Construction method of tunnel portal assembly type canopy based on BIM technology

Abstract

The present application relates to the technical field of tunnel portal canopy, more specifically, it relates to a tunnel portal assembly type canopy construction method based on BIM technology, comprising the following steps: S1, constructing a BIM model and deepening drawing design; S2, precasting canopy components; S3, U-shaped groove structure construction and pre-embedding of canopy column foundation reinforcement; S4, canopy installation; S5, column foot sealing mold and grouting; S6, hoisting horizontal and vertical beams; S7, column head and beam upper iron construction; S8, hoisting side beams and double T plates; S9, pouring post-poured concrete construction; S10, canopy top waterproof layer construction. This method greatly improves construction safety, greatly reduces construction risk level, and ensures the operation safety of the operating line. The present application is mainly applied to the construction of tunnel portal canopy.

Description

Technical Field

[0001] This invention relates to the field of tunnel entrance canopy technology, and more specifically, to a construction method for prefabricated tunnel entrance canopies based on BIM technology. Background Technology

[0002] With the continuous development of my country's transportation industry, tunnel engineering has become an essential structural design in mountainous areas. At the tunnel entrance, canopy structures are constructed. Traditional canopy construction uses cast-in-place technology, requiring scaffolding. Conventional cast-in-place construction methods require the scaffolding to be erected only after the concrete strength of the U-shaped channel bottom slab and sidewalls reaches the standard, followed by operations such as column, beam, and slab formwork, beam and slab reinforcement binding, and concrete pouring. This results in a long construction cycle. Due to the long operation cycle, high labor requirements, and the need for consumable materials such as scaffolding and formwork, construction costs are high. Furthermore, the large investment in building materials and the long-term use of machinery lead to poor environmental performance during construction. Summary of the Invention

[0003] To overcome the shortcomings of the existing technologies, this invention provides a construction method for prefabricated canopies at tunnel entrances based on BIM technology. This method is applicable to the construction of canopies at railway tunnel entrances. Utilizing prefabricated canopy technology ensures structural safety and rapid construction. Furthermore, all components are manufactured in the factory, offering advantages such as energy saving, land saving, environmental friendliness, and high efficiency, significantly reducing construction time. On-site work involves only the hoisting and assembly of prefabricated components, greatly improving construction safety, significantly reducing construction risks, and ensuring the operational safety of the railway line.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0005] The construction method for prefabricated canopies at tunnel entrances based on BIM technology includes the following steps:

[0006] S1. Constructing a BIM model and refining the drawing design: Using Revit software, two-dimensional drawings of the canopy at any angle, any section, and different components are provided in real time to complete the detailed design of the drawings. The three-dimensional model is then projected onto a large screen for technical communication through visualization equipment, and technical personnel conduct three-dimensional visualization technology briefings through the three-dimensional model.

[0007] S2. Precast canopy components: The precast canopy components adopt fair-faced concrete construction technology, including precast columns, longitudinal beams, transverse beams, double-T roof panels, and edge beams;

[0008] S3. Construction of U-shaped channel structure and pre-embedding of reinforcement bars for canopy column foundation: The construction of U-shaped channel structure includes bottom slab structure and side wall structure. The structure construction adopts cast-in-place construction technology. The bottom slab structure construction includes pile foundation construction and testing, external waterproofing laying, bottom slab reinforcement installation and formwork erection and concrete pouring; the side wall structure construction includes reinforcement binding, pre-embedding of canopy column reinforcement bars, formwork erection, trolley positioning and concrete pouring.

