CFA Piling rig

What Is Pile Testing?

Pile testing can be used to evaluate the integrity, ultimate capacity and settlement performance of piles. Piles are deep foundation elements that transfer the load of a structure to deeper, more stable soil layers or rock formations. This blog explores the different types of pile testing, their importance, methods, and applications.

Concrete foundations and piling

Benefits of Pile Testing

Pile testing serves several essential purposes:

  1. Ensuring Safety: Where lower partial safety factors are adopted within the pile design calculations, to ensure economical design depths are scheduled, pile load testing will confirm that the piles can support the intended loads without excessive settlement, ensuring the safety of the completed structure and its occupants.
  2. Quality Control: Certain pile testing techniques can be used to confirm that the piles have been installed correctly and meet the required specifications.
  3. Design Verification: When load testing is required, the results are used to validate the design assumptions and help refine future designs by providing real-world load/settlement data.
  4. Cost Efficiency: Taking positive benefit from previous pile load testing results, helps avoid overdesigning or under designing piles on future projects, leading to optimal use of materials and resources.
  5. Regulatory Compliance: The scope of required pile testing will often be determined by the Project Engineer, or the Building Warrantor’s Engineer. Proving compliance with this schedule regime of testing ensures that the construction meets the required building codes and standards.

Bath project close up of piling machinery

Types of Pile Testing

There are several methods of pile testing, each serving a specific purpose and providing different types of data. The primary methods include:

1. Static Load Testing

Preliminary static load testing of sacrificial test piles is the most direct method of determining a pile’s load-bearing capacity, through measurement of the applied load at the achievement a predetermined ‘failure’ criterion. More commonly, static load testing is carried out at working pile locations, with the load/displacement response recorded in gradual load increments, up to a maximum of 150% of working load.

  • Procedure: A hydraulic jack applies a load to the pile, and the displacement (settlement) is measured using precise instruments. The load is applied incrementally until the pile reaches the desired load or fails.
  • Types: Static load tests can be axial (compression or tension) or lateral, depending on the direction of the applied load.
  • Applications: Preliminary static load testing is used for critical projects where precise load capacity data is required, such as high-rise buildings, bridges, and industrial structures. Maintained load testing to working piles is carried out where specified by the project team, or where the partial safety factors adopted in design require design validation.

2. Dynamic Load Testing

Dynamic load testing evaluates the pile’s performance by applying a dynamic load, usually via a hammer blow, and analysis of the pile’s settlement response.

  • Procedure: A pile-driving hammer strikes the pile, and sensors measure the resulting stress waves and displacement. The data is analyzed to determine the estimated pile head deflection at working loads.
  • Advantages: Faster and less expensive than static load testing. It can be performed during or after completion of the pile installation and allows a greater number of piles to be tested.
  • Applications: Commonly used for driven piles, especially in large-scale projects where many piles need testing.
  • Disadvantages: The application of a dynamic load does not accurately replicate the long term load/displacement performance of a deep foundation, particularly when piles are embedded in fine grained Clay soils.

3. Pile Integrity Testing (PIT)

Pile integrity testing assesses the structural integrity and continuity of augered piles, identifying defects such as cracks, voids, and inclusions.

  • Procedure: A small hammer is used to tap the pile at surface level, following pile cropping, and the response is measured using accelerometer also placed on the surface of the cropped pile. The resulting signal is analyzed to detect anomalies.
  • Types: Low strain (impact echo) and high strain methods are available, with the choice depending on the required detail and depth of analysis.
  • Applications: Used for quality control in new augered pile installations and to assess the condition of existing piles in older structures.

4. Crosshole Sonic Logging (CSL)

Crosshole sonic logging is a non-destructive testing method used to evaluate the integrity of cast-in-place concrete piles or drilled shafts.

  • Procedure: Tubes are installed in the pile before pouring the concrete. After curing, ultrasonic transducers are lowered into the tubes, sending and receiving signals through the concrete. The signal quality indicates the concrete’s integrity.
  • Advantages: Provides detailed information about the pile’s internal structure, including defects like voids or honeycombing.
  • Applications: Ideal for critical infrastructure projects requiring high confidence in pile integrity, such as bridges, dams, and high-rise buildings.

5. Bi-directional Load Testing

Bi-directional load testing, also known as Osterberg Cell testing, uses an embedded hydraulic jack to apply loads to the pile from within.

  • Procedure: A hydraulic jack (Osterberg Cell) is installed at a specific depth within the pile. The load cell expansion reacts against the concreted pile above & below the cell location, and the pile’s response is measured.
  • Advantages: Allows testing of very large piles and provides a detailed understanding of load distribution along the pile length.
  • Applications: Used for large-diameter bored piles and drilled shafts in heavy construction projects.

Drilling foundation tool