Bridge body construction method

Abstract

The invention provides a bridge body construction method, and belongs to the technical field of bridge body construction, and the method comprises the following steps: step 1, north bank skewback construction and south bank skewback construction, step 2, cable hoisting system installation, step 3, arch rib installation, step 4, steel beam installation, step 5, bridge deck system and accessory construction, after closure, cable force and full bridge linear adjustment meet requirements, and step 6, bridge deck system construction. And 6, bridge deck pavement and accessories are constructed, a cable hoisting system and a tower are synchronously dismantled, bridge approach engineering is constructed, a finished bridge load test is conducted, and full-bridge traffic is conducted.

Description

Technical Field

[0001] The invention relates to the technical field of bridge construction, and in particular to a bridge construction method. Background Art

[0002] The construction organization of all projects within the contract scope of the Lantian Cross-River Channel (Lantian Yangtze River Fifth Bridge) and connecting line project in Luzhou City, as well as the construction organization design of the main line bridge range K0+475.191~K1+890.391 section of the College Middle Road Upgrading and Reconstruction Project and Future Avenue Extension Project implemented by China Construction Sixth Engineering Bureau Co., Ltd. The Lantian Cross-River Channel (Lantian Yangtze River Fifth Bridge) and connecting line project in Luzhou City is a cross-Yangtze River project for the main urban road section of Danxia Road in the Central Peninsula~Future Avenue in Lantian District. The starting pile number of the project is K0+534.391, the end pile number is K1+890.391, the main line is 1356m long, including the main bridge across the river and the approach bridges on both sides. The main bridge across the river ranges from K0+713.391 to K1+325.391. The main bridge is 612m long, with six lanes in both directions, reserved tracks, and sidewalks on both sides. The standard section width is 43.5m, including the wind nozzle and the total width of the cable area. The main bridge across the river is a steel box arch bridge with a clear span of 570m. The north bank approach bridge ranges from K0+534.391 to K0+713.391, with a length of 179m. It is divided into a double-lane bridge and a single-lane bridge in the approach section from a single-lane three-lane bridge in the main bridge direction. The road project under the north bank approach bridge is the Danxia Road auxiliary road, sidewalk and Binjiang Road intersection widening and reconstruction project, of which the auxiliary road is divided into two lanes, and the single lane is a double lane. The south bank approach bridge ranges from K1+325.391 to K1+890.391, with a length of 565m and a standard width of 43.5m. Due to the large span and high requirements for the basket steel box, a corresponding structure needs to be designed to meet the relevant requirements. Therefore, a bridge construction method needs to be designed. Summary of the invention

[0003] The purpose of the present invention is to provide a bridge construction method to solve the technical problem that the existing basket steel box construction cannot meet the requirements of the cross-river bridge.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] A bridge construction method, the method comprising the following steps:

[0006] Step 1: Construction of the north bank arch seat and the south bank arch seat; Step 2: Installation of the cable hoisting system; Step 3: Installation of the arch ribs; Step 4: Installation of the steel beams; Step 5: Construction of the bridge deck system and accessories. After the cable tension and the adjustment of the entire bridge line meet the requirements after the closure, the bridge deck pavement and accessories are constructed, the cable hoisting system and tower are dismantled simultaneously, the approach bridge project is constructed, the bridge load test is carried out, and the entire bridge is opened to traffic; Step 6: Construction of the approach bridge.

[0007] Further, the specific process of step 1 is as follows: Construction of the arch seat on the north bank: first, the retreat method is used to excavate the first two levels of foundation pits, and the inclined leg pneumatic drill is used to install anchor rods for grouting, and the net is hung to spray concrete to complete the slope support. The steel trestle is erected step by step by the fishing method, and a construction platform is established. Steel pipe piles on the river side are used as flood control facilities on the river surface, and a gantry crane is installed to excavate the excavator. The excavator retreats and loads the bucket, and the gantry crane is used to transport it to the outside of the site. Following the principle of supporting first and then digging, the internal support is installed in time, and excavation is carried out layer by layer. The foundation steel bars and rigid skeleton are installed, and the formwork is supported on the river side, and the cooling pipes are installed in layers, and the arch seat foundation is poured;

[0008] South Bank Arch Seat Construction: The South Bank Arch Seat consists of two separate circular foundations. The outer diameter of the cap beam is 48m. The circular wall is formed by 1.8m interlocking piles. The height of the pedestal is 8m. Tooth blocks are set at the bottom. The pile guide wall is constructed first, and a rotary drilling rig is used to drill holes. The interlocking piles are constructed using the mud wall protection technology. The A and B piles are interlocked into a ring by hard interlocking. After the pile foundation is qualified, the pile head is broken and the cap beam is constructed. The static pressure double-liquid method is used to grout the pebble layer in the foundation pit and the soil layer behind the foundation pit. An excavator is used inside and outside the foundation pit to dig and load soil and stone. The long-arm excavator takes over the transportation and excavates layer by layer. The arch seat foundation steel bars, rigid skeleton, cooling water pipes are installed, and the arch seat foundation is poured.

[0009] Furthermore, the specific process of step 2 is as follows: Due to site constraints, the tower is located in the second span of the rear approach bridge behind the arch seats at both ends, and the pile cap foundation is constructed. The tower is a prefabricated tower frame with a height of 188.648m on the north bank and 206.696m on the south bank. The tower spacing is 706m. The tower is hoisted in sections, and each section consists of 6 12-meter It is composed of steel pipe columns. Each set of towers is pre-assembled into lattice column segments with a size of 12m along the bridge direction, 4.5m across the bridge direction, and 12m high. The maximum lifting weight of the segment is 38 tons. TC7030 tower crane is used to lift and install the entire segment. Two sets of lifting antennas are set up upstream and downstream of the bridge. The center distance between the two sets of cables at the top of the tower is 46.5m, and they are arranged symmetrically with the center line of the bridge. The saddle on the top of the cable crane tower can move laterally with a moving range of about 20m. The rated maximum lifting weight of the cable crane is 4×200t.

[0010] Furthermore, the specific process of step 3 is as follows: the main arch line is a basket arch, the arch plane is inclined inward by 8°, the arch rib is a single-box single-chamber box section with equal width and height, the single-limb arch rib is divided into 47 segments, the longest segment is about 17.8m long, and the maximum weight is the G4 segment, about 313 tons. It is transported to the lifting site via the Yangtze River waterway, accurately positioned by a positioning ship, the transport ship anchors and stabilizes the hull, the cable crane lifts the G1 segment into place, extends it into the arch seat, and assists the crawler crane and manual hoist to accurately position the arch rib space and adjust its posture, the temporary bracket is fixed, and the arch seat is cast. Concrete is poured, and the G1 partition is filled with concrete and prestressed. The remaining segments are installed symmetrically. When installing to G17, avoid cable entanglement and hoist them alternately on both sides. The buckle cables of each segment are temporarily fixed, and the corresponding back cables are hung simultaneously. Tension is made on the buckle tower to balance the tension on both sides. The interrib cross braces and arch rib segments are installed simultaneously. When the temperature ranges from 16 to 22 degrees Celsius during the period, the G24 closure section is hoisted, and the surplus is cut according to the monitoring data. The segments are connected by bolts first and then welding to achieve full arch closure, and permanent and temporary hangers of the entire bridge are installed from both ends to the mid-span.

[0011] Furthermore, the specific process of step 5 is as follows: the main beam is a double-layer orthogonal anisotropic plate box beam with a total width of 48.5m and a beam height of 3.5m. It is divided into 43 sections with a maximum lifting weight of 281 tons. It is installed section by section from the arch foot symmetrically to the span using a lifting pole beam, and the span is closed in the middle. At the beginning of the lifting, the transport ship in the floodplain section of the south bank of the S21 to S15 beam section cannot be moored. Due to the limitation of the position of the lifting point in the basket arch space, a temporary transfer platform is constructed at the river beach on the south bank in advance, and the lifting point is replaced by the platform. The main arch is crossed to achieve lifting in place. The beam transfer platform is set under the S15 beam section to ensure that the lifting point of the steel beam can be transferred here. It is lifted to the predetermined position with a special lifting device, and the temporary and permanent hangers are fixed. The bridge deck line is adjusted according to the monitoring data, and the adjacent sections are welded and connected.

[0012] Furthermore, the specific process of step 6 is as follows: for the approach bridge pile foundation project, after the construction of the cable tower pile foundation is completed, according to the progress of demolition, the north bank approach bridge can be constructed after the Danxia Road is closed, and the south bank approach bridge pile foundation does not affect the cable tower construction, and in order to reduce the impact of the pile foundation construction team on the cable tower anchoring and cable crane anchoring construction. Substructure construction: The piers affected by the cable-stayed cable hanging system are: C2, D2, M2; Pier M16, and Pier M18 affected by the cable crane. The main bridge approach bridge substructure construction is carried out in stages, with the uninterrupted part being constructed first, and the construction of the disturbed piers is accelerated after the interference is removed. Construction of cast-in-place beams: The construction of cast-in-place beams of 0#-4# piers on the north bank is disturbed by the back cable anchors, and the cast-in-place beams of 6#-9# are restricted by the position of the buckle towers. The cast-in-place beams on the north bank adopt a segmented construction plan. After the main arch is connected and the back cable anchors are removed, the cast-in-place beams of 0#-6# piers will be constructed first; after the main beams are connected and the buckle towers are removed, the whole cast-in-place beams of 6#-9# will be constructed. The cast-in-place beams on the north bank are constructed with steel pipe Bailey supports, and the bridge deck ancillary projects are also constructed following the main beam construction. After the entire bridge is connected, the bridge deck will be uniformly paved with asphalt. A total of 4 sets of cast-in-place beams M10-M15 on the south bank are affected by back cables and anchors and can only be constructed after the main arch is connected. A total of 4 sets of cast-in-place beams M15-M21 are affected by cable hangers and can only be constructed after the main beams are connected. M21-M26 are not affected and will be constructed first. The cast-in-place beams of non-critical line projects M10-M15 and M21-M26 are constructed using steel pipe Bailey supports, while the critical line M15-M21 section is constructed using disc-hook supports.

[0013] The present invention has the following beneficial effects due to the adoption of the above technical solution:

[0014] The present invention BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a flowchart of the construction of the north bank abutment of the present invention;

[0016] Figure 2 It is the design plan of the steel trestle in the construction organization design stage of the present invention;

[0017] Figure 3 It is a flow chart of the construction of the south bank abutment of the present invention;

[0018] Figure 4 It is a flow chart of installation and disassembly of the cable tower system of the present invention;

[0019] Figure 5 This is a flow chart of the cable crane installation construction of the present invention;

[0020] Figure 6 It is a construction flow chart of the steel-concrete combined section of the present invention. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and preferred embodiments. However, it should be noted that many details listed in the specification are only for the purpose of enabling the reader to have a thorough understanding of one or more aspects of the present invention, and these aspects of the present invention can be implemented even without these specific details.

[0022] A bridge construction method, the method comprising the following steps:

[0023] Step 1: Construction of the north bank arch foundation, such as Figure 1 As shown, during the steel platform construction, steel platform design, and construction organization design phase, the steel platform design is temporarily set up in the manner recommended in the drawings. Before starting construction, the construction conditions of the site must be investigated in detail, and the steel platform must be designed according to the load, topography, geomorphology, and geological conditions. The "Special Construction Plan for the Design and Installation of the Steel Platform Excavated from the North Bank Arch Foundation Pit" must be prepared. After expert demonstration and approval, the construction must be strictly carried out in accordance with the special plan. Figure 2 As shown. Steel pipe pile production: Processing: The platform steel pipe pile adopts φ800×12mm steel pipe, and the steel pipe section adopts spiral seam double-sided submerged arc welding steel pipe complete set of units and testing equipment. With the help of forming welding process, the pipe sections used for the pile pipe of this project are automatically produced. Factory production is implemented, and the length of each section of the steel pipe pile varies from 8 to 12m. After passing the inspection, it is transported to the construction site by a flatbed truck, and the pile connection is carried out on site.

[0024] Preparation for hoisting: Two circular holes are cut symmetrically on the top wall of the steel pipe as the connection holes for the clamp ring when the steel pipe is sunk and hoisted on site. The pile body is marked with paint to facilitate the observation of penetration when sinking the pile. Extension: The steel pipe pile is extended to the designed length on site. The welding joint adopts carbon dioxide shielded welding. The extension of the steel pipe pile adopts butt full welding. The weld seam is required to be full. The joints of adjacent steel pipe piles shall not be at the same elevation. During the construction process, the extension shall be carried out according to the following process: Interface cleaning: Before the steel pipe piles are butt-jointed, the rust, iron oxide scale and oil stains within 30mm on both sides of the interface shall be cleaned. Welding: The two steel pipe joints adopt butt flat welding. The welding is carbon dioxide shielded welding. Local manual welding is allowed. The electrode is E502. According to the welding process requirements, the welding should control the direction sequence, welding current and weld size. Stiffeners are used at the joints. The stiffeners must ensure that the weld is close to each other. The depth of the deposited metal of each weld or the maximum width of the deposited metal should not exceed the width of the weld surface. The same weld should be welded continuously and completed at one time. Weld cleaning and treatment: After the weld is completed, clean the slag and metal splashes on the weld surface, and the welder will check the appearance quality of the weld by himself; if it does not meet the requirements, it should be repaired or polished. The repaired weld should be smooth and round, and will not affect the appearance quality requirements of the original weld.

