A method for constructing a bridge from a reverse cover-excavation type passing highway

Abstract

This invention relates to the field of road construction technology and discloses a reverse-construction cut-and-cover method for converting a highway into a bridge. The method includes the following steps: construction preparation and half-width closure, integrated pile-column construction, cap beam and superstructure construction, traffic diversion, reverse-construction cut-and-cover of the soil under the bridge, pier appearance treatment, and repeated construction. This invention directly constructs an integrated pile-column structure on the existing road surface, completely eliminating the need for deep foundation pit excavation (over 9 meters). It transforms high-risk deep foundation pit projects into low-risk shallow foundation pit projects, effectively avoiding safety accidents such as foundation pit collapse and roadbed slippage. Simultaneously, it eliminates the interference of deep foundation pit construction on adjacent highways, ensuring the safety of both construction personnel and passing vehicles.

Description

Technical Field

[0001] This invention relates to the field of road construction technology, specifically to a reverse-construction cut-and-cover method for converting a highway into a bridge. Background Technology

[0002] With the rapid development of my country's expressway network, the number of existing expressway reconstruction and expansion projects is increasing. Road-to-bridge conversion is a common engineering form, requiring bridge construction to be completed while ensuring the continued operation of the expressway. The traditional road-to-bridge construction method adopts the excavation-then-construction process, that is, first excavating the existing roadbed to form a deep foundation pit, then constructing the bridge pile foundation, piers and other substructures within the deep foundation pit, followed by the construction of the cap beams, beams and slabs and other superstructures, and finally backfilling the foundation pit.

[0003] However, the excavation-then-construction process has many technical drawbacks: First, the deep foundation pit excavation is close to the half of the highway that is open to traffic, which can easily cause the foundation pit to collapse and the roadbed to slide, posing a major threat to the safety of passing vehicles and construction workers; Second, the deep foundation pit requires a complex support system, and the construction of the cap beam requires high-altitude operations using the clamp method, which is complicated and difficult to carry out; Third, the investment in deep foundation pit support and high-altitude operations is large, and the time required to maintain traffic flow is long, resulting in high construction costs; Fourth, the half-width closure construction has a significant impact on traffic, which can easily cause congestion and affect the efficiency of public travel.

[0004] Therefore, we propose a reverse-construction cut-and-cover method for converting highways into bridges. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned shortcomings and provide a reverse-construction cut-and-cover method for converting highways into bridges.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for constructing a bridge on a reverse-cut / cover-and-cover type highway, comprising the following steps: S1. Construction preparation and half-width closure: The construction highway is measured and verified and geological samples are taken. The construction site is cleared, half of the road is closed as a construction area, and safety guardrails and warning signs are set up. The other half remains open to traffic. S2. Pile and column integrated molding construction: The bridge pier and pile foundation are designed as an integrated structure. The diameter and concrete grade of both are determined. Drilled cast-in-place pile technology is used for construction on closed road surfaces. After drilling, smooth steel pipes are installed as permanent outer formwork for the pier. Then, the steel cage is installed and concrete is poured to form an integrated pile and column. S3. Construction of cap beam and superstructure: Excavate a shallow foundation pit on the top of the pile-column integrated structure, pour the cushion layer and lay the bottom formwork, construct the cap beam and bearing pad stone, then erect the beam slab, construct the bridge deck system and traffic safety facilities. S4. Traffic diversion: After the half of the bridge passes inspection, highway traffic will be diverted to the half of the bridge, and the original half of the road will be closed. S5. Reverse excavation and cover removal of soil under the bridge: The soil under the bridge that is already open to traffic on half of the bridge is removed by a one-time full-section cover excavation and cover removal from top to bottom; S6. Pier appearance treatment: Rust removal, anti-corrosion and painting treatment of exposed smooth steel pipes under the bridge; S7. Repeated construction: Complete the construction of another bridge according to steps 1-6 above to achieve the completion of the entire road-to-bridge conversion project.

[0007] Furthermore, the safety railing is composed of four enclosures, with threaded holes on the bottom sides of both ends of the enclosures. Support legs for supporting the enclosures are threaded through the internal threads of the threaded holes, and supports are fixed to the ends of the support legs located outside the threaded holes.