[0009] S4. Awning Installation: S41. Hoisting Precast Columns; S42. Diagonal Bracing Installation; Precision Adjustment;

[0010] S5. Column Base Formwork Sealing and Grouting: S51. Column Base Formwork Sealing: Before sealing, clean the holes, cover the gaps with flexible double-sided tape, then install and reinforce the formwork; S52. Grouting: Leave one hole in the lower row of grouting holes for easy construction, and seal the others with rubber plugs before grouting. As grouting proceeds, wait for the grout column to flow out of the vent hole. Use a fullness monitor to seal the grout outlet hole, maintain a pressure of 0.1MPa for 1 minute, and observe that the liquid level on the monitor does not drop, ensuring the compactness of the grout; S53. Equal Strength and Curing: The equal strength stage requires at least 24 hours. After equal strength curing, use micro-expansion high-strength mortar to seal the holes and smooth the joints;

[0011] S6. Lifting of Horizontal and Longitudinal Beams: S61. Lifting of Horizontal Beams: After the horizontal main beam is lifted to the designated position, first connect the diagonal support to the pre-embedded nut of the precast column, adjust the length to make the support under stress, then remove the upper temporary channel steel, measure the position accuracy of the cantilever part, and after fine-tuning it into place through the diagonal support, weld the bottom of the beam to the pre-embedded steel plate on the corbel. After ensuring the stability of the beam, remove the lifting hook; S62. Lifting of Longitudinal Beams: When lifting, pay attention to the positional relationship between the bottom main reinforcement and column reinforcement at both ends and the horizontal main beam reinforcement, and ensure that it is placed in place according to the drawings. Weld the bottom of the beam to the pre-embedded steel plate on the corbel. After ensuring the stability of the beam, remove the lifting hook;

[0012] S7. Construction of column head and beam top reinforcement: Tie the stirrups according to the node diagram. First tie the column head stirrups, and then tie the main reinforcement of the horizontal and vertical beam top reinforcement.

[0013] S8. Lifting of edge beams and double-T slabs: Lifting begins after the concrete rebound strength of the beam-column joint reaches 100% of the design value. After placement, the embedded steel plates are immediately welded to ensure component safety. All openings or pre-embedded parts for double-T slabs are completed in the factory in advance. After being transported to the site, a 4-point lifting method is used. After placement, the data is checked against the control lines, points, and design requirements. If any discrepancies are found, adjustments are made immediately.

[0014] S9. Concrete pouring after pouring;

[0015] S10. Construction of roof waterproofing layer: After the leveling layer reaches the required strength and is cleaned, the waterproof membrane is laid. SBS modified bitumen waterproof membrane is used. After the waterproof membrane is laid and passes the inspection, the surface is cleaned and a light gray protective coating is sprayed in layers.

[0016] In step S2, before binding the canopy column reinforcement, the grouting sleeve is connected to the main reinforcement, and then the column reinforcement is bound; the pre-embedded nuts for demolding lifting points, pre-embedded nuts for inclined supports, hooks, and channels are installed, and protective measures are taken for external leakage points to ensure installation accuracy; concrete is poured and fully vibrated, and steam curing is adopted. The formwork can be removed and the components can be hoisted to a special storage site only when the components reach the design strength.

[0017] In step S3, after the reinforcement bars of the widened foundation of the canopy column are tied along with the side wall, the reinforcement bars of the precast column foundation are pre-embedded. 24 column insert bars with a diameter of 36mm are reserved in the foundation of the canopy column. The column insert bars penetrate 1.5m into the side wall structure. The column insert bars are fixed by a reinforcement positioning frame. The reinforcement positioning frame is composed of two steel plates, upper and lower, and the corners are fixed by M36 bolts. The reinforcement bars of the canopy column foundation are hoisted as a whole. During the hoisting process, multiple people take turns to measure and position. After positioning, angle steel is immediately used to weld and fix it to the integral side wall trolley.

