The procedure for undertaking a pile tension test typically involves several steps, including preparation, instrumentation, loading, and data analysis. A general outline of the process follows:

Preparation:

• Select the pile(s) to be tested based on project specifications and requirements
• Clear the area around the pile(s) to ensure safe and unobstructed access
• Install any necessary equipment, such as reaction frames or anchors, to apply and measure the tensile load
• Ensure that the pile is properly installed and secured in the ground according to design specifications

Instrumentation:

• Install instrumentation to measure parameters such as load, displacement, and strain.
• Common instruments used include load cells, displacement transducers, and strain gauges.
• Calibrate the instrumentation to ensure accurate measurement of the applied load and pile response.

Loading:

• Apply the tensile load to the pile using hydraulic jacks, winches, or other appropriate equipment
• Gradually increase the load in increments while monitoring the pile’s response as per the Client’s requirements
• Record data at regular intervals, including load applied, pile displacement as per the Client’s requirements

Data Collection:

• Continuously monitor and record data throughout the loading process
• Measure and record any settlement or movement of the pile and surrounding soil
• Ensure that data collection is performed accurately and consistently to capture relevant information

Unload and Analysis:

• After reaching the desired load level or observing specific pile behavior, gradually unload the pile

Reporting:

• Present the collected data for assessment by Engineer

Throughout the entire process, safety precautions should be strictly followed to prevent accidents or damage to equipment and personnel. This includes setting up a working area at least 20m around the testing site ensuring personel who are not actively involved in the test cannot enter the area.

The jack applies force simultaneously upward against the shaft resistance above its location and downward against the combined resistance below the jack assembly (including the toe or base resistance).

The cage is equipped with instrumentation to measure shaft and toe movements, as well as soil resistance from the applied load. Load-cells can be installed in various types of deep foundation elements, including bore holes and continuous flight auger (CFA).

Bi-Directional Static Load Test Benefits include

• High-capacity static load test method for deep foundation elements.
• Separates soil/rock resistance and movement data for shaft and toe.
• Determines magnitude of the mobilised shaft and toe resistances.
• Embedded strain gauges within the foundation element determine the soil/rock resistance distribution along the foundation length for optimizing foundation design.
• Not restricted by structural or geotechnical limit of load frame, reaction beams, or reaction piles.
• Multiple Load-Cells can be used at a single jack assembly location or at multiple jack assembly locations to apply larger loads.

Generalized plan and elevation views of single Load-Cell jack assemblies

Generalized plan and elevation views of multiple Load-Cell jack assemblies

The test consists of attaching one or two accelerometers to a pile and using a hand-held hammer to impact the pile top. The PIT collects the acceleration data and displays curves that reveal any significant changes in a cross section that may exist along the shaft. The impact of the hammer generates a stress wave that propagates down the foundation and reflects back up. The accelerometer collects data that reveals the pattern of wave propagation and reflection.

PIT tests may also help estimate the depth of the pile toe (the pile length) if the pile is intact with embedment less than 30 times the pile diameter. Initial PIT data is evaluated in the field and later transferred to a computer for further analysis.

During a lateral load test, a horizontal force is applied to the structure at a specified height above the ground level. This force is can be applied by pulling piles together or pushing them apart. 

Typically applied gradually using hydraulic jacks or other load-applying devices. Instruments such as load cells, strain gauges, or displacement transducers are used to measure the applied force and the resulting lateral displacement or deflection of the structure.

Laterally loaded screw piles using hollow cylinder and load cell arrangement with 4 displacement sensors

These screw piles are being pulled together laterally. The method uses a hollow hydraulic cylinder and load cell.