Quy trình kỹ thuật thi công cọc khoan nhồi đường kính nhỏ

  1. Fluid circulation bored pile is a foundation solution with many advantages in terms of design, based on geological documents the designer can determine the pile depth so that the load capacity of the foundation is equivalent to the bearing capacity. material load of the pile (Pv equivalent to Pd), which cannot be achieved with the driving or static pressing method, which is the condition leading to a more reasonable and economical foundation solution
    Works in tight terrain. However, there are also shortcomings in construction management, it is difficult to check the quality of concrete stuffed into piles. Therefore, it requires the experience and skill of the contractor and construction supervisor, the construction supervision must be very strict, fully complying with the processes.
    Process-engineering-construction-pile-drilling-stuffing-small-diameter.jpg

    I. PREPARATION FOR CONSTRUCTION OF DRILLING JOINT STOCK COMPANY

    1. Site preparation

    The ground before construction must be leveled.
    Make sure not to sink the machinery during construction.
    Make sure the drainage ditches in case it rains heavily.

    2. Locating the landmark heart

    Identify each position of the center of the pile and the center of the column, using bamboo poles to mark.
    Arrange the hearts of columns, auxiliary landmarks on the wall so that when losing traces, the method of tensioning can be used to restore the lost hearts.
    The error of the pile center after construction is less than D/4 but not more than 15cm for the middle pile and less than D/6 but not more than 10cm for the side pile.

    3. Gather equipment – supplies

    After the site preparation is complete, gather equipment and materials.
    Equipment is neatly gathered, arranged for placement of concrete pipes, drill rods and equipment for construction work…
    Iron materials must be kept in a high place to avoid flooding and soiling.

    II. STEPS OF CONSTRUCTION OF DRILLING PILES

    1. Diagram of drilling location

    Each drill is arranged in a certain area to avoid entanglement in construction work.
    Arrange drilling sequence from the inside to the outside to avoid the situation that the drill truck runs on the top of the new pile when pouring concrete.
    The posterior heart is only drilled next to the heart before the concrete of the anterior heart reaches more than 24 hours.

    2. Pile drilling

    When putting the machine into position, align the center of the previously positioned landmark.
    Lift the machine to ensure that it is not tilted when the machine is in operation.
    Check the verticality of the tower by 2 leveling bubbles mounted on both sides of the drilling tower body (during the drilling process, these two bubbles must also be continuously monitored).
    After adjusting the machine, use a drill to drill a depth of about 2m and lower the birth pipe (the wall pipe is 2m in length) to prevent landslides and water loss while drilling.
    Drilling is carried out with a break drill to the design height of the pile.
    When drilling for geological monitoring and recording, if there is much difference from the geological exploration document, immediately notify the investor and design consultant to adjust the pile depth.
    While drilling need to check the appropriate amount of bentonite.
    For piles with a diameter of 500mm or more, it must be checked by tests of solution density, viscosity, and sand deposition according to prescribed standards (Due to drilling by solution circulation method, we usually check when blowing wash and clean boreholes)
    Process-engineering-construction-pile-drilling-stuffed-diameter-small-1.jpg
    The bentonite solution has the effect of bringing the drilling mud from the bottom of the borehole to the solution hole and keeping the wall of the borehole from collapsing. therefore, in any case of stopping construction due to weather, having to stop overnight due to the end of working hours … it is still necessary to ensure that the borehole is always filled with solution.
    During the drilling process, if the water is lost through the large permeable layer quickly, then quickly add bentonite to the solution for waterproofing.
    Construction in high groundwater level should pay attention not to drill two pile centers close to each other to avoid flooding between one pile and the other, leading to wall collapse.
    After the first drilling is completed, lower the hidden drill bit B to pull up the remaining soil, this step can be done 1 to 2 times.
    When lowering the concealed drill B, the operation is still the same as when drilling the breaking bit. but when pulling up, do not rotate the drill bit to avoid the dirt falling back into the drill hole.

    3. Depth inspection of boreholes.

    Use a tape measure with a plumb to drop into the borehole or measure the length of the drill rod or concreting pipe.
    While drilling some drilling mulch is left in the borehole, so we cannot drop it to check, so now we check the drill hole height based on the length and number of drill rods to calculate, the length of each rod. drill is 3.05m.
    After using the hidden drill bit B to pull all the drilling mud up, we drop the plumb to check the borehole, then release the steel cage and the concrete pipe.
    After releasing the steel cage and concrete pipe, we proceed to drop and measure the height of the borehole to determine the thickness of the sediment layer.
    After cleaning the borehole, we drop a plumb to measure the borehole’s altitude again to re-determine the sediment layer to ensure < 10cm.
    If the case of cleaning is finished but there is no concrete pouring immediately, before pouring concrete, we must check again to make sure the sediment layer is within the allowable limit.

    4. Reinforcement work

    Rebar processing is carried out in a dry place and checked and accepted before lowering into the borehole.
    Steel cages are processed into 5.8m or 11.7m long cages depending on the design and are fully tied with concrete blocks to ensure the concrete layer is protected by sliding wheels.
    When lowering the steel cage, the cage must be kept upright, the part connected to the other section must ensure the correct center of the steel cage.
    Reinforced joints use abductor joints, the length of the reinforcement overlap is 30D and are connected by two clamps. the number of rods to be connected is 50% of the total number of joints. The remaining bars are tied with wire.
    When releasing the steel cage, care must be taken not to let the steel cage head poke into the wall.
    The steel cage when released must not reach the bottom and must be about 100 mm from the bottom of the borehole as shown in the design drawings.
    With piles requiring ultrasonic testing

    • The ultrasonic tube is made of steel or PVC with a diameter of 49mm, a thickness of 3mm .
    • Arrange two pipes symmetrically through the center of the pile all the way from the top of the pile to the bottom of the pile.
    • The ultrasonic steel pipe is tied to the main reinforcement by zinc wire and connected by a sleeve with a gene to ensure tight sealing to prevent the concrete from entering and clogging the pipe. Particularly in the bottom steel cage is welded to the host steel to ensure correct positioning.
    • While lowering the ultrasonic tube, it must be sealed at the bottom two ends and lowered to where it must be filled with water. After lowering and filling the pipe with water, we seal the top end so that when pouring concrete to avoid concrete falling in and clogging the pipe.