[0018] In step S4, the precast columns are hoisted by installing steel wire ropes and guy ropes to ensure the stability of the column during hoisting. The width of the column hanger is equal to the distance between the hoisting points. All columns need to be transported to the ground and then hoisted again. During the hoisting process, the operation method of slow lifting, steady lifting, and slow lowering should be followed throughout. To prevent damage to the edges and corners during the flipping of the precast components, flexible materials should be used for protection during the flipping process. The diagonal support is installed on one side of the precast column diagonal support on the top wall of the U-shaped channel, and on the other side on the outside of the U-shaped channel. After the precast column is hoisted and the diagonal support is installed, the hook is not removed temporarily. The center points on the four sides of the bottom of the column are marked in advance and aligned with the U-shaped channel layout points to ensure the accurate position of the root plane. Then, the upper part of the column is measured with a total station. The verticality, elevation, axis distance, and column distance of the column are accurately positioned by adjusting the shims and supports. The hook is removed after the accuracy is achieved.

[0019] In step S6, the cantilevered parts at both ends of the lifting device are connected by hand hoists instead of steel wire ropes, which facilitates length adjustment during lifting and ensures uniform force distribution.

[0020] In step S7, the column head node uses a customized aluminum formwork, and the transverse main beam does not have corbels within 30cm of the node to ensure the integrity of the aluminum formwork and effective installation space; nuts are pre-embedded every 30cm vertically on the sides of the precast transverse and longitudinal main beams to facilitate the fixing of the aluminum formwork to the beam; and four tie bolts are set vertically in the center of each side of the aluminum formwork.

[0021] In step S8, if the result is satisfactory, welding is performed at one end. Only after the welding is completed and the result is deemed satisfactory can the hook be released and the next component be installed, until all installation tasks in the flow section are completed.

[0022] In step S9, the joint between the beam and the slab is sealed using a stainless steel plate, 1.5mm thick, which is laid above the joint and fixed firmly. The stainless steel plate overlaps the double T-plates on both sides by no less than 6cm. Then, anti-crack reinforcement is laid on the beam and slab as a whole. The reinforcement specifications in the width direction of the slab are φ8@100, and the reinforcement specifications in the length direction of the slab are φ6@200. Finally, a 50mm thick concrete is poured and vibrated to level the surface.

[0023] In step S10, a baseline should be marked out before laying the roll material. The roll material should be slowly pushed forward along the baseline, and deviations should be corrected in time. When pasting the roll material, it should not be stretched. After pasting, use a rubber roller to roll it forward and to both sides to expel air and make the roll material firmly pasted on the base layer.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] This construction method, through design verification and stress monitoring, ensures the safety, stability, and applicability of the prefabricated canopy structure. While using fewer materials, it also boasts high wind resistance and stability. The prefabrication of canopy components in the factory allows for more standardized and regulated quality control in material acceptance, rebar installation, concrete pouring, and curing, resulting in higher construction efficiency and more controllable quality. Deep integration with BIM technology provides simulation and guidance in modeling, design, and construction, offering a clear and convenient view of the project, reducing errors, and accelerating progress. The prefabricated construction process enhances construction safety, reduces risks associated with adjacent existing railway lines, significantly reduces on-site construction work and personnel, effectively lowers construction costs and environmental pollution, and aligns with the trend of green construction. On-site work involves only the hoisting and assembly of prefabricated components, greatly improving construction safety, significantly reducing construction risks, and ensuring the operational safety of the railway line. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the construction process of the present invention;

[0027] Figure 2 This is a structural diagram of the canopy of the present invention;

[0028] Figure 3 This is an axial view of the canopy frame column in this invention;

[0029] Figure 4 This is a structural diagram of the canopy beams and columns of the present invention;

[0030] In the diagram: 1 is a U-shaped channel, 2 is a precast column, 3 is a corbel, 4 is a side beam, 5 is a crossbeam, 6 is a double T-slab, 7 is a canopy column, and 8 is a longitudinal beam. Detailed Implementation

[0031] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0032] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0033] like Figures 1 to 4 As shown, the construction method for prefabricated canopies at tunnel entrances based on BIM technology includes the following steps:

