Methodology guide

PIT on foundation piles: how the Pulse Echo Test works

Low-strain testing at the pile head: impact, receiver, return time and the limits of estimating pile length using PIT.

An unusual signal is not yet a diagnosis. The client needs to establish what information supports the decision and which test can obtain it under the actual pile conditions.

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Impact and receiver at the pile head

PIT is a low-strain dynamic test: an impact generates a wave at the pile head and a receiver records the response. In acceleration-based systems, velocity is obtained by integrating the signal.

Receiver position, contact quality and impact area affect recording. Execution should distinguish pile response from local head disturbances.

Propagation, reflections and impedance

The wave travels through the pile and may reflect at the toe or an impedance change. Material properties and cross-section contribute, alongside ground interaction and restraints.

A reflectogram change does not automatically mean a casting defect. Compare it with pile shape and construction records; attenuation can make the toe reflection difficult to recognise.

Estimating length with the echo method

In 2L = Vm × T, L is estimated length, Vm the assumed average velocity and T the round-trip time of the reflection attributed to the toe. Therefore L = Vm × T / 2.

Uncertain velocity or an unidentifiable return makes the length estimate uncertain. No standard concrete velocity or universal geometric ratio is assigned here; manual criteria require case-specific verification.

Pile-head condition and readability

The head should provide concrete suitable for impact and receiver contact, without degraded material or local elements dominating the measurement. Agree on preparation and access before the visit.

Repeated recordings and comparison with geometry and stratigraphy support interpretation. Declare unreadable signals as such: they alone establish neither integrity nor a defect, and do not measure load-bearing capacity.

Related guides

How to interpret a PIT reflectogram: pile length and anomaliesHow to prepare a pile integrity testMechanical admittance of piles: the Transient Response MethodCross-Hole, PIT or mechanical admittance: which pile test should you choose?
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Frequently asked questions

Do integrity tests measure load-bearing capacity?
No. They assess aspects of integrity or pile response within method limitations; they do not replace a load-capacity assessment.
Which method is always best?
None: the objective, access and pile conditions determine what information can be obtained.
Is estimated length certain?
No: it depends on velocity assumptions, identifying the response and boundary conditions.

References and documentary scope

What information does your project need?

Share the objective, site constraints and required deliverables so we can assess an appropriate survey strategy.

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