Calculation formula for bored pile
Borehole bottom elevation = measured hole depth + ground elevation
Total length of reinforcing cage =Borehole bottom elevation - - Pile top elevation? + anchorage length (0.5m or 1.0)
Cage top elevation = pile top elevation? -Anchorage length (0.5m or 1.0m)
Suspension length = top pile elevation? - Ground elevation - anchorage length (0.5m or 1.0m) +0.2 m, cage bottom elevation = measured hole depth + ground elevation
From the bottom of the hole = (between 30 cm ----50 cm)
Effective length of the pile? = measured hole depth - top of pile elevation + ground elevation
Theoretical square footage =(effective pile length? + design concrete loose layer length 1.5)×3.14×πr 2
Filling factor? = actual concrete volume ÷ theoretical concrete volume
Collapse degree (between 180-220mm)
Slag thickness (0---5cm )
Specific gravity of slurry (1.15--1.2)
Conduit length (m)÷2.5=number of sections of the conduit
Conduit length - final depth = conduit Higher than the ground
Final hole depth (m ) - Slag thickness? (cm) (0.02--0.03- 0.04) = Depth after second clearing (m)
Initial filling = Overfilling height × (pile diameter ÷ 2) 2 × 3.14 × Filling factor? + conduit depth ÷ 2 × (conduit diameter 250mm) 0.1252 × 3.14
Expanded information:
Construction Methods
Construction of drilled piles, depending on the selected retaining wall formation, there are two types of mud retaining wall method and full set of pipe construction method.
Mud shielding construction method
Impact drilling, punching and grasping drilling and rotary drilling can be used to form the mud shielding construction method. The process of this construction method is:
leveling the site→mud preparation→buried shoring→laying the working platform→installing the drilling rig and positioning→drilling the hole→cleaning the hole and checking the quality of the hole→lowering the reinforcing cage→flooding the underwater concrete→pulling out the shoring→checking the quality.
Construction sequence:
(1)Construction preparation
Construction preparation includes: selection of drilling rig, drilling tools, site layout and so on.
The drilling rig is the main equipment for drilled pile construction, which can be selected according to the geological condition and the application conditions of various drilling rigs.
(2)Installation and positioning of drilling rig
If the foundation for installing the drilling rig is not stable, the construction is prone to adverse effects such as tilting of the drilling rig, tilting of the pile and eccentricity of the pile, so it is required that the installation foundation is stable. For the foundation with soft stratum and slope, bulldozer can be used to bulldoze the foundation, and then padded with steel plate or sleeper to reinforce it.
In order to prevent the inaccurate pile position, it is very important to set the center position and correctly install the drilling rig during the construction. For the drilling rig with drilling tower, first use the power of the drilling rig to cooperate with the nearby ground cage to move the drilling rod roughly to locate the drilling rod, and then jack up the frame with jacks to accurately locate it, so that the lifting pulley, drilling head or the fixed drilling rod of the card hole and the center of the sheath are in a plumb line in order to guarantee the perpendicularity of the drilling rig. The deviation of the position of the drilling rig is not more than 2cm. after aligning the piles, use sleepers to pad the beam of the drilling rig, and pull the cable on the top of the tower symmetrically on the axis of the drilling rig.
(3)Buried protection tube
The key to the success or failure of drilling is to prevent the hole wall from collapsing. When drilling deeper, below the water table in the hole wall soil under hydrostatic pressure will be collapsed to the hole, and even the phenomenon of sand flow. If you can maintain a higher head than the water table in the borehole, increase the hydrostatic pressure in the borehole, which can balance the groundwater pressure outside the borehole for the borehole wall or increase the hydrodynamic force in the borehole, preventing the collapse of the borehole. In addition to this role, there is also isolation of surface water, protection of the ground at the mouth of the hole, fixing the position of the pile hole and the role of the drill bit guidance.
The materials used to make the shield are wood, steel and reinforced concrete. The inner diameter of the shield should be larger than the diameter of the drill hole (rotary drilling is about 20-30cm, submersible drilling, percussion or punch grabbing cone is about 30-40cm), and the length of each section is about 2~6m. steel shield is commonly used in general.
(4) mud preparation
Drilling mud consists of water, clay (bentonite) and additives. It has the effect of floating suspended slag, cooling the drill bit, lubricating the drilling tools, increasing hydrostatic pressure, and forming a mud skin on the hole wall, isolating the hole from internal and external seepage, and preventing the collapse of the hole. Modulation of drilling mud and after circulation purification of mud, should be based on the drilling method and stratum to determine the consistency of mud, mud consistency should be depending on the stratum changes or operational requirements of maneuvering to grasp the mud is too thin, slag removal capacity is small, poor wall effect; mud is too thick will weaken the impact function of the bit, reducing the speed of drilling.
(5) drilling
Drilling is a key process, in the construction must be strictly in accordance with the operating requirements to ensure the quality of the hole, first of all, pay attention to the quality of the hole, which must be a good center line and verticality, and good pressure protection cylinder. In the construction, attention should be paid to the continuous addition of mud and slag pumping (percussion type), but also at any time to check whether there is a skew phenomenon into the hole. When using impact or punch and grab drilling rig construction, the nearby soil layer is affected by the vibration and the stability of the neighboring holes. Therefore, the drilled holes should be cleared in time for lowering the reinforcing cage and filling the underwater concrete. The order of drilling should also be planned in advance to ensure that the construction of the next pile hole does not affect the previous pile hole, but also so that the drilling rigs do not move too far and interfere with each other.
(6) Clearing
The depth, diameter, position and shape of the drilled holes are directly related to the quality of pile formation and the curvature of the pile body. For this reason, in addition to close observation and supervision during the drilling process, the depth, position, shape and diameter of the hole should be checked after the hole reaches the design depth. When the final hole check fully meets the design requirements, the bottom of the hole should be cleaned up immediately to avoid too long an interval so that the mud settles and causes the hole to collapse. For the friction pile when the hole wall is easy to collapse, required in the filling of underwater concrete before the slag thickness of not more than 30cm;
When the hole wall is not easy to collapse, not more than 20cm.
For the column pile, the requirements of the water or wind shot before the slag thickness of not more than 5cm.
Clearing method is to use a different drilling rigs and the application of flexible. Usually can be used positive circulation rotary drilling rig, reverse circulation rotary machine vacuum mud suction machine and slag pumping cylinder and other clearing holes. One of the suction mud machine to clear the hole, the required equipment is not much, easy to operate, clear the hole is also more thorough, but in the unstable soil layer should be used with caution. The principle is to use the compressor to produce high-pressure air blown into the suction mud machine pipeline will be blown out of the mud.
(7)Filling underwater concrete
After clearing the hole, the prefabricated reinforcing cage can be vertically lifted into the hole, and it should be fixed after positioning, and then the conduit is used to fill the concrete, and the concrete should not be interrupted when filling, or else it will be easy to break the pile phenomenon.
Baidu Encyclopedia - Drilled Pile