O‑Cell ® Testing

The O-Cell® load test is a method used to measure the load-bearing capacity of deep foundations. Geotechnical engineers use this method to assess bored piles, drilled shafts, continuous flight auger (CFA piles), precast piles and barrettes. As this method is a bi-directional load test, we extract data from the upward force and downward force. This allows us to build load displacement curves combining uplift and compression components, helping engineers to make informed decisions on the total capacity.

An Osterberg cell is a hydraulic jack that we install inside a drilled shaft or pile. The O-Cell® (Osterberg cell) test allows engineers to measure movement (displacement), load transfer and ultimate capacity. By measuring with an upward force, as well as the equivalent top load, we can understand maximum capacity and limits that should be followed in infrastructure design.

In conventional load testing methods, maximum load is applied at the pile head and a downward force is applied. This relies on reaction systems such as kentledge, anchor piles and reaction frames. This measures overall pile head load-settlement behaviour, usually combining shaft and base resistance.

O-Cell® testing applies the load internally, within the pile body, measuring upwards force against shaft resistance and downward against end bearing.

The main difference between O-Cell® testing and standard test methods is the measured behaviour and amount of equipment required. O-Cell® is usually more practical for very large or deep piles as there is no need for anchor piles or large test platforms. You also get better diagnostics from O-Cell® tests, as it separately measures shaft resistance and end bearing.

There are several advantages to this method of load testing, particularly if you are looking for deep foundation load testing.

No external reaction system is needed

With conventional load testing methods, a downward force is directly applied to the pile to test its load capacity. This requires the careful installation of external reaction piles or kentledge to collect data from the downward force.

The O-Cell® load test is different. A hydraulic jack reaction system is cast within the pile, eliminating the need for external reaction systems. This is not only space saving, but many don't realise significant cost savings that can be achieved throughout a project’s life cycle.

High loads possible

The main advantage of the Osterberg cell test is also related to equipment usage. Conventional load testing methods become logistically complex as pile capacities increase. When it comes to large diameter bored piles, offshore piles or barrettes, a traditional static test is sometimes impractical or impossible but often structurally risky. An O-Cell® test eliminates this risk as load paths are internal, allowing you to test higher loads and gain more accurate insight on your site or project.

Insight accuracy

In some cases, a bi-directional load test is a 'nice to have'. However, there are several examples of areas that reliable foundation capacity data is imperative to design and risk management. At Fugro we often support large infrastructure projects, such a high-rise buildings, offshore platforms and bridges, which require precise accuracy at a large scale.

Improved safety and efficiency

The O-Cell® load test is seen as safer than traditional static load tests because it removes the need for massive kentledge stacks, anchor piles or large steel reaction frames. This equipment introduces several risks to a site, including congested worksites, crane lifts and potential structural instability or collapse.

As the O-Cell® generates the load inside the pile, relying on the ground itself to produce the reaction, there's no need to use heavy equipment at ground surface level. Overall, this reduces lifting hazards, temporary work risks and onsite accidents.

Significant cost savings

As touched upon in the previous sections, there are significant cost saving opportunities with Osterberg cell testing. A traditional static pile load test requires large reaction systems. This means the process takes longer to set up, and longer to get the test results. It also requires more equipment and labour, adding to the total cost.

The O-Cell® test requires installation of specialised cells inside the pile, but once complete load testing can begin. This set up requires less personnel on the ground and is faster overall, reducing the cost of the project.