Rotary Drilling Cast-in-Place Pile Construction: Process and Technical Specifications

1. Construction Characteristics of Rotary Drilling Cast-in-Place Piles

(1) High Automation, Fast Drilling Speed, and Superior Quality

The rotary drilling rig is fully hydraulically driven and computer-controlled, enabling precise positioning, automatic correction of drilling verticality, and automatic depth measurement, ensuring maximum drilling quality. Its efficiency is 20 times higher than conventional circulation drills, guaranteeing both project quality and progress.

(2) Telescopic Drill Pipe Enhances Efficiency

The telescopic drill rod not only transmits torque and axial pressure to the drill bit but also enables rapid lifting and lowering of the drill head for quick soil discharge, reducing auxiliary operation time and improving drilling efficiency.

(3) Environmentally Friendly Construction

Rotary drilling rigs extract soil via the drill head and discharge it outside the hole using a Kelly telescopic rod. The slurry is used only for wall protection, not for slag removal, meaning the slurry volume equals the hole volume. After sedimentation and desanding, the slurry can be reused multiple times. This significantly reduces urban construction sewage discharge costs and improves site cleanliness.

(4) Strong Adaptability to Various Ground Conditions

The crawler chassis provides low ground pressure, making it suitable for diverse working conditions. The rig moves flexibly on-site, ensuring accurate pile positioning. It is compatible with silty clay, clay, sand, pebble layers, and other strata. The spiral grooves formed on the hole wall enhance pile friction resistance.

(5) Convenient Construction Layout

The process facilitates reinforcement cage placement and concrete pouring. The rig’s self-contained diesel engine eliminates reliance on external power, reducing safety risks from power cables.

2. Construction Principles of Rotary Drilling Piles

The static slurry wall protection with bucket soil extraction method distinguishes rotary drilling from other pile foundations. The process involves:

• The rig rotates in place while the drill rod and bit cut into the soil under gravity.

• For hard soil layers, hydraulic pressure is applied to force the bit into the ground.

• Once the bucket is full, it is lifted, and the soil is discharged automatically.

• The rig relocates quickly after hole completion.

3. Construction Process

4. Measurement and Layout of Pile Position & Elevation

• Use a total station to mark pile coordinates based on design drawings.

• Verify positions with wooden stakes and iron nails before excavation.

• Ensure all measuring instruments (total station, level, steel tape) are calibrated.

• Conduct measurement checks using coordinate control points.

• Mark pile centers with rebar and outline pile diameters with lime.

5. Wet Process Hole Formation (For High Water Table Conditions)

(1) Site Preparation

• Level the ground, remove debris, and reinforce soft soil areas to prevent uneven settlement.

• Construct slurry and sedimentation ponds with safety barriers.

(2) Pile Positioning

• Use a total station to mark pile centers accurately before drilling.

(3) Slurry Preparation

• Mix high-quality clay, water, and bentonite to achieve:

  • Sand content ≤ 4%

  • Colloid rate ≥ 96%

  • Slurry density ≥ 1.2

(4) Casing Installation

• Install a 1.5 m-high steel casing (20cm wider than the pile diameter).

• Ensure verticality deviation ≤ 1% and center deviation ≤ 5cm.

(5) Drilling Process

• Start drilling at low pressure near the casing.

• Maintain slurry levels to prevent wall collapse.

• Use barrel-type drill bits for soil extraction.

(6) Hole Cleaning

• After reaching design depth, clean the hole using slurry replacement.

• Ensure sediment thickness ≤ 100mm before reinforcement cage placement.

6. Hole Inspection

• Verify hole depth and bearing layer with supervision approval.

• Conduct two-stage inspections:

  1. Check bearing layer thickness.

  2. Final depth confirmation before concreting.

7. Reinforcement Cage Fabrication & Installation

• Use welded longitudinal bars (14–25mm diameter) and spiral stirrups.

• Split long cages into sections (15–40m) for easier handling.

• Lift and align sections using two 35-ton cranes.

• Install grouting pipes (Φ57mm) and ultrasonic testing tubes as specified.

8. Underwater Concrete Pouring

• Ensure continuous pouring to prevent segregation.

• Maintain 3–6m (avoid over-pulling).

• Overpour 0.5×pile diameter above design height for later trimming.

9. Pile Testing & Inspection

• Conduct ultrasonic testing (≥30% of piles) and static load tests (≥1%, min. 3 piles).

• Test only after concrete reaches 70% design strength (≥15MPa).

10. Common Issues & Solutions

Grouting Reinforcement Method:

1. Drill inspection holes to identify weak zones.

2. Flush with high-pressure water (0.5–0.7MPa).

3. Inject cement slurry (0.4–0.8 ) in stages.