinforced concrete arch 4, and the pipe curtain arch foot 12 extends to the inside of the tunnel.

[0062] Example 3

[0063] Project Overview and Geological Risk Analysis. A tunnel construction project in China involves a maximum burial depth of 110.46m and a minimum overburden depth of only 5m. According to the survey data, the surrounding rock of the tunnel is composed of silty clay, dense coarse gravelly soil, argillaceous sandstone, and weakly weathered strata, classified as Class V surrounding rock. The surrounding rock is relatively weak and easily connected to surface water systems, potentially leading to collapse accidents. Surface water is abundant in the tunnel area, the roof rock mass is fractured, joints and fissures are well-developed, and the water-bearing capacity is high.

[0064] Comprehensive construction measures for shallow-buried, water-rich tunnels. Pipe jacking was employed, with 39 pipes installed within a 140° radius of the tunnel arch. Hot-rolled seamless tempered steel pipes with an outer diameter of 194mm and a wall thickness of 8mm were used, spaced 30cm circumferentially at the center, with an external insertion angle of 10°~15°. The pipe jacking provided macroscopic support, acting as a load-bearing framework and forming an initial water barrier.

[0065] The tunnel top is excavated using open-cut machinery, with each excavation cycle not exceeding 1.0m to prevent slope collapse. When the excavation depth reaches 2m, a single layer of steel mesh is laid on the slope and shotcrete is applied for slope support. After the open excavation is completed, the reinforced concrete arch support is constructed.

[0066] After the reinforced concrete arch support reaches the required strength, the two-step method will be used to excavate the main tunnel section. The upper step is 5.8m high, and the lower step is 2.3m high. Excavation follows the principle of "first excavating the central section, then expanding the perimeter," with a 30cm layer of rock reserved around the perimeter for finishing. The final section will be finished to the design outline in one go. The construction procedure will proceed in step sequence: first, excavate the upper step and construct initial support, including initial shotcrete, erecting the arch frame, laying the steel mesh, and installing anchor bolts and advance support. After the concrete strength reaches the required level, the excavation will continue in cycles. After advancing 5-10m on the upper step, excavate the lower step and construct corresponding initial support. When the lower step has been excavated to no more than 25m, promptly excavate the invert and complete its initial support. Before excavating the invert, anchor bolts must be installed to enhance the stability of the arch foot. The single excavation advance limit for the invert is 3m to control foundation deformation. The initial support of the invert arch must be implemented in a timely manner and closed into a ring. The distance between the closed section and the tunnel face must be strictly controlled within 35m to effectively constrain the tunnel perimeter convergence.

[0067] After the initial support is completed, a new type of fully enclosed waterproof lining is constructed using a novel reverse-adhesive waterproof membrane that forms a permanent "skin-like" bond with the water-facing surface of the secondary lining 1 concrete, effectively preventing water seepage. After the waterproof layer 2 is completed, the supporting columns 6 and the secondary lining 1 are constructed.

[0068] By monitoring surface subsidence, the graph shows the changes in surface subsidence displacement and the rate of displacement change above the monitoring section over time, as shown in the figure. Figure 2 As shown, the maximum surface displacement was 17.9 mm. During the excavation stage, due to the redistribution of surrounding rock stress, radial stress decreased while tangential stress increased, leading to a significant increase in displacement. The surface displacement rate reached a maximum of 0.73 mm / d in the early stages of excavation. After initial support, the deformation and deformation rate decreased significantly in this stage, with the deformation rate ranging from 0.09 mm / d to 0.28 mm / d. The waterproof layer 2 and secondary lining 1 further reduced the surface displacement deformation. In the later monitoring period, the increase in surface displacement was slow, and the deformation rate only varied within the range of 0.04 mm / d to 0.22 mm / d, indicating good support effect.

[0069] Figure 3 The curves show the tunnel convergence deformation and its rate of change. During the excavation stage, due to the decrease in radial stress and the increase in tangential stress, the tunnel convergence deformation increases significantly, reaching 22.34 mm, with a deformation rate of 1.35 mm / d. The support force provided by the initial support gradually reaches a new equilibrium with the tunnel deformation pressure, and the range of tunnel convergence deformation rate changes significantly decreases (0.05 mm / d to 0.48 mm / d). Secondary lining 1 further reduces the residual deformation of the tunnel. After this stage, the tunnel deformation and deformation rate further decrease and eventually tend to stabilize.

[0070] In summary, this invention can solve the problems of shallow buried section collapse, soil erosion, and waterproofing failure.

