An arch bridge structure for a tunnel spanning a giant karst cave and its backfilling and injection molding construction method

Abstract

Disclosed is a backfilling and injection molding construction method for an arch bridge structure spanning a giant karst cave in a tunnel, comprising the following steps: performing surcharge preloading and grouting reinforcement on the foundation; forming a ground mold on the upper surface of the foundation; processing and binding steel bars and installing them on the ground mold; pouring to form two arch abutments at opposite ends of the foundation along the extension direction of the tunnel; segmentally pouring to form an arch ring above the ground mold; the arch ring comprises a plurality of arch ring units, a first construction joint is provided between adjacent arch ring units, and a pier is provided below the first construction joint; performing layered backfilling construction above the arch ring. The arch bridge structure spanning a giant karst cave in a tunnel and its backfilling and injection molding construction method provided in this specification can reduce the construction difficulty, simplify the construction process, and have both practicability and high efficiency.

Description

Technical Field

[0001] This specification relates to the technical field of tunnel construction, and particularly to an arch bridge structure for a tunnel spanning a giant karst cave and its backfilling and injection molding construction method. Background Art

[0002] During the construction process of tunnel excavation, karst caves may be encountered, resulting in a situation of a bottom cavity. Currently, the commonly used treatment methods include backfilling and reinforcement of the tunnel bottom and spanning with a pile-raft structure. However, due to the possibility of loss of the tunnel bottom filling material and the high requirements of the ballastless track of high-speed railways for foundation settlement, these two methods have certain limitations. For karst caves with high settlement requirements and relatively deep depths, the arch bridge spanning method can be used. However, due to the narrow construction space in the tunnel, it is difficult for large machinery and precast components to enter the site, resulting in low construction efficiency of the bridge in the tunnel. The traditional support erection method is difficult and it is difficult to ensure construction safety. Therefore, there are many aspects of the construction method of the arch bridge in the tunnel that need to be optimized urgently.

[0003] The patent with publication number CN111851252A, "A Steel-Concrete Composite Arch Bridge for Spanning Karst Caves in a Tunnel and Its Construction Method", discloses an arch bridge-supported tunnel structure and construction method. However, this method uses steel sections spliced arch ribs as the main support structure and pours concrete arch ribs on the steel section arch ribs. Its arch bridge structure has many components, the splicing is cumbersome, and the construction process is complex. Moreover, in a tunnel with a narrow construction space, there is also the problem that it is difficult for the splicing machinery and prefabricated products to enter the site, and the application conditions are relatively limited. The patent with publication number CN114607420A, "An Integral Arch-Tunnel Structure for Spanning Large Karst Caves in a Tunnel", discloses an integral arch-tunnel structure for spanning large karst caves in a tunnel. This invention mainly optimizes the connection between the tunnel lining and the arch bridge and the structural waterproofing and drainage, and does not involve the problem of difficult construction of the arch bridge structure. Summary of the Invention

[0004] In view of the deficiencies of the prior art, an object of this specification is to provide an arch bridge structure for a tunnel spanning a giant karst cave and its backfilling and injection molding construction method, which can reduce the construction difficulty, simplify the construction procedure, and have both practicality and high efficiency.

[0005] To achieve the above object, an embodiment of this specification provides a backfilling and injection molding construction method for an arch bridge structure of a tunnel spanning a giant karst cave, including the following steps:

[0006] Perform surcharge preloading and grouting reinforcement on the foundation;

[0007] Form a ground mold on the upper surface of the foundation;

[0008] Process and bind steel bars and install them on the ground mold;

[0009] Pour and form two arch seats at opposite ends of the foundation along the extension direction of the tunnel;

[0010] Cast in segments to form an arch ring above the ground formwork; the arch ring includes a plurality of arch ring units, a first construction joint is provided between adjacent arch ring units, and a pier is provided below the first construction joint;

[0011] Backfill and construct in layers above the arch ring.

[0012] As a preferred embodiment, in the step of preloading and grouting and reinforcing the base, the preloading time is greater than or equal to 48h, and the preloading load is greater than or equal to 1.1 times the weight of the arch ring.

[0013] As a preferred embodiment, between the step of preloading and grouting and reinforcing the base and the step of forming the ground formwork, there is also a step: measuring and setting out on the upper surface of the base to determine the bottom contour line of the arch bridge.

