Super practical foundation and foundation engineering construction technology?

A, concrete chute construction technology

0 1 technical principle

The mass floor is located at the bottom of the foundation pit, and the concrete is transported downwards from the edge of the foundation pit. Pumping construction is the most common concrete floor pouring method. For super-large floors, when large-scale pouring is needed, multiple concrete pumps need to be arranged. For example, 20 tractor pumps and 2 truck pumps were used in the mass floor construction of Beijing CCTV Building, and 12 truck pump, 4 tractor pumps and 2 truck pumps were used in the mass floor construction of Shanghai Center. Click me: get the engineering gift package. Disadvantages: This requires a large construction site for placing concrete pumps and parking concrete tankers. For super-high-rise building projects usually built in the city center, it is very difficult to construct because of its narrow construction site.

In addition, pumping concrete requires high concrete performance and good workability, especially the infiltration rate, otherwise it will easily lead to pipe plugging, and it also requires high aggregate particle size and gradation. The construction speed of pumping concrete is also greatly limited, and a single pump can only reach 30m3/h. The chute is a groove with a certain slope erected from the edge of the foundation pit to the bottom. Concrete flows in the groove by its own weight and is transported to the floor pouring working face. Using chute to transport concrete is a rapid pouring method, and the pouring speed of concrete can be greater than 300 ~ 500m3/h.

Advantages of chute structure:

(1) Chute pouring concrete belongs to the category of non-pumping, which can greatly reduce the slump of concrete, reduce the unit water consumption and avoid concrete drying shrinkage. (2) Using chute to pour concrete is more conducive to the heat dissipation of mass concrete in summer construction, reducing the temperature of mold entry and hydration heat. (3) Chute pouring concrete can avoid the blockage of pump pipes in conventional construction, which has higher work efficiency and can ensure the continuous pouring of mass concrete.

Scope of application of chute structure:

(1) The foundation pit has a certain depth, and the length L of the chute is 2.5 ~ 3.5 times of the depth H of the foundation pit, so the chute can effectively cover the floor concrete within this range. (2) The thickness of the bottom plate is greater than 1m, with a large area, and the single concrete pouring amount is about 1 10,000 m3. Chutes provide temporary construction measures for concrete pouring, so it is necessary to dismantle the frame after concrete pouring. If the pouring quantity is small, the use of chute is relatively expensive. (3) At the top of the foundation pit, there is a site with a discharge port for parking concrete tankers.

02 design points

The plane layout of the chute shall meet the requirements of quick unloading of the concrete tank car, the pouring surface covering the whole bottom plate (local corners can be closed by ground pumps), and there is no cold joint of concrete between adjacent unloading points, as follows:

(1) Main chute number setting:

The number of main chutes is related to the floor area, concrete pouring quantity and the site at the top of the foundation pit, so the pouring time of mass concrete should not be too long. Especially in the city center, concrete pouring is limited by the morning and evening rush hours, and the required number of chutes can be calculated according to the average pouring of 400m3/h per chute.

(2) Direction and spacing of chutes:

Set chutes to ensure that the distance between the discharging points at the bottom of the foundation pit is greater than 15m, and two concrete tankers are on standby at each discharging point at the top of the foundation pit; The spacing of blanking points in the foundation pit should be 12 ~ 18m, giving full consideration to the fluidity of floor concrete and the needs of workers' vibrating operation surface.

(3) Setting of branch chute and string tube:

On the premise of meeting the pouring time limit, branch chutes and tandem rollers can be used to expand the coverage of chutes.

The installation of chute ensures the need of concrete transportation and pedestrian passage, which is convenient for managers to check. The selection of chute width meets the requirements of blanking width and operation of concrete tank car. Pedestrian passage is set along the chute, and dense mesh net and large mesh net are hung to ensure safety. The width of the chute should be 650-800mm, and the height of the side wall of the chute body is 200 mm. It is made of sheet metal and lined with wooden scaffolding.

