Quy trình thi công móng cọc

  1. Process-construction-foundation-pile-1.jpg

    Preparing the construction site

    • Pile stacking area must be outside the concrete pile pressing area, the path from the pile placement to the concrete pile pressing place must be flat, not bumpy, concave.
    • The pile must have a center line already marked so that when pressed it is convenient for weighing and adjusting.
    • Remove piles that do not meet technical requirements.
    • Prepare full technical reports of geological survey, static penetration results….
    • Positioning and project foundation.

    Sequence of construction of reinforced concrete piles

    a: Prepare.

    • Accurately determine the position of piles to be pressed through positioning and foundation work.
    • If the soil subsides, it is necessary to use a wooden backing board first to ensure the base is stable and flat during the process of pressing the concrete pile.
    • The crane installs the base frame in the right design position.
    • Counterweight to the base frame.
    • The crane mounts the press rack to the base frame, accurately positioning and adjusting for the presser to stand upright.

    b: Construction process of pressing concrete piles. (includes 4 steps)
    STEP 1:

    • Pressing the first pile segment C1, hoisting the pile into the press rack, adjusting the pile tip to the right design position and adjusting the vertical pile shaft.
    • The verticality of the first pile segment greatly affects the verticality of the entire pile, so the first pile segment C1 must be carefully erected, aligned so that the axis of C1 coincides with the axis of the jack passing through the fixed point. pile position. The eccentricity is not more than 1 cm.
    • The upper end of C1 must be fastened to the guide bar of the chassis.. If the machine does not have a guide bar, the bottom of the jack (or piston head) must have a guide bar. Then the pile head must be in close contact with them.
    • When the two friction sides are in close contact with the side of pile C1, the valve control gradually increases the pressure. In the first seconds, the head pressure increases slowly, so that the C1 segment slowly deepens into the soil with a penetration speed of no more than 1 cm/s.
    • When tilt is detected, stop, align immediately.

    Process-construction-foundation-pile-2.jpg
    STEP 2:

    • Pressing to the design depth (pressing the intermediate pile segment C2):
    • When the first pile C1 is pressed to the designed depth, proceed to connect and press the intermediate pile segments C2.
    • Check the surface of the two ends of segment C2 , fix it to be flat.
    • Check the details of the pile joint and prepare the welding machine.
    • Install segment C2 into the pressing position. Align so that the axis of C2 coincides with the axis of jack and the axis of C1. The inclination of C2 is not more than 1%. Before and after welding, the verticality of the piles must be checked with nickel. Apply a force to the pile to create contact so that the pressure on the contact surface is about 3-4 KG/cm2 and then proceed to weld the piles in accordance with regulations. of design.
    • Pressing the C2 pile. Gradually increase the compressive pressure so that the press has the necessary time to create enough pressure to overcome the friction and resistance of the soil at the tip of the pile for the pile to move.
    • At the beginning, C2 goes deep into the ground with a penetration speed of no more than 1 cm/s.
    • When section C2 moves uniformly, the pile will move with a penetration speed of not more than 2 cm/s.
    • When the compressive force increases suddenly, ie the tip of the pile meets the harder soil layer (or encounters a local foreign body), it is necessary to reduce the compression speed so that the pile can have enough ability to enter the harder soil (or check for foreign objects to handle). and keep so that the pressure does not exceed the maximum allowable value.
    • In the process of pressing concrete piles, a counterweight must be added to the frame at the same time as the process of increasing the pressure. On request, the counterweight is applied to the frame at the same time as the pressure is increased. As required, the counterweight should be increased by 1.5 times the force. Because the pile consists of many segments, when pressing each pile segment, it must be connected to the pile by lifting the movable frame of the presser rack, lifting the next section to the presser rack.

    Requirements for the method of pressing reinforced concrete piles:

    • The axis of the pile segment is connected to coincide with the direction of compression.
    • The concrete surface at the two pile readers must be in close contact with each other, in case of non-close contact, measures must be taken to seal.
    • The size of the weld must be guaranteed compared to the design.
    • The weld seam connecting the pile segments must be evenly distributed on all 4 sides of the pile according to the design.
    • The surface of the contacts must be flat, deviated by no more than 1% and free of burrs.

    Process-construction-foundation-pile-3.jpg
    STEP 3: EXTRACTION
    When pressing the last pile to the ground, the crane erects the core pile (steel) to the top of the pile and then continues to press the core so that the pile head is plugged to the design depth. This core segment will be pulled up to continue for another pile.
    STEP 4:

    • After pressing a pile, slide the press rack system on the base frame to the next position to continue pressing. In the process of pressing the concrete pile on the first foundation, use the second platform crane to position the second foundation pit. two.
    • After pressing a foundation, move the whole press frame system to the 2nd base frame which is placed first in the 2nd foundation pit. Then crane counterweight from base 1 to base 2.
    • Finish pressing a pile:

    The pile is recognized as finished pressing when the following two conditions are satisfied:

    • The length of piles pressed deep into the ground is not less than the shortest length specified by the design.
    • The force at the final moment must reach the specified design value throughout the penetration depth greater than three times the diameter or side of the pile. In that interval, the penetration velocity does not exceed 1 cm/s.

