Pis aller
1. Hole collapse and shrinkage:
Drilling and pouring pile construction is predominantly carried out in Quaternary loose strata, making hole collapse the most common accident during pile installation.
(1) Precursor signs before the accident
Collapse and shrinkage of drill holes during drilling operations generally do not occur suddenly. There are usually some precursors before their occurrence. These may include a sudden drop in water level within the casing, mud discharge at the casing location, increased rotary resistance of drilling tools during drilling, and elevated mud specific gravity (which may be difficult to detect during rotary drilling).
(2) Cause of the accident:
① Improper selection of irrigation solution;
② Improper installation of the protective sleeve;
③ Low water head pressure.
(3) Preventive Measures
① Except for clay layers, other strata should be drilled with mud wall protection methods compatible with their properties.
② The casing should be buried in strata suitable for casing placement, with surrounding areas compacted using clay, and the burial position must be concentric with the borehole location.
③ When drilling loose silty-sand layers, the footage rate should be appropriately controlled, as rapid penetration will inevitably backfire.
④After final drilling, sufficient water supply should still be ensured during the preparation for concrete pouring.
⑤ The outer diameter of the drill bit must be at least equal to the designed pile diameter, and its diameter should be regularly checked to prevent diameter reduction.
(4) Accident Handling
In case of porosity formation, the following measures should be taken: control drilling speed, perform low-speed drilling, adopt repeated hole sweeping methods or increase drill bit diameter.
Upon detecting a hole collapse, drilling must be immediately halted. The affected section should be located and addressed promptly. Typically, if the collapse is not severe, the drilling mud can be increased.
The viscosity, specific gravity, and water head height in the borehole should be measured, and the drilling should be performed at a slow speed and light pressure for a standard duration. If the hole collapse continues to worsen, drilling should be halted and the hole backfilled with clay (typically filling up to 1.5 meters above the collapse point; in severe cases, the entire hole should be backfilled). After staged compaction, drilling should be resumed.
2. Stuck:
The rock constituting borehole walls loses stability when drilled through, often resulting in instability, particularly where exposed wall surfaces are extensive. Near surface layers such as aeolian deposits, alluvial layers, gravel layers, and卵砾 layers, as well as deeper fractured zones, are susceptible to factors like fluid immersion, erosion, and vibrations from drill string rotation. These conditions can lead to wall fragmentation or collapse, causing drill string sticking incidents.
In the event of a stuck pipe incident, initial response should avoid panic. The location and type of the stuck pipe must be identified, followed by tailored measures based on specific circumstances.
3. Drill burial:
Drill burial accidents typically occur following incidents such as hole collapse, drill jamming, or main rope rupture. These accidents are generally classified as major incidents and must be prevented at all costs.
（l） cause
①The mud properties did not meet the formation requirements, resulting in borehole collapse and subsequent drill bit burial.
② Prolonged response time for incidents such as main drill string fracture leads to significant sediment accumulation, resulting in drill entrapment.
(2) Management Measures
Different methods are adopted according to different types of drilling.
① Gas lift loosening method: Based on the principle of gas lift counter-circulation, the collapsed material and sediment deposited during drilling are extracted from the borehole, thereby removing the buried drillings.
② Auxiliary lifting method: When the drill bit is not severely buried, auxiliary lifting tools such as cranes are used to directly extract the buried drill bit from the hole.
③ Drilling and waste removal method: When severe borehole burial occurs, one or more pilot holes are drilled near the accident hole.
Loosen the buried drill bit and lift it out of the hole.
4. Hole skew:
Borehole deviation occurs when encountering large, smooth boulders or protruding rocks in loose formations that displace drilling tools from the axis of the borehole. When transitioning from soft strata to hard formations or sand-gravel layers with significant particle size variations, uneven resistance experienced by drill bits causes tool deviation, resulting in borehole tilt. Alternatively, positional misalignment of drilling rigs or localized subsidence of the base may also lead to inclined drilling paths.
preventive measure ：
① Utilize mud effectively to maintain hole wall stability;
② Reduce the drilling speed;
③ Reinforce the drilling rig base to enhance ground bearing capacity.
④ Use a rotary drilling rig with excellent directional guidance and high mast rigidity for construction.
5. Slurry leakage:
The occurrence of slurry leakage incidents is primarily associated with groundwater levels and slurry properties. In cases of large fissure slurry leakage,
Backfilling should be employed for treatment. For minor slurry leakage, the slurry properties should be adjusted to ensure the formed mud skin possesses sufficient toughness.
6. Drill bit dropped:
The drill pipe and drill bit connection is not secure, or the square interface of the drill bit is not welded firmly with the drill bit body, or the penetration pin strength is insufficient, all of which may lead to drill bit detachment.
Regular inspection can serve as a preventive measure.
7. Clay layer shrinkage and drill sticking:
The clay layer has strong slurry-making ability and water-expanding property. In drilling, besides controlling the increase of slurry viscosity, some gravel should be put into the hole to prevent sticking. It is not suitable to use the sand scoop to drill.
The method of repeated scanning by top and bottom is used to enlarge the aperture.
8. Plum blossom hole
Phenomenon: The cross-sectional shape of the pore is irregular, presenting a plum blossom-like pattern.
Preventive measures: Regularly inspect the steering mechanism for flexibility. Select slurry with appropriate viscosity and specific gravity, and remove debris as needed. When using low stroke, periodically switch to higher stroke to allow sufficient rotation time for the impact cone.