[0008] Furthermore, the fence has multiple slidably connected baffles 1 inside, each baffle 1 having a slot at its bottom end, and baffles 2 being slidably inserted into the slot. The ends of baffles 2 located outside the slot extend through to the bottom of the fence, and the bottom end of the fence has a sliding groove, in which baffles 2 slide.

[0009] Furthermore, the first stop bar has a sliding groove communicating with the slot. The two ends of the stop bar located inside the slot are fixed with limiting blocks that are slidably inserted into the sliding groove. Both ends of the enclosure are slidably connected to a transmission plate. The middle of the transmission plate has a sliding groove. The first stop bar slides inside the sliding groove. The limiting blocks cooperate with the transmission plate. Multiple mounting blocks that abut against the transmission plate are fixed on the outer sides of both ends of the first stop bar. The top of the enclosure has mounting holes that slidably cooperate with the first stop bar and the mounting blocks.

[0010] Furthermore, the diameter of the first stop bar is greater than the width of the groove opening.

[0011] Furthermore, both ends of the enclosure are provided with lead screws, the threads at both ends of the lead screws are in opposite directions, the transmission plate is threadedly sleeved on the outside of the lead screws, one end of the lead screw is rotatably connected to the inner wall at the bottom of the enclosure, and the other end of the lead screw passes through to the top of the enclosure and is fixed with a toggle block. One end of the toggle block is threaded with a bolt, and the outer side of the lead screw is provided with multiple threaded grooves opened at the top of the enclosure around the lead screw as the center. The bolt is threaded into the adjacent threaded groove.

[0012] Furthermore, the smooth steel pipe is a permanent structure that is not removed after construction, serving as a permanent outer formwork for the pier column to ensure the verticality and appearance quality of the structure.

[0013] Furthermore, the excavation and covering of the soil under the bridge is carried out within a closed area, with specific safety protection measures in place to prevent soil from falling or machinery from colliding with the bridge structure.

[0014] Furthermore, the beam erection is carried out using a dual-machine lifting or bridge erecting machine.

[0015] Furthermore, the site clearing process must confirm that the foundation bearing capacity is above 100 kPa, and that there are no high-voltage lines or other obstacles within 15 meters of the drilling rig's operating area.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention allows for the direct construction of integrated pile and column structures on existing road surfaces, completely eliminating the need for deep foundation pit excavation exceeding 9m. It transforms high-risk deep foundation pit projects into low-risk shallow foundation pit projects, effectively avoiding safety accidents such as foundation pit collapse and roadbed slippage. At the same time, it eliminates the interference of deep foundation pit construction on nearby highways, ensuring the dual safety of construction personnel and passing vehicles.

[0017] 2. This invention transforms high-altitude operations into shallow ground-level foundation pit operations, eliminating the need for high-altitude formwork using clamping methods, reducing construction procedures, and eliminating the need for complex deep foundation pit support structures, further simplifying the construction process and reducing construction difficulty.

[0018] 3. The safety railing of this invention can prevent people from approaching the pile hole. The height of the safety railing can be flexibly adjusted according to the construction environment. A barrier can be set between the safety railing and the ground to prevent external debris or small animals from entering the pile hole through the gap between the safety railing and the ground during construction. When the ground below the safety railing is uneven, the barrier component will adaptively move vertically to adapt to the uneven ground, thus achieving high performance.

[0019] 4. This invention allows construction workers to easily adjust the position of the barrier components according to protection requirements. It is easy to use and allows construction personnel to easily disassemble damaged barrier components for easy maintenance. Attached Figure Description

[0020] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of a safety guardrail used in a reverse-cut-and-cover highway bridge conversion construction method. Figure 2 This is a schematic diagram of the construction barriers used in a reverse-construction cut-and-cover highway-to-bridge conversion method. Figure 3 This is a cross-sectional view of the enclosure used in a reverse-construction cut-and-cover highway-to-bridge conversion construction method. Figure 4 for Figure 2Enlarged structural diagram at point A; Figure 5 for Figure 3 Enlarged structural diagram at point B; Figure 6 for Figure 3 Enlarged structural diagram at point C.

