Key points for rotary drilling construction:#drilling rig machine manufacturers#
1) A trial drilling should be conducted before formal construction.
2) Rotary drilling of bored piles should employ dry drilling, mud wall drilling, or casing drilling techniques, depending on the geological conditions and groundwater depth.
Dry drilling
Mud wall drilling
Casing drilling
3) Drilling rig installation and positioning: Due to the heavy weight of the rotary drilling rig, the ground bearing capacity must be no less than 100 kPa, and the track should be placed on a flat surface with a slope no greater than 3°. (Firstly, verticality adjustment by hydraulic cylinders alone has limitations; secondly, it easily leads to power loss and a larger tilt angle during rotation, resulting in a higher center of gravity and a higher risk of accidents; thirdly, it prevents tilting and displacement.)
If necessary, steel plates or subgrades (roadbed plates) can be laid on the site to ensure safe movement and operation.
4) Pile driving: The pile points must be inspected according to the pre-inspection results, pass self-inspection, and be verified by the client or supervisor before two perpendicular straight lines intersect at the pile point, and a cross control point is marked.
5) Aligning the hole position: First, adjust the mast of the rotary drilling rig so that the center of the auger bit or the center of the drill bucket is aligned with the hole position before drilling.
6) Each pile should be equipped with a steel casing, which should meet the relevant specifications.
The functions of the casing are: (1) to fix the pile position and guide the drilling;
(2) to protect the hole opening and prevent the soil layer at the hole opening from collapsing. (3) Isolate surface water and maintain the water level in the borehole above the construction water level to stabilize the borehole wall.
Casing installation: After setting the cross control stakes, install the casing, measure the borehole depth, use a level to transfer the elevation to the top of the casing, and record the data.
7) Casing inspection: Check the casing's deviation based on the cross control points. If it exceeds the acceptable range, it should be re-established. (1) The deviation between the casing center and the pile center should not exceed 50 mm. (2) The casing can be made of 4-8 mm thick steel plate, and its inner diameter should be 100 mm larger than the drill bit diameter. One or two overflow holes should be opened at the top.
8) Mud preparation is the same as for other mud-walled bored piles. (For wet drilling)
9) Rotary drilling: Select the shape and specifications of the cutting teeth at the bottom of the drill bit, the type of drill rod, and the length of the wire rope according to the geological characteristics. Several points to note:
(1) During rotary drilling rig construction, ensure mechanical stability and safe operation. If necessary, lay steel plates or subgrade (roadbed) on the site to ensure safe movement and operation.#drilling rig machine manufacturers#
(2) Before drilling and each time the drill bucket is retrieved, check the condition of the drill bucket and drill rod connecting pins, the drill bucket door connecting pins, and the wire rope. Remove any debris from the drill bucket.
(3) Rotary drilling rigs should use a skip-drilling method. The minimum distance between the soil dumped from the drill bucket and the borehole opening should be greater than 6 meters, and this soil should be removed promptly. Mud should be replenished synchronously according to the drilling speed to maintain the required mud level.
(4) To ensure borehole stability, depending on the thickness of the loose topsoil layer, insert an appropriately long casing at the borehole opening and maintain the mud level. As mud is consumed and the borehole depth increases, replenish mud into the borehole promptly to maintain pressure balance.
(5) When encountering soft layers, especially cohesive soil layers, use a drill bit with longer teeth and a larger tooth spacing to avoid clogging. After lifting the drill bit, frequently check the bottom cutting teeth, promptly clean the mud between the teeth, and replace any dull teeth.
When encountering hard soil layers, if it is found that the drilling depth per pass is too shallow and the amount of debris in the drill bit is too small, switch to a smaller diameter drill bit, drill a small hole first, and then enlarge the hole with a drill bit of appropriate diameter.
(6) When drilling sand and gravel layers, to reinforce the borehole wall and facilitate the removal of sand and gravel, a suitable amount of firewood balls can be placed into the hole beforehand. Use a double-layer bottom plate sand-retrieving drill bit to prevent sand and gravel from leaking out from the bottom during drill lifting.
(7) Lifting the drill bit too quickly can easily generate negative pressure, causing the borehole wall to collapse. Generally, follow the manufacturer's requirements.
(8) When drilling into the bearing stratum at the pile tip, the lifting of the drill bit may cause loosening of the bearing stratum. Therefore, attention should be paid to the lifting speed of the drill bit when approaching the bottom elevation of the hole.
10) For unstable strata, full casing drilling should be used for extremely unstable strata.
11) Hole cleaning and inspection: When the borehole reaches the design depth, a hole cleaning drill bit or other reliable methods should be used for hole cleaning.
According to the pile foundation specifications, the hole position, depth, diameter, verticality, and thickness of sediment at the bottom of the hole should be checked.
12) Inspection of the reinforcing cage: The inspection is the same as other cast-in-place pile construction methods.
The reinforcing cage is transported on-site, hoisted into place, and lowered into the hole.
The reinforcing cage should not undergo permanent deformation. 14) Conduit Inspection: Before use, the conduit should be test-fitted and pressure-tested. The minimum pressure is 0.6-1.0 MPa.
15) Lowering the Conduit: The conduit connection should be sealed and straight. The lower end of the conduit should be about 300-500 mm from the bottom of the hole. For smaller diameter piles, the distance can be increased. The conduit platform should be flat, and the clamps should be firm and reliable.#drilling rig machine manufacturers#