[0071] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. An environmentally friendly arch support structure suitable for shallow-buried tunnel crossings, characterized in that, include: The tunnel lining structure includes a secondary lining (1), a waterproof layer (2), and a shotcrete layer (3) arranged sequentially from the inside to the outside. The arch support structure includes an arch support set at the top of the tunnel and support columns (6) set at both ends of the arch support; the arch support includes a reinforced concrete arch support (4) and a pipe curtain arch support (5) set at both ends of the reinforced concrete arch support (4); the support columns (6) are set on the pipe curtain arch support (5); the support columns (6) are integrally cast with the secondary lining (1); a pipe curtain arch foot (12) is set at one end of the pipe curtain arch support (5) away from the reinforced concrete arch support (4); the pipe curtain arch foot (12) extends to the inside of the tunnel, and one side of the pipe curtain arch foot (12) is connected to the support column (6); The arch backfill structure (7) is constructed by backfilling the top of the reinforced concrete arch (4) in layers with geotextile reinforced soil, and laying bidirectional geogrids (8) between the layers.

2. The environmentally friendly arch support structure suitable for shallow-buried tunnel crossings according to claim 1, characterized in that, The concrete mix proportion of the sprayed concrete layer (3) by mass is cement: fly ash: sand: gravel: water-reducing agent: quick-setting agent: water = 336: 84: 833: 902: 4.20: 25.2:

165.

3. The environmentally friendly arch support structure suitable for shallow-buried tunnel crossings according to claim 1, characterized in that, The secondary lining (1) includes an inverted arch lining (9) at the bottom of the tunnel, a lower step lining (10) in the middle of the tunnel, and an upper step lining (11) at the top of the tunnel; the steel cages inside the inverted arch lining (9), the lower step lining (10), and the upper step lining (11) are connected in sequence.

4. The environmentally friendly arch support structure suitable for shallow-buried tunnel crossings according to claim 1, characterized in that, The steel cage inside the reinforced concrete arch (4) is fixedly connected to the steel pipe inside the pipe curtain arch (5) near one end of the reinforced concrete arch (4).

5. The environmentally friendly arch support structure suitable for shallow-buried tunnel crossings according to claim 1, characterized in that, The thickness of each layer of backfill in the arched structure (7) is 100mm to 300mm, and the thickness of the first layer of backfill is not less than 300mm.

6. The environmentally friendly arch support structure suitable for shallow-buried tunnel crossings according to claim 1, characterized in that, The maximum particle size of the backfill material used in the arch backfill structure (7) is no more than 60 mm.

7. The environmentally friendly arch support structure suitable for shallow-buried tunnel crossings according to claim 1, characterized in that, The joints of the upper and lower geogrids (8) are staggered, and the staggered distance is not less than 500mm.

8. A construction method for an environmentally friendly arch support structure suitable for shallow-buried tunnel crossings, as described in any one of claims 1-7, characterized in that, Includes the following steps: The pipe curtain arch protection (5) is constructed according to the thickness of the overburden at the top of the tunnel; The tunnel top is covered with soil and the reinforced concrete arch (4) is constructed. The open excavation is carried out until the pipe curtain arch (5) is exposed at both ends. The steel cage is tied between the pipe curtain arch (5) at both ends and the two ends of the steel cage are welded to the pipe curtain arch (5). After the support formwork is supported, the reinforced concrete arch (4) is poured. Excavation and shotcreting of the tunnel upper step area; Excavation and shotcreting of the lower bench area of ​​the tunnel; Excavation of the invert arch and shotcrete application; Waterproofing layer (2) construction; The invert is filled and grouted, and the connecting bars of the support column (6) are reserved during the invert grouted; Construction of support column (6) and secondary lining (1): The steel cages of support column (6) and secondary lining (1) are tied simultaneously and welded to the pipe curtain arch (5); after the support formwork is installed, the support column (6) and secondary lining (1) are poured. For the arch backfilling construction, geotextile reinforced soil is used to backfill the top of the reinforced concrete arch (4) in layers, and bidirectional geogrid (8) is laid between the layers.

9. The construction method for an environmentally friendly arch support structure suitable for shallow-buried tunnel crossings according to claim 8, characterized in that, When the thickness of the soil cover at the top of the tunnel is greater than 8m, the pipe curtain arch protection (5) construction shall be carried out; when the pipe curtain arch protection (5) construction is carried out, it shall be carried out from both sides of the arch top towards the middle in sequence; if the thickness of the soil cover at the top of the tunnel is greater than 8m, the open excavation of the soil cover and the reinforced concrete arch protection (4) construction at the top of the tunnel shall not be carried out.

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