9. Broken pile
Phenomenon: After pile installation, there is no concrete in the middle section of the pile body, with soil interposed.
Preventive Measures: Concrete slump must be strictly controlled according to design specifications or industry standards. Prior to pouring, inspect the workability and flowability of ready-mixed concrete to prevent pipe blockage during placement. Remove casing pipes while concreting to ensure continuous operation without interruption. Monitor the concrete surface elevation during pouring and track the casing depth in real-time to avoid excessive burial or detachment from the concrete surface. Weld main reinforcement joints of the steel cage flush with concrete, and cover the casing flange connection with a conical tinplate cover matching flange dimensions. Secure the cover onto the casing head to prevent flange interference with the steel cage during pipe lifting operations.
10. Steel bar cage spalling:
cause ：
1. Bending deformation of the steel cage;
2. The concrete top surface is bent or the upper part has begun to set;
3. There are large mud blocks in the hole;
4. Deep catheter embedding;
5. Hook cage during catheter elevation.
preventive measure ：
1. The processing and assembly accuracy of the steel cage framework should be improved to prevent deformation during lifting, and the formed cages should be stacked in a straight manner.
2. The workability and fluidity of concrete should be maintained, with slump controlled within 18-22 cm.
3. Before the first cleaning, the mud clumps at the bottom of the hole should be broken up with a drill bit, and the ground stones should be avoided from falling into the hole.
4. When the concrete surface approaches the bottom of the formwork cage, the pipe should be embedded approximately 3 meters below the concrete surface, and the pouring rate should be appropriately reduced.
5. The catheter should be placed centrally to avoid contact with the cage. During catheter elevation, maintain stable central positioning and reduce the lifting speed.
11. Concrete blockage of the conduit:
cause ：
1. Insufficient slump of concrete, poor fluidity, or uneven mixing.
2. Large stone fragments are present in the concrete.
3. Excessive concrete pouring time leads to initial setting of surface concrete or prolonged retention time in the pipe, resulting in loss of fluidity.
4. The catheter is buried too deep, the bottom opening of the catheter has less pressure, and the concrete inside the catheter is not easy to flow out.
preventive measure ：
1. The concrete shall have good workability and fluidity, and the slump shall be controlled within 18-22 cm.
2. Maintain continuity during concrete pouring. Inspect all mechanical equipment for normal operation prior to pouring to prevent delays caused by malfunctions.
3. The buried depth of the catheter is greater than 3 m but less than 10 m.
preventive measure
1. Operators should be regularly reminded to inspect the thread wear and aging at the drill pipe-borehole bit connection, and replace it promptly if any issues are detected. During drilling operations, the drill string must be aligned with the target hole position. First, lower the drill pipe until the bit contacts the ground, then rotate the drill pipe. Avoid rotating or shaking the drill pipe while lowering it.
2. During drilling operations, the lower drilling speed should be adjusted according to geological conditions to prevent drill string sticking. Operators must closely monitor the pressure and rotational speed indicators in the cab as well as variations in drilling load, and apply additional pressure or raise the drill string when necessary.
3. During drilling operations, if sudden vibration of the drill pipe or rhythmic/abnormal noises occur in the borehole, drilling must be immediately halted. Operations may resume only after identifying the cause and implementing corrective measures.
4. During drilling operations, when encountering stuck pipe or other issues, strictly limit the lifting speed of drill pipes to the capacity of the main winch during rod lifting.
5. During drilling operations, avoid abrupt lifting or dropping of drill tools, and do not perform parallel operations simultaneously.
6. When using a cable winch to lift heavy loads, the lifting capacity must not be exceeded. The load should be positioned directly in front of the top pulley, and the angle between the steel wire rope and the column must not exceed 300 degrees.
In adverse weather conditions such as heavy rain, fog, or winds exceeding force 6, operations must be halted. When wind speeds surpass force 7 or a severe typhoon warning is issued, position the drilling rig downwind, lower the mast to ground level, and reduce the power head to its lowest position. If feasible, disassemble the drill mast for optimal safety. During thunderstorms, personnel must remain away from the rig and install lightning rods as required.
8. Unauthorized personnel are strictly prohibited from entering the designated work radius. Only personnel and vehicles on-site may proceed under the direction of supervisors.
9. Maintain water head pressure within the borehole to ensure wall stability and prevent drilling accidents.
10. When lowering the lower protective sleeve, adjust the column angle to prevent collisions between the sleeve and components such as the power head tubing.
11. The drilling footage per pass should be determined based on depth measurement instruments, guided by drilling speed and drilling pressure torque, avoiding excessive or insufficient drilling. Overdrilling increases auxiliary time, while underdrilling results in reduced pass footage and decreased efficiency.
Upon reaching the designed elevation, drilling shall cease immediately, followed by a slurry replacement procedure for hole cleaning. The method involves: after completing the final hole, the rig is operated directly. During cleaning, the drill bit is lifted 10-20 cm above the hole bottom, with the rotary table rotating to create a continuous slurry circulation while periodically rotating the drill string to enhance cleaning efficiency. The duration of a single cleaning cycle should not be fixed but determined by the sediment thickness at the hole bottom during the rig’s descent test and the slurry return ratio. The slurry’s initial density must be below 1.15, and the return slurry density below 1.30. The slurry should feel particle-free upon touch, with sediment thickness under 8 cm, indicating the cleaning is complete.
Post time: Mar-19-2026