1. How to Prevent and Correct Deviations in Bored Piles?
Quality Issues and Phenomena
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The pile hole is not vertical after drilling, with a deviation exceeding the specified L/100.
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The reinforcement cage cannot be smoothly lowered into the hole.
Causes
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The drilling rig is not level, or the construction site is not properly leveled and compacted, leading to uneven settlement during drilling.
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The base of the offshore drilling platform is unstable or not level, causing deformation of the rig frame during drilling.
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The drill pipe is bent or has loose connections, resulting in excessive wobbling of the drill bit.
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Obstructions near old structures push the drill bit to one side.
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Uneven soil hardness or encountering boulders and protruding rocks causes uneven force on the drill bit.
Preventive Measures
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Level and compact the construction site before positioning the rig. Ensure the rig remains level during drilling. Offshore platforms must be stable and level before drilling begins.
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Align the rig’s pulley groove, drill pipe chuck, and pile hole center vertically to prevent excessive movement.
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Conduct pre-drilling surveys near old structures and use impact drilling if obstructions are found.
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Regularly inspect and replace bent drill pipes.
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Use controlled impact drilling with secondary hole formation to ensure verticality.
Corrective Actions
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Use impact drilling to break through boulders.
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If deviation exceeds limits, backfill with clay and re-drill after compaction.
2. How to Handle Hole Shrinkage During Drilling?
Quality Issues and Phenomena
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The hole diameter narrows at certain sections, preventing inspection tools from reaching the bottom.
Causes
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Weak soil layers compress inward under pressure.
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Plastic soil layers expand when exposed to water.
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Worn drill bits are not repaired in time.
Preventive Measures
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Frequently ream holes when drilling through weak or plastic soil layers.
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Regularly inspect and repair worn drill bits to maintain the required diameter.
Corrective Actions
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Ream the hole repeatedly until the design diameter is achieved.
3. How to Deal with Hole Collapse During Drilling?
Quality Issues and Phenomena
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The borehole walls collapse during or after drilling.
Causes
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Insufficiently dense slurry, leaks in the casing, or inadequate slurry head pressure.
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Rapid drilling in loose sand layers.
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Long pauses in drilling reduce slurry pressure.
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Equipment or vehicle vibrations near the site.
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Delayed concrete pouring after hole cleaning.
Preventive Measures
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Avoid heavy equipment near the drilling site.
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Seal the casing bottom and sides with compacted clay (50 cm thick).
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Adjust slurry density and viscosity based on soil conditions.
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Maintain continuous drilling operations.
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Ensure gentle handling of the drill bit and reinforcement cage.
Corrective Actions
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If collapse occurs, backfill and re-drill after stabilization.
4. How to Free a Stuck Drill Bit?
Quality Issues and Phenomena
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The drill bit becomes stuck and cannot rotate.
Causes
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Irregular hole shapes (e.g., “bellmouth” holes or protruding rocks).
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Sudden lowering of the drill bit or excessive slack in the cable.
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Falling debris or tools blocking the bit.
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Overly aggressive drilling after bit repair.
Preventive Measures
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Gently maneuver the bit to loosen it.
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Avoid abrupt lowering of the drill bit.
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Ensure repaired bits match the hole diameter.
Corrective Actions
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Use controlled blasting (in rock) to loosen the bit.
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Apply a vertical or lateral force to free the bit.
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Use jacks or pulley systems (ensure hole stability).
5. How to Prevent Casing Bottom Collapse?
Quality Issues and Phenomena
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The casing bottom collapses, causing the rig to tilt.
Causes
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Poor compaction around the casing.
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Casing is placed in weak soil or sand layers.
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Insufficient casing diameter.
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Water infiltration loosens backfill.
Preventive Measures
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Backfill casing bottom with at least 50 cm of clay.
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Extend casing through weak soil layers.
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Use a casing 20–40 cm larger than the drill bit diameter.
Corrective Actions
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For offshore drilling, sink the casing deeper.
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Relocate the rig, reinstall the casing, and re-drill.
6. How to Prevent Reinforcement Cage Deformation During Installation?
Quality Issues and Phenomena
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The cage twists or bends during lifting.
Causes
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Lack of temporary bracing for long cages.
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Incorrect lifting points.
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Insufficient stiffening ring spacing.
Preventive Measures
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Add stiffening rings every 2–2.5 m and reinforce lifting points.
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Minimize splicing; use temporary supports for long cages.
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Choose optimal lifting points (1–2 points based on length).
Corrective Actions
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If severely deformed, dismantle and reconstruct the cage.
7. How to Secure the Reinforcement Cage to Prevent Shifting?
Quality Issues and Phenomena
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The cage sinks or shifts after placement.
Causes
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Inadequate fixation.
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Measurement errors or collisions with the concrete tube.
Preventive Measures
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Secure the cage to wooden blocks on the casing.
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Compact backfill around the casing.
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Double-check positioning before pouring.
Corrective Actions
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Use a crane to reposition the cage before the concrete sets.
8. How to Prevent Reinforcement Cage Floating During Concrete Pouring?
Quality Issues and Phenomena
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The cage rises during concrete placement.
Causes
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Fast pouring near the cage bottom.
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The concrete tube snags the cage during lifting.
Preventive Measures
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Slow pouring near the cage; maintain 2 m clearance.
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Center the tube and prevent snagging.
Corrective Actions
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Rotate the tube to detach it; apply downward force if needed.
9. How to Avoid Concrete Segregation (Broken Piles)?
Quality Issues and Phenomena
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Mud enters the tube, causing voids or layers in the pile.
Causes
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Blocked tubes due to poor concrete mix.
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Excessive tube extraction.
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Leaky tube joints.
Preventive Measures
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Test tubes for leaks before use.
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Maintain 40–50 cm tube-to-bottom clearance.
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Use workable concrete (18–22 cm slump).
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Avoid over-deep tube embedding (2–4 m ideal).
Corrective Actions
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Vibrate or rod the tube to clear blockages.