[0021] In the diagram: 1. Enclosure; 2. Threaded hole; 3. Support leg; 4. Support; 5. Stop bar one; 6. Stop bar two; 7. Limiting block; 8. Slide groove; 9. Transmission plate; 10. Sliding groove; 11. Lead screw; 12. Actuating block; 13. Bolt; 14. Threaded groove; 15. Mounting hole; 16. Mounting block. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1: Combination Figure 1 The following is a method for constructing a reverse-cut-and-cover highway bridge in this embodiment: S1. Construction preparation and half-width closure: The construction highway is measured and verified and geological samples are taken. The construction site is cleared and half of the road is closed as a construction area. Safety guardrails and warning signs are set up. The other half is kept open to traffic. Geological sampling is required to clarify the soil layer distribution, bearing capacity and groundwater level to provide a basis for adjusting drilling parameters. S2. Integrated Pile and Column Construction: The bridge pier and pile foundation are designed as an integrated structure. The diameters and concrete grades of both are determined. Drilled cast-in-place piles are constructed on closed road surfaces. After drilling, a smooth steel pipe is installed as the permanent outer formwork of the pier. Then, the reinforcement cage is installed and concrete is poured to form an integrated pile and column. During the drilled cast-in-place pile construction, a 2cm reamer is welded around the drill bit. The diameter of the formed pile hole is the designed pile diameter + 4cm. Low-speed drilling is used within the depth range of the pier. After drilling to the designed depth of the pile bottom, high-speed drilling is used. After drilling, the hole position, diameter, depth, and inclination are checked. The inclination is required to be above 1%, and the pile length is below 500mm. A smooth steel pipe with a wall thickness of 1cm is hoisted as the permanent outer formwork of the pier. The length of the steel pipe covers the entire depth of the pier. It is fixed to the road surface with a φ20mm lifting rod. The top of the steel pipe is flush with the ground. The integrated pile and column reinforcement cage is installed and poured using underwater concrete pouring technology. Friction piles are below 300mm and support piles are below 50mm. S3. Construction of cap beam and superstructure: Excavate a shallow foundation pit at the top of the pile-column integrated structure. The depth of the foundation pit is less than 3.8 meters. The slope excavation method is adopted. The cushion layer is poured and the bottom formwork is laid. The bottom formwork is bamboo plywood. The cap beam and bearing pad stone are constructed. Then the beam slab is erected and the bridge deck system and traffic safety facilities are constructed. S4. Traffic diversion: After the half of the bridge passes inspection, highway traffic will be diverted to the half of the bridge, and the original half of the road will be closed. S5. Reverse excavation and cover-up of soil under bridge: The soil under the bridge of the half-width bridge that has been opened to traffic is removed by one-time full-section cover-up and cover-up from top to bottom. The excavation height is about 5m. After excavation, the top surface of the soil is more than 2m away from the bottom of the beam. The soil cover-up and cover-up operation is carried out in a closed area and special safety protection measures are set up to avoid soil falling or mechanical collision with the bridge structure. S6. Pier Column Appearance Treatment: The exposed smooth steel pipes under the bridge are treated with rust removal, anti-corrosion and coating. After sandblasting to Sa2.5 standard, epoxy zinc-rich primer, epoxy micaceous iron oxide intermediate paint and acrylic aliphatic polyurethane topcoat are applied in sequence to complete the anti-corrosion and coating beautification. The thickness of epoxy zinc-rich primer is more than 60μm, the thickness of epoxy micaceous iron oxide intermediate paint is more than 140μm, and the thickness of acrylic aliphatic polyurethane topcoat is more than 80μm. S7. Repeated construction: Complete the construction of another bridge according to steps 1-6 above to achieve the completion of the entire road-to-bridge conversion project.

[0024] The smooth steel pipe is a permanent structure that will not be removed after construction. It serves as a permanent outer formwork for the pier column to ensure the verticality and appearance quality of the structure.

[0025] The excavation and covering of the soil under the bridge is carried out in a closed area, with special safety protection measures in place to prevent soil from falling or machinery from colliding with the bridge structure.