[0034] S1. Constructing a BIM model and refining the design drawings: Utilizing Revit software to provide real-time 2D drawings of the canopy from any angle, with any section, and featuring different components, completing the detailed design of the drawings. The 3D model is then projected onto a large technical communication screen via visualization equipment, allowing technical personnel to conduct 3D visualization technical briefings using the 3D model. For changes in the cross-section of the prefabricated canopy structure, the prefabricated components change synchronously. BIM models of structural dimensions and components are created for each prefabricated column 2, longitudinal and transverse beam 5, wet joint reinforcement binding, and construction joint layout. This allows for rapid, comprehensive, and accurate drawing optimization.

[0035] S2. Precast canopy components: The precast canopy components adopt fair-faced concrete construction technology, including 2 precast columns, 8 longitudinal beams, 5 transverse beams, double-T roof panels, and 4 edge beams. High requirements are placed on appearance and dimensional accuracy. The surface should be smooth and flat, without looseness, honeycomb, etc. Therefore, the mold must have a certain rigidity and strength, as well as strong overall stability. At the same time, the template surface must have a high degree of flatness.

[0036] S3, U-shaped channel 1 structural construction and canopy column 7 foundation reinforcement pre-embedding: The U-shaped channel 1 structural construction includes the base slab structure and side wall structure. The structural construction adopts the cast-in-place construction process. The base slab structure construction includes pile foundation construction and testing, external waterproofing laying, base slab reinforcement installation and formwork erection and concrete pouring; the side wall structure construction includes reinforcement binding, pre-embedding of canopy column 7 reinforcement, formwork erection, trolley positioning and concrete pouring.

[0037] S4. Canopy Installation: S41. Hoisting of precast columns 2; S42. Installation of diagonal supports; precision adjustment; Before hoisting, straighten, grind, and level the embedded steel bars, and grind the ends of the steel bars into rounded corners for easy installation. Roughen the concrete contact surface. At a distance of 2cm from the main reinforcement bars at the four corners of the column, measure the elevation and set steel shims for temporary support of the column.

[0038] S5. Column Base Formwork Sealing and Grouting: S51. Column Base Formwork Sealing: Before sealing, clean the holes by using a powerful air compressor to blow air from top to bottom, or by using a grouting machine to inject water to clean the holes. Cover the gaps with flexible double-sided tape, then install and reinforce the formwork; S52. Grouting: Leave one hole in the lower row of grouting holes for easy construction, and seal the others with rubber plugs before grouting. As grouting progresses, wait for the grout column to flow out of the vent hole. Use a fullness monitor to seal the grout outlet hole, maintain a pressure of 0.1MPa for 1 minute, and observe whether the liquid level on the monitor drops to ensure the compactness of the grout; S53. Equal Strength and Curing: The equal strength stage requires at least 24 hours. A warning line should be set up for protection, and collisions with the precast column 2 are strictly prohibited. Mechanical equipment operation is prohibited in the surrounding area to prevent the grout from being affected by external forces during the setting process. After equal strength curing, use micro-expansion high-strength mortar to seal the holes and flatten the joints.

[0039] S6. Lifting of horizontal and longitudinal beams 8: Before lifting, pre-embed one Ф20 connecting nut on each side of the corbel 3 at the cantilevered part of the horizontal beam 5, and install two temporary supports. S61. Lifting of horizontal beam 5: After the horizontal beam 5 is lifted to the designated position, first connect the diagonal support to the pre-embedded nut on the precast column 2, adjust the length to make the support in a stressed state, then remove the upper temporary channel steel, measure the accuracy of the position of the cantilevered part, and after fine-tuning it into place through the diagonal support, weld the bottom of the beam to the pre-embedded steel plate on the corbel 3. After ensuring the stability of the beam, remove the hook. S62. Lifting of longitudinal beam 8: When lifting, pay attention to the positional relationship between the bottom main reinforcement at both ends and the column reinforcement and the reinforcement of the horizontal beam 5, and ensure that it is placed in place according to the drawing requirements. Weld the bottom of the beam to the pre-embedded steel plate on the corbel 3. After ensuring the stability of the beam, remove the hook.

