Bi-directional static load testing (BDSLT) by James Fisher Strainstall is a highly effective static load testing technique that delivers accurate and reliable data.
BDSLT provides high resolution results for design engineers to confidently optimise pile design, based on achieved test results. In comparison to traditional methods of load testing, BDSLT is safer, faster and provides more accurate data. It is often the only solution for restricted access or low headroom situations where installation of anchor piles or other reaction systems are not possible.
Using a combination of hydraulic, high-capacity bi-directional jacks to deliver the required test load, BDSLT provides separate measurements of a pile’s end-bearing and skin friction along the pile’s length. JF Strainstall has utilised BDSLT for over 15 years, having successfully completed over 2,000 tests worldwide. During this time, JF Strainstall has refined the equipment used and techniques deployed on-site to ensure reliable and accurate results.
JF Strainstall's highly skilled testing team can provide a tailored service, using the latest innovative James Fisher products. JF Strainstall's global presence and depth of experience enables it to deliver a rapid response service for quick on-site evaluations and remote monitoring services.
BDSLT is suitable for a range of both commercial and non-commercial applications, including the assessment of cast in-situ piles for (but not limited to):
• Railway lines
• High-rise housing
JF Strainstall's BDSLT method is fully compliant with the ASTM D8169 / D8169M – 18 standard.
- Enhanced safety and reliability in comparison to traditional load testing methods
- No risk of oil contamination in the event of fluid spills during testing as standard mineral water is used for the hydraulic fluid
- Greatly reduced risk for larger test loads without the need to stack Kentledge blocks above the test pile (BDSLT loads in excess of 10,000T have been successfully achieved)
- BDSLT eliminates the need for overhead beams or reaction piles making the test more mobile and space efficient in comparison to other methods
- Preparation for the installation of the pre-manufactured bi-directional hydraulic jack(s) can be completed within a few days, saving time on tight building schedules
- Proven to be more cost-effective as loads increase in comparison to traditional load testing methods due to the fixed costs of materials, jacks, plates and installation time
- Precision testing provides engineers with separate data on the end-bearing and friction resistance of the shaft BDSLT is a versatile method that can be applied to barrette, bored piles (compression or tension), inclined piles or belled shafts
- The test pile can be reused to carry working loads after testing by grouting the pile, creating value for money
- Installation process forms part of the rebar cage fabrication which speeds up installation time
- Minimal work space required during testing in comparison to conventional tests, meaning other works can continue on-site and at the same time
- No soil stabilisation is required prior to set-up/testing
- All test results are automated and streamed to a site laptop at a sampling rate of one per minute
- Only need to cast the pile to cut-off level, eliminating the need for a king post or hacking back a test pile when testing is complete
Hydraulic jacks are positioned between two load bearing plates and attached to the reinforced steel cage prior to lowering. Positioning is calculated to provide equal capacities above and below the hydraulic jack assembly. Concrete casting is performed as normal, with cube tests indicating when testing can commence. A full method statement is provided prior to installation to outline the test design and procedure.
Hydraulic pressure is applied to the jack assembly. As load is applied, the hydraulic jacks begin to move in two directions - upward against upper skin friction and downward against lower skin friction and base resistance. Types of tests include:
1. An ultimate load test (ULT) includes strain gauges installed along the pile length, with the pile being loaded until either the shear resistance or base resistance of the pile has been fully mobilised. Strain gauge data is used to plot the load distribution along the pile length which is used to determine the ultimate soil capacity of the test pile.
2. A working load test (WLT) loads the pile within the acceptable working load limits. This type of test is used to validate whether the pile head displacement for the given load conforms to the allowable pile head settlement criteria.
Following test completion, a full test report is supplied including the obtained soil parameters and equivalent top loaded settlement values. Both documents can be sent for professional engineer endorsement, if required.
Test equipment supplied and utilised by JF Strainstall's experienced engineers, including:
- Combination of hydraulic jacks to apply the test load
- Steel bearing plates to position the hydraulic jacks
- Displacement transducers, connected to tell-tale rods
- Strain gauges installed along pile length
- Fully automated data logger to monitor and record the data signals
- JF Strainstall's pileSENTINEL software to visually display live readings throughout testing
BDSLT case studies
Delivering an industry first in Singapore
JF Strainstall successfully pile tested a 10,000 tonne load – the highest capacity ever tested for Dongah Geological Engineering Co. Ltd in Singapore.
The pile test was conducted at the confluence of different soil formations, making it challenging to design a test which could acquire meaningful data.
JF Strainstall was able to overcome this difficulty using BDSLT together with its experience and understanding of
Accommodating short time frames in Malaysian residential project
JF Strainstall supported Sunway Group Berhad with its maintain load test requirements on a short time frame of nine months for the construction of its residential condominium in Kelana Jaya.
The high test load and space restrictions made alternative methods, such as the Kentledge test, impossible due to the short time frame.
JF Strainstall was able to surmount these obstacles by carrying out two tests simultaneously using the BDSLT method.
Overcoming height restrictions in Kuala Lumpur
JF Strainstall was brought on board for testing of the TRX Exchange Shopping Mall situated in the heart of the new RM8 billion Lifestyle Quarter under construction in Kuala Lumpur.
The four-storey mall will feature 500 retail lots with a net lettable area of 1.35 million sq. ft.
Due to the height restrictions of the build, JF Strainstall recommended the BDSLT method, as this would prove to be the most cost-efficient method to conduct a maintain load test within these limitations.