Lightweight Deflectometer: Measurement Process
A Light Weight Deflectometer is one of the fastest and most efficient tools for evaluating soil compaction and load-bearing capacity directly on site. Contractors, civil engineers, and quality control personnel use this dynamic testing device to verify whether earthworks and foundation layers meet project specifications before construction continues.
The measurement process is simple and can be completed within just a few minutes. First, the Lightweight Deflectometer is placed on the surface to be tested. After connecting the device to the smartphone app via Bluetooth, the operator can immediately begin the testing procedure.
During the test, a series of controlled impact loads is applied to the ground surface. The integrated geophone continuously record the resulting settlement and deformation behavior of the tested material. After each impact, the smartphone display shows the measured deflection in millimeters as well as the corresponding deflection curve. This allows the operator to visually assess the response of the soil, aggregate, or unbound layer in real time.
Once the measurement sequence is completed, the application automatically calculates and displays the EVd value in MPa. This dynamic deformation modulus provides valuable information about the stiffness and bearing capacity of the tested layer. The results can be stored digitally, transferred to a computer, or incorporated directly into professional compaction reports for quality assurance and documentation purposes.
The Light Weight Deflectometer is widely used in earthworks, road construction, railway projects, pipeline installation, utility trench construction, landscaping, and sports field development. Because measurements can be performed directly on the construction site, project managers receive immediate feedback on compaction quality and can identify potential deficiencies before costly delays occur.
One of the major advantages of a modern Lightweight Deflectometer is the significant reduction in dependence on external testing laboratories. Site personnel can perform routine quality control independently and obtain reliable results in less than two minutes. This allows construction activities to continue without waiting for laboratory schedules or external inspectors.
In many cases, the investment in a Light Weight Deflectometer is recovered within a relatively short period through reduced testing costs, improved productivity, and fewer project interruptions. Combined with digital data collection, GPS positioning, smartphone connectivity, and automated reporting functions, the device has become an essential tool for modern construction quality control and compaction verification.
Important: A project-specific correlation between the dynamic results obtained with the Light Weight Deflectometer and the static plate load test should always be established where required by project specifications, standards, or local regulations. This ensures reliable interpretation of the measured EVd values and supports compliance with quality assurance requirements.
Testing with the Light Weight Deflectometer (LWD)
During routine construction quality control, the Light Weight Deflectometer (LWD) may be used as a rapid testing method, provided that a correlation for the respective materials and layers has previously been established on a test section.
The correlation is determined by comparing the results obtained with the Light Weight Deflectometer (LWD) to reference values such as dry density (Proctor density) or the deformation modulus obtained from the static plate load test.
The established correlations can only be considered reliable if sufficient homogeneity exists within each layer with respect to material properties, layer thickness, moisture content, and layer structure. In addition, the different measuring depths of the respective test methods must be taken into account. Measurements on overlapping roller tracks should be avoided, as they may distort the correlation.
Reliable correlations can generally be established by comparing at least 10 different test locations within the test section. For each location, the average value of several repeated measurements should be used. Areas with both high and low bearing capacities should deliberately be included in order to obtain a meaningful correlation.