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
Mastering the Press: Good Practices for Jacked Piling in Singapore
Jacked-in (or jacked) piles have become a staple in Singapore’s urban construction landscape, favored for their low noise and vibration compared to traditional driven piles. However, the efficiency of this method depends heavily on following rigorous installation standards.
Drawing from the Geotechnical Society of Singapore (GeoSS) Guideline on Jacked Piles, this post outlines the essential "good practices" for successful installation. 1. Rigorous Termination (Set) Criteria
One of the most critical phases is determining when a pile has reached its required capacity. According to GeoSS standards, the "set" process in Singapore typically follows these steps: Jacking Force ( Pjcap P sub j
): The pile is jacked into the ground with a force adjusted in steps, usually reaching a value of 2.0 to 2.5 times the Working Load (WL).
The "Set" Measurement: Once practical refusal is reached, the force is released to zero and immediately reapplied. The downward movement between the original jack and this "re-jack" is the first set. Verticality: The pile must be held rigid and
Acceptance Limit: 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.
Consistency: It is a recommended practice to achieve two consistent sets before termination. 2. Operational Good Practices
To maintain structural integrity and site safety, the GeoSS guidelines highlight several operational mandates:
No Forced Alignment: Never adjust a pile’s alignment by force once installation has begun.
Strategic Sequencing: For large pile groups, install from the inside out to manage soil displacement and prevent "heave" (upward movement) of previously installed piles.
Machine Distribution: When multiple jacking machines are on-site, avoid clustering them too closely to minimize excessive ground movement.
Working Platform Quality: Because jack-in machines are exceptionally heavy, the working platform must be high-quality, emphasizing proper compaction and site drainage. 3. Addressing Local Geological Challenges
Singapore's diverse geology, such as the Jurong Formation or Bukit Timah Granite, presents unique hurdles:
Varying Pile Lengths: Folded rock profiles can lead to drastically different pile lengths within a single pile cap. Designers must be vigilant and may require probe holes at every pile location in erratic areas like limestone.
Pre-boring Requirements: In thick layers of soft ground, jacked piles (being displacement piles) can cause lateral soil movement. In such cases, pre-boring or relief holes may be necessary to protect adjacent structures. 4. Regulatory Compliance & Quality Control
All piling works must align with the Building and Construction Authority (BCA) regulations and Singapore Standards (SS CP4):
Integrity Testing: Specialist builders must perform Sonic Logging or PDA/PIT tests to detect hidden underground defects.
Calibration: Both load gauges and pressure gauges on the jacking rig must be calibrated to ensure accurate force application.
Safety First: Per Ministry of Manpower (MOM) guidelines, pile testing must be supervised by a "designated person" with strict exclusion zones during loading cycles.
By adhering to these GeoSS recommended practices, contractors can ensure that jacked piling remains a high-performance, low-impact solution for Singapore's densifying urban environment.
The Geotechnical Society of Singapore (GeoSS) has established comprehensive good practices for the installation of jacked foundation piles, a method favored in Singapore’s urban environment for being vibration-free and low-noise Course Hero Overview of Jacked Piling in Singapore
Jacked piling utilizes a hydraulic jacking system to press pre-formed piles (such as prestressed concrete spun piles or RC piles) into the ground using a dead weight (kentledge) for reaction. While the market now supports machines with capacities up to 800 tonnes, GeoSS recommends operating these machines at no more than 75% of their maximum capacity to maintain safety and efficiency. Course Hero Installation and Termination Criteria
A critical aspect of GeoSS practice is the standardisation of pile termination to ensure geotechnical capacity: Jacking Force: The required jacking force ( cap P sub j 15) | Maintain constant jacking force
) is typically related to the ultimate geotechnical capacity ( cap P sub u ), often set at 2.0 to 2.5 times the working load (WL) Set Criterion:
A pile is generally considered "set" if the downward movement does not exceed over a holding time of at least 30 seconds Re-jacking Procedure:
The jacking force should be released to zero and re-applied without pause. GeoSS recommends obtaining two consistent "sets" to verify stability. Slenderness Ratio:
Research suggests that for piles where the depth is less than 37 times the diameter, the ultimate capacity ( cap P sub u ) may be less than the jacking force ( cap P sub j isomer-user-content.by.gov.sg Protective Measures for Adjacent Structures
Because jacked piling involves significant soil displacement, GeoSS emphasizes measures to protect nearby buildings, especially in dense residential areas: Relief Wells:
Installing 400 mm to 600 mm diameter bored holes (often using perforated steel pipes) at strategic boundaries to reduce ground movement. Pre-boring:
Pre-drilling at the pile point to a specified depth (e.g., above sensitive utility lines) to minimize displacement. The hole diameter should be slightly smaller than the pile to maintain shaft resistance. Machine Management:
When multiple machines are on-site, they should not be clustered closely together, as this aggregates ground movement risks. Open Trenches:
Using temporary open trenches or earth-retaining walls to contain ground movement within the project boundary. isomer-user-content.by.gov.sg Operational Good Practices Platform Preparation:
Given the massive weight of jacking machines, the working platform must be high-quality, with strict requirements for compaction and site drainage. Verticality:
Continuous checks on pile verticality are essential during the initial jacking stages. Record Keeping:
High-frequency recording of jacking force—typically at every 0.5 m to 1.0 m of penetration—is recommended for quality assurance. isomer-user-content.by.gov.sg Load Testing Standards
GeoSS provides specific guidelines for safe pile load testing, particularly the Kentledge Method
. This includes verifying the geotechnical bearing capacity of the kentledge base itself to prevent sudden settlement or instability during testing. Course Hero used for spun piles in Singapore?