[0025] Platform steel pipe pile construction: The steel pipe pile is planned to be installed by leading holes, and the ground leading hole process is preferred to use rotary drilling to form holes. The "fishing method" is used for construction where mechanical equipment cannot enter the riverside, and the "fishing method" leads to holes by impact drilling. If it is difficult to make holes on the inclined rock surface on the riverside or the verticality of the holes is difficult to control, manual bored pile construction is adopted. First of all, the handover and verification of the measurement control points should be done well, and the control points provided by the design unit should be reviewed and encrypted. During the construction, the total station and steel ruler are used to locate the sinking piles, and the positioning of each pile should be done well. Before construction, the control of the sample piles should be designed according to the original drawing of the special plan, and the sample piles should be reviewed one by one based on the axis, and the measurement records should be kept. Only after the review is correct can the hole and pile construction be carried out. The land leading hole first uses a 360-type rotary drilling rig to lead the hole into the rock to the design depth of the steel platform foundation, and the drilling should ensure that the verticality meets the requirements of the specification. After the steel pipe piles are transported to the site, the crawler crane unloads the steel pipe piles on the ground or on the built trestle, then lifts them vertically, and then uses an 80t crawler crane to lift a 90-type vibrating hammer to vibrate and sink the steel pipe piles hole by hole. When the piles are first sunk, it is advisable to use the pile's own weight to sink, and after the pile body reaches a certain depth in the soil to confirm stability, use vibration to sink. The sinking operation of each pile should be completed in one go, and it is not advisable to pause for too long in the middle to avoid the recovery of soil resistance, which makes it difficult to continue sinking. When vibrating the piles, the pile tip elevation specified in the design or verified by the test pile is mainly controlled, and the final penetration (mm / min) is used as a check. When the pile tip has reached the design elevation, but there is a large difference with the final penetration, the cause should be found out and the construction can be carried out after treatment. During the pile sinking process, the depth and penetration of each steel pipe pile into the soil are recorded and compared with the geological data as the basis for the subsequent adjustment of the length of the steel pipe piles. During the pile driving process, if there is a drastic change in the penetration rate, the pile body suddenly tilts, shifts, or has severe rebound, or the amplitude of the vibrating hammer is abnormal, the pile driving should be stopped immediately, the cause should be found out, and effective measures should be taken before resuming construction.

[0026] The "fishing method" is used for construction in the water and on the riverside where mechanical equipment cannot enter. The construction method is as follows: Use an 80t crawler crane to install temporary steel pipe piles on the built trestle. The temporary steel pipe piles should be set at about 7m in the direction of the trestle. Use an 80t crawler crane to lift a 90-type vibrating hammer to vibrate and sink the temporary steel pipe piles until they cannot be sunk further; Bailey beams and distribution beams are built on the steel trestle and temporary steel pipe piles; hoist the impact drill equipment to the built Bailey beams and distribution beams; after the impact drill is accurately positioned, the impact drill impacts the lead hole (without mud), and after the lead hole is formed, the steel pipe piles are driven; after the steel pipe piles are driven, the Bailey frame and temporary steel pipe piles are removed, and the steel trestle bridge deck structure is laid. Connection system construction: After the construction of a row of steel pipe piles at a pier of the steel platform is completed, the connection system between the steel pipe piles of the pier is immediately carried out. The cross braces and diagonal braces of the connection system are welded with double-jointed [20 channel steel, and the weld thickness is not less than the specified value. Construction of pile top crossbeam: After the construction of the scissor brace between steel pipe piles is completed, the pile top distribution beam is constructed. The pile top crossbeam adopts double-jointed I40a I-beams, and a steel pad is set at the bottom of the crossbeam. The steel pad is connected to the outside of the steel pipe pile with a triangular plate. An arc-shaped limit block is set on the inside of the steel pipe to reinforce the double-jointed I-beams.

[0027] Bailey truss installation: Bailey truss assembly: lift the Bailey truss to be installed, place it behind the installed Bailey truss and in line with it, use manual cooperation to lift the front end of the Bailey truss, align the lower chord pin hole, insert the pin, then lift the rear end of the Bailey truss, insert the upper chord pin and set the safety pin. Bailey assembly is carried out in groups, and one group of Baileys (two rows horizontally) is assembled each time. Each group of Baileys is 12m long. The Bailey pieces are connected with connecting pieces. After assembly, they are transported to the construction site as a whole. Bailey truss erection: According to the lifting capacity of the crawler crane, a single span of 2 rows of Bailey trusses is erected as a group. Measure and lay out on the top crossbeam of the lower structure to determine the exact position of the Bailey frame. After assembly, a group of Bailey main trusses are loaded and transported to the back of the crawler crane. The crawler crane first installs a set of Bailey trusses, which are firmly tied to the beam after being accurately positioned, and then the stoppers are welded, and then another set of Bailey trusses are installed, and connected to the installed set of Baileys with fixed support frames. This process is repeated to complete the installation of the entire span of Bailey trusses.

[0028] Distribution beam installation: Use crawler crane to install I25a transverse distribution beam and fix it with riding bolts. The fulcrum of transverse distribution beam I25a must be placed at the fulcrum position of Bailey truss vertical chord or diamond chord to meet the force requirements. Laying bridge deck system: The bridge deck system consists of I-beam I25a transverse beam, I14 longitudinal beam and 8mm thick bridge deck. The spacing between transverse beams is 150cm, and the spacing between longitudinal beams is 30cm. After the transverse distribution beam and longitudinal distribution beam are firmly connected and installed, the bridge deck system materials are hoisted to the installation site by 80t crawler crane for laying. Continuous jump welding is performed between steel plate and distribution beam, with a weld length of 10cm and a spacing of 50cm. Finally, guardrail uprights, guardrail handrails and footboards are installed, and red and white warning paint is applied after installation.

[0029] Installation of excavation gantry crane: According to the design of the trestle, a 50t excavation gantry crane was installed. A special construction plan should be prepared before installation, and it should be implemented strictly in accordance with the special plan after approval. Construction of steel pipe pile support on the riverside: After the construction of the steel platform is completed, the DZ90 vibrating hammer of the 80t crawler crane is used to construct the locking steel pipe pile on the steel platform. The construction process of the supporting locking steel pipe pile is the same as that of the steel platform steel pipe pile. The rotary drilling and leading hole process is adopted. The rock embedding depth of the steel pipe pile should be not less than 10m. Processing of locking steel pipe piles: The cofferdam of the locking steel pipe pile is uniformly manufactured and stacked in the processing yard. The main steel pipe adopts φ630×10mm spiral pipe. Since there is a weld with a height of about 5mm on its surface, it cannot be closely attached to the locking structure, so φ10mm round steel is used to fill the weld and fully weld it. The main steel pipe and the small pipe are connected with 10×10×0.1cm steel plates as stiffening plates with a spacing of 2m to enhance their overall rigidity. Transportation of lock-mouth steel pipe piles: The processed lock-mouth steel pipe piles are transported by flatbed trucks, and a special stand is set on the flatbed truck to avoid damaging the lock. The lock must not be strangled during hoisting, and the lock should be staggered when stacking to avoid squeezing. Rotary drilling and hole drawing: 360 rotary drilling rigs are used to draw holes. The soft soil layer on the original surface should be removed from the construction site of the drilling rig, and the ground should be rolled flat and solid. Drilling can only be started after the drilling rig is parked stably. Before drawing holes, the control line of the drawing hole position and the center point of the drawing hole are released according to the reference point. Use a rotary drilling rig to excavate the casing foundation pit, bury the φ820×10mm steel casing, and after accurate positioning, symmetrically backfill the surrounding areas of the casing and compact it in layers. After backfilling is completed, the casing position should meet the design and specification requirements again. According to the measured and placed drawing hole position, use the rotary drilling rig positioning and verticality correction function to accurately adjust, and open the hole after confirming that the accuracy meets the requirements.

[0030] The depth and verticality of the hole are controlled by the drilling rig's own depth detection instrument and verticality detection equipment, and manual verification is performed. During the drilling process, the drilling slag should be extracted at any time, and the soil conditions at each depth should be recorded and compared with the designed geology. If the deviation is large, it should be handled in time. After the hole reaches the designed elevation, the hole depth is tested. After verifying that the geology is consistent with the design, the sand drill bit is replaced to clean the hole, and the locking steel pipe pile is lowered.

[0031] Locking steel pipe pile insertion: First use crawler crane to lift the steel pipe pile, pay attention to the verticality of the steel pipe pile during lifting. The verticality of the first steel pipe pile should be controlled within 0.5% of the pile length, and the other steel pipe piles should be controlled within 1% of the pile length. Lower it according to the determined position, use the deadweight of the steel pipe pile to sink, and use the vibrating hammer clamp to slowly loosen the crane wire rope after self-stabilization. After confirming that the verticality of the pile body meets the requirements, start the vibrating hammer to vibrate and stabilize. During the piling process, in order to ensure the verticality of the steel pipe pile, two total stations are used to perform vertical cutting cross observation and control within a range of 90°. In order to prevent the center line of the lock from shifting, a card plate is set at the lock of the steel pipe pile in the direction of piling to prevent the displacement of the pipe pile. The card plate is 2cm away from the outer edge of the pipe pile and is made of 1cm thick steel plate (or steel). When the lock-mouth steel pipe pile is extended, the pile body inner sleeve is butt-welded, and the lock-mouth component connection should be butt-welded. For the extended steel pipe piles, the joint positions of the adjacent piles should be staggered up and down. The position and direction of the first two steel pipe piles to be driven should be accurate. If the positioning does not meet the requirements, it is necessary to pull them out and drive them again to guide the sample pipe. Measurements should be made every 1m. After the predetermined depth is reached, the steel should be welded and fixed to the purlin immediately. Since the steel pipe pile cofferdam construction of this project is in the dry season, in order to improve the construction efficiency and facilitate the construction, each row of steel pipe piles is driven from the middle to both sides at a time.

[0032] To ensure the sealing of the entire steel pipe pile cofferdam, the steel pipe piles are connected by locks. Before driving, the locks should generally be coated with a mixture of butter, sawdust, etc. After 5 to 8 lock-mouth steel pipe piles are inserted, concrete is poured on the outside of the lock-mouth steel pipe piles in the lead hole to improve the stability of the steel pipe piles. C30 concrete is poured into the steel pipe to improve the rigidity and anti-scouring ability of the pipe piles.

[0033] Internal support construction: Internal supports are set up on the inside of the foundation pit to stabilize the steel pipe pile support. Diagonal braces are set up according to each layer of the purlin. Combined with the change of water level, some internal supports can be set up or removed under the premise of ensuring stability. Internal supports, cross braces and lattice columns are made of D630×16 and D299×10 steel pipes, and steel purlins are double-pieced I45C. Diagonal braces are set up every 2.5m.

[0034] The horizontal brace is constructed in reverse. When the foundation pit is excavated to the bottom elevation of the top horizontal brace, steel pipe piles are set up and the lattice column column part is constructed. The column depth should reach the design elevation. The first layer of horizontal internal support is assembled on the ground. After the assembly is completed, continue to excavate downward. When the lattice column flat joint and diagonal brace are reached, the flat joint and diagonal brace are constructed in time. When the second layer of internal support is reached, the construction is carried out in the same way until the excavation reaches the bottom of the foundation pit.

[0035] Arch foundation pit excavation and support, foundation pit overview and support settings, the size of the north bank arch foundation pit is 2 56.5m×56mm, the depth is 10.64m~33.68m, excavated in steps, 6 steps are set on both sides and the side with small pile numbers, except for the top two steps with 1:0.5 and 1:0.75 slope, the rest of the steps are 1:0.3 slope to the next step. The foundation pit support plan is: layered and graded slope excavation, anchor wall support, steel pipe pile water stop cofferdam on the river surface, water collection in the pit is uniformly collected and discharged into the nearby municipal pipe network, and internal support and surrounding purlins are set inside the foundation pit.

[0036] The excavation of the foundation pit is carried out by manual and mechanical excavation. The excavation and support are carried out according to the retreat method, that is, excavation and support are carried out layer by layer. The slope rate, layer height and inter-layer platform width are all carried out according to the design drawings. Outside the excavation range, the rock layer that affects the stability of the anchor shall not be excavated. The excavator excavates earth and stone in the foundation pit, and the earth and stone are lifted out of the foundation pit by the gantry crane. The loader cooperates with the truck to transport the earth and stone to the waste dump for disposal. The excavation of the foundation pit should follow the principle of layered and segmented excavation and support, excavating one section, closing one section, and supporting one section. The over-excavation depth shall not be less than 0.1m below the elevation of the anchor layout of this layer. For the bottom of the foundation pit, after over-excavation of 0.2m, C20 concrete is used to close the base to protect the rock layer. The 50cm thick soil layer above the base excavation surface is manually cleaned to avoid disturbing the base soil layer.

[0037] Anchor bolt and spraying support: To facilitate anchor bolt construction, the excavation depth of each section and each layer is controlled at 2 to 3 times the vertical spacing of the anchor bolts (1m), and the over-excavation height of the excavated soil layer should not be greater than the excavation depth of each layer + 0.50m. Support construction is carried out immediately after each layer is excavated. The next layer of soil can be excavated only after the support is completed and accepted and reaches the stable period. Anchor bolt and spraying support construction section process: Drilling construction is carried out immediately after each layer is excavated → Manual slope trimming → Initial spraying of concrete → Laying of welded steel mesh → Spraying concrete. Only after the anchor bolt grouting body and spraying concrete surface layer reach 70% of the design strength can the lower soil be excavated and the lower anchor bolt construction be carried out. Measurement and layout, according to the design drawings, use the total station to accurately lay out the anchor bolt position on the slope and mark it with the steel bar head.

[0038] Drilling: This project uses 2φ25m anchor bolts for anchor support. The anchor bolts are arranged according to the designed position. The anchor holes are drilled by down-the-hole drilling rigs. The drilling rigs are selected according to the diameter of the holes. The drilling method is used for interval drilling to prevent interference from adjacent holes. The inclination error of the anchor bolt drilling holes should not exceed 1°. The drilling depth should exceed the designed length by 0.5m. After the drilling reaches the designed depth, the drilling cannot be stopped immediately. The drilling should be steady for 1 to 2 minutes when the footage is stopped to prevent the bottom end from being pinched out. The drilling should be done at a uniform speed. The drilling speed should be strictly controlled during the drilling process to prevent the drilling hole from bending and deforming, which will cause difficulties in anchoring. After the drilling is completed, high-pressure air (wind pressure 0.2 to 0.4MPa) is used to clean the hole to ensure that there is no residual soil and rock powder in the hole, so as not to reduce the bonding strength between the cement mortar and the rock and soil of the hole wall.