[0014] As a preferred embodiment, in the step of forming the ground formwork, the number of segments of the ground formwork construction is equal to the number of arch ring units; when constructing each segment of the ground formwork, use an excavator to correct the ground, after passing the formwork erection acceptance, pour concrete with a predetermined thickness, and then perform form removal maintenance and treatment of the second construction joint; after the ground formwork construction is completed, sprinkle water for moisture conservation and maintenance, and after the strength reaches 75% of the design strength, perform the step of processing and tying steel bars.

[0015] As a preferred embodiment, the step of processing, tying steel bars and installing them on the ground formwork includes:

[0016] Tie the inner steel bars, and install protective layer pads between the ground formwork and the inner steel bars;

[0017] Lay out the steel bar skeleton, and then tie the outer steel bars and stirrups in sequence.

[0018] As a preferred embodiment, the step of casting to form two arch seats at opposite ends of the base along the extension direction of the tunnel includes:

[0019] Embed cold water pipes;

[0020] Cast the arch seats in horizontal layers symmetrically, and the casting process is continuous.

[0021] As a preferred embodiment, in the step of casting in segments to form an arch ring above the ground formwork, six first construction joints are provided, a closure section is provided in the middle of the arch ring, and the length of the pier in the extension direction is 10 - 15m.

[0022] As a preferred embodiment, in the step of layered backfilling construction, the height of each layer matches the position of the steel support structure in the foundation pit excavation, and the layering is divided into three layers.

[0023] The embodiment of the present application further provides an arch bridge structure for a tunnel to cross a giant karst cave, including:

[0024] A foundation base that has been subjected to surcharge preloading and grouting reinforcement;

[0025] Two abutments located at opposite ends of the foundation base along the extension direction of the tunnel;

[0026] A ground mold disposed above the foundation base and between the two abutments;

[0027] An arch ring located above the ground mold, the arch ring includes a plurality of arch ring units formed by segmented pouring, a first construction joint is provided between adjacent arch ring units, and a pier is provided below the first construction joint;

[0028] A layered backfilling structure located above the arch ring.

[0029] As a preferred embodiment, the foundation base includes a plurality of grouting units uniformly arranged perpendicular to the extension direction, each grouting unit includes a plurality of grouting holes extending vertically and uniformly arranged along the extension direction, and the grouting holes of adjacent grouting units are staggered.

[0030] Advantageous effects:

[0031] The backfilling and casting construction method of the arch bridge structure for a tunnel to cross a giant karst cave provided by this embodiment performs surcharge preloading and grouting reinforcement on the foundation base, then forms a ground mold on the upper surface of the foundation base, binds steel bars relying on the ground mold and then constructs the abutments. After the abutments meet the strength requirements, the arch ring is cast in segments, and finally the backfilling above the arch is completed to finish the construction of the arch bridge. This can reduce the construction difficulty, simplify the construction procedure, and has both practicality and high efficiency. This backfilling and casting construction method is applicable to the construction environment of a karst cave tunnel with a small space. By using a foundation base that has been subjected to surcharge preloading and grouting reinforcement and constructing a ground mold, the construction safety is fully ensured and the construction quality is guaranteed; forming the arch ring by segmented pouring can effectively avoid the difficulty of large precast formwork entering the site, thereby reducing the construction difficulty and construction cost.

[0032] Referring to the following description and the accompanying drawings, specific embodiments of the present invention are disclosed in detail, indicating the ways in which the principles of the present invention can be adopted. It should be understood that the embodiments of the present invention are not limited in scope thereby.

[0033] Features described and / or illustrated for one embodiment can be used in the same or similar way in one or more other embodiments, combined with the features in other embodiments, or replace the features in other embodiments.

[0034] It should be emphasized that the term "comprising / including", as used herein, refers to the presence of features, whole units, steps or components, but does not exclude the presence or addition of one or more other features, whole units, steps or components. Description of the Drawings

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those skilled in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0036] Figure 1 It is a step flow chart of an arch bridge structure for a tunnel to cross a giant karst cave and its backfill injection molding construction method provided in this embodiment;

[0037] Figure 2 It is a longitudinal section structure diagram of an arch bridge structure for a tunnel to cross a giant karst cave and a tunnel provided in this embodiment;

[0038] Figure 3 It is a plan layout diagram of the positions of grouting holes provided in this embodiment;

[0039] Figure 4 It is an elevation view of a ground mold provided in this embodiment;

[0040] Figure 5 It is a longitudinal section view of half an arch ring provided in this embodiment;

[0041] Figure 6 It is a longitudinal section view of a segmented arch ring provided in this embodiment;

[0042] Figure 7 It is an elevation view of a layered backfill structure provided in this embodiment.

