Construction Process Flow Chart for Pile Foundation Work

Section 1: Construction Preparation and Site Leveling

1. Site Preparation
   • Complete “Three Connections and One Leveling” (water, electricity, road access, and site leveling) before excavation.
   • Remove all obstacles such as underground cables, pipelines, and equipment foundations.
   • Ensure temporary facilities (temporary power, water, safety measures) are ready.
2. Review Documentation
   • Study construction drawings and geological data (soil and hydrogeological conditions).
3. Safety Inspection
   • Conduct thorough safety checks on cranes and other equipment before operation.
4. Site Leveling
   • Level the site according to design elevation requirements.
   • Clear all obstructions (rocks, tree roots, debris) at pile locations.
   • Backfill and compact low-lying areas.

Section 2: Survey and Positioning

• Establish control points using a total station based on coordinates provided by planning authorities.
• Verify points with the client and supervisor before proceeding with axis and pile positioning.
• Use concrete-protected control points to prevent displacement.
• Conduct initial and secondary pile position checks before and after installing guide sleeves.
• Drive a Φ12 positioning rebar as a reference for the drilling machine alignment.
• Verify elevation using a leveling instrument before construction begins.

Section 3: Guide Sleeve Installation

1. Installation Requirements
   • Center deviation ≤ 20mm, inclination ≤ 1%.
   • Made of 4–8mm steel plate, inner diameter ≥ design pile diameter + 200mm.
   • Equipped with 1–2 overflow holes.
2. Embedment Depth
   • ≥ 1.5m in clay, ≥ 2.0m in sandy soil.
   • Extend 30cm above ground level.
3. Purpose
   • Protects the hole opening, guides positioning, isolates surface water, stabilizes slurry level, prevents collapse, and secures the rebar cage.
4. Cross-Marking for Alignment
   • Set four Φ20 rebar markers in a “+” pattern outside the sleeve for alignment verification.
   • Secure markers with concrete and mark them with red paint for visibility.

Section 4: Drilling Rig Positioning

• Place the rig on stable sleepers to prevent shifting.
• Ensure the drill bit center aligns with the guide sleeve (deviation ≤ 20mm).
• Maintain slurry level ≥ 1m above groundwater (or 1.5m in fluctuating conditions).
• Impact Drilling Advantages: Effective in gravel layers, enhances hole wall stability, and improves pile bearing capacity.

Mud Pump (3PNL-12 Type)

• Critical for slurry circulation during drilling.
• Components: Pump body, impeller, seals, motor, etc.

Section 5: Impact Drilling Process

1. Initial Setup
   • Fill the guide sleeve with clay and water for slurry formation.
2. Slurry Requirements
   • Density ≤ 1.25, viscosity 18–20s, sand content ≤ 6%.
3. Rock Interface & Final Hole Inspection
   • Compare samples with geological reports.
   • Confirm the intermediate weathered tuff layer before final approval.
4. Drilling Technique
   • Start with low-impact (0.4–0.6m height), then increase to 1.5–2.0m after reaching 3–4m depth.
   • Check verticality every 1–2m; correct deviations immediately.

Section 6: Primary Slurry Cleaning

• After drilling, circulate slurry to remove sediment.
• Standards: Sand content ≤ 6%, density ≤ 1.25, sediment thickness ≤ 50mm.
• Verify the hole depth before proceeding.

Inspection Tools

• Slurry viscometer, density meter, sediment gauge.

Section 7: Rebar Cage Construction

7.1 Material Inspection

• Verify supplier certifications, test reports, and mechanical properties.
• For seismic zones:
  • Tensile-to-yield strength ratio ≥ 1.25.
  • Yield-to-standard strength ratio ≤ 1.3.

7.2 Cage Fabrication

• Segment per design, with stiffening rings every 2m.
• Welding: 10d overlap (d = rebar diameter), staggered joints.
• Use spacer blocks (≥3 per section) for concrete cover.

7.3 Installation

• Lift with a crane using dual slings to prevent deformation.
• Align carefully; weld the top support to the guide sleeve.

7.4 Quality Checks

• Length (±100mm), diameter (±10mm), spacing (±10mm main, ±20mm stirrups), verticality (≤1%).

Section 8: Secondary Slurry Cleaning

• Remove post-cage sediment via slurry replacement.
• Final Criteria: Density ≤ 1.25, sand content ≤ 6%, sediment ≤ 50mm.

Section 9: Concrete Pouring

1. Method: Tremie pipe with bottom-up displacement.
2. Initial Pour: Ensure 1.0–1.3m pipe embedment to prevent slurry intrusion.
3. Continuous Pour: Complete within 2–4 hours; no cold joints.
4. Monitoring: Maintain 2–6m pipe embedment; measure slump (160–220mm).

Section 10: Key Control Points

1. Pile position verification
2. Hole depth accuracy
3. Rock interface confirmation
4. Secondary cleaning
5. Rebar quality
6. Cage welding & placement
7. Initial concrete pour

Section 11: Common Defects & Solutions

11.1 Position Deviation

• Cause: Survey or rig misalignment.
• Fix: Double-check positioning.

11.2 Hole Inclination

• Cause: Unlevel ground or obstructions.
• Fix: Compact soil; clear blockages.

11.3 Necking

• Cause: Collapse or fast pipe extraction.
• Fix: Optimize slurry; control pipe speed.

11.4 Collapse

• Cause: Weak slurry or high water pressure.
• Fix: Use denser slurry; extend sleeves.

11.5 Excess Sediment

• Cause: Soil fall-in or delayed pouring.
• Fix: Clean promptly; pour quickly.

11.6 Cage Float

• Cause: Upward concrete pressure.
• Fix: Secure cage; slow initial pour.

11.7 Pipe Leak

• Cause: Insufficient concrete or broken seals.
• Fix: Ream and repour; check joints.

11.8 Blockage

• Cause: Poor mix or machine failure.
• Fix: Vibrate pipe; use backups.

11.9 Buried Pipe

• Cause: Excessive embedment.
• Fix: Limit to 6–8m; vibrate gently.

11.10 Broken Pile

• Cause: Slurry intrusion or bad concrete.
• Fix: Ensure continuous pour; test mix.

Section 12: Pile Testing

• Methods: Low-strain integrity test, static load test (per JGJ 106-2003).
• Scope: 100% integrity check; ≥1% load tests (min. 3 piles).