Geoss Good Practice For: Installation Of Jacked Foundation Piles In Singapore

Executive Summary Jacked piles are installed using hydraulic pressure to push precast concrete or steel piles into the ground, displacing soil laterally without excavation. Although they offer significant environmental benefits—low noise and negligible vibration—they are not without construction risks. Past projects in Singapore have recorded issues such as short piles and pile heave , which can compromise foundation adequacy if not detected early. To address these challenges, Singapore has issued a joint BCA/IES/ACES/GeoSS circular (APPBCA-2022-15) mandating that the design and construction of driven or jacked piles comply with Eurocode 7 and BS EN 12699 . This article outlines a risk-based approach for the installation of jacked piles, covering everything from pre-installation planning and pile heave monitoring to termination criteria, load testing, and site supervision. It serves as a practical guide for implementing GeoSS good practices on construction sites in Singapore. 1. Understanding Jacked Piles in the Singapore Context Jacked piles are displacement piles —meaning they are installed by forcing soil aside rather than removing it. Displacement piles are defined as piles installed into the ground by driving, jacking, vibration, or screwing, without excavation or removal of materials except to limit heave, reduce vibration, remove obstructions, or assist penetration (BS EN 12699). In Singapore, jacked piles are particularly advantageous in built-up areas with nearby structures and sensitive residents. The jacked piling system uses dead weights to exert hydraulic pressure to push piles into the ground, producing less noise and vibration compared to driven piles, making it suitable for projects in urban areas where residents are sensitive to noise and vibrations. Common types of jacked piles in Singapore include:

Precast reinforced concrete piles Jack‑in steel pipe piles Jack‑in steel H-piles

Jacked-in steel pipe piles and jack‑in steel H-piles are explicitly listed as acceptable pile types by HDB, alongside bored piles and micropiles (timber piles are not acceptable). All pile foundations in Singapore must be designed with a minimum safety factor of 2.5 times the nominal working load to ensure structural resilience and public safety. 2. Regulatory Framework: The Joint BCA/IES/ACES/GeoSS Circular (APPBCA-2022-15) The cornerstone of good practice for jacked pile installation in Singapore is the joint circular issued on 1 September 2022, titled “Requirements and Guidelines on the Use of Driven or Jacked Piles for Building Foundation” (APPBCA-2022-15). This circular consolidates industry best practices into a single regulatory framework that all QPs, accredited checkers, site supervisors, builders, specialist builders, and developers must comply with for projects adopting driven or jacked piles for building foundations. The circular applies to projects with the first structural plan submitted on or after 1 September 2022 and is enforceable by the BCA. 2.1. Why the Circular Was Issued Observations from past projects have indicated that short piles and pile heave during piling work are issues that may be encountered during construction. If these issues are not detected and arrested early, the adequacy of the foundation could be undermined. Hence, design and construction of driven or jacked piles must be performed in accordance with the requirements and guidelines stipulated in the circular, particularly for high‑rise buildings underlain by thick layers of soft clay deposits. 2.2. Risk‑Based Approach To ensure that driven or jacked piles are installed properly, a differentiated approach based on the risk category of the buildings as tabulated in Appendix A of the circular is adopted. Depending on the classification of the building, requirements include:

Additional information to be indicated on the piling plan submitted to BCA for approval (listed in Table B1 of Appendix B) Heave monitoring of driven or jacked piles during installation A written confirmation from the Commissioner of Building Control before any structural works above the constructed pile (e.g., pile caps) may commence Executive Summary Jacked piles are installed using hydraulic

2.3. Documentation Requirements Project parties must submit in a timely manner the following documents in the Piling Advice Letter issued by the Commissioner of Building Control together with the Notice of Approval for the first piling plan:

Annex C form : “Interim Certificate of Supervision on Piling Works” in Piling Advice Letter at 50% and 100% of pile installation for all piling works Annex D form : “Certificate of Monitoring Building Settlement” in Piling Advice Letter at the completion of erection of every multiple of 5 storeys until the final roof level