[0040] S7. Construction of column head and beam top reinforcement: Tie the stirrups according to the node diagram. First tie the column head stirrups, and then tie the main reinforcement of the horizontal and vertical beams 8.

[0041] S8, hoisting of edge beam 4 and double T plate 6: Hoisting begins after the concrete rebound strength of the beam-column joint reaches 100% of the design value. After placement, the embedded steel plates are immediately welded to ensure component safety. All openings or pre-embedded parts for double T plate 6 are completed in the factory in advance. After being transported to the site, a 4-point hoisting method is used. After hoisting and placement, the data is checked against the control lines, points and design requirements. If it is not up to standard, it is adjusted immediately.

[0042] S9. Concrete pouring after pouring;

[0043] S10. Construction of roof waterproofing layer: After the leveling layer reaches the required strength and is cleaned, the waterproof membrane is laid. SBS modified bitumen waterproof membrane is used. After the waterproof membrane is laid and passes the inspection, the surface is cleaned and a light gray protective coating is sprayed in layers.

[0044] Preferably, in step S2, before binding the reinforcing bars of the canopy column 7, the grouting sleeve is connected to the main reinforcement, and then the column reinforcement is bound; the pre-embedded nuts for the demolding lifting points, the pre-embedded nuts for the diagonal supports, the hooks, and the channels are installed, and protective measures are taken for external exposed points to ensure installation accuracy; concrete is poured and fully vibrated, and steam curing is used. The formwork can only be removed and hoisted to a dedicated storage area when the component reaches the design strength. The quality of the formwork joints and reinforcement is checked, and attention is paid to cleaning the edges and corners.

[0045] Preferably, in step S3, after the reinforcement bars of the widened foundation of the canopy column 7 are tied along with the side wall, the foundation reinforcement bars of the precast column 2 are pre-embedded. 24 column inserts with a diameter of 36mm are reserved in the foundation of the canopy column 7. The column inserts penetrate 1.5m into the side wall structure and are fixed by a reinforcement positioning frame. The reinforcement positioning frame consists of two steel plates, upper and lower, fixed at the corners with M36 bolts. Each steel plate has pre-drilled holes according to the designed reinforcement diameter. Simultaneously, a "shackle" type small component is added to the upper steel plate for fixation, in order to control the accurate positioning of the column inserts and improve the steel plate reuse rate. The foundation reinforcement bars of the canopy column 7 are hoisted as a whole. During the hoisting process, multiple people take turns measuring and positioning. After positioning, angle steel is immediately used to weld and fix it to the integral side wall trolley to ensure the foundation reinforcement bars are firmly fixed. After pouring, measurement and verification are immediately carried out, and any problems are adjusted in a timely manner. The side wall of the U-shaped channel 1 structure is poured at one time to a height of 9.05m to 1.50m.

[0046] Preferably, in step S4, the precast column 2 is hoisted by installing wire ropes and guy ropes to ensure the stability of the column during hoisting. The width of the column hanger is equal to the distance between the hoisting points. All columns need to be transported to the ground before being hoisted again. Throughout the hoisting process, the operation method of slow lifting, steady raising, and gentle lowering should be followed. To prevent damage to the edges and corners during the flipping of the precast components, flexible materials should be used for protection during the flipping process. After lifting 30cm off the ground, the column should remain stationary for 30 seconds to ensure reliable connection and that there is no risk of the wire rope and lifting equipment falling off. The column should be smoothly hoisted to a position 30cm above the designated location and then brought to a standstill. The direction and position should be adjusted, and the column should be slowly lowered to the designated position. The diagonal supports should then be installed. Diagonal bracing installation: One side of the diagonal bracing for precast column 2 is placed on the top wall of U-shaped channel 1, and the other side is placed on the outside of U-shaped channel 1. Precision adjustment: After the precast column 2 is hoisted and the diagonal bracing is installed, the hooks are not removed immediately. The center points on all four sides of the column bottom are marked in advance and aligned with the layout points of U-shaped channel 1 to ensure accurate root plane positioning. Then, the upper part of the column is measured using a total station, and the verticality, elevation, axis distance, and column spacing of the column are accurately positioned by adjusting shims and supports. After achieving the required accuracy, the hooks are removed. The crane crew continues to prepare for the hoisting of the next component. The grouting and formwork support for the precast column 2 that has been hoisted are immediately organized.

