The following is the relevant content about the construction plan of bridge pile foundation brought to you by Zhongda Consulting for your reference.
1 Pile foundation construction
This method is adopted when the geological conditions are complex and the water is deep, and it is impossible to carry out open excavation and expanded foundation construction. Pile foundations are divided into friction piles and support piles. Applicable conditions for friction piles and support piles: Applicable conditions for friction piles: water depth and complex ground support. The ground support drilling data shows that there is no rock layer even at a depth of 50 or 60 meters. The bottom of the pile can only use the sand layer as the supporting layer. The bearing capacity is calculated based on the friction around the pile. Applicable conditions for supporting piles: water depth, complex geology, geological drilling data show that there is a rock bearing layer, the bottom of the pile is embedded in rock to the weakly phosphorized layer 2.53.5m, the uniaxial bearing capacity of the rock layer is not less than 800kpa, and the rock layer is allowed to Bearing capacity is used to calculate the bearing capacity of piles.
1.1 Pile foundation drilling construction method
The commonly used machines for pile foundation drilling are rotary drilling rigs and impact machines. Both of these machines are used to drill mud, sand and rocks. Crush it into pieces, and then use mud circulation to clear the waste out of the pile holes. Construction method:
① Set up the drilling rig platform at an elevation higher than the designed construction water level. Normal drilling cannot be affected by soaking the machine due to changes in water level. Generally, it is a steel pile steel platform.
② When constructing a steel casing, the diameter of the steel casing should be 10cm-2Ocm larger than the pile diameter. The bottom of the steel casing should be embedded in the strongly weathered rock formation and
pass through the weak layer. The elevation of the tube top should be higher than the design construction water level. The welds of the steel casing must be firmly welded without cracks or leaks. The thickness of the steel casing steel plate is generally 8mm-10mm. The functions of the steel casing are: positioning of pier piles, drilling guide, separating the inside and outside of the pile hole, and preventing water level changes from affecting drilling. During hole construction (the water level inside the hole should be higher than the water level outside the hole), the mud circulates from the top of the steel casing back into the mud pool. When the steel casing leaks or the wall of the pile hole leaks, the mud cannot circulate and the waste material cannot be cleared out of the hole. , the pile hole cannot be drilled; when the pile foundation is poured with concrete, the concrete surface must be exposed to the water surface before the pile can be connected dryly. From the underwater ground to the water surface, the steel casing is used as a template. Stay under water and do not pull out.
③ Mechanical drilling; after the drilling rig platform is set up, install the drilling rig on the platform and position the drilling rig accurately. The center line of the drill bit or punch of the drilling rig must be offset from the center of the pile hole. Then start the drill to drill.
④Circulating mud ballast cleaning: Generally equipped with a high-pressure mud pump, the mud pump presses the mud in the mud pool to the bottom of the pile hole through the mud pressure pipe. The mud sticks to the waste ballast to form suspended matter. The mud pump does not Stop the operation and continuously apply pressure to the bottom of the hole. When the applied pressure is greater than the weight of the mud waste in the pile hole, the mud is fully discharged from the top of the steel casing, and the mud flows back into the mud pool through the chute. The flow rate of mud in the chute should be slow to give the mud a certain amount of time to settle. In this way, most of the waste ballast will settle in the chute. The ballast remaining in the chute will be manually fished out of the chute to increase the ballast content of the mud flowing back to the mud pool. Want less. The role of mud is generally to use soil with good clay properties to be crushed and diluted. The concentration should be based on the actual situation and should be able to suspend the ballast. If it is too thick, it will not be easy to settle in the chute and it will be inconvenient to clean the ballast. If it is too thin, it will cause the ballast to settle. Can't levitate. Another function of the mud is that the vertical movement of the drill bit cements the clay in the mud to the wall of the pile hole, thereby consolidating the hole wall, preventing the mud water in the pile hole from leaking out of the pile hole, and keeping the pile in place. The water level inside the hole is higher than the water level outside the hole, and the specific gravity of the mud is greater than the specific gravity of the clear water outside the pile hole. The water pressure inside the pile is greater than the water pressure outside the hole, so it is not easy for the hole to collapse. If the steel casing leaks, when the water level outside the pile hole changes and the water pressure inside and outside the hole collides, the hole will inevitably collapse. The situation of the hole collapse is very complicated, and the method of dealing with the collapse hole is also very troublesome, which will not be discussed here.
⑤ Pile hole clearing: The hole can be completed after the drilling reaches the designed pile bottom elevation. After the final hole, there is a lot of ballast in the pile hole, the mud concentration is high, and the sand content of the mud is very high. At this time, the hole needs to be cleaned. The sand content and consistency of the mud must meet the requirements of the "Specifications". The general method is: replace the For clay mud, use a mud pump to replace the old mud in the pile hole. After the sand content is less than 4%, add water to reduce the mud consistency.