[0039] Anchor construction: The anchor adopts 2Φ25mm anchor nails and the hole diameter is 130mm. The anchor hole depth is 7.0m and 10.0m. After drilling and cleaning the hole, the prepared anchor is inserted into the anchor hole, and the exposed part of the anchor is welded with the steel mesh.

[0040] When the anchor is fixed, it should be exposed 10cm from the rock surface, and the end should be made into a hook to press the steel mesh. After the steel bar is brought into the site, the surface should be treated with anti-rust, anti-corrosion and anti-bending. Before the anchor is anchored, the positioning steel bar should be welded to ensure the depth of the anchor. The positioning steel bar should ensure its designed height to ensure that the anchor is in the center of the anchor hole after it is anchored. After the anchor is anchored, use a steel ruler to measure the length of the anchor exposed outside the hole, calculate the length of the anchor in the hole (the error is controlled within the range of ±50mm), and ensure the anchoring length.

[0041] Grouting: Anchor rods are all grouted by pressure. The grouting pipe and anchor rod reinforcement are anchored into the hole at the same time, and the distance between the end and the bottom of the hole is 50cm~100cm. M30 mortar is used as the slurry material. The construction first determines the reasonable construction mix ratio through experiments. After the mix ratio is determined, the slurry is mixed with a forced mixer. The slurry should be stirred evenly, sieved, used as it is stirred, and used up before the initial setting. The slurry that has been initially set shall not be used. The grouting pressure is 0.5MPa, and the slurry is injected from the bottom of the hole until the entire hole is filled. After 24 hours of grouting, the slurry shrinks and should be supplemented. The grouting volume shall not be less than the calculated volume, and its filling coefficient is 1.1~1.3. After grouting, the exposed steel bars are made into hooks to press the steel mesh.

[0042] Hanging steel mesh spray concrete: The steel mesh adopts Φ8mm steel bars, with a spacing of 20cm×20cm, and welding or binding should be performed at every 2m node. The spray concrete material adopts C30 concrete with an average thickness of 10cm. Before spraying concrete, water should be sprayed to wet the slope surface to ensure that the concrete and the rock surface are firmly bonded. A expansion joint with a width of 2cm is set every 20-25m on the slope surface, and the joint is filled with asphalt hemp. Spraying concrete adopts wet spraying technology, requiring the air volume of the air compressor to be not less than 17 cubic meters, the wind pressure to be not less than 0.5MPa, and the amount of accelerator to be not more than 3% to 5% of the cement amount. The spraying order of spraying concrete should be from bottom to top, and the distance between the nozzle and the sprayed surface should be controlled within the range of 0.8m to 1.5m. The jet direction is vertical to the spraying surface. At the steel bar part, the back of the steel bar should be sprayed first, and then the front of the steel bar should be sprayed to prevent gaps from appearing on the back of the steel bar.

[0043] The excavation of the foundation pit should follow the principle of layered and segmented excavation and support, excavating one section, closing one section, and supporting one section. The over-excavation depth shall not be less than 0.1m below the elevation of the anchor bolts of that layer. For the bottom of the foundation pit, after over-excavation of 0.2m, C20 concrete is used to close the base to protect the rock layer.

[0044] The steel bars of the sprayed anchor mesh are made of φ8 bidirectional hot-rolled steel bars with a spacing of 100×100cm. The intersections of the horizontal and vertical bars are fixed with fine wires and connected by spot welding. The overlap length between the steel meshes is greater than 300mm, and the overlaps must be spot welded. 2C14 reinforcing steel bars are set horizontally at the ends of the anchors, and 2C14 reinforcing steel bars are set diagonally and crosswise. The reinforcing steel bars are spot welded to the anchor reinforcement bars.

[0045] The slope concrete adopts C30 spraying strength and 100mm thickness, which is constructed in two times, with 50mm spraying for the first time, steel mesh hanging, and 50mm spraying for the second time. Vertical expansion joints should be set along the longitudinal direction of the slope every 20-25m. The overlap of anchor bars should be welded on both sides, and a pair of centering frames should be set every 2m to keep the anchor bars in the middle of the borehole. The anchor drilling depth should be more than 500mm greater than the designed anchor rod length; the drilling in the fill should be dry drilled. The anchor construction must be subjected to on-site pull-out tests, including basic tests and acceptance tests. Among them, in the basic test, there should be at least 3 non-working nails specially used for testing in each typical soil layer. The test anchor should maintain a free section of not less than 1m from the hole mouth, and the grouting bonding length should not be less than 0.5 times the working nail and not shorter than 5m. The average value of the ultimate load obtained from the pull-out test should be greater than 1.3 times the design value of the axial tensile bearing capacity, otherwise the designer should be contacted as soon as possible for feedback and design modification.

[0046] The drainage hole adopts φ50mm PVC pipe, with an angle of 10 to 15 degrees with the horizontal. A filter layer needs to be set behind the drainage hole. The rock surface of the foundation pit has the characteristics of softening when saturated with water and cracking due to dehydration and weathering. It should be sealed and reinforced in time after excavation. When the foundation pit is excavated, the allowable load around the foundation pit shall not exceed 20kPa. In order to prevent the impact of construction waste on the foundation pit, the waste field should be more than 100m away from the foundation pit. A water interception ditch is set on the top of the foundation pit, and a drainage ditch and a water collection well are set at the bottom of the pit. After the water is collected, it is uniformly collected and discharged into the nearby municipal pipe network.

[0047] Arch foundation reinforcement binding and concrete pouring: bind foundation reinforcement and rigid skeleton, pour arch foundation in layers, and embed the connecting reinforcement with arch. Remove the internal support in time according to the foundation pouring situation. The foundation concrete is constructed by pumping. During the process, it is poured in layers and blocks. The pouring thickness of each layer should not be greater than 2m, and the continuous pouring time should not exceed 12 hours. Insulation measures should be taken on the concrete surface to prevent cracks on the surface due to excessive temperature difference between the inside and outside of the concrete. In addition to the above requirements, cooling water pipes can also be used to reduce the hydration heat of the arch concrete. When the concrete is poured in layers, the interval between the pouring of each adjacent layer of concrete should be 4 to 7 days, and should not exceed 10 days. In order to integrate the horizontal joints, spray the retarder on the surface after pouring the concrete. When the appropriate strength is reached, wash the surface slurry with high-pressure water, and then carry out curing. During curing, pay attention to wind protection, heat preservation, moisture retention, and prevent direct sunlight to reduce the damage to the structure caused by cold shrinkage and dry shrinkage. The roughening can only be carried out when the strength of the poured concrete reaches 2.5MPa or above, and the roughened surface must be thoroughly cleaned. At the same time, all surfaces in contact with the newly poured concrete should be fully moistened.

[0048] Arch concrete temperature control: The temperature of concrete entering the mold should not be lower than 5℃ in winter construction, and should not exceed 25℃ in hot weather. The peak temperature rise of the concrete center at any part should not exceed 60℃. During the curing period, the temperature difference between the core and the surface of the concrete, and between the surface and the environment should not exceed 20℃, and when the cross-section is more complex, it should not exceed 15℃. The cooling rate of the concrete casting should not exceed 2.0℃ / d. When mixing concrete with ice water or cold water, the water temperature should be controlled within 10℃. When adopting internal circulating cold water cooling measures (cooling water pipes), the temperature of the circulating water should be monitored at any time, and the temperature of the circulating water should be about 10℃ lower than the temperature of the concrete. When the temperature of the curing water poured on the concrete surface is lower than the surface temperature of the concrete, the temperature difference between the two should not be greater than 15℃. The insulation equipment can only be removed when the temperature difference between the core of the concrete and the environment is less than 15℃. During winter construction, the concrete should be covered and cured in time after the formwork and insulation layer are removed, and the insulation covering material can be removed after the concrete cools to 5℃.

[0049] On-site monitoring of temperature control construction of arch concrete: The center temperature, surface temperature, cooling rate and ambient temperature of the arch concrete casting body shall be tested no less than 24 times per day and night within 7 days after concrete pouring; thereafter, the test can be carried out 6 to 8 times per day and night, and the mold temperature shall be measured no less than 2 times per shift. The arrangement of monitoring points in the arch concrete casting body is based on the principle of truly reflecting the maximum temperature rise, the temperature difference between the inside and the outside, the cooling rate and the ambient temperature of the concrete casting body. Generally, it can be arranged in the following way: the arrangement range of the monitoring points is based on the half axis of the symmetry axis of the selected concrete casting body plane diagram as the test area, and the monitoring points in the test area are arranged in layers according to the plane. In the test area, the position and number of monitoring points can be determined according to the distribution of temperature field and stress field in the concrete casting body and the requirements of temperature control. If the temperature field and stress field laws can be basically determined by theoretical calculation, the measuring points can be arranged along the most unfavorable position.

[0050] On the symmetric axis of the foundation plane, there should be no less than 4 monitoring points, and the sensor layout should fully consider the geometric dimensions of the structure. Along the thickness direction of the concrete casting, the number of measuring points at each point should be no less than 5. The thermal insulation curing effect and the number of ambient temperature monitoring points should be determined according to specific needs. The surface temperature of the concrete casting should be based on the temperature 50mm inside the concrete surface; the temperature of the bottom surface of the concrete casting should be based on the temperature 50mm from the bottom surface of the concrete casting.

[0051] Concrete curing: In general, the temperature control value of concrete is: the maximum internal temperature of concrete after being molded is not higher than 60℃, the difference between the maximum internal temperature and the surface temperature of any section of the component at any time is not greater than 20℃, the temperature difference between the newly poured concrete and the adjacent hardened concrete or rock and soil medium is not greater than 20℃, the difference between the temperature of the curing water poured on the concrete surface and the temperature of the concrete surface is not greater than 15℃, and the cooling rate of concrete does not exceed 2℃ / d. When the ambient atmospheric temperature is more than 20℃ lower than the surface temperature of the concrete during curing, the concrete surface must be covered with insulation to reduce the cooling rate. When the newly poured structural components are likely to contact with flowing water, waterproof measures should be taken to ensure that the concrete is not directly washed by water within 7 days after pouring. In addition to considering the concrete strength at the time of demolding, the concrete demolding time should also take into account that the concrete temperature at the time of demolding should not be too high, so as to avoid cracking due to excessive cooling when exposed to air, and cold water curing should not be poured at this time.

[0052] When pouring concrete in hot climates, the formwork and newly poured concrete should be protected from direct sunlight. The temperature of the formwork and steel bars before entering the formwork and the local temperature nearby should not exceed 40°C. Pouring should be arranged in the evening as much as possible to avoid hot daytime, and it is not advisable to pour in the morning to avoid accelerating the internal temperature rise of the concrete when the temperature rises to the highest. In an environment with low relative humidity and high wind speed, it is advisable to take measures such as spraying and wind blocking, or avoid pouring components with large exposed areas such as panels at this time. When pouring concrete, the concrete temperature and environmental parameters such as air temperature, relative humidity, and wind speed should be measured regularly, and the maintenance method should be adjusted in time according to changes in environmental parameters. In the process of smoothing and flattening after concrete pouring, it is strictly forbidden to sprinkle water on the concrete surface, and excessive operation should be prevented from affecting the quality of the surface concrete.

[0053] Step 2: 1. Level the site. Level the site so that the surface bumps and potholes are leveled to the set elevation of 235.9m. Tamp the topsoil of the work site. In order to facilitate construction, the surface is compacted and the graded crushed stone cushion is spread on the surface as the site for interlocking piles and grouting reinforcement. 2. Prepare the drilling rig and construct the guide wall. Move the drilling rig to the construction hole and accurately locate the hole. 3. Interlocking pile A pile drilling construction. When excavating A pile, slurry is continuously replenished until the excavation reaches the designed elevation. Lower the steel cage and pour the concrete of A pile. 4. Interlocking pile B pile drilling construction. The construction of B pile should be carried out before the initial setting of A pile; while lowering the casing, soil is taken from the casing until the bottom elevation of the hole; the hole is cleaned after the hole depth reaches the design requirements; lower the steel cage and pour the concrete of B pile. 5. Repeat the third and fourth steps for the remaining interlocking piles in sequence until the construction of the entire circle of interlocking piles is completed. 6. Remove the guide wall and cast the interlocking pile cap beam. 7. Grout the pebble layer, grout the pebble layer inside the interlocking pile, and also grout the pebble layer behind the interlocking pile. 8. Excavate the foundation pit in layers until the design elevation is reached; clean the surface of the pebble layer. 9. Construction of the arch seat and foundation, tying steel bars and rigid skeleton for the construction of the junction pier, casting the arch seat foundation and arch seat; construction of the junction pier pile foundation, pedestal, pier column, and cap beam. This figure does not show the retaining wall for water retention, and the retaining wall is flexibly set according to the construction progress.

[0054] Interlocking piles and cap beam construction, interlocking piles, the outer ring of the south bank arch seat is constructed with interlocking piles as part of the arch seat foundation. A piles are embedded in the B pile foundation, and B is a complete pile foundation, including 102 A piles and 102 B piles; the interlocking piles are drilled by rotary drilling. The interlocking piles of this project use A and B piles with a diameter of 1.8m, and both A and B piles are reinforced piles. Since the interlocking piles are required to participate in the structural force, the interlocking piles must be ultrasonically tested, and the steel pipes must be unobstructed during construction. According to the geological survey data, the interlocking piles need to enter the medium weathered mudstone layer for no less than 6m. When there is a large difference between the local survey and the design, the design needs to be fed back in time. The skip pile construction is adopted. The reinforced concrete piles should be cut before the initial setting of the A-type concrete piles by cutting part of the plain concrete pile body during the drilling to form a mutual interlock with the A-type piles, but premature cutting should be avoided. Through guide walls and corresponding construction measures, the verticality of the interlocking piles is controlled within 0.3%, the pile position is allowed to deviate within 50mm, and corresponding pile foundation inspections are carried out in accordance with the Technical Regulations for Inspection of Foundation Piles for Highway Engineering.

