1. Scope of Application
This guide applies to the construction of cement deep mixing piles (CDM) for soft soil ground improvement, ensuring stability and load-bearing capacity.
2. Pre-Construction Preparation
2.1 Site Preparation
- Ensure “Three Supplies and One Leveling” (water, electricity, road access, and leveled ground).
- Clear the site of debris, underground obstacles, and construction waste.
- For low-lying areas, ponds, or marshes, drain water, remove silt, and backfill with compacted clay soil (avoid using mixed waste or garbage).
2.2 Technical & Survey Preparation
- Review design documents and technical specifications.
- Conduct a survey and stakeout with ≤ 20mm deviation tolerance.
- Organize a technical briefing for the construction team.
2.3 Equipment Setup
- Deploy cement mixing pile machines and conduct pre-operation checks.
- Ensure smooth operation of drilling and grout pumping systems.
3. Technical Requirements
3.1 Trial Pile Testing
- Perform test piles in representative areas to verify:
- Soil conditions
- Equipment suitability
- Optimal parameters (drilling speed, rotation speed, pressure, current)
- Confirm pile strength meets design requirements before full-scale construction.
3.2 Pile Specifications
- Ensure pile diameter, length, and spacing comply with design standards.
4. Construction Process & Workflow
4.1 Construction Sequence
- Ground leveling
- Survey & marking
- Drilling machine positioning
- Drilling & grout injection
- Lifting & mixing
- Re-mixing (if required)
- Pile completion & machine relocation
4.2 Workflow Diagram
(Refer to Figure 1 for the detailed cement mixing pile construction process.)
5. Construction Requirements
5.1 Construction Methodology
5.1.1 Pre-Construction Preparation
- Select cement & additives based on lab-tested mix designs.
- Determine water-cement ratio, admixture dosage, and grout fluidity.
- Mark pile locations with numbered stakes (≤ 50mm deviation tolerance).
- Calibrate drilling depth using reference scales on the machine.
5.1.2 Pile Construction Process
- Drilling:
- Maintain vertical alignment (≤ 1.5% deviation).
- Control sinking speed (0.5–0.6 m/min) with current ≤ 70A.
- Avoid water injection unless necessary for hard soil layers.
- Grout Mixing & Injection:
- Prepare fresh cement slurry (sieve-filtered, no sedimentation).
- Pump grout within 50m distance to prevent clogging.
- Lifting & Mixing:
- Maintain a consistent lifting speed for uniform mixing.
- For interrupted operations, re-drill 0.5m below the stoppage point before resuming.
- Final Quality Check:
- Record grout volume, mixing time, and depth accuracy.
5.1.3 Quality Control Measures
- Monitor grout density to prevent segregation.
- Check pipe connections for leaks.
- Clean equipment daily to avoid clogging.
- For delays >3 hours, dismantle & clean pipelines before restarting.
- Overlap adjacent piles by ≥50cm for continuity.
6. Workforce Organization
| Role | Quantity |
|---|---|
| Site Supervisor | 1 |
| Technical Engineer | 1 |
| Safety/QC/Survey Team | 5–6 |
| Machine Operators & Laborers | 5–6 |
7. Material Requirements
- Cement: Use fresh Portland cement (no clumping or moisture).
- Water: Comply with JGJ63 Concrete Mixing Water Standards.
8. Equipment List
| Equipment | Model | Qty |
|---|---|---|
| Pile Machine | SJB-II | 1 |
| Grout Pump | UB-3 | 1 |
| Mixing Machine | Vertical Type | 1 |
9. Quality Control & Testing
9.1 Key Standards
- Pile positioning error ≤50mm, verticality ≤ 1.5%.
- Grout must be continuous (no sedimentation).
- Base grouting: Hold for 30 sec at the pile bottom.
- Overlap adjacent piles by ≥20cm (within 24 hours).
9.2 Testing Methods
- 7-day strength check: Light penetration test or core sampling.
- 28-day load test: For bearing capacity verification.
10. Safety & Environmental Compliance
10.1 Safety Measures
- Hard hats & harnesses mandatory.
- Electrical safety: Use grounded, insulated wiring.
- Railway proximity work: Maintain 2m clearance from tracks.
10.2 Environmental Protection
- Prevent cement spillage into water bodies.
- Proper waste disposal (no on-site dumping).
- Minimize noise & dust pollution.
Conclusion
This cement deep mixing pile (CDM) construction guide ensures high-quality soft soil stabilization while adhering to safety, efficiency, and environmental standards. Proper execution guarantees long-term structural integrity and compliance with international construction best practices.
