The Geotechnical Society of Singapore (GeoSS) provides specific guidelines for the installation of jacked foundation piles to manage ground displacement and protect adjacent structures, which is critical in Singapore's dense urban environment. Key Good Practice Guidelines (GeoSS)
According to the GeoSS draft guidelines, several proactive measures should be implemented to mitigate the adverse impacts of ground movement:
Relief Wells: Install bored holes (typically 400mm to 600mm in diameter) at strategic locations, such as boundaries near neighboring services or structures, to provide a path for displaced soil.
Pre-boring: Use pre-boring at the pile point to reduce the force required for installation and minimize soil displacement.
Machine Management: When using multiple jacking machines, avoid clustering them close together to prevent cumulative ground movements.
Platform Quality: Ensure the working platform is of high quality, specifically regarding compaction and site drainage, as jacked machines can be extremely heavy.
Monitoring Programs: Implement rigorous monitoring of ground and building movement throughout the piling process.
Trial Installations: Conduct a trial on the first pile installation to observe ground performance before proceeding with full-scale work.
Recording Data: Maintain records of the jacking force at every 0.5m to 1.0m of penetration to verify performance against design assumptions. Relevant Reports and Regulatory Documents
For more detailed technical requirements, you can refer to these official resources:
Good Practice for Installation of Jacked Foundation Piles (BCA): A key guideline published on October 8, 2015, which aligns with industry best practices.
GeoSS Guideline on Jacked Piles (Draft): A comprehensive technical draft covering ground movement control and protective measures.
Performance-Based Pile Design Guidelines: A joint circular from BCA, IES, ACES, and GeoSS (2022) regarding ultimate load testing and design verification.
Requirements and Guidelines on Driven or Jacked Piles: The Building and Construction Authority (BCA) updated these requirements as of September 1, 2022. Guidelines for ST Plan Applications
Geotechnical Society of Singapore (GeoSS) Building and Construction Authority (BCA)
provide guidelines for the installation of jacked foundation piles to ensure structural safety and minimize environmental impact Course Hero
. Jacked piling is preferred in urban areas due to its vibration-free, low-noise, and air-pollution-free nature Course Hero Core Installation Requirements According to the GeoSS Guideline on Jacked Piles , installation must adhere to these key practices: Jacking Capacity Reduce jacking rate to 10 mm/s when within
: It is recommended that jacking machines operate at approximately 75% of their maximum capacity
to maintain machine health and ensure successful installation Course Hero Installation Sequence
: For large pile groups, the recommended sequence is from the inside out
or in a specific direction (e.g., left to right) to manage soil displacement and prevent heave Course Hero Alignment and Verticality
: Piles must be checked for verticality throughout the process. Crucially, their alignment should never be adjusted by force during installation Course Hero : Piles are typically joined by several sections together as penetration progresses Final Settlement and "Set" Criteria
The "set" of a jacked pile is verified through a rigorous re-jacking process to confirm stability Course Hero The pile is jacked to a force ( cap P sub j ) usually between 2.0 to 2.5 times the Working Load (WL) until practical refusal Course Hero
The pressure is released to zero and immediately re-applied.
The pile is considered "set" if the downward movement during re-jacking does not exceed with a minimum holding time of 30 seconds Course Hero Engineers typically recommend achieving two consistent sets for final acceptance Course Hero Risk Mitigation and Monitoring
To manage challenges unique to displacement piles in Singapore's diverse soil, the following measures are recommended: Soil Displacement Controls : In sensitive areas, use relief wells pre-boring
at the pile point to reduce ground movement and prevent damage to adjacent structures Course Hero Negative Skin Friction
: If piles penetrate consolidating soft soil, designers must account for long-term downdrag forces
(negative skin friction) by adjusting the required jacking load ( cap P sub j ) during installation Heave Monitoring
: Pile heave must be proactively monitored. If piles heave due to the installation of adjacent piles, their capacity may be compromised, requiring redriving or additional testing BCA Academy Site Stability
: Given the extreme weight of jacking machines (some exceeding 800 tonnes), the working platform must be high-quality, well-compacted, and have excellent site drainage Course Hero Quality Control and Testing All piling works must comply with Eurocode 7 standards and Singapore's national annexes Integrity Testing
: Necessary tests (e.g., PDA, PIT, or sonic logging) must be carried out to verify the structural integrity of the piles Singapore Accreditation Council Permissible Tolerances
: Standard practice allows for an individual pile deviation of up to from its true position Building and Construction Authority Load Testing a) Jacking Force vs
The Geotechnical Society of Singapore (GeoSS) published a foundational guideline titled "Good Practice for Installation of Jacked Foundation Piles in Singapore" (October 2015) to standardize the use of this eco-friendly piling method.