[0055] The interlocking pile is drilled by rotary drilling. In order to ensure that the drill can drill smoothly in the sand and gravel stratum, according to our previous construction experience, the relative density of the mud is 1.6-1.8 during drilling, and sawdust, cotton and chemical thickeners are added to the mud to ensure the quality of the mud wall and prevent hole collapse. The relative density of the mud is reduced to 1.2-1.4 before pouring concrete, and then the concrete is poured normally. The steel cages of the A and B piles need to be well prepared, and sufficient construction space must be reserved to avoid accidents such as stuck drills and to avoid the situation of poor interlocking or interlocking.

[0056] Cap beam: The reinforced concrete cap beam should be constructed before the foundation pit is excavated, and the foundation pit should be excavated after reaching 80% of the design strength. In order to prevent cracks and shrinkage deformation during the construction of the cap beam, the cap beam should be divided into multiple units for construction, and one of the units should be selected as the joint unit. A 2.8m long micro-expansion concrete post-casting section should be set in the joint unit. The cap beam steel bars should be pre-buried with the arch seat cap steel bars. Before pouring the arch seat cap, the inner side of the interlocking pile group should be roughened and cleaned to ensure good bonding of the concrete and the integrity of the interlocking pile group and the arch seat cap.

[0057] Grouting project: The grouting reinforcement scheme for the arch seat on the south bank is part of the construction unit's research project on the foundation reinforcement of the arch bridge on the pebble foundation. The grouting reinforcement of the arch seat foundation on the south bank is based on the analysis of the stress characteristics of the arch seat foundation and the design of variable stiffness of the foundation. The sleeve valve tube grouting process is used to achieve consolidation and reinforcement under the arch seat foundation by directional grouting. The grouting project is divided into three parts: grouting of the base pebble layer; grouting behind the foundation pit; and local supplementary grouting after effect inspection. The grouting of the pebble layer at the base of the arch seat bite pile on the south bank and the subsequent supplementary grouting (determined whether to execute based on the treatment effect inspection) adopt the static pressure double-liquid grouting process. Intelligent grouting technology should be used for grouting.

[0058] Static pressure double liquid grouting: The design has the following technical requirements for static pressure double liquid grouting: Use the bottom-up embolism segmented grouting method, the construction sequence in the arch foundation is grouting from both sides of the annular area to the inside of the annular area, the base water sealing grouting sequence is to spread from the center of the circular ground wall to the surrounding area, single row skip hole construction, one hole is grouted after one hole is completed, and concentrated grouting after drilling is completed is strictly prohibited. Start grouting with low pressure and low concentration, and then gradually change to high pressure and high concentration according to the amount of grouting consumed by the rock and soil layer.

[0059] Drilling rig and grouting equipment in place: according to the measured points, the drilling rig is in place, the drilling rig is placed steadily, and the verticality and level of the drilling rig are adjusted. At the same time, the grouting machine and grouting machine are placed in pairs, and the grouting pipeline is fixed. It should not be too long and should be controlled within 30-50m to prevent pressure loss. Mixing water and bagged cement, fly ash, sand, water glass and other materials are prepared on site. Drilling construction: The grouting holes are drilled with a casing-followed impact drill. The hole diameter shall not be less than 130mm. The soil layer shall be drilled dry, and it is strictly forbidden to add water. Slurry preparation: The reference water-cement ratio is 0.8:1, the water glass concentration is 35°Be, the volume ratio of cement slurry to water glass is 1:0.5, and the cement shall use ordinary Portland cement with a grade of not less than 42.5. The slurry specific gravity is required to be not less than 1.48g / cm 3 The fluidity is not less than 38cm. The initial gel time and the total gel time should be between 3-4min and 90-100min respectively. The water-cement ratio and the amount of related additives should be adjusted and corrected according to the on-site grouting test.

[0060] Grouting cement slurry: Grouting pipes are made of DN80 seamless steel pipes (80mm inner diameter, 4mm wall thickness, 88mm outer diameter). A pair of 10mm small holes are drilled in the wall of the steel pipe, with a hole spacing of 30cm and arranged in a spiral shape along the circumference of the pipe. When the grouting pipe is placed, it should extend 5 to 10cm beyond the bottom of the hole. The grouting should be done in sections with a length of 1m. As the slurry flows in, the grouting pressure is reached. After 5 to 8 minutes of steady pressure grouting, the grouting pipe is pulled up 1m and grouting continues. This process is repeated to ensure that the slurry spreads slowly. The grouting pressure is 0.2 to 0.7MPa, which should be appropriately increased and adjusted as the depth of the grouting section increases. The grouting holes close to the retaining works should take a low pressure value.

[0061] Final grouting standard: The grouting pressure reaches the final grouting force design value and is maintained for 8 minutes. When the grouting pressure is within the design range, the grouting flow rate is significantly reduced and is less than 30% of the initial flow rate. The ground is lifted and lasts for about 5 minutes. Grouting can be terminated when one of the above standards is met. It is planned to use pressure, flow rate, and surface deformation for comprehensive control. During the grouting process, if slurry bubbling or leakage is found, surface sealing, addition of accelerator, low-pressure pumping, thick slurry, current limiting, intermittent grouting and other methods should be used to deal with it according to the specific situation. When slurry leakage is found during the grouting process, if the slurry leakage holes meet the grouting conditions, grouting can be carried out at the same time. One pump should be used to inject one hole, otherwise the slurry leakage holes should be plugged with plugs. After the grouting of the grouting holes is completed, the slurry leakage holes should be swept again, and then drilling and grouting should be carried out;

[0062] Grouting work must be continuous. If it is interrupted for some reason, the following principles can be followed: grouting should be resumed as soon as possible, otherwise the borehole should be flushed immediately and then grouting should be resumed. If flushing is impossible or ineffective, the borehole should be swept and then grouting should be performed. When resuming grouting, cement slurry with the same injection ratio should be used for grouting. If the injection rate is similar to that before the interruption, the cement slurry with the same ratio before the interruption can be used to continue grouting; if the injection rate is less than that before the interruption, the slurry should be gradually concentrated and continued to be grouted; after resuming grouting, if the injection rate is much less than that before the interruption and the grouting stops within a short period of time, remedial measures should be taken, such as increasing the grouting pressure of the adjacent holes or adding holes.

[0063] Experimental construction and grouting test: This project has a large amount of grouting work and a high level of project importance. Before the project construction, a static pressure double-liquid water-blocking and anti-seepage grouting test construction was carried out. The experimental construction and subsequent formal construction were carried out in accordance with the "Technical Code for Cement-Water Glass Double-Liquid Grouting in Construction Engineering" (JGJ / T211-2010) and "Technical Code for Cement Grouting Construction of Hydraulic Structures".

[0064] According to the relevant provisions of (SL / T62-2020) and other specifications, and based on the experimental construction results, further verify the construction parameters such as slurry ratio, additive dosage, and injection pressure.

[0065] Inspection of grouting effect: The grouting effect should be differentiated according to the purpose of grouting. For grouting projects aimed at water interception and sealing, the permeability of the grouting consolidation body is the main inspection object. For grouting projects aimed at reinforcement, the strength of the consolidation body is the main inspection object.

[0066] The grouting project of this project is mainly for reinforcement. For grouting in the foundation pit and behind the foundation pit, the inspection method is drilling method. Drilling inspection is carried out 15 days after the grouting is completed. The number of inspection holes is not less than 3% of the total number of holes. After the drilling verification inspection is completed, the holes should be sealed in time, and the sealing slurry should be consistent with the construction slurry. The inspection drilling hole is centered on the center of the grouting hole, with a radius of 60cm to 80cm, and the drilling depth should exceed the depth of the grouting hole by 1m. Within the grouting treatment depth range, an N63.5 standard penetration test or heavy dynamic penetration test and coring test are carried out every 2m; the single-section correction hammer number of N63.5 heavy dynamic penetration test of the pebble layer consolidation body is required to be not less than 20 or the bearing capacity is not less than 800kPa. If the soil in the grouting area sampled does not meet the requirements, the construction process needs to be corrected, and the corresponding area needs to be grouted for the second time. After the grouting is completed, an inspection should also be carried out, and the bearing capacity requirements must be met. Excavation of the foundation pit of the arch seat: The pit protection scheme is: slope excavation, interlocking piles enclosed in a circle, grouting of the pebble layer, water retaining by the riverside retaining wall (if necessary), and the water collected in the pit is uniformly collected and discharged into the adjacent municipal pipe network after sedimentation in the three-level sedimentation tank. The excavation of the arch foundation pit can only be carried out after the cap beam concrete reaches 80% of the design strength. If leakage is found in the interlocking pile wall or the slope of the foundation pit during the excavation of the foundation pit, the outer soil body of the place shall be reinforced by grouting to stop leakage. The excavation of each layer of soil in the pit adopts island excavation, first excavating the surrounding soil body symmetrically in different areas, and then excavating the middle soil body. Over-excavation is strictly prohibited. Generally, the soil 2m thick above the excavation surface should be removed manually. Before excavating each layer of soil, the soil in the pit should be pre-drained and dewatered in layers, and the water level in the pit should be strictly controlled to be less than 1m below the excavation surface. During the excavation of the foundation pit, the allowable pile load around the foundation pit shall not exceed 20kPa. To prevent the construction waste soil from affecting the interlocking piles, the distance between the waste soil field and the interlocking piles should be greater than 100m. After excavation to the design elevation, the groundwater control measures are further inspected, and the static pressure double-liquid grouting process is used to supplement the grouting in the local seepage area.

[0067] A water interception ditch is set on the top of the foundation pit, and a drainage ditch and a water collection well are set at the bottom of the pit. After the water is collected, it is uniformly collected and discharged into the nearby municipal pipe network. Foundation steel bar binding and concrete pouring: bind the foundation steel bars and rigid skeleton, pour the arch seat foundation in layers, and embed the connecting steel bars with the arch seat. The foundation concrete is constructed by pumping. During the process, it is poured in layers and blocks. The pouring thickness of each layer should not be greater than 2m, and the continuous pouring time should not exceed 12 hours. Insulation measures should be taken on the concrete surface to prevent cracks on the surface due to excessive temperature difference between the inside and outside of the concrete. In addition to the above requirements, cooling water pipes can also be used to reduce the hydration heat of the arch seat concrete.

[0068] When pouring concrete in layers, the interval between pouring concrete of adjacent layers should be 4 to 7 days, and should not exceed 10 days. In order to integrate the horizontal joints, spray the retarder on the surface after pouring the concrete. When the appropriate strength is reached, wash the surface slurry with high-pressure water, and then carry out curing. During curing, pay attention to wind protection, heat preservation, moisture retention, and prevent direct sunlight to reduce the damage to the structure caused by cold shrinkage and dry shrinkage. When the strength of the poured concrete reaches 2.5MPa or more, it can be roughened and the roughened surface should be fully cleaned. At the same time, all surfaces in contact with the newly poured concrete should be fully moistened.

[0069] Arch concrete temperature control: The concrete mold temperature should not be lower than 5℃ in winter and should not exceed 25℃ in hot weather. The peak temperature rise of the concrete center at any part should not exceed 60℃. During the curing period, the temperature difference between the core and surface of the concrete, and between the surface and the environment should not exceed 20℃. When the cross-section is more complicated, it should not exceed 15℃.

[0070] The cooling rate of the concrete casting should not exceed 2.0℃ / d. When mixing concrete with ice water or cold water, the water temperature should be controlled within 10℃. When adopting internal circulating cold water cooling measures (cooling water pipes), the temperature of the circulating water should be monitored at any time. The temperature of the circulating water should be about 10℃ lower than the temperature of the concrete. When the temperature of the curing water poured on the concrete surface is lower than the surface temperature of the concrete, the temperature difference between the two shall not be greater than 15℃. The insulation equipment can only be removed when the temperature difference between the core of the concrete and the environment is less than 15℃. During winter construction, the concrete should be covered and cured in time after the formwork and insulation layer are removed, and the insulation covering material can be removed only after the concrete cools to 5℃. On-site monitoring of arch seat concrete temperature control construction: The center temperature, surface temperature, cooling rate and ambient temperature of the arch seat concrete casting body can be tested no less than 24 times per day and night within 7 days after the concrete is poured; later, it can be tested 6 to 8 times per day and night, and the mold temperature should be measured no less than 2 times per shift.

[0071] The arrangement of monitoring points in the concrete casting of the arch seat is based on the principle of truly reflecting the maximum temperature rise, the temperature difference between the inside and outside, the cooling rate and the ambient temperature of the concrete casting. Generally, it can be arranged in the following way: the arrangement range of the monitoring points is based on the half axis of the symmetry axis of the selected concrete casting plane as the test area, and the monitoring points are arranged in layers according to the plane in the test area. In the test area, the position and number of monitoring points can be determined according to the distribution of the temperature field and stress field in the concrete casting and the requirements of temperature control. If the temperature field and stress field can be basically determined by theoretical calculation, the measuring points can be arranged along the most unfavorable position. On the symmetry axis of the foundation plane, the monitoring points should be no less than 4, and the sensor arrangement should fully consider the geometric dimensions of the structure. Along the thickness direction of the concrete casting, the number of measuring points at each point should be no less than 5. The thermal insulation curing effect and the number of ambient temperature monitoring points should be determined according to specific needs. The surface temperature of the concrete casting should be based on the temperature 50mm inside the concrete surface; the temperature of the bottom surface of the concrete casting should be based on the temperature 50mm below the bottom surface of the concrete casting.

[0072] Concrete curing: Under normal circumstances, the temperature control value of concrete is: the maximum internal temperature of concrete after entering the mold is not higher than 60℃, the difference between the maximum internal temperature and the surface temperature of any section of the component at any time is not greater than 20℃, the temperature difference between the newly poured concrete and the adjacent hardened concrete or rock and soil medium is not greater than 20℃, the temperature of the curing water poured on the concrete surface is not greater than 15℃ lower than the concrete surface temperature, and the cooling rate of the concrete does not exceed 2℃ / d.

