Statnamic Load Test - How IT Works

How It Works

Statnamic testing works by accelerating a mass upward that in turn imparts a load onto the foundation pile below the Statnamic device. The load is applied and removed smoothly resulting in load application of 100 to 200 milliseconds. This is 30 to 40 times the duration of dynamic pile load testing. As the duration of the loading is relatively long, piles less than 40m in length remain in compression throughout resulting in negligible stress wave effects and potentially simpler analysis. For foundation design it is necessary to derive the equivalent static load-settlement curve from the Statnamic data. The simplest form of Statnamic analysis used to obtain equivalent static pile response is known as the unloading point method (UPM) The UPM analysis method was conceived to be simple and based on measured results alone (Middendorp et al., 1992).

The Statnamic test applies a force to the pile head over a typical duration of 120 milliseconds by the controlled venting of high pressure gas. The gas is the product of the combustion of a fast burning fuel within a piston (fuel chamber) (Figure 1). At the top of the piston are vent holes that are sealed by the load hanger retaining the reaction mass. At some point the pressure within the piston is of such a magnitude to force the load hanger arrangement upward at accelerations in order of 196m/s2 (20g). This process applies a load downwards on the test pile.

During the loading sequence the load applied to the test pile is monitored by a calibrated load cell incorporated in the base of the combustion piston. Pile settlement is measured using a remote laser reference source that falls on a photovoltaic cell incorporated in the piston. The laser reference source should be placed at least 15m from the test pile to avoid the influence of test induced ground surface wave disturbance (Brown & Hyde, 2006). Data capture is undertaken using a data acquisition system connected to a laptop computer. It is recommended to allow accurate data processing that sampling should be undertaken at frequencies above 1 kHz.

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