CROSSHOLE SONIC LOGGING – sometimes you have to hear concrete quality

One of the methods that allows engineers to look inside a pile without excavating or damaging it is Crosshole Sonic Logging (CSL)

It is a proven non-destructive testing method used to assess the homogeneity and integrity of concrete in bored piles 😉

How does Crosshole Sonic Logging work?

CSL is based on the principle that ultrasonic waves travel through concrete in a predictable way — provided the material is uniform and properly executed.

In measurement tubes cast into the pile, engineers lower:

a transmitting probe,
a receiving probe.

An ultrasonic pulse is sent between them, and the system records:

the first arrival time (FAT)

the signal energy

the resulting sound wave velocity in the concrete

What do the results tell us?

For homogeneous, well-compacted concrete, these parameters remain stable and consistent along the entire pile length.

If defects such as:

voids,
segregation,
or so-called rock nests,

are present, the signal clearly indicates a problem:
- delayed arrival,
- reduced energy,
- changes in wave velocity.

These variations allow engineers to precisely identify potential defects.

CSL report – data you can trust

A CSL report leaves no room for guesswork. It includes:
- velocity and energy profiles,
- waterfall plots,
- clearly defined evaluation criteria,
- an unambiguous classification of results.

This enables an objective assessment of pile quality — based on measured data, not assumptions.

Why is CSL so important at acceptance stage?

CSL is particularly valuable during foundation acceptance because it:
- verifies concrete quality throughout the entire pile volume,
- supports fast, well-informed technical decisions,
- reduces the risk of costly remedial works at later stages,
- provides investors and contractors with solid, measurable evidence of quality.

Conclusions

Crosshole Sonic Logging is a clear answer to a key engineering question:
Has the pile been constructed correctly over its full length?

At DMT, CSL is an essential part of foundation quality control — a tool that helps us understand what lies beneath the surface.
Because good engineering starts with understanding what cannot be seen with the naked eye💡

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