[0026] The beams and slabs are erected using a dual-machine lifting or bridge erecting machine. During the erection process, the beams are kept stable to avoid collisions with the pile and column structures.

[0027] The site clearing work must be carried out in accordance with the requirement that the foundation bearing capacity is above 100 kPa and that there are no high-voltage lines or other obstacles within 15 meters of the drilling rig's operating area.

[0028] Working Principle: Personnel are trained to familiarize themselves with construction drawings and quality standards. The elevation and pile positions of the existing highway are measured and verified. Geological conditions are sampled and analyzed. Material samples are taken and sent for testing. The site flatness and bearing capacity meet the drilling requirements. Excavation and slag removal routes and on-site vehicle routes are planned. Half of the existing highway is closed as a construction zone, with clear traffic signs and guardrails installed. The other half remains open to ensure uninterrupted highway traffic during construction. A total station is used to determine the legal axis, pile positions are located and marked. The rotary drilling rig is directly positioned on the existing asphalt pavement. The drill rod verticality is corrected, and the rig base is fixed to prevent displacement. A 2cm reamer is welded around the drill bit. The diameter of the formed pile hole is the design pile diameter + 4cm, ensuring smooth installation of the subsequent smooth steel pipe. Low-speed drilling is used within 9 meters of the pier depth to ensure hole position deviation and verticality. After reaching the pier depth, high-speed drilling is used to reach the design pile depth. The hole position, diameter, depth, and inclination are checked, requiring the drilling inclination to be within 1%. For piles less than 500mm in length, with a borehole diameter not less than the designed pile diameter, and sediment thickness meeting specifications, a factory-processed smooth steel pipe with a wall thickness of 1cm and a length covering the full depth of the pier is used. A crane is used to lift the pipe, allowing it to be slowly lowered into the borehole by its own weight. The top of the pipe is flush with the existing road surface. Two φ20mm lifting rods are used to fix the pipe to the road surface. The pipe is a permanent structure and will not be removed; it serves as the outer formwork for the pier to ensure the verticality and appearance quality of the subsequent pier. After cleaning the borehole and installing the reinforcing cage (with the pile foundation and pier reinforcing cage forming an integrated structure), the underwater concrete pouring process is used for the installation of the guide pipe. The concrete grade is uniformly matched to the pile foundation design grade, forming an integrated pile-column structure. After the integrated pile-column concrete reaches the design strength, the pile head is removed, and pile foundation testing is completed. Subsequent construction can only proceed after the test is passed. The excavation line is 10cm below the bottom of the cap beam, using a slope excavation method with an excavation depth of 3 meters.For sections less than 8 meters deep, avoid deep foundation pit construction. Pour a concrete foundation layer for the cap beam, and lay bamboo plywood on the foundation layer as a bottom formwork. Directly construct the cap beam reinforcement, formwork, and concrete pouring on the ground. Complete the construction of the bearing pad stones. Use factory-prefabricated beams and slabs, and erect the beams and slabs using a double-machine lifting or bridge erecting machine. Then, construct the bridge deck paving, guardrails, asphalt paving, corrugated guardrails, signs, and other traffic safety facilities in sequence to ensure that the requirements for highway traffic are met. After the completion of half of the bridge construction, organize the three parties of the highway, the supervision unit, and the construction unit for acceptance. After the acceptance is qualified, the traffic of the existing highway will be diverted to the completed half of the bridge, and the original traffic will be closed. The construction of the other half of the road was carried out in preparation for the excavation of the other half of the bridge, which was already open to traffic. The excavation was carried out in reverse under the existing half of the bridge, using a top-down, full-section, one-time excavation method. The excavation height was approximately 5 meters, and the top surface of the excavated soil was more than 2 meters away from the beam to avoid impacting the bridge structure. The reverse excavation was carried out after traffic diversion, when the original half of the road was closed, so the excavation would not pose a safety hazard to highway traffic. After the excavation under the bridge was completed, the smooth steel pipes outside the piers were exposed. The steel pipes underwent rust removal and grinding, and anti-corrosion treatment using the same design for steel box girders was applied. Finally, an aesthetic coating was applied to ensure the appearance quality of the piers.

