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Comprehensive Guide to Preventing and Handling Quality Accidents in Bored Pile Construction

Introduction

In bored pile construction, attention to detail determines success. Adequate preparation and effective construction measures are essential to prevent quality accidents and minimize potential risks. This guide provides detailed preventive measures and emergency response plans for various quality issues during bored pile construction.

1. Preventive Measures for Quality Accidents

1.1 Construction Preparation

  • Casing Length Selection:

    • Use different casing lengths based on geology, but do not exceed 7 meters to avoid difficulty in extraction after concrete pouring.

    • For underwater piles, ensure the casing penetrates the silt layer. If the silt layer is too thick, consider leaving the casing in place.

  • Conduit Water Tightness Test:

    • Conduct a water-tightness test before each use. Replace damaged seals or leaking/bent pipe sections immediately.

  • Drill Bit Diameter:

    • Use a drill bit 2-3 cm smaller than the pile diameter. Inspect before drilling—do not proceed if the size is incorrect.

  • Equipment Inspection:

    • Check welding machines, slurry pumps, and measuring ropes for proper function.

    • Ensure sufficient bentonite reserves to avoid delays.

  • Hole Positioning:

    • Verify alignment using a cross-line method before drilling to prevent excessive deviation.

    • After measuring casing elevation, technicians must double-check and confirm drilling depth and reinforcement bar lengths.

1.2 Drilling Process

  • First Pile in Each Pier:

    • Collect drilling cuttings every 2 meters for inspection.

    • In unstable strata (e.g., silt, quicksand), increase rotation speed, slow feed rate, and reinforce the hole wall with clay blocks.

  • Loose Sand Layer:

    • Increase slurry density (≥1.1) to stabilize the hole.

    • If sand content suddenly rises, check for hole collapse.

  • Soft Clay Layer:

    • If drilling becomes too easy, inspect cuttings. If soft clay is detected, slow feed rate, sweep the hole, and reinforce with clay blocks.

  • Slurry Level Control:

    • Maintain slurry level 0.5 m below casing top and 1.5 m above groundwater level.

    • Limit simultaneous drilling to two piles per site to control progress.

1.3 Reinforcement Cage Installation

  • Top Reinforcement Ring:

    • Weld securely to prevent cracking during lifting.

  • Lifting Bars:

    • For Φ150 cm piles, use Φ16 mm or thicker bars—never Φ10 mm coiled bars.

    • Inspect all welds to ensure load-bearing capacity.

  • Bearing Beams:

    • Use sturdy beams (reinforce with channel steel if necessary).

  • Ultrasonic Testing Tubes:

    • Inspect bottom seals and welds. Only bind (do not weld) to reinforcement rings.

1.4 Underwater Concrete Pouring

  • Conduit Handling:

    • Keep the conduit centered to avoid snagging the cage.

    • Monitor the concrete surface level and conduit depth to prevent pipe lifting errors.

  • Concrete Quality Control:

    • Install a 10×10 cm grid on the funnel to block debris.

    • Check slump and consistency—stop pouring if segregation or excessive dryness occurs.

  • Supply Coordination:

    • Submit concrete supply plans one day in advance.

    • Assign a coordinator to confirm the batching schedules.

  • Pouring Interruptions:

    • If delays exceed 30 minutes, reduce conduit depth to 2 m and move the conduit slightly every 5 minutes to prevent clogging.

2. Emergency Response Plans for Bored Pile Accidents

2.1 Hole Collapse

  • Cause: Common in silt and quicksand layers.

  • Solution:

    • Increase slurry density (1.2-1.4).

    • If severe, backfill with clay blocks and redrill.

2.2 Hole Shrinkage

  • Cause: Common in soft/hard clay layers.

  • Solution:

    • Sweep the hole repeatedly to correct the deviation.

    • For severe cases, backfill with a clay and stone mix before redrilling.

2.3 Drill Bit Burial/Sticking

  • Solution:

    • Maintain slurry pressure to stabilize the hole.

    • Use high-power pumps to remove sediment before slow extraction.

2.4 Drill Bit Drop

  • Solution:

    • Maintain slurry level and density (1.15-1.3).

    • Use an L-shaped hook to retrieve the bit.

2.5 Casing Sinking

  • Solution:

    • If early stage: Backfill and reset casing.

    • If near completion: Increase slurry density, support casing with timber and beams, and minimize cleaning time.

2.6 Reinforcement Cage Drop

  • Solution:

    • Increase slurry density (1.15-1.4).

    • If before pouring, retrieve with double hooks.

    • If, after partial pouring,you  replace the cage within 2 hours.

2.7 Reinforcement Cage Floating

  • Solution:

    • Stop pouring, adjust conduit depth, and reduce discharge speed.

2.8 Initial Pouring Failure

  • Solution:

    • Use a high-power pump to remove concrete before re-pouring.

2.9 Conduit Clogging

  • Solution:

    • Use a steel rod (Φ12-14 mm) to clear the blockage manually.

2.10 Cage Snagging

  • Solution:

    • Lower and rotate the conduit to reposition before lifting.

2.11 Difficulty Pouring Near Pile Top

  • Solution:

    • Use a large hopper to increase head pressure and reduce conduit depth.

2.12 Broken Pile

  • Shallow Break (<10 m):

    • Excavate, clean, and cast new concrete with a wooden mold.

  • Deep Break:

    • Backfill, use an impact drill to crush the pile, and reconstruct.

Conclusion

By implementing these preventive measures and emergency protocols, construction teams can significantly reduce quality accidents and ensure efficient, safe bored pile construction. Proper planning, real-time monitoring, and quick response are key to avoiding costly delays and defects.

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