A cast-in-situ beam combined support construction method for crossing a river channel while ensuring traffic

Abstract

The application provides a cast-in-situ beam combined support construction method for crossing a river and ensuring traffic, comprising the following steps: S1, pile foundation construction; S2, strip foundation construction; S3, main support steel pipe support installation; S4, main beam and distribution beam erection, not less than three I-beams are placed on the top of the steel pipe in the transverse direction of the bridge, and the main beam and the steel pipe are fixed through a hoop; I-beams are placed on the top of the main beam between the steel pipes; standard bailey pieces are erected on the top of the main beam between the remaining steel pipes as distribution beams; the standard bailey pieces are connected through a pin rod, the position of the pin rod is provided with a flower stand and is fixed with the standard bailey piece; and S5, secondary beam and disc buckle support installation, so as to solve the technical problems of insufficient bearing capacity of the old river soft and hard plastic foundation, easy deformation and instability of the existing support, and the incoordination between construction and traffic preservation.

Description

Technical Field

[0001] This invention belongs to the field of bridge engineering construction, specifically involving a construction method for cast-in-place beam composite supports that spans old river channels while ensuring traffic flow. It is particularly suitable for special construction scenarios where old river channels have soft and hard plastic foundations, strict requirements for maintaining traffic flow on site, and cast-in-place beams have variable cross-section structures. It can achieve the dual goals of high load-bearing capacity, high stability, and coordinated construction and traffic flow maintenance of the support system. It is suitable for river-crossing construction of various cast-in-place beam bridge projects such as highways, railways, and urban rail transit. Background Technology

[0002] Cast-in-place beams have become the core structural form for highway, railway, and rail transit bridge engineering due to their advantages such as large span, convenient construction of irregular cross-sections, fast construction progress, and strong structural bearing capacity. The mainstream construction methods include the scaffolding method and the hanging basket method. Among them, the scaffolding method has significant advantages over the hanging basket method in terms of short construction period, less equipment investment, and high on-site construction efficiency, and its application rate in the construction of small and medium span cast-in-place beams exceeds 80%.

[0003] However, in the special construction scenarios of crossing old river channels, existing scaffolding construction technologies have insurmountable industry pain points, with the core issues concentrated in three dimensions: foundation adaptability, scaffolding stability, and scenario compatibility. 1. The foundation of the old river channel is mostly soft and hard plastic soil layer, and the bearing capacity of the foundation is generally lower than 80kPa. The conventional disc-lock scaffold is prone to overall settlement when directly erected. Moreover, the bearing capacity of the disc-lock scaffold is greatly reduced after the erection height exceeds 10m due to the stiffness of its own members, which cannot meet the height and load requirements of the variable cross-section cast-in-place beam. 2. The conventional solution for improving the bearing capacity of the foundation is to drive steel sheet piles / steel pipe piles. However, the driving depth of steel sheet piles in hard plastic foundations is limited (generally ≤6m), and the bearing capacity of a single pile is ≤150kN. This is insufficient to withstand the instantaneous impact load of cast-in-place beam concrete pouring (single-point load can reach more than 300kN). This can easily lead to safety risks such as pile body deflection and support deformation and instability. The essence is that the existing pile foundation solution only does "vertical force reinforcement" and does not consider the overall coordinated force between piles, resulting in a lack of resistance to lateral displacement and deformation. 3. The existing support system is a "single structure design" that only considers construction load requirements and lacks a special design for traffic control. The erection of the support system can easily occupy the passageway. If the spacing of the support system is arbitrarily adjusted in order to take into account traffic, it will further damage the rationality of the support system's stress, resulting in the inability to achieve construction safety and traffic control in a coordinated manner. This is the core design defect of the existing technology.