[0029] Example 2: Combination Figure 1 , Figure 2 Figure 3 Figure 4 , Figure 5 and Figure 6 This embodiment, based on embodiment 1, further improves upon the following: the safety guardrail consists of four enclosures 1. Threaded holes 2 are provided on the bottom sides of both ends of the enclosures 1. Support legs 3 for supporting the enclosures 1 are threaded through the internal threads of the threaded holes 2. Supports 4 are fixed to the ends of the support legs 3 located outside the threaded holes 2. By setting up a safety guardrail consisting of four enclosures 1 around the pile hole, the outside of the pile hole can be protected, preventing people from approaching the pile hole. The enclosures 1 are supported by the supports 4 and the support legs 3. When construction workers place the enclosures 1 on the construction site, the height of the enclosures 1 can be adjusted according to the placement environment. Rotating the supports 4 causes the support legs 3 to rotate. Through the threaded engagement between the support legs 3 and the threaded holes 2, the support legs 3 and the supports 4 can be vertically displaced, thereby adjusting the height of the enclosures 1. After adjusting the position of the supports 4, bolts or other fasteners can be used to fix the supports 4 to the construction site. At this time, the outside of the pile hole can be protected by the safety guardrail consisting of four enclosures 1.

[0030] The enclosure 1 has multiple sliding stops 5 inside. The bottom end of the stops 5 has a slot, and the stops 6 are slidably inserted into the slot. The end of the stops 6 outside the slot extends to the bottom of the enclosure 1. The bottom end of the enclosure 1 has a groove 8, and the stops 6 slide inside the groove 8. The stops 5 below the enclosure 1 can prevent debris or small animals from entering the pile hole through the gap between the enclosure 1 and the ground during construction. When the ground below the enclosure 1 is uneven, the stops 6 will adaptively move vertically through the sliding cooperation of the slot and the stops 6 to adapt to the uneven ground.

[0031] The first stop bar 5 has a sliding groove communicating with the slot. The end of the second stop bar 6, located inside the slot, is fixed with a limiting block 7 that slides inside the sliding groove. Both ends of the enclosure 1 are slidably connected to transmission plates 9. A sliding groove 10 is formed in the middle of the transmission plate 9. The first stop bar 5 slides inside the sliding groove 10. The limiting block 7 works in conjunction with the transmission plate 9. Multiple mounting blocks 16 that abut against the transmission plates 9 are fixed to the outer sides of both ends of the first stop bar 5. The top of the enclosure 1 has mounting holes 15 that slide in conjunction with the first stop bar 5 and the mounting blocks 16. When construction workers install the enclosure 1, the two transmission plates 9 move towards each other. When the displaced transmission plate 9 abuts against the limiting block 7, the displaced transmission plate... 9 will cause the limiting block 7 and the second stop bar 6 to move vertically. When the second stop bar 6 enters the enclosure 1, the construction personnel can easily install the enclosure 1. This avoids the second stop bar 6 interfering with the construction personnel's installation of the enclosure 1. After the enclosure 1 is installed, the two transmission plates 9 will move away from each other. As the transmission plates 9 move, the limiting block 7 and the second stop bar 6 will fall naturally. At this time, the naturally falling second stop bar 6 can adapt to the uneven ground. When the two transmission plates 9 move away from each other and abut against the mounting block 16, the mounting block 16 is fixed inside the enclosure 1 by the transmission plates 9. At this time, the positions of the first stop bar 5 and the second stop bar 6 are fixed.

