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Methods to Prevent Hole Collapse in Rotary Drilling Rig Construction

Abstract

During the construction of cast-in-place piles using rotary drilling rigs, hole collapse poses the most significant challenge in the boring process. Through technical research and engineering practice, two effective methods have been developed to mitigate collapse: the manual concrete lining method and the concrete backfill lining method.

Introduction

With the rapid development of infrastructure, particularly in urban construction, high-rise and super high-rise buildings increasingly rely on pile foundations. Rotary drilling rigs are widely favored for their safety, environmental friendliness, speed, and efficiency in constructing cast-in-place piles. However, the adoption of new equipment and technology often requires continuous improvement. One major challenge encountered is hole collapse, which significantly hinders the boring process. Through extensive research and field application, the manual concrete lining method and concrete backfill lining method have emerged as the most effective solutions to prevent collapse.

1. Applicability

These methods are specifically designed to address severe hole collapse caused by gravel, quicksand, and water inflow during rotary drilling. Compared to traditional solutions such as slurry wall protection, clay backfilling, and pre-grouting, these techniques offer higher precision and feasibility.

2. Technical Principles

The core principle involves reinforcing the collapsed section using concrete to form a stable lining:

  • Shallow collapse: Manual excavation followed by concrete lining before rotary drilling resumes.

  • Deep collapse: Immediate low-grade concrete backfilling (C15), allowing 48 hours for curing before resuming drilling.

2.1 Manual Concrete Lining Method

Based on geotechnical reports and prior borehole data, if collapse occurs in shallow sections:

  1. Manual excavation proceeds to the collapse base.

  2. Concrete lining is applied in stages to stabilize the walls.

  3. Once cured, rotary drilling continues to the target depth.

2.2 Concrete Backfill Lining Method

For mid-depth or deep collapses:

  1. Drilling pauses at the collapse zone.

  2. Lightly collapsed debris is cleared, and C15 concrete is poured underwater to fill the void.

  3. After 48 hours, drilling resumes—the hardened concrete acts as a permanent lining.

  4. Severe collapses may require layered concrete filling and phased drilling until stability is achieved.

3. Construction Process & Key Steps

3.1 Construction Workflow

3.1.1 Manual Concrete Lining Method

  • Stakeout & elevation marking →

  • First-stage excavation →

  • Formwork setup & initial concrete pour →

  • Recheck alignment & install support systems →

  • Repeat excavation-lining cycles until the collapse zone is secured →

  • Rotary drilling to final depth.

3.1.2 Concrete Backfill Lining Method

  • Rig positioning →

  • Drilling to collapse depth →

  • Steel casing installation →

  • C15 concrete pouring via tremie pipe →

  • Resumed drilling post-curing.

3.2 Critical Execution Points

3.2.1 Manual Lining

  • Safety: Ensure 36V low-voltage lighting, secure covers, and strict no-overhead-load rules.

  • Efficiency: Excavated soil must be hauled ≥2m from the pit; vehicles keep ≥3m clearance.

3.2.2 Concrete Backfill

  • Precision: Rig must be level; casing centered within 50mm tolerance.

  • Stability: Use “low pressure, slow drilling” near water tables to prevent turbulence-induced collapse.

  • Concrete specs: C15 mix with 160–190mm slump, poured continuously to the collapse rim (or waterline if submerged).

4. Quality Control

4.1 Curing Duration & Lining Integrity

  • Manual lining: Fast-setting sulfoaluminate cement (12h minimum cure before formwork removal).

  • Backfill lining: 48h natural curing for C15 concrete before drilling.

4.2 Preventing Deviation

  • Causes: Obstructions (boulders/hard strata), rig instability.

  • Solutions: Reinforce rig base; use rigid-mast drills; reduce speed in heterogeneous layers.

4.3 Inspection Methods

  • Alignment: Calipers.

  • Depth: Sounding line.

  • Verticality: Borehole scanner.

  • Slurry: Density meter, sand content gauge.

  • Post-construction: Ultrasonic integrity testing.

5. Safety Protocols

  1. Mandatory PPE (helmets, non-slip boots, gloves).

  2. No unattended operations during drilling.

  3. Hazard zones are marked with barriers.

  4. Electrical safety: Licensed personnel only; buried/raised cables.

  5. Post-drilling: Cover all openings; backfill unused holes.

6. Environmental Benefits

  • Noise: <65 dB (low-vibration operation).

  • Waste reduction: Minimal slurry vs. traditional methods.

  • Soil management: On-site dewatering for waterlogged spoil enables eco-friendly transport.

7. Conclusion

These collapse-prevention techniques enhance speed, success rate, and adaptability while reducing mud waste and noise pollution. By overcoming key limitations of rotary drilling—collapse risks, slurry disposal, and delays—they deliver superior quality with minimal environmental impact.

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