[0004] In summary, existing technologies have consistently failed to solve the technical coordination problem of "strengthening the bearing capacity of weak foundations, stabilizing the overall support system, and balancing construction and traffic maintenance scenarios." The industry urgently needs a comprehensive combined support construction method for the special scenarios of old river channels to achieve synergistic optimization across various technical dimensions. Summary of the Invention

[0005] Addressing the core shortcomings of existing technologies, this invention, through the creative concept of "integrated basic system, hierarchical support system, and scenario-based design scheme," provides a construction method for cast-in-place beam composite supports that spans old river channels while ensuring traffic flow. This method solves the technical problems of insufficient bearing capacity of soft and hard plastic foundations in old river channels, the susceptibility of existing supports to deformation and instability, and the inability to coordinate construction with traffic flow maintenance. The core objectives are as follows: This increases the bearing capacity of the support foundation system in soft and hard plastic soil to over 300kN, meeting the load requirements for cast-in-place beam construction. This transforms the support system from "single vertical force bearing" to "spatial overall force bearing," eliminating the risk of deformation and instability. While ensuring the safety of the scaffolding construction, the requirements for clearance and passage width for maintaining smooth traffic flow on site must be met; It adapts to the height and cross-sectional variation requirements of cast-in-place beams with variable cross-sections, improving the scenario adaptability of the support system.

[0006] To achieve the above objectives, firstly, this application provides a construction method for a cast-in-place beam composite support system that spans a river while ensuring traffic flow, comprising the following steps: S1. Pile foundation construction: Drilled cast-in-place piles are laid in the soft and hard plastic foundation of the old river channel. The pile tip is embedded into the bearing layer for no less than 2m. Differentiated reinforcement cages are pre-embedded in the pile foundation. Reinforced concrete transverse tie beams are poured between adjacent drilled cast-in-place piles to form a group pile overall force system. S2. Strip foundation construction: Concrete strip foundations are poured on the top of the pile foundations and in the land areas on both sides of the river. Steel plates with anchor bars are pre-embedded in the foundations, and the steel plates are rigidly connected to the foundations. S3. Main support steel pipe bracket installation: Steel pipes are used as the main support, and the bottom of the steel pipes is fixedly connected to the pre-embedded steel plates. The distance between the steel pipes and the original bridge deck is ≥3m. Several rows of steel pipes are installed along the bridge direction. Double-span passage gates are set at intersections, and several rows of steel pipes are set across the Qifeng Bridge area. The spacing of the steel pipes along the bridge direction is 12m+4m+9m+3m+7.5m+10.5m+10.5m+6m. In the transverse direction, the first to fifth rows have 4 pipes per row with a spacing of 4.5m, and the sixth to twelfth rows have 5 pipes per row with a spacing of 4.0m. Channel steel horizontal bracing and diagonal bracing are set between the steel pipes to form a spatial truss structure. S4. Erection of main beams and distribution beams: A main beam of no less than three I-beams is placed transversely on the top of the steel pipes, and the main beams are fixed to the steel pipes with clamps; I-beam secondary beams are placed on the top of the main beams between the rows of steel pipes; standard Bailey panels are erected on the top of the main beams between the remaining steel pipes as distribution beams; standard Bailey sections are connected by pins, and flower racks are set at the pin positions and fixed to the standard Bailey panels. S5. Installation of secondary beams and disc-lock scaffolds: Place I-beams on top of the distribution beams and I-beam secondary beams; install adjustable base supports of socket-type disc-lock full-span scaffolds on the I-beams, and erect disc-lock scaffolds; after the disc-lock scaffolds are erected, conduct a pre-loading test, with the pre-loading load being 1.2 times the design load.

[0007] Optionally, the main reinforcement of the differentiated reinforcement cage is N1Φ16, the stirrups are N2Φ10 with a stirrup spacing of 250mm, the reinforcing bars are N3Φ25 with a reinforcing bar spacing of 1000mm, and the hoisting center deviation of the reinforcement cage is ≤50mm.

[0008] Optionally, the transverse tie beam is a reinforced concrete structure with a width of 0.8m and a height of 1.0m. The interface between the transverse tie beam and the pile foundation is roughened. The transverse tie beam connects the pile group into a whole, so that the pile foundation changes from single pile independent force to group pile collaborative force.

[0009] Optionally, the steel plate with pre-embedded anchor bars is 20mm thick, and Φ18 anchor bars are welded to the bottom of the steel plate. The anchor bars are embedded in the strip foundation to a depth of ≥400mm. After the strip foundation is poured, it is cured until the concrete strength reaches more than 80% of the design strength before the subsequent steel pipe support installation is carried out.

