Lightweight Deflectometer Testing: Powerful, Portable and Precise

Why does lightweight deflectometer testing matter?

Unexpected ground behaviour is one of the biggest risks to construction projects. Soft spots, poorly compacted fill, or variable subgrades can lead to delays, redesigns, or even failures. Traditional testing methods such as nuclear densometers or static plate load tests are often slow, expensive, or impractical for routine QA, particularly in tight spaces or remote settings.

The lightweight deflectometer (LWD) changes this. Portable and quick to use, it provides engineers with a direct measure of soil stiffness in minutes. By applying a series of controlled impacts through a rigid plate and measuring surface deflections, the LWD gives a realistic picture of how the ground will respond to loads in the field.

Why Use an LWD?

• Speed: Each test takes just a few minutes, so multiple locations can be covered in a single site visit.

• Practicality: Compact equipment, no need for large reaction masses, heavy jacks, or multiple operators.

• Accuracy: Results include dynamic modulus (Evd) values that correlate to subgrade performance and compaction quality.

• Flexibility: Suitable for a wide range of applications, from road formation to crane platforms.

Typical Applications

• Earthworks QA during subdivision construction

• Roading and rail formation stiffness checks

• Verification of working platforms for cranes and piling rigs

• Remote or constrained sites where heavier tests are impractical

How the Test Works

• A 10 kg drop weight is released onto a steel plate (usually 300 mm diameter).

• The resulting surface deflection is measured with a geophone or accelerometer.

• Multiple drops are recorded to ensure repeatability of results.

• Software calculates the dynamic modulus (Evd), which can be compared to project specifications or correlated with design parameters such as CBR or subgrade modulus.

Key Things to Consider

• Standard to follow: ASTM E2835.

• Plate size: 300 mm, its applicability depends on particle size and site conditions.

• Number of tests: Depends on variability of ground conditions and QA requirements. A core strength of LWD is many tests can be carried out efficiently during one visit.

• Data interpretation: Should be reviewed by qualified geotechnical staff to ensure correct correlations are applied.

Our Experience

At Cook Costello, we use LWD testing alongside other geotechnical tools to give our clients confidence in their ground conditions. The ability to quickly test multiple points means risks are identified early, and earthworks can be signed off with certainty.

Planning earthworks of platform construction?

Talk to our geotechnical team about scoping an LWD programme. The right advice upfront means no wasted time on site and no costly rework later.

Contact Cook Costello’s Geotechnical Team today and build with certainty.