Chutes are generally erected with steel pipe scaffolding. Scaffolding is supported on angle steel bracket, and the spacing between vertical rod and horizontal rod is determined according to calculation. When calculating the scaffold, the self-weight of the chute, the gravity of the concrete in the chute when pouring concrete and the construction load of the operators on the pedestrian passage are mainly considered, and the overall stability and lateral stability are checked. Angle steel support is generally used with the temporary support frame of steel bar on the bottom plate. Therefore, when designing the angle steel support under the chute, we should not only consider the load handed down by the chute scaffold, but also consider the self-weight of the steel bar on the bottom plate, and check the strength and stability of the fillet weld of the column and crossbar.

03 application example

◆ China International Trade Center Phase III A

The main tower of Phase A Project of China International Trade Center Phase III is 330 m high, the standard thickness of the bottom plate is 4.5m, the length and width are 64m×64m, the area is about 4200m2, the concrete strength grade is C45, the slump requirement is 160- 180mm, the total pouring volume is about 22,000m3, and the total pouring time is less than two days. It is planned to adopt chute construction technology and inclined plane layered pouring method for one-time continuous seamless pouring of foundation slab. The plan of the main building is shown in the figure.

In order to meet the continuous pouring of mass concrete, three main chutes are used in the site, which start from the south side of the foundation pit and extend to the upper part of the foundation slab according to the slope of 1:3. The whole chute frame is about 19m high, and the chute width is 3.2m, showing a herringbone shape. In order to ensure that the concrete pouring covers the whole floor, four sub-chutes are set on the giant chutes on both sides, small chutes are set at the ends of the sub-chutes, and tandem drums are set at the corresponding positions of the chutes.

Second, the basement roof post-pouring belt pre-sealing technology

0 1 technical principle

Implementation/optimization effect: In order to backfill the basement roof with soil in advance, construction sites and roads are provided. Applicable Project/Scope: Post-poured zone of basement roof settlement.

1, innovation:

After the basement roof structure construction is completed, cover the post-cast strip with 120mm thick precast reinforced concrete cover plate, and leave a φ 300 hole (continuous slab reinforcement) on the precast cover plate every 4m, and erect a 3m-long precast reinforced concrete pipe (φ 300) on the hole as concrete pouring hole. After that, the waterproof layer and backfill soil will be constructed synchronously with the whole structure in the post-pouring zone. After the settlement of the structure is stable, the self-compacting expansive concrete is poured into the post-pouring belt through the pouring hole, and the settlement post-pouring belt is closed.

2. Technical features:

Watering holes should be arranged every 4m, and both ends must be arranged. A hole must be added at the corner of post-cast strip (i.e. the spacing should be reduced to 2 ~ 3m) to prevent self-compacting concrete from flowing forward due to the increase of resistance at the corner.

Third, cancel the construction technology of post-cast strip

0 1 technical background

At present, in the construction of super-long and super-large volume concrete, the method of leaving post-cast strip is usually used to control concrete cracks, which brings a lot of inconvenience to the construction quality and progress. Cancelling the construction technology of post-pouring belt can not only solve the problem of concrete cracks, but also save a lot of labor and material costs for retaining post-pouring belt and speed up the construction period.

Methods and basis of canceling post-pouring belt

Advantages of canceling post-pouring belt

1) to improve the quality.

The cancellation of post-pouring belt enhances the structural integrity, earthquake resistance, durability and impermeability, avoids all kinds of hidden dangers caused by improper treatment of post-pouring belt, and ensures the engineering quality.

2), shorten the construction period.

Cancellation of post-pouring zone, reduction of gouging and secondary pouring procedures, and early closure of the structure create conditions for the early insertion of the secondary structure and decoration work, which can greatly shorten the construction period. 、

3), save costs.

After the post-cast strip is cancelled, the formwork and support need not be set separately, and the formwork and support in this position can be removed together with the formwork and support system of the floor and used in turn, which can save the template rental cost; No need for secondary planing and cleaning, saving labor cost; No need for separate protection, saving protection cost; Water stop can be set less or not, saving the cost of water stop.