[0032] When the positions of stop lever 5 and stop lever 6 need to be adjusted, the two transmission plates 9 move towards each other. After the two transmission plates 9 separate from the adjacent mounting block 16, stop lever 5 and stop lever 6 can be pushed. Through the sliding engagement of stop lever 5 with the enclosure 1, through the sliding engagement of stop lever 5 with the sliding groove 10, and through the sliding engagement of stop lever 6 with the sliding groove 8, stop lever 5 and stop lever 6 are moved, and their positions can be adjusted. After the positions of stop lever 5 and stop lever 6 are adjusted, the two transmission plates 9 move away from each other. When the two moving transmission plates 9 abut against the mounting block 16, the mounting block 16 is fixed inside the enclosure 1 by the transmission plates 9. At this time, the positions of stop lever 5 and stop lever 6 are fixed. When a stop lever 5 inside the enclosure 1 is damaged and needs to be disassembled, the two transmission plates 9 move away from each other. When the two transmission plates 9 separate from the adjacent mounting blocks 16, they can push the corresponding stop rods 1-5 and 2-6. Through the sliding engagement of stop rod 1-5 with the enclosure 1, the sliding engagement of stop rod 1-5 with the sliding groove 10, and the sliding engagement of stop rod 2-6 with the sliding groove 8, stop rods 1-5 and 2-6 are moved. When the stop rods 1-5 and 2-6 that need to be replaced correspond to the mounting holes 15, stop rods 1-5 and 2-6 are rotated. When the mounting block 16 on stop rod 1-5 corresponds to the mounting holes 15, stop rods 1-5 and 2-6 can be pushed. Through the sliding engagement of stop rod 1-5 with the sliding groove 10, the sliding engagement of stop rod 2-6 with the sliding groove 8, and the sliding engagement of stop rod 1-5 with the mounting block 16 and the mounting holes 15, stop rods 1-5 and 2-6 are moved vertically. At this time, the damaged stop rods 1-5 and 2-6 can be removed from the enclosure 1.

[0033] The diameter of the stop bar 5 is greater than the width of the groove opening of the slide 8. By using the stop bar 5, whose diameter is greater than the width of the groove opening of the slide 8, the stop bar 5 can be prevented from entering the interior of the slide 8.

[0034] Both ends of the enclosure 1 are equipped with lead screws 11, with opposite thread directions at both ends. A transmission plate 9 is threaded onto the outside of the lead screws 11. One end of the lead screw 11 is rotatably connected to the inner wall at the bottom of the enclosure 1, and the other end of the lead screw 11 extends through to the top of the enclosure 1 and is fixed with a lever block 12. One end of the lever block 12 is threaded with a bolt 13. Multiple threaded grooves 14 are provided circumferentially around the lead screw 11 on the outer side of the lead screw 11, located at the top of the enclosure 1. The bolts 13 are threaded into adjacent threaded grooves 14. The lead screw 11 can be locked by the threaded engagement of the bolts 13 and the threaded grooves 14. When adjustment of the transmission plate 9 is required... When the position of the movable plate 9 is adjusted, the rotatable bolt 13 can be rotated. Through the threaded engagement between the bolt 13 and the threaded groove 14, the bolt 13 is moved. After the bolt 13 is disengaged from the threaded groove 14, the movable block 12 can be rotated, causing the lead screw 11 to rotate. Through the threaded engagement between the lead screw 11 and the transmission plate 9, the transmission plate 9 is moved towards or away from each other. After the position of the transmission plate 9 is adjusted, the bolt 13 can be rotated. Through the threaded engagement between the bolt 13 and the threaded groove 14, the bolt 13 is moved. When the bolt 13 enters the adjacent threaded groove 14, the lead screw 11 is locked, and the position of the transmission plate 9 is fixed.

[0035] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for constructing a reverse-cut-and-cover type highway bridge, characterized in that: Includes the following steps: S1. Construction preparation and half-width closure: The construction highway is measured and verified and geological samples are taken. The construction site is cleared, half of the road is closed as a construction area, and safety guardrails and warning signs are set up. The other half remains open to traffic. S2. Pile and column integrated molding construction: The bridge pier and pile foundation are designed as an integrated structure. The diameter and concrete grade of both are determined. Drilled cast-in-place pile technology is used for construction on closed road surfaces. After drilling, smooth steel pipes are installed as permanent outer formwork for the pier. Then, the steel cage is installed and concrete is poured to form an integrated pile and column. S3. Construction of cap beam and superstructure: Excavate a shallow foundation pit on the top of the pile-column integrated structure, pour the cushion layer and lay the bottom formwork, construct the cap beam and bearing pad stone, then erect the beam slab, construct the bridge deck system and traffic safety facilities. S4. Traffic diversion: After the half of the bridge passes inspection, highway traffic will be diverted to the half of the bridge, and the original half of the road will be closed. S5. Reverse excavation and cover removal of soil under the bridge: The soil under the bridge that is already open to traffic on half of the bridge is removed by a one-time full-section cover excavation and cover removal from top to bottom; S6. Pier appearance treatment: Rust removal, anti-corrosion and painting treatment of exposed smooth steel pipes under the bridge; S7. Repeated construction: Complete the construction of another bridge according to steps 1-6 above to achieve the completion of the entire road-to-bridge conversion project.