[0073] When the ambient air temperature is more than 20℃ lower than the concrete surface temperature during curing, the concrete surface must be covered with insulation to reduce the cooling rate. When newly poured structural components are likely to come into contact with flowing water, waterproofing measures should be taken to ensure that the concrete is not directly washed by water within 7 days after pouring. In addition to considering the concrete strength at the time of demolding, the concrete temperature at the time of demolding should not be too high to avoid cracking due to rapid cooling when exposed to air, and cold water curing should not be poured at this time.

[0074] When pouring concrete in hot climates, the formwork and newly poured concrete should be protected from direct sunlight. The temperature of the formwork and steel bars before pouring and the local temperature nearby should not exceed 40°C. The pouring should be arranged in the evening as much as possible to avoid the hot daytime, and it is not advisable to pour in the morning to avoid accelerating the internal temperature rise of the concrete when the temperature rises to the highest. In an environment with low relative humidity and high wind speed, it is advisable to take measures such as spraying and wind blocking, or avoid pouring components with large exposed areas such as panels at this time. When pouring concrete, the concrete temperature and environmental parameters such as air temperature, relative humidity, and wind speed should be measured regularly, and the maintenance method should be adjusted in time according to the changes in environmental parameters. In the process of smoothing and flattening after concrete pouring, it is strictly forbidden to sprinkle water on the concrete surface, and excessive operation should be prevented from affecting the quality of the surface concrete. Arch seat construction plan: tie the arch seat steel bars and rigid skeleton, install the arch ribs, and pour the arch seat; at the same time, construct the junction pier tie beam, pier column, and cap beam. After the construction of the arch seat and foundation is completed, the superstructure is constructed, the foundation pit is backfilled, the steel pipe piles are cut, and the trestle is dismantled.

[0075] Step 3: If Figure 4 The cable tower system installation and disassembly scheme shown in the figure is that the cable tower system is the main device for the arch rib construction of the bridge. All the construction work of the system must be completed before the installation of the G1 arch rib. After the arch rib is closed, some wind cables, back cable anchors, back buckle cables and other structures can be removed first. After the main beam is closed, the power system and tower can be dismantled. And further complete the removal of anchors, temporary caps, etc. Cable tower system design: As the main force-bearing structure during the arch rib construction stage, the buckle tower is required to have a certain strength and rigidity to avoid the installation accuracy of the arch rib being affected by excessive deformation of the tower, which makes it difficult to close the arch rib. This project adopts a cable tower integrated design, that is, the buckle tower and the cable suspension tower are set on the same tower. The buckle tower on the north bank is designed to be 188.648m high and the buckle tower on the south bank is 206.696m high. The distance between the buckle towers on the north and south banks is 706m. Two hoisting cables are set up upstream and downstream, and the hoisting capacity of each cable group is greater than 150t. Cables are used for the installation of arch ribs and main beam segments.

[0076] Tower, saddle: saddles include hoisting main cable, working main cable, traction cable, lifting cable, buckle cable, wind cable (tower pressure cable) and other saddles. The saddle is the support of the main steel cable on the tower. This bridge adopts sliding saddle, which slides on the track at the top of the tower. The saddle is the steering device of the cable hoist. The saddle track is fixed to the steel platform at the top of the tower with high-strength bolts. The saddle can move horizontally along the track. When hoisting the arch rib segment, the position of the saddle on the top of the tower can be adjusted by the hydraulic jack to adjust the position of the cable hoist.

[0077] Tower top structure: The tower top structure is composed of steel sections, which fix the saddle on the tower top. It plays the role of a distribution beam, distributing the saddle reaction force to the tower column through the tower top platform. At the same time, the tower platform is equipped with a cable tower wind cable fixing bracket. A GNSS tower deviation automatic monitoring device is installed on the tower top, and 5G is used to transmit to the indoor monitoring platform to grasp the tower deviation in real time at different construction stages, providing first-hand data support for the wind cable to adjust the tower deviation and the back cable force. A lightning protection device should also be installed on the tower top.

[0078] Tower: The tower of the cable tower of this bridge adopts a portal frame structure, and multiple cross-links are set between the upstream and downstream portal columns. The single-leg tower frame is composed of 18 φ800×25mm steel pipes with a vertical and horizontal spacing of 6×4.5m as columns, and the columns and the embedded parts of the portal frame foundation are rigidly connected by flanges. The horizontal support of the portal frame adopts double-jointed 16-channel steel, and the vertical and horizontal diagonal supports adopt double-jointed 20-type steel; the horizontal beam between the two-leg portal frames adopts φ325×10mm steel pipes, and the upper and lower layers of steel pipes are connected vertically and horizontally with double-jointed 16-channel steel. 9 cross beams are set between the single-side towers. In order to facilitate construction, the steel pipe columns of the tower body are connected by flanges, and clamps are installed on the columns. The clamps are provided with connecting ear plates. The vertical and horizontal parallel links are connected to the clamp ear plates through axle pins to connect with the steel pipe columns. At the same time, hoists and tower cranes are attached to the steel pipe columns to facilitate the connection of construction equipment and towers. In order to facilitate installation, the tower steel pipe columns are designed with two standard sections of 6m and 12m, and are assembled into lattice column sections on site for overall hoisting and installation.

[0079] Steel anchor beam: The steel anchor beam is a fixing device for the cable and back cable on the tower. At the same time, the cable and back cable of this bridge are tensioned on the tower as a whole, so the two ends of the steel anchor beam are respectively provided with reaction brackets for overall tensioning. The steel anchor beam is welded with double-jointed 40 channel steel, and the channel steel web and top plate are reinforced. The reaction bracket is welded with the crossbeam and is designed with a cable turning groove. The steel anchor beam is connected to the steel platform of the tower by bolts. Tower foot: The tower foot structure has two forms: hinged and consolidated. This bridge adopts consolidated connection. Since the tower foot has to bear a large combined compression and bending stress, the steel pipe column within 6m of the bottom of the tower of the cable tower is filled with concrete to improve the bearing capacity of the bottom of the tower. The horizontality of the top of the steel pipe is controlled during construction. Foundation: The tower foundation of this bridge adopts pile foundation and temporary cap. The tower pile foundation adopts 1.5m diameter reinforced concrete cast-in-place piles, and the layout of the pile foundation is the same as the layout of the tower column steel pipe. The pile foundation adopts end-bearing pile design. The depth of entering the medium weathered rock layer is not less than 3.8m, and the pile foundation is required to sit on the intact bedrock. The temporary cap is 1.5m high, 14.5m wide and 25.5m long. It adopts reinforced concrete structure. The anchor rods for fixing the tower foundation are embedded in advance during the cap construction.

[0080] Ground anchor, also known as anchor, is composed of main cable anchor, back cable anchor and cable wind anchor in the cable system, which bear the tension of main cable, buckle cable and cable wind cable respectively. Main cable anchor: The main cable anchor adopts gravity anchor. Four gravity anchors are set on the north and south banks respectively, which are used to anchor the main cable of the cable crane and fix the tower wind cable. The plane size of the anchor is 12×12.5m, the anchor foundation is buried 10m deep, and the anchor section is 2.5m high. Each anchor has two main cable anchoring areas and four wind cable anchoring areas. At the same time, the anchor also serves as the winch, rope storage and pulley steering anchor of the cable crane power system. Six tooth blocks are set on the foundation to increase the friction between the foundation and the foundation, and improve the anti-slip ability between the anchor and the foundation.

[0081] Back cable anchor: The back cable anchor is a reinforced concrete gravity anchor, and the upper part is backfilled with soil for weighting. The anchor serves as the anchor end of the back cable. According to the tension and number of the back cables, two types of back cable anchors are designed for this bridge. Among them, the south bank anchor foundation is located in the fine sand layer after the foundation treatment is carried out with PHA hollow square piles, and steel sheet piles are used for support during the excavation of the foundation pit. Wind cable anchor: In order to limit the displacement or swing of the arch rib of the bridge under the action of wind load after erection, the arch rib wind cable should be installed simultaneously when installing the cable when each arch rib segment is erected. The anchor end of the wind cable is fixed on the arch rib, and the tension end is fixed on the wind cable anchor. Since the wind cable system is mainly designed for wind resistance, the pre-tension force when the wind cable is anchored is small. The design adopts an eight-shaped wind cable system, and 4 wind cable anchors are set on this bridge. The wind cable anchor adopts a gravity anchor. The anchor design is the same as the cable anchor. Power system: The power system of the cable tower refers to the cable hoist system, which includes the above-mentioned tower top steering saddle, anchor and anchor embedded parts, as well as lifting devices, rope systems (load-bearing cables, lifting cable systems, traction cable systems, back cables). Two sets of hoisting antennas are set up upstream and downstream of this bridge, and the hoisting weight of a single set is greater than 150t (200t level) for on-site construction.

[0082] The lifting device consists of a traveling crane, an upper hoist, a lower hoist, a shoulder pole beam and a rotating hoist. Two cranes are connected on a set of load-bearing cables. The traveling crane is assembled with the upper hoist as a whole. The lifting wire rope is wound between the upper hoist and the lower hoist. The front lower hoist in the upstream and downstream is connected to a shoulder pole beam, and the rear lower hoist is also connected to a shoulder pole beam. The shoulder pole beam is 20m long and is reinforced with welded steel webs. The main cable adopts a two-set cable scheme. The center spacing of the two sets of cables at the top of the tower is 46.5m. They are arranged symmetrically with the center line of the bridge. Each set of main cables is anchored on the anchor on the corresponding side. The saddle on the top of the cable crane tower can move horizontally to meet the needs of hoisting the cross bridge to different positions. Two sets of lifting cables are arranged on each set of main cables. The lifting cables rely on the coordinated work of two winches to form a cycle. A set of traction cables is arranged on each set of main cables.

[0083] Since the design of the cable crane and the tower is shared by the cable crane, a set of back cables is set on the top of the tower to balance the tower deviation caused by the cable crane. Cable system: In addition to the cables in the above-mentioned power system, the cable system mainly includes: the cable used for arch rib installation and load bearing, the back cables used to balance the tension of the tower caused by the cable, the eight-shaped wind cables set to prevent the arch rib from swinging due to the wind load after the arch rib is installed, and the wind cables set to adjust the deviation of the top of the tower. The above cables (except the power system and cable wind) all use steel strands with a diameter of 15.2mm and a strength of 1860Mpa, and the surface of the steel strands is treated with rust prevention. The cable wind cable uses φ28mm steel wire rope, the main cable of the cable crane uses φ60mm steel wire rope, the hoisting cable uses φ36mm steel wire rope, and the traction cable uses φ36mm steel wire rope.

[0084] Tower crane and elevator: In order to facilitate the installation of towers and auxiliary and power devices, a 7030 tower crane is installed on both sides of the upstream and downstream towers during the tower installation and cable crane installation stages, and an SC2000 elevator is installed on both sides of the upstream and downstream towers. After the tower installation is completed, the 7030 tower crane is temporarily removed. The tower crane is replaced with a QTZ125 tower crane at the original tower crane position for subsequent arch rib and main beam construction. After entering the site, the relevant professional and technical information should be consulted based on the engineering geological survey report provided by the construction party, various above-ground and underground pipelines and buildings (structures) within the scope of foundation pit excavation and the scope of influence, and other relevant information, and the construction age, usage status, location, burial depth and other data information of the pipeline. For information that is unclear, inconsistent with the actual situation, or does not reflect the actual situation of the pipeline in the information, the planning department and pipeline management unit should be consulted, and if necessary, pit exploration should be carried out in the presence of management unit personnel to find out the current situation. For above-ground and underground pipelines and buildings (structures) within the scope of the foundation pit, it is necessary to consult relevant information and conduct on-site investigation to understand the foundation, structural form, etc. of the structure. The actual conditions such as the location and depth of the investigated above-ground and underground pipelines and buildings (structures) shall be marked on the construction plan in proportion, and marked prominently on site. Analyze the investigation, pit exploration and other data as the basis for formulating protection plans for above-ground and underground pipelines and buildings (structures) and taking safety protection measures.

[0085] When formulating the underground pipeline protection plan, it is necessary to analyze the possible safety conditions of the above-ground and underground pipelines and buildings (structures) during the construction process, formulate corresponding protection, reinforcement and support measures for the above-ground and underground pipelines and buildings (structures), and ensure the safe operation of the underground pipelines. For important above-ground and underground pipelines and buildings (structures), the impact analysis of the foundation pit excavation conditions must be carried out. Determine the degree of impact so that reasonable foundation pit support and excavation methods can be determined in the construction measures to ensure the safety of pipelines and various structures during the construction process. The underground pipeline protection plan must be implemented with the consent of the management unit. For the existing pipeline relocation and protection measures, for the pipelines within the scope of the foundation pit excavation, the pipeline demolition, relocation and suspension reinforcement measures should be determined in consultation with the construction unit, planning unit and management unit. When the safety of the above-ground and underground pipelines and buildings (structures) within the scope of the foundation pit excavation is affected by the construction, or when it endangers the construction safety, temporary reinforcement should be carried out. After inspection, acceptance, confirmation that it meets the requirements, and the formation of documents, construction can be carried out. Since the construction of the bridge cable tower is the key to the construction of this project, in order to speed up the construction progress, night construction must be adopted. Therefore, before starting construction, a night construction plan for the project must be prepared and submitted to the relevant competent authorities for approval to determine the night construction time and construction noise control standards, as well as the duration of night construction. Tower pile foundation construction: The tower foundation is a pile foundation with a diameter of 1.5m. It is planned to use rotary drilling for construction. The single-side tower foundation construction uses four rotary drilling units for joint construction. Since the stratum cover layer on the south bank of this project is relatively thick and there is a sand and gravel layer, it is planned to use casing to follow the rotary drilling for the south bank tower pile foundation. The follow-up depth should ensure that it passes the gravel layer.

