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.

Testing capabilities

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):

• Bridges
• Structures
• Railway lines
• High-rise housing

JF Strainstall's BDSLT method is fully compliant with the ASTM D8169 / D8169M – 18 standard.

HSE benefits
  • 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)


Cost benefits
  • 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


Time benefits
  • 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
Set up

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.


During testing

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.


Post testing

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

Strainstall bi-directional static load test (BDSLT)

Strainstall’s bi-directional static load test (BDSLT) is a truly innovative and highly effective static load testing technique. The speed and accuracy of the testing method has made BDSLT a valuable tool and the wealth of information produced is the reason so many engineers are now turning to this method.

Contact us

If you are making an enquiry about a product or service, please use our sales enquiry form.

JF Strainstall
Registered office: Fisher House, PO Box 4, Barrow-in-Furness, Cumbria, LA14 1HR, UK Registered in England no. 4042929 E: