1 pier and abutment construction
Pier excavation: firstly, restore the axial piles to the pier, and set out the upper edge line of the excavated pier foundation pit according to the geological conditions. Excavators are used to cooperate with manual excavation for the excavation pier, and the bottom of the foundation pit is 0.5m wider than each side of the design section, which shall be leveled manually, rammed by rammer, crushed stones of 15cm shall be laid at the bottom of the pit, and plain concrete shall be poured in time. When there is water in the foundation pit, the bottom of the foundation pit is widened by 1.0m compared with each side of the design section, and a collection well and a collection well are added. The pier formwork adopts composite steel formwork, only supporting side formwork, and the bottom formwork is replaced by plain concrete. Steel bars shall be bound in place by conventional methods. The concrete of pier and abutment is supplied by mixing station, transported by light dump truck on site, put into formwork through string drum and chute, vibrated by plug-in vibrator, and maintained by wet method.
Construction method of the water part of the pile cap: firstly, pull out the steel pipe in the pile cap and sink it into the construction steel box by vibration method. Steel sleeve box&; 5 steel plate production, L75*5 stiffening plate every 50cm, the plane size is greater than 500mm on each side, the maximum depth above the construction water surface is 500mm, it is advisable to bury the lower mouth 2~3m underground, and the precipitation depth reaches 50cm below the construction water surface, which meets the requirements of dry construction. Then clamp the steel hoop on the pile, and spread the channel steel and wooden board on it. The schematic diagram is as follows:
2 column construction scheme and technical measures
The column is C30 cast-in-place concrete structure. In the process of construction, we should not only control its internal quality, but also ensure its appearance quality, so as to achieve high quality and beauty. This project will further optimize the construction technical scheme, ensure the quality of various materials, carefully design the column formwork, ensure that the formwork is flat and smooth, reinforce the formwork at the bottom of the column, strengthen the fixation of the formwork at the top of the column, and adopt scientific column concrete pouring technology to ensure the construction quality and appearance quality of the column.
(1) column reinforcement
After the steel binding of the bearing platform is completed, the main reinforcement of the column shall be positioned. Spot-weld a column stirrup on the reinforcement of the pile cap layer, then insert the main reinforcement of the column, and weld it with the lower part of the column in the pile cap after correct positioning (accepted by the supervisor). The welded joints of the same section shall not exceed 50% and shall be staggered by1m. And set up a simple fixed scaffold for positioning. Therefore, the binding stage of column reinforcement mainly includes the binding of stirrups and the erection of vertical reinforcement.
First of all, clean up the steel bar, and clean up the concrete stuck to the steel bar when pouring the bearing platform. At the same time, the contact surface between the column and the pile cap should be chiseled and rinsed with water. After the stirrup binding, before the formwork erection, the protective mortar cushion should be firmly bound with the main reinforcement. Gaskets should be staggered with a spacing of 50 cm.
Before the construction of column reinforcement and formwork, two rows of working platforms (around the outside of the column) shall be set up with φ48 bowl buckle brackets, and bamboo row pedestrian passages shall be laid between the two rows of scaffold pipes, and escalators shall be set up. For the columns that should be provided with settlement observation points according to the design requirements, attention should be paid to the embedding of points, and the anchoring reinforcement of settlement observation points should be welded firmly with the main reinforcement.
Reinforced protective cushion block: As the pier is made of high-performance concrete, the protective cushion block is made of I-shaped or tapered. When making cushion blocks, its own strength is higher than that of pier concrete. There are at least 4 pads /m2 on the side of pier, and the wire ends for binding pads and reinforcement shall not extend into the protective layer.
(2) Column formwork
Column is the main exposed component, and the key to improve the appearance quality of concrete is the quality of formwork. The columns of this project are all made of shaped steel molds, which are made by professional manufacturers. In the production process, the surface smoothness and installation accuracy should be strictly controlled, and special personnel should be assigned to supervise the production. After the template exists, try to adjust the installation error.
The formwork structure is as follows: the horizontal beam adopts double-channel 8# channel steel with a spacing of 50cm, the horizontal beam is welded firmly on the formwork, and the vertical beam adopts 4 16# channel steel per formwork. On the cross section, the column template is divided into four pieces, and the flat-fell seam is blocked with rubber water stop.
Column formwork shall be installed after the acceptance of reinforcement. The formwork shall be hoisted in place by 25t truck crane, and tightened around with 3' steel wire rope and φ 1800 tensioner to ensure sufficient rigidity. After the installation of column formwork, use theodolite to check its verticality in two directions, and carry out column concrete construction after the supervision and acceptance. Schematic diagram of column formwork structure is as follows.
(3) Column concrete construction
Before concrete construction, the platform and escalator shall be erected around the column formwork with φ48 steel pipe for the use of construction personnel. One-step casting molding.
C30 concrete is proposed for this project. Choose clean, hard, uniform and continuous graded aggregate, and use qualified cement and additives. When mixing concrete, control the mixing time strictly according to the specification requirements, and strictly control the addition amount of additives; Mix the concrete in strict accordance with the design mixture ratio.
Concrete pouring: the concrete will be transported to the site by tanker, and the concrete will be pumped into the mould, and the slump will be controlled at12 3 cm. Due to the height of the column, in order to prevent concrete segregation, the concrete string tube is used for ash discharge, and the string tube is connected with the discharge port of the pump truck through 6~7m hoses. Fix with a bayonet. When pouring, take 50cm as the lower ash layer, vibrate with 70-type vibrating rod, and 2.0m is a section. When pouring the lower part of the second quarter, the vibrating hand will enter the template for vibrating, and shall not touch the template. When concrete construction reaches the top, it is required to adopt secondary vibration and secondary plastering, and scrape off laitance to ensure the compactness of concrete;
Column formwork removal: When the compressive strength of concrete reaches 2.5Mpa, the side formwork can be removed. When dismantling the formwork, attention should be paid to protecting the surface and edge of the column. Dismantle the steel wire rope used to adjust the formwork first, dismantle the formwork in the reverse order of formwork installation, unload it piece by piece with a crane, hoist it into a flat site or a site with dead wood, remove the concrete stuck on the formwork, and brush the machine oil for later use.
After form removal, the concrete surface is sprayed with vinyl chloride curing solution. In order to protect column concrete from damage and pollution during construction and prevent water loss, PVC plastic film is used for enclosure, sealing and moisture curing.
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