Bi-directional Static Load Test
Test reference Standard: TR-63 (ISC 93.020) – Technical Reference for Bi-Directional Static Axial Load
ASTM D8169 – Standard Test method for Deep Foundations Under Bi-Directional Static Axial Compressive Load
ABOUT THE TEST
The bi-directional static load test (BDSLT) is a type of static load testing method specifically designed for deep foundations. It is suitable for both ultimate load tests and working load tests. The core concept involves installing a
bi-directional jack assembly at a strategic location along the pile shaft—typically where the geotechnical resistance above and below the jack is approximately equal—creating a ‘balanced’ point.
The objective of the test is to mobilize as much geotechnical resistance as possible, with a focus on activating both end bearing and shaft friction within the competent stratum. The jack assembly, consisting of hydraulic jacks welded between two steel plates, is integrated into the reinforcement cage and lowered into the borehole.
During testing, the jack assembly is pressurized to expand simultaneously in upward and downward directions. This action mobilizes the upper shaft friction and the combination of lower shaft friction and end bearing. Since the upper and lower segments of the pile provide resistance against each other, they act as counterweights,
eliminating the need for external kentledge or reaction systems.
Instrumentation such as tell-tale extensometers and vibrating wire strain gauges are typically installed to monitor pile movement and strain throughout the test.
This method is well-suited for bored piles with diameters as
small as 900 mm, as well as for barrette piles.
QUALITY ASSURANCE
Ultimate Load Tests (ULTs) are critical milestones in any project, as construction activities such as piling can only proceed upon successful test results. The bi-directional static load test (BDSLT) method involves embedding a sacrificial jack assembly within the foundation, meaning there is no margin for error—each test must be executed flawlessly.
At Geolutions, we uphold the highest standards in the fabrication and execution of our bi-directional load test systems. Every hydraulic jack is meticulously QAQC by the manufacturer before delivery. Upon arrival, we conduct calibration at Malayan Daching Laboratory (MDC Tech Centre), a SAC-SINGLAS accredited laboratory, to verify accuracy and ensure jack can be pressurized to the rated pressure.
Only after passing these stringent checks, do we proceed with fabrication. The jack assembly is constructed in-house at our workshop, where our certified and experienced welders ensure the highest quality welds. All welding works are carefully designed and reviewed by our technical team to guarantee structuralintegrity during cage lowering and
concreting.
Furthermore, the hydraulic lines undergo repeated pressure testing to confirm that every component is uncompromised. Over the years, our extensive experience in conducting
bi-directional load tests has allowed us to refine our Standard Operating Procedures (SOPs), enabling us to anticipate and overcome unforeseen challenges with confidence.
At Geolutions, we are experienced, meticulous, and always prepared.
WORKING LOAD TEST (WLT) USING BDSLT
In accordance with TR 63 by the Singapore Standards Council (SSC), Working Load Tests (WLTs) are permitted to be conducted using the bi-directional static load test (BDSLT) method. This approach offers a safer and more cost-effective alternative for performing WLTs, aligning with the pile testing schedule stipulated by the Building and Construction Authority (BCA).
There are some occurrence that project QP may express concerns that the BDSLT method may compromise pile integrity by introducing a discontinuity in the reinforcement. However, with advancements in technology and engineering practices, Geolutions has successfully addressed and overcome these concerns.
The jack can be strategically positioned beyond the pile’s pay length. For piles with deep cut-off levels (COLs), the jack may be installed above the COL—provided geotechnical conditions are suitable. Alternatively, for cases requiring deeper testing, the jack can be placed below the toe level by extending the pile length. Following each WLT, the pile is grouted using high-strength epoxy and non-shrink grout to seal all voids and ensure the structural integrity of the pile is fully restored. To further verify the pile’s condition,
non-destructive pile integrity tests can be conducted by our team.
At Geolutions, we manage the entire testing process
in-house—from jack fabrication, instrumentation, and monitoring to data interpretation, QP endorsement, post-test grouting, and integrity testing. We do not subcontract any part of the process. This end-to-end control reflects our unwavering commitment to quality and accountability, ensuring a smooth and reliable experience
from test proposal to final acceptance.
Geolutions has successfully executed WLTs using the BDSLT method across a wide range of projects, including HDB
developments, LTA projects such as the North-South Corridor (NSC), Jurong Region Line (JRL), and Cross-Island Line (CRL), as well as JTC projects and high-profile private
developments like Marina Bay Sands IR2 and numerous residential and commercial buildings across Singapore.