⑥Install the steel cage: After the hole cleaning is completed, the pile foundation steel cage can be installed.
Generally, a truck crane or the main engine of a drilling rig is used for hoisting. The pile holes are hoisted in sections and welded in sections. The embedded detection pipes must also be connected and installed at the same time as the steel cage. When hoisting the steel cage, it must be vertical to avoid cutting the pile hole guard wall and causing collapse of the hole.
⑦ Underwater pouring of concrete: The key to the quality of a pile is how to operate it when pouring concrete underwater. After the grouting conduit is installed into the pile hole, the grouting conduit must be used to clean the hole again. The reason is that it takes five or six hours to complete the installation of the steel cage and grouting conduit, and the mud in the pile hole has stopped for five or six hours. Without circulation, sediment must be produced and sink to the bottom of the pile, and it must be cleaned until there is no more sediment.
If the concrete slurry is poured directly into the water, the cement slurry will inevitably be lost and the sand and gravel will sink to the bottom. To separate the concrete in the pile holes, special devices and special construction methods must be used. This special device consists of a duct and a hopper filled with concrete slurry. The hopper is connected to the duct, and a switch is installed in the hopper. The principle of underwater concrete pouring is: after the conduit and hopper are installed, put the bottom of the conduit to the bottom of the pile hole, and then lift the conduit up 0.3m; fill the hopper with concrete slurry, prepare several cubic meters of concrete slurry, and use a winch to The switch in the hopper is turned on, and the concrete slurry suddenly moves along the conduit, squeezing the muddy water in the conduit down the bottom of the pile and out of the conduit. The concrete slurry falls from high to low, and the energy generated by the free fall motion and the impact force push the pile. The mud and ballast at the bottom lift away from the bottom of the hole, and the concrete slurry occupies the bottom of the pile. Under the action of the impact force, the concrete slurry is lifted upward along the pile hole and the bottom of the conduit is buried. At this time, the inside of the conduit and The bottom of the pile is filled with concrete and there is no muddy water. Subsequent concrete is continuously fed into the conduit, the concrete slurry in the pile hole also rises, and the mud water in the pile also rises until it is discharged out of the pile hole. The operation of pouring concrete underwater is very critical:
(1) The conduit is connected by numerous sections (each section is 2.5-3.Om). The joints must be tightened with rubber pad bolts to prevent water leakage. .
(2) The first bucket of slurry must be lowered to the bottom of the pile hole, that is, the depth of the buried pipe must not be less than 1.0-1.5m. Calculate the volume of the hopper after the diameter of the pile. How big is the volume of the hopper? When the length exceeds 20m, the empirical data indicates that the hopper volume shall not be less than 4m3.
(3) In order to make the concrete slurry in the hopper drop to the bottom of the pile quickly, the shape of the hopper and the friction of the hopper must be fully considered to reduce the friction as much as possible.
(4) During the pouring process, the height of the reverse insertion of the conduit cannot be too high, and the depth of the buried concrete pipe must be strictly controlled to not be less than 6m.
(5) As the height of the concrete in the pile hole increases, the pipe must be lifted upward, and one or two sections must be removed to a certain extent. The order of pipe removal is from top to bottom. After each lifting and removal of the pipe, the depth of the buried pipe must be controlled to not be less than 6m.
(6) Adjust the conduit to the center of the pile hole at any time, and do not scrape the steel cage to lift the conduit.
(7) Check the depth of buried pipe at any time, and frequently insert it up and down to prevent pipe stuck.
(8) Control the concrete slump at any time, generally within 20-23cm.
(9) Estimate the time for pouring a pile and calculate the amount of retarding admixture for each plate of concrete slurry.
(10) Every time a pipe is dismantled, it is necessary to check whether water has entered the pipe. Every time a pipe is dismantled, records must be kept, including the length of the pipe, the depth of the pipe, the height of the concrete surface, and other construction records.
2 Construction layout
The construction environment of each bridge is different. According to the actual situation, the impact of environmental pollution during the construction process must be taken into consideration, and the concrete mixing station should be arranged reasonably. Location, according to the hoisting equipment, terrain, and site conditions, reasonably arrange the location of the beam and plate prefabrication site, consider what means to use for hoisting, and what method of transportation the prefabricated parts should be used for. Determine a reasonable lifting plan and transportation plan.