[0043] Explanation of the Reference Numerals in the Drawings:

[0044] 1. Tunnel lining; 2. Top surface of the inner rail; 3. Foundation; 4. Grouting hole; 5. Abutment; 6. Arch ring; 7. Layered backfill structure; 8. Horse path; 9. Tunnel floor; 10. Ground mold; 11. First construction joint; 12. Pier. Detailed Embodiment

[0045] To enable those skilled in the art to better understand the technical solutions in the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0046] It should be noted that when an element is referred to as being "disposed on" another element, it can be directly on the other element or there can also be another element in the middle. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be another element in the middle at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are only for the purpose of illustration and do not represent the only implementation manner.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the description of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0048] Please refer to Figure 1 . The embodiments of the present application provide a backfill injection molding construction method for an arch bridge structure spanning a giant karst cave in a tunnel, including the following steps:

[0049] Step S10: Perform surcharge preloading and grouting reinforcement on the foundation base 3.

[0050] Among them, the foundation base 3 is the foundation after the foundation pit excavation is completed and is located below the arch ring 6. Performing surcharge preloading and grouting reinforcement on the foundation base 3, that is, performing reinforcement treatment on the foundation base 3, can limit the foundation settlement and ensure the construction accuracy of the arch ring 6.

[0051] In step S10, the preloading time is greater than or equal to 48h, and the preloading load is greater than or equal to 1.1 times the weight of the arch ring 6. Grouting reinforcement can use Ф110 PVC perforated pipes with a length of 8m for grouting. As Figure 2 and Figure 3 shown, the longitudinal section and plane layout of the grouting holes 4 are presented. The grouting holes 4 use Ф130 drill pipes, with a transverse spacing of 4.9m and a longitudinal spacing of 4.36m, arranged in a plum blossom pattern. Among them, the longitudinal direction refers to the extension direction of the tunnel, and the transverse direction is perpendicular to the longitudinal direction and parallel to the horizontal plane.

[0052] Specifically, the base 3 includes a plurality of grouting units uniformly arranged along a direction perpendicular to the extension direction, that is, Figure 3 Each horizontal row of grouting holes 4 constitutes a grouting unit. The grouting unit includes a plurality of grouting holes 4 extending in the vertical direction and uniformly arranged along the extending direction. The grouting holes 4 of adjacent grouting units are staggered, and the grouting holes 4 of two grouting units separated by one grouting unit are aligned, so that the reinforcement effect can be better.

[0053] Step S30 : forming a ground mold 10 on the upper surface of the substrate 3 .

[0054] Wherein, step S20 may be further included between step S10 and step S30: measuring and setting out the upper surface of the base 3 to determine the bottom contour of the arch bridge.

[0055] In step S20, the arch bridge control points and elevations are laid out on the upper surface of the base 3, and the surveying personnel conduct surveying and laying out instructions to the construction team. The construction personnel mark the bottom contour of the arch bridge with ink lines based on the control points.

[0056] In step S30, Figure 4 As shown, 20cm thick concrete can be used for construction to form the ground formwork 10. The number of sections of the ground formwork 10 is equal to the number of the arch ring units. A second construction joint is provided between each section of the ground formwork 10. When constructing each section of the ground formwork 10, an excavator is used to correct the ground, and after the formwork is accepted, concrete of a predetermined thickness is poured, and then the formwork is removed for maintenance and the second construction joint treatment is carried out. Specifically, the excavator corrects the first section of the ground, and after the formwork is accepted, the first section of 20cm thick concrete is poured, and then the formwork is removed for maintenance and the second construction joint treatment is carried out, and then the second section of the road surface is corrected, and the above steps are repeated until the construction of the ground formwork 10 is completed. After the construction of the ground formwork 10 is completed, water is sprinkled for moisturizing and maintenance. After the strength reaches 75% of the design strength, the following steps of processing and binding steel bars are carried out.

[0057] Step S40: Process and tie the steel bars and install them on the ground formwork 10.