The Geotechnical Society of Singapore (GeoSS) provides essential guidelines for the installation of jacked foundation piles, a method widely favored in urban construction due to its low noise and vibration levels. These "Good Practice" standards ensure structural integrity and geotechnical stability in Singapore's diverse soil conditions, such as the Old Alluvium or soft marine clays. Core Installation Principles
According to the GeoSS Guideline on Jacked Piles, several critical practices must be observed during the installation phase:
Avoid Forced Alignment: Piles should never have their vertical alignment adjusted by force once installation has begun.
Sequential Jacking: For larger pile groups, it is recommended to jack from the inside out or in a consistent direction (e.g., left to right) to manage soil displacement effects. install centralizing guide
Verticality Monitoring: Constant checks on the verticality of the pile and the quality of welding for joining pile sections are mandatory.
Heave Control: Because jacked piles are displacement piles, they can cause "pile heave" in adjacent piles. Monitoring for heave is critical, and pro-active measures like pre-boring or relief wells should be used if necessary. Termination Criteria and "Set" Measurement
In Singapore, the termination of a jacked pile is not determined solely by depth but by achieving a specific "set" under a defined jacking force ( Pjcap P sub j
Jacking Force: Typically, piles are jacked with a force adjusted in steps to a value of 2 to 2.5 times the Working Load (WL) until practical refusal is reached. The Set Procedure: Pjcap P sub j is released to zero and immediately re-applied.
The downward movement between the initial "virgin jack" and the "re-jack" is measured as the "first set".
A pile is generally considered "set" if the downward movement does not exceed 10 mm with a minimum holding time of 30 seconds.
Short Piles: If termination criteria are met but the pile is significantly shorter than the design depth (e.g., due to boulders), the designer must substantiative the capacity, often through a working load test. Design Considerations for Singapore Soils
Installation practices must adapt to the specific geotechnical challenges found in Singapore:
Negative Skin Friction: If a pile penetrates a consolidating soft soil layer, designers must account for "downdrag" forces. This reversal of force (from positive to negative skin friction) must be considered when determining the required jacking load ( Pjcap P sub j
Old Alluvium: While considered construction-friendly, the mobilized shaft and base resistance in this formation can vary. GeoSS recommends caution when using load test results from adjacent sites, as workmanship significantly impacts these values.
Obstructions: Encountering boulders or hard intermediate layers can lead to short piles. If a pile is more than 20% shorter than planned, an amendment plan submission to the authorities is typically required. Quality Assurance and Testing
To ensure the finished product meets Eurocode 7 (EC7) requirements, GeoSS highlights several testing protocols:
Ultimate Load Tests (ULT): Used to verify design parameters. Trial piles should be tested to loads as high as 3.5 WL to reach the ultimate limit state.
Integrity Testing: Specialist builders must perform integrity tests (such as PDA or sonic logging) to demonstrate that piles are free of hidden defects.
Specialist Personnel: Piling works must be overseen by qualified personnel with relevant experience, and machinery (such as jack rigs) must undergo regular maintenance with documented checklists.
Unlike impact hammers, jacked piles allow force-guided installation. GEOSS defines three control modes:
| Mode | Condition | Objective | |------|-----------|------------| | Force control | Soft to medium stiff clay (N < 15) | Maintain constant jacking force, record penetration rate (mm/min). | | Rate control | Dense sand / Old Alluvium (N > 30) | Limit penetration rate to < 5 mm/sec to avoid excessive load spikes. | | Stroke control | Final set-up (refusal) | Advance in 50 mm strokes; record final jacking pressure at each stroke. |
| Problem | Cause | Good Practice Solution | |---------|-------|------------------------| | Pile refuses before design depth | Dense sand layer / Old Alluvium | Pre-bore 50–70% of pile depth; use shoe; reduce spacing of reaction piles | | Pile cracks during jacking | Tensile bending during eccentric load | Reduce rate; install centralizing guide; reject pile if crack >0.2 mm | | Adjacent ground heave | Full displacement in clay | Re-jack perimeter piles; install relief holes (100 mm dia., 2 m deep) | | Jacking force drops suddenly | Void / old trench backfill | Stop, inject grout, re-jack next day with lower rate | | Neighbour complaint (vibration) | Even jacking has micro-vibration | Use rubber pad at pile head; monitor with PPV <5 mm/s |
This is the core of the "Good Practice" guide, covering: