| Defect | Likely Cause | GEOSS Recommended Action | | :--- | :--- | :--- | | Sudden drop in jacking force (≥20%) | Pile fracture or soft pocket | Stop, extract if possible, install replacement pile. | | Refusal above design depth (≥1 m) | Boulder / old timber pile | Use pre-boring (300 mm dia.) to 500 mm below refusal depth, then re-jack. | | Excessive heave (>25 mm) | Rapid jacking in clay | Restrike all piles within heave zone after 7 days. | | Verticality drift > 1:100 | Inclined bedrock or poor jig | Install raking micro-piles as supplement. |
Accurate, real-time logging of jacking pressure, pile depth, and time is crucial for QC. Summary of GEOSS Best Practices Action Area Good Practice Principle Site Prep Conduct probe holes at all pile locations to map cavities. Handling Never force alignment during jacking. Installation Maintain constant verticality checks. Sequence Jack in an inside-out sequence for groups. Pressure Use 2–2.5 times WL and re-apply load at refusal. | Defect | Likely Cause | GEOSS Recommended
[ Hydraulic Jacking Rig ] │ ▼ (Static Compression Force) [ Prefabricated Pile Segment ] │ ▼ ┌─────────────────────┐ │ Soft Clay Layer │ ◄── Smooth Penetration ├─────────────────────┤ │ Residual Soil / │ ◄── Increased Resistance │ Bedrock Layer │ (Target Stratum) └─────────────────────┘ Key Components of a Jacked Piling System | | Verticality drift > 1:100 | Inclined
A pile is generally considered "set" if the downward movement does not exceed 5mm to 10mm while holding the force for at least 30 seconds . Handling Never force alignment during jacking
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: Engineers must review deep borehole logs to identify soil stratigraphy, groundwater levels, and the depth of the founding stratum (such as the Kallang Formation or Old Alluvium).