Construction scheme of foundation and basement of high-rise commercial complex building?

Construction scheme of foundation and basement engineering of high-rise commercial complex building

1 Overview of Foundation and Basement Engineering

After the foundation pit enclosure is completed, one of the key and difficult points of this project is the second floor basement project, which must be organized reasonably. All adopt pumped commercial concrete.

Due to the large area of foundation pit, in order to avoid structural cracks caused by uneven settlement, three expansion joints are designed in the middle of axis 4 -5, axis 9-10 and axis 17-18, and the whole basement project will be divided into three construction sections.

2 construction procedures

In view of the large area and high requirements of local underground projects, the word "grab" must be highlighted in the construction arrangement, that is, the construction period of underground projects should be shortened as much as possible, and the manpower and material resources invested should be arranged in advance to ensure that they are in place. The construction will be divided into three sections, namely three sections. The concrete of this project will be carried out according to the requirements of mass concrete.

The construction sequence is as follows:

Topsoil excavation → well point dewatering → excavation of soil nails → excavation of pile caps and foundation beams (artificial) → pile top treatment → brick tire mold of pile caps → concrete tire mold and cushion of ground beams → elastic line → reinforcement of pile caps and bottom plates → formwork support → concrete pouring → maintenance and formwork removal → wallboard reinforcement and formwork support → wallboard concrete reinforcement and formwork support → roofing concrete → wallboard waterproofing.

The whole underground project, including earthwork, is scheduled to be completed within 50 days.

The whole foundation and basement project will be implemented in stages, and the construction quality will be controlled according to the different characteristics of each stage. Specifically divided into: 1, foundation pile caps, foundation beams, basement floor construction; 2, the basement wallboard construction (including internal shear wall); 3, the basement roof construction; 4, waterproof treatment and backfill engineering

3 Construction of pile caps, foundation beams and basement floor

This part of the structure is the most critical part of the whole basement project, and the construction is the most difficult. Maximum cap of main building 1700. The construction of this part should focus on the word "grab" and be completed in the shortest time. Specifically, after the completion of earthwork, the brick tire mold is laid and the cushion layer is poured. The construction process is as follows: brick, concrete tire mold and cushion → pile head treatment → steel bar binding → formwork support of bottom plate → concrete pouring.

① tire mold engineering

According to the actual situation and design requirements, the formwork of the down-turned structure bearing platform is built with brick tire formwork and cement mortar; The ground beam adopts plain concrete tire mold, and the concrete tire mold is poured with wooden mold. The tire mold project follows closely behind the excavation project, and the masonry should be done quickly and in time. Accelerator can be added into the cement mortar of brick tire mold to increase the collapse resistance of brick tire mold.

The formwork support of bottom plate adopts the combination of brick tire formwork and composite wooden formwork.

(2), steel engineering

Because the foundation and basement floor are connected together, the reinforcement project is complicated and complicated, and the workload is very large. It is necessary to equip enough labor to catch up with the work progress.

According to the requirements of design drawings, steel bars above φ 16 are connected by butt welding, and steel bars above φ 25 are connected by straight thread sleeve. (See the main reinforcement project for the construction technology of mechanical connection joints) and make them in the off-site workshop. Steel bars of various specifications shall be neatly stacked and properly kept to prevent pollution and corrosion. Before the steel bar is used, tensile test and welding test should be carried out respectively, and it can be used only after it is qualified.

The processing workshop should be equipped with machines, butt welding machines, cutting machines, bending machines, straightening machines and electric welding machines, and processed into finished products or semi-finished products, and then transported to various parts for installation.

During excavation, the reinforcement shall be made in the reinforcement workshop, and the reinforcement shall be bound according to the specifications. The upper reinforcement of foundation beam is overlapped at the support, and the lower reinforcement is overlapped at the minimum bending moment 1/3 from the support, and butt welded in the middle. Because there are many dowel bars, support scheme should be adopted. Steel pipes are used for bracing, diagonal braces and cross bars are bound and fixed with steel bars, and the lower steel bars are fixed by electric welding to ensure the correct position of columns and wallboard steel bars.

The specifications of floor reinforcement are relatively uniform. According to the pop-up reinforcement position line, the lower floor reinforcement shall be laid first. According to the stress of the bottom plate, decide which direction the lower reinforcement is below. In general, short-term steel bars are laid first, and then long-term steel bars are laid.