[0047] Preferably, in step S6, the cantilevered ends of the lifting device are connected by hand-operated hoists instead of wire ropes, which facilitates length adjustment during lifting and ensures uniform force distribution. Since the bottom reinforcement of the longitudinal beam 8 is above the transverse beam 5, the longitudinal beam 8 can only be lifted after the two transverse beams 5 in the same span have been lifted. The lifting device for the transverse beam 5 does not need to be removed; the longitudinal beam 8 can be lifted directly.

[0048] Preferably, in step S7, a custom-made aluminum formwork is used for the column head joint. No corbels 3 are installed within 30cm of the joint on the horizontal beam 5 to ensure the integrity of the aluminum formwork and sufficient installation space. Nuts are pre-embedded vertically every 30cm along the edges of the precast horizontal and longitudinal main beams to facilitate fixing the aluminum formwork to the beams. Four tie bolts are installed vertically in the center on each side of the aluminum formwork. Micro-expansion concrete of a grade one grade higher than the beam concrete is used for pouring. The column head joint is poured first, followed by the top concrete of the horizontal and longitudinal beams 8 to ensure strength and reduce shrinkage cracks. The concrete is then vibrated and leveled. The aluminum formwork is removed 2-3 days after pouring, and the next construction step is carried out only after the concrete strength meets the requirements.

[0049] Preferably, in step S8, if the work is qualified, welding is performed at one end. After the welding is completed and the work is accepted, the hook can be released and the next component can be installed until all installation tasks in the flow section are completed.

[0050] In step S9, the joint between the beam and slab is sealed using a stainless steel plate, 1.5mm thick, laid above the joint and firmly fixed. The stainless steel plate overlaps the double T-plates on both sides by no less than 6cm. Then, anti-crack reinforcement is laid on the beam and slab as a whole, with the reinforcement specifications being φ8@100 in the width direction and φ6@200 in the length direction. Finally, a 50mm thick concrete is poured and vibrated to level the surface.

[0051] Preferably, in step S10, after the leveling layer reaches the required strength and is cleaned, the waterproof membrane is laid, using SBS modified bitumen waterproof membrane. Before laying the membrane, a baseline should be marked, and the membrane should be slowly pushed forward along the baseline, not too quickly, and deviations should be corrected promptly. The membrane should not be stretched forcefully during application. After application, immediately use a rubber roller to roll it forward and to the sides to expel air and ensure the membrane is firmly adhered to the substrate. The protective coating layer should be of uniform thickness and should not be missed.

[0052] The above description only illustrates the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention, and all such changes should be included within the protection scope of the present invention.