[0010] Optionally, the channel steel horizontal bracing is installed every 3m along the vertical direction of the steel pipe, and the channel steel diagonal bracing is arranged at 45° and forms a stable triangular structure with the steel pipe. The deflection deviation of the steel pipe support is ≤L / 1000, where L is the span of the steel pipe.

[0011] Optionally, the standard Bailey panel has a size of 1.5m × 3m, the pin is inserted into the standard Bailey panel to a depth of ≥150mm, and the flower stand is fixed to the standard Bailey panel with M24 bolts.

[0012] Optionally, the adjustable base support has an adjustment height range of 0-300mm, the preloading time of the preloading test is ≥72h, and the subsequent cast-in-place beam construction is carried out after the settlement of the support stabilizes at ≤2mm / 24h.

[0013] Optionally, the borehole pile has a single pile bearing capacity of ≥400kN and the maximum settlement of the support system during the entire construction process is ≤5mm.

[0014] This invention provides a construction method for a cast-in-place beam composite support system that spans a river while ensuring traffic flow. Compared with existing technologies, its advantages are as follows: This invention, through the creative concept of "integrated foundation, hierarchical support, and scenario-based design," substantially improves the existing construction technology for cast-in-place beam supports spanning rivers, solves the core defects of existing technologies, and achieves multi-dimensional technological breakthroughs. Compared with existing technologies, it has the following significant and non-obvious advantages, all of which have been verified through engineering practice in the fourth construction section of Jinan Metro Line 8. It has the advantages of qualitatively improving the bearing capacity and stability of the foundation system, achieving synergistic optimization of construction safety and traffic flow, perfectly adapting to the construction requirements of variable cross-section cast-in-place beams, and having a scientific and efficient construction process that is economical, environmentally friendly, and has a scientific and reasonable stress transmission. Attached Figure Description

[0015] The accompanying drawings, which form part of this application, are used to provide a further understanding of the application and to make other features, objects, and advantages of the application more apparent. The illustrative embodiments and descriptions of this application are used to explain the application and do not constitute an undue limitation of the application. In the drawings: Figure 1 This is a schematic diagram of the layout of a bored pile foundation; Figure 2 This is a schematic diagram of the layout of the cast-in-place steel pipe Bailey bridge combined support; Figure 3 This is a schematic diagram showing the details of the installation of the cast-in-place steel pipe Bailey cloth beam. Figure 4 This is a diagram of the reinforcement details. Detailed Implementation

[0016] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0017] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this application described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0018] In this application, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing this application and its embodiments, and are not intended to limit the indicated device, element, or component to having a specific orientation, or to be constructed and operated in a specific orientation.

[0019] Furthermore, in addition to indicating location or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in some cases to indicate a certain dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0020] In addition, the term "multiple" should mean two or more.

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0022] A construction method for cast-in-place beam composite supports that spans river channels while ensuring traffic flow is proposed. Addressing the shortcomings of existing sheet pile foundations ("single pile bearing capacity and poor lateral displacement resistance"), this method employs an integrated foundation design combining bored piles and transverse tie beams. The bored piles reinforce the vertical bearing capacity, while the transverse tie beams connect the discrete pile foundations into a spatially integrated load-bearing system. This transforms the pile foundation from "independent single pile bearing capacity" to "collaborative pile bearing capacity," significantly improving the foundation system's resistance to lateral displacement and deformation. The reinforcement design of the steel cage is differentiated based on the bending and shear characteristics of the pile foundation, ensuring the inherent stiffness of the pile foundation.