2. The method for constructing a reverse-cut-and-cover type highway bridge as described in claim 1, characterized in that: The safety railing is composed of four enclosures (1). Threaded holes (2) are provided on the bottom side of both ends of the enclosures (1). Support legs (3) for supporting the enclosures (1) are threaded through the inside of the threaded holes (2). Supports (4) are fixed at the ends of the support legs (3) located outside the threaded holes (2).

3. The method for constructing a reverse-cut-and-cover type highway bridge as described in claim 2, characterized in that: The enclosure (1) has multiple first-bars (5) slidably connected inside. The bottom end of the first-bars (5) has a slot. The second-bars (6) are slidably inserted inside the slot. The end of the second-bars (6) located outside the slot extends through to the bottom of the enclosure (1). The bottom end of the enclosure (1) has a groove (8). The second-bars (6) slide inside the groove (8).

4. The method for constructing a reverse-cut-and-cover type highway bridge as described in claim 3, characterized in that: The first stop bar (5) has a sliding groove communicating with the slot. The end of the second stop bar (6) located inside the slot is fixed with a limiting block (7) that is slidably inserted into the sliding groove. Both ends of the enclosure (1) are slidably connected to a transmission plate (9). The middle part of the transmission plate (9) has a sliding groove (10). The first stop bar (5) slides inside the sliding groove (10). The limiting block (7) works in cooperation with the transmission plate (9). Multiple mounting blocks (16) that abut against the transmission plate (9) are fixed on the outer sides of both ends of the first stop bar (5). The top of the enclosure (1) has a mounting hole (15) that slides in cooperation with the first stop bar (5) and the mounting block (16).

5. The method for constructing a reverse-cut-and-cover type highway bridge as described in claim 3, characterized in that: The diameter of the stop bar (5) is greater than the width of the groove (8).

6. The method for constructing a reverse-cut-and-cover type highway bridge as described in claim 4, characterized in that: Both ends of the enclosure (1) are provided with lead screws (11), and the threads at both ends of the lead screws (11) are opposite. The transmission plate (9) is threaded onto the outside of the lead screws (11). One end of the lead screws (11) is rotatably connected to the inner wall at the bottom of the enclosure (1). The other end of the lead screws (11) extends through to the top of the enclosure (1) and is fixed with a toggle block (12). One end of the toggle block (12) is threaded with a bolt (13). The outer side of the lead screws (11) is provided with multiple threaded grooves (14) opened at the top of the enclosure (1) around the lead screws (11). The bolts (13) are threaded into the adjacent threaded grooves (14).

7. The method for constructing a reverse-cut-and-cover type highway bridge as described in claim 1, characterized in that: The smooth steel pipe is a permanent structure that will not be removed after construction. It serves as a permanent outer formwork for the pier column to ensure the verticality and appearance quality of the structure.

8. The method for constructing a reverse-cut-and-cover type highway bridge as described in claim 1, characterized in that: The excavation and covering of the soil under the bridge is carried out in a closed area, with special safety protection measures in place to prevent soil from falling or machinery from colliding with the bridge structure.

9. The method for constructing a reverse-cut-and-cover type highway bridge as described in claim 1, characterized in that: The beams and slabs are erected using a dual-machine lifting system or a bridge erecting machine.

10. The method for constructing a reverse-cut-and-cover type highway bridge as described in claim 1, characterized in that: The site clearing work must be carried out in accordance with the requirement that the foundation bearing capacity is above 100 kPa and that there are no high-voltage lines or other obstacles within 15 meters of the drilling rig's operating area.

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