3. Key Technical Requirements for Jacked Pile Installation 3.1. Pile Termination Criteria Termination criteria determine when a jacked pile has reached its required founding depth and capacity. The final jacking force can be smaller than 2.5 times the design load for very long piles, but should be larger than 2.5 times the design load for piles shorter than 37 times the pile diameter . All jacked piles should be installed to an appropriate depth into a suitable bearing stratum as determined by the geotechnical engineer or local practice. 3.2. Load Testing Requirements All jacked piles must be load tested to 1.5 times the desired working load . The test load is limited by the maximum safe operating ram pressure of the ram, the available dead load of the existing foundation, or the structural capacity of the foundation, whichever is less. Pile load tests are useful tools for the QP who designs and supervises the pile foundation. Good practices in pile load tests help QPs fulfil their key roles under the Building Control Regulations. 3.3. Instrumentation and Monitoring Advanced pile instrumentation techniques enable engineers to monitor pile performance during load tests. The GLOSTREXT method has been introduced for driven, jacked‑in and bored cast‑in‑place piles load tests in Malaysia, Singapore and Thailand. This method enables installation of instrumentation after pile installation, virtually eliminating the risk of instrument damage during pile production and installation. The post‑install nature of the method enables engineers to select instrumentation levels along the as‑built depth of piles using pile installation records and site investigation data as guides. It reliably measures segmental shortening and strains over an entire section of the test pile during each loading step of a typical static load test, integrating individual measurements over a larger and more representative sample than conventional strain gauges. 4. Good Practices for Installation 4.1. Pre‑Installation Planning Before any jacked pile installation commences, the following preparatory steps are essential: Adequate Site Investigation (SI): It is imperative to conduct an adequate site investigation to identify all ground formations and layers, and to determine ground properties. The extent must include a sufficient number of site investigation boreholes and sufficient exploration depth. Unnecessary cutting down in site investigation costs may prove to be “penny wise, pound foolish”—a cost too hefty to pay. Rock Identification: For bored piles (and relevant for jacked piles that socket into rock), guidelines provide recommendations on criteria to be met for samples retrieved during pile installation to be identified as rock of weathering grade III or better. The point load test apparatus, properly calibrated by an accredited laboratory, could be used to measure the point load test index I(s(50)) of rock samples, providing a more objective basis to determine whether the sample retrieved is rock of weathering grade III or better. Performance‑Based Pile Design: Under performance‑based pile design (joint BCA/IES/ACES/GeoSS circular 2022), BCA allows the flexibility for QP(D) to submit more than one set of pile design and pile design parameters in a single submission for approval for projects adopting bored pile foundation. After obtaining written approval from the CBC of the adopted design and pile design parameters, installation of working piles can commence on site. Under the performance‑based pile design, pile optimisation can be carried out on site without the need to wait for the approval to the amendment plan. 4.2. During Installation During the actual jacked pile installation, the following good practices should be observed: Heave Monitoring: Heave monitoring of driven or jacked piles during installation is mandatory. This ensures that soil displacement does not cause adjacent piles to rise, which could lead to loss of capacity. Pile Jacking Machine and Accessories: Specialist builders must have detailed procedures, method statements, and instructions for the application of appropriate regulations, codes of practice, standards, specifications, guidance documents, and customer requirements. Jacked piles (steel, concrete) require a pile jacking machine with accessories. Competent Piling Personnel: Piling work must be supervised by competent and suitably qualified persons with comparable experience (BS EN 12699). “Lack of quality assurance and quality control by contractors and lack of proper site supervision by suitably qualified engineers” is commonly cited as one of the major causes for project problems/failures (delay, cost overrun, distress, etc.). 4.3. Post‑Installation Verification Interim Certification: The “Interim Certificate of Supervision on Piling Works” in the Piling Advice Letter must be submitted at 50% and 100% of pile installation for all piling works. Building Settlement Monitoring: The “Certificate of Monitoring Building Settlement” in the Piling Advice Letter must be submitted at the completion of erection of every multiple of 5 storeys until the final roof level. 5. Common Installation Challenges and Mitigation Measures 5.1. Short Piles Short piles occur when a pile cannot be jacked to the required depth due to unexpected obstructions or variable ground conditions. The risk of short piles is heightened in areas with limestone cavities or boulders. Mitigation measures include: To address these challenges, Singapore has issued a

Conducting probing or pilot holes ahead of pile installation in challenging ground Using geophysical surveys to identify cavities before piling Implementing a risk‑based approach with enhanced site investigation in high‑risk areas (e.g., western Singapore with limestone formations)

5.2. Pile Heave Pile heave occurs when the jacking of piles displaces soil, causing adjacent piles to rise. If undetected, heave can result in piles losing their shaft friction and bearing capacity. Mitigation measures include:

Mandatory heave monitoring during jacked pile installation Sequential installation patterns to minimise soil displacement Regular survey checks to detect any vertical movement of previously installed piles causing adjacent piles to rise.

5.3. Cavities and Slump Zones In western Singapore, natural limestone formations feature cavities and slump zones at considerable depths. Although no documented instances of surface sinkholes have occurred, piles penetrating deep into the ground may encounter limestone cavities or slump zones during installation, posing construction challenges and affecting load carrying capacity. Mitigation measures include:

Early and thorough site checks using boreholes, probe holes, and geophysical surveys Smarter risk categorisation by ground conditions and building type Cavity treatments before piling Clear contingency steps if cavities are uncovered during works Stronger testing and submission requirements