    5. Drilling hole cleaning

    This is the most important step in the drilling process. After drilling to the design depth, the amount of drilled workpiece cannot fully emerge. When drilling is stopped, the drill pieces suspended in the solution or the large-sized drill pieces that the solution does not bring up from the borehole will settle back in the bottom of the borehole.
    We divide the sediment treatment process into 2 steps.
    The processing steps are as follows:

    • Sediment treatment step 1: Sediment treatment is large-diameter particles.

    This work is done immediately after drilling and creating holes. After drilling to the design height, do not immediately raise the drilling equipment, but let it continue to pump up the soil wastewater. Then pull up the drill bit and put the drill bit with cover B down to pull the sediments, which are large lumps of earth. time)

    • Sediment treatment step 2: Treatment of sediments which are particles of small diameter

    This work is done before pouring concrete. After settling the sediment in step 1, we put the steel cage and concrete pipe down to the bottom of the borehole, put an air pipe into the BT pipe to 2 m from the bottom, using compressed air to pump the borehole solution back out. Outside by the BT pouring pipe, the drill bits tend to settle down will be sucked into the BT pourer and pushed back up and out of the mouth of the pour pipe (see figure) until there are no more mixed and satisfactory deposits. bridge.
    Using a ruler with a plumb to check the borehole sediment must be <10 cm.
    After processing is completed, BT must be poured immediately.
    Note: During the pumping of compressed air, the borehole must always be filled with liquid to ensure that the borehole does not collapse. In monitoring practice, the two sides will pour into the borehole some flint or 1*2 rock, when pumped up, use a mesh basket to catch it for inspection. If the amount of rock 1 * 2 from the bottom of the borehole that the pump pipe can pump out a large part of the rock poured into the borehole and there is no associated mud, then the cleaning is acceptable.

    6. Pile concrete pouring work

    Concrete pouring pipe is a steel pipe with diameter from 114mm to 138mm depending on the pile diameter, connected by many segments, each 1.5 m long, the mouth of the pipe is fitted with a funnel to pour concrete.
    For the construction of piles with a diameter of 400 to 800mm for large projects before pouring concrete, we need to make a water ball, this water blocking ball is made of flexible cement and wrapped with a thin cloth. When it reaches the bottom, the thin layer of fabric will loosen and the cement will mix into the concrete, which will be better for the bottom of the pile.
    When starting to pour concrete, do not stuff and pull the pipe up until the concrete is full to the top of the pouring hopper.
    In principle, concrete works as bored piles must comply with regulations on pouring concrete under water. The method of construction of concrete poured under water of bored piles is to use pipes.
    Before placing concrete, the measuring tools must be checked to convert back to the required amount of concrete. The actual total amount of concrete poured into the pile should not be more than 20% of the concrete according to the nominal diameter of the pile. pile
    The concrete is brought to the bottom of the borehole through the pour pipe, the concrete rises gradually and pushes the liquid water to the top of the borehole. The concrete pipe is always submerged in the concrete for a minimum of 2.0 m to ensure that the concrete does not mix with the solution.
    The concrete compaction is done by the concrete pouring pipe itself through the pipe tapping action.
    Time to pour concrete for piles must not last more than 4 hours (to ensure quality and strength of concrete throughout the length of the pile). If the concreting process is blocked … then there are measures to handle it quickly, the processing time does not exceed the upper limit. In case it cannot be handled, the construction must be stopped for at least 24 hours, then cleaned the borehole again before continuing to pour concrete.
    Pipe cutting procedure: Technicians and supervisors can monitor the pitch of the concrete rise in the borehole by rough calculation of the amount of concrete injected into the pile according to the nominal diameter of the pile, but the actual diameter. will be from 10% to 20% depending on the drilling floor or check directly by dropping the beam down to measure.
    In practice, before cutting the pour pipe, you must loosen the cable, raise the pour pipe to determine the “sitting” of the pipe in the concrete, then cut the pipe.
    After the concrete reaches the mouth of the birth pipe 20cm above the ground, we pull the birth pipe up to 1m above the ground and continue to pour the concrete.
    When the concrete rises to the mouth of the birth pipe, although the cleaning has been done thoroughly, the top layer of concrete is often contaminated with mud during the rising process. This layer of concrete should be allowed to flow out of the borehole until it is visually determined that the next layer of concrete meets the requirements, then stop pouring.
    The volume of concrete poured into the pile should not exceed 20% of the nominal pile volume. If a larger amount of concrete is found when pouring, notify the supervisory and design consultant for consideration and treatment.
    After pouring concrete, about 20-30 minutes, proceed to withdraw the birth pipe to complete the concreting work.
    When the piles are close to each other, when constructing the following piles, it is necessary to wait for the concrete of the previous pile to reach at least 24 hours before drilling.
    Concrete testing problem:

    • Before pouring concrete, measure the slump with a standard cone to ensure the slump Sn = 180 ± 20mm
    • Take a concrete test sample using a square sample of 15x15x15 cm to test concrete strength.

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