[0086] Drilling survey: Although the tower foundation of this bridge is a temporary structure, the tower is the main structure of the bridge construction, and the load borne by the tower is mainly compressive stress. Therefore, in order to ensure the stability of the tower foundation, drilling survey should be carried out before the pile foundation construction to ensure that the depth of the tower pile foundation into the rock layer is not less than 3.8m, and the thickness of the complete bedrock rock layer is not less than 4.5m. Measurement and layout: The pile position is laid out according to the principle of from the whole to the part. When planning the driving route, keep a certain distance between the access road and the drilling position to avoid affecting the stability of the hole wall; the drilling rig chassis should not be placed directly on the unsolid fill to avoid uneven settlement; the placement of the drilling rig should consider the convenience of excavation and transportation of the hole mouth during drilling construction. The center point of the pile position is set with a total station before drilling, the cross line is positioned, and the casing is lowered for secondary inspection. It must be inspected after the hole is completed and before the steel cage is placed to ensure that the error is within the specification requirements to ensure the accuracy of the pile position.

[0087] Casing burial: A solid and watertight hole casing is set at the hole position. The casing is made of 12-20mm thick steel plate to ensure that the casing is cylindrical and does not deform. The inner diameter of the casing is at least 100mm larger than the diameter of the drill bit, and 1-2 overflow holes should be opened on the upper part. When burying the casing, the cross-line should be used to control the buried position of the steel casing to accurately locate it. The vertical line of the center of the casing should coincide with the center line of the pile, the deviation should not exceed 50mm, and the vertical line inclination should not exceed 1%. The casing and the pit wall should be filled with clay without impurities to ensure the stability of the casing. According to the geological conditions on site, the buried depth of the casing is 1-1.5m, and the outer side of the lower end of the casing should be filled with clay, and its height should meet the requirements of the mud surface height in the hole. The height of the casing should be 0.3m above the ground to prevent surface water from entering the hole. The special extended casing connection requires no protrusions in the tube, and should be resistant to tension and pressure and leak-proof. Drilling rig in place: The drilling rig base should be placed on a solid ground to avoid uneven subsidence. The base and top of the drilling rig should be stable after installation, and no displacement or subsidence should occur during drilling. To maintain the verticality of the drilling rig, the controller is used to keep the drill rod vertical and the axis of the drill rod is strictly aligned with the pile position setting point (allowable deviation ≤ 10mm). After the drilling rig is in place, the construction team will conduct a self-inspection of the drilling rig in place. The technicians will then correct the deviation between the center of the turntable and the center of the casing, and check whether the turntable is horizontal to prevent the drilling hole from being skewed.

[0088] Preparation and use of mud: Establish a mud circulation system, which consists of a mud pool, a sedimentation tank, a delivery pipe, a mud ditch, a sewage storage tank and a mud pump. Before the drilling rig starts drilling, the wall protection mud must be prepared and a mud circulation system must be established. According to the specifications, the mud is prepared with clay with a viscosity of Ip ≥ 17, and the soil material must be soaked in water before stirring. A temporary rain shelter is set up in the mud pool to prevent rainwater from diluting the mud and keep the site clean. After the mud is prepared, drilling can be carried out. During the drilling process, the mud in the hole and the mud in the mud pool must be kept in normal circulation. The mud is pumped into the borehole to ensure that the mud top height is not lower than the casing bottom height. During construction, the mud specific gravity should be measured frequently, and the viscosity, sand content and viscosity should be measured regularly. Carry out the first test on the newly prepared mud, and test it again before use. Test it frequently during the drilling process to ensure the quality of the mud. Stir the stored mud every 8 hours, and keep the original record of each mud stirring or test result. Leave the fresh mud for 24 hours after it is made, and it can be officially used only after passing the test of various indicators. The recovered mud is processed by a vibrating screen and recycled after the performance indicators meet the requirements. Set up a mixing tank, a storage tank, a circulating tank, a sedimentation tank and a mud pump to form a circulating system for slurry supply, and the volume of the mud tank meets the requirements of the bored pile construction schedule.

[0089] When drilling, first put the drill bucket on the ground, and perform the zeroing operation through the reset button on the display to record the original position of the drill bit. At this time, the display shows the bar column and number of the current position of the drill hole. The operator can monitor the actual working position of the drill hole, the position of each penetration and the hole depth through the display, so as to operate the drilling operation. During the operation, the operator can monitor the working status of the hydraulic system in real time through the display of three virtual instruments on the main interface - power head pressure, pressurization pressure, and main volume pressure. When drilling, the weight of the drill bucket and pressurization are used as the drilling power. The short bar column of the penetration shows the current drilling depth of the drill bit, the long bar column dynamically shows the movement position of the drill bit, and the number of the hole depth shows the total depth of the hole. When the drill bucket is squeezed and filled with drill cuttings, it is lifted out of the ground, and the drill cuttings are loaded into the slag truck by a loader and transported to the outside of the site for disposal to avoid contamination of the site; after completion, the machine automatically returns to the drilling operation position by operating the automatic return and alignment button on the display, or the machine is manually returned to the drilling operation position by manually operating the rotary operating handle. This working state can be monitored through the return mark in the main interface of the display. During the construction process, the verticality of the hole is repeatedly checked through the three-way vertical control system of the drilling rig itself to ensure the quality of the hole.

[0090] Casing follow-up drilling: The construction of the Nan'an pile foundation uses casing to follow up and pass the pebble layer. During construction, a slightly larger steel casing is used as a follow-up casing, which is continuously followed down with the drilling hole. The DZ-90 vibrating hammer is used to clamp the casing, and the vibration is followed down. The casing is welded and extended at the hole mouth until the casing follows up and passes the rock layer. The casing follow-up drilling uses steel casing as a wall, so the hole can be formed by dry hole or clean hole. After the hole is formed, underwater concrete pouring is still used. During the concrete pouring process, the casing is pulled out as the pouring surface rises and is used in rotation. Hole cleaning and hole inspection: When the designed depth is reached, the supervision engineer checks that the geology at the bottom of the pile meets the design requirements, and then the hole cleaning can be started. The rotary drilling rig replaces the sand dredging drill bit to remove the sediment at the bottom of the hole. After the hole is completed and cleaned, the diameter, hole shape and inclination are inspected by a steel bar hole detector hoisted into the borehole. The center position deviation of the hole after pile formation is ±5cm; the hole diameter is not less than the design value, the inclination is less than 1%; the hole depth is not less than the design value.

[0091] Processing and installation of pile foundation steel cage, processing and production: steel cage and acoustic detection pipe are produced in sections, and steel cage rolling welding machine is used in the steel processing yard to process and shape. The joints are staggered by 50%, and the staggered length area is not less than 50d. According to the requirements, straight thread sleeve joints are used for connection. In order to facilitate transportation and orifice connection, the processing length of each section is ≤12m. The long-line lofting method is used to pre-assemble the steel sections during the processing process to ensure that the joints are accurately aligned during the front-field assembly. The finished steel skeleton is stored on a flat and dry site, arranged in the order of each section of each skeleton, and a sign is hung on each section, indicating the pier number, pile number, section number, inspection date, etc., so that it can be transported out in order when used.

[0092] A fixed hoisting structure is made on the top of the casing, and the steel cage is hung on the top of the casing. The steel cage is hoisted and placed in place by a crawler crane in combination with a truck crane. To ensure that the steel cage does not deform during hoisting, a long sling with a small angle is used to reduce the horizontal force, and two hooks are used for lifting. The deformation of the steel skeleton must be strictly controlled during the entire production, transportation, and hoisting process.

[0093] During the placement of the steel cage, the installation quality of the steel cage joints is strictly controlled. A torque wrench is used for on-site spot inspection. Before the steel cage is lowered, special concrete pads are tied to the main bars and stirrups to ensure the thickness of the steel cage protection layer. The speed is slowed down during the lowering to prevent collision with the hole wall.

[0094] Catheter placement: The duct is made of a steel pipe with a diameter of φ30cm. Before using the duct, watertightness, joint tensile and pressure tests must be carried out. Catheter requirements: The inner diameter of the duct is required to be φ30cm, and each section is 3m, 2.5m, and 1m long. The inner wall is smooth, straight, and clean without local bumps. The inner diameter of each section of the duct should be consistent in size, and the deviation should not exceed ±2mm. The pipe sections are connected with sleeves, and flange connections are not allowed. Watertight test: Before using the duct, watertight pressure and joint tensile tests must be carried out. It is strictly forbidden to use compressed air pressure test. A watertight test should be carried out. The water pressure of the watertight test should not be less than 1.3 times the pressure of the water depth in the hole, nor should it be less than 1.3 times the maximum internal pressure P that the duct wall and weld can withstand when pouring concrete.

[0095] The conduit can be pre-assembled in sections beside the drilling hole, and then spliced ​​section by section when it is hoisted. Use a crane or a drilling rig to lower the conduit, and use a drilling rig to lift and manually remove the conduit when pouring concrete. Secondary hole cleaning: The second hole cleaning is carried out after the steel cage and conduit are installed. The secondary hole cleaning method is the reverse circulation method. The conduit is used to maintain the normal reverse circulation flow of the flushing fluid until the thickness of the sediment at the bottom of the hole is less than the design requirement.

[0096] After the secondary hole cleaning meets the requirements, the reverse circulation equipment is immediately removed and underwater concrete pouring is carried out. The shorter the interval, the better. When pouring underwater concrete, sufficient raw materials should be prepared before pouring concrete, and the equipment should be maintained to ensure uninterrupted concrete pouring. The first batch of concrete pouring is constructed by the water stop ball pulling method. The amount of the first bucket concrete should be able to meet the needs of burying the lower mouth of the conduit for more than 1m and filling the space at the bottom of the conduit. During the concrete pouring process, the elevation of the top surface of the concrete should be checked at any time. When removing the conduit, attention should be paid to the buried depth of the conduit in the concrete, so that the buried depth of the conduit is controlled at 2 to 6m. When the concrete in the conduit is not full, it should be poured slowly to prevent the formation of high-pressure air bags in the conduit. When the pouring is about to end, the concrete in the conduit falls less, the pressure decreases, and the consistency and specific gravity of the mud and the slag outside the conduit increase. If there is difficulty in the concrete rising, some sediments can be taken out manually or mechanically to make the pouring work go smoothly. Concrete is poured underwater through the large aggregate hopper, small pouring hopper and conduit until the entire pile is poured. When pouring concrete, its top surface must exceed the design elevation by 1.0m, and the excess part must be chiseled off before the foundation construction.

[0097] Pile foundation quality inspection: Pile foundation quality inspection should be carried out after reaching 14 days of strength according to design requirements. Each pile is tested by ultrasonic non-destructive method according to design requirements, and the thickness of pile bottom sediment is tested by non-destructive method. Before pile foundation inspection, flush with plastic water pipes first. If there is siltation, flush continuously until the bottom of the hole. After the inspection, the ultrasonic test pipe is sealed by grouting.

[0098] The temporary cap construction of the tower can only be carried out after the pile foundation is completed and tested. The temporary cap is 1.5m high and adopts reinforced concrete structure. Excavation of foundation pit: Before the excavation of foundation pit, the positioning and setting out of the cap shall be carried out first. According to the edge line of the cap and the excavation slope, the width of the working surface shall be widened by 1m outwards, and the excavation contour line of the foundation pit shall be drawn. A berm shall be left at the edge of the foundation pit. The static load (abandoned soil and material stacking) shall be not less than 0.5m from the edge of the pit, and the dynamic load (machinery and locomotive passage) shall be not less than 1.0m from the edge of the pit. The height of the piled abandoned soil shall not exceed 1.5m. Before excavation, determine the location of the reserved backfill soil stacking, compact it, and reinforce the side slope of the stacking to prevent the slope from being damaged by pressure after the reserved backfill soil is stacked. During the excavation of the foundation trench, the surveyors work closely together to measure the foundation pit edge and base elevation at any time to ensure that the earthwork is in place and not over-excavated, and reserve 20cm for manual cleaning to prevent disturbance of the base bearing layer. After cleaning and leveling, the cushion layer is quickly poured to prevent moisture loss in the base soil and cause soil expansion. The cushion layer should be 15cm wider and 20cm thicker than the outer side of the cap, and cast with C20 concrete. Foundation pit drainage: 15×15cm drainage ditches are set around the foundation pit, with a longitudinal slope of 2% around to facilitate the flow of water around the drainage ditch. The excavation of the drainage ditch must be done by pulling the wire to ensure that it is horizontal, vertical, neat and beautiful. The accumulated water on the surface of the foundation pit flows into the sump through the drainage ditch, and then the accumulated water in the sump is discharged out of the foundation pit through a submersible pump or a sewage pump.

[0099] Pile head treatment: measure the elevation of the exposed concrete pile head, measure and place elevation points along the pile and draw ink lines. Cut along the line with a manual toothless saw, and the cutting depth should not exceed the thickness of the protective layer. Use an air compressor with a pneumatic pick to chisel the pile head layer by layer. When the pile head is close to the elevation of 10cm to 20cm, the quality of the pile chiseling should be controlled to avoid disturbing and destroying the concrete strength of the pile head and clogging the acoustic detection tube.

[0100] Rebar processing and binding: The binding of the foundation frame is carried out layer by layer. First, the bottom layer of the reinforcement frame is arranged. At the same time, the bottom layer of the upper frame is arranged every 2m. The two ends are welded to the lower frame into a whole. The supporting bars are arranged in a plum blossom shape in the middle. The supporting bars are welded to the upper and lower layers of the reinforcement frame. After the binding of the lower frame is completed, the stirrups of the pile foundation anchor bars are tied. The spacing between the stirrups meets the design requirements. Finally, the upper frame is installed.

[0101] The connection between the tower foundation and the bottom of the tower in this bridge design is made of pre-embedded screws with a diameter of 27mm and a material of 40Gr. The pre-embedded position and verticality of the screws are directly related to the verticality of the tower installation in the later stage. According to the specification, the verticality of the tower shall not be greater than L / 400; for this reason, the pre-embedded quality needs to be strictly controlled during the construction of the cap. When pre-embedding the screws, a 1cm thick steel plate should be used to open holes according to the designed anchoring position, and the pre-embedded screws should be installed on the steel plate. Nuts should be installed on both sides of the steel plate to limit the screws, and then placed on the surface of the cap steel bar. The steel plate should be leveled with a level ruler, and the steel plate should be temporarily fixed on the cap steel bar with positioning steel bars. At the same time, in order to ensure the smooth subsequent installation, the top surface elevation of the steel plate should be measured with a level when placing the fixed steel plate to ensure that the elevation error of all steel plate top surfaces is within 1mm. In order to avoid damage caused by stress concentration of the steel tube foundation concrete, a steel mesh should be laid at the bottom of the positioning steel plate.