[0023] The specific construction steps are as follows: I. Pile Foundation Construction The core design principle of this step is as follows: Addressing the shortcomings of existing sheet pile foundations, which suffer from "single pile stress and poor lateral displacement resistance," an integrated foundation design combining bored piles and transverse tie beams is adopted. The bored piles reinforce the vertical bearing capacity, while the transverse tie beams connect the discrete pile foundations into a spatially integrated load-bearing system. This transforms the pile foundation from "independent single pile stress" to "collaborative pile stress," significantly improving the foundation system's resistance to lateral displacement and deformation. The reinforcement design of the steel cage is differentiated based on the bending and shear characteristics of the pile foundation to ensure its inherent stiffness. Specific construction steps: Based on the calculation results of the upper load of the cast-in-place beam (calculated under the most unfavorable working condition, including concrete pouring impact load and construction live load), the design parameters of the bored pile are determined as follows: pile length 10m, pile diameter 1.0m, and the pile end is embedded into the bearing layer of the old river channel for no less than 2m to ensure the vertical bearing capacity of the pile foundation. A pre-embedded steel cage is used in the pile foundation. The steel cage adopts a differentiated reinforcement scheme: the main reinforcement is N1Φ16 (tensile main reinforcement, evenly distributed along the circumference of the pile foundation to bear the vertical tensile force of the pile foundation), the stirrups are N2Φ10 (circumferential stirrups, spaced at 250mm, to restrain the pile foundation concrete and improve shear resistance), and the reinforcing reinforcement is N3Φ25 (longitudinal reinforcing reinforcement, spaced at 1000mm, to improve the overall rigidity of the steel cage and prevent deformation during hoisting). Rotary drilling was used for drilling. After drilling, the hole was cleaned until the sediment thickness at the bottom of the hole was ≤50mm. After hoisting the steel cage, C30 underwater concrete was poured and cured until the concrete strength reached 100% of the design strength (curing time ≥28d). After all pile foundations are constructed, reinforced concrete transverse tie beams are poured on top of adjacent pile foundations. The tie beams are 0.8m wide and 1.0m high, forming a rigid connection with the pile foundations, making the pile group a unified whole and collaboratively bearing the upper horizontal and vertical loads. Key quality control points: Pile foundation hole verticality deviation ≤1%; reinforcement cage hoisting center deviation ≤50mm; the interface between the transverse tie beams and the pile foundations is roughened to ensure connection strength.

[0024] II. Strip Foundation Construction The core design principle of this step is as follows: C30 plain concrete strip foundations are poured on top of the pile foundations and in the land areas on both sides of the river. Firstly, this provides a horizontal and flat support surface for the steel pipe support, ensuring uniform stress distribution at the bottom and preventing settlement caused by localized stress concentration. Secondly, the surface load-bearing capacity of the strip foundation evenly transfers the localized load of the steel pipe support to the pile foundation and the ground, achieving a step-by-step transfer of "point load - surface load - group pile load". Thirdly, steel plates are pre-embedded in the strip foundation to achieve rigid fixation between the steel pipe support and the foundation, eliminating the risk of bottom slippage of the steel pipe support. Specific construction steps: The top of the pile foundation and the land construction area shall be leveled and compacted, with a compaction degree of ≥95%; Erect strip foundation formwork using steel molds to ensure rigidity and prevent deformation during pouring; A Q235B steel plate (20mm thick) is pre-embedded in the strip foundation. Anchor bars (Φ18, 500mm long) are welded to the bottom of the steel plate. The anchor bars are embedded in the strip foundation to a depth of ≥400mm to ensure the connection strength between the steel plate and the foundation. C30 plain concrete should be poured and compacted using a vibrator. It should be cured until the strength reaches more than 80% of the design strength before the subsequent steel pipe support installation can proceed.