The following technical paper outlines the core principles and "good practice" standards derived from GeoSS recommendations and local industry standards.
Technical Paper: Good Practice for Jacked Pile Installation in Singapore 1. Introduction
Jacked piling has over 20 years of history in Singapore, evolving from small-scale underpinning to supporting high-rise structures. It is favored for being vibration-free, air pollution-free, and generating low noise levels, making it ideal for urban infill sites. Modern jacking machines in the local market now reach capacities of up to 800 tonnes. 2. Machine Capacity and Operational Limits
Safety Margin: GeoSS recommends that jacking machines be operated at approximately 75% of their maximum rated capacity to ensure stability and mechanical longevity.
Machine Requirements: Specialist builders must maintain a regular maintenance regime and provide daily, monthly, and yearly checklists to ensure equipment reliability. 3. Installation and Termination Criteria
The termination of a jacked pile is not solely based on depth but on a rigorous "set" verification process: Jacking Force ( Pjcap P sub j
): The pile is typically jacked in steps until the force reaches 2.0 to 2.5 times the Working Load (WL).
"Set" Definition: After reaching the target force, the pressure is released and reapplied without pause.
Criterion: The downward movement between the initial jack and the re-jack must not exceed 10 mm with a minimum holding time of 30 seconds.
Consistency: GeoSS recommends achieving two consistent sets before final termination. 4. Ground Monitoring and Mitigation
As jacked piles are displacement piles, they can cause significant lateral soil movement and heaving, especially in soft clay or dense sand.
Monitoring: Continuous monitoring of ground movement and adjacent structures is mandatory to prevent damage.
Protective Measures: If displacement risks are high, engineers may utilize relief wells or pre-boring to mitigate excessive soil pressure.
Heave Control: In formations like Bukit Timah Granite, recorded heaves of 10 mm to 60 mm have occurred, requiring verification through additional working load tests. 5. Design and Compliance
Standards: Designs must comply with Eurocode 7 (EC7) and the National Annex, which superseded SS CP4 in April 2015. specifically regarding compaction and site drainage
Settlement Limits: Standard acceptance criteria typically limit pile head settlement to 15 mm at 1.5x WL and 25 mm at 2.0x WL. 6. Conclusion
Following GeoSS good practices ensures that jacked piles provide superior verticality and stability while minimizing the environmental impact on Singapore's dense urban landscape. Successful installation relies on matching machine capacity to site conditions and strictly adhering to multi-cycle termination criteria.
The Geotechnical Society of Singapore (GeoSS) provides guidelines for the installation of jacked piles, emphasizing that it is a "friendly method" due to being vibration-free, air pollution-free, and low-noise. This method is particularly suitable for congested urban environments in Singapore, like high-density condominium developments. Core Installation Guidelines
Machine Capacity: It is recommended that the jacking machine be used at approximately 75% of its maximum capacity. In Singapore, machines with capacities up to 800 tonnes are available.
Platform Preparation: Because jacking machines are heavy, the working platform must be of high quality, with rigorous compaction and proper site drainage to ensure stability.
Ground Movement Control: To protect sensitive adjacent structures, GeoSS recommends:
Installing relief wells at strategic locations (e.g., at boundaries near neighboring structures). Pre-boring at the pile point.
Constructing an opened trench or temporary earth retaining walls if necessary.
Continuous Monitoring: During the first pile installation, a trial should be conducted to observe performance. Ongoing monitoring of both ground and building movement is required throughout the piling works. Termination and Technical Standards
Termination Criteria: Designers typically specify required pile penetration depth based on site investigation (SI) boreholes. The method allows for a form of load testing on every pile by recording the jacked force at every 0.5m to 1.0m of penetration.
Verticality and Precision: Jacked piling is noted for its superior verticality compared to other driven methods.
Maintenance: Piling machines must undergo a regular maintenance regime by a dedicated team, with daily, monthly, and yearly checklists to ensure equipment is always in good condition. Compliance and Regulatory Framework
Codes of Practice: The design and installation of piles in Singapore are governed by the Singapore Standard Code of Practice for Foundations (SS CP 4) and Eurocode 7 (EC7).
Qualified Person (QP) Submission: Upon completion of piling works, the QP must submit as-built piling plans and certificates of supervision within 28 days to regulatory bodies.
Specialist Builder Requirements: For high-capacity projects, Specialist Builders (categories G2 and G3) must maintain a minimum number of jacked rigs with specific counterweight requirements (e.g., 200-ton and 400-ton minimums). AI responses may include mistakes. Learn more
Before delving into "good practice," it is essential to understand why jacked piles have become the default choice for many medium- to high-rise developments on the island.
GEOSS documents a series of "lessons learned" from local failures and near-misses in jacked piling.
| 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. |