[0058] Among them, the required steel bars are transported to the site and processed according to the design drawings. After the construction of the ground formwork 10 is completed, the steel bars of the arch ring 6 are hoisted. Specifically, the steel bars are centrally cut and processed in the steel bar processing shed, and the cutting, processing, and various steel bar positions and specifications are strictly guaranteed according to the requirements of the design drawings. The present invention adopts a construction method of first constructing the ground formwork 10 and then tying the steel bars. After the construction of the ground formwork 10 is completed, the main bars are extended and the stirrups are installed.

[0059] Step S40 may specifically include: tying the inner steel bars and installing protective layer cushion blocks between the ground mold 10 and the inner steel bars; arranging the steel bar framework, and then successively tying the outer steel bars and stirrups. When tying the inner steel bars, the protective layer cushion blocks are installed synchronously. The protective layer cushion blocks can be made of C55 concrete and have a height of 4 cm. During the process of steel bar tying, the spacing between the main bars and stirrups is strictly controlled, and the thickness of the steel bar framework is controlled according to the thickness of the arch bridge.

[0060] Step S50: Pour and form two arch seats 5 at opposite ends of the base 3 along the extension direction of the tunnel.

[0061] Among them, after the steel bar construction of the arch ring 6 is completed, the construction of the arch seat 5 (i.e., step S50) is carried out under the condition that the deformation of the surrounding rock and the initial support is basically stable. In step S50, before pouring the concrete of the arch seat 5, cold water pipes are pre-buried to reduce the influence of the hydration heat of the mass concrete. Subsequently, the concrete is used to pour the arch seat 5 in a horizontal layered and symmetric manner. The pouring process of the arch seat 5 needs to be continuous to avoid cold joints caused by stoppages. If the intermittent time exceeds 2 h, it shall be treated as a construction joint. The arch seat 5 of the open-cut stepped concrete foundation can be adopted, and it is directly excavated by trenching and then cast in place.

[0062] Step S60: Pour in sections to form the arch ring 6 above the ground mold 10.

[0063] Among them, the arch ring 6 is formed by segmental in-situ casting construction of C55 reinforced concrete. The arch ring 6 includes a plurality of arch ring units, and a first construction joint 11 is provided between adjacent arch ring units. As Figure 5 and Figure 6 shown, six first construction joints 11 can be set. A closure section can be set in the middle of the arch ring 6, and the length of the closure section along the extension direction can be 2 m. A pier 12 is provided below the first construction joint 11. The material of the pier 12 can be C55 concrete, and the length of the pier 12 in the extension direction is 10 - 15 m. Preferably, the length of the pier 12 in the extension direction is 13 m. The plurality of arch ring units are disconnected by partitions at the first construction joint 11, and the deformation joint can be filled with asphalt hemp floss. The arch ring 6 in this embodiment is formed of reinforced concrete.

[0064] Step S70: Backfill and construct in layers above the arch ring 6.

[0065] Among them, after the construction of the arch ring 6 is completed, backfill construction of the superstructure of the arch is required to form a layered backfill structure 7. The amount of backfill concrete is large and the strength is high, and it cannot be constructed at one time. Therefore, the backfill is constructed in layers as Figure 7 shown. The layered height is set in combination with the layout position of the steel support structure for foundation pit excavation. For example, Figure 7There is a first steel support structure and a second steel support structure, so the layered backfill structure 7 is poured in three layers. The layered backfill structure 7 can be made of C35 reinforced concrete.

[0066] As Figure 1 shown, the top surface of the layered backfill structure 7 is flush with the top surface of the tunnel floor 9. Above the tunnel floor 9 are the top surface of the inner rail 2 and the tunnel lining 1. On the sides of the layered backfill structure 7 and the tunnel floor 9 is a ramp 8. The lowest point of the ramp 8 is above the lowest point of the layered backfill structure 7, and the top surface of the ramp 8 is flush with the top surface of the tunnel floor 9.