3 Prefabrication of prestressed beams and plates
Prestressed beams and plates can be divided into: pre-tensioning prestressing and post-tensioning prestressing. Generally, 16-20m beams are prestressed by the pre-tensioning method, and 30-50m beams are prestressed by the post-tensioning method. For beams prestressed by the pre-tensioning method, the construction of the prefabricated site is more complicated and requires multiple tensioning lines. Each tensioning line consists of a tensioning pedestal, a tensioning beam, a pedestal support and a loose anchor sand box.
In post-tensioning prestressing, after the beam is prefabricated and the concrete grade reaches 100%, the two ends of the beam are used as pedestals and the beam body is used as the supporting beam for steel hinge line tensioning. There is no need to build a tensioning pedestal.
3.1 Prefabrication method of pre-tensioned prestressed beams
The construction of pre-tensioned prestressed beams is to first pass steel strands through the steel beams, and both ends of the prefabricated field are There are pedestals and steel beams. One end of the beam is equipped with a Songhua River anchor sand box, and a tensioning jack tensions the steel strand on the other end of the beam. According to the pre-tension stress required by the design, each steel strand should be controlled at 20%, 30%, 50%, 80%, and 100% of the stress, that is, after all the steel strands of a tension line are stretched to 20%, then Carry out 30% tensioning, repeat tensioning to 100%, and finally perform a super-tensioning anchoring to loosen the jack. When the steel strands are stretched, protective measures must be taken in the prefabrication site to prevent injuries caused by the steel strands being broken. During the steel strand tensioning process and after the tensioning is completed, electric welding is not allowed in the prefabricated site, because at this time the steel strand becomes a ground wire, sparks will be generated and the steel strand will be burned. After the steel strand tensioning is completed, the prefabrication of the beam plate can be carried out. When the concrete mark of the beam plate reaches 100%, it can be relaxed. The method of relaxing is: slowly release the sand in the sand box to eliminate it. Add pre-stress to the steel beams, and finally use a cutting machine to cut the steel strands of each beam. The prefabricated beams are completed and can be hoisted to the outside for storage.
3.2 Post-tensioned prestressed beam prefabrication method.
After the installation of the steel bars of the beam is completed, install the crossing pipe, pass the steel strand into the corrugated pipe, install the anchor plate, and then install the mold and pour concrete. After the curing concrete mark reaches 100%, according to the design To pre-tension stress, tension jacks are used to tension each bundle of steel strands at both ends of the beam. The same is done in staggered tension of 20%, 30%, 50%, 80% and 100% of the controlled stress, and finally the tensioning is anchored. Release the jack. After the tensioning is completed, the corrugated pipes are filled with high-pressure cement slurry, the steel strands are consolidated and cured for a few days, and the beam can be lifted.
4 Concrete production system
The key to the quality of a bridge lies in the concrete production system. To ensure that the concrete label remains stable, a batching control system is required. The sand, gravel, cement, and water used are now controlled by microcomputer weights, and then sent to the mixer for mixing through the system, thus avoiding the instability of concrete grades caused by inaccurate manual weighing.
5 Bridge Installation
For arch box hoisting of large-span box arch bridges, tower cable hoisting is generally used, which is technically complex. At present, the most commonly used one is the 20-40 span prefabricated hoisting system. Stressed beam slab bridges are generally hoisted by gantry cranes in conjunction with bridge erecting machines. The designs of the bridge erecting machines and gantry cranes are complex and will not be introduced here.
6 Construction of simple-supported and continuous beams first
Generally, it is prefabricated based on simply supported beams. During the prefabrication process, steel bars are first buried and negative bending moment steel strand channels are reserved. After the beam is hoisted onto the bridge, the embedded steel bars between the beams are welded. After the wet joint concrete curing mark of the pouring joint reaches 100%, multi-bending moment steel strands are put through, the steel strands are tensioned, and grouting is completed. Construction of continuous beams
7 Introduction to the construction of the superstructure of centrally supported bridges
Centrally supported bridges are generally long-span bridges, and the bridge deck beams and plates are suspended by steel cables. The construction procedures are: first construct the pier (platform) and prefabricate the arch ribs, and then use tower cables to hoist the arch ribs. After the arch ribs are closed, the horizontal contact wind structural ribs are cast in-situ; the suspension beams are prefabricated and hoisted using cables, and each beam is Use steel cables to hang from the arch ribs, and adjust each beam to the predetermined elevation according to the design requirements. After all the suspension beams are installed, use the beams as supporting points to install the bottom formwork, install the longitudinal beam plate steel bars, and then pour concrete continuously to integrate the longitudinal beam plates and the suspended beams (the beam plates have pre-embedded steel bars) into a whole, and the bridge deck construction After completion, according to the design requirements, readjust each steel cable so that the height of the corresponding section of the bridge deck reaches the design requirements, and finally seal the anchors at both ends of the steel cables.
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