    Piles that are tilted beyond regulation (greater than 1%), unfinished pressed piles due to foreign objects in sand drives, abnormally hard clay seams, broken piles, etc. must all be handled by uprooting or pressing new piles. specified by design).
    Use appropriate drilling methods to break foreign bodies, through sand drives, hard clay seams, etc.
    When the pressure has just reached the design value but the pile cannot go down anymore, while the pressure acting on the pile continues to increase beyond the maximum pressure (Pep)max, before stopping pressing, a valve must be used to maintain the force. (Pep)max for 5 minutes.
    In case the press does not have a holding valve, it must be pressed three to five times with the pressure (Pep)max .
    c: Allowed error.
    At the high position of the bottom of the pile top, the error must not exceed 75mm compared to the design position, the inclination of the pile is not more than 1%.
    d: Time to lock the pile head.

    • The time to lock the pile head partially or simultaneously is specified by the design.
    • The purpose of locking the pile head is to: Mobilize the pile to work at an appropriate time in the process of increasing the load of the work and ensure that the work is not subject to large settlements or irregular settlements.
    • The locking of the pile head must be fully implemented:
      • Fix the pile head for the correct design height.
      • In case the concrete pile hole does not ensure the prescribed taper, it is necessary to repair the taper and sand the sides of the pile hole.
      • Fill around the pile with medium grain sand, compacted to the height of the concrete lining.
      • Place wire mesh for pile head.
    • The concrete of the pile head must have a mark not less than that of the concrete of the foundation and must have an expansion additive, ensuring an expansion rate of 0.02
    • For the stakes to be attached to the 10 cm tower, the top of the piles must be at a height of – 1.55 m.
    • Pillar head gasket type.

    Process-construction-foundation-pile-4.jpg

    Rebar processing

    Straighten and rust.
    a: Straighten the reinforcement.
    With hammer: applied to small, bent reinforcements;
    By bending machine: applicable to reinforcement with diameter greater than 24mm.
    By winch: applicable to coiled steel or can be folded if no winch is available.
    b: Rust.
    By iron brush: applicable to all types of reinforcement.
    By human strength, pulling through piles of gritty sand.
    Cut and bend.
    a: Cut.
    The reinforcement must be cut according to the requirements of the design, can be used:

    • Knife, using human power: can only cut steel bars under 12mm.
    • Cutting machine: can cut steel bars up to 40mm in diameter.
    • Welding: cutting steel bars with a diameter of more than 40mm.

    b: Bending.
    The reinforcement must be bent according to the requirements of the design and drawings:

    • By hand: Using crab claws, only rebars up to 25mm in diameter can be bent.
    • By bending machine: bending reinforcement bars with diameter greater than 25mm.

    Rebar connection.
    If you want to have long rebars or want to take advantage of short rebars, you must connect them.
    Manual connection: tie the reinforcement with flexible zinc wires and adhere to the following rules:

    • For plain steel:
      • Placed in the area of ​​dual-bearing concrete, the two ends of the reinforcement must be bent into hooks and placed on top of each other for a length of 30-45d, using zinc wire to wrap around the bend.
      • Placed in the compressive concrete area, it is not necessary to bend the hook, but the steel wire must be bent around the joint, the intersection must be 20-40d long.
    • For barbed wire:
      • Placed in the tensioned concrete area, it is not necessary to bend the hook but also bend the steel wire around the joint, the intersection must be 30-45d long.
      • Placed in the compressive concrete area, it is not necessary to bend the hook but also bend the steel wire around the joint, the intersection must be from 20-40d.

    Process-construction-foundation-pile-5.jpg

    Install formwork.

    Firm, reaching the required thickness, not deformed due to the weight of concrete, reinforcement and loads during construction.
    Formwork must be tight so as not to leak cement water during concrete pouring and compacting.
    Formwork must be the correct shape and size of the member.
    The supporting tree must be of quality and specification, the density of the support tree must be calculated specifically, the supporting wood must be supported on a wooden base and firmly fixed to avoid movement during construction.
    Formwork can be wood or tole with standard sizes for each type of concrete structure to be cast.
    On the other hand, the floor formwork can be lined with canvas on the board to avoid the loss of cement water.
    When constructing formwork, it is necessary to pay attention to the bearing capacity of wood planks and scaffolding.
    The center of the foundation and the neck of the column must always be located and determined to be the height.
    Process-construction-foundation-piles-6.jpg

    Pouring a concrete foundation

    Pouring concrete for foundation:

    • Primer concrete is used to line the ground before pouring concrete foundation. Concrete lining is responsible for cleaning the bottom of the foundation concrete. The concrete lining must be solid, not destroyed under the impact of the surrounding environment (flow, groundwater, works next to the construction..
    • Finished digging the soil area of ​​the foundation, dredging all the mud at the bottom of the foundation and pouring concrete lining. Digging the soil in each area, dredging mud and pouring concrete immediately, this lining layer protects the newly excavated soil layer, from destruction or sludge deposition.
    • The concrete base layer is 10cm thick.

    Process-construction-foundation-piles-7.jpg
    Pouring a concrete foundation:

    • The cross section of the concrete has a trapezoidal shape, the roof slope is small, there is no need to join the top formwork, but only need to join the two sides. Can be used in combination with the trowel for construction. Concrete mix is ​​relatively dry because the compaction is easy to flow. It is recommended to use a wooden jig according to the shape of the foundation to check. Pour concrete foundation according to the principle of pouring in the position far ahead, near behind. The working floor should be mounted across the foundation pit so as not to stand directly on the formwork wall or the reinforcement, causing erroneous position
    • Before pouring concrete, it is necessary to check the formwork, reinforcement, floor system. Clean floor system, formwork, reinforcement. Correct defects if any.
    • Water formwork, floor system before pouring to avoid water absorption of concrete.

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