Claims

1. A construction method for prefabricated canopies at tunnel entrances based on BIM technology, characterized in that: Includes the following steps: S1. Constructing a BIM model and refining the drawing design: Using Revit software, two-dimensional drawings of the canopy at any angle, any section, and different components are provided in real time to complete the detailed design of the drawings. The three-dimensional model is then projected onto a large screen for technical communication through visualization equipment, and technical personnel conduct three-dimensional visualization technology briefings through the three-dimensional model. S2. Precast canopy components: The precast canopy components adopt fair-faced concrete construction technology, including precast columns, longitudinal beams, transverse beams, double-T roof panels, and edge beams; S3. Construction of U-shaped channel structure and pre-embedding of reinforcement bars for canopy column foundation: The construction of U-shaped channel structure includes bottom slab structure and side wall structure. The structure construction adopts cast-in-place construction technology. The bottom slab structure construction includes pile foundation construction and testing, external waterproofing laying, bottom slab reinforcement installation and formwork erection and concrete pouring; the side wall structure construction includes reinforcement binding, pre-embedding of canopy column reinforcement bars, formwork erection, trolley positioning and concrete pouring. S4. Awning Installation: S41. Hoisting Precast Columns; S42. Diagonal Bracing Installation; Precision Adjustment; S5. Column Base Formwork Sealing and Grouting: S51. Column Base Formwork Sealing: Before sealing, clean the holes, cover the gaps with flexible double-sided tape, then install and reinforce the formwork; S52. Grouting: Leave one hole in the lower row of grouting holes for easy construction, and seal the others with rubber plugs before grouting. As grouting proceeds, wait for the grout column to flow out of the vent hole. Use a fullness monitor to seal the grout outlet hole, maintain a pressure of 0.1MPa for 1 minute, and observe that the liquid level on the monitor does not drop, ensuring the compactness of the grout; S53. Equal Strength and Curing: The equal strength stage requires at least 24 hours. After equal strength curing, use micro-expansion high-strength mortar to seal the holes and smooth the joints; S6. Lifting of Horizontal and Longitudinal Beams: S61. Lifting of Horizontal Beams: After the horizontal main beam is lifted to the designated position, first connect the diagonal support to the pre-embedded nut of the precast column, adjust the length to make the support under stress, then remove the upper temporary channel steel, measure the position accuracy of the cantilever part, and after fine-tuning it into place through the diagonal support, weld the bottom of the beam to the pre-embedded steel plate on the corbel. After ensuring the stability of the beam, remove the lifting hook; S62. Lifting of Longitudinal Beams: When lifting, pay attention to the positional relationship between the bottom main reinforcement and column reinforcement at both ends and the horizontal main beam reinforcement, and ensure that it is placed in place according to the drawings. Weld the bottom of the beam to the pre-embedded steel plate on the corbel. After ensuring the stability of the beam, remove the lifting hook; S7. Construction of column head and beam top reinforcement: Tie the stirrups according to the node diagram. First tie the column head stirrups, and then tie the main reinforcement of the horizontal and vertical beam top reinforcement. S8. Lifting of edge beams and double-T slabs: Lifting begins after the concrete rebound strength of the beam-column joint reaches 100% of the design value. After placement, the embedded steel plates are immediately welded to ensure component safety. All openings or pre-embedded parts for double-T slabs are completed in the factory in advance. After being transported to the site, a 4-point lifting method is used. After placement, the data is checked against the control lines, points, and design requirements. If any discrepancies are found, adjustments are made immediately. S9. Concrete pouring after pouring; S10. Construction of roof waterproofing layer: After the leveling layer reaches the required strength and is cleaned, the waterproof membrane is laid. SBS modified bitumen waterproof membrane is used. After the waterproof membrane is laid and passes the inspection, the surface is cleaned and a light gray protective coating is sprayed in layers.

2. The construction method for prefabricated canopies at tunnel entrances based on BIM technology according to claim 1, characterized in that: In step S2, before binding the canopy column reinforcement, the grouting sleeve is connected to the main reinforcement, and then the column reinforcement is bound; the pre-embedded nuts for demolding lifting points, pre-embedded nuts for inclined supports, hooks, and channels are installed, and protective measures are taken for external leakage points to ensure installation accuracy; concrete is poured and fully vibrated, and steam curing is adopted. The formwork can be removed and the components can be hoisted to a special storage site only when the components reach the design strength.