04 engineering example

1), PPP project of relocation project of Shuangliu First People's Hospital:

The building area is 209,000m2, underground 1 floor, with a single floor area of about 68,000m2 and 5-9 floors above ground. The original design of the whole project is * * * 7295m temperature post-pouring belt, 2 172m settlement post-pouring belt, and all temperature post-pouring belts are finally cancelled. The construction period was advanced by 50 days, saving 564,000 yuan.

2) Mei Lanfang Grand Theatre:

The building area is161643m2, with three floors underground and twenty floors above ground. The east-west length of foundation slab is 197.6m, and the north-south length is 87m. The maximum thickness of the bottom plate is 2.25m, the total concrete pouring amount of the bottom plate is 19800m3, and the total pouring amount at one time is about 7500m3. The total length of the post-cast strip originally designed for this project was 5350m, which was finally cancelled, saving about1069600 yuan.

3) Building C of Jinding Business District:

Located in Shijingshan, the building area is 153815m2, with two buildings on the ground15 floors, two buildings with 9 floors, a podium with 5 floors and 3 floors underground. The foundation soil is pebble bed, and the anti-beam raft foundation. Cancel the expansion post-cast strip of 4950m and the settlement post-cast strip of 1950m.

Four, different forms of tower crane foundation design and construction technology

0 1 tower crane foundation form selection

Pile bearing foot

When the local foundation soil is soft soil and the shallow foundation can't meet the requirements of tower crane for foundation bearing capacity and deformation, tower crane foundation can adopt pile foundation. Tower crane pile foundation can be new foundation pile. On the premise of satisfying the safe and reasonable layout, it is also possible to consider partially or completely using slope protection piles and engineering piles as tower crane foundation piles.

Slope protection piles are used for pile foundation.

When the tower crane is located at the outer edge of the foundation pit, one or two slope protection piles can be considered as the tower crane foundation piles, which together with the tower crane piles and pile caps form the tower crane foundation.

Engineering piles are used for pile foundation.

When the tower crane is located in the foundation pit, several engineering piles can be considered as the foundation piles of the tower crane to save the cost of the tower crane.

Combined foundation

The composite foundation can be composed of concrete pile caps or steel platforms, lattice steel columns or steel pipe columns, cast-in-place piles or steel pipe piles, etc. The tower crane foundation can be constructed in advance under the condition that the foundation pit is not excavated, so that the tower crane can serve the foundation pit excavation and internal support construction stages, and is suitable for foundation pit projects with internal support and lattice columns or projects requiring tower cranes in the foundation pit stage.

Design points of different foundation forms

Pile foundations are all newly added foundation piles.

1. It is necessary to calculate the stress of tower crane foundation in working state and non-working state respectively, and select the most unfavorable state for pile foundation and cap design.

2. The calculation of pile foundation should include the calculation of pile top effect, vertical compressive and uplift bearing capacity of pile foundation, bearing capacity of pile body and pile cap. 3. The calculation of pile caps should include the calculation of bending and shearing bearing capacity and punching. 4. Post-grouting technology of pile can obviously improve the bearing capacity of pile, shorten the length of pile, reduce the cost and speed up the construction progress.

Slope protection piles are used for pile foundation.

1. It is necessary to calculate the stress of tower crane foundation in working state and non-working state respectively, and select the most unfavorable state for pile foundation and cap design. 2. According to the calculation results, check the bearing capacity of slope protection piles. Before the construction of slope protection pile, the pile length and reinforcement of slope protection pile should be rechecked, and it is considered that the pile body within the excavation range can not provide bearing capacity, and the pile body within the excavation range belongs to the free end.

3. According to the actual situation, strengthen the foundation pit support (increase tension measures such as anchor cable and soil nail). 4. Post-grouting technology of pile can obviously improve the bearing capacity of pile, shorten the length of pile, reduce the cost and speed up the construction progress.

Engineering piles are used for pile foundation.

1. It is necessary to calculate the stress of tower crane foundation in working state and non-working state respectively, and select the most unfavorable state for pile foundation and cap design. 2. According to the calculation results, check the bearing capacity of engineering piles. 3. Post-grouting technology of pile can obviously improve the bearing capacity of pile, shorten the length of pile, reduce the cost and speed up the construction progress.