[0067] The backfill casting construction method of the arch bridge structure for a tunnel spanning a giant karst cave provided by this embodiment mainly aims at the treatment of the bottom cavity when the tunnel spans the karst cave. The foundation 3 is preloaded and grouted for reinforcement, and then a ground mold 10 is formed on the upper surface of the foundation 3. After tying the steel bars relying on the ground mold 10, the arch seat 5 is constructed. After the arch seat 5 meets the strength, the arch ring 6 is cast in segments. Finally, the backfill above the arch is completed to finish the construction of the arch bridge, which can reduce the construction difficulty, simplify the construction procedure, and has both practicability and high efficiency. This backfill casting construction method is applicable to the construction environment of karst cave tunnels with small spaces. By using the foundation 3 that has been preloaded and grouted for reinforcement and constructing the ground mold 10, the construction safety is fully guaranteed and the construction quality is ensured; the arch ring 6 is formed by segmented casting, which can effectively avoid the difficulty of large precast formwork entering the site, thereby reducing the construction difficulty and construction cost.

[0068] In this embodiment, after steps S60 and S70, the concrete surface should be kept moist at all times for curing the concrete. After step S70, the karst cave cavity outside the scope of the tunnel retaining wall is backfilled with waste slag in layers from low to high. For the part that cannot be filled with waste slag near the top of the cave, pumped C20 concrete is used to fill it.

[0069] Based on the same concept, an arch bridge structure for a tunnel spanning a giant karst cave is also provided in an embodiment of the present invention, as described in the following embodiment. Since the principle of solving problems and the technical effects that can be achieved by this arch bridge structure are similar to those of the backfill casting construction method of the arch bridge structure for a tunnel spanning a giant karst cave described above, the implementation of this arch bridge structure can refer to the implementation of the above backfill casting construction method, and the repeated parts will not be elaborated.

[0070] An embodiment of the present invention further provides an arch bridge structure for a tunnel to span a giant karst cave, including a foundation base 3 that has been preloaded and grouted for reinforcement, two arch abutments 5 located at opposite ends of the foundation base 3 along the extension direction of the tunnel, a ground formwork 10 arranged above the foundation base 3 and between the two arch abutments 5, an arch ring 6 located above the ground formwork 10, and a layered backfill structure 7 located above the arch ring 6. The arch ring 6 includes a plurality of arch ring units formed by segmented casting, and a first construction joint 11 is provided between adjacent arch ring units, and a pier 12 is provided below the first construction joint 11.

[0071] The foundation base 3 is backfilled and preloaded and grouted for reinforcement to form a construction working surface for the main structure of the arch bridge (i.e., the ground formwork 10 and the arch ring 6), and has a certain supporting effect on the main structure. The cast-in-place arch ring 6 constructed based on the ground formwork 10 arranged on the foundation base 3 has good integrity, simple construction, no redundant connecting components, and meets the supporting strength requirements of the arch ring 6.

[0072] It should be noted that in the description of this specification, terms such as "first" and "second" are only used for descriptive purposes and to distinguish similar objects, and there is no sequential order between the two, nor can it be understood as indicating or implying relative importance. In addition, in the description of this specification, unless otherwise stated, the meaning of "a plurality" is two or more.

[0073] Any numerical value cited herein includes all values increasing in units of one from the lower value to the upper value between the lower limit value and the upper limit value, provided that there is an interval of at least two units between any lower value and any higher value. For example, if the value of the quantity of a component or a process variable (such as temperature, pressure, time, etc.) is stated as ranging from 1 to 90, preferably from 20 to 80, and more preferably from 30 to 70, it is intended to illustrate that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32, etc. are also explicitly listed in this specification. For values less than 1, a unit is appropriately considered to be 0.0001, 0.001, 0.01, 0.1. These are merely examples of what is intended to be clearly expressed, and it can be considered that all possible combinations of the numerical values listed between the lowest value and the highest value are explicitly set forth in this specification in a similar manner.

[0074] Unless otherwise stated, all ranges include the endpoints and all the numbers between the endpoints. "About" or "approximate" used in conjunction with a range applies to both endpoints of the range. Thus, "about 20 to 30" is intended to cover "about 20 to about 30", including at least the specified endpoints.

[0075] All articles and references disclosed, including patent applications and publications, are incorporated herein by reference for various purposes. The term "consisting essentially of" in describing a combination shall include the identified elements, ingredients, components or steps as well as other elements, ingredients, components or steps that do not materially affect the basic novel characteristics of the combination. The use of the terms "comprising" or "including" to describe the combinations of elements, ingredients, components or steps herein also contemplates embodiments consisting essentially of these elements, ingredients, components or steps. By using the term "may" herein, it is intended that any of the attributes described as "may" include are optional.