When steel bars are bound, two rows of intersections near the periphery should be bound at each point, and the intersections in the middle part can be bound at staggered intervals. All steel bars subjected to biaxial stress must be bound at the intersection of steel bars. If a straight buckle is used, the direction should be staggered, and a splayed buckle can also be used, but the reinforcement shall not be displaced.

Place mortar pads for the concrete protective layer of the bottom plate. The thickness of the bonding pad is equal to the thickness of the protective layer, and the spacing is set as required.

After the lower reinforcement is bound to the foundation slab, a reinforcement horse stool or a reinforcement bracket is placed, and positioning reinforcement in both vertical and horizontal directions is placed on the horse stool. The order and fastening method of upper and lower reinforcement are the same as those of the lower reinforcement of the plate.

The binding joint position of floor reinforcement should meet the requirements of construction specifications, and the reinforcement should be fastened with iron pieces in the middle and at both ends. If welded joints are used, in addition to sampling according to the welding regulations, the joint position should also comply with the construction specifications.

Due to the particularity of foundation slab and foundation beam, the fracture position of upper and lower reinforcement should meet the design requirements.

According to the played wall column position line, the steel dowel inserted into the wall column foundation should be firmly bound, the depth of the inserted foundation should meet the design requirements, and the length of the sling should not be too long. Measures should be taken at the upper end to ensure that the sling is vertical and will not be skewed, dumped or displaced.

(2), commercial concrete is cast

Commercial concrete for concrete. In order to speed up the construction progress, all concrete is pumped, which is transported to the structural parts by the concrete pump truck through its own placing boom and pump pipe. Concrete engineering should be carried out in accordance with the requirements of mass concrete. Concrete shall be poured at one time in each construction section, and the pumping concrete shall be calculated at 30 cubic meters per hour. It is planned to continuously pour 1 pump truck.

When cast, the concrete worker should keep up with the speed of the pump truck in time, with 40 concrete workers and 0/5 auxiliary workers/kloc. Due to the large amount of concrete cast and compacted at one time, the construction needs to be fought day and night continuously, so the ZuoYeDui should be prepared to fight hard and match two groups.

The test block shall be made in time and the person in charge shall be responsible for it. Witnesses of Party A or the supervision unit shall participate in the production to avoid fraud. After production, the date, number, location and label of the test block should be marked to avoid confusion.

Construction requirements of mass concrete:

1, measures to prevent temperature cracks

Due to the large area of this project, the post-pouring belt is designed according to the design requirements. To ensure the quality of mass concrete, in addition to meeting the general requirements of concrete such as strength grade, impermeability and internal and external light, the key lies in strictly controlling the internal and external temperature difference caused by hydration heat in the hardening process of concrete to prevent concrete from cracking due to excessive internal and external temperature difference. Therefore, the following measures are taken:

1) Reasonably determine the mix proportion, use additives TEA expansion agent, retarder, FDN- 1 water reducer, use slag cement, medium sand and crushed stone, and reduce the dosage of cement while ensuring the strength and impermeability of concrete, so as to reduce the hydration heat. The specific mixture ratio should be determined by trial matching with commercial concrete suppliers.

2) Improve the concrete vibrating technology. Before the vibrating limit, the poured concrete shall be vibrated and lightened for the second time, so as to eliminate the moisture and cracks caused by the bleeding of concrete at the lower part of coarse aggregate horizontal reinforcement, improve the binding force between concrete and reinforcement, and prevent concrete from cracking due to settlement.

3) To control the temperature of concrete entering the mold, we can set up a sunshade on the mixer, cover the concrete horizontal conveying pipe with thermal insulation materials such as straw bags, and often spray water to cool down, adopt a slope, pour in thin layers, advance step by step, and reach the top once, so as to reduce the exposed surface of concrete, increase the pouring intensity, shorten the pouring time and prevent concrete from being sunburned.

4) Do a good job in thermal insulation and moisture curing of concrete, and use 1 layer plastic sheeting and two layers of straw bags for thermal insulation and water storage, so as to reduce the temperature gradient on the surface of concrete, extend the heat dissipation time, give full play to the potential of concrete and the relaxation characteristics of materials, make the tensile stress generated by the average total temperature difference of concrete less than the tensile strength of concrete, and prevent surface cracks. The hydration speed of fresh concrete is fast, and proper moisture conditions can prevent drying shrinkage, which is beneficial to continue hydration.

2. Concrete pouring method: 2-3 pouring trucks are used to pour the concrete in a thin layer with a gradient and advance the concrete in sequence. See preface.