Combined foundation

1. It is necessary to calculate the stress of tower crane foundation under working and non-working conditions respectively, and select the most unfavorable state for pile foundation design, pile cap, section selection of lattice column (steel pipe column), component calculation (column limb calculation, component design, inter-column support calculation, load-bearing beam calculation), etc. 2. The overall stability analysis (PKPM, Etabs) of lattice column system in cantilever section should be considered, and the connection nodes between lattice column and vertical supporting piles, waterproof nodes between lattice column and structural bottom plate (welded water-stop steel plate) and connection between lattice column and bearing platform should be handled well. 3. The basement tower crane foundation pile should avoid the foundation beam, pile cap, post-cast strip or floor reinforcement strip.

03

Construction points of different foundation forms

Pile bearing foot

Key points of construction: 1. When constructing foundation piles at designated elevation, no less than 500mm of protective soil must be reserved during construction. 2, according to different engineering environment and geological conditions, choose the appropriate construction technology. 3. As the main supporting system of tower crane foundation, the construction quality control of foundation pile is very important, including its pile diameter, pile length and verticality, as well as the quality problems such as broken pile and shrinking pile that may be encountered in the construction process, which has a great influence on the quality of finished pile. 4. When the concrete strength of the foundation pile reaches a certain requirement, remove the loose concrete and laitance at the pile head and control the elevation of the pile top. 5. After the strength of plain concrete of cushion reaches 60%, the embedded parts can be constructed. 6. The flatness deviation of embedded joints shall not be greater than 65438 0 ‰. 7. Waterproof treatment of pile head should be done well in the construction process.

Combined foundation

Construction technology: determine pile location → drill positioning → drill hole → first hole cleaning → hole depth measurement → placing reinforcing cage → fixing lattice column → downcomer → second hole cleaning → hole depth measurement (qualified) → pouring concrete.

Construction technology: 1. When hoisting the lattice steel column of composite foundation, ensure that the verticality and upper end deviation value do not exceed the allowable values. 2. With the layered excavation of earthwork in foundation pit, steel supports should be set outside the lattice steel columns in time to connect the lattice steel columns into a whole. 3. The lattice steel column of composite foundation should be protected during foundation pit excavation. 4. After excavation to the design elevation, the engineering concrete foundation cushion shall be poured immediately.

Verb (abbreviation of verb) Selection and application of water-stop curtain form

0 1

Cement-soil mixing curtain

Cement-soil mixing method can not only form a cement-soil retaining wall with two functions of foundation pit sealing and supporting, but also form an independent waterproof curtain with anti-seepage function, and can also be combined with supporting piles or soil nailing walls to play the role of anti-seepage and supporting. It mixes undisturbed soil with cement to form cement soil, and its permeability coefficient is much smaller than that of natural undisturbed soil. This method includes two kinds of construction techniques, dry method and wet method, with short construction period and low requirements for construction conditions.

Tianjin Kerry Center

The area of the foundation pit is about 73,000m2, and the excavation depth is 15.4m~ 16.3m, and local area is 18m, which is a super-large deep foundation pit project. The enclosure adopts bored piles combined with single row triaxial cement-soil mixing piles with a diameter of Ф 850 @ 600. The waterproof curtain of cement-soil mixing pile enters ⑦6 layer with relatively low permeability, about 1.5m, which isolates ⑦3 layer and ⑦5 layer of confined water.

02

Waterproof curtain for underground continuous wall

Diaphragm wall integrates the functions of seepage prevention and foundation pit support, has good integrity and water-stopping effect, and is widely used. When used as a temporary structure alone, the project cost is high, and generally the type of supporting (waterproof) combined with basement exterior wall is adopted.

Tianjin Jinta

The excavation depth of the foundation pit of Tianjin Jinta Project is between-20.6 and-25.5 m, and the deepest part of the pit is -32. 1m (elevator pit of the main building). The retaining structure around the foundation pit is an underground continuous wall with two walls in one, and four reinforced concrete internal support systems are set in the foundation pit.