[0025] III. Installation of Main Support Steel Pipe Support The core design principle of this step is as follows: Φ630×10mm thick-walled steel pipes are used as the main support system. The thick-walled steel pipes have a large moment of inertia and high compressive bearing capacity (compressive bearing capacity of a single steel pipe ≥500kN), suitable for the large load requirements of the upper structure. The specialized doorway design determines the doorway size based on the site's traffic clearance (clear width ≥12m, clear height ≥5m), avoiding core traffic passages. The spatial connection design of horizontal bracing and diagonal bracing with channel steel creates a spatial truss structure for the steel pipe support, bearing the upper horizontal load and wind load, preventing unilateral tilting of the steel pipe support, and achieving dual load-bearing capacity of "vertical compressive resistance + horizontal lateral resistance." Specific construction steps: Φ630×10mm seamless steel pipe is used as the main support. The bottom of the steel pipe is connected to the pre-embedded steel plate on the strip foundation by full welding (weld height ≥10mm) to achieve rigid fixation between the steel pipe and the foundation and eliminate the risk of bottom slippage. The steel pipe support should be erected at a distance of ≥3m from the original bridge deck to avoid affecting traffic on the original bridge deck during construction, while ensuring construction operation space. Twelve rows of steel pipes are installed along the bridge direction. In accordance with the on-site traffic control requirements, a 2×12m double-span passageway (12m clear width / span, ≥5m clear height) is set in the core passage area of ​​the intersection to meet the passage requirements of motor vehicles and non-motor vehicles. Nine rows of steel pipes are installed across the Qifeng Bridge area to match the structural span of the Qifeng Bridge. The spacing of the steel pipes is designed differently according to the distribution characteristics of the superstructure load: the spacing along the bridge direction is 12m+4m+9m+3m+7.5m+10.5m+10.5m+6m (the spacing is smaller in areas with large loads and larger in areas with small loads, so as to achieve a match between stress and spacing); in the transverse direction, the first to fifth rows have 4 pipes per row with a spacing of 4.5m (corresponding to the narrower sections of the cast-in-place beam), and the sixth to twelfth rows have 5 pipes per row with a spacing of 4.0m (corresponding to the wider sections of the cast-in-place beam), so that the stress of the steel pipe support is matched with the load distribution height of the cast-in-place beam; Horizontal bracing and diagonal bracing of channel steel are welded between the steel pipe supports. Horizontal bracing is installed every 3m along the vertical direction of the steel pipes, and diagonal bracing is arranged at 45° angles, forming a stable triangular structure with the steel pipes. This makes the steel pipe supports a spatial truss system, improving overall stability. Design basis: The design of the steel pipe spacing follows the principle of "load and stiffness matching," calculated according to the "Steel Structure Design Standard" (GB 50017-2017), ensuring that the deflection deviation of the steel pipe supports is ≤L / 1000 (L is the span of the steel pipe).

[0026] IV. Erection of Main Beams and Distribution Beams The core design principle of this step is as follows: A hierarchical load-bearing design is adopted, consisting of "I-beam main beams + Bailey bridges / I-beam distribution beams." The I-beam main beams bear the overall load of the upper structure and evenly distribute the load to the lower steel pipe supports. The Bailey bridges, acting as distribution beams, have advantages such as light weight, high load-bearing capacity, and flexible assembly, adapting to the load distribution variations of variable cross-section cast-in-place beams. A dual connection method of pin connections and bracket bolt fixation solves the defects of Bailey bridges being prone to overturning and slippage, enabling the Bailey bridges to form an integrated load-bearing system. Specific construction steps: No less than three I45a I-beams are placed horizontally on top of the steel pipe support. The spacing of the I-beams is consistent with the horizontal spacing of the steel pipe support. The I-beams are bolted together to ensure the overall rigidity of the main beam. The main beam is fixed to the top of the steel pipe support with clamps to prevent the main beam from slipping. For the main beam area between the steel pipes (the area with concentrated load), I45a I-beams are placed as secondary beams with a transverse bridge spacing of 90cm. The concentrated load is distributed by the dense secondary beams. For the main beam area between the remaining steel pipes, 1.5m×3m standard Bailey panels are erected as distribution beams with a transverse spacing of 45cm. The assembly direction of the Bailey panels is consistent with the longitudinal direction of the cast-in-place beam, which is compatible with the casting direction of the cast-in-place beam. The standard sections of the Bailey bridge are rigidly connected by pins with an insertion depth of ≥150mm. A steel flower rack is installed at the pin connection position. The flower rack is fixed to the Bailey bridge section with M24 bolts to form an integral whole and prevent the Bailey bridge section from overturning or sliding under load. Rubber pads are used to pave the joint surfaces of the I-beams and Bailey bridges to reduce stress concentration during load transfer.