3. Transportation and pumping of concrete: Commercial concrete is transported to the site by concrete mixer and pumped into the mould by concrete pump truck. According to the selected pouring intensity, two pump trucks will be selected.

4. Vibrating of concrete: According to the actual situation that concrete naturally forms slopes when pumping, two vibrators are arranged in front of and behind each pouring belt. The first line is arranged at the concrete unloading point, mainly to solve the tamping of the upper concrete. Due to the dense spacing of bottom skin reinforcement, the second way is arranged at the slope angle of concrete to ensure the compactness of the lower concrete. With the advancement of concrete pouring, the vibrator keeps up accordingly to ensure the concrete quality of the whole height. As shown in the figure:

5. Treatment of concrete bleeding: During the pouring and vibrating of high fluidity concrete, bleeding and laitance flow from the upwelling place along the concrete slope to the bottom of the pit. Outside the flow pit along the bottom seam of the formwork on both sides, a small amount of bleeding that cannot be eliminated is driven to the top of the foundation pit with the advancement of concrete pouring, and discharged from the pit by the reserved hole at the bottom of the formwork at the top.

When the toe of concrete slope approaches the top formwork, the concrete pouring direction is changed, that is, the concrete is poured back from the top, which intersects with the original pouring slope to form a sump, and the concrete pouring strength at the formwork on both sides is consciously strengthened, so that the sump gradually shrinks into a pool in the middle, and it is eliminated in time with a flexible shaft pump. This eliminates all exudation in the final stage. As shown in the figure:

6. Concrete surface treatment: The cement slurry on the surface of mass concrete is thick, so it should be treated carefully after concrete pouring. After about 4-5h, level with a long scraper according to the elevation. Before initial setting (the initial setting time is extended to 6-8h due to the addition of calcium lignosulfonate powder to concrete), it is rolled several times with an iron roller, and then it is polished and compacted with a wooden crab to close the water-collecting cracks. After about12 ~14 hours, cover with a layer of plastic cloth and two layers of straw bags for adequate watering, wetting and maintenance.

Strengthen the construction organization and management plan, mainly including:

A, strict construction organization, responsibility to the people. A temporary command team will be set up at the site, under the command of the project manager, and will be on duty by turns day and night until the end of concrete pouring. The command group consists of dispatching, technical quality, material machinery, and external coordination of logistics services. A clear division of labor, responsibility to people, so that all participants know fairly well and work in an orderly way.

B do a good job in coordinating with other units to gain support and understanding. After the concrete casting scheme is determined, a coordination meeting will be held for transportation, city appearance, sanitation, commodity concrete supply and other units to understand the progress of the project and win support;

C mixer comes into play with walkie-talkie contact coordination.

★ Pumping process:

Pumping is a continuous operation process. If the preparatory work is not sufficient, it will cause accidents such as midway interruption, which will definitely affect the construction quality of the project. In order to ensure the quality of castings, it is necessary to make full preparations and implement them strictly according to the requirements.

1) Before pumping concrete, the fresh water in the storage hopper should be pumped out of the pipeline to wet and clean the pipeline, and then cement mortar (or 1:2 cement mortar) in the same proportion as the concrete should be added into the hopper, and the concrete should be pumped after the pipeline passes.

2) At the beginning of pumping, the pumping speed tends to slow down, and the oil pressure change should be within the allowable range. When the pumping is smooth, the pumping is carried out at a normal speed.

3) When pumping, the amount of concrete in the hopper should not be less than 100mm at the cylinder mouth, and the hopper mouth should be between 150mm, so as to avoid low suction efficiency, easy suction of air, pipe blockage, overflow when pumping back too much, and increase the load of the mixing shaft.

4) The concrete pump should run continuously, and the pumping speed should be reduced when the supply of concrete is not enough. When the pumping is temporarily interrupted, the stirring should not stop. When the blade is stuck, it needs to be reversed, then reversed for a certain period of time, and then pumping is continued after the forward rotation is smooth.

5) If the pump is stopped for more than 20 minutes during pumping and the pipeline is long, the pump should be started every 5 minutes. When the pumping pipeline is short, it can be reversed for 2 ~ 3 times every 5 minutes to make the concrete in the pipeline creep and prevent bleeding and segregation. Stopping the pump for a long time (more than 45min), high temperature and small concrete slump will all cause pipe blockage, so it is recommended to remove the concrete in the pump and delivery pipe.

6) Pump far before near, and gradually dismantle the pipeline during pouring.

7) The sum of the horizontal conversion distances of the pumping pipeline shall be less than the maximum pumping distance of the equipment.

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