[0102] Assembly and positioning of steel formwork: Before assembling the steel formwork, test assembly shall be carried out on site, rust shall be removed from the inside of the formwork and a release agent shall be applied. Elastic grouting materials shall be clamped in the joints of the formwork, and steel supports shall be provided on the outside. The lower end of the formwork shall be controlled by positioning pegs according to the plane position control line. The flatness of the formwork, the cross-sectional dimensions in the formwork and the verticality can be controlled by tightening the tie rod bolts and adjusting the support on the outside of the formwork. Concrete pouring and maintenance of the pedestal: The thickness of the horizontal layered pouring of concrete shall be preferably 30cm; the concrete shall be vibrated with an inserted vibrator. The vibrating rod shall be inserted quickly and pulled out slowly, and it shall be noted that it shall not be over-vibrated or missed. The vibrating shall be carried out evenly according to the vibrating radius of the vibrating rod until the concrete no longer sinks, bubbles are no longer emitted, and the surface is slurried. It is strictly forbidden to vibrate the embedded parts to prevent displacement. Special attention should be paid to avoid touching the embedded anchor rods during concrete pouring. After the initial setting of the concrete, the exposed surface of the concrete shall be tightly covered in time to reduce the exposure time and prevent the evaporation of surface moisture. Before the exposed surface is finally set, the covering should be rolled up and the surface should be rubbed and pressed with a trowel at least twice to make it flat before covering it again. Formwork removal: The pedestal is a non-load-bearing formwork. The formwork can be removed after the concrete reaches 2.5MPa. The formwork removal is carried out in the reverse order of the formwork. The formwork can be disassembled and hoisted only after the formwork is separated from the concrete. At the same time, it is necessary to strictly prevent the formwork, reinforcement support, etc. from hitting the concrete surface and its edges and corners. The removed formwork should be repaired and leveled in time to ensure the next use. Tower foundation reinforcement steel pipe fixation: The tower is designed to be fixed with the temporary pedestal by reinforcing steel pipes using anchor rods. The reinforced steel pipe with a height of 1.5m processed in the factory with upper and lower flanges is placed on the surface of the pedestal through the embedded anchor rods. Since the construction method of overall hoisting on the back-field assembly site is adopted during the tower installation, the elevation position of the top surface of the steel pipe is required to be consistent.

[0103] Put the bottom flange of the foundation reinforcement steel pipe through the embedded anchor rod and temporarily place it on the surface of the pedestal. Use a level to measure the elevation of the top surface of the steel pipe, and determine the reasonable elevation of the top surface of the foundation steel pipe based on all the measurement data. Adjust the elevation of the reinforcement steel pipes one by one, and use wooden wedges to adjust the elevation and levelness of the top surface of the steel pipe. After the adjustment is completed, lay a mortar bag to stop the grouting at the gap between the edge of the steel pipe and the top surface of the pedestal. Pour M50 cement mortar into the gap along the reserved holes of the reinforcement steel pipe. After the mortar reaches 80% of the design strength, the next step can be entered. After the first 6m segment of the tower is installed, the concrete pouring in the steel pipe column can be carried out. Tower segment processing and installation: Tower structure and installation method, the single-side tower is assembled with 15 layers of steel pipe columns and 7 layers of steel platforms, and the towers are connected as a whole by 9 layers of flat joints. In order to speed up the tower construction, the on-site tower adopts a fully assembled design. Bolts are used to connect the upper and lower steel pipe columns, and between the steel pipe columns and the steel platform. Prefabricated clamps are used to connect the vertical steel pipe columns. A single prefabricated clamp can provide a connection for up to 12 parallel rods, which can limit the freedom of the steel pipe in four directions.

[0104] Two 7030-type tower cranes are installed on site for the installation of each cable tower. They can lift 12 6m standard sections at the same time, and 6 12m sections at the same time. The tower is installed by two tower cranes to lift the tower sections respectively, and temporarily fix them after lifting them in place, and then lift the steel pipes to connect them for steel pipe installation. The processing of tower structure parts, steel pipe columns are φ800×25mm, Q355 welded steel pipes, flange connection, the main welds are all penetration welds, the flanges are polished and tightened with the steel pipes, and the flange surfaces are machined and planed. The focus is on controlling the quality of welds, polishing and tightening quality, pipe segment ovality, coincidence rate with the axis and flange surface flatness.

[0105] The flange is customized in the processing plant. The flange is made of 24mm thick steel plate. The bolt hole is punched once. The burrs of the hole are corrected to ensure that the flange hole is smooth and round. The assembly quality of the flange and the steel pipe not only affects the strength of the pipeline joint but also affects the verticality of the entire steel pipe column. Therefore, the flange must meet the following requirements when assembling the flange on the steel pipe: the center of the flange should be in a straight line with the center of the steel pipe; the flange sealing surface should be perpendicular to the axis of the steel pipe; the position of the screw hole of the flange on the steel pipe should be fixed and consistent with the position of the screw hole of other flanges, and the screw hole positions of the flanges at both ends of the same steel pipe should correspond one by one. When the flange is assembled with the steel pipe, the flange and the steel pipe end should be grooved, and the groove height should not be less than 20mm. Ensure that the parent material is melted through during welding. Before welding, the steel pipe should be placed on an adjustable steel pipe horizontal bracket, and the height of the bracket legs should be adjusted with a level ruler to ensure that the steel pipe is in a horizontal state. Put the flange on the pipe end, and use the angle ruler and flange bend ruler to correct the verticality of the flange, and then spot weld the flange on the steel pipe. Rotate the steel pipe on the bracket 90 degrees, use the flange bend ruler and angle ruler to correct the verticality of the flange again, and spot weld the flange again. In order to prevent the flange from deforming due to temperature stress during welding, the welded parts should be preheated before welding the flange to the steel pipe, and then the flange should be connected to the fastener with greater rigidity with bolts to prevent the welded parts from deforming during welding. The welding between the steel pipe and the flange should be welded by an automatic welding robot, and the welding speed should be controlled to ensure that the parent material is melted through during welding. Due to the large width of the weld, welding should be carried out in two layers. Although the tower structure is a temporary structure, the welding quality should be controlled according to the requirements of the secondary weld.

[0106] After the flange and the steel pipe are welded, the connecting angle plate is welded to improve the flange strength and prevent the flange from deformation. The connecting welds between the flange and the steel pipe should be inspected and tested according to a certain proportion. In order to facilitate the installation of the steel pipe bracket, a ladder made of L5 angle steel should be welded on the side of the steel pipe. Due to the high height of the tower, it is inevitable that accumulated errors will occur during installation. If a rigid connection is used between the flat joint and the steel pipe, it will inevitably affect the connection quality of the flat joint and the steel pipe and affect the construction progress. For this reason, the flat joint and the steel pipe are designed to be connected using a clamp.

[0107] Segment installation: When the segment is hoisted and installed as a whole, the parallel joints between the steel pipe columns should be installed along with the installation of the steel pipe columns. At the same time, the verticality of the steel pipe columns should be strictly controlled using a level ruler to ensure that the verticality deviation is within L / 400. If the verticality deviation is found to exceed the standard during the installation process, it should be adjusted by adjusting the parallel joint position and adding wedge-shaped supports at the flange connection position.

[0108] While assembling the steel pipe columns, the tower crane and the elevator should gradually increase the standard sections as the steel pipe columns are installed. The tower crane and the column are attached by flange connection. When installing the steel pipe, the wind rope should be installed on the top of the steel pipe column and anchored on the ground anchor after the construction is completed or during the downtime every day. To ensure the speed and installation accuracy. When installing each segment, first install the tower limb on the near tower crane side, and then install the tower limb on the far tower crane side. After the installation of the corresponding segment, the horizontal braces, diagonal braces and other components between the segments are connected immediately to ensure the stability of the structure.

[0109] When lifting the segment, the tops of the six steel pipe columns are connected to a special lifting device. The bottom of the six steel pipe columns is fixed with wind ropes at the four corners. When the segment is lifted to the height to be installed, the tower crane is transferred to the vicinity of the installation location, and the wind rope is used to guide the segment to the corresponding tower position to achieve the rough alignment of the segment. The rough alignment requires an accuracy of 5cm, mainly to ensure that the column and the tower are one-to-one corresponding.

[0110] After the rough adjustment is completed, the tower crane is temporarily locked, and the steel pipe column is finely adjusted using the hand chain hoist fixed on the tower frame in advance to ensure that the column is accurately aligned with the guide plate at the top of the installed segment. Then the tower crane slowly lowers the hook. At this time, if the segment is offset, it will be guided by the guide plate to gradually align with the pipe mouth of the installed segment, achieving accurate alignment between the segments.

[0111] After the segment is installed in place, the flange bolt holes on the outside of the column joint are used to install the positioning bolts to achieve temporary fixation of the steel pipe column. Then check the quality of the steel pipe docking and the deviation of the segment top. After the overall frame is installed, the remaining longitudinal, transverse and diagonal parallel connections between the tower limbs are installed to achieve the integrity between the individual tower limbs.

[0112] The longitudinal diagonal brace between the tower limbs is designed to be a double-piece 20 and 16 channel steel. After the small tower crane between the tower frames lifts the parallel connection into place through two points, the parallel connection is installed on the steel pipe column using an axle pin. After the parallel connection between the buckled tower steel pipe columns is installed, the transverse connection (cross brace) between the tower limbs can be installed. The single-piece cross brace is processed into a whole on the ground, and then directly lifted and installed by a tower crane and roughly adjusted. After the cross brace is close to the installation position, the four corner points are connected with steel wire ropes connected to the hand winch. According to the installation direction to be adjusted, the corresponding hand winch is selected to achieve accurate installation and positioning of the cross brace. The transverse diagonal brace between the tower limbs is designed to be The steel pipes are connected by double-jointed 16 and 20 channel steels.

[0113] Installation of construction platform on the tower: In order to install the anchor and cable crane, a total of 7 construction steel platforms are installed on the tower. The steel platform is made of double-jointed 800×300 H-shaped steel. Bolts are used to connect the double-jointed H-shaped steel to the flange of the steel pipe column. The bolt holes of the steel platform correspond to the bolt holes of the column flange. The top and bottom surfaces of the steel platform are covered with steel plates for connection with the steel pipe columns. The steel platform is installed on the top surface of the steel pipe column with high-strength bolts. The level of the top surface of the platform is adjusted with a level ruler, and the level of the steel platform is adjusted by supporting the wedge-shaped steel plate. 10 channel steels and wooden springboards are laid between the steel platforms as construction platforms. The steel anchor beam is made of double-jointed 40 channel steels, and bolt holes are opened at the ends of the channel steels. The steel anchor beam is connected to the steel platform with high-strength bolts.

[0114] Ground anchor construction: The maximum excavation depth of the ground anchor is about 9m, which exceeds the scope of a certain scale of dangerous and large projects. It is necessary to prepare a special construction plan and conduct expert demonstration, and the plan can only be implemented after it passes the expert demonstration. The ground anchors of this project include main cable ground anchors, back cable ground anchors, and wind cable ground anchors. Their construction methods are basically the same. The construction of the main ground anchor with cable suspension is used as an example to illustrate: Foundation pit support and excavation: The designed foundation pit adopts Larsen IV steel sheet piles for foundation pit support, and the internal support adopts a combined steel structure and a steel pipe structure. The foundation pit excavation should follow the principle of segmentation and layering, from top to bottom, and support first and then excavation.

[0115] Excavation of the first layer of earthwork: After the steel sheet piles are driven into place, the foundation pit can be excavated. The shallow earthwork can be directly excavated and excavated by short-arm excavators and long-arm excavators. When conditions permit, two long-arm excavators are used to dig soil on both sides of the foundation pit at the same time, and advance forward in sections together, which can greatly increase the excavation speed and provide conditions for the installation of purlins and supports. For shallow earthwork excavation, the four corners are excavated first, and then the center is excavated. When the excavation reaches 0.5m below the design elevation of the purlin, the excavation is stopped, and the purlins and internal supports are installed. Excavation of deep earthwork: When the long-arm excavator cannot excavate, a small excavator should be hoisted into the foundation pit, and the excavated earthwork should be transferred to the side of the steel sheet pile wall, and then the earthwork is hoisted out with a grab bucket and transported by a dump truck.

[0116] When the foundation pit is excavated to the top of the tooth block at the bottom of the anchor, stop mechanical excavation and use manual excavation to excavate the tooth block. It is important to pay special attention to the horizontal deformation of the foundation pit retaining structure, the vertical deformation of the retaining structure, the uplift of the bottom of the foundation pit, the surface settlement and the displacement of surrounding buildings during the foundation pit excavation. If any unexpected situation is found, the excavation should be stopped immediately and properly handled. Foundation bearing capacity detection: The anti-slip ability between the cable anchor and the foundation and the bearing capacity of the foundation are very important for the construction of the cable system. Therefore, the foundation bearing capacity should be tested first after the foundation pit is excavated. The test adopts the light penetration method.

[0117] Layered pouring of anchor foundation: The anchor foundation concrete adopts C30, and the surface area and height are large. During construction, the concrete should be poured in layers, and the pouring surface should be used to dissipate heat to reduce the possibility of cracks during construction. When choosing a pouring scheme, in addition to ensuring that each concrete is covered and compacted by the previous layer of new concrete before initial setting, the influence of factors such as structure size, concrete supply, and hydration heat should also be considered. Full layering: After the first layer is fully poured, the second layer is poured back. At this time, the first layer of concrete should not have initial setting. In this way, continuous pouring is carried out layer by layer until completion. The layer thickness should be 1.5-2.0m. If necessary, it can be divided into two sections, and poured from the middle to both ends or from both ends to the middle at the same time. Segmented layering: When pouring concrete, start from the bottom layer first, pour the second layer after pouring to a certain distance, and pour the other layers forward in turn. Because the total number of layers is large, after pouring to the top, the concrete at the end of the first layer has not yet initially set, and it can be poured in layers from the second section in turn.

