Below is the recommended step-by-step procedure for installing a jacked precast concrete spun pile (typical 350 mm dia, 15 m length) in Singapore’s east coast marine clay over Old Alluvium.
Maintain a daily piling record including:
GEOSS documents a series of "lessons learned" from local failures and near-misses in jacked piling. GEOSS Good Practice 8
| Problem | Typical Cause | GEOSS Good Practice | |---------|---------------|----------------------| | Pile head crushing | Uneven load distribution / misaligned cap | Use steel distribution plate (min 25 mm thick) and plastic cushion. | | Buckling during jacking | Weak pile section or lateral soil movement | Limit free length above ground to < 3 m; use lateral guides. | | Ground heave (adjacent piles lift) | Installation in sensitive clay without sequence control | Install in sequence away from existing piles; adopt “temporary rest period” of 4 hours between adjacent piles. | | Refusal above design depth | Hard lens (e.g., ferricrete layer) | Stop jacking if force jumps > 300 kN over 10 mm. Perform pilot pre-boring (≤ 80% pile diameter) after geotechnical approval. | | Hydraulic oil leakage | Overpressure during set achievement | Install pressure relief valve set at 110% of rig’s rated capacity. |
GEOSS Good Practice 8.1 – Submit the following to QP (Geotech) before backfilling: extract if possible
5.1 Mandatory Records (per pile)
5.2 Heave & Lateral Displacement
5.3 Integrity Testing
| 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. | 5.2 Heave & Lateral Displacement