[0027] V. Installation of Secondary Beams and Disc-lock Brackets The core design principle of this step is as follows: I14 I-beams are installed on top of the Bailey distribution beam and the secondary I-beams as transition supports for the disc-lock scaffolding, ensuring the load of the disc-lock scaffolding is evenly transferred to the distribution beam. The socket-type disc-lock full-span scaffolding has advantages such as flexible erection height, adjustable spacing, and high overall rigidity. It can flexibly adjust the erection height and horizontal and vertical spacing of the scaffolding according to the height and cross-section changes of the variable cross-section cast-in-place beam, perfectly adapting to the construction requirements of variable cross-section cast-in-place beams and solving the defects of existing scaffolding systems that are "fixed in height and cannot adapt to variable cross-sections." Specific construction steps: On top of the Bailey distribution beam and the I45a I-beam secondary beam, I14 I-beams are placed transversely. The spacing of the I14 I-beams is consistent with the transverse spacing of the subsequent disc-lock brackets (90cm). The I-beams are connected by spot welding to prevent slippage. An adjustable base support for a socket-type disc-lock full-span scaffold is installed on the top of the I14 I-beam. The height of the base support can be adjusted from 0 to 300 mm. The erection height of the disc-lock scaffold can be adjusted by the base support to adapt to different height requirements of the variable cross-section cast-in-place beam. Anti-slip pads are used to fix the base to the I14 I-beam to prevent the disc-buckle bracket from slipping during construction. The disc-buckle bracket is installed with a horizontal bridge spacing of 90cm and a longitudinal bridge spacing of 60cm, with a step distance of 1.5m to ensure the overall rigidity of the bracket. After the disc-lock scaffold is erected, a preloading test is conducted (the preloading load is 1.2 times the design load). The preloading time is ≥72h. The settlement of the scaffold is monitored. Only after the settlement stabilizes at ≤2mm / 24h can the subsequent cast-in-place beam formwork erection and concrete pouring construction be carried out.

[0028] The combined support system of this invention forms a hierarchical force transfer path: cast-in-place beam construction load (concrete self-weight + construction live load) - disc-lock scaffold - I14 H-beam - Bailey bridge / I45a H-beam - three-section I45a H-beam main beam - Φ630×10mm steel pipe support - C30 plain concrete strip foundation - bored pile - transverse tie beam integral foundation - old riverbed foundation. This force transfer path achieves a gradual and uniform transfer of load, avoids local stress concentration, and ensures that each structure bears its appropriate load.

[0029] The following effects are achieved after implementing the above method: The bearing capacity and stability of the foundation system have been significantly improved: The integrated foundation design of 1.0m diameter, 10m length bored piles and transverse tie beams, combined with differentiated reinforcement cages, has increased the bearing capacity of a single pile to over 400kN. The overall bearing capacity of the foundation system is 167% higher than that of the existing sheet pile scheme. The transverse tie beams connect the pile group into a whole, increasing the lateral stiffness of the foundation system by over 200%. The settlement of the support structure is ≤5mm throughout the construction process, with no deformation or instability, fundamentally eliminating the risk of deformation and instability.

[0030] Achieving synergistic optimization between construction safety and traffic flow: Through the specialized design of the 2×12m double-span passageway, coupled with a safety distance of ≥3m between the steel pipe support and the original bridge deck, the normal passage requirements of motor vehicles and non-motor vehicles on site were met, and traffic efficiency was not affected during construction; at the same time, the passageway design did not compromise the stress rationality of the support system, and the overall rigidity and load-bearing capacity of the support were not reduced due to the passageway, achieving an industry breakthrough of "construction without road closure and traffic flow without sacrificing safety".

[0031] Perfectly adapted to the construction requirements of variable cross-section cast-in-place beams: Through the combined design of adjustable base support and socket-type disc-lock full-span scaffolding, the scaffolding erection height (adjustment range 0-300mm) and spacing can be flexibly adjusted according to the height and cross-section changes of the variable cross-section cast-in-place beam, adapting to the construction of cast-in-place beams with different cross-section forms; at the same time, the hierarchical support system can flexibly adjust the spacing of the distribution beams and secondary beams according to the load distribution of the cast-in-place beam, achieving "precise matching between load distribution and scaffolding stress", resulting in excellent cast-in-place beam forming quality with a cross-section deviation ≤5mm, far exceeding the standard requirements.

[0032] The construction process is scientific, efficient, economical, and environmentally friendly: The combined support system of this invention uses standardized components (steel pipes, I-beams, Bailey bridges, and disc-lock scaffolds) for assembly. The components are reusable, and the equipment investment cost is reduced by more than 40% compared to the existing hanging basket method. The construction process is simple, with smooth connections between each process, and the construction efficiency is increased by more than 30% compared to the existing steel sheet pile + disc-lock scaffold scheme. Rotary drilling and grouting pile construction is used, eliminating the need for large-scale vibrating equipment, causing no damage to the surrounding environment of the old river channel, and generating no construction waste during the construction process, which meets the requirements of green construction. Rigid connections (full welding, clamps, bolts, and pins) are used between the various structures, resulting in high connection strength and no safety accidents throughout the construction process, significantly improving safety and reliability.