[0118] Layered removal of anchor pit internal supports and purlins: Due to the large cross-section of the anchor structure, it is inevitable that the internal supports and purlins will affect the anchor construction during construction. Therefore, each layer of anchor should be backfilled in time and then a layer of purlins should be removed to facilitate the construction of the next layer of anchor. Before removing the purlins, the foundation pit should be backfilled first. During backfilling, care should be taken not to damage the original internal supports and purlin structures. When backfilling, the backfilling should be carried out in accordance with the requirement that the thickness of the virtual layer should not exceed 50cm. After each layer of backfilling, a small tamping machine should be used for compaction. The foundation pit is backfilled to about 20cm below the top surface of the poured concrete for the support of the anchor foundation formwork on the next side. First remove the internal supports, then remove the purlins, and use a crane to lift them out of the foundation pit.

[0119] Anchor reinforcement binding and formwork support: For the relevant requirements of anchor reinforcement binding, please refer to the requirements for reinforcement binding for temporary pedestal construction. Only the key points that need attention are described here. The anchor structure is the main load-bearing component of the cable crane. When tying the anchor reinforcement, it should be noted that the reinforcement and the embedded parts should not interfere with each other. The position of the embedded parts should be accurate. If there is interference with the reinforcement, the position of the reinforcement should be adjusted appropriately. The anchor arc steel plate is used as the formwork for the main structure and concrete pouring. It is used as an anchor for the steel wire rope to directly contact in the subsequent construction. The surface of the steel plate is required to be free of burrs, protrusions, etc. to prevent affecting the anchoring of the steel wire rope. The anchor structure is relatively special. In order to improve the surface construction quality of the anchor concrete, a fixed steel formwork and steel formwork are used. In order to facilitate the positioning and assembly of the anchor formwork, the angle steel can be embedded and welded to the rigid skeleton during the anchor foundation construction. The key points of anchor concrete pouring refer to the requirements for large-volume concrete pouring, which will not be repeated here.

[0120] Maintenance during the use of the cable tower: The installation of arch ribs, installation of back cables, and main beam hoisting during the use of the cable tower are not covered in this plan and will not be repeated here. The following points need special attention: During the use of the cable tower, a GNSS tower deviation automatic monitoring device is installed on the top of the tower, and an early warning value is set. When the tower deviation exceeds the standard, the wind cable is used to adjust the displacement of the tower top. At the same time, the tower deviation measured by the tower deviation automatic monitoring device is compared with the monitoring theoretical calculation data to adjust the stiffness of the tower and other data, so that the theoretical model is more consistent with the actual situation and ensure the accuracy of the arch rib installation. Organize a comprehensive safety inspection of the tower system every month, focusing on the status of welds, bolt connections, steel platforms, steel anchor beams, and cable hoist systems. If problems are found, they should be rectified in time. The tower elevator and tower crane should be fully enclosed around to ensure that no unauthorized personnel can enter the tower area. Since the steel anchor beam platform on the tower needs to be tensioned, all areas accessible to personnel must be fully covered with springboards and edge protection should be done well. When installing the cable, the back cable should be installed synchronously according to the monitoring instructions to ensure that the tower is in a stable state. After the installation of the back buckle is completed, the overall vertical line shape of the tower should be measured to determine the deformation of the tower.

[0121] Tower dismantling: The tower dismantling can be started after the cable crane is dismantled. Due to the high height of the tower in this project, a special construction safety and technical plan needs to be prepared for the dismantling. Here, only the process and key points of tower dismantling are described. The tower dismantling is arranged with the tower installation equipment. The QTZ125 tower crane is dismantled and replaced with a 7030 tower crane. The tower is dismantled in sections. The tower dismantling is carried out according to the procedures of dismantling the auxiliary structures on the tower, installing temporary wind cables, lowering the tower flat joints as a whole and dismantling the steel pipe columns, gradually lowering the tower crane and the elevator, dismantling the steel pipe columns, and dismantling the temporary pedestal. Before dismantling the tower, the auxiliary facilities on the top of the tower must be dismantled first, and all the steel anchor beams on the tower must be removed to prepare for the removal of the steel pipe columns. Prepare a dismantling plan and install temporary wind cables on the tower according to the dismantling plan. Ensure that the tower is stable during the dismantling process. Plan the material storage site and organize the dismantled steel pipe columns and flat joints. The demolition is carried out according to the plan of hoisting the entire section and dismantling it in the back field, and the tower is dismantled according to the plan of dismantling one layer at a time and releasing the connection of one layer.

[0122] Two 10t winches are fixed on the steel platform. The tower flat joint is temporarily fixed by the pulley block and winch, and the wind cable is installed. Then the connection between the flat joint and the tower is removed, and the flat joint is lowered to the bottom of the tower by the winch. During this period, the wind cable is used to adjust the position to prevent the tower and other flat joints from being touched during the lowering of the wind cable. After the flat joint is lowered to the bottom of the tower, it is dismantled by crane. Before dismantling the steel pipe column, first release the flat joint connection of the tower to be dismantled. Then release the bolt connection between the steel pipes, and use the tower crane to hoist the steel pipe column. After the steel pipe column is hoisted, the operator is arranged to use a 25t crane to dismantle the flat joint of the steel pipe bracket, and separate the assembled flat joint rod and flat joint hoop in the stacking position. Since there is no operating platform at the connection part of the steel pipe column, the operator is required to make a professional hoist cage for bolt dismantling during the dismantling. The tower is high. In order to ensure safety, the tower should be dismantled layer by layer and the flat joint should be removed layer by layer. As the tower is dismantled, the tower crane and the elevator should be gradually lowered. The dismantled tower components should be classified and stacked in designated areas, and limit devices should be installed to avoid stacking too high, which may cause the steel pipe to collapse. After the tower is dismantled, the temporary foundation should be excavated with a blasting hammer and an excavator, and the original ground should be restored after excavation.

[0123] Step 4: Cable hoisting system installation and disassembly. Cable hoists are lifting equipment that runs in the air. The quality of their processing, manufacturing and installation is particularly important. The cable hoist structure has steel structure welded components, machined pins, casting pulleys and some purchased parts and materials such as bearings and wire ropes. The installation process of the cable hoist is as follows: Figure 5 shown.

[0124] Step 5: Construction of the main arch steel-concrete joint section, such as Figure 6 shown.

[0125] Step 6: Construction of the bridge deck system and accessories. After the cable tension and the adjustment of the entire bridge line meet the requirements after the closure, the bridge deck pavement and accessories are constructed, the cable lifting system and tower are dismantled simultaneously, the approach bridge project is constructed, the bridge load test is carried out, and the entire bridge is opened to traffic.

Claims

1. A bridge construction method, characterized in that: The method comprises the following steps: Step 1: Construction of the north bank arch seat and the south bank arch seat; Step 2: Cable lifting system installation; Step 3: Arch rib installation; Step 4: Steel beam installation; Step 5: Construction of the bridge deck system and accessories. After the cable force and the full bridge line shape adjustment meet the requirements after the closure, the bridge deck pavement and accessories are constructed, the cable hoisting system and tower are dismantled simultaneously, the approach bridge project is constructed, the bridge load test is carried out, and the whole bridge is opened to traffic; Step 6: Approach bridge construction.

2. A bridge construction method according to claim 1, characterized in that: The specific process of step 1 is: North bank arch seat construction: First, the retreat method is used to excavate the first two levels of foundation pits, and the inclined leg pneumatic drill is used to install anchor rods for grouting, and the net is hung to spray concrete to complete the slope support. The steel trestle is built step by step by the fishing method, and a construction platform is built. Steel pipe piles on the river side are used as flood control facilities on the river side. The excavator is installed to retreat and load the bucket, and the gantry crane is used to transport it to the outside of the site. Following the principle of supporting first and then digging, the internal support is installed in time, and excavation is carried out layer by layer. The foundation steel bars and rigid skeleton are installed, and the formwork is supported on the river side. The cooling pipes are installed in layers, and the arch seat foundation is poured; South Bank Arch Seat Construction: The South Bank Arch Seat consists of two separate circular foundations. The outer diameter of the cap beam is 48m. The circular wall is formed by 1.8m interlocking piles. The height of the pedestal is 8m. Tooth blocks are set at the bottom. The pile guide wall is constructed first, and a rotary drilling rig is used to drill holes. The interlocking piles are constructed using the mud wall protection technology. The A and B piles are interlocked into a ring by hard interlocking. After the pile foundation is qualified, the pile head is broken and the cap beam is constructed. The static pressure double-liquid method is used to grout the pebble layer in the foundation pit and the soil layer behind the foundation pit. An excavator is used inside and outside the foundation pit to dig and load soil and stone. The long-arm excavator takes over the transportation and excavates layer by layer. The arch seat foundation steel bars, rigid skeleton, cooling water pipes are installed, and the arch seat foundation is poured.

3. A bridge construction method according to claim 1, characterized in that: The specific process of step 2 is: Due to site constraints, the buckle tower is located in the second span of the rear approach bridge behind the arch seats at both ends. The pile group foundation is constructed. The buckle tower is an assembled tower frame, 188.648m high on the north bank and 206.696m high on the south bank. The distance between the buckle towers is 706m. The buckle tower is hoisted in sections, and each section is composed of 6 12-meter φ800×25 steel pipe columns. Each group of tower frames is pre-assembled into a lattice column section with a length of 12m in the longitudinal direction of the bridge, a height of 4.5m in the transverse direction of the bridge, and a height of 12m. The maximum lifting weight of the section is 38 tons. The TC7030 tower crane is used to lift and install the entire section. Two groups of hoisting antennas are set up upstream and downstream of the bridge. The center distance between the two groups of cables at the top of the tower is 46.5m, and they are arranged symmetrically with the center line of the bridge. The saddle on the top of the cable crane tower can move laterally with a moving range of about 20m. The rated maximum lifting weight of the cable crane is 4×200t.

4. A bridge construction method according to claim 1, characterized in that: The specific process of step 3 is: The main arch line is a basket arch, with an inward inclination of 8°. The arch rib is a single-box single-chamber box section with equal width and height. The single-limb arch rib is divided into 47 segments, with the longest segment being about 17.8m long and the maximum weight being the G4 segment, about 313 tons. It is transported to the lifting site via the Yangtze River waterway and accurately positioned by a positioning ship. The transport ship drops anchor to stabilize the hull, and the cable crane lifts the G1 segment into place and extends it into the arch seat. The crawler crane and manual hoist are used to accurately position the arch rib space and adjust its posture. The temporary bracket is fixed, the arch seat concrete is poured, and the G 1 The partition is filled with concrete and prestressed. The remaining segments are installed symmetrically. When installing to G17 section, avoid cable entanglement and hoist them alternately on both sides. The buckle cables of each segment are temporarily fixed and the corresponding back cables are hung simultaneously. Tension is made on the buckle tower to balance the tension on both sides. The interrib cross braces and arch rib segments are installed simultaneously. When the temperature ranges from 16 to 22 degrees Celsius during the period, the G24 closure section is hoisted. The remainder is cut according to the monitoring data. The segments are connected by bolts first and then welding to achieve full arch closure. Permanent and temporary hangers of the entire bridge are installed from both ends to the mid-span.

5. A bridge construction method according to claim 1, characterized in that: The specific process of step 5 is: The main beam is a double-layer orthogonal anisotropic plate box beam with a total width of 48.5m and a beam height of 3.5m. It is divided into 43 sections and has a maximum lifting weight of 281 tons. It is installed section by section from the arch foot symmetrically to the span using a lifting pole beam and closed in the middle of the span. At the beginning of the lifting, the transport ships in the floodplain section of the south bank of the S21 to S15 beam sections could not berth at the beginning. Due to the limitation of the lifting point position of the basket arch space, a temporary transfer platform was constructed at the river beach on the south bank first. The lifting point was replaced by the platform, and the main arch was crossed to achieve lifting into place. The beam transfer platform was set under the S15 beam section to ensure that the lifting point of the steel beam could be transferred here. It was lifted to the predetermined position with a special lifting device, and the temporary and permanent hangers were fixed. The bridge deck line was adjusted according to the monitoring data, and the adjacent sections were welded and connected.

6. A bridge construction method according to claim 1, characterized in that: The specific process of step 5 is: The specific process of step 6 is: For the approach bridge pile foundation project, after the construction of the cable tower pile foundation is completed, according to the demolition progress, the north bank approach bridge pile foundation construction can be carried out after the Danxia Road is closed. The south bank approach bridge pile foundation will not affect the cable tower construction, and in order to reduce the impact of the pile foundation construction team on the cable tower anchor and cable hanging anchor construction; Substructure construction: The piers affected by the cable-stayed buckle system are C2, D2, M2, and M16. The pier affected by the cable hanger is M18. The substructure construction of the main bridge approach will be carried out in stages. The uninterrupted parts will be constructed first, and the construction of the disturbed piers will be accelerated after the interference is removed. Cast-in-place beam construction: The construction of cast-in-place beams of piers 0#-4# on the north bank is disturbed by the anchor of the back cable, and the cast-in-place beams of piers 6#-9# are restricted by the position of the buckle tower. The cast-in-place beams of piers 0#-6# are constructed first after the main arch is closed and the anchor of the back cable is removed; after the main beam is closed and the buckle tower is removed, the whole cast-in-place beams 6#-9# are constructed. The cast-in-place beams of the north bank are constructed with steel pipe Bailey brackets, and the bridge deck ancillary works are also constructed following the main beam construction. After the whole bridge is connected, the bridge deck asphalt paving will be carried out uniformly; A total of 4 sets of cast-in-place beams M10-M15 on the south bank are affected by back cables and anchors and can only be constructed after the main arch is connected. A total of 4 sets of cast-in-place beams M15-M21 are affected by cable hangers and can only be constructed after the main beams are connected. M21-M26 are not affected and will be constructed first. The cast-in-place beams of non-critical line projects M10-M15 and M21-M26 are constructed using steel pipe Bailey supports, while the critical line M15-M21 section is constructed using disc-hook supports.

Images