[0076] A plurality of elements, ingredients, components or steps can be provided by a single integrated element, ingredient, component or step. Alternatively, a single integrated element, ingredient, component or step can be separated into discrete plural elements, ingredients, components or steps. The disclosure of "a" or "an" to describe an element, ingredient, component or step does not mean to exclude other elements, ingredients, components or steps.

[0077] It should be understood that the above description is for purposes of illustration and not of limitation. Many embodiments and many applications other than the examples provided will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of the present teachings should not be determined with reference to the above description, but should be determined with reference to the appended claims and the full scope of equivalents to which those claims are entitled. For the sake of completeness, all articles and references including patent applications and published disclosures are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein from the foregoing claims is not a waiver of that subject matter, nor should it be considered that the inventor did not consider that subject matter to be part of the disclosed inventive subject matter.

Claims

1. A backfill injection molding construction method for an arch bridge structure spanning a giant karst cave in a tunnel, characterized in that, It includes the following steps: Perform surcharge preloading and grouting reinforcement on the foundation; Form a ground mold on the upper surface of the foundation; Fabricate and bind steel bars and install them on the ground mold; Pour and form two arch abutments at opposite ends of the foundation along the extension direction of the tunnel; Pour in sections to form an arch ring above the ground mold; the arch ring includes a plurality of arch ring units, and a first construction joint is provided between adjacent arch ring units, and a pier is provided below the first construction joint; Backfill and construct in layers above the arch ring; In the step of forming the ground mold, the number of segments of the ground mold construction is equal to the number of arch ring units; when constructing each segment of the ground mold, use an excavator to correct the ground, after passing the formwork erection acceptance, pour concrete with a predetermined thickness, and then perform formwork removal maintenance and second construction joint treatment; after the ground mold construction is completed, sprinkle water for moisture conservation maintenance, and after the strength reaches 75% of the design strength, perform the step of fabricating and binding steel bars; The foundation includes a plurality of grouting units uniformly arranged perpendicular to the extension direction, and each grouting unit includes a plurality of grouting holes extending vertically and uniformly arranged along the extension direction, and the grouting holes of adjacent grouting units are staggered; 2. The backfill injection molding construction method according to claim 1, characterized in that In the step of performing surcharge preloading and grouting reinforcement on the foundation, the preloading time is greater than or equal to 48h, and the preloading load is greater than or equal to 1.1 times the weight of the arch ring; 3. The backfill injection molding construction method according to claim 1, characterized in that Between the step of performing surcharge preloading and grouting reinforcement on the foundation and the step of forming the ground mold, there is also a step: perform measurement and lofting on the upper surface of the foundation to determine the bottom contour line of the arch bridge; 4. The backfill injection molding construction method according to claim 1, characterized in that The step of fabricating and binding steel bars and installing them on the ground mold includes: Bind the inner steel bars, and install protective layer pads between the ground mold and the inner steel bars; Layout the steel bar cage, and then bind the outer steel bars and stirrups in sequence; 5. The backfill injection molding construction method according to claim 1, characterized in that, The step of pouring and forming two arch abutments at opposite ends of the foundation along the extension direction of the tunnel includes: Embed cold water pipes; Pour the arch abutment in horizontal layers symmetrically, and the pouring process is continuous; 6. The backfill injection molding construction method according to claim 1, characterized in that, In the step of pouring in sections to form an arch ring above the ground mold, six first construction joints are provided, a closure section is provided in the middle of the arch ring, and the length of the pier in the extension direction is 10 - 15m; 7. The backfill injection molding construction method according to claim 1, characterized in that, In the step of backfilling and constructing in layers, the height of each layer matches the position of the steel support structure for foundation pit excavation, and the layers are divided into three layers; 8. An arch bridge structure for a tunnel to cross a giant karst cave, characterized in that, It includes: A foundation that has undergone surcharge preloading and grouting reinforcement; Two arch abutments at opposite ends of the foundation along the extension direction of the tunnel; A ground mold disposed above the foundation and between the two arch abutments; An arch ring located above the ground mold, the arch ring includes a plurality of arch ring units cast in sections, a first construction joint is provided between adjacent arch ring units, and a pier is provided below the first construction joint; A layered backfill structure located above the arch ring; the foundation includes a plurality of grouting units uniformly arranged perpendicular to the extension direction, and each grouting unit includes a plurality of grouting holes extending vertically and uniformly arranged along the extension direction, and the grouting holes of adjacent grouting units are staggered.

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