The Bidirectional Static Pile Load Test (BDSPLT), commonly known as the Osterberg Cell (O-cell) Test, is the latest service offered by SGES. This test is used to assess the load-carrying capacity of deep foundations, particularly piles. Unlike traditional pile load tests where load is applied from the top, the BDSPLT applies load internally (with the help of hydraulic jacks installed within the pile body), directly within the foundation element. The primary objective is to determine the performance of the pile under both end-bearing and shaft friction conditions, without requiring the need for massive reaction structures.

This process requires carefully identifying the balance level point within the reinforcement cage—a theoretical point where the skin friction of the upper portion of the pile approximately equals the combined skin friction of the lower part and the end-bearing component. This identification requires accurate geotechnical investigation and lab testing. At the balance level, jack (jacks’ assembly) are installed prior to casting. During testing, hydraulic pressure is applied to the jacks, creating bidirectional forces that push upwards against the pile shaft and downwards against the pile toe. Displacement in the pile is measured at four points (the pile top, pile toe, jack top, and jack bottom) using telltales that extend to the pile top.

The BDSPLT method allows for the independent assessment of shaft friction and end-bearing resistance, providing a more detailed understanding of pile behaviour. Strain gauges can be installed at various levels within the reinforcement cage, prior to concreting to achieve this. The test results provide separate data on soil/rock resistance and movement for both the shaft and the toe, offering insights into the magnitudes of mobilized resistances. The load versus displacement data obtained at the jack level is then used to generate an equivalent top-loaded load versus displacement curve.

Bidirectional load testing is generally less expensive than traditional static pile testing, mainly because it requires fewer resources and can be performed in a shorter period. The time and cost savings provided by bidirectional load testing can be particularly beneficial for projects with tight schedules or budget constraints. Furthermore, bidirectional load testing can be performed using a smaller reaction frame compared to static pile testing. This means that it can be performed in locations with limited space or challenging access. This is particularly important in densely populated urban areas where construction sites are often located in tight spaces.

SGES Experience/Credentials:

SGES has successfully completed two instrumented pile load tests – one on the west coast and the other on the south coast of India – achieving the highest level of customer satisfaction. Additionally, numerous projects are in the pipeline.