03

CSM cement-soil double-wheel milling mixing wall water-stop curtain

The construction technology of CSM cement-soil continuous mixing wall waterproof curtain is a circular improved column which is different from the traditional single-axis or multi-axis vertical rotation by combining the original equipment of hydraulic slotting machine with deep mixing technology. In this technology, two groups of grinding wheels rotate on the horizontal axis to stir the undisturbed soil, thus forming improved soil with rectangular groove section. Compared with other deep mixing processes, this construction process reduces the number of joints, increases the effective area, and has better water stopping effect; It has high adaptability to strata, can cut hard strata (gravel layer, rock layer), and can be used in cutoff wall, retaining wall, foundation reinforcement and other projects.

Tianjin Financial Street Peace Center

The excavation depth of the foundation pit of Hua Ting Project of Tianjin Financial Street (Peace) Center Project is about 18.6m, and the local pit depth is 23.55m The soil layer is mainly clay, silty clay, silty sand and fine sand, and the groundwater level is 4.00~3.00m The foundation pit is supported by slope protection piles and three reinforced concrete internal supports. The southeast side of the foundation pit is close to Tianjin Metro Line 3, and the environmental deformation control requirements are strict. φ 1400 @ 1600 bored pile is adopted. In other areas, φ 1200m @ 1400m bored piles are used. In order to ensure the water-stopping effect and reduce the influence of foundation pit construction on the surrounding environment and subway, a deep mixing cement-soil water-stopping curtain is adopted around the foundation pit.

04

High-pressure jet grouting pile and sleeve valve tube grouting combined water-stop curtain

There is no effective and reliable waterproof curtain in the water-rich stratum with thick pebble layer and large particle size. High-pressure jet grouting pile uses high pressure to spray cement slurry into the stratum through rotating nozzle, forming a gap between cement-soil and solid cast-in-place pile. The outer sleeve valve tube forms a closed retaining wall, the inner steel sleeve valve tube is grouted, and the gravel gap is further filled by means of infiltration, compaction and splitting, and the advantages of the two are combined to form a closed water-stop curtain.

Shenzhen ping' an financial center

The foundation pit of Shenzhen Ping 'an Financial Center is 33.8 m deep. The north side of the foundation pit is adjacent to the operating subway 1 line, and the underground of Yitian Road on the east side is the planned Guangzhou-Shenzhen-Hong Kong high-speed railway. There are many above-ground and underground buildings and complex pipelines around the foundation pit, so the safety of foundation pit is very important. The whole foundation pit is supported by slope protection piles combined with five concrete internal supports, and a combined water-stop curtain with high-pressure jet grouting combined with sleeve valve pipe grouting is adopted.

05

Composite water-stop curtain at the bottom of groove for secondary excavation of ultra-deep foundation pit

The construction technology of composite waterproof curtain at the bottom of ultra-deep foundation pit is that after the foundation pit is excavated to the bottom of the pit, the upper soil layer, completely weathered and strongly weathered rock layers, etc. High-pressure jet grouting is carried out from top to bottom on the peripheral working face inside the pit bottom. The cracks of moderately weathered rock and slightly weathered rock in the lower part are filled and compacted in turn by circulating grouting technology; The combination of the two forms a continuous composite water-stop curtain from top to bottom. It is suitable for projects that need a lot of secondary excavation after the ultra-deep foundation pit is excavated to the bottom of the groove. This kind of composite waterproof curtain has irreplaceable advantages for rock strata with abundant groundwater and developed cracks.

Shenzhen ping' an financial center

The giant pile of the main tower of pile-raft foundation in Shenzhen Ping 'an Financial Center has a hole diameter of 9.5m and a maximum hole depth of 40.3m, which belongs to the ultra-deep "pit-in-pit" in ultra-deep foundation pit. After the foundation pit is excavated to the bottom of the trough, from the working face of the bottom to the top of moderately weathered rock, a high-pressure jet grouting water-stop curtain is used around the inside of the bottom, and the moderately weathered rock is overlapped by 5 meters to 0.5 meters, and a bedrock fissure grouting water-stop curtain is used.

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