[0033] Scientific and rational force transmission: The constructed hierarchical force transmission path ensures that the construction load is uniformly transmitted from the superstructure to the foundation in stages. The force on each structure is within its design bearing capacity, and there is no local stress concentration. The overall stiffness and stability of the support system are greatly improved.

[0034] The following is a specific engineering example and appendix from the construction project of the cast-in-place beam crossing the old river channel in the fourth construction section of Jinan Metro Line 8. Figure 1 -Appendix Figure 4 The specific embodiments of the present invention will be further described in detail below. The construction parameters and effects in this example are all actual test results of the project and can be used as the basis for engineering verification of the present invention.

[0035] (I) Background of the Engineering Case Project Name: Construction Project of Cast-in-Place Beams Crossing the Tuhe River (Old Riverbed) in Section 4 of Jinan Metro Line 8; Engineering geology: The foundation of the old riverbed of the Tuhe River is soft and hard plastic clay with a bearing capacity of 75 kPa, which is a typical low bearing capacity foundation; Construction requirements: The cast-in-place beams are variable cross-section continuous beams with a height of 2.0-3.5m and a single span of 20m. The maximum construction load is 320kN / point. Strict traffic control requirements must be maintained on site, ensuring normal traffic flow in both directions on two lanes, and road closures are not permitted for construction. Construction challenges include low foundation bearing capacity, high requirements for adapting variable cross-section cast-in-place beams, and significant difficulties in coordinating construction with traffic maintenance.

[0036] (II) Specific construction steps This project example uses a construction method for a cast-in-place beam combined support that spans an old river channel while ensuring traffic flow, as described in this invention. The specific construction steps are completely consistent with the "Invention Content - Technical Solution" section of this invention, and will not be repeated here.

[0037] (III) Project Implementation Results After adopting the construction method of this invention, the following significant engineering results were achieved through on-site testing and construction summary, fully verifying the scientific nature, inventiveness, and practicality of this invention: Foundation system: The bearing capacity test result of a single bored pile is 420kN, which meets the design requirements; the transverse tie beam forms an integral whole with the pile foundation, and the lateral stiffness of the pile group foundation is 2.5×10^6N / m, which is 210% higher than the existing steel sheet pile scheme; Support system: The pre-stress test results of the support system showed that the maximum settlement was 4mm, and there was no rebound after the settlement stabilized, which met the specifications; the support system did not deform or become unstable throughout the construction process, and the overall stability was excellent. Traffic flow was maintained: the 2×12m passageway meets the requirements for two-way two-lane traffic, and traffic efficiency was not affected during the construction period, with no traffic congestion. Construction efficiency: The overall construction period is 22 days per span, which is 27% shorter than the existing technology's 30 days per span, resulting in a significant improvement in construction efficiency; Forming quality: After the cast-in-place beam was formed, it was tested and found that the cross-sectional deviation of the beam was 3mm, the axial deviation was 2mm, and the flatness was 2mm, which is far better than the requirements of the "Construction Quality Acceptance Standard for Urban Rail Transit Bridge Engineering" (CJJ / T 291-2019); Economic cost: The equipment investment cost of this invention is RMB 1.8 million per span, which is 40% lower than the RMB 3 million per span of the hanging basket method, resulting in significant savings in construction costs.

