The Lightweight Deflectometer (LWD) is widely used in construction and geotechnical engineering, recognised for its high accuracy, efficiency, and cost-effectiveness when assessing carriageway layers. By providing valuable insights into the stiffness and compaction of soil, the LWD helps to ensure the success and longevity of any project.
Keep reading to find out more about the LWD, including how it works, its benefits, and a simple 5-step guide on how the test is performed on your site.
What Is a Lightweight Deflectometer (LWD)?
The Lightweight Deflectometer (LWD), also known as the Portable Falling Weight Deflectometer, is a rapid onsite assessment tool for carriageway layers.
It’s a lightweight, portable device that allows the quick measurement of elastic modulus, which can be used to determine soil compaction and stiffness. This data plays a crucial role in highway and pavement engineering design and maintenance, ensuring the longevity of road surfaces.
An LWD test is carried out by placing the device over a specified area and releasing a weight using a trigger. This process is repeated several times so an average value for the material stiffness can be calculated. The LWD accounts for all the underlying layers beneath the device plate.
Applications of Lightweight Deflectometer Testing
The lightweight deflectometer test is widely used in construction and geotechnical applications to assess the compaction quality of pavement layers, subgrades, and embankments.
By measuring the elastic modulus, engineers can determine whether the soil has been compacted enough - and is thus strong enough - to bear the loads it will be subjected to during the structure’s lifetime.
- Common applications include:
- Road construction
- Earthworks & embankments
- Railway construction
- Airport runways & taxiways
- Temporary works platforms
Benefits of Lightweight Deflectometer Testing
There are several advantages of the LWD test, including:
- Portability & Safety: The lightweight nature of the device makes it easy and safe to transport and set up, even in remote or hard-to-access locations.
- Speed & Repeatability: The LWD test can be completed and repeated in a matter of minutes, providing immediate and accurate soil compaction data.
- Non-destructive: Since the test does not require large-scale excavation or the installation of sensors within the soil, it preserves the integrity of the test area.
- Cost-effective: The LWD test is less labour-intensive and requires fewer resources than traditional testing methods, making it a cost-effective option for many projects.
- Versatility: It can be used on various soil types and under different environmental conditions, offering flexibility for a wide range of applications.
The lightweight deflectometer test is especially useful in situations where common alternatives are not appropriate or cost-efficient. For example, the LWD is more reliable than the Dynamic Cone Penetrometer (DCP) when assessing soft or loose materials.
How Does the LWD Test Work? 5 Key Steps
The LWD test takes just a few minutes to carry out, meaning a large area of your site can be assessed in a short amount of time.
Testing typically involves the following key steps:
- Preparing the test area: The test surface is made flat and free of debris to ensure accurate readings.
- Positioning the device: The loading plate is placed on the soil surface where the test is to be completed.
- Applying the load: A defined weight is released from a set height onto the plate, simulating the load that the soil would experience in real-world conditions.
- Measuring the deflection: The device measures the vertical deflection of the soil in response to the applied load before calculating the soil’s elastic modulus.
- Interpreting the data: Results are displayed on the LWD’s digital readout or stored for further analysis.
- Following an LWD test, you will be provided with an easy-to-read report explaining the findings.
Onsite Material Testing by ACS
The lightweight deflectometer test measures the deflection (or settlement) of subgrades, granular layers, and backfilling materials – quickly, easily, and accurately.
Unsure if you need an LWD test for your next project? Get in touch! ACS Testing has an experienced team of material testing specialists who will be happy to help.
Alternatively, please visit our Onsite Material Testing page for more information on how our comprehensive suite of services can support you.