3. The construction method for prefabricated canopies at tunnel entrances based on BIM technology according to claim 1, characterized in that: In step S3, after the reinforcement bars of the widened foundation of the canopy column are tied along with the side wall, the reinforcement bars of the precast column foundation are pre-embedded. 24 column insert bars with a diameter of 36mm are reserved in the foundation of the canopy column. The column insert bars penetrate 1.5m into the side wall structure. The column insert bars are fixed by a reinforcement positioning frame. The reinforcement positioning frame is composed of two steel plates, upper and lower, and the corners are fixed by M36 bolts. The reinforcement bars of the canopy column foundation are hoisted as a whole. During the hoisting process, multiple people take turns to measure and position. After positioning, angle steel is immediately used to weld and fix it to the integral side wall trolley.

4. The construction method for prefabricated canopies at tunnel entrances based on BIM technology according to claim 1, characterized in that: In step S4, the precast columns are hoisted by installing steel wire ropes and guy ropes to ensure the stability of the column during hoisting. The width of the column hanger is equal to the distance between the hoisting points. All columns need to be transported to the ground and then hoisted again. During the hoisting process, the operation method of slow lifting, steady lifting, and slow lowering should be followed throughout. To prevent damage to the edges and corners during the flipping of the precast components, flexible materials should be used for protection during the flipping process. The diagonal support is installed on one side of the precast column diagonal support on the top wall of the U-shaped channel, and on the other side on the outside of the U-shaped channel. After the precast column is hoisted and the diagonal support is installed, the hook is not removed temporarily. The center points on the four sides of the bottom of the column are marked in advance and aligned with the U-shaped channel layout points to ensure the accurate position of the root plane. Then, the upper part of the column is measured with a total station. The verticality, elevation, axis distance, and column distance of the column are accurately positioned by adjusting the shims and supports. The hook is removed after the accuracy is achieved.

5. The construction method for prefabricated canopies at tunnel entrances based on BIM technology according to claim 1, characterized in that: In step S6, the cantilevered parts at both ends of the lifting device are connected by hand hoists instead of steel wire ropes, which facilitates length adjustment during lifting and ensures uniform force distribution.

6. The construction method for prefabricated canopies at tunnel entrances based on BIM technology according to claim 1, characterized in that: In step S7, the column head node uses a customized aluminum formwork, and the transverse main beam does not have corbels within 30cm of the node to ensure the integrity of the aluminum formwork and effective installation space; nuts are pre-embedded every 30cm vertically on the sides of the precast transverse and longitudinal main beams to facilitate the fixing of the aluminum formwork to the beam; and four tie bolts are set vertically in the center of each side of the aluminum formwork.

7. The construction method for prefabricated canopies at tunnel entrances based on BIM technology according to claim 1, characterized in that: In step S8, if the result is satisfactory, welding is performed at one end. Only after the welding is completed and the result is deemed satisfactory can the hook be released and the next component be installed, until all installation tasks in the flow section are completed.

8. The construction method for prefabricated canopies at tunnel entrances based on BIM technology according to claim 1, characterized in that: In step S9, the joint between the beam and the slab is sealed using a stainless steel plate, 1.5mm thick, which is laid above the joint and fixed firmly. The stainless steel plate overlaps the double T-plates on both sides by no less than 6cm. Then, anti-crack reinforcement is laid on the beam and slab as a whole. The reinforcement specifications in the width direction of the slab are φ8@100, and the reinforcement specifications in the length direction of the slab are φ6@200. Finally, a 50mm thick concrete is poured and vibrated to level the surface.

9. The construction method for prefabricated canopies at tunnel entrances based on BIM technology according to claim 1, characterized in that: In step S10, a baseline should be marked out before laying the roll material. The roll material should be slowly pushed forward along the baseline, and deviations should be corrected in time. When pasting the roll material, it should not be stretched. After pasting, use a rubber roller to roll it forward and to both sides to expel air and make the roll material firmly pasted on the base layer.

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