[0038] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A construction method for a cast-in-place beam composite support system that spans a river while ensuring traffic flow, characterized in that, Includes the following steps: S1. Pile foundation construction: Drilled cast-in-place piles are laid in the soft and hard plastic foundation of the old river channel. The pile tip is embedded into the bearing layer for no less than 2m. Differentiated reinforcement cages are pre-embedded in the pile foundation. Reinforced concrete transverse tie beams are poured between adjacent drilled cast-in-place piles to form a group pile overall force system. S2. Strip foundation construction: Concrete strip foundations are poured on the top of the pile foundations and in the land area on both sides of the river. Steel plates with anchor bars are pre-embedded in the foundations, and the steel plates are rigidly connected to the foundations. S3. Main support steel pipe bracket installation: Steel pipes are used as the main support, and the bottom of the steel pipes is fixedly connected to the pre-embedded steel plates. The distance between the steel pipes and the original bridge deck is ≥3m. Several rows of steel pipes are installed along the bridge direction. Double-span passage gates are set at intersections, and several rows of steel pipes are set across the Qifeng Bridge area. The spacing of the steel pipes along the bridge direction is 12m+4m+9m+3m+7.5m+10.5m+10.5m+6m. In the transverse direction, the first to fifth rows have 4 pipes per row with a spacing of 4.5m, and the sixth to twelfth rows have 5 pipes per row with a spacing of 4.0m. Channel steel horizontal bracing and diagonal bracing are set between the steel pipes to form a spatial truss structure. S4. Erection of main beams and distribution beams: A main beam of no less than three I-beams is placed transversely on the top of the steel pipes, and the main beams are fixed to the steel pipes with clamps; I-beam secondary beams are placed on the top of the main beams between the rows of steel pipes; standard Bailey panels are erected on the top of the main beams between the remaining steel pipes as distribution beams; standard Bailey sections are connected by pins, and flower racks are set at the pin positions and fixed to the standard Bailey panels. S5. Installation of secondary beams and disc-lock scaffolds: Place I-beams on top of the distribution beams and I-beam secondary beams; install adjustable base supports of socket-type disc-lock full-span scaffolds on the I-beams, and erect disc-lock scaffolds; after the disc-lock scaffolds are erected, conduct a pre-loading test, with the pre-loading load being 1.2 times the design load.

2. The construction method of a cast-in-place beam composite support system for crossing a river while ensuring traffic flow, as described in claim 1, is characterized in that: The main reinforcement of the differentiated reinforcement cage is N1Φ16, the stirrups are N2Φ10 with a stirrup spacing of 250mm, the reinforcing bars are N3Φ25 with a reinforcing bar spacing of 1000mm, and the hoisting center deviation of the reinforcement cage is ≤50mm.

3. The construction method of a cast-in-place beam composite support system for crossing a river while ensuring traffic flow, as described in claim 1, is characterized in that: The transverse tie beam is a reinforced concrete structure with a width of 0.8m and a height of 1.0m. The interface between the transverse tie beam and the pile foundation is roughened. The transverse tie beam connects the pile group into a whole, so that the pile foundation changes from single pile independent force to group pile collaborative force.

4. The construction method of a cast-in-place beam composite support system for crossing a river while ensuring traffic flow, as described in claim 1, is characterized in that: The steel plate with pre-embedded anchor bars is 20mm thick. Φ18 anchor bars are welded to the bottom of the steel plate. The anchor bars are embedded in the strip foundation to a depth of ≥400mm. After the strip foundation is poured, it is cured until the concrete strength reaches more than 80% of the design strength before subsequent steel pipe support installation.

5. A construction method for a cast-in-place beam composite support system that spans a river and ensures traffic flow, as described in claim 1, characterized in that: The channel steel horizontal bracing is installed every 3m along the vertical of the steel pipe, and the channel steel diagonal bracing is arranged at 45° to form a stable triangular structure with the steel pipe. The deflection deviation of the steel pipe support is ≤L / 1000, where L is the span of the steel pipe.

6. The construction method of a cast-in-place beam composite support system for crossing a river while ensuring traffic flow, as described in claim 1, is characterized in that: The standard Bailey panel is 1.5m × 3m in size, and the pin is inserted into the standard Bailey panel to a depth of ≥150mm. The flower stand is fixed to the standard Bailey panel with M24 bolts.

7. The construction method of a cast-in-place beam composite support system for crossing a river while ensuring traffic flow, as described in claim 1, is characterized in that: The adjustable base support has an adjustment height range of 0-300mm. The preloading time for the preloading test is ≥72h. Subsequent cast-in-place beam construction can proceed after the support settlement stabilizes at ≤2mm / 24h.

8. The construction method of a cast-in-place beam composite support system for crossing a river while ensuring traffic flow, as described in claim 7, is characterized in that: The borehole pile has a single pile bearing capacity of ≥400kN and the maximum settlement of the support